WO2022200765A1

WO2022200765A1 - Process to modify the surface of a lithium nickel metal oxide material

Info

Publication number: WO2022200765A1
Application number: PCT/GB2022/050619
Authority: WO
Inventors: Daniel CAIRNS; Paul CONNAGHAN; Andrew Diamond; Andrew Charles FRY; Stuart Johnson
Original assignee: Ev Metals Uk Limited
Priority date: 2021-03-24
Filing date: 2022-03-10
Publication date: 2022-09-29
Also published as: GB202104080D0

Abstract

A process for producing a surface-modified particulate lithium nickel metal oxide material is provided. The process comprises contacting the lithium nickel metal oxide particles with at least one metal-containing compound to provide a coated powder followed by a calcination step in a rotary calciner.

Description

PROCESS TO MODIFY THE SURFACE OF A LITHIUM NICKEL METAL OXIDE MATERIAL

Field of the Invention

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

Background of the Invention

Lithium nickel metal oxide materials having a layered structure find utility as cathode materials in secondary lithium-ion batteries. Varying amounts of the nickel in such materials may be substituted with other metals to improve electrochemical stability and cycling performance. It has also been found that increasing or enriching the amount of certain metal elements at the particle surface or, in the case of secondary particles, at the grain boundary between adjacent primary particles, can be an effective way to improve electrochemical performance.

Typically, grain boundary enrichment is achieved by immersion of secondary particles of the lithium nickel metal oxide material in a solution of one of more metal-containing compounds and then removal of the solvent through evaporation, followed by a subsequent heat treatment or calcination step.

For example, WO2013025328 describes a particle including a plurality of crystallites including a lithium nickel metal oxide composition having a layered a-NaFeC>2-type structure, and a grain boundary between adjacent crystallites, wherein a concentration of cobalt in the grain boundaries is greater than in the crystallites. Example 2 of WO2013025328 has the composition Li1.01Mg0.024Ni0.88Co0.12O2.03 and has cobalt-enriched grain boundaries. In order to achieve enrichment of the grain boundaries, secondary particles of a lithium nickel metal oxide material are added to an aqueous solution of lithium nitrate and cobalt nitrate and the resulting slurry subsequently spray dried before a heat treatment step.

The heat treatment step performed after the immersion and spray drying steps involves heating the material within a roller hearth kiln (RHK). WO 2013/025328 described above involves calcination in an alumina crucible on the lab scale, the industrial scale equivalent of which would be calcination in an RHK, as is commonly used in the battery material industry. The material is loaded into large crucibles known as saggars before being placed in the kiln and heated to the desired temperature for the desired time. This process tends to be cumbersome and expensive, with RHK equipment being extremely large and costly to operate and maintain. Furthermore, the saggars necessary for heating material in the kiln eventually deteriorate and need to be replaced, further increasing the cost and complexity of the overall process.

The use of surface modification and / or grain boundary enrichment has the drawback that additional process steps are required, leading to higher energy consumption, increased levels of process waste, and higher manufacturing costs. This can impact on the commercial viability of such materials and have environmental impacts. These are exacerbated by the use of an RHK due to the drawbacks described above. There remains a need for improved processes for the manufacture of lithium nickel metal oxide materials. In particular, there remains a need for improvements in processes which lead to surface modification and / or grain boundary enrichment.

Summary of the Invention

The present inventors have surprisingly found that an improved process is provided by the incorporation of rotary calcination equipment in the place of the typical RHK for the manufacture of surface-modified particulate lithium nickel metal oxide materials. The use of a rotary calciner or rotary kiln for the heat treatment step after coating provides a more efficient process in terms of both cost and energy consumption and also saves on materials since there is no need to use saggars during the calcination. The footprint of the process equipment is considerably reduced due to the smaller size of the rotary calciner compared with an RHK of equivalent functionality.

Accordingly, in a first aspect of the invention there is provided a process for producing a surface-modified particulate lithium nickel metal oxide material having a composition according to Formula 1:

LiaNixMyAzC>2_+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 the process comprising the steps of:

(i) providing lithium nickel metal oxide particles in the form of secondary particles comprising a plurality of primary particles;

(ii) contacting the lithium nickel metal oxide particles with at least one metal- containing compound to provide a coated powder; and

(iii) calcining the coated powder in a rotary calciner to form the surface-modified particulate lithium nickel metal oxide material.

In a second aspect, of the invention there is provided a surface-modified particulate lithium nickel metal oxide obtained or obtainable by a process described herein.

Brief Description of the Drawings

Figure 1 shows particle size distributions for granules of precursor particles after granulation, and after being fed through a twin screw feeding mechanism for several different time periods.

Figure 2 is an SEM image of an agglomerated material made during the process according to the invention, at a magnification of 100x.

Figure 3 is an SEM image of an agglomerated material made during the process according to the invention, at a magnification of 1000x.

Figure 4 is an SEM image of an agglomerated material made during the process according to the invention, at a magnification of 5000x.

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 surface-modified particulate lithium nickel metal oxide materials having a composition according to Formula I as defined above.

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 Li_aNi_xCoyiMn_y2A_z0_2+b, wherein y1+y2 satisfies 0 < y1+y2 £ 0.5, wherein either y1 or y2 may be 0. It may be preferred that M is Co alone, i.e. the surface-modified lithium nickel metal oxide contains no Mn.

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 / or Al, optionally in combination with one or more of V, Ti, B, Zr, Cu, Sn, Cr, Fe, Ga, Si, Zn, Sr, Ca, S, Ce, La, Mo, Nb, P, Sb and W, or A is Al and / 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 surface-modified particulate lithium nickel metal oxide material is a crystalline (or substantially crystalline material). It may have the a-NaFeC>2-type structure.

Typically, the surface-modified lithium nickel metal oxide particles 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 primary particles are separated by grain boundaries.

The particulate lithium nickel metal oxide material of Formula I is surface-modified. Herein, the term “surface-modified” refers to a particulate material which comprises primary and / or secondary particles which have undergone a surface modification process to increase the concentration of at least one element near to the surface of the particles, i.e. that the particles comprise a layer of material at or near to the surface of the particles which contains a greater concentration of at least one element than the remaining material of the particle, i.e. the core of the particle. The surface modification results from contacting the particles with one or more further metal-containing compounds, and then heating the material. For clarity, the discussions of the composition according to Formula I herein, when in the context of surface-modified particles, relate to the overall particle, i.e. the particle including the modified surface layer.

The particulate lithium nickel metal oxide material of Formula I may comprise enriched grain boundaries, i.e. that the concentration of one or more metals at the grain boundaries is greater than the concentration of the one or more metals in the primary particles. The grain boundaries may be enriched with, for example, cobalt and / or aluminium.

It may be preferred that M includes cobalt and that the concentration of cobalt at the grain boundaries between the primary particles is greater than the concentration of cobalt in the primary particles. Alternatively, or in addition, it may be further preferred that the concentration of aluminium at the grain boundaries between the primary particles is greater than the concentration of aluminium in the primary particles.

The concentration of cobalt in the primary particles may be at least 0.5 atom %, e.g. at least 1 atom %, at least 2 atom % or at least 2.5 atom % with respect to the total content of Ni, M and A in the primary particle. The concentration of cobalt in the primary particle may be 35 atom % or less, e.g. 30 atom % or less, 20 atom % or less, 15 atom % or less, 10 atom % or less, 8 atom % or less or 5 atom % or less with respect to the total content of Ni, M and A in the primary particles.

The concentration of cobalt at the grain boundaries may be at least 1 atom %, at least 2 atom %, at least 2.5 atom % or at least 3 atom % with respect to the total content of Ni, M, and A at the grain boundaries. The concentration of cobalt at the grain boundaries may be 40 atom % or less, e.g. 35 atom % or less, 30 atom % or less, 20 atom % or less, 15 atom % or less, 10 atom % or less, or 8 atom % or less with respect to the total content of Ni, M and A in the primary particles.

