WO2022118022A1

WO2022118022A1 - Cathode materials

Info

Publication number: WO2022118022A1
Application number: PCT/GB2021/053146
Authority: WO
Inventors: Carlos MARIN FLORIDO; Guoxian Liang; Andreas Laumann; Eva-Maria Hammer
Original assignee: Johnson Matthey Public Limited Company
Priority date: 2020-12-03
Filing date: 2021-12-02
Publication date: 2022-06-09
Also published as: GB202019122D0

Abstract

The present invention relates to improved lithium nickel composite oxide materials which have utility as cathode materials in secondary lithium-ion batteries, to electrodes and electrochemical cells incorporating such lithium nickel composite oxide materials, and to improved processes for making lithium nickel composite oxide materials.

Description

CATHODE MATERIALS

Field of the Invention

Background of the Invention

Lithium nickel composite oxide materials having a layered structure find utility as cathode materials in secondary lithium-ion batteries. Typically, lithium nickel composite oxide materials are produced by mixing metal precursors, such as hydroxides or oxyhydroxides, with a source of lithium, and then calcining the mixture. During the calcination process, the nickel metal precursor is lithiated and oxidised and undergoes a crystal structure transformation via intermediate phases to form the desired layered LiNiC>2 structure.

Studies of UNO2 and similar materials have shown that there is a phase transition from one hexagonal phase (H2) to another hexagonal phase (H3) during delithiation which occurs at high voltages (around 4.2 V vs Li⁺/Li) i.e. when the material has a significantly reduced lithium content. This phase transition is accompanied by a large and sudden reduction in volume of the unit cell caused by c-axis contraction. This c-axis contraction results in permanent structural damage to the material which has been linked to capacity fade upon cycling.

With increasing demand for lithium-ion batteries in applications such as electric vehicles (EVs), it is imperative to use cathode materials which provide not only high discharge capacity across a range of discharge rates but which also retain structural stability, so that the range of the vehicle after each charge over its lifetime is as consistent as possible.

US 10,501 ,335 B1 (CAMX Power LLC) describes electrochemically active secondary particles with grain boundaries enriched with cobalt and aluminium. Table 1 discloses a material of composition Li1.03Mg0.01Ni0.92Co0.08O2 and a material surface-modified with cobalt and aluminium of composition Lii.oiMgo.oiNio.86Coo.nAlooi902.

There remains a need for improved lithium nickel composite oxide materials and processes for their manufacture. In particular, there remains a need for improvements in structural stability upon repeated charge and discharge cycles and increased retention of discharge capacity. of the Invention

The present inventors have found that the presence of certain levels of magnesium in combination with certain levels of boron in lithium nickel composite oxide materials provides enhanced structural stability during electrochemical cycling in particular with regards to the H2-H3 transition, and also provides improved capacity retention when the materials are used as a cathode material in a lithium secondary battery.

Therefore, in a first aspect of the invention there is provided a particulate lithium nickel composite oxide material having a composition according to Formula (1):

Li_aNixCOyMg_zAlbB_cO2+d

Formula (1) in which:

0.8 < a < 1.2

0.8 < x < 1

0 < y < 0.2

0 < z < 0.05

0 < b < 0.05

0 < c < 0.02

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

The present inventors have also found that optimisation of processes used to produce lithium nickel composite oxide materials can yield further improvements in electrochemical performance. Therefore, in a second aspect of the invention there is provided a process for preparing a particulate lithium nickel composite oxide material with a composition according to Formula 2:

Li_aNixCOyMg_zAlbB_cMeO2+d Formula 2 in which:

0.8 < a < 1.2

0.8 < x < 1

0 < y < 0.2

0 < z < 0.05

0 < b < 0.05

0 < c < 0.02

0 < e < 0.1 -0.2 < d < 0.2 x + y + z + b + c+ e = 1 wherein M is selected from Mn, V, Ti, Zr, Sr, Ca, Ce, Cu, Sn, Cr, Fe, Ga, Si, W, Mo, Ta, Y, Sc, Nb, Pb, Ru, Rh and Zn and combinations thereof, the process comprising the steps of:

(i) mixing a lithium-containing compound with a nickel-containing compound, a cobalt-containing compound, a magnesium-containing compound, a boron- containing compound, optionally an aluminium-containing compound, and optionally an M-containing compound, wherein a single compound may optionally contain two or more of Ni, Co, Mg, Al, B, and M, to obtain a mixture;

(ii) calcining the mixture to obtain a calcined material; and

(iii) optionally contacting the calcined material with at least one of an aluminium- containing compound, a cobalt-containing compound, and an M-containing compound in a surface-modification step to form an enriched surface layer on the calcined material.

