Related applications

This application claims the priority of UK application GB 2117617.7 filed on 7 December 2021 , the contents of which are incorporated by reference herein in their entirety.

Field of the Invention

The present invention relates to improved processes for making electrochemically active oxide materials, such as lithium nickel composite oxide materials, which have utility as cathode materials in secondary lithium-ion batteries.

Background of the Invention

Methods of manufacturing electrochemically active oxide materials typically involve the precipitation of a mixed metal precursor from a mixed metal solution. The mixed metal precursor is isolated from the formed slurry via filtration, and the filter cake is dried to yield particles of the mixed metal precursor. The mixed metal precursor is then heat treated to produce the electrochemically active material. The heat treatment involves heating the material, typically in the presence of one or more lithium compounds, in an industrial kiln at an elevated temperature to form the active phase of the final electrode material. In some cases, a primary heat treatment process is performed, for example to convert a hydroxide precursor material into an oxide intermediate, followed by a secondary heat treatment after applying a coating to the intermediate, to provide a surface-modified oxide product.

The heat treatment step(s) are typically performed in a roller hearth kiln (RHK). The precursor material is loaded into large ceramic crucibles known as saggars before being placed in the kiln and being heated to the desired temperature for the desired time. Achieving efficiency in the heat treatment step along with a high-quality product is difficult. The heat treatment time required to provide a satisfactory product is often long and the requirement to introduce gases and saggars to the kiln reduces the energy efficiency of the process. Furthermore, the mass of material that can be loaded into the saggars can be limited by factors such as powder density and packing, and by limited gas diffusion through the powder bed in the saggar. This means that, in order to achieve a desired manufacturing throughput, a larger kiln is necessary reducing process efficiency, for example through increased energy demands and through the use of large numbers of saggars.

In addition, powder loss may be observed during heat treatment processes performed during the manufacture of electrode materials where gases streams are used due to the entrainment of some of the powder into the gas stream which carries it out of the kiln where it may be lost as waste. There remains a need for improved processes for the manufacture of electrochemically active oxide materials, such as lithium nickel composite oxide materials. In particular, there remains a need for improvements in processes which lead to an increased production throughput and yield of the final electrode material product (for a certain machine size) and reduced specific energy consumption (energy consumption per kg of product).

Summary of the Invention

The present inventors have surprisingly found that particles of precursors of electrochemically active oxide materials may granulated prior to heat treatment with no detrimental effect on the electrochemical properties of the formed materials, despite the heat treatment being performed on granules rather than a powder material. The present inventors have also found that the granules may be formed directly from the precursor filter cake formed during isolation of the precipitated precursor avoiding any requirement to dry the filter cake prior to granulation, therefore significantly increasing process efficiency.

The granulated material offers increased loading of saggars used in heat treatment through increases in density of precursor material and I or more efficient gas flow through the powder bed. The use of granulated material also offers a reduction in losses of precursor material in gas flows during heat treatment.

Therefore, in a first aspect of the invention there is provided a process for producing an electrochemically active oxide material, the process comprising the steps of:

(i) providing a slurry of a precursor of the electrochemically active oxide material;

(ii) filtering the slurry to yield a precursor filter cake;

(iii) granulating a mixture of the precursor filter cake and at least one lithium- containing compound to form a granulated precursor blend;

(iv) heat treating the granulated precursor blend to form the electrochemically active oxide material; and

(v) optionally de-agglomerating the electrochemically active oxide material.

In a second aspect of the invention there is provided an electrochemically active oxide material obtained or obtainable by a process as described herein.

Detailed Description

Preferred and/or optional features of the invention will now be set out. Any aspect of the invention may be combined with any other aspect of the invention unless the context demands otherwise. Any of the preferred and/or optional features of any aspect may be combined, either singly or in combination, with any aspect of the invention unless the context demands otherwise. The present invention provides a process for the production of an electrochemically active oxide material. In some embodiments, the electrochemically active oxide material comprises an electrochemically active oxide cathode material. In some embodiments, the electrochemically active oxide material comprises an electrochemically active mixed-metal oxide cathode material. In some embodiments, the electrochemically active oxide material comprises an electrochemically active lithium mixed-metal oxide cathode material, such as a lithium mixed transition metal oxide cathode material. Non-limiting examples of electrochemically active oxide materials which may be manufactured according to the method of the invention include lithium nickel composite oxides, including doped or undoped lithium nickel cobalt aluminium oxides (NCA) and doped or undoped lithium nickel manganese cobalt oxides (NMC). The skilled person understands that these materials may be manufactured by analogous processes which involve the preparation of a mixed-metal hydroxide which is subsequently heat treated, typically in the presence of one of more lithium-containing compounds.

