PROCESS FOR WASHING A CATHODE ACTIVE MATERIAL

FIELD OF THE INVENTION

The disclosure relates to a method for processing a cathode active material comprising the steps of washing, filtering and drying the cathode active material.

BACKGROUND

Rechargeable or 'secondary' batteries find widespread use as electrical power supplies and energy storage systems. For example, in automobiles, battery packs formed of a plurality of battery modules, wherein each battery module includes a plurality of electrochemical cells, are provided as a means of effective storage and utilization of electric power.

Secondary batteries such a lithium ion batteries comprise a positive active material, or "cathode active material", and a negative active material or "anode active material" that form the electrochemically active components of the cathode and anode respectively.

Suitable cathode active materials include composites of nickel, cobalt and manganese or "NMC materials". These may also be referred to as "Li-NMC" materials when intercalated with lithium ions.

Typically, cathode active materials such as Li-NCM are fabricated by combining and calcining lithium, nickel, cobalt and manganese-containing precursors. The resultant Li- NMC material often does not have a surface optimized for use in a battery and thus further processing steps are required.

For example, a newly formed Li-NMC material may have an excess of lithium ions, which can be detrimental to the function of a battery. It is therefore common practice to remove the excess lithium ions before preparing a cathode from the cathode active material.

Impurities such as lithium may be removed by washing, filtering and drying the cathode active material. During washing, a cathode active material comprising impurities may be contacted with a dispersing agent to separate the impurities and the cathode active material. The resultant cathode active material and dispersing agent mixture may then be filtered to remove the dispersing agent. Finally, the cathode active material is dried to remove any residual dispersing agent. The treated cathode active material may then be formulated into the cathode, for instance by mixing with a binder and coated onto a current collector. Common wash-filter-dry processes are either batchwise or continuous.

Typically, the drying step of a batchwise processes is slow and has a limited processing capacity. Moreover, batch-dryers typically have high operational costs. There may also be the need for buffer storage of partially processed product between the washing, filtration and drying steps in order to manage the mismatch in the speed and capacity of each step. The problem of process mismatch is particularly acute between the filtration and drying steps.

On the other hand, the problem of buffer storage does not arise in a continuous process. However, known continuous filtration methods are typically inefficient and poor at removing the dispersing agent, resulting in a less efficient and much slower drying process with high operational costs. The filtration step of a continuous process is therefore often a bottle neck, limiting speed and efficiency. Moreover, continuous filtration processes are often associated with a high yield of product loss resulting in high costs and may potentially require extra processing steps to recover lost product.

There is therefore a need for an improved way to process cathode active materials that provides the efficiency advantages of a batchwise process as well as the operational advantages of a continuous process.

SUMMARY

The object of the present disclosure is to provide a method of processing a cathode active material.

The present disclosure provides a method of processing cathode active material that improves process time, maximizes processing capacity and thus reduces processing costs. The method of the invention further mitigates the need for buffer storage between the washing, filtration and drying steps.

According to a first aspect of the disclosure is provided a method for processing a cathode active material, the method comprising, in order: a) a washing step in which a cathode active material is contacted with a dispersing agent to provide a washed material; b) a filtration step in which the washed material is processed with a tube press filter to reduce the amount of dispersing agent in the mixture to provide a filtered material; and c) a drying step in which the remaining dispersing agent is removed from the cathode active material to provide a dried material; wherein the washing step is a batch process; wherein the filtration step is a batch process; and wherein the drying step is configured to operate with a batchwise input and a continuous output.

The method of disclosure combines the benefits of batchwise processing and continuous processing.

Providing a drying step wherein the input is batchwise and the output is continuous allows for a high processing capacity, and eliminates the need for buffer storage of the filtered material, as well as buffer storage of the dried product before it is processed further in the overall production line. This is only possible if the filtered material is dry enough that the process can be converted from batchwise to continuous over the course of the drying step, and the output of the filtering step is provided at intervals compatible with the dryer to ensure that it can run continuously.

Previously, coupling a batchwise filtration process with a drying process comprising a batchwise input and a continuous output has been difficult due to mismatch in processing speeds. However, the use of a tube press filter allows the advantages of a batchwise process to be combined with the advantages of a continuous process.

While the disclosure is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example and will be described in detail. It should be understood, however, that other embodiments, beyond the particular embodiments described, are possible as well. All modifications, equivalents, and alternative embodiments falling within the spirit and scope of the appended claims are covered as well.

