Particle for a mixed metal oxide material

Abstract

A lithium nickel manganese cobalt oxide particle is described, in which aluminium is uniformly distributed through the bulk of the particle. A material comprising a plurality of the particles is also described. The material is useful as an electrode material, in particular as a cathode material within an electrochemical cell or battery. A method of manufacturing the particle is also described.

Description

[0001] PARTICLE FOR A MIXED METAL OXIDE MATERIAL

[0002] BACKGROUND

[0003] Lithium-ion secondary batteries are the leading battery technology currently used in applications from small personal devices to electric vehicles. Lithium-ion batteries are favoured for their high energy density and long cycle life, among other benefits. They contain a plurality of lithium-ion secondary cells, which is one example of an alkali metal ion secondary cell.

[0004] One type of electrochemically active material commonly used in the cathodes of lithium- ion secondary cells is lithium nickel manganese cobalt oxide (NMC). These materials are mixed metal oxides having a layered structure.

[0005] It has been found that a compound with an improved capacity can be achieved by reducing the amount of excess lithium and increasing the amount of nickel and / or cobalt and introducing an amount of aluminium. Without wishing to be bound by theory, it is understood that the presence of a particular amount of nickel and / or cobalt with an amount of aluminium enables greater oxygen redox activity and thereby improves the electrochemical capacity of the material.

[0006] However, the successful addition and incorporation of aluminium to lithium-rich layered materials is an experimentally challenging task. To date, the main known routes involve ball milling and co-precipitation of all the metals at the same time to produce the desired material, generally resulting in only partial and not homogeneous evidence of aluminium insertion in the final product. Additionally, insertion of aluminium in micron-scale cathode particles by these methods often results in the formation of lithium aluminate impurity (LiAlCh) on the surface of the material. The lithium aluminate formation also takes up a certain amount of lithium in the process, meaning that the addition of a “stoichiometric” quantity of lithium would result in a product that is lithium-deficient, negatively affecting the performance of the material. SUMMARY

[0007] In a first aspect, the present invention provides a particle having a composition according to the general formula: wherein 0.2 < x < 0.55,

[0008] 0 < y < 0.325, and

[0009] 0.005 < z < 0.075, for example such as 0.025 < z < 0.075; wherein the aluminium (Al) is uniformly distributed through the bulk of the particle.

[0010] Unlike previous techniques for the addition of aluminium, which result in limited and non-homogenous aluminium insertion as well as lithium aluminate formation on a particle surface, the present inventors have developed a lithium transition metal oxide particle in which aluminium is inserted and uniformly distributed through the bulk of the particle. The generation of lithium aluminate on the surface may also be beneficially diminished. When an electrode material is formed from a plurality of the particles of the invention, the material may exhibit excellent electrochemical properties, including coulombic efficiency and reversibility.

[0011] By “uniformly distributed through the bulk of the particle”, it is meant that the presence of aluminium is spread throughout the significant majority of the particle, in a generally consistent manner.

[0012] In energy-dispersive X-ray spectroscopy (EDS), a sample is scanned by an electron beam and the characteristic X-ray spectra generated by the electron beam are acquired pixel by pixel. It is known in the art to use EDS, in order to analyse the elemental composition of samples (e.g. mixed metal oxide particles or materials comprising a plurality of such particles) by performing elemental point analysis, elemental line scans or elemental mapping. An elemental line scan is made by using EDS to measure the elemental composition of each pixel along a user-defined one-dimensional line across a particle, whereas elemental point analysis measures the elemental composition at a single pixel. Meanwhile, elemental mapping is carried out by two-dimensional scanning over a specimen area, before visualising the distribution of the constituent elements by two- dimensionally displaying the characteristic X-ray intensities or concentrations of the elements.

[0013] Generally, in order to take an EDS elemental line scan of a particle, the particle is cut open to provide a cross-section (typically a cross-section that essentially passes through the bulk of the particle), before the line scan is taken across the cross-section (i.e. a diameter of the cross-section). Similarly, when carrying out EDS elemental mapping of a particle, the mapping is done on a two-dimensional surface formed by such a cross-section. The particle may be cut open by using an ion beam polisher.

[0014] In an EDS elemental line scan taken across a cross-section of the particle, there may be at least 0.5 wt%, or at least 0.6 wt% of Al along at least 80% of the line scan. That is to say, along at least 80% of the length of the line graph generated from the EDS elemental line scan (taken across a diameter of the cross-section), the weight percentage of Al observed in the sample may be at least 0.5 wt%, or at least 0.6 wt%. In particular, it can be said that the Al is uniformly distributed through the bulk of the particle.

[0015] The wt% values and ranges disclosed herein are based on the total mass of the particle.

[0016] In an EDS elemental line scan taken across a cross-section of the particle, there may be at least 0.5 wt%, or at least 0.6 wt%, or at least 0.8 wt%, or at least 1.0 wt%, or at least 1.2 wt% of Al along at least 80% of the line scan.

[0017] In an EDS elemental line scan taken across a cross-section of the particle, there may be at most 4.0 wt%, or at most 3.6 wt%, or at most 3.3 wt%, or at most 3.0 wt%, or at most 2.8 wt%, or at most 2.6 wt% of Al along at least 80% of the line scan.

[0018] In an EDS elemental line scan taken across a cross-section of the particle, there may be at most 3.0 wt% of Al along at least 80% of the line scan. In an EDS elemental line scan taken across a cross-section of the particle, there may be from 0.5 wt% to 3.0 wt%, such as from 0.6 wt% to 3.0 wt% of Al along at least 80 wt% of the line scan. In particular, it can be said that the presence of aluminium is spread throughout the significant majority of the particle in a generally consistent manner.

[0019] In an EDS elemental line scan taken across a cross-section of the particle, there may be at least 0.5 wt%, or at least 0.6 wt%, or at least 0.8 wt%, or at least 1.0 wt%, or at least 1.2 wt% of Al along at least 90% of the line scan.