In some embodiments, the electrochemically active oxide material comprises or consists of lithium nickel composite oxide, in which the material contains one or more further metal elements other than lithium or nickel. In some embodiments, the electrochemically active oxide material comprises or consists of lithium nickel composite oxide, wherein the amount of Ni in the material is at least 50 mol% of the total amount of non-lithium metals in the material, such as from 50 mol% to 98 mol%.

In preferred embodiments the electrochemically active oxide material comprises or consists of a lithium nickel composite oxide material having a composition according to Formula 1:

Li _a NixMyA _z O2+b

Formula 1 in which:

M is one or more of Co and Mn;

A is one or more of Al, V, Ti, B, Zr, Cu, Sn, Cr, Fe, Ga, Si, Zn, Mg, Sr, Ca, S, Ce, La, Mo, Nb, P, Sb and W

0.8 < a < 1.2

0.5 < x < 1

0 < y < 0.5

0 < z < 0.2

-0.2 < b < 0.2 x + y + z = 1.

In Formula I, 0.8 < a < 1 .2. It may be preferred that a is greater than or equal to 0.9, or 0.95. It may be preferred that a is less than or equal to 1.1 , or less than or equal to 1.05. It may be preferred that 0.90 < a < 1.10, for example 0.95 < a < 1.05, or that a = 1 or about 1.

In Formula I, 0.5 < x < 1. It may be preferred that 0.6 < x < 1 , for example that 0.7 < x < 1 , 0.75 < x < 1 , 0.8 < x < 1 , 0.85 < x < 1 or 0.9 < x < 1. It may be preferred that x is less than or equal to 0.99, 0.98, 0.97, 0.96 or 0.95. It may be preferred that 0.75 < x < 1 , for example 0.75 < x < 0.99, 0.75 < x < 0.98, 0.75 < x < 0.97, 0.75 < x < 0.96 or 0.75 < x < 0.95. It may be further preferred that 0.8 < x < 1 , for example 0.8 < x < 0.99, 0.8 < x < 0.98,

0.8 < x < 0.97, 0.8 < x < 0.96 or 0.8 < x < 0.95. It may also be preferred that 0.85 < x < 1 , for example 0.85 < x < 0.99, 0.85 < x < 0.98, 0.85 < x < 0.97, 0.85 < x < 0.96 or 0.85 < x < 0.95.

M is one or more of Co and Mn. In other words, the general formula may alternatively be written as LiaNixCOyiMn _y 2A _z O2+b, wherein y1+y2 satisfies 0 < y1+y2 < 0.5, wherein either y1 or y2 may be 0.

In Formula 1 , 0 < y < 0.5. It may be preferred that y is greater than or equal to 0.01 , 0.02 or 0.03. It may be preferred that y is less than or equal to 0.4, 0.3, 0.2, 0.15, 0.1 or 0.05. It may also be preferred that 0.01 < y < 0.5, 0.02 < y < 0.5, 0.03 < y < 0.5, 0.01 < y < 0.4, 0.01 < y < 0.3, 0.01 < y < 0.2, 0.01 < y < 0.1 or 0.03 < y < 0.1.

A is one or more of Al, V, Ti, B, Zr, Cu, Sn, Cr, Fe, Ga, Si, Zn, Mg, Sr, Ca, S, Ce, La, Mo, Nb, P, Sb and W. A may be one or more of Al, V, Ti, B, Zr, Cu, Sn, Cr, Fe, Ga, Si, Zn, Mg, Sr, and Ca. A may be one or more of Al, Ti, B, Zr, and Mg. Preferably, A is at least Mg and I or Al, or A is Al and I or Mg. Where A comprises more than one element, z is the sum of the amount of each of the elements making up A.

In Formula I, 0 < z < 0.2. It may be preferred that 0 < z < 0.15, 0 < z < 0.10, 0 < z < 0.05, 0 < z < 0.04, 0 < z < 0.03, or 0 < z < 0.02. In some embodiments, z is 0.