In a third aspect of the invention there is provided an electrode comprising a lithium nickel composite oxide compound of the first aspect or obtained or obtainable from the process of the second aspect.

In a fourth aspect of the invention there is provided an electrochemical cell comprising an electrode according to the third aspect.

Brief Description of the Drawings

Figure 1 shows scanning electron microscopy (SEM) images of the lithium nickel composite oxide materials formed in Examples 2A to 2D.

Figure 2 shows the results of C-rate testing of the materials produced in Examples 2A to 2D.

Figure 3 shows the results of discharge capacity retention testing of the materials produced in Examples 2A to 2D.

Figure 4 shows the results of full cell discharge capacity retention testing of the materials produced in Example 2C and Example 3 and a comparative example.

Figure 5 shows a dQ/DV plot of a material produced in accordance with Example 2C and a comparative example. 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 lithium nickel composite oxide materials according to Formula 1. The lithium nickel composite oxide materials are crystalline or substantially crystalline materials. The materials may have an a-NaFeC>2-type structure.

The compositions recited herein may be determined by Inductively Coupled Plasma (ICP) analysis as described in the Examples section below. It may be preferred that the compositions recited herein are ICP compositions.

In Formula 1 , 0.8 < a < 1.2. It may be preferred that a is greater than or equal to 0.90, or greater than or equal to 0.95. It may be preferred that a is less than or equal to 1.10, 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. It may be preferred that a = 1.

In Formula I, 0.8 < x < 1. It may be preferred that 0.83 < x < 1 , 0.85 < x < 1 , or that 0.90 < 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 0.83 < x < 1 , for example 0.83 < x < 0.99, 0.83 < x < 0.98, 0.83 < x < 0.97, 0.83 < x < 0.96 or 0.83 < x < 0.95.

In Formula 1 , 0 < y < 0.2. It may also be preferred that 0.01 < y < 0.2, 0.02 < y < 0.2, 0.03 < y < 0.2, 0.01 < y < 0.17, 0.01 < y < 0.15, or 0.01 < y < 0.10.

In Formula I, 0 < z < 0.05. It may be preferred that z is greater than or equal to 0.001, 0.002, 0.003, 0.004, or 0.005. It may be preferred that z is less than or equal to 0.04, 0.03, 0.02, or 0.01. It may be preferred that 0 < z < 0.04, 0 < z < 0.03, or 0 < z < 0.02. It may be further preferred that 0.001 < z < 0.05, 0.002 < z < 0.05, 0.003 < z < 0.05, 0.004 < z < 0.05, 0.005 < z < 0.05, 0.005 < z < 0.04, 0.005 < z < 0.03, or 0.005 < z < 0.02.

In Formula I, 0 < b < 0.05. It may be preferred that b is greater than or equal to 0.001, 0.002, 0.003, 0.004, or 0.005. It may be preferred that b is less than or equal to 0.04, 0.03, 0.02, 0.015, or 0.01. It may be preferred that 0 < b < 0.04, 0 < b < 0.03, or 0 < b < 0.02, or 0 < b < 0.015. It may be further preferred that 0.001 < b < 0.05, 0.002 < b < 0.05, 0.003 < b < 0.05, 0.004 < b < 0.05, 0.005 < b < 0.05, 0.005 < b < 0.04, 0.005 < b < 0.03, or 0.005 < b < 0.02, or 0.005 < b < 0.015. It may be further preferred that b = 0.

In Formula I, 0 < c < 0.02. It may be preferred that c is greater than or equal to 0.001 , 0.002, or 0.003. It may be preferred that c is less than or equal to 0.019, 0.018, 0.017, 0.016, or 0.015. It may be preferred that 0 < c < 0.019, 0 < c < 0.018, 0 < c < 0.017, 0 < c < 0.016, or 0

< c < 0.015. It may be further preferred that 0.001 < c < 0.019, 0.001 < c < 0.018, 0.001 < c

< 0.017, 0.001 < c < 0.016, 0.001 < c < 0.015, 0.001 < c < 0.014, 0.001 < c < 0.013, 0.001 < c < 0.012, 0.001 < c < 0.011 , or 0.001 < c < 0.010. It may be particularly preferred that 0.002

< c < 0.010.

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

It may be preferred that 0.8 < a < 1.2, 0.83 < x < 1 , 0 < y < 0.17, 0 < z < 0.05, 0 < b < 0.05, 0

< c < 0.02, -0.2 < d < 0.2 and x + y + z + b + c = 1. It may also be preferred that 0.8 < a < 1.2, 0.83 < x < 1 , 0 < y < 0.17, 0 < z < 0.05, 0 < b < 0.05, 0.002 < c < 0.010, -0.2 < d < 0.2 and x + y + z + b + c = 1. It may be further preferred that 0.8 < a < 1.2, 0.83 < x < 1 , 0 < y < 0.17, 0 < z < 0.05, b = 0, 0.002 < c < 0.010, -0.2 < d < 0.2 and x + y + z + b + c = 1.