The above discussion is not intended to represent every example embodiment or every implementation within the scope of the current or future Claim sets. The figures and Detailed Description that follow also exemplify various example embodiments. Various example embodiments may be more completely understood in consideration of the following Detailed Description. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a schematic of one embodiment of the disclosure, wherein the washing step is batchwise, the filtration step is batchwise and the drying step comprises a batchwise input and a continuous output.

Figure 1 further demonstrates and optional plurality of washing and filtration steps that serve to increase the output of the filtration process and increase process throughput.

Figure 1 further shows buffer storage of unprocessed cathode active material before the batchwise washing step.

Figure 2 shows schematically the operating steps of a tube press filter.

Figure 3 shows particle size distribution curves for material that has been filtered by a process according to the disclosure (Figure 3A), and for material that has been filtered by a process not according to the disclosure (Figure 3B).

DETAILED DESCRIPTION

Process

The method of the disclosure relates to processing a cathode active material.

In the context of the disclosure, "processing" refers to the steps of washing, filtering and drying a cathode active material. After processing, the level of impurities in a cathode active material is lower than the level of impurities in an unprocessed cathode active material.

An "unprocessed cathode active material" in the context of the disclosure refers to a cathode active material that has not been processed to remove impurities after its formation by calcination. An unprocessed cathode active material is therefore a cathode active material that comprises impurities.

A "partially processed cathode active material" may be used to refer to a cathode active material that has been washed or washed and filtered according to the method of the disclosure. A "processed cathode active material" may be used to refer to a cathode active material that has been washed, filtered and dried according to the method of the disclosure.

A processed cathode active material may be directly combined with a binder and a conductive additive in order to form a slurry suitable for preparing a positive electrode coating on a current collector substrate. Alternatively, a processed cathode active material may be further processed before fabricating the cathode.

The process of the disclosure may occur before, during or after a calcination step or any other cathode active material processing step.

Preferably, the method of the disclosure is carried out on a calcined cathode active material.

Thus, preferably the method of the disclosure includes a step prior to step a) comprising calcining a cathode active material.

Alternatively, step a) in the method of the disclosure may comprise a) a washing step in which a calcined cathode active material is contacted with a dispersing agent to provide a washed material.

If the process preceding the method of the disclosure is a continuous process (i.e. the formation of the unprocessed cathode active material), buffer storage of unprocessed cathode active material may be required before the washing step as shown in the schematic of Figure 1.

In the context of this disclosure, "buffer storage" refers to storage of material in preparation for a batchwise step, for instance to ensure that there is suitable quantities available to carry out a batchwise step. It is preferable to minimise the amount of buffer storage in a commercial process, since it introduces inefficiency in the production line and may risk degradation of the material when not stored in a stable state. For instance, a dispersing agent may impact the properties of a cathode active material during storage, such as the surface area and surface properties.

Cathode active material

The disclosure relates to a method of processing a cathode active material. In the context of this disclosure, "cathode active material" refers to any material that is suitable for use as the electrochemically active material in a cathode, and suitable for use in a battery. The term "electrochemically active material" is to be understood as an electrochemical species which can be oxidized and reduced in a system which enables a battery to produce electric energy during discharge. The role of the cathode active material is to reversibly intercalate ions (such as lithium ions) during battery charge and discharge cycles.

Preferably, the cathode active material is an intercalation material.

Preferably the cathode active material is a transition metal complex such as nickel manganese cobalt oxide (NMC) material. Even more preferably, the cathode active material is an NMC material intercalated within lithium or an "Li-NMC" material.

Exemplary cathode active materials include lithium iron phosphate, nickel-cobalt- manganese (NMC) composite oxides and lithium NMC (Li-NMC) composite oxides such as lithium cobalt oxide (LiCoCh), lithium nickel oxide (LiNiCh), lithium manganese oxide (LiMn?O4), lithium nickel cobalt oxide (LiNixCoi-xC (0<x<l) or LiNii-x-yCoxAlyC ((0<x<0.2, 0<y<0.1)) as well as lithium nickel cobalt manganese (NCM) oxide (LiNii-x-yCOxMnyCh (0<x+y<l)).

In some embodiments, the cathode active material comprises lithium nickel cobalt manganese oxides (NMC) (LibNii-x- _y COxMn _y AzO ₂ (0<x+y<l)), where A is an element other than Li, Ni, Co, Mn or O and wherein 0<z<0.05, preferably 0<z<0.03, more preferably 0.001<z<0.01, and wherein 0.9<b<1.2. A is one or more chosen from the group Al, B, Zr, Ba, Ca, Ti, Mg, Ta, Nb, V, Fe, Ru, Re, Pt and Mo. Preferably, A is chosen from the group Al and Zr.