The difference between the concentration of cobalt in the primary particles and at the grain boundaries may at least 1 atom %, e.g. at least 3 atom % or at least 5 atom % (calculated by subtracting the concentration of cobalt in the primary particles in atom % from the concentration of cobalt at the grain boundaries in atom %).

The concentration of a metal, such as cobalt or aluminium, at the grain boundaries and in the primary particles may be determined by energy dispersive X-ray (EDX) analysis of the centre of a grain boundary and the centre of an adjacent primary particle for a thinly sliced (e.g. 100-150 nm thick) section of a particle by a sectioning technique such as focused ion beam milling.

The particles of surface-modified lithium nickel metal oxide may have a cobalt-rich coating on their surface. The concentration of cobalt in the particles (e.g. secondary particles) may decrease in a direction from the surface of the particles to the centre of the particles. The difference between the concentration of cobalt at the surface of the particles and in the centre of the particles may be at least 1 atom %, e.g. at least 3 atom % or at least 5 atom % (calculated by subtracting the concentration of cobalt at the surface of the particles in atom % from the concentration of cobalt at the centre of the particles in atom %). The concentration of cobalt may be determined as defined above for the grain boundaries and primary particles.

Alternatively, or in addition, the particles of surface-modified lithium nickel metal oxide may have an aluminium-rich coating on their surface. The concentration of aluminium in the particles (e.g. secondary particles) may decrease in a direction from the surface of the particles to the centre of the particles. The difference between the concentration of aluminium at the surface of the particles and in the centre of the particles may at least 1 atom %, e.g. at least 3 atom % or at least 5 atom % (calculated by subtracting the concentration of aluminium at the surface of the particles in atom % from the concentration of aluminium at the centre of the particles in atom %). The concentration of aluminium may be determined as defined above for the level of cobalt at the grain boundaries and primary particles.

The particles, e.g. secondary particles, of surface-modified lithium nickel metal oxide typically have a volumetric D50 particle size of at least 1pm, e.g. at least 2pm, at least 4pm or at least 5pm. The particles of surface-modified lithium nickel metal oxide (e.g. secondary particles) typically have a D50 particle size of 30pm or less, e.g. 20pm or less or 15pm or less. It may be preferred that the particles of surface-modified lithium nickel metal oxide have a D50 of 1pm to 30pm, such as between 2pm and 20pm, or 5pm and 15pm. The term D50 as used throughout the disclosure refers to the volume-based particle size (the value of particle diameter at 50% in the cumulative volume distribution, i.e. 50 vol% of the particles in the sample have a diameter smaller than this value), as measured using a laser diffraction method, for example by suspending the particles in air and analysing using a Malvern Mastersizer 3000.

The process as described herein comprises contacting the lithium nickel metal oxide particles with a metal-containing compound. The process as described herein may comprise coating the lithium nickel metal oxide particles with a metal-containing compound. For example, the process may comprise the addition of a coating liquid to lithium nickel metal oxide particles.

It will be understood by the skilled person that the one or more metal-containing compound(s) are selected to include those elements which are desired to be present in the surface layer of the particulate surface-modified lithium nickel metal oxide material. The metal-containing compounds are typically metal salts, inorganic metal salts, for example metal oxides, hydroxides, nitrates, sulfates, citrates or acetates. Nitrates may be particularly preferred.

In some embodiments, the or each metal-containing compound present is independently selected from an M-containing compound and an A-containing compound (and optionally a Li-containing compound). The lithium nickel metal oxide particles may be contacted with one or more of each of these options, e.g. one or more A-containing compounds, wherein the identity of A is different within each compound. In some embodiments, the lithium nickel metal oxide particles are contacted with at least one metal-containing nitrate, wherein each metal-containing nitrate present is independently selected from an M-containing nitrate and an A-containing nitrate (and optionally a Li- containing nitrate).

In some embodiments, the lithium nickel metal oxide particles are contacted with at least one M-containing compound and at least one A-containing compound and, optionally at least one Li-containing compound. In some embodiments, the p lithium nickel metal oxide particles are contacted with a single M-containing compound, a single A-containing compound, and optionally a single Li-containing compound. In some embodiments, the lithium nickel metal oxide particles are contacted with a single M-containing nitrate, a single A-containing nitrate and a single Li-containing nitrate.

Preferably, the lithium nickel metal oxide particles are contacted with an aluminium- containing compound. The aluminium-containing compound is typically an aluminium salt, such as an inorganic aluminium salt, for example aluminium nitrate. The use of an aluminium-containing compound can lead to an increase in the concentration of aluminium at the grain boundaries and/or at or near to the surface of the lithium nickel metal oxide particles.

Alternatively, or in addition, it is preferred that the lithium nickel metal oxide particles are contacted with a cobalt-containing compound. The cobalt-containing compound is typically a cobalt salt, such as an inorganic cobalt salt, for example cobalt nitrate. The use of a cobalt- containing compound can lead to an increase in the concentration of cobalt at the grain boundaries and/or at or near to the surface of the lithium nickel metal oxide particles.

Typically, the lithium nickel metal oxide particles are provided in the form of secondary particles comprising a plurality of primary particles. The particles prior to coating may be known as the ‘base material’. In some embodiments the particles of the base material have a composition according to Formula (II)

I— Ia1 Nix1 Myl A_zl 02+b1

Formula II 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 £ a1 £ 1.2 0.5 £ x1 < 1 0 < y1 £ 0.5 0 £ z1 £ 0.2 -0.2 £ b1 £ 0.2 x + y + z = 1

It may be preferred that A in Formula II is not Al. In such cases A is one or more of V, Ti, B, Zr, Cu, Sn, Cr, Fe, Ga, Si, Zn, Mg, Sr, Ca, S, Ce, La, Mo, Nb, P, Sb and W. It may also be preferred that M in Formula II is Co alone, i.e. that the base material contains no Mn.

It will be understood by the skilled person that the values a1 , x1 , y1 , z1 and b1 , and the element(s) A, are selected so as to achieve the desired composition of Formula 1 after the process as described herein.

The base materials are produced by methods well known to the person skilled in the art. These methods involve the co-precipitation of a mixed metal hydroxide from a solution of metal salts, such as metal sulfates, for example in the presence of ammonia and a base, such as NaOH. In some cases, suitable mixed metal hydroxides may be obtainable from commercial suppliers known to the skilled person. The mixed metal hydroxides are then mixed with a lithium-containing compound, such as lithium hydroxide or lithium carbonate, and hydrated forms thereof, prior to a calcination step to form the base material.

The base material is contacted with a metal-containing compound to provide a coated lithium nickel metal oxide powder which is then subjected to calcination in the rotary kiln to form the surface-modified lithium nickel metal oxide particles. The contacting may be achieved by any suitable method. In some embodiments, contacting comprises coating the base material with a metal-containing compound. In some embodiments, coating is achieved by immersing lithium nickel metal oxide particles (base material) in a solution of one or more metal-containing compounds, then removing solvent from the solution, for example by drying. For example, coating may be achieved by a method as described in WO 2013/025328. In some embodiments, contacting comprises mixing the lithium nickel metal oxide particles with the one or more metal-containing compounds in the absence of any liquid medium (i.e. dry mixing). For example, base material may be mixed with alumina nanoparticles to provide modified particles comprising a core derived from the base material and an outer layer of alumina.

However in preferred embodiments the step of contacting the lithium nickel metal oxide particles with at least one metal-containing compound comprises (a) providing a coating liquid, the coating liquid comprising at least one metal-containing compound, and (b) adding the coating liquid to the lithium nickel metal oxide particles to form an impregnated powder, the volume of coating liquid added corresponding to 50 to 150 % of the apparent pore volume of the lithium nickel metal oxide particles. In such embodiments, the process then comprises a step of calcining the impregnated powder in a rotary calciner.