Typically, the lithium nickel composite oxide materials have a volume-based particle size distribution such that the D50 is in the range of and including 2 to 20 pm. The term D50 as used herein refers to the median particle diameter of the volume-weighted distribution. The D50 may be determined by using a laser diffraction method. For example, the D50 may be determined by suspending the particles in water and analysing using a Malvern Mastersizer 3000. It may be preferred that the D50 is in the range of and including 3 to 18 pm. It may be further preferred that the D50 is in the range of and including 5 to 15 pm.

Typically, the particulate lithium nickel composite oxide materials are in the form of secondary particles comprising a plurality of primary particles, also known as crystal grains (made up from one or more crystallites). The primary particles grains are separated by grain boundaries.

Typically, the primary particles at the surface of the secondary particles have an oval or stick shape (i.e. the primary particles at the surface of the secondary particles are not spherical).

It may be preferred that the particulate lithium nickel composite oxide material of Formula 1 comprises an enriched surface, i.e. comprises a core material which has been surface modified (subjected to a surface modification process) to form an enriched surface layer. Typically, the surface modification results from contacting the core material with one or more further metal-containing compounds, and then optionally carrying out calcination of the material. The compounds may be in solution, and in such context herein the term “compound” refers to the corresponding dissolved species. 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 enriched surface layer. The inclusion of an enriched surface layer offers protection against material degradation through electrolyte interaction, reduction in surface impurity levels and improvements in capacity retention.

Herein, the terms “surface modified”, “enriched surface” and “enriched surface layer” refer to a particulate material which comprises a core material which has undergone a surface modification or surface enrichment process to increase the concentration of an element at or near to the surface of the particles. The term “enriched surface layer” therefore refers to a layer of material at or near to the surface of the particles which contains a greater concentration of at least one element (such as at least one of aluminium and cobalt) than the remaining material of the particle, i.e. the core of the particle.

It may be preferred that the particles comprise a greater concentration of Al in the enriched surface layer than in the core. In some embodiments, all or substantially all of the Al in the particle is in the enriched surface layer. In some embodiments, the core does not contain Al or contains substantially no Al, for example less than 0.01 wt% Al based on the total particle weight. As used herein, the content of a given element in the surface enriched layer is calculated by determining the wt% of that element in the particulate lithium nickel composite oxide material prior to surface enrichment (sometimes referred to herein as the first calcined material or the core material) by ICP to give value A, determining the wt% of that element in the final particulate lithium nickel composite oxide material after surface enrichment (and optional further calcination) by ICP to give value B, and subtracting value A from value B. Similarly, the content of a given element in the core may be determined by determining the wt% of that element in the particulate lithium nickel composite oxide material prior to surface enrichment (sometimes referred to herein as the first calcined material or the core material) by ICP.

As the skilled person will understand, elements may migrate between the core and the surface layer during preparation, storage or use of the material. Herein, where an element is stated to be present in (or absent from, or present in certain quantities in) the core, this is to be understood to refer to that element being intentionally added to, (or excluded from, or added in a particular quantity to) the core, and is not intended to exclude from the scope of protection materials where the distribution of elements is altered by migration during preparation, storage or use. Similarly, where an element is stated to be present in (or absent from, or present in certain quantities in) the surface enriched layer, this is to be understood to refer to that element being intentionally added to, (or excluded from, or added in a particular quantity to) the surface enriched layer, and is not intended to exclude from the scope of protection materials where the distribution of elements is altered by migration during preparation, storage or use. For example, where all or substantially all of the Al in the particle is in the enriched surface layer, this means that all or substantially all of the Al is added in the surface enrichment step, but does not preclude materials where some of the Al added in the surface enrichment step has migrated into the core.

It may be preferred that the particles comprise a greater concentration of cobalt in an enriched surface layer than in the core. It may be further preferred that the particles comprise a greater concentration of cobalt and aluminium in an enriched surface layer than in the core.

Alternatively, or in addition, it may be preferred that the particles of the lithium nickel composite oxide material comprise enriched grain boundaries, i.e. the concentration of one or more elements (such as at least one of Co, Al, Mg and B) at the grain boundaries is greater than the concentration of the one or more elements in the crystal grains. It may be preferred that the concentration of cobalt at the grain boundaries between the crystal grains of the lithium nickel composite oxide material is greater than the concentration of cobalt in the crystal grains. Alternatively, or in addition, it may be further preferred that the concentration of aluminium at the grain boundaries between the crystal grains is greater than the concentration of aluminium in the crystal grains. The enrichment of grain boundaries with cobalt and I or aluminium offers protection from particle degradation and improved electrode lifetime.