In preferred embodiments, the NMC cathode materials are lithium rich. As such, the cathode active material typically comprises lithium nickel cobalt manganese oxides (NMC) represented by the formula LibNii-x- _y COxMn _y AzO ₂ (0<x+y<l), where A is an element other than Li, Ni, Co, Mn or O and wherein 0<z<0.05, preferably 0<z<0.03, more preferably 0.001<z<0.01, and wherein 1.05<b<1.2. A is one or more chosen from the group Al, B, Zr, Ba, Ca, Ti, Mg, Ta, Nb, V, Fe, Ru, Re, Pt and Mo.

Impurities

The disclosure relates to a method of removing impurities from a cathode active material. In the context of the disclosure, "impurities" or "impurity" refer to any material that is not desired in a processed cathode active material. Additionally, the term impurities may also be used to refer to a material that is present in excess.

For example, "impurities" may be used to refer to lithium and lithium ions that are in excess in an unprocessed Li-NMC material. "Impurities" may further be used to refer to counter ions or by-products of the Li-NMC fabrication processes.

An example of an impurity is lithium.

The impurities of the disclosure are preferably dispersible or soluble in the dispersing agent.

Washing

The method of the disclosure comprises a washing step. In the context of the disclosure, "washing" refers to contacting an unprocessed cathode active material with a dispersing agent, the dispersing agent preferably comprising water, to produce a mixture of cathode active material and dispersing agent.

The object of the washing step is to separate the cathode active material from any impurities. Once the washing step is complete, a washed material is obtained. The washed material is mixture of cathode active material and dispersing agent, said dispersing agent containing impurities.

The washing step may be continuous or batchwise. Preferably the washing step is batchwise and may, for example, be carried out in a tank with an agitator.

Preferably, the washing step is carried out for long enough and with enough dispersing agent such that the impurities are separated from the cathode active material. The washing step should not however be carried out for so long that the particle size and/or surface area of the cathode active material is substantially changed.

It is further desirable to keep the washing step as short as possible in order to minimize the adverse effects of contacting the active material with a dispersing agent for too long. These adverse effects include loss of product, deterioration of the cathode active material particles and is associated with an unwanted increase in the BET surface area.

In the context of the disclosure, the time in which the dispersing agent and the cathode active material are in contact is the "dispersing agent contact" time. The dispersing agent contact time encompasses the washing step, the filtration step and any time delay between washing and filtering the cathode active material.

The "dispersing agent contact" time is therefore the time elapsed between the start of the washing step and the end of the filtration step. After filtering, the amount of dispersing agent present in the cathode active material is minimal, and it is thus not associated with the negative side-effects of dispersing agent contact.

Preferably, the dispersing agent contact time is kept to a minimum. For example, the dispersing agent contact time may be between 2 minutes and 20 minutes, for instance between 4 minutes and 20 minutes.

The dispersing agent contact time can be reduced by decreasing the duration of the washing step, decreasing the duration of the filtration step, or decreasing the delay between the end of the washing step and the start of the filtration step.

To decrease the duration of the washing step, the amount of dispersing agent or the temperature of the dispersing agent may be adjusted.

Accordingly, the weight ratio of dispersing agent to unprocessed cathode active material in the washing step may be from 5: 1 to 1: 1. For example, the weight ratio of the dispersing agent to cathode active material may be from 4: 1 to 1: 1, from 3: 1 to 1 : 1, or from 5:2 to 1: 1, or from 2: 1 to 1: 1. Preferably the weight ratio of dispersing agent to unprocessed cathode active material is between 3: 1 and 1 : 1, or between 2: 1 and 1: 1, or between 3: 1 and 3:2.

The duration of the washing step may be between 20 seconds and 10 minutes, such as between 30 seconds and 8 minutes, 60 seconds and 6 minutes, 60 seconds and 5 minutes or 90 seconds and 4 minutes. Preferably the duration of the washing step is between 90 seconds and 4 minutes.

A washing step with a high weight ratio of dispersing agent to unprocessed cathode active material, may have a relatively short duration. That is, a washing step with a large excess of dispersing agent may have a duration that is significantly shorter than a washing step with a 1 : 1 ratio of dispersing agent to cathode active material.

Typically, the washing step is carried out at a temperature of between 12°C and 35°C, for example between 15°C and 32°C, between 18°C and 30°C, between 20°C and 28°C, or between 20°C and 25°C. Preferably, the washing step is carried out at a temperature of between 20 °C and 25°C.