The inventors have surprisingly found that immersion of lithium nickel metal oxide particles in a solution of one or more metal-containing compounds is not required to achieve grain boundary enrichment, and that the addition of a controlled volume of a coating liquid to secondary particles of lithium nickel metal oxide materials can be used to modify the composition at the grain boundaries without the requirement for significant solvent evaporation. It has further been found that the electrochemical performance of materials produced by immersion-evaporation methods may be matched by materials produced by the herein described process, with the advantage that a spray-drying or an equivalent evaporation step is not required during the manufacturing process, significantly reducing energy consumption and industrial waste.

The specific combination of the addition of a controlled volume of a coating liquid with the later step of calcining in a rotary calciner provides significantly improved efficiency and reduced energy consumption of the overall process.

In some embodiments the coating liquid is provided at a temperature of at least 50°C.

The coating liquid comprises at least one metal-containing compound. It will be understood by the skilled person that the coating liquid comprises those elements which are desired to be present in the surface layer of the surface-modified particulate lithium nickel metal oxide material. The metal-containing compounds are typically metal salts, such as nitrates, sulfates, citrates or acetates. It may be preferred that the metal containing compounds are inorganic metal salts. Nitrates may be particularly preferred.

In some embodiments, the coating liquid comprises at least one metal selected from M, A and Li (where M and A are as defined above). In some embodiments, the coating liquid comprises at least one metal-containing compound, wherein the or each metal-containing compound present is independently selected from an M-containing compound and an A- containing compound, optionally in combination with a Li-containing compound. The coating liquid may include one or more of each of these options, e.g. one or more A-containing compounds, wherein the identity of A is different within each compound.

In some embodiments, the coating liquid comprises at least one metal-containing nitrate, wherein each metal-containing nitrate present is independently selected from an M- containing nitrate and an A-containing nitrate, and optionally a Li-containing nitrate.

In some embodiments, the coating liquid comprises at least one M-containing compound, at least one A-containing compound and at least one Li-containing compound. In some embodiments, the coating liquid comprises a single M-containing compound, a single A- containing compound and a single Li-containing compound. In some embodiments, the coating liquid comprises a single M-containing nitrate, a single A-containing nitrate and a single Li-containing nitrate.

Preferably, the coating liquid comprises an aluminium-containing compound. The aluminium-containing compound is typically an aluminium salt, such as an inorganic aluminium salt, for example aluminium nitrate. The use of an aluminium-containing compound in the coating liquid can lead to an increase in the concentration of aluminium at the grain boundaries and/or at or near to the surface of the surface-modified lithium nickel metal oxide particles.

Alternatively, or in addition, it is preferred that the coating liquid comprises a cobalt- containing compound. The cobalt-containing compound is typically a cobalt salt, such as an inorganic cobalt salt, for example cobalt nitrate. The use of a cobalt-containing compound in the coating liquid can lead to an increase in the concentration of cobalt at the grain boundaries and/or at or near to the surface of the surface-modified lithium nickel metal oxide particles.

The coating liquid may comprise a zirconium-containing compound. In some embodiments, the zirconium-containing compound is present in the coating liquid alongside one or both of a cobalt-containing compound and an aluminium-containing compound. In some embodiments, the coating liquid comprises a zirconium-containing compound but does not contain either of a cobalt-containing compound and an aluminium-containing compound. In some embodiments, the zirconium-containing compound is present in the coating liquid as the sole metal-containing compound.

Optionally, the coating liquid comprises a lithium-containing compound. It proposed that this may be beneficial in order to avoid voids or defects in the structure of the surface-modified particulate lithium nickel metal oxide material which may lead to a reduced lifetime.

It may be preferred that the one or more metal-containing compound(s) are provided as hydrates of metal salts, for example a hydrate of a metal nitrate, such as a hydrate of cobalt nitrate and / or aluminium nitrate, optionally in combination with lithium nitrate, or a hydrate of lithium nitrate.

It may be particularly preferred that the one or more metal salt hydrates are heated to form the coating liquid. Advantageously, such materials dehydrate upon heating leading to a phase change and formation of a liquid suitable for coating with a high metal concentration. Furthermore, metal salt hydrates are typically more economical than de-hydrated equivalents. Optionally, and if required, further water may be added to achieve the required volume of coating liquid.

In some embodiments, the coating liquid is provided at a temperature of at least 50°C. This reduces the likelihood of crystallisation of the one or more metal-containing compound(s) during addition which would lead to poor mixing and an inhomogeneous coating. Furthermore, the use of an elevated temperature allows for the use of metal salts at high concentration and for the coating liquid to be prepared by heating metal salt hydrates.

Typically, the coating liquid is provided at a temperature of from 50 to 80 °C, such as from 50 to 75 °C, 55 to 75 °C, 60 to 75 °C, or 65 to 75 °C.

Typically, the total molar concentration of metal in the coating liquid (i.e. the sum of the molar concentration of each metal in the coating liquid) is at least 0.5 mol/L. The skilled person will understand that the total metal concentration of the coating liquid used will depend on the amount of metal that is required to be applied to the base material and also the apparent pore volume of the base material. However, total metal concentrations less than 0.5 mol/L may not provide a consistent coating of the base material and / or grain boundary enrichment. Preferably, the total molar concentration of metal in the coating liquid is at least 0.75 mol/L, 1.0 mol/L, 1.25 mol/L, 1.5 mol/L, 1.75 mol/L, 2.0 mol/L, 2.5 mol/L or 3 mol/L. The skilled person will understand that the total molar concentration will be limited by the solubility of the metal-containing compounds in the required volume of coating liquid. Typically, the total molar concentration of metal in the coating liquid is less than 7 mol/L. Typically, the total molar concentration of metal in the coating liquid is from 0.5 mol/L to 7 mol/L, such as from 1 mol/L to 7 mol/L, 2 mol/L to 7 mol/L, 3 mol/L to 7 mol/L, or 4 mol/L to 7 mol/L.

The coating liquid is added to the lithium nickel metal oxide particles. Typically, the lithium nickel metal oxide particles are loaded into a mixing vessel prior to the addition of the coating liquid. Typically, the particles are mixed during the coating liquid addition, for example through stirring or agitation. This ensures an even distribution of the coating liquid.

It may be preferable that the addition step may be carried out under a controlled atmosphere, such as an atmosphere free of CC>2and / or moisture, which may reduce the level of impurities, such as lithium carbonate, in the formed surface-modified lithium nickel metal oxide particles.

The addition may be carried out by a number of means, such as portionwise addition to a mixing vessel via an inlet pipe, or by spraying the coating liquid onto the lithium nickel metal oxide particles. It is considered that spraying the coating liquid may lead to a more consistent distribution of the coating liquid, a more reproducible coating process.

The addition step may be carried out at ambient temperature or an elevated temperature, i.e. the temperature at which the vessel containing the lithium nickel metal oxide particles is heated to is higher than ambient temperature prior to addition of the coating liquid, such as a temperature greater than 25°C, preferably greater than 30°C, or greater than 40°C. The use of an elevated temperature during the addition step reduces the likelihood of solidification or crystallisation of the components of the coating liquid during the addition step, therefore helping to ensure a homogenous coating.

It may be preferable to carry out the addition step with powder at a temperature of from 40 °C to 80 °C, such as from 50 °C to 70 °C, or from 55°C to 65 °C. The use of such addition temperatures may lead to improved electrochemical performance of the surface-modified particulate lithium nickel metal oxide, for example an improved capacity retention. In the process as described herein the coating liquid is added to the lithium nickel metal oxide particles in a volume corresponding to 50 to 150 % of the apparent pore volume of the lithium nickel metal oxide particles. The use of a volume of coating liquid less than 50 % of the apparent pore volume of the particles may lead to an inhomogeneous surface- modification. It has been found that the use of a volume of coating liquid greater than 150% of the apparent pore volume of the particles is not required in order to achieve surface- modification and grain boundary enrichment, and detrimentally leads to an increased need for solvent removal and / or drying and associated energy consumption.