[0020] In an EDS elemental line scan taken across a cross-section of the particle, there may be at least 0.5 wt%, or at least 0.6 wt% of Al along at least 90% of the line scan.

[0021] In an EDS elemental line scan taken across a cross-section of the particle, there may be at most 4.0 wt%, or at most 3.6 wt%, or at most 3.3 wt%, or at most 3.0 wt%, or at most 2.8 wt%, or at most 2.6 wt% of Al along at least 90% of the line scan.

[0022] In an EDS elemental line scan taken across a cross-section of the particle, there may be at most 3.0 wt% of Al along at least 90% of the line scan.

[0023] In an EDS elemental line scan taken across a cross-section of the particle, there may be from 0.5 wt% to 3.0 wt%, such as from 0.6 wt% to 3.0 wt% of Al along at least 90 wt% of the line scan.

[0024] In an EDS elemental line scan taken across a cross-section of the particle, there may be at least 0.5 wt%, or at least 0.6 wt%, or at least 0.8 wt%, or at least 1.0 wt%, or at least 1.2 wt% of Al along any part of the line scan corresponding to the material of the particle. By “any part of the line scan corresponding to the material of the particle”, it is meant that parts of the of the line scan corresponding to cracks, cavities, pores, defects or the like in the particle are excluded. In an EDS elemental line scan taken across a cross-section of the particle, there may be at least 0.5 wt%, or at least 0.6 wt% of Al along any part of the line scan corresponding to the material of the particle.

[0025] In an EDS elemental line scan taken across a cross-section of the particle, there may be at most 4.0 wt%, or at most 3.6 wt%, or at most 3.3 wt%, or at most 3.0 wt%, or at most 2.8 wt%, or at most 2.6 wt% of Al along any part of the line scan corresponding to the material of the particle.

[0026] In an EDS elemental line scan taken across a cross-section of the particle, there may be at most 3.0 wt% of Al along any part of the line scan corresponding to the material of the particle.

[0027] In an EDS elemental line scan taken across a cross-section of the particle, there may be from 0.5 wt% to 3.0 wt%, such as from 0.6 wt% to 3.0 wt% of Al along any part of the line scan corresponding to the material of the particle.

[0028] The EDS elemental line scan may be taken by the methods described herein. The EDS elemental line scan may be taken at a voltage in the range of from 5 to 15 kV (such as about 5 kV, about 10 kV or about 15 kV). The EDS elemental line scan may be taken at a current in the range of from 1 to 3.5 picoamps (such as about 3.3 picoamps). The EDS elemental line scan may be taken under high vacuum (such as at a pressure of at most about 0.1 Pa). The EDS elemental line scan may be taken at room temperature.

[0029] In EDS elemental mapping of a surface of a cross-section of the particle, at least 80% of the surface may show at least 0.5 wt%, or at least 0.6 wt% of Al present. That is to say, on a two-dimensional surface formed by taking a cross-section through the particle, the weight percentage of Al observed in at least 80% of the area of the surface in the EDS elemental map generated may be at least 0.5 wt%, or at least 0.6 wt%. In particular, it can be said that the Al is uniformly distributed through the bulk of the particle. In EDS elemental mapping of a surface of a cross-section of the particle, at least 80% of the surface may show at least 0.5 wt%, or at least 0.6 wt%, or at least 0.8 wt%, or at least 1.0 wt%, or at least 1.2 wt% of Al present.

[0030] In EDS elemental mapping of a surface of a cross-section of the particle, at least 80% of the surface may show at most 4.0 wt%, or at most 3.6 wt%, or at most 3.3 wt%, or at most 3.0 wt%, or at most 2.8 wt%, or at most 2.6 wt% of Al present.

[0031] In EDS elemental mapping of a surface of a cross-section of the particle, at least 80% of the surface may show at most 3.0 wt% of Al present.

[0032] In EDS elemental mapping of a surface of a cross-section of the particle, at least 80% of the surface may show from 0.5 wt% to 3.0 wt%, such as from 0.6 wt% to 3.0 wt% of Al present. In particular, it can be said that the presence of aluminium is spread throughout the significant majority of the particle in a generally consistent manner.

[0033] In EDS elemental mapping of a surface of a cross-section of the particle, at least 90% of the surface may show at least 0.5 wt%, or at least 0.6 wt%, or at least 0.8 wt%, or at least 1.0 wt%, or at least 1.2 wt% of Al present.

[0034] In EDS elemental mapping of a surface of a cross-section of the particle, at least 90% of the surface may show at least 0.5 wt%, or at least 0.6 wt% of Al present.

[0035] In EDS elemental mapping of a surface of a cross-section of the particle, at least 90% of the surface may show at most 4.0 wt%, or at most 3.6 wt%, or at most 3.3 wt%, or at most 3.0 wt%, or at most 2.8 wt%, or at most 2.6 wt% of Al present.

[0036] In EDS elemental mapping of a surface of a cross-section of the particle, at least 90% of the surface may show at most 3.0 wt% of Al present. In EDS elemental mapping of a surface of a cross-section of the particle, at least 90% of the surface may show from 0.5 wt% to 3.0 wt%, such as from 0.6 wt% to 3.0 wt% of Al present.

[0037] In EDS elemental mapping of a surface of a cross-section of the particle, any point of the cross-section corresponding to the material of the particle may show at least 0.5 wt%, or at least 0.6 wt%, or at least 0.8 wt%, or at least 1.0 wt%, or at least 1.2 wt% of Al present. By “any part of the cross-section corresponding to the material of the particle”, it is meant that parts of the of the cross-section corresponding to cracks, cavities, pores, defects or the like in the particle are excluded.

[0038] In EDS elemental mapping of a surface of a cross-section of the particle, any point of the cross-section corresponding to the material of the particle may show at least 0.5 wt%, or at least 0.6 wt% of Al present.