In Formula I, -0.2 < b < 0.2. It may be preferred that b is greater than or equal to -0.1. It may also be preferred that b is less than or equal to 0.1. It may be further preferred that -0.1 < b < 0.1. In some embodiments, b is 0 or about 0.

Typically, the electrochemically active oxide material, for example the lithium nickel composite oxide, is a crystalline (or substantially crystalline material). It may have the a- NaFeO2-type structure.

Typically, the particles of the electrochemically active oxide material, for example the lithium nickel composite oxide material, are in the form of secondary particles which comprise a plurality of primary particles (made up from one or more crystallites). The primary particles may also be known as crystal grains.

The particles of electrochemically active oxide material, for example the lithium nickel composite oxide material, typically have a Dv50 particle size of at least 1 pm, e.g. at least 2 pm, at least 4 pm or at least 5 pm. The particles of electrochemically active oxide material typically have a Dv50 particle size of 25 pm or less, e.g. 20 pm or less or 15 pm or less. It may be preferred that the particles of electrochemically active oxide material have a Dv50 in the range of and including 1 pm to 25 pm, such as in the range of and including 2 pm and 20 pm, or 5 pm and 15 pm. Unless otherwise specified herein, the term Dv50 as used herein refers to the median particle diameter of the volume-weighted distribution. The Dv50 may be determined by using a laser diffraction method. For example, the Dv50 may be determined by suspending the particles in water and analysing the particle size distribution by laser diffraction, for example using a Malvern Mastersizer 3000.

The process as described herein comprises a step of (i) forming a slurry of a precursor of the electrochemically active material. As used herein the term ‘slurry of a precursor of the electrochemical active material’ means a mixture of a liquid, typically an aqueous liquid, and the precursor in the form of insoluble particles.

Typically, the precursor is a mixed metal hydroxide. It may be preferred that the mixed metal hydroxide particles comprise a compound according to Formula II:

[NixiMyiA _z i][Op(OH) _q ]a,

Formula II wherein:

M is one or more of Co and Mn;

A is one or more of Al, V, Ti, B, Zr, Cu, Sn, Cr, Fe, Ga, Si, Zn, Mg, Sr, Ca, S, Ce, La, Mo, Nb, P, Sb, W;

0.5 < x1 < 1

0 < y1 < 0.5

0 < z1 < 0.2 wherein p is in the range 0 < p < 1; q is in the range 0 < q < 2; x1 + y1 + z1 = 1 ; and a is selected such that the overall charge balance is 0. Preferably in Formula II, p is 0, and q is 2. In other words, preferably the nickel metal precursor is a pure metal hydroxide having the general formula [Ni _x iM _y iA _z i][(OH)2]a.

As discussed above, a is selected such that the overall charge balance is 0. a may therefore satisfy 0.5 < a < 1.5. For example, a may be 1 . Where A includes one or more metals not having a +2 valence state, or not present in a +2 valence state, a may be other than 1.

It will be understood by the skilled person that the values x1 , y1 , and z1 , and the element(s) A, are selected so as to achieve the desired composition after the process as described herein.

Methods of forming a slurry of precursor are known to those skilled in the art. Typically such methods comprise co-precipitation of a mixed metal hydroxide from a mixed solution of metal salts at high pH in the presence of ammonia or an ammonium salt. For example, methods of preparation of a slurry of nickel-based hydroxide precursors (such as mixed metal hydroxide precursors of composition Nio.9iCoo.o8Mgo.oi(OH) ₂ ) is described in WO2021/074641A1 (Johnson Matthey Public Limited Company) which is incorporated herein by reference.

Typically, the slurry comprises precursor particles, for example particles of mixed metal hydroxide material, with a Dv50 particle size of at least 1 pm, e.g. at least 2 pm, at least 4 pm or at least 5 pm. The particles of the precursor typically have a Dv50 particle size of 20 pm or less, e.g. 15 pm or less. It may be preferred that the particles of particles of the precursor have a Dv50 in the range of and including 1 pm to 20 pm, such as between 2 pm and 20 pm, or 5 pm and 15 pm. Unless otherwise specified herein, the term Dv50 refers to the median particle diameter of the volume-weighted distribution. The Dv50 of the precursor particles may be determined by using a laser diffraction method. For example, the Dv50 may be determined by suspending the particles in water and analysing using a Malvern Mastersizer 3000. Typically, the precursor particles are in the form of secondary particles comprising a plurality of primary particles.