If the washing temperature is too high, there may be insufficient separation of the impurities and the cathode active material.

The "dispersing agent" may be a solvent or a mixture of solvents. For example, the dispersing agent may be a mixture of water and other solvents, wherein the impurities are dispersible or soluble in either water or one of the other solvents. Alternatively, the dispersing agent may be water.

Preferably, the dispersing agent is water, even more preferably the dispersing agent in deionized water. For example, the deionized water may have a resistivity of 18MQcm ¹ such as MiliQ water.

The washing step may be considered complete when the level of impurities in the dispersing agent is lOOppm or more.

Preferably, the washing step may be considered complete when the level of lithium in the dispersing agent is lOOppm or more.

Preferably, the particle size distribution of the cathode active material is substantially unchanged by the washing step. This means that the particle size distribution of the unprocessed cathode active material and the washed material is substantially the same.

In the context of the disclosure, "particle size distribution" refers to the DIO particle size, D50 particle size and the D90 particle size.

In the context of the disclosure "substantially the same" in relation to particle size distribution refers to no more than a 50% change in the DIO particle size, no more than a 30% change in the D50 particle size, and no more than a 20% change in the D90 particle size. For example, the particle size distribution of the washed material may have a DIO particle size that is within 50% of the D10 particle size of the unprocessed cathode active material, a D50 particle size that is within 30% and a D90 that is within 20%.

The terms substantially the same and "substantially unchanged" may be used interchangeably in the context of this disclosure. Conversely, the term "substantially changed" may be used to refer to a material wherein the DIO, D50 and D90 particle sizes are not within 50%, 30% and 20% respectively.

Preferably, the DIO particle size of the washed material is within 40% of the of the DIO particle size of the unprocessed cathode active material, for instance within 30%, within 25%, within 20%, or within 10%.

Preferably, the D50 particle size of the washed material is within 25% of the of the D50 particle size of the unprocessed cathode active material, for instance within 20%, or within 10%.

Preferably, the D90 particle size of the washed material is within 15% of the of the D90 particle size of the unprocessed cathode active material, for instance within 10%, within 8% or within 5%.

The "D10 particle size" in the context of the disclosure means that 10% of the particles have a diameter than is smaller than the D10 particle size.

Similarly, the "D50 particle size" in the context of the disclosure means that 50% of the particles have a diameter than is smaller than the D50 particle size, and the "D90 particle size" means that 90% of the particles have a diameter that is smaller than the D90 particle size.

A change in the D10 particle size is indicative of a change in the number of small particles in the material. On the other hand, a change in the D90 particle size is indicative of a change in the number of large particles in the material. Small particles in the cathode active material are most at risk of changing size during the process of the disclosure. Accordingly, the D10 particles size is highly sensitive to the process of the invention as demonstrated by Figures 3A and 3B.

The D10, D50 and D90 particles sizes may be measured by laser diffraction for instance using a Malvern Mastersizer 3000.

Suitable methodologies for measuring particle size and particle size distributions by laser diffraction are detailed in ISO 13320:2020.

Laser diffraction measures particle size distributions by measuring the angular variation in intensity of light scattered as a laser beam passes through a dispersed particulate sample. Large particles scatter light at small angles relative to the laser beam and small particles scatter light at large angles. The angular scattering intensity data is then analysed to calculate the size of the particles responsible for creating the scattering pattern, using the Mie theory of light scattering. The particle size is reported as a volume equivalent sphere diameter (i.e. the D[4,3] value).

Preferably, the particle properties (DIO, D50 and D90 particle sizes) are measured when dispersed in water.

For dry samples, the particles may be resuspended before measuring the particle size, according to the equipment specifications.

In an example, the cathode active material particles are suspended in water and analysed using a Mastersizer 3000, wherein the the Mastersizer 3000 is set a follows:

Mode: Single mode

Laser light: Red and blue laser light

Measurement time: 10 seconds per measurement

Obscuration range: 4 to 7%

Stabilization time: 30 seconds

The particle size analysis is then be carried out using Mie theory (volume equivalent sphere). To use Mie theory, it is usually necessary to know the refractive index and adsorption index of the sample. These may be determined by any suitable method.

If it is not possible to complete the washing step - i.e., achieve an impurity concentration of lOOppm in the dispersing agent without substantially changing the particle size distribution (D10, D50 and D90) - it will be appreciated that a different dispersing agent composition, weight ratio of dispersing agent to unprocessed cathode active material, washing step duration or temperature may be required.