[0039] In EDS elemental mapping of a surface of a cross-section of the particle, any point of the cross-section corresponding to the material of the particle may show at most 4.0 wt%, or at most 3.6 wt%, or at most 3.3 wt%, or at most 3.0 wt%, or at most 2.8 wt%, or at most 2.6 wt% of Al present.

[0040] In EDS elemental mapping of a surface of a cross-section of the particle, any point of the cross-section corresponding to the material of the particle may show at most 3.0 wt% of Al present.

[0041] In EDS elemental mapping of a surface of a cross-section of the particle, any point of the cross-section corresponding to the material of the particle may show from 0.5 wt% to 3.0 wt%, such as from 0.6 wt% to 3.0 wt% of Al present.

[0042] The EDS elemental mapping may be performed by the methods described herein. The EDS elemental mapping may be performed at a voltage in the range of from 5 to 15 kV (such as about 5 kV, about 10 kV or about 15 kV). The EDS elemental line scan may be taken at a current in the range of from 1 to 3.5 picoamps (such as about 3.3 picoamps). The EDS elemental mapping may be performed under high vacuum (such as at a pressure of at most about 0.1 Pa). The EDS elemental mapping may be performed at room temperature.

[0043] The cross-section of the particle used for taking an EDS elemental line scan may be the same as or may be different from the cross-section used for EDS elemental mapping. One or both of an EDS elemental line scan and EDS elemental mapping may be carried out a particle.

[0044] The cross-section may pass through a core region of the particle, wherein the core region is defined as a spherical volume having a 1 pm radius and a centre that is the centre-of-mass of the particle.

[0045] That is to say, if a notional sphere of 1 pm radius is imagined in the particle, the centre of which sphere is the centre-of-mass of the particle, then the cross-section will bisect this sphere (i.e. notionally divide the sphere into two parts, which may be of same or different volumes). The skilled person will appreciate that the centre-of-mass of the particle is the unique point at the centre of a distribution of mass of the particle in space that has the property that the weighted position vectors relative to this point sum to zero. The centre-of- mass may be approximated by assuming that the particle has uniform density.

[0046] Alternative core regions may be defined as a spherical volume having a radius of 0.25 pm, or 0.5 pm, or 1.5 pm, or 2 pm, or 2.5 pm, and a centre that is the centre-of-mass of the particle.

[0047] In an EDS elemental line scan taken across a cross-section of the particle, the line scan may be taken from a first boundary region of the cross-section passing through the core region (as defined herein) to a second boundary region of the cross-section.

[0048] In an EDS elemental line scan taken across a cross-section of the particle, the line scan may be taken from a first boundary region of the cross-section passing through a central region to a second boundary region of the cross-section, wherein the central region is defined as a circular area on the cross-section having a 1 gm radius and a centre that is the centre-of-mass of the cross-section, being taken as two-dimensional.

[0049] That is to say, if a notional circle of 1 gm radius is imagined on the two-dimensional surface of the cross-section, the centre of which circle is the centre-of-mass of the crosssection, then the line scan will bisect this circle (i.e. notionally divide the circle into two parts, which may be of same or different volumes). The skilled person will appreciate that the centre-of-mass of the cross-section is the unique point at the centre of a distribution of mass of the two-dimensional cross-section in space that has the property that the weighted position vectors relative to this point sum to zero. The centre-of-mass may be approximated by assuming that the cross-section has uniform density.

[0050] Alternative central regions may be defined as a circular area having a radius of 0.25 pm, or 0.5 pm, or 1.5 pm, or 2 pm, or 2.5 pm, and a centre that is the centre-of-mass of the crosssection, being taken as two-dimensional.

[0051] The term “boundary region” refers to a part of the cross-section that is at or near to the perimeter of the cross-section. Thus, suitably, a one-dimensional line of a line scan may originate from a first point at or near the perimeter of the cross-section, the line may pass through the core region (defined with respect to the centre-of-mass of the particle, as described herein) or through the central region (defined with respect to the centre-of-mass of the cross-section, as described herein), and the line may terminate at a second point at or near the perimeter of the cross-section. The first boundary region and the second boundary region may be approximately diametrically opposed.

[0052] The particle may have a shape which is approximately spherical, approximately ovoid, or potato-like. The particle may have a sphericity of at least 60 %, for example at least 70 %, at least 75 %, at least 80 %, at least 85 %, at least 90 %, or at least 95 %.

[0053] The particle may have a diameter of greater than 2 pm, or greater than 3 pm, or greater than 4 pm, or greater than 5 pm, or greater than 6 pm, or greater than 7 pm, or greater than 8 pm. The particle may have a diameter of greater than 4 pm. The particle may have a diameter of less than 20 pm, or less than 18 pm, or less than 16 pm, or less than 14 pm, or less than 12 pm, or less than 11 pm, or less than 10 pm. The particle may have a diameter of less than 14 pm.

[0054] The particle may have a diameter of from greater than 4 pm to less than 20 pm.

[0055] The diameter of a particle may refer to the longest dimension across the particle (i.e. the maximum distance between any two points on the edge of the particle). A diameter of a cross-section may similarly refer to the longest dimension across the cross-section (i.e. the maximum distance between any two points on the edge of the cross-section). The size of a particle or a cross-section thereof may be measured by SEM or laser diffraction.

[0056] The particle is a mixed metal oxide, specifically a lithium transition metal oxide, having a composition according to the general formula described herein.

[0057] In some embodiments, 0.2 < x < 0.4. In some embodiments, 0.2 < x < 0.3. In some embodiments, 0.2 < x < 0.25. In some embodiments, x may be 0.25.

[0058] In some embodiments, 0.025 < y < 0.325. In some embodiments, 0.025 < y < 0.2, or 0.025 < y < 0.15, or 0.025 < y < 0.1. In some embodiments, y may be 0.05.