The process comprises a step of (ii) filtering the slurry to yield a precursor filter cake. Suitable methods of filtration are known to the skilled person, for example vacuum filtration. The filtration process results in a filter cake of solid precursor material which is collected by the filter and a filtrate. Preferably, the filter cake is washed to remove residual reactants and impurities. Typically, this washing step involves one or more washes of the filter cake with water and I or an aqueous solution of a base.

The filter cake typically comprises at least 5 wt% water. The water content of the filter cake may be in the range of and including 5 to 30 wt% of water, for example in the range of and including 10 to 30 wt%, or 10 to 25 wt%. It has been found that the filter cake comprising such levels of water can be advantageously granulated therefore avoiding drying of the filter cake and increasing process efficiency. The water content of the filter cake may be determined by measuring weight loss of a sample of the filter cake after heating to 120 °C. Suitably, the water content may be measured by a moisture analyser, for example a halogen moisture analyser available from Mettler Toledo.

Step (iii) of the process comprises granulating a mixture of the precursor filter cake and at least one lithium-containing compound to form a granulated precursor blend. Preferably, the filter cake is mixed with the at least one lithium-containing compound and granulated in a single process step, i.e. the mixing and granulation is carried out in the same equipment.

Suitable lithium-containing compounds include lithium salts, such as inorganic lithium salts, for example lithium hydroxide (e.g. LiOH or LiOH.H ₂ O) or lithium carbonate (U2CO3). Lithium hydroxide may be particularly preferred. It will be apparent to the skilled person that the amount of the at least one lithium-containing compound to be added to the filter cake will depend on the molar amount of precursor in the filter cake and the required ratio of lithium to non-lithium metals in the final electrode active material. Typically the filter cake is blended with 1 .0 to 1.1 molar equivalent of a lithium-containing compound with respect to precursor.

The method used to achieve agglomeration is not limited, but examples include treatment of the mixture of the filter cake and the at least one lithium-containing compound in a high shear mixer. An example of equipment which may be used to perform agglomeration is a high-shear mixer from Maschinenfabrik Gustav Eirich GmbH & Co KG, such as a Eirich EL1. Preferably the agglomeration comprises mixing at high speeds (for example a tip speed of at least 4 m/s, e.g. at least 5 m/s, at least 10 m/s, at least 15 m/s, or at least 25 m/s), to ensure good dispersion of moisture through the mixture and to ensure correct growth of the agglomerated particles.

It has been found that the water content of the filter cake facilitates granulation, however the addition of an aqueous medium, such as water, during granulation may be required or desired in order to achieve the desired granule size.

It has been found that the use of additional binders or agglomerating agent is not necessary during granulation, since it has been observed that the water contained in the filter cake and I or added during the granulation process facilitates agglomeration on its own without the need for further binders or agglomerating agents. Thus in some embodiments the granulation step comprises performing granulation of the material in the presence of the water, and preferably in the absence of any additional binder or agglomerating agent. This reduces the level of contaminants in the final product and I or the amount of waste generated during the process. Typically, the granulated precursor blend has a Dv50 greater than or equal to 30 pm. It may be preferred that the granulated precursor blend has a Dv50 greater than or equal to 50 pm, greater than or equal to 70 pm, or greater than equal to 100 pm. Typically, the granulated precursor blend has a Dv50 less than or equal to 1000 pm. It may be preferred that the granulated precursor blend has a Dv50 less than or equal to 900 pm, or less than or equal to 800 pm. It may be preferred that the granulated precursor blend has a Dv50 in the range of and including 30 pm to 1000 pm, or in the range of and including 50 pm to 1000 pm, or in the range of and including 70 pm to 1000 pm, or in the range of and including 100 pm to 1000 pm, or in the range of and including 200 pm to 800 pm. Unless otherwise specified herein, the term Dv50 refers to the median particle diameter of the volume-weighted distribution. The Dv50 of the granulated material may be determined by using a laser diffraction method. For example, the Dv50 of the granules may be determined by analysing the particle size distribution by laser diffraction using air dispersion at a pressure of 3 bar, for example using a Malvern Mastersizer 3000 Aero S.

The average size of the material is increased using the granulation process, i.e. the average particle size of the granulated precursor blend material is greater than that of the precursor particles in the precursor filter cake. The average particle size may be the Dv50 volumebased particle size measured as set out herein. It may be preferred that granulation is performed such that the difference between Dv50 of the granulated precursor blend and the Dv50 of the precursor is at least 10 pm, at least 20 pm, at least 50 pm, at least 70 pm, or at least 100 pm.