Filtration

The method of the disclosure comprises a filtration step.

In the context of the disclosure, "filtration" or "filtering" is to be understood as processing the washing material (i.e., a mixture of cathode active material and dispersing agent) to reduce the amount of dispersing agent in the mixture. The object of the filtration step is to remove and separate the dispersing agent comprising impurities from the cathode active material. After the filtration step is complete, a filtered material is obtained. The filtered material is a cathode active material comprising residual dispersing agent, wherein the amount of impurities is lower than the amount of impurities in the unprocessed cathode active material.

The wt % of dispersing agent in the filtered material may be less than 20%, such as less than 15%, less than 10, or less than 8%. Preferably the wt % of dispersing agent in the filtered material is less than 10%, more preferably less than 9%, or even more preferably less than 8%.

The wt % of dispersing agent in the filtered material may be determined by gravimetric analysis, or any other suitable analysis method.

The filtration step of the disclosure is batchwise. Batchwise filtration has a low operational cost and is thus highly favourable in industrial processes. The batchwise filtration process further provides the benefit of a high filtration efficiency and a low product yield loss.

The filtration step of the disclosure comprises processing the washed material with a tube press filter. A tube press filter is a pressure filter that separates liquid and solid phases by application of high pressure, for example 100 bar. The higher the pressure, the higher or faster the degree of separation.

Furthermore, the efficiency of the tube press filter allows for the duration of the filtration step to be as short as possible. This in turn limits the dispersing agent contact time of the filtration step, and the adverse effects of dispersing agent contact time may be mitigated in the processed cathode active material.

An exemplary tube press filter is shown schematically in Figure 2. The tube press filter in its empty state (1) comprises two concentric cylinders (10, 13) defining an annular space (12). During operation, tube press filter operation may comprise feeding the washed material (20) i.e., a mixture of cathode active material and dispersing agent, into the annular space (12) between two concentric cylinders (10 and 13), as show in step 2 of Figure 2. Optionally, the washed material may be drawn into the annular space (12) by a hydraulic force. The inner cylinder (10) comprises a filtration surface (11) and is capable of channeling liquid media out of the system. The outer cylinder (13) is configured to apply pressure for instance via a hydraulic force such that the annular space (12) is reduced in volume, urging the material in the annular space (12) against the filtration surface (11). The pressure applied forces any liquid in the material contained in the annular space (12) through the filtration surface to be channeled out of the tube press filter (30), with the solid material being retained in the annular space, shown in step 3 of Figure 2. The filter cake typically is discharged from the bottom of the tube press filter (40), for instance by the inner cylinder (10) moving relative to the outer cylinder (13) urging the filter cake out of the apparatus show in step 4 of Figure 2.

In the context of the disclosure, any processes wherein the washed material is compressed under high pressure (>5 bar, preferably >10 bar) such that the washed material is urged against a filtration surface resulting in separation of the liquid phase and the solid phase is considered a tube press filtration process.

A tube press filter is a highly efficient filtration process that quickly reduces the dispersing agent content of the washed material. The fast throughput time is also beneficial for coupling the tube press filtration process with a substantially continuous drying step. It is further beneficial for minimizing the dispersing agent-cathode active material contact time.

A drawback with filtration via standard tube press filter operation is that the high pressure applied (often as high as 100 bar) may grind or comminute the cathode active material particles, substantially increasing the number of smaller particles. A cathode comprising fine ground cathode active material particles is likely to have suboptimal properties and thus it is preferable to avoid comminuting the particles during filtration.

In an embodiment, the cathode active material of the disclosure is characterised by being comminuted when processed in a tube press filter at a pressure of 100 bar, for instance the cathode active material is comminuted at a pressure of 80 bar, 60 bar or 50 bar. Preferably therefore, the filtration step of the disclosure comprises processing the washed material at a pressure such that the cathode active material particles are not comminuted.

In the context of the disclosure, "comminuting" refers to a process wherein the particle size distribution is significantly changed. The term comminuting may be interchangeably used with "grinding" in the context of the disclosure.

Accordingly, the particle size distribution is substantially unchanged by the filtration step of the disclosure. That is, the particle size distribution of the unprocessed material and the filtered material is substantially the same. In the context of the disclosure "substantially the same" in relation to particle size distribution refers to no more than a 50% change in the DIO particle size, no more than a 30% change in the D50 particle size, and no more than a 20% change in the D90 particle size. For example, the particle size distribution of the filtered material may have a DIO particle size that is within 50% of the DIO particle size of the unprocessed cathode active material, a D50 particle size that is within 30% and a D90 that is within 20%.