[0059] In some embodiments, 0.025 < z < 0.05, or 0.05 < z < 0.075. In some embodiments, z may be 0.05.

[0060] In some embodiments, 0.2 < x < 0.4 or x may be 0.25, and 0.025 < y < 0.1, and 0.025 < z < 0.075.

[0061] In some embodiments, 0.025 < y < 0.2 or y may be 0.05, and 0.2 < x < 0.3, and 0.025 < z < 0.075. In some embodiments, 0.01 < z < 0.075, or 0.015 < z < 0.075, or 0.02 < z < 0.075, or 0.025 < z < 0.075.

[0062] In some embodiments, 0.01 < z < 0.05, or 0.015 < z < 0.05, or 0.02 < z < 0.05, or 0.025 < z < 0.05.

[0063] In some embodiments, 0.01 < z < 0.03, or 0.015 < z < 0.03, or 0.02 < z < 0.03, or 0.025 < z < 0.03.

[0064] In some embodiments, 0.025 < z < 0.05, and 0.2 < x < 0.3, and 0.025 < y < 0.2 or 0.025 < y < 0.1.

[0065] In some embodiments, 0.05 < z < 0.075, and 0.2 < x < 0.3, and 0.025 < y < 0.2 or 0.025 < y < 0.1.

[0066] In some embodiments, z may be 0.05, and 0.2 < x < 0.3, and 0.025 < y < 0.1.

[0067] In some embodiments, z may be 0.05, and x + y may be equal to or greater than 0.25 and less than or equal to 0.35.

[0068] In some embodiments, x + y + z may be equal to or greater than 0.3 and equal to or less than 0.6.

[0069] In some embodiments, x + y + z may be equal to or greater than 0.3 and equal to or less than 0.4.

[0070] In some embodiments, x may be 0.25, y may be 0.05, and z may be 0.05. For example, the particle may have a composition according to the formula Li1.133Ni0.25Mn0.5i67Co0.05Al0.05O2.

[0071] In some embodiments, x may be 0.4, y may be 0, and z may be 0.05. For example, the particle may have a composition according to the formula Li1.05Ni0.4Al0.05Mn0.5O2. In some embodiments, x may be 0.401, y may be 0, and z may be 0.048. For example, the particle may have a composition according to the formula Lio.996Nio.4oiMno.53oAlo.o4s02.

[0072] In some embodiments, x may be 0.269, y may be 0.056, and z may be 0.005. For example, the particle may have a composition according to the formula Lil.l26Nio.269Mno.538Coo.056Alo.00502.

[0073] The particle may be manufactured by a method which includes formation of a transition metal oxide precursor compound by calcination of a transition metal carbonate compound, followed by reaction of the transition metal precursor compound with an aluminium source and calcination, followed by reaction with a lithium source and further calcination to form the particle. The reaction with the aluminium source may comprise precipitation of aluminium hydroxide on the transition metal oxide precursor compound. Such methods are described in more detail below.

[0074] A second aspect of the invention provides a lithium transition metal oxide material comprising a plurality of particles according to the first aspect.

[0075] The lithium transition metal oxide material may be a particulate material, i.e. made up of a plurality of particles. Suitably, the lithium transition metal oxide material may be an electrochemically active material. The material may be described as an electrode material, such as a cathode material (e.g. positive active material). The material may be defined as having a layered structure.

[0076] The term “intra-particle porosity” refers to the porosity within the particle structure, and excludes porosity arising from the spaces between particles in the material (which is referred to as “inter-particle porosity”). As such, intra-particle porosity impacts the ability of electrolyte to penetrate any given particle, whereas inter-particle porosity instead impacts only the ability of the electrolyte to diffuse through the spaces between the particles, i.e. diffuse through the material itself. As used herein, intra-particle porosity refers to the volume of “open” pores within the particles as a percentage of the total volume occupied by the particles. Only the open pores are taken into account for intra-particle porosity, since mercury is unable to intrude into closed pores, so such pores are “invisible” to mercury intrusion porosimetry. For the avoidance of doubt, the “total volume occupied by the particles” for the purposes of calculating intra-particle porosity does not include the voids between particles. In other words, the intra-particle porosity is an intrinsic property of the material and is independent of properties of the bulk material, such as particle packing or bulk density.

[0077] The lithium transition metal oxide material may have an intra-particle porosity of at least 2%, or at least 3%, or at least 4%, or at least 6%, or at least 8%, or at least 10%, as determined by mercury intrusion porosimetry.

[0078] The lithium transition metal oxide material may have an intra-particle porosity of at most 25%, or at most 22%, or at most 20%, or at most 18%, or at most 16%, or at most 14%, as determined by mercury intrusion porosimetry.

[0079] The lithium transition metal oxide material may have an intra-particle porosity of from 3% to 20%, as determined by mercury intrusion porosimetry.

[0080] The use of mercury intrusion porosimetry to determine the characteristics of material porosity is well known. The method involves the gradual increase in the pressure applied to a column of mercury which is in contact with the material to be tested. As the pressure is increased, larger voids and pores will fill with mercury first, followed by smaller pores at higher pressures. For a typical material, inter-particle pores (voids) are larger than intra- particle pores. So, for a material with both inter-particle voids and intra-particle pores, it is possible to distinguish these during mercury intrusion porosimetry due to the higher pressure necessary to impregnate the intra-particle pores with mercury. The result is one or more low-pressure volume intrusion peaks for the filling of the larger inter-particle voids, along with one or more separate high-pressure volume intrusion peaks for the filling of the smaller intra-particle pores. For example, the presence of peaks at a pressure greater than 400 psia may be indicative of the presence of intra-particle porosity. A material lacking intra-particle porosity would only exhibit the low-pressure volume intrusion peak(s) for the filling of the larger inter-particle voids. The intra-particle porosity may be measured on 1 g of the material.