Preferably, the coating liquid is added to the lithium nickel metal oxide particles in a volume corresponding to 70 to 150 %, or more preferably 90 to 150 %, of the apparent pore volume of the lithium nickel metal oxide particles. The use of a volume of coating liquid greater than 70 %, or greater than 90% of the available pore volume, enables the use of use of higher amounts of the one or more metal-containing compound, which may lead to enhanced grain boundary enrichment.

Preferably, the coating liquid is added to the lithium nickel metal oxide particles in a volume corresponding to 70 to 125%, or more preferably 90 to 125 % of the apparent pore volume of the lithium nickel metal oxide particles. Use of a volume of coating liquid less than 125% of the apparent pore volume leads to a lower requirement for drying and evaporation. It has also been observed that the use of a volume of coating liquid greater than 125% of the apparent pore volume of the particles can lead to pooling of the coating liquid in the vessel containing the lithium nickel metal oxide particles once the coating liquid has been added which may be detrimental to achieving a homogeneous surface-modification. It may be preferred that the volume of coating liquid added corresponds to 95 % to 120 % of the apparent pore volume of the particles, or 95 % to 115 %, or 95 % to 110 %, or 95 % to 105 %.

It may also be preferred that the volume of coating liquid added corresponds to 100 % to 150 % of the apparent pore volume of the particles, or 100 to 125 %, 100 to 120 %, 100 to 115 % or 100 to 110 %.

The apparent pore volume per unit mass of base material is determined using a torque measurement system, such as a Brabender Adsorptometer “C”. This method involves the measurement of torque during a mixing process. Water is added to the lithium nickel metal oxide particles whilst mixing, leading to a torque peak on a volume added-torque curve. The volume of water added per unit mass of particles at the point of onset of the torque peak is the apparent pore volume per unit mass of particles.

Following complete addition of the coating liquid the particles may be mixed for a period of time. Typically, the particles may be mixed for a period of from 1 to 60 minutes following complete addition of the coating liquid. It may be preferred that, after complete addition of the coating liquid, the impregnated particles are subjected directly to the calcination step, without the requirement for additional drying. Advantageously, the impregnated particles may be transferred directly from the vessel used for the addition of the coating liquid to a calciner.

The coated (e.g. impregnated) particles are then subjected to a calcination step in a rotary calciner. The skilled person is aware of the construction and use of rotary calciners generally for the calcination of powder materials. In general, a rotary calciner (or rotary kiln) is a piece of kiln equipment comprising a cylindrical or tubular drum into which the material to be thermally treated is loaded. During calcination the drum is rotated slowly to agitate the material and transport the powder to the discharge of the kiln.

The inventors have found unique benefits when using a rotary calciner in the calcination step of the process of the invention when compared with calcination within a standard static oven or kiln, or in an RHK. Firstly, the footprint of the process equipment is greatly reduced for a given amount of material to be calcined, due to the smaller size of a rotary calciner.

Secondly, the energy consumption of the process is reduced because the rotary calciner delivers heat more efficiently to the material, with less wasted heat. Thirdly, due to the removal of the need for saggars, there is a further reduction in energy use and in use of consumable items. Finally, the calcination performance of the rotary calciner is at least equivalent to other types of kiln such as RHK, providing high performance of the product, including improved stability and electrochemical performance.

The inventors have found that the mean residence time of the powder in the heated zone of the rotary calciner is an important consideration, and that certain mean residence times surprisingly lead to significantly improved electrochemical performance of the product. In some embodiments, the mean residence time of the powder in the heated zone is at least 120 mins, for example at least 125 mins, at least 130 mins, at least 135 mins, at least 140 mins, at least 150 mins, at least 160 mins, at least 170 mins, at least 180 mins, at least 190 mins or at least 200 mins. When such a mean residence time in the heated zone is provided, the electrochemical performance of the product, including its discharge capacity and capacity retention, is equivalent to static calcination. In some embodiments, the mean residence time in the heated zone is from 120 to 200 mins, for example from 130 to 200 mins, from 140 to 200 mins, from 120 to 190 mins, from 130 to 190 mins, from 140 to 190 mins, from 150 to 200 mins, from 150 to 190 mins, from 160 to 200 mins or from 160 to 190 mins.

The mean residence time of the powder in the heated zone of the rotary calciner may be determined as follows. After a steady state of powder flow through the rotary calciner has been achieved, the product flow rate, R, out of the calciner in kg/min is determined and recorded. The material feed to the calciner is then terminated but the rotation of the calciner is maintained until no further material passes out of the calciner. The angle of the calciner is increased during this period to ensure maximum possible extraction of freely moving powder from the calciner. The total mass of powder, M, in kg which leaves the calciner between the time at which the material feed was terminated and the time at which no further material passes out of the calciner is determined by weighing said material. The overall residence time, t, during the steady state production period is then determined according to the following equation: t = M/R and the mean residence time in the heated zone (t_h) is determined according to: t_h = t^*(L_h/L) where U is the length of the heated zone within the calciner and L is the total length of the calciner tube which contains material between the inlet and outlet.

Preferably the calcination step is carried out at a temperature of from 600 °C to 750 °C. This temperature range has been observed to provide optimal product electrochemical characteristics. The temperatures here refer to the temperature within the heated zone of the rotary calciner, specified for calcination. It will be understood that other zones may be present along the length of the calciner tube or drum which operate at lower temperatures for other purposes, for example a cooling zone downstream of the heated zone.

In some embodiments the calcination step is carried out at a temperature of from 600 °C to 750 °C, for example from 650 °C to 750 °C, from 680 °C to 750 °C or from 700 °C to 750 °C, and the mean residence time in the heated zone is from 120 to 200 mins, for example from 130 to 200 mins, from 140 to 200 mins, from 120 to 190 mins, from 130 to 190 mins, from 140 to 190 mins, from 150 to 200 mins, from 150 to 190 mins, from 160 to 200 mins or from 160 to 190 mins.

The calcination step may be carried out under a CC 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. 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.

It may be preferred that the CC>2-free atmosphere comprises a mixture of O2 and N2. It may be further preferred that the mixture comprises a greater amount of N2 than O2. In some embodiments, the mixture comprises N2 and O2 in a ratio of from 50:50 to 90:10, for example from 60:40 to 90:10, for example about 80:20. It may be preferred that the volumetric concentration of oxygen is between 10 vol% and 100 vol%, preferably between 15 vol% and 25 vol%. The volumetric concentration of oxygen may be at least 21 vol%.

In some embodiments, step (iii) of calcining the coated powder in a rotary calciner to form the surface-modified particulate lithium nickel metal oxide material is a continuous process step in which the coated powder is continuously fed to the rotary calciner and the calcined surface-modified particulate lithium nickel metal oxide material is continuously removed from the rotary calciner. The coated powder may be fed into one end of a heating drum of the rotary calciner and removed from another end of the heating drum of the rotary calciner, wherein the rotary calciner is adapted to provide a desired calcination mean residence time of the material within the heating drum. The desired mean residence time may be provided by setting the rotational axis of the drum at an angle a to the horizontal, wherein a ³ 0.5°. In some embodiments, 0.5° £ a £ 5°. Such an angle allows the material to advance along the drum of the rotary calciner under the influence of gravity as the drum rotates. The skilled person can choose an appropriate angle within this range to provide the desired mean residence time based on factors including the length of the drum and the flow properties of the material, rotation speed, tube diameter. The inventors have found that an angle of less than 0.5° hinders the steady flow of material along the drum and angles of greater than 5° do not provide a sufficiently efficient design to achieve sufficiently long mean residence time of the material within the calciner. In some embodiments, when the calcination step in the rotary calciner is continuous as described above, a baffle extending inwards from the inner wall into the drum is mounted on the inner wall of the drum of the rotary calciner. The baffle may extend continuously around the entire circumference of the drum, thereby presenting a barrier to the advancement of the material along the drum of the rotary calciner. The height of the baffle (i.e. the distance the baffle extends inwards from the surface of the inner wall of the drum) is less than the inner radius of the drum, providing a pathway for the material to pass over the top of the baffle and continue to advance axially along the tube. The presence of the baffle provides a means to increase the powder bed depth and therefore increase the mean residence time of the material within the rotary calciner to allow the volume of the powder bed to increase. As the amount of material held up by the baffle increases, eventually the material will flow over the baffle and continue to advance along the drum. In this way, it is possible to provide a longer mean residence time of material for a tube of given length. In other words, by introducing the baffle the length of the rotary calciner may be reduced while maintaining the same mean residence time. As a result, the footprint of the process equipment may be even further reduced, improving efficiency.