The process as described herein comprises a step (iv) heat treating the granulated precursor blend to form the electrochemically active oxide material. Any suitable heat treatment equipment may be used, including but not limited to, a roller hearth kiln (RHK) and rotary calciner (also known as a rotary kiln). It may be preferred that the heat treatment is carried out in a rotary calciner.

The heat treatment step may be carried out at a temperature of at least 400 °C, at least 500 °C, at least 600 °C or at least 650 °C. The heat treatment step may be carried out at a temperature of 1200 °C or less, 1100 °C or less, 1000 °C or less, 900 °C or less, 800 °C or less or 750 °C or less. It may be preferred that the heat treatment step comprises heating to a temperature in the range of and including 400 to 1000 °C. It may be further preferred that the heat treatment step comprises heating to a temperature in the range of and including 600 to 900 °C.

The material to be heated may be at a temperature of 400 °C, at least 500 °C, at least 600 °C, or at least 650 °C for a period of at least 30 minutes, at least 1 hour, or at least 2 hours. The period may be less than 12 hours, or less than 8 hours. Preferably, the heat treatment step comprises heating to a temperature in the range of and including 400 to 1000 °C for a period of from 30 mins to 12 hours. It may be further preferred that the heat treatment step comprises heating to a temperature in the range of and including 600 to 900 °C for a period of from 2 hours to 8 hours.

The heat treatment step may be carried out under a CCh-free atmosphere. For example, CC>2-free air may be flowed over the materials during heating and optionally during cooling. The CC>2-free air may, for example, be a mix of oxygen and nitrogen. Preferably, the atmosphere is an oxidising atmosphere. It may be preferred that the CCh-free atmosphere comprises a mixture of O2 and N2. It may be preferred that volumetric concentration of oxygen is between 10 vol% and 100 vol%, such as between 80 and 100 vol%. The volumetric concentration of oxygen may be at least 21 vol%.

As used herein, the term “CC>2-free” is intended to include atmospheres including less than 100 ppm CO2, e.g. less than 50 ppm CO2, less than 20 ppm CO2 or less than 10 ppm CO2. These CO2 levels may be achieved by using a CO2 scrubber to remove CO2.

Optionally, the process comprises the step of modifying the surface of the electrochemically active oxide material after heat treatment step (iv) and I or after optional deagglomeration step (v). Typically, surface modification comprises contacting the electrochemically active oxide material with at least one metal-containing compound (such as a compound selected from a cobalt-containing compound, and an M-containing compound (such as an aluminium- containing compound)) in a surface-modification step to form an enriched surface layer on the electrochemically active oxide material.

The metal-containing compound (such as a cobalt-containing compound, and I or M- containing compound) may be independently selected from nitrates, sulfates or acetates. Nitrates may be particularly preferred. The compounds may be provided in solution (e.g. aqueous solution). The compounds may be soluble in water. Where the metal-containing compounds are provided in solution, the mixture of the solution with the electrochemically active oxide material may be dried, e.g. by evaporation of the solvent or by spray drying.

The surface modification step may be followed by a second calcination step. The second calcination step may be carried out at a temperature of at least 400 °C, at least 500 °C, at least 600 °C or at least 650 °C. The second calcination step may be carried out at a temperature of 1000 °C or less, 900 °C or less, 800 °C or less or 750 °C or less. The material to be calcined may be held at a temperature of 400 °C, at least 500 °C, at least 600 °C, or at least 650 °C for a period of at least 30 minutes, at least 1 hour, or at least 2 hours. The period may be less than 24 hours. The second calcination step may be carried out under a CCh-free atmosphere as described above with reference to the first calcination step.

The process may include step (v) optionally de-agglomerating the electrochemically active oxide material. The nature of the equipment used for deagglomeration is not particularly limited. For example, it may be a ball mill, a planetary ball mill, pin mill, jet mill or a rolling bed mill. The milling may be carried out until the particles reach the desired size. For example, the particles of the electrochemically active oxide material, e.g. lithium nickel composite oxide material, may be milled until they have a particle size distribution such that the Dv50 particle size is 20 pm or less, e.g. 15 pm or less, 14 pm or less, 13 pm or less, or 12 pm or less, for example until the Dv50 particle size is in the range of 1 to 20 pm.