[0081] The lithium transition metal oxide material may exhibit a bimodal pore size distribution when determined by mercury intrusion porosimetry. The bimodal pore size distribution may arise from a first peak resulting from the intrusion of mercury at lower pressure into inter-particle voids, and a second peak resulting from the intrusion of mercury at higher pressure into intra-particle pores.

[0082] The lithium transition metal oxide material may comprise lithium aluminate on a surface thereof in an amount of at most 500 ppm (i.e. in the range of from 0 to 500 ppm), for example in an amount of less than 500 ppm, less than 450 ppm, less than 400 ppm, less than 350 ppm, less than 300 ppm, less than 250 ppm, less than 200 ppm, less than 150 ppm, less than 100 ppm, or less than 50 ppm. The lithium transition metal oxide material may comprise essentially no lithium aluminate on a surface thereof. As described herein, minimisation of the formation of lithium aluminate impurity of the surface of the material is beneficial, for example because this process uses up an amount of lithium, resulting in a material with inferior performance due to lithium deficiency.

[0083] The lithium transition metal oxide material may be for an electrode, such as a positive electrode (cathode).

[0084] A third aspect of the invention provides an electrode comprising the lithium transition metal oxide material according to the second aspect.

[0085] The electrode may comprise the lithium transition metal oxide material according to the second aspect and a binder. The binder may comprise a polymer (such as PVDF, PTFE, NaCMC or NaAlginate). The lithium transition metal oxide material may make up at least 50 vol% of the electrode, based on the total volume of electrode, for example at least 55 vol%, at least 60 vol%, at least 62 vol%, at least 64 vol%, or at least 65 vol%.

[0086] The lithium transition metal oxide material may make up at most 80 vol% of the electrode, based on the total volume of electrode.

[0087] The lithium transition metal oxide material may make up from 64 vol% to 80 vol% of the electrode, based on the total volume of electrode.

[0088] The electrode may be a positive electrode (cathode).

[0089] The cathode may be a solid, solvent-cast cathode. Alternatively, the cathode may be a polymer gel cathode, comprising a gelled polymer matrix made up of a polymer-electrolyte gel matrix phase and a dispersed phase, wherein the dispersed phase comprises the lithium transition metal oxide material (positive active material).

[0090] The polymer-electrolyte gel matrix phase may be formed from one or more electrolyte components and at least one gelling polymer.

[0091] The one or more electrolyte components may include a solvent suitable for use as an electrolyte solvent in a gel electrode, for example an organic solvent. The one or more electrolyte components may include a salt. The one or more electrolyte components may constitute an electrolyte salt solution or liquid electrolyte.

[0092] The one or more electrolyte components may comprise a solvent comprising one or more cyclic or linear carbonate compounds. The solvent may comprise one or more cyclic carbonate compounds. The solvent may comprise one or more of ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, fluoroethylene carbonate, fluoropropylene carbonate and y-butyrolactone. The solvent may comprise a blend of at least two different compounds, for example at least three or at least four different compounds. The solvent may comprise a blend of at least two different organic carbonate compounds, for example at least three or at least four different organic carbonate compounds.

[0093] The electrolyte component(s) may comprise a solvent with low vapour pressure and high flash point to enable safe processing. An example of a solvent fulfilling these criteria is propylene carbonate. Accordingly, the one or more electrolyte components may comprise or consist of propylene carbonate, or a blend of propylene carbonate with one or more of the above listed solvents.

[0094] The one or more electrolyte components may comprise an alkali metal salt. The alkali metal of the alkali metal salt may be any suitable alkali metal (Group I of the periodic table). The alkali metal salt may be a lithium, sodium, or potassium salt.

[0095] The anion of the alkali metal salt may be any suitable anion. Typical anions are known to the skilled person and may be chosen based on the kind of alkali metal. For example, when the alkali metal is lithium, the anion of the salt comprises a halogen such as fluorine. Examples include BFF, PF6“, TFSF, FSF, OTF, DFOB’ and TDF.

[0096] The one or more electrolyte components may comprise a lithium salt. The electrolyte may comprise a mixture of at least two different lithium salts. Examples of suitable lithium salts include LiPFe, LiBF4, LiTFSI, LiFSI, LiOTf, LiDFOB and LiTDI. The salt may be a thermally stable salt. It has been found that LiPFe has relatively low thermal stability relative to other available lithium salts, and accordingly use of LiPFe may be avoided - that is, in some instances, the electrolyte component(s) do not include LiPFe.

[0097] One or more kinds of alkali metal salt may be used in accordance with the present invention. Typically, but not exclusively, when more than one kind of alkali metal salt is used, they share a common alkali metal. The polymer-electrolyte gel matrix phase may comprise a gel matrix formed by the gelling of one or more gelling polymers when the polymer(s) absorb a liquid electrolyte. The polymer-electrolyte gel matrix phase may therefore comprise a gel comprising the polymer(s) and absorbed liquid electrolyte.