In some embodiments, the inner wall of the drum of the rotary calciner comprises a single baffle extending inwards from the inner wall into the drum. In some embodiments, the inner wall of the drum of the rotary calciner comprises two or more baffles extending inwards from the inner wall into the drum, axially spaced along the drum.

When the calcination step in the rotary calciner is continuous as described above, the length of the drum of the rotary calciner may also be varied as a means to vary the mean residence time.

As explained above, the chosen drum length, presence of a baffle and angle to the horizontal all have an impact on mean residence time. So, the selection of any one of these factors is influenced by the other two. In general, mean residence time of the material in the calciner will increase (a) as drum length increases, (b) if a baffle is incorporated into the drum, (c) if the angle of the rotational axis of the drum to the horizontal is decreased, and (d) if the rotation speed is reduced. Therefore the skilled person may use any one or more of these features to control the mean residence time of the material in the rotary calciner. For example, if a longer mean residence time is desired, the skilled person may do one or more of increase the drum length, incorporate one or more baffles into the drum and reduce the angle of the rotational axis of the drum to the horizontal or reduce the rotation speed. A smaller equipment footprint is achieved by both reducing the angle a and incorporating one or more baffles into the drum as described above or reducing the rotation speed of the kiln, because this allows the length of the drum (and therefore the overall size and cost of the equipment) to be reduced while maintaining a sufficiently long mean residence time for the material in the calciner. However the inventors have found that it is undesirable to significantly reduce a because this leads to inconsistent material flow through the calciner. Thus in some embodiments, when the calcination step in the rotary calciner is continuous as described above, the inner wall of the drum of the rotary calciner comprises a baffle extending inwards from the inner wall into the drum and 0.5° £ a £ 5°, for example 1° £ a £ 5°.

Preferably the rotary kiln is operated to achieve a Froude number of at least 0.0005, for example from 0.0005 to 0.02. The Froude number is a dimensionless number defined as w²R/g, wherein w is rotation speed in rad/s, R is the tube radius and g is acceleration due to gravity. Providing such Froude numbers when the kiln is in operation ensures that the powder does not merely slide or slump down the curved side of the kiln as the tube rotates. Rather, at Froude numbers within the above range the powder is more likely to “roll”, resulting in radial mixing of the powder. In some embodiments, the speed of rotation of the rotary kiln is selected to achieve a Froude number of at least 0.0005, for example from 0.0005 to 0.02.

In some embodiments, the inner wall of the drum of the rotary calciner comprises an elongate raised feature extending along at least a portion of the axial length of the inner wall of the drum. The axial length refers to the length parallel with the rotational axis of the drum. Due to the extension of the elongate raised feature along at least a portion of the axial length of the drum, as the drum rotates, the feature passes through the powder bed. In this way, radial mixing of the material within the calciner is improved relative to a calciner having a smooth internal surface. Radial mixing can be achieved without sufficient powder disturbance leading to increased powder entrainment into the purge gas flow. The precise size and shape of the elongate raised feature is not limited provided that it presents a barrier to the material of some longitudinal extent as the drum rotates. In some embodiments, the elongate raised feature may take the form of a linear raised feature extending in a direction substantially parallel to the rotational axis of the drum, such as a fin or rib. In some embodiments a plurality of elongate raised features may be provided.

As explained above, in some embodiments the impregnated particles may be transferred directly from the vessel used for the addition of the coating liquid to the calciner. However in some cases it may be preferable to perform an additional step of drying the material after coating but before addition to the calciner to reduce the water content of the material. The use of material of reduced water content provides the benefits of reduced risk of blockage of feeding mechanisms such as screw feeders, increased ease of movement along the calciner drum and reduced corrosion of the internal drum surface. The intensity of drying required will be lower than is necessary in traditional processes which use immersion coating, because the initial water content of the material after coating is much lower, so the process of the invention still provides benefits of reduced energy consumption. The drying method is not limited and any suitable drying technique may be used, including paddle drying and oven drying. The impregnated particles may be dried prior to the calcination step, for example by heating to a temperature of from 100 to 250 °C, such as 120°C or 200 °C, for example for a period of time of from 1 to 10 hours or from 1 to 5 hours, such as 2 hours or 8 hours.

In some embodiments, the process comprises a step of agglomerating the powder after the contacting step (ii) but before the calcination step (iii). In some embodiments the agglomeration comprises agglomerating the base material to form agglomerates having an average particle size larger than that of the base material before agglomeration. Agglomeration is the process of treating the powder to increase its average particle size. Including such a agglomeration step provides significant benefits to the process. The present inventors have surprisingly found that the incorporation of a powder agglomeration step into the process of preparing the material, prior to calcination, provides a higher product yield from the process with no detrimental effect on the electrochemical properties of the material. In particular, there is a reduction of powder loss from the feed into the calciner under conditions where powders have the potential to become entrained into purge gases due to reduced quantities of powder being released into the purge gas exhaust.

Surprisingly, this benefit is achieved without any detrimental effect on the electrochemical properties of the material, despite the calcination being performed with an agglomerated rather than powder material.

Further benefits are also provided by the process of the invention. The bulk density of the agglomerated material is higher than the bulk density of the corresponding powder before agglomeration. The material as a powder had a measured poured density of 1.6kg/litre and the same material after agglomeration and drying had a measured poured density of 1 94kg/litre. This is because the density within each agglomerate is high enough to outweigh the density-reducing effect of the larger spaces between agglomerates. As a result, a given weight of agglomerated material occupies a smaller volume within the powder bed within the calciner, as compared with powder material. This means that a similar sized calciner with a similar volumetric throughput may be used to process a higher mass throughput, improving the efficiency of the process. Despite the higher density of the agglomerated material, the electrochemical properties of the calcined material are not detrimentally affected. Without wishing to be bound by theory, it is believed that the larger spaces between agglomerates allow for better heat and gas diffusion within the material during calcination, ensuring that equivalent electrochemical properties compared to powdered material are obtained. Gas diffusion may involve diffusion of purge gases into the powder bed or diffusion of reaction product gases from the powder bed into the surrounding atmosphere. A further problem encountered when fine, non-agglomerated powders are fed to a calciner is that they are cohesive and cause blockages in equipment (for example screw feeders and hoppers), which leads to disruption to the process operation. By first agglomerating the powder, it can be made less cohesive and therefore the risk of blockages is reduced, minimising the need for costly shut-down of equipment.

The term “agglomeration” refers to a process whereby the average particle size (D50) is increased relative to the precursor particles by the process. One example of how agglomeration may be achieved is subjecting the powdered material to high-shear mixing during which optionally a liquid medium is added to the powder, allowing liquid bridges to form. This causes agglomeration of the particles within the material to increase the average particle size.

In some embodiments, the D50 particle size of the material before agglomeration is less than 100 pm, for example less than 90 pm, less than 80 pm, less than 70 pm, less than 60 pm, less than 50 pm, less than 40 pm, less than 30 pm, less than 20 pm, less than 10 pm or less than or equal to 5 pm. If such a material is subjected to the purge gas flow within a calciner, due to their relatively small size, particles become entrained into the purge gas stream which would then pass out of the calciner and will either require reworking (thus increasing required calciner sizes and energy use) or will be discarded as waste. By agglomerating the material to increase the particle size, the amount of material lost in this way is reduced. This reduction is due to Stokes’ law, according to which the terminal settling velocity of a particle is proportional to the square of its radius. When fed into the kiln, particles may be released into the purge gas stream due material being lifted by the rolling motion of the kiln, mechanically lifted with lifting devices or because they adhere to the kiln wall and are released when removed by mechanical knocking devices. They may also be lifted from the powder due to saltation. For small particle sizes, their settling velocity is insufficiently high to allow them to fall back to the powder bed, therefore they are ejected from the kiln with the purge gas.