Preferably, the D10 particle size of the filtered material is within 40% of the of the D10 particle size of the unprocessed cathode active material, for instance within 30%, within 25%, within 20%, or within 10%.

Preferably, the D50 particle size of the filtered material is within 25% of the of the D50 particle size of the unprocessed material, for instance within 20%, or within 10%.

Preferably, the D90 particle size of the filtered material is within 15% of the of the D90 particle size of the unprocessed material, for instance within 10%, within 8% or within 5%.

In an embodiment, the washed cathode active material of the disclosure is characterised by being comminuted when processed with a tube press filter at high pressure, for instance by displaying a reduction in D10 particle size of more than 50% when processed with a tube press filter at 100 bar, or by displaying a reduction in D10 particle size of more than 50% when processed with a tube press filter at 80 bar, or by displaying a reduction in D10 particle size of more than 50% when processed with a tube press filter at 60 bar, or by displaying a reduction in D10 particle size of more than 50% when processed with a tube press filter at 50 bar, or

- for instance, by displaying a reduction in D10 particle size of more than 40% when processed with a tube press filter at 100 bar, or

- for instance, by displaying a reduction in D10 particle size of more than 40% when processed with a tube press filter at 80 bar, or

- for instance, by displaying a reduction in D10 particle size of more than 40% when processed with a tube press filter at 60 bar, or

- for instance, by displaying a reduction in D10 particle size of more than 40% when processed with a tube press filter at 50 bar, or

- for instance, by displaying a reduction in D10 particle size of more than 25% when processed with a tube press filter at 100 bar, or - for instance, by displaying a reduction in DIO particle size of more than 25% when processed with a tube press filter at 80 bar, or

- for instance, by displaying a reduction in DIO particle size of more than 25% when processed with a tube press filter at 60 bar, or

- for instance, by displaying a reduction in DIO particle size of more than 25% when processed with a tube press filter at 50 bar, or

- for instance, by displaying a reduction in D50 particle size of more than 30% when processed with a tube press filter at 100 bar, or

- for instance, by displaying a reduction in D50 particle size of more than 30% when processed with a tube press filter at 80 bar, or

- for instance, by displaying a reduction in D50 particle size of more than 30% when processed with a tube press filter at 60 bar, or

- for instance, by displaying a reduction in D50 particle size of more than 30% when processed with a tube press filter at 50 bar, or

- for instance, by displaying a reduction in D50 particle size of more than 25% when processed with a tube press filter at 100 bar, or

- for instance, by displaying a reduction in D50 particle size of more than 25% when processed with a tube press filter at 80 bar, or

- for instance, by displaying a reduction in D50 particle size of more than 25% when processed with a tube press filter at 60 bar, or

- for instance, by displaying a reduction in D50 particle size of more than 25% when processed with a tube press filter at 50 bar, or

- for instance, by displaying a reduction in D90 particle size of more than 20% when processed with a tube press filter at 100 bar, or

- for instance, by displaying a reduction in D90 particle size of more than 20% when processed with a tube press filter at 80 bar, or

- for instance, by displaying a reduction in D90 particle size of more than 20% when processed with a tube press filter at 60 bar, or

- for instance, by displaying a reduction in D90 particle size of more than 20% when processed with a tube press filter at 50 bar, or

- for instance, by displaying a reduction in D90 particle size of more than 15% when processed with a tube press filter at 100 bar, or

- for instance, by displaying a reduction in D90 particle size of more than 15% when processed with a tube press filter at 80 bar, or

- for instance, by displaying a reduction in D90 particle size of more than 15% when processed with a tube press filter at 60 bar, or

- for instance, by displaying a reduction in D90 particle size of more than 15% when processed with a tube press filter at 50 bar. Typically, the process of the invention reduces the particle sizes. Therefore, with all of the relative particle sizes disclosed herein, the particle size of the processed material (be that either after the wash step or after the filtration step) is preferably within the stated percentage below the pre-processed particle size (either DIO, D50 or D90).

In other words, the DIO particle size of the filtered material is no more than 50% lower than the of the DIO particle size of the unprocessed cathode active material, for instance no more than 40% lower, no more than 30% lower, no more than 25% lower, no more than 20% lower, or no more than 10% lower.

It may have previously been considered that a tube press filter is unsuitable for providing a filtered material comprising active material particles that are substantially the same size as the particles of the washed material.