[0098] The gelling polymer may comprise one or more gelling polymers independently selected from carboxymethyl cellulose (CMC), poly(ethyleneglycol dimethacrylate), poly(ethyleneglycol diacrylate), poly(propyleneglycol dimethacrylate), poly(propyleneglycol diacrylate), poly(methyl methacrylate) (PMMA), poly(acrylonitrile) (PAN), polyurethane (PU), poly(vinylidene difluoride) (PVDF), poly(vinylidene fluoride- co-hexafluoropropylene) (PVDF-HFP), polyethylene oxide) (PEO), poly-L-lactic acid (PLA), polystyrene (PS), poly(ethyleneglycol dimethylether), poly(ethyleneglycol diethylether), poly [bi s(m ethoxy ethoxyethoxide)-phosphazene], poly(dimethylsiloxane) (PDMS), polyacene, polydisulfide, polystyrene, polystyrene sulfonate, polypyrrole, polyaniline, polythiophene, polythione, polyvinyl pyridine (PVP), polyvinyl chloride (PVC), polyaniline, poly(3,4-ethylenedioxythiophene) (PEDOT), poly(p-phenylene), poly(triphenylene), polyazulene, polyfluorene, polynaphthalene, polyanthracene, polyfuran, polycarbazole, tetrathiafulvalene- substituted polystyrene, ferrocene- substituted polyethylene, carbazole-substituted polyethylene, polyoxyphenazine, poly(heteroacene), poly[(4-styrenesulfonyl)(trifluoromethanesulfonyl)imide-co-methoxy- polyethyleneglycolacrylate] (Li[PSTFSI-co-MPEGA]), sulfonated poly(phenylene oxide) (PPO), N,N-dimethylacryl amide (DMAAm), lithium 2-acrylamido-2-methyl-l -propane sulfonate (LiAMPS), Poly(lithium 2-Acryl ami do-2 -Methylpropanesulfonic Acid-Co- Vinyl Triethoxysilane), polyethyleneoxide(PEO) / poly(lithium sorbate), PEO / poly(lithium muconate), PEO / [poly(lithium sorbate)+BF3], PEO copolymer, PEO terpolymer, and NIPPON SHOKUB Al® polymer, or mixtures or co-polymers thereof.

[0099] In some examples, the gelling polymer may comprise one or more gelling polymers independently selected from carboxymethyl cellulose (CMC), poly(vinylidene difluoride) (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), poly(methyl methacrylate) (PMMA), poly(ethylene oxide) (PEO), poly-L-lactic acid (PLA) and polystyrene (PS) The polymer-electrolyte gel matrix phase may make up from 20 vol% to 50 vol% of the cathode, for example from 25 vol% to 45 vol%, from 28 vol% to 42 vol%, from 30 vol% to 40 vol%, from 31 vol% to 39 vol% or from 32 vol% to 38 vol%. Suitably, the polymer- electrolyte gel matrix phase may make up about 33.52 vol%, about 34.11 vol%, or about 34.72 vol% of the cathode.

[0100] The gel cathode may be produced by processing a cathode precursor composition to form a film or coating.

[0101] The processing may comprise thermal processing and / or extrusion. The gel cathode may be an extruded cathode. Alternatively, the gel cathode may be a hot-rolled cathode. Alternatively, the gel cathode may be prepared by extruding a cathode precursor composition through a die to form a film.

[0102] The gel cathode may be both extruded and hot-rolled, for example by a process which comprises first extruding the cathode through a die followed by hot-rolling the cathode down to a desired thickness.

[0103] The cathode may be a solid, solvent-cast cathode. Such solid, solvent-cast cathodes may be prepared by mixing the positive active material, binder and optional further additive(s) with a solvent, before casting onto a foil layer and drying to remove solvent. Calendaring may then be performed after drying.

[0104] The cathode may comprise the positive active material, a conductive additive and a binder. The conductive additive may comprise or consist of carbon, for example carbon black and / or carbon nanotubes. The polymer may comprise or consist of one or more of the polymers set out in the list of gelling polymers above. The polymer may comprise or consist of PvDF, or PvDF-HFP.

[0105] The cathode may be for a lithium-ion secondary electrochemical cell or battery. A fourth aspect of the invention provides an electrochemical secondary cell or battery comprising the electrode according to the third aspect.

[0106] The electrochemical secondary cell or battery may comprise the electrode according to the third aspect, a second electrode, and an electrolyte (between the two electrodes). The electrode according to the third aspect may be a positive electrode (cathode) and the second electrode is a negative electrode (anode).

[0107] The cell may be an alkali metal ion secondary cell, for example a sodium-ion secondary cell or a lithium-ion secondary cell. The cell may be a lithium-ion secondary cell. The electrochemical secondary cell may comprise an electrode according to the third aspect that is a cathode laminated with a current collector, for example a metallic foil.

[0108] A fifth aspect of the invention provides an electrochemical device or a vehicle comprising the cell or battery according to the fourth aspect.

[0109] A sixth aspect of the invention provides a method of manufacturing the particle of the first aspect, the method comprising: forming a transition metal oxide precursor compound by calcining a transition metal carbonate compound, optionally at a temperature in the range of from 400 °C to 600 °C; adding an aluminium source to the transition metal oxide precursor compound, and calcining to form an aluminium-containing pre-particle; and adding a lithium source to the aluminium-containing pre-particle, and calcining the mixture of the lithium source and the aluminium-containing pre-particle to form the particle.

[0110] The transition metal carbonate compound may be formed by a reaction between a transition metal sulfate compound and a carbonate, optionally sodium carbonate. This reaction may be performed in a stirred tank reactor.

[0111] The transition metal oxide precursor compound may be formed by calcining the transition metal carbonate compound at a temperature of at least 400 °C, such as at least 450 °C or at least 500 °C. Without wishing to be bound by theory, it is believed that an intra-particle pore structure of the particle results at least in part from the use of the transition metal carbonate compound (suitably a mixed metal carbonate compound) during synthesis. When such a carbonate is subsequently calcined to form the transition metal oxide precursor compound, carbon dioxide is evolved during the calcination, creating a network of pores through the entire body of the particle, the pores being open to the particle surface and extend radially from the surface towards the particle centre, as observed by a qualitative assessment of the pores in an SEM image. Such pores have low tortuosity and form an essentially continuous network of intra-particle porosity. Since all or substantially all of this porosity is open to the particle surface, the present inventors have found that aluminium can be subsequently inserted and uniformly distributed in the compound, and electrolyte can more easily diffuse deep into the body of the particle, allowing lithium ions to diffuse quickly through the entire material of a particle.