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

In a second aspect of the invention there is provided a process for making lithium nickel composite oxide materials according to Formula 2. In Formula 2, each of a, x, y, z, b, c and d are as defined herein for Formula 1 .

In Formula 2, M is selected from Mn, V, Ti, Zr, Sr, Ca, Ce Cu, Sn, Cr, Fe, Ga, Si, W, Mo, Ta, Y, Sc, Nb, Pb, Ru, Rh, Zn, and combinations thereof. It may be preferred that M is selected from V, Ti, Zr, Sr, Ca, Ce, Cu, Sn, Cr, Fe, Ga, Si, W, Mo, Ta, Y, Sc, Nb, Pb, Ru, Rh, Zn, and combinations thereof.

In Formula 2, 0 < e < 0.1. It may be preferred that e is greater than or equal to 0.001 , 0.002, 0.003, 0.004, or 0.005. It may be preferred that e is less than or equal to 0.09, 0.08, 0.07, 0.06, or 0.05. It may be preferred that 0 < e < 0.09, 0 < e < 0.08, or 0 < e < 0.07, or 0 < e < 0.06 or 0 < e < 0.05. It may be further preferred that e=0.

It may be preferred that the particulate lithium nickel composite oxide material of Formula 2 comprises an enriched surface, i.e. comprises a core material which has been surface modified (subjected to a surface modification process) to form an enriched surface layer. It may be preferred that the particles comprise a greater concentration of M in the enriched surface layer than in the core. In some embodiments, all or substantially all of the M in the particle is in the enriched surface layer. In some embodiments, the core does not contain M or contains substantially no M, for example less than 0.01 wt% M based on the total particle weight.

Preferably, the process is for making lithium nickel composite oxide materials according to Formula 1 as defined hereinbefore.

The process comprises the step of mixing a lithium-containing compound with a nickel- containing compound, a cobalt-containing compound, a magnesium-containing compound, a boron-containing compound, optionally an aluminium-containing compound, and optionally an M-containing compound, wherein a single compound may optionally contain two or more of Ni, Co, Mg, Al, B, and M, to obtain a mixture.

Suitable lithium-containing compounds include lithium salts, such as inorganic lithium salts, for example lithium hydroxide (e.g. LiOH or LiOH.FW), lithium carbonate (U2CO3), and hydrated forms thereof. Lithium hydroxide may be particularly preferred.

Suitable nickel-containing compounds include nickel hydroxide (Ni(OH)2), nickel oxide (NiO), nickel oxyhydroxide (NiOOH), nickel sulfate, nickel nitrate, nickel acetate and hydrated forms thereof. Nickel hydroxide may be particularly preferred. Suitable cobalt-containing compounds include from cobalt hydroxide (Co(OH)2), cobalt oxide (CoO, CO2O3, CO3O4), cobalt oxyhydroxide (CoOOH), cobalt sulfate, cobalt nitrate, cobalt acetate and hydrated forms thereof. Cobalt hydroxide may be particularly preferred.

Suitable magnesium-containing compounds include lithium salts, such as inorganic magnesium salts, for example magnesium hydroxide (Mg(OH)2), magnesium oxide (MgO), magnesium sulfate, magnesium nitrate, magnesium acetate and hydrated forms thereof. Magnesium hydroxide may be particularly preferred.

Suitable boron-containing compounds include boron trioxide (B2O3), boric acid (H3BO3), lithium tetraborate (LiaB^O?), lithium metaborate (L1BO2), lithium triborate (UB3O5), lithium borate (U2B4O7), boron nitride, boron carbide, boron trifluoride, boron phosphate, and sodium borate. Boron trioxide may be particularly preferred.

Suitable aluminium-containing compounds include aluminium salts, such as inorganic aluminium salts, for example aluminium oxide, aluminium hydroxide, aluminium sulphate, aluminium nitrate, aluminium acetate and hydrated forms thereof.

Suitable M-containing compounds may be selected from M hydroxide, M oxide, M nitrate, M sulfate, M carbonate or M acetate and hydrated forms thereof. M hydroxide may be particularly preferred.

It is preferred that the nickel-containing compound and the cobalt-containing compound are in the form of a mixed metal hydroxide. The mixed metal hydroxide may be a coprecipitated hydroxide. It may be polycrystalline.