Surprisingly, it is possible to operate a tube press filter such that comminuting is avoided, whilst also providing a filtration step that removes the majority of the dispersing agent in a short amount of time. One way in which this can be achieved is by operating the tube press filter at a reduced pressure (i.e. lower than the standard operating pressure).

For example, the tube press filter may be operated at a pressure of less than 100% of the maximum operating pressure, such as less than 60%, less than 50%, or less than 40%. Preferably the tube press filter is operated at less than 30% of the maximum operating pressure.

For example, the tube press filter may be operated at a pressure of 60 bar or less, such as 50 bar or less, for instance 40 bar or less. Preferably the tube press filter is operated at 30 bar or less, most preferably 25 bar or less.

Figures 3A and 3B show the particle size distribution for material that has been filtered with a tube press filter according to the method of the disclosure, and using a method outside of the disclosure.

The particle size distribution of the sample of Figure 3A was substantially unchanged by the filtration step and indicated by a single peak in the particle size distribution curve. The filtration step used to process the material of Figure 3A is thus according to the disclosure. In contrast to Figure 3A, the particle size distribution of Figure 3B is substantially changed by the filtration step. The distribution curve of Figure 3B comprises a shoulder representing an increase in the number of small particles. The increase in the number of small particles may be attributed to grinding or comminution of the particles during filtration.

The DIO particle size of the sample of Figure 3B is not within 50% of the DIO particle size of the unprocessed material. The material was therefore substantially changed by the filtration step. The filtration step used to process the material of Figure 3B is therefore not according to the disclosure.

It will be appreciated that whether a filtration step, and specifically whether the pressure applied during the filtration step, is according to the disclosure will depend on the nature of the material being processed.

The optimum pressure and duration of the filtration step will be dependent on the particle size or type of cathode active material in the washed material.

For example, a dense material comprising small particles may require a longer filtration time than a material with larger particles. Alternatively, a material comprising small particles may be more resistant to comminuting, and as such, the tube press filter may be operated at a higher pressure than for a material comprising large particles.

Whilst reducing the pressure mitigates the comminuting of the active material particles, it also has the drawback of less efficient filtration and hence higher levels of residual dispersing agent in the filtered material.

A balance needs therefore to be found between avoiding particle comminution whilst also providing a filtration step that removes enough dispersing agent. In some instances, this balance may be achieved by varying the duration of the filtration step, or alternatively by performing more than one filtration step.

Preferably, the tube press is operated such that the dispersing agent contact time is as short as possible, whilst also ensuring that the particles are not comminuted. For cathode active material particles that are resistant to comminuting, it may be beneficial to carry out the filtration step at high pressure, or even maximum tube press pressure. Specifically, the filtration step of the disclosure is a batchwise process with an output such that it is compatible with a high-capacity drying step that quickly converts from a batchwise drying step to a continuous drying step.

Preferably, the filtration step comprises a plurality of tube press filtration processes running concurrently, the plurality of tube press filtration processes being phased to ensure a regular, batchwise output from the filtration step. This allows for a maximized throughput capacity and a reduced production cost and time.

In the context of the disclosure, a "phase" is the time interval between tube press filtration cycles for processes (i.e. the time interval between the start of the previous and the start of the subsequent tube press filtration step) wherein a plurality of tube press filters are operated. For example, if the cycle time of one press is T, and the number of presses is X, then the phase (Y) is within 20% of T/X. In this instance, the cycle time can be expressed as the mean average time for a number of cycles, for instance five cycles.

For example, if the cycle time for one tube press filter is 12 minutes, and there are three tube press filters, the phase is four minutes +/- 48 seconds. This means that there is an output of filtered material from one of the tube press filters in the plurality of tube press filters around every four minutes.

Tube press filters typically operate with a short cycle time, typically from 5 to 10 minutes, for example 8 minutes or less. It is therefore possible to provide a short phase time with relatively few tube press filters, further reducing the capital costs for a short filtration to drying step transition.

This may optionally be coupled with a plurality of batchwise washing processes with the same phase as the plurality of tube press filtration processes, and configured such that one washing process is in synchrony with one filtration process. An example of such a configuration is demonstrated in the schematic of Figure 1.

Drying

The method of the disclosure comprises a drying step. In the context of the disclosure, "drying" refers to processing the filtered material (i.e., a cathode active material with residual dispersing agent) to reduce the amount of dispersing agent in the mixture.