[0112] The transition metal oxide precursor compound may be formed by calcining the transition metal carbonate compound for at least 1 hour, or at least 2 hours, or at least 3 hours, or at least 4 hours, or at least 5 hours. The transition metal oxide precursor compound may be formed by calcining the transition metal carbonate compound for at most 10 hours, or at most 8 hours, or at most 6 hours. The transition metal oxide precursor compound may be formed by calcining the transition metal carbonate compound for a time in the range of from 3 hours to 8 hours. The transition metal oxide precursor compound may be formed by calcining the transition metal carbonate compound at a temperature of at least 400 °C for a time in the range of from 3 hours to 8 hours.

[0113] The transition metal oxide precursor compound may be formed by calcining the transition metal carbonate compound at a temperature in the range of from 400 °C to 600 °C. The transition metal oxide precursor compound may be formed by calcining the transition metal carbonate compound at a temperature in the range of from 400 °C to 600 °C for between 3 hours and 8 hours.

[0114] The transition metal oxide precursor compound may be formed by calcining the transition metal carbonate compound at a temperature in the range of from 450 °C to 550 °C. The transition metal oxide precursor compound may be formed by calcining the transition metal carbonate compound at a temperature in the range of from 450 °C to 550 °C for a time in the range of from 3 hours to 8 hours.

[0115] The transition metal oxide precursor compound may be formed by calcining the transition metal carbonate compound at a temperature of about 500 °C for about 5 hours.

[0116] The step of adding the aluminium source may comprise precipitating aluminium hydroxide on the transition metal oxide precursor compound. The aluminium hydroxide in this step may be formed by adding a metal hydroxide to aluminium sulfate in the presence of the transition metal oxide precursor compound. Thus, aluminium sulfate may be added to the transition metal oxide precursor compound (optionally in water), and then a metal hydroxide may be added. The metal hydroxide may be a Group I or Group II metal hydroxide. For example, the metal hydroxide may be sodium hydroxide.

[0117] The precipitation may be performed in any suitable vessel or reactor. The precipitation may be performed in a stirred tank reactor. The precipitation may be performed in a reactor which comprises a heater, for example an external heating jacket. The temperature in the reactor may be in the range of 40 °C to 80 °C during the precipitation reaction. Alternatively, the precipitation may be performed at room temperature. The precipitation reaction may be performed in batch or continuous mode.

[0118] After the precipitation reaction is complete or has progressed to a desired extent of reaction, the reactor may be emptied to isolate the reaction product (i.e. the product of adding the aluminium source to the transition metal oxide precursor compound). The reaction product may be washed with a solvent, such as water. The reaction product may be filtered. After washing and optionally filtering, the reaction product may be dried, e.g. at a temperature in the range of from 30 °C to 100 °C for a time in the range of from 2 to 20 hours.

[0119] The step of calcining the product of adding the aluminium source to the transition metal oxide precursor compound may be performed at a temperature of at least 180 °C, such as at least 200 °C, at least 220 °C or at least 240 °C. The step of calcining the product of adding the aluminium source to the transition metal oxide precursor compound may be performed at a temperature of about 240 °C.

[0120] The step of calcining the product of adding the aluminium source to the transition metal oxide precursor compound may be performed for at least 1 hour, or at least 2 hours, or at least 3 hours, or at least 4 hours, or at least 5 hours. The step of calcining the product of adding the aluminium source to the transition metal oxide precursor compound may be performed for at most 10 hours, or at most 8 hours, or at most 6 hours. The step of calcining the product of adding the aluminium source to the transition metal oxide precursor compound may be performed for a time in the range of from 3 hours to 8 hours. The step of calcining the product of adding the aluminium source to the transition metal oxide precursor compound may be performed at a temperature of at least 400 °C for a time in the range of from 3 hours to 8 hours.

[0121] The step of calcining the product of adding the aluminium source to the transition metal oxide precursor compound may be performed at a temperature in the range of from 200 °C to 600 °C. The step of calcining the product of adding the aluminium source to the transition metal oxide precursor compound may be performed at a temperature in the range of from 200 °C to 600 °C for a time in the range of from 3 hours to 8 hours.

[0122] The transition metal oxide precursor compound may be formed by calcining the transition metal carbonate compound at a temperature of about 240 °C for about 5 hours.

[0123] It is believed that the heating facilitates the insertion and uniform distribution of the added aluminium in the porous compound, thus forming the aluminium-containing pre-particle.

[0124] In the step of adding the lithium source to the aluminium-containing pre-particle, the lithium source may comprise or consist of a lithium compound or a lithium salt. For example, the lithium source may be selected from lithium carbonate, lithium hydroxide and lithium nitrate. The step of adding the lithium source to the aluminium-containing pre-particle may be carried out by any suitable mixed method and apparatus. For example, a ball mill may be used (e.g. at about 100 rpm for at least about 30 minutes). Alternatively, acoustic mixing may be used (e.g. with a Resodyn acoustic mixer).

[0125] Calcining the mixture of the lithium source and the aluminium-containing precursor may comprise a first step at a temperature Ti and a second step at a temperature T2.

[0126] Ti may be at least 200 °C, such as at least 220 °C, or at least 240 °C.

[0127] Ti may be at most 600 °C, such as at most 500 °C, or at most 400 °C, or at most 300 °C.

[0128] Ti may be from 200 °C to 600 °C, such as from 200 °C to 300 °C.

[0129] The calcining at temperature Ti may be performed for at least 1 hour, or at least 2 hours, or at least 3 hours, or at least 4 hours, or at least 5 hours. The calcining at temperature Ti may be performed for at most 10 hours, or at most 8 hours, or at most 6 hours. The calcining at temperature Ti may be performed for a time in the range of from 3 hours to 8 hours. The calcining at temperature Ti may be performed for a time in the range of from 3 hours to 8 hours, where Ti is at least 200 °C. The calcining at temperature Ti may be performed for a time in the range of from 3 hours to 8 hours, where Ti is in the range of from 200 °C to 600 °C.