The mixed metal hydroxide may have a composition according to Formula III:

NixCo_yMg_zAlbBcMe [Op(OH)_q]_a Formula III in which x, y, z, b, c and e are each independently as defined herein and wherein p is in the range 0 < p < 1 ; q is in the range 0 < q < 2; and a is selected such that the overall charge balance is 0.

Typically, the mixed metal hydroxide materials have a volume-based particle size distribution such that the D50 is in the range of and including 2 to 20 pm. The term D50 as used herein refers to the median particle diameter of the volume-weighted distribution. The D50 may be determined by using a laser diffraction method. For example, the D50 may be determined by suspending the particles in water and analysing using a Malvern Mastersizer 3000. It may be preferred that the D50 is in the range of and including 3 to 18 pm. It may be further preferred that the D50 is in the range of and including 5 to 15 pm.

Typically, the particles of the mixed metal hydroxide are provided in the form of secondary particles comprising a plurality of primary particles.

It may be preferred that the mixed metal hydroxide does not include boron, i.e. in Formula III c = 0. In such cases a separate boron-containing compound is added in step (i) of the process. It may be preferred that the ratio of the average size (D50) of the mixed metal hydroxide to the average size (D50) of the boron-containing compound is in the range of and including 10:1 to 2000:1. Control of the size of the boron-containing compound can lead to increased homogeneity of primary particle morphology and increases in discharge capacity.

It may be preferred that the boron-containing compound is milled prior to the mixing step (i). The milling may preferably be carried out under a moisture-free atmosphere, for example a moisture-free air or moisture-free inert atmosphere, such as nitrogen or argon. As used herein, the term “moisture-free” is intended to include atmospheres including less than 100 ppm H2O, e.g. less than 50 ppm H2O, less than 20 ppm H2O, or less than 10 ppm H2O. These moisture levels may be achieved by using commercial sources of dry gases or through the use of a desiccator.

It may be further preferred that the mixed metal hydroxide is a nickel cobalt magnesium hydroxide, i.e. that b, c and e in Formula III equals zero. In such cases, step (i) of the process as described herein comprises the step of mixing a lithium-containing compound (such as lithium hydroxide) with a nickel cobalt magnesium hydroxide, a boron-containing compound (such as boron trioxide), optionally an aluminium-containing compound, and optionally an M-containing compound.

Such mixed metal hydroxides may be prepared by co-precipitation methods well-known to the person skilled in the art. These methods may involve the co-precipitation of the 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 mixture is then calcined to obtain a calcined material. The calcination step may be carried out at a temperature of at least 600 °C, or at least 650 °C. The 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 at a temperature of at least 600 °C or at least 650 °C for a period of at least 2 hours, at least 3 hours, at least 4 hours or at least 5 hours. The period may be less than 8 hours.

It may be preferred that the calcination comprises heating to a temperature in the range of and including 650 to 750 °C for a period of from 4 to 8 hours. It may be further preferred that the calcination comprises heating to a temperature in the range of and including 680 to 720 °C for a period of from 4 to 8 hours.

The calcination step may be carried out under a CC>2-free atmosphere. For example, CC>2-free air may be flowed over the materials to be calcined during calcination and optionally during cooling. The CC>2-free air may, for example, be a mix of oxygen and nitrogen. Preferably the CC>2-atmosphere comprises at least 90 vol% oxygen, or more preferably the CC>2-free atmosphere may be oxygen (e.g. pure oxygen). 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.

The calcination may be carried out in any suitable furnace known to the person skilled in the art, for example a static kiln (such as a tube furnace or a muffle furnace), a tunnel furnace (in which static beds of material are moved through the furnace, such as a roller hearth kiln or push-through furnace), or a rotary furnace (including a screw-fed or auger-fed rotary furnace). The furnace used for calcination is typically capable of being operated under a controlled gas atmosphere. It may be preferred to carry out the calcination step in a furnace with a static bed of material, such as a static furnace or tunnel furnace (e.g. roller hearth kiln or push-through furnace).

Where the calcination is carried out in a furnace with a static bed of material, the material is typically loaded into a calcination vessel (e.g. saggar or other suitable crucible) prior to calcination.

The process comprises optionally contacting the calcined material with at least one of an aluminium-containing compound, a cobalt-containing compound, and an M-containing compound in a surface-modification step to form an enriched surface layer on the calcined material. It may be preferred that, in addition to the aluminium-containing compound, a cobalt-containing compound, and I or an M-containing compound, the calcined material is contacted with a lithium-containing compound.

The aluminium-containing compound, cobalt-containing compound, and I or M-containing compound (and optionally lithium containing compound) may be provided in solution, for example in aqueous solution.