The drying step of the disclosure has a batchwise input from the filtration step and is configured to provide a continuous output. The drying step may comprise a semi- continuous process. In the context of the disclosure, a semi-continuous process is a process that is between a batchwise and a continuous process. That is, a semi-continuous process is neither fully batchwise (input and output) nor fully continuous (input and output).

The object of the drying step is to remove the residual dispersing agent in the filtered material. On completion of the drying step, a dried material is obtained. The dried material is a cathode active material that is substantially free from dispersing agent.

In the context of the disclosure "substantially free from dispersing agent" is to be understood as the wt % of dispersing agent in the dried material being less than 2%. For example, the wt % of dispersing agent in the dried material may be as less 1.5%, less than 1%, less than 0.5%, less than 0.2% or less than 0.1%. Preferably the wt % of dispersing agent in the filtered material is less than 0.2%, even more preferably less than 0.1%.

The drying step of the disclosure converts a batchwise input to a continuous output. The filtered material is dispensed batchwise into the drying step, for instance directly after being ejected from the tube press filter. The batches of filtered material become combined as the dispersing agent content is reduced, resulting in a continuous output by the end of the drying step. The benefit of a continuous drying process is maintaining a high processing capacity while minimizing both capital and operational costs.

Preferably, the drying step of the invention has a duration of no more than 10 hours, such as no more than 8 hours, no more than 6 hours or no more than 4 hours. Typically, the drying step has a duration of from 1 to 4 hours, such as from 1 to 3 hours, or alternatively between 2 and 4 hours.

The drying step of the disclosure may be carried out at a temperature of between 100°C and 250°C, such as between 150°C and 225°C, or between 175°C and 225°C. Preferably the drying step is carried out at a temperature of between 180°C and 220°C.

Preferably, the drying step comprises mechanical agitation. Mechanical agitation is beneficial for breaking up the filtered material so that it can be dried more efficiently, and to ensure that the batchwise input is quickly combined such that the drying step is substantially continuous. Preferably, the drying step comprises constant mechanical agitation to ensure that homogenous drying is achieved. The drying step may be carried out using any suitable drying apparatus suitable for receiving a batchwise input and producing a continuous output. Suitable drying apparatus for carrying out the drying step of the disclosure include a rotary dryer or paddle dryer.

The dyer may comprise a vacuum pump to drive off the volatilized residual dispersing agent thus further improving the drying efficiency.

The particle size of the filtered material is not substantially changed during the drying process. Instead, coagulated particles may be broken apart as they dry such that the filter cake is formed into a dry, free flowing powder.

Preferably, in the overall process, the particle size distribution is substantially unchanged. That is, the particle size distribution of the unprocessed material and the dried material is substantially the same.

In the context of the disclosure "substantially the same" in relation to particle size distribution refers to no more than a 50% change in the DIO particle size, no more than a 30% change in the D50 particle size, and no more than a 20% change in the D90 particle size. For example, the particle size distribution of the dried material may have a DIO particle size that is within 50% of the DIO particle size of the unprocessed cathode active material, a D50 particle size that is within 30% and a D90 that is within 20%.

The terms substantially the same and "substantially unchanged" may be used interchangeably in the context of this disclosure. Conversely, the term "substantially changed" may be used to refer to a material wherein the D10, D50 and D90 particle sizes are not within 50%, 30% and 20% respectively.

Preferably, the D10 particle size of the dried material is within 40% of the of the D10 particle size of the unprocessed cathode active material, for instance within 30%, within 25%, within 20%, or within 10%.

Preferably, the D50 particle size of the dried material is within 25% of the of the D50 particle size of the unprocessed cathode active material, for instance within 20%, or within 10%.

Preferably, the D90 particle size of the dried material is within 15% of the of the D90 particle size of the unprocessed cathode active material, for instance within 10%, within 8% or within 5%. EXAMPLE

An exemplary process according to the disclosure involved washing an NMC cathode active material in water at room temperature for approximately 3 minutes. The particles were then processed in a tube press filter for 6 minutes operating at either 20 bar or 100 bar. Following filtration, the resultant powder was dried in a paddle dryer.

The particle size distribution (D[4,3] volume distributed calculated using Mie theory) of the particles after processing with the paddle dryer were measured using a Malvern Mastersizer 3000. Three samples were analysed to report the average. An exemplary distribution for the batch processed at 20 bar is shown in Figure 3A, while the batch processed at 100 bar is shown in Figure 3B. The D10, D50 and D90 values for the particles before processing were, respectively, 6.2 pm, 12.1 pm and 23.4 pm.