[0130] The calcining at temperature Ti may be performed for about 5 hours, where Ti is about 240 °C.

[0131] T2 may be at least 800 °C, such as at least 825 °C, or at least 850 °C.

[0132] T2 may be at most 1000 °C, such as at most 950 °C, or at most 900 °C.

[0133] T2 may be in the range of from 800 °C to 1000 °C, such as in the range of from 800 °C to 900 °C. The calcining at temperature T2 may be performed for at least 2 hours, or at least 4 hours, or at least 6 hours, or at least 8 hours, or at least 10 hours. The calcining at temperature T2 may be performed for at most 24 hours, or at most 18 hours, or at most 12 hours. The calcining at temperature T2 may be performed for a time in the range of from 6 hours to 18 hours. The calcining at temperature T2 may be performed for a time in the range of from 6 hours to 18 hours, where T2 is at least 800 °C. The calcining at temperature T2 may be performed for a time in the range of from 6 hours to 18 hours, where T2 is in the range of from 800 °C to 1000 °C.

[0134] The calcining at temperature T2 may be performed for about 10 hours, where T2 is about 850 °C.

[0135] The heating to Ti may be performed at a ramping rate in the range of from 0.5 to 10 °C / min, such as in the range of from 1 to 5 °C / min.

[0136] The heating from Ti to T2 may be performed at a ramping rate in the range of from 0.5 to 10 °C / min, such as in the range of from 1 to 5 °C / min.

[0137] The heating to Ti and the heating from Ti to T2 may each be performed at a ramping rate in the range of from 0.5 to 10 °C / min, such as in the range of from 1 to 5 °C / min.

[0138] Any one or more of the calcination steps may be performed in any suitable calciner or furnace, e.g. a muffle furnace, rotary furnace or roller hearth kiln (RHK).

[0139] BRIEF DESCRIPTION OF THE DRAWINGS

[0140] Figure 1 shows an SEM image of a transition metal oxide material according to Example 1 of the invention (image (a)), as well as EDS elemental maps for carbon, oxygen, aluminium, manganese, cobalt and nickel (maps (b) to (g) respectively).

[0141] Figure 2 shows an SEM image of a further transition metal oxide material according to Example 1 of the invention (image (a)), as well as EDS elemental maps for carbon, oxygen, aluminium, manganese, cobalt and nickel (maps (b) to (g) respectively). Figure 3 shows an annotated SEM image of a different particle in the material of Figure 2 (image (a)), as well as EDS elemental point analysis graphs at three different points (graphs (b) to (d)).

[0142] Figure 4 shows an SEM image of a comparative transition metal oxide material (image (a)), as well as EDS elemental maps for oxygen, carbon, manganese, nickel and aluminium (maps (b) to (f) respectively).

[0143] Figure 5 shows an EDS elemental point analysis graph at a point on the comparative material of Figure 4.

[0144] Figure 6 shows an annotated SEM image of a transition metal oxide material according to Example 1 of the invention (image (a)), as well as EDS elemental line scans for aluminium, carbon, nickel and oxygen (graphs (b) to (e) respectively), and SEM images with the line scans for aluminium and carbon superimposed (graphs (f) and (g) respectively).

[0145] Figure 7 shows an annotated SEM image of a comparative example transition metal oxide material (image (a)), as well as an EDS elemental line scan for aluminium (graph (b)).

[0146] Figure 8 shows annotated XRD spectra for a comparative example transition metal oxide material and for pure lithium aluminate.

[0147] Figure 9 shows an annotated XRD spectrum for a transition metal oxide material according to Example 1 of the invention.

[0148] Figure 10 shows a graph comparing electrochemical performance of a transition metal oxide material according to Example 1 of the invention with a material not containing aluminium. Figure 11 shows a graph comparing capacity retention over a number of cycles for the materials of Figure 10.

[0149] Figure 12 shows a scanning electron microscope (SEM) image of a transition metal oxide material according to Example 2 of the invention (image (a)), as well as EDS elemental aluminium maps of the SEM images for three different individual particles of the material according to Example 2 of the invention having different porosities (SEM images and maps (b) to (d) respectively).

[0150] Figure 13 shows an annotated SEM image of a transition metal oxide material according to Example 2 of the invention (image (a)), as well as an EDS elemental line scan for aluminium (graph (a)).

[0151] EXAMPLES & DETAILED DESCRIPTION

[0152] The SEM and EDS analyses described herein were performed using a Thermo Fisher Phenom XL scanning electron microscope and its standard associated user interface software. The EDS measurements were taken at a voltage of in the range of from 5 to 15 kV and a current of 3.3 picoamps under high vacuum at room temperature. Alternative instruments such as a JEOL 7900F SEM and software such as Oxford Instruments AZtec may also be used.

[0153] The XRF analysis described herein was performed using a Rigaku Supermini200 WD-XRF spectrometer, run by 2 gas flows: PIO gas (always, for X-ray path inside) and helium gas (for measurement atmosphere, only during measurement). PIO gas is 90% argon and 10% methane. ZSX Guidance software was used.

[0154] The XRD spectra described herein were obtained using a PANalytical Aeris Powder X-ray Diffractometer, using CuKa radiation with an X-ray wavelength of 1.54056 A.

[0155] Example 1

[0156] An NMC carbonate material was formed in a co-precipitation reaction, by dissolving NiSO4.6H2O, MnSO4.H2O and COSO4.6H2O in deionised water to give a 3.5 M solution, and then combining this solution with an aqueous sodium carbonate solution (3.5 M) and an aqueous ammonia solution (0.34 M) in a 1 L stirred tank reactor. 7.5 g of the NMC carbonate material was then heated to 500 °C for 5 hours. This resulted in the evolution of carbon dioxide, forming an NMC oxide