The optional surface-modification step of the processes of the invention (also referred to herein as a surface enrichment step) increases the concentration of aluminium, cobalt, and I or M in the grain boundaries and/or at or near to the surface of the particles. Typically, the surface-modification step (also referred to herein as a surface enrichment step) comprises contacting the core material with additional metal selected from one or more of cobalt, aluminium, and M, to increase the concentration of such metal in the grain boundaries and/or at or near to the surface of the particles. The surface modification may be carried out by contacting the calcined material at least one of an aluminium-containing compound, a cobalt containing compound, and one or more further metal-containing compounds. For example, the compounds 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.

The mixture of the calcined material with the aluminium-containing compound, cobalt- containing compound and I or metal-containing compound may be heated, for example to a temperature of at least 40 °C, e.g. at least 50 °C. The temperature may be less than 100 °C or less than 80 °C. Where the aluminium-containing compound, cobalt-containing compound and I or metal-containing compound are provided in solution, the mixture of the solution with the intermediate 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 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 shorter than the first calcination step. The second calcination step may be carried out under a CC>2-free atmosphere as described above with reference to the first calcination step.

After calcination and I or after the optional surface modification step, the process may include one or more milling steps. The nature of the milling equipment is not particularly limited. For example, it may be a ball mill, a planetary ball mill or a rolling bed mill. The milling may be carried out until the particles (e.g. secondary particles) reach the desired size. For example, the particles of lithium nickel composite oxide (e.g. secondary particles) are typically milled until they have a D50 particle size of at least 3 pm, e.g. at least 5 pm. The particles of lithium nickel composite oxide (e.g. secondary particles) are typically milled until they have a D50 particle size of 20 pm or less, e.g. 15 pm or less.

The process of the present invention may further comprise the step of forming an electrode (typically a cathode) comprising the lithium nickel composite oxide material. Typically, this is carried out by forming a slurry of the particulate lithium nickel composite oxide, 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, at least 3 g/cm³, or at least 3.3 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 lithium nickel composite oxide. 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 - Example preparation of a precursor material of formula Nio.9iCoo.o8Mgooi(OH)2 A mixed metal sulphate solution (1.33 M) comprising nickel sulphate hexahydrate, cobalt sulphate heptahydrate and magnesium sulphate at a metal molar ratio of 0.91:0.08:0.01, base solution (2M NaOH) and ammonia solution (15wt%) were co-fed to a sealed jacket reactor vessel, fitted with an agitator and keeping the temperature at 60 °C. The solutions were pumped to the vessel, using peristaltic pumps over a period of 20 hours with the reaction temperature maintained at 60 °C. The pH for the precipitation in this example was 10.6. The mixed metal flow rate was kept constant at about 3 mL/min, the ammonia solution was fed in at a fixed rate in a 2:1 molar ratio with the metals solution and the pH of the solution adjusted by varying the flow rate of the base solution. The slurry was then vacuum filtered. The obtained solid was washed with hot (about 40 °C) deionised water. The washed filter cake was then tray dried at 120 °C overnight.

Example 2 - Formation of lithium nickel composite oxide materials with milling of boron precursor.

B2O3 (40g, Alfa Aesar) was loaded into a milling pot in a glove box and then sealed in a nitrogen atmosphere with zirconia beads. The B2O3 was milled for 25 minutes (5 minutes milling followed by 10 minutes resting) in a ball mill. A precursor material of formula Nio.9iCoo.o8Mgo.oi(OH)2 (D50 10pm, 115g) was mixed with LiOH (anhydrous, Example 2A 30.4 g, Example 2B 30.7 g, Example 2C 30.5 g, Example 2D 30.8 g) and B2O3 (milled, Example 2A 0g (Comparative Example), Example 2B 0.440g, Example 2C 0.224g, Example 2D 0.671g) in a glove box under a nitrogen atmosphere. The samples were then further mixed using a shaker mixer (WAB Turbula type T2F) for 30 minutes. The samples were each placed into a saggar and calcined under an oxygen atmosphere using the following profile: heating at a rate of 5 °C/min to a temperature of 450 °C, holding at a temperature of 450 °C for 2 hours, heating at a rate of 2 °C/min to a temperature of 700 °C, holding at a temperature of 700 °C for 6 hours. The samples were allowed to cool to 100 °C and then transferred to a glove box. The samples were ground using a pestle and mortar and then passed through a sieve (56 pm).

The samples were analysed by ICP-OES. For that, 0.1 g of material are digested with aqua regia (3:1 ratio of hydrochloric acid and nitric acid) at ~130°C and made up to 100 mL. The ICP-OES analysis was carried out on an Agilent 5110 using matrix matched calibration standards and yttrium as an internal standard. The lines and calibration standards used were instrument-recommended.