In some embodiments, the D50 of the material before agglomeration is from 1 pm to 100 pm, for example from 5 pm to 100 pm, from 1 pm to 30 pm, from 5 pm to 30 pm, from 5 pm to 25 pm, from 5 pm to 20 pm, or from 5 pm to 15 pm.

In some embodiments, this step comprises agglomeration of the powder until the particles have a D50 of at least 10 pm, e.g. at least 11 pm, at least 12 pm or at least 15 pm. Agglomerating until the particles reach this D50 ensures a reduction in the amount of material lost from the calciner in the flow of purging gas. In some embodiments, agglomeration is performed until the particles have a volumetric D50 of at least 100 pm, e.g. at least 200 pm, at least 300 pm or at least 400 pm. In some embodiments, agglomeration is performed until the particles have a volumetric D50 of up to 3500 pm, e.g. up to 2000 pm, up to 1000 pm or up to 700 pm.

In some embodiments, agglomeration is performed until the particles have a volumetric D50 particle size of from 10 pm to 3500 pm, for example from 100 pm to 3500 pm, from 100 pm to 3000 pm, from 200 pm to 3500 pm, from 200 pm to 3000 pm, from 300 pm to 3500 pm, from 300 pm to 3000 pm, from 10 pm to 2000 pm, from 100 pm to 2000 pm, from 200 pm to 2000 pm, from 300 pm to 2000 pm, from 400 pm to 2000 pm, from 400 pm to 1500 pm or from 400 pm to 1000 pm. In some embodiments, agglomeration is performed until the particles have a volumetric D10 particle size of at least 1 pm, e.g. at least 10 pm, at least 100 pm or at least 250 pm. In some embodiments, agglomeration is performed until the particles have a volumetric D10 particle size of from 1 pm to 1000 pm, for example from 10 pm to 1000 pm, from 100 pm to 1000 pm, from 200 pm to 500 pm or from 250 pm to 300 pm.

In some embodiments, agglomeration is performed until the particles have a volumetric D90 particle size of at least 100 pm, e.g. at least 500 pm, at least 1000 pm, at least 1500 pm, at least 2000 pm or at least 2200 pm. In some embodiments, agglomeration is performed until the particles have a volumetric D90 particle size of from 100 pm to 5000 pm, for example from 100 pm to 3000 pm, from 100 pm to 1500 pm, from 500 pm to 2500 pm or from 1000 pm to 3000 pm.

In some embodiments, agglomeration is performed until the particles have a volumetric D10 particle size of from 250 pm to 300 pm, a volumetric D50 particle size of from 400 pm to 1000 pm and a volumetric D90 particle size of from 1000 pm to 3000 pm.

In some embodiments, agglomeration is performed such that the difference between D50_g, the volumetric D50 particle size after agglomeration has been completed, and D50_p, the volumetric D50 particle size of the powder before agglomeration, (D50_g - D50_p) is at least 50 pm, for example at least 100 pm, at least 200 pm, at least 500 pm, at least 800 pm, at least 1000 pm or at least 1200 pm.

The agglomeration step may provide further surprising benefits. It is believed that the use of agglomerated material in the calcination reduces the required calcination time without any detrimental impact on the electrochemical performance. Agglomeration may therefore further improve the energy efficiency of the process.

The method used to achieve agglomeration is not limited, but examples include treatment of the material in a high shear mixer in the presence of a liquid medium. The liquid medium may be water. The liquid medium may in some embodiments have a composition equivalent to the coating liquid which may be used in step (ii) of the process, thereby ensuring that the composition of the powder is not adversely affected or altered by the agglomeration step. A further benefit of this is that no presence of any additional binder or agglomerating agent is necessary during the agglomeration process, since it has been observed that the coating liquid containing the metal-containing compound facilitates agglomeration on its own without the need for further auxiliary binders or agglomerating agents. Thus in some embodiments the agglomeration step comprises performing agglomeration of the material in the presence of the coating liquid, but in the absence of any additional binder or agglomerating agent.

This reduces the level of contaminants in the final product since the amount of auxiliary processing agents in the material is minimised.

In embodiments where the process includes both a drying step and an agglomeration step between the contacting and calcining steps, the powder is preferably agglomerated first, followed by drying. In this way, any residual moisture and coating agents from the contacting (e.g. coating) step can be used as the liquid vehicle for agglomeration, with additional liquid (solvent) added if necessary, without changing the coating composition. Drying may be achieved by any suitable method known to the skilled person, for example oven drying, rotary drying or paddle drying.

An example of equipment which may be used to perform agglomeration is a high-intensity mixer from Maschinenfabrik Gustav Eirich GmbH & Co KG. Preferably the agglomeration comprises mixing at high speeds (for example a tip speed of at least 10 m/s, e.g. 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 dried agglomerated powder is able to be fed through standard powder feeding mechanisms, such as a twin auger screw feeder, without any substantial change in the average particle size of the agglomerates, even when prolonged feeding times are used. Thus the agglomerates retain their relatively large average size for the calcination process, providing the benefits described above. Tests have shown that the agglomerate form is also retained through the calcination such that calcined agglomerates can be poured from the calciner container after cooling.

The process may include one or more milling steps, which may be carried out after the calcination step. The nature of the milling equipment 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 surface-modified lithium nickel metal oxide material may be milled until they have a volume particle size distribution such that the D50 is at least 5 pm, e.g. at least 5.5 pm, at least 6 pm or at least 6.5 pm. The particles of surface-modified lithium nickel metal oxide material may be milled until they have a volume particle size distribution such that the D50 is 15 pm or less, e.g. 14 pm or less or 13 pm or less. The process of the present invention may further comprise the step of forming an electrode (typically a cathode) comprising the surface-modified lithium nickel metal oxide material. Typically, this is carried out by forming a slurry of the surface-modified lithium nickel metal 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/cm³, at least 2.8 g/cm³ or at least 3 g/cm³. It may have an electrode density of

4.5 g/cm³ or less, or 4 g/cm³ 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 surface-modified lithium nickel metal 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

(Li1.03Ni0.91Co0.08Mg0.01O2, Base Material A)

Nio_.9iCoo_.o₈Mgo_.oi(OH)₂ (100g, Brunp) and LiOH (26.3g) were dry mixed in a poly-propylene bottle for 1 hour. The LiOH was pre-dried at 200 °C under vacuum for 24 hours and kept dry in a purged glovebox filled with dry N2.

The powder mixture was loaded into 99%+ alumina crucibles and calcined under C0₂-free air. Calcination was performed as follows: to 450 °C (5°C/min) with 2 hours hold, ramp to 700 °C (2 °C/min) with a 6 hour hold and cooled naturally to 130 °C. The C0₂-free air was flowed over the powder bed throughout the calcination and cooling. The title compound was thereby obtained.

The samples were then removed from the furnace at 130 °C and transferred to a high- alumina lined mill pot and milled on a rolling bed mill until D50 was between 9.5 and 10.5 pm.

Example 2 - Method of producing a surface-modified lithium nickel metal oxide material by immersion in coating solution Base Material A was added to a solution containing dissolved cobalt nitrate, aluminium nitrate and lithium nitrate, and the base material was coated using a method analogous to that described in Example 2 of WO 2013/025328, including spray-drying of the material after coating.