The process of the present invention may further comprise the step of forming an electrode (typically a cathode) comprising the electrochemically active oxide material, e.g. lithium nickel composite oxide material. Typically, this is carried out by forming a slurry of the electrochemically active oxide material, e.g. lithium nickel composite oxide material, applying the slurry to the surface of a current collector (e.g. an aluminium current collector), and optionally processing (e.g. calendaring) to increase the density of the electrode. The slurry may comprise one or more of a solvent, a binder, carbon material and further additives.

Typically, the electrode of the present invention will have an electrode density of at least

2.5 g/cm ³ , at least 2.8 g/cm ³ or at least 3 g/cm ³ . It may have an electrode density of

4.5 g/cm ³ or less, or 4 g/cm ³ or less. The electrode density is the electrode density (mass/volume) of the electrode, not including the current collector the electrode is formed on. It therefore includes contributions from the active material, any additives, any additional carbon material, and any remaining binder.

The process of the present invention may further comprise constructing a battery or electrochemical cell including the electrode comprising the electrochemically active oxide material, e.g. lithium nickel composite oxide material. The battery or cell typically further comprises an anode and an electrolyte. The battery or cell may typically be a secondary (rechargeable) lithium (e.g. lithium ion) battery.

The present invention will now be described with reference to the following examples, which are provided to assist with understanding the present invention and are not intended to limit its scope.

Examples

Example 1 - Manufacture of a lithium nickel composite oxide material with granulation of the precursor filter cake Production of a precursor filter cake

A suspension of a precursor with a composition of Nio.92Coo.o8Mgo.oi(OH)2 was prepared by a co-precipitation method analogous to that described in WO2021/074641A1 (Sample A, with no drying step).

The formed slurry was filtered using a vacuum belt filter to yield a precursor filter cake which was washed with water. The water content of the precursor filter cake was measured to be 16 wt % using a using a Mettler Toledo Halogen Moisture Analyzer HC103 by heating a small amount of material (~1g) to 120°C rapidly and measuring the weight loss.

Granulation of the precursor filter cake

473.5g of precursor filter cake (395.8g precursor) and 104.2g LiOH were loaded in to a Eirich EL-1 mixer in the diagonal position using a star rotor. The rotor speed was set to 20- 28 m/s for 5 minutes to break up the filter cake and mix it with the LiOH. The rotor speed was then set to 10 - 15 m/s and water (<50 mis) added dropwise to granulate the material.

Heat treatment of the granules

The granules were heat-treated using the following heat treatment profile: 5°C/min to 450°C, 2h hold at 450°C, 2°C/min to 700°C, 6h hold at 700°C, cooling to ambient temperature to form a lithium nickel composite oxide active material.

Electrochemical testing

A sample of the material after heat treatment was analysed for electrochemical performance. This was compared to a reference sample with the same composition and produced during using the same heat treatment process (without a granulation step). The results of testing for discharge capacity at 0.1 C and 2 C are shown in Table 1 . The results show that equivalent discharge capacity is achieved despite the direct granulation of the precursor filter cake as a blend with lithium hydroxide prior to calcination.

Testing protocol - Electrodes were prepared in a dry room (low humidity) by combining 94%wt of the lithium nickel composite oxide active material, 3%wt of Carbon-065 as conductive additive and 3%wt of polyvinylidene fluoride (PVDF) as binder in N-methyl-2- pyrrolidine (NMP) as solvent. The slurry was added into the reservoir of a 125 pm doctor blade which coated aluminium foil using an Erichsen coater. The electrode sheet was dried at 120 °C for 2 hours before being pressed to achieve a target density of 3.1 g/cm3. The target electrode loading is 9 mg/cm2. The pressed electrode sheet was cut into 14 mm disks and further dried at 120 °C under vacuum for 2 hours. Electrochemical test was performed with a CR2025 coin-cell type, which was assembled in an argon filled glove box (MBraun). Lithium foil was used as an anode. A microporous polypropylene membrane (Celgard 2500) was used as a separator. 1M LiPF6 in 1:1:1 mixture of ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) with 1% of vinyl carbonate (VC) was used as electrolyte.

The cells were tested with a MACCOR battery cycler and were charged and discharged between 3.0 and 4.3 V.C-rate and retention tests were used to characterise the cells. The C-rate test charged and discharged cells between 0.1C and 5C. The cells were kept at 23 °C throughout the testing process. Table 1 - Electrochemical results