ICP-OES analysis indicated the lithium nickel composite oxide materials had the following compositional formulae: Example 2A Lii.oiNio.9nCoo.o8oMgo.oo902

Example 2B Lii.oiNio.904Coo.o8oMgo.oo8Bo.oo802

Example 2C Lii.oiNio.907Coo.o8oMgo.oo9Bo.oo402

Example 2D Lii.oiNio.9ooCoo.o8oMgo.oo8Bo.oi202

Examples 2A to 2D were analysed by scanning electron microscope (SEM). SEM images of the particles produced in Examples 2A - 2D are shown in Figure 2A to 2D. These figures show that the materials in Example 2B to 2D have a different surface morphology in comparison with the undoped material 2A with some primary particle elongation. The degree of elongation decreases with secondary particle size.

Example 3 - Formation of a surface-modified lithium nickel composite oxide material

80g of the lithium nickel composite oxide formed in Example 2C was suspended in deionised water (60 mL) and heated to 65 °C. A solution of lithium nitrate (0.94g), cobalt nitrate (4.76g) and aluminium nitrate (1.96g) in de-ionised water. The nitrate solution was added to the slurry of the lithium nickel composite oxide and the mixture was stirred under reflux until the supernatant became colourless. The slurry was spray dried and then calcined (calcination profile: heating at 5 °C/min to 450 °C; 1 h hold at 450 °C; heating at 2 °C/min to 700 °C; 450-700 °C; 2 hrs hold at 700 °C; furnace cooled to less or equal to 200 °C). The sample was unloaded into glovebox port for cooling to ambient temperature. The material was the ground with pestle and mortar and sieved (56 micron sieve) in the glovebox.

ICP-OES analysis indicated the surface-modified lithium nickel composite oxide materials had the following compositional formulae: Lio.994Nio.889Coo.o98Mgo.oo8Boo4Alo.oo602

Example 4 - Formation of lithium nickel composite oxide materials with milling of boron

The method of Example 2C was repeated without milling of the B2O3 starting material.

Electrochemical testing - Coin Cell

Electrochemical Protocol: The pressed electrodes were cut into 14 mm disks and further dried at 120 °C under vacuum for 12 hours. Electrochemical testing 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 (Celgard 2500) was used as a separator. 1M LiPFe 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 using a voltage range of between 3.0 and 4.3 V. The C-rate test charged the cells at 0.5C and discharged them at 0.1 C and 5 C (1C = 200 mA/g). The capacity retention test was carried out at 1C charge/discharge over 50 cycles..

The results of testing of Examples 2A - 2D are provided in Table 1 and Figure 2 (C-rate test) and Figure 3 (capacity retention test). This data shows that the addition of boron has increased the retention of discharge capacity. Examples 2B and 2C also show a significant increase in discharge capacity, in particular at high discharge rates.

The results of electrochemical testing of the surface-modified material of Example 3 are also provided in Table 1. This data indicates that the surface-modified material also provides an increase in discharge capacity retention in comparison with the boron-free material Example 2A.

The effect of milling the boron precursor was analysed in Example 4 and the results of electrochemical testing of the material produced are provided in Table 1. This shows that the materials produced with milling of the boron precursor (Example 2C) has an increased 0.1C discharge capacity in comparison with material produced without milling the boron precursor (Example 4).

Table 1 - Results of electrochemical testing

Electrochemical testing - Full cell:

Electrodes were prepared by blending 94%wt of 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.

Full cell electrochemical testing was performed with a CR2032 coin-cell type, which was assembled in an argon filled glove box (M Braun). Graphite electrodes in 90:5:5 (Graphite:C65:PVDF) were used as anode and balanced to reach a N/P ratio between 1.1- 1.3. A glass fibre F disk was used as separator and 1M LiPFe 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 using a conditioning step at slow rate, followed by C-rate and retention steps using a voltage range of between 2.7 and 4.2 V. The C-rate test charged cells at 0.5C and discharged cells at 0.1 C and 3 C (0.1C = 200 mAh/g). The capacity retention test was carried out by a 0.5C charge and 1C discharge over 240 cycles.

The results of full cell capacity retention testing of a materials produced in accordance with the method of Examples 2C and 3 are shown in Figure 4. Also shown is a boron-free surface-modified comparative example of composition Lii.oiMgo.oiNio.syCoo.i lo.ooeOz prepared using a surface-modification according to the method of Example 3. This shows the material of Example 2C and Example 3 have a significantly improved discharge capacity retention when compared to the comparative example. The surface-modified boron- containing material (Example 3) shows the greatest capacity retention over the cycling period.