Example 3 - Method of producing a surface-modified lithium nickel metal oxide material using a controlled volume of coating liquid

(Lil.OlNio.867COo.115Alo.006Mgo.01202)

(A) Calculation of the apparent pore volume of the base material

92.7g of a lithium nickel metal oxide base material of formula Li1.03Ni0.91 Co0.08Mg0.01 O2 (Base Material A) was loaded into a Brabendar absorptometer B torque measurement system and demineralised water added at 4 ml/min. The torque readings were plotted against the amount of liquid added per mass of solid material. The torque readings showed a peak value at 0.14 ml / g. The onset of the torque increase leading to this peak was then taken as the apparent pore volume per unit mass of the lithium nickel metal oxide base material (0.12 ml / g).

(B) Calculation of volume of coating liquid to be used

(1) Based on a desired surface-modified lithium nickel metal oxide composition of

I _ i 1 .01 Nio_.867Coo_.i 15Alo_.006Mgo_.012O2, the amounts of Co, Al and Li that were required to be added to a 500g sample of lithium nickel metal oxide Base Material A were calculated (as set out below), and hence the amounts of the nitrate crystals to be used.

Mass of base: 500g

Mass of cobalt to be added: 11.96 g Weight of Co(N0₃)₂.6H₂0: 59.04 g

Mass of aluminium to be added: 0.88 g Weight of AI(N0₃)₂.9H₂0: 12.18 g Mass of lithium to be added: 1.65 g Weight LiN0₃: 16.39 g

(2) The volume of liquid obtained when the mixed nitrate crystals were heated to 60 °C was measured as 52 ml_.

(3) The apparent pore volume of the lithium nickel metal oxide Base Material A (500g) was calculated as 60 ml_ (0.12 mL/g * 500 g).

(4) The amount of water to be added to the nitrate crystals to achieve a volume of coating liquid corresponding to approximately 120% of the apparent pore volume was calculated as 20 ml_

(C) Preparation of surface-modified lithium nickel metal oxide material

(Lil.OlNio.867COo.115Alo.006Mgo.01202)

Cobalt (II) nitrate hexahydrate (59.0 g, ACS, 98 - 102%, from Alfa Aesar), aluminium nitrate nonahydrate (12.2 g, 98% from Alfa Aesar) and lithium nitrate (16.4 g, anhydrous, 99%, from Alfa Aesar) were combined with water (20 ml) and then heated to approximately 60°C to form the coating liquid.

A sample of Base Material A (500g) was loaded into a Winkworth Mixer model MZ05 and heated to 60°C with the mixer running at 50 rpm. The coating liquid was then added to the base material using a pipette over a period of 5 minutes. The mixer was then left to run for 15 minutes before discharging the sample.

Example 4 - Calcination of coated material using a rotary calciner

The surface-modified lithium nickel metal oxide materials prepared according to the methods of Examples 2 and 3 were subjected to calcination in a rotary calciner.

A Nabertherm rotary calciner was used, including a FeCrAlloy (Kanthal APM) tube of 2000 mm length and 100 mm internal diameter, with a heated zone of length 750 mm, heated by electrical elements.

Multiple Runs were performed under various calcination conditions, firstly using the spray- dried material of Example 2 and secondly using the controlled-volume coated material of Example 3.

Calcination parameters for the various runs are set out in Tables 1 and 2 below. Feed rate to the calciner was controlled automatically using a loss in weight feeder unit (Coperion K-Tron KT-20 feeder). This was cross-checked through the trial using manual recording of the feeder weight and elapsed time.

The kiln angle was measured manually by measuring the height of the feed end of the calciner from the kiln frame and the distance of this measurement point to the kiln pivot.

The equation

Angle = tan^-1 (Height/Length) was then used to calculate the angle.

The rotation speed was set on an automatic controller and cross-checked by measuring the amount of time required for a single revolution.

The gas flow was measured using a rotameter.

Mean residence time in the heated zone was calculated using the method described in detail above.

Table 1 - Runs using material made in Example 2:

Table 2 - Runs using material made in Example 3:

For Runs 1-13 the rotary calciner drum did not contain any internal baffles. For Runs 14 and 15 a dam ring (annular baffle) was installed in the cooling zone of the tube, downstream of the heated zone, to increase the mean residence time of the powder in the drum. The height of the baffle was 20 mm above the inner surface of the tube.

Example 5A - Granulation of coated material After the coating as described in Example 3, 543.6 g of the material was transferred to a high-shear mixer which was set with the mixing pan at an small angle to the horizontal with no further drying (EL1 Eirich high-intensity granulator from Maschinenfabrik Gustav Eirich GmbH & Co KG) and agglomerated using the following process. The powder was mixed for 5 minutes with a tip speed of 10m/s, followed by a further 5 minutes with a tip speed of 16 m/s. After adding 5ml of demineralised water dropwise to the material over a period of 5 minutes agglomerates began to form (sample 1C). The form of these agglomerates was consolidated after the addition of a further 5ml of water and mixing for 5 minutes (sample 1 D). Further addition of water and further mixing resulted in large lumps forming in the mixer. The trial was repeated using 602 g of powder and 12.5ml of water added and the mixer operated with a tip speed of 16 m/s (sample 2A). The particle size distribution for these samples was as follows

Example 5B - Coating and agglomeration in a single step

300 g of Base Material A was added to a high-shear mixer (EL1 Eirich high-intensity granulator from Maschinenfabrik Gustav Eirich GmbH & Co KG) with a tip velocity of 1.3 m/s and a horizontal bowl.

A coating mixture was prepared using 35.49 g of cobalt nitrate, 7.32 g of aluminium nitrate crystals, 5.65 g of lithium nitrate crystals and 9.79 ml_ of demineralised water. This corresponded to a coating volume 101 % of the powder pore volume. The coating mixture was added to the mixer over 5 minutes, the speed increased to 10 m/s for 1 minute, then 20 m/s for minute and finally 27.9 m/s for 1 minute. It was noted at this point that the material was granular but with a lot of fine powder.

The bowl was moved to its angled position and the agitator started at 5m/s tip speed for 5 minutes. At this condition, well-formed granules (agglomerates) with little fine powder were observed.

Example 6 - Feeding test on agglomerated material

Tests were conducted to assess any effects on the particle size distribution of the agglomerated material (material from a trial similar to Example 5A) caused by subjecting the material to the forces experienced during feeding to a calciner.

A Coperion KT20 feeder including twin auger screws was used for these tests. PSD was determined according to ASTM D4464 - 15 (2020) under the Mie scattering theory using a Malvern Mastersizer 3000 with air dispersion. The agglomerated material was first dried at 200 °C for 8 hours in a static oven. The PSD for the agglomerated material before feeding was determined. The material was then fed through the feeder for 10 minutes and a sample was taken for PSD assessment (10 minute sample). The material was then fed through the feeder for a further 10 minutes and a sample was taken for PSD assessment (20 minute sample). Finally the material was fed through the feeder for yet another 10 minute period and a sample was taken for PSD assessment (30 minute sample).

The PSD results are shown in Figure 1. It is evident that very little change in PSD of the agglomerated material is observed after feeding through the auger screw feeder.

Example 7 - Calcination of agglomerated material

Agglomerates from Example 5A were removed from the granulator and calcined in a Carbolite Gero GPC1200 furnace with CO2 free air supplied from a scrubber. The purge gas flow rate was 2.4 L/min during the calcination. The material was loaded into saggars having dimensions 5 x 5 x 3.4 cm with a wall thickness of 0.45 cm. The loading of material in the saggars was 3.6 g/cm².

The material was calcined by heating at 5 °C/min to 450 °C, 1 hour hold at 450 °C, heating at 2 °C/min to 700 °C, 2 hour hold at 700 °C, cool to RT with 4 ml/min flow rate of CO2 free air.

Comparative Example 7

A calcination was performed using the same method as Example 7, except that the powder material from Example 3, having a D50 of around 10 pm, was used (i.e. agglomeration of the material was not performed).

Example 8 - Calcination of agglomerated material

Agglomerates from Example 5B were removed from the granulator and calcined using the same method as Example 7.