The structural stability of the cathode materials upon repeated cycling was also assessed. Figure 5 shows a dQ/DV plot of a material produced in accordance with Example 2C (boron base) and a comparative example matching the composition of Example 2A. The material of Example 2C shows significantly enhanced structural stability in comparison with the comparative example, in particular with retention of a peak at 4.1 to 4.2 V corresponding to the H2-H3 transition.

Claims

1. A particulate lithium nickel composite oxide material having a composition according to Formula (1):

Li_aNixCOyMg_zAlbB_cO2+d Formula 1 in which:

0.8 < a < 1.2

0.8 < x < 1

0 < y < 0.2 0 < z < 0.05 0 < b < 0.05 0 < c < 0.02 -0.2 < d < 0.2 x + y + z + b + c = 1.

2. A particulate lithium nickel composite oxide material according to claim 1 wherein 0.95 < a < 1.05, preferably 0.98 < a < 1.02.

3. A particulate lithium nickel composite oxide material according to claim 1 or claim 2 wherein 0.83 < x < 1 and 0 < y < 0.17.

4. A particulate lithium nickel composite oxide material according to any one of the preceding claims wherein 0.001 < z < 0.03, preferably 0.005 < z < 0.01.

5. A particulate lithium nickel composite oxide material according to any one of the preceding claims wherein 0.001 < b < 0.05, preferably 0.001 < b < 0.03.

6. A particulate lithium nickel composite oxide material according to any one of the preceding claims wherein 0.001 < c < 0.015, preferably 0.001 < c < 0.010.

7. A particulate lithium nickel composite oxide material according to any one of the preceding claims in the form of secondary particles comprising a plurality of primary particles.

8. A particulate lithium nickel composite oxide material according to claim 7 wherein the concentration of cobalt at the grain boundaries between the primary particles of the lithium nickel composite oxide material is greater than the concentration of cobalt in the primary particles. A particulate lithium nickel composite oxide material according to claim 7 or claim 8 wherein the concentration of aluminium at the grain boundaries between the primary particles of the lithium nickel composite oxide material is greater than the concentration of aluminium in the primary particles. A particulate lithium nickel composite oxide material according to any one of the preceding claims wherein particles comprise a core and an enriched surface layer at the surface of the core, wherein the enriched surface layer comprises cobalt and I or aluminium. A process for preparing a particulate lithium nickel composite oxide material with a composition according to Formula 2:

Li_aNixCOyMg_zAlbB_cMeO2+d

Formula 2 in which:

0.8 < a < 1.2

0.8 < x < 1

0 < y < 0.2

0 < z < 0.05

0 < b < 0.05

0 < c < 0.02

0 < e < 0.1

-0.2 < d < 0.2 x + y + z + b + c + e = 1 wherein M is selected from Mn, V, Ti, Zr, Sr, Ca, Ce, Cu, Sn, Cr, Fe, Ga, Si, W, Mo, Ta, Y, Sc, Nb, Pb, Ru, Rh and Zn and combinations thereof, the process comprising the steps of:

(ii) calcining the mixture to obtain a calcined material; and (iii) optionally contacting the calcined material with at least one of an aluminium- containing compound, a cobalt-containing compound, and an M-containing compound in a surface-modification step to form an enriched surface layer on the calcined material.

12. A process according to claim 11 wherein the particulate lithium nickel composite oxide material is a material according to any one of claims 1 to 10.

13. A process according to claim 11 or claim 12 wherein in step (i) the nickel-containing compound and the cobalt-containing compound are in the form of a mixed metal hydroxide.

14. A process according to 13 wherein in step (i) the ratio of the average size of the mixed metal hydroxide to the average size of the boron-containing compound is 10:1 to 2000:1.

15. A process according to any one of claims 11 to 14 wherein the calcination comprises heating to at least 650 °C, preferably for a period of between 4 and 8 hours.

16. A process according to any one of claims 11 to 15 wherein the calcination is carried out under an atmosphere comprising at least 90 vol% oxygen.

17. A process according to any one of claims 11 to 16 wherein in step (iii) the first calcined material is contacted with a cobalt-containing compound, preferably with a cobalt-containing compound and an aluminium-containing compound.

18. A process according to any one of claims 11 to 17, wherein in step (iii) the surfacemodification step comprises a heat-treatment.

19. A process according to any one of claims 1 to 18 further comprising the step of forming an electrode comprising the lithium nickel composite oxide material.

20. A process according to claim 19 further comprising the step of constructing a battery or electrochemical cell including the electrode comprising the lithium nickel composite oxide material.

21. An electrode comprising a lithium nickel composite oxide material according to any one of claims 1 to 10, or a lithium nickel composite oxide material obtained or obtainable by a process according to any one of claims 11 to 18. 22. An electrochemical cell comprising an electrode according to claim 19.

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