Example 9 - Electrochemical testing

The samples from Examples 4, 7, 8 and Comparative Example 7 were electrochemically tested using the protocol set out below.

Electrochemical Protocol

The electrodes were prepared by blending 94%wt of the lithium nickel metal oxide active material, 3%wt of Super-C as conductive additive and 3%wt of polyvinylidene fluoride (PVDF) as binder in N-methyl-2-pyrrolidine (NMP) as solvent. The slurry was added onto a reservoir and a 125 pm doctor blade coating (Erichsen) was applied to aluminium foil. The electrode was dried at 120 °C for 1 hour before being pressed to achieve a density of 3.0 g/cm³. Typically, loadings of active is 9 mg/cm². The pressed electrode was cut into 14 mm disks and further dried at 120 °C under vacuum for 12 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 porous polypropylene membrane (Celgrad 2400) 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 on a MACCOR 4000 series and were charged and discharged at 0.1C, 2C and 5C (1C=200 mAh/g) between 3.0 and 4.3 V at 23 °C.

The cells were tested on a MACCOR 4000 series using C-rate and retention tests. The C- rate test charged and discharged cells between 0.1C and 5C. The retention test was carried out at 1C with samples charged and discharged over 50 cycles. Both tests were carried out at 23 °C

Electrochemical results

The results of the testing of electrochemical performance of the materials produced in Runs 1-16 are shown in Table 3 below.

Table 3 also provides details on the equivalent NO3 amount in the product in ppm, which provides an indication of the residual level of nitrates in the product. High levels of residual nitrate can have a detrimental effect on the product performance.

Table 3

*not measured

The results in Table 3 show that good discharge capacity and capacity retention is attainable by calcining the material in the rotary calciner. At lower mean residence times (Runs 1-13) the 0.1C second cycle discharge capacity is comparable with statically calcined material and the process provides the benefits of reduced equipment footprint and efficiency discussed in detail above. At higher mean residence times (Runs 14-16) the 0.1C second cycle discharge capacity at least matches that of statically calcined material.

The results show that a significant improvement in discharge capacity at both low and high discharge rates, with comparable capacity retention, is observed when the mean residence time of the powder in the heated zone of the calciner is increased. Runs 5 and 6, which used mean residence times of 75 minutes achieved discharge capacity of around 205 mAh g ¹ at 0.1 C and around 170 mAh g^-1 at 5C. By contrast, when mean residence time was increased to 200 mins for Runs 14 and 15, discharge capacity increased to around 212 mAh g^-1 at 0.1 C and around 180 mAh g^-1 at 5C. The equivalent residual nitrate content in the material prepared in Run 15 was also low.

The materials from Runs 1-13 showed high capacity retention, and the materials of Runs 14, 15 and 16 surprisingly retained high capacity retention while also showing increased initial discharge capacity.

The results of the testing of electrochemical performance of Example 7 and Comparative Example 7 are shown in Table 4 below.

Table 4

The results in Table 4 show that the 0.1C and 2C discharge capacities are comparable for the Example and Comparative Example, indicating that there is no detrimental effect of introducing the granulation step on the electrochemical performance of the product.

The observed 50 cycle retention for the materials of Examples 7 and 8 is also satisfactory and in line with what would be expected for these materials.

Claims

1. A process for producing a surface-modified particulate lithium nickel metal oxide material having a composition according to Formula 1:

LiaNixMyAzC>2_+b Formula 1 in which:

M is one or more of Co and Mn;

2. A process according to claim 1 wherein step (ii) comprises providing a coating liquid, the coating liquid comprising at least one metal-containing compound; and adding the coating liquid to the lithium nickel metal oxide particles to form an impregnated powder, the volume of coating liquid added corresponding to 50 to 150 % of the apparent pore volume of the lithium nickel metal oxide particles; and step (iii) comprises calcining the impregnated powder in a rotary calciner to form the surface-modified particulate lithium nickel metal oxide material.

3. A process according to claim 1 or 2 wherein M includes Co and step (ii) comprises contacting the lithium nickel metal oxide particles with a cobalt-containing compound, preferably cobalt nitrate.

4. A process according to claim 3 wherein the concentration of cobalt at the grain boundaries of the surface-modified particulate lithium nickel metal oxide is greater than the concentration of cobalt in the primary particles of the surface-modified particulate lithium nickel metal oxide.

5. A process according to any one of claims 1 to 4 wherein step (ii) comprises contacting the lithium nickel metal oxide particles with an aluminium-containing compound, preferably aluminium nitrate.

6. A process according to claim 5 wherein the concentration of aluminium at the grain boundaries of the surface-modified particulate lithium nickel metal oxide is greater than the concentration of aluminium in the primary particles of the surface-modified particulate lithium nickel metal oxide.

7. A process according to any one of claims 2 to 6 wherein the coating liquid comprises a lithium-containing compound, preferably lithium nitrate.

8. A process according to any one of claims 2 to 7 wherein the coating liquid is provided at a temperature from 50 to 80 °C.

9. A process according to any one of claims 2 to 8 wherein the addition step is carried out at temperature from 40 to 80 °C.

10. A process according to any one of claims 2 to 9 wherein the coating liquid is formed by heating at least one hydrated metal salt.

11. A process according to any one of claims 2 to 10 wherein the total molar concentration of metal in the coating liquid is at least 0.5 mol/L, at least 0.75 mol/L, at least 1 mol/L, at least 1.25 mol/L, at least 1.5 mol/L, at least 1.75 mol/L or at least 2 mol/L.

12. A process according to any one of claims 2 to 11 wherein the coating liquid is added to the lithium nickel metal oxide particles by spraying the coating liquid onto the particles.

13. A process according to any one of claims 2 to 12 wherein the volume of coating liquid added corresponds to 70 to 150 % of the apparent pore volume of the lithium nickel metal oxide particles, preferably 90 to 150 % or 90 to 125 % of the apparent pore volume of the lithium nickel metal oxide particles.

14. A process according to any one of claims 2 to 13 wherein the volume of coating liquid added corresponds to 100 to 150 % of the apparent pore volume of the lithium nickel metal oxide particles, preferably 100 to 125 % of the apparent pore volume of the lithium nickel metal oxide particles.

15. A process according to any one of claims 1 to 14 wherein A is Al and / or Mg, optionally in combination with one or more of V, Ti, B, Zr, Cu, Sn, Cr, Fe, Ga, Si, Zn, Sr, Ca, S, Ce, La, Mo, Nb, P, Sb, and W.

16. A process according to any one of claims 1 to 15 wherein M is Co.

17. A process according to any one of claims 1 to 16 wherein the calcination step is carried out at a temperature from 400 to 1000 °C.

18. A process according to any one of claims 1 to 17 further comprising the step of forming an electrode comprising the surface-modified lithium nickel metal oxide material.

19. A process according to claim 18 further comprising the step of constructing a battery or electrochemical cell including the electrode comprising the surface-modified lithium nickel metal oxide material.

20. A process according to any one of the preceding claims, wherein the step (iii) is a continuous process step in which the coated powder is continuously fed to the rotary calciner and the calcined surface-modified particulate lithium nickel metal oxide material is continuously removed from the rotary calciner.

21. A process according to claim 20, wherein the inner wall of the drum of the rotary calciner comprises a baffle extending inwards from the inner wall into the drum.

22. A process according to any one of the preceding claims, wherein the inner wall of the drum of the rotary calciner comprises an elongate raised feature extending along at least a portion of the axial length of the inner wall of the drum.

23. A process according to any one of the preceding claims, comprising a step of drying the powder after the contacting step (ii) but before the calcination step (iii) to reduce the water content of the powder.

24. A process according to any one of the preceding claims, comprising a step of agglomerating the powder after the contacting step (ii) but before the calcination step (iii).

25. A process according to any one of the preceding claims, wherein the mean residence time of the coated powder in the heated zone of the rotary calciner is at least 120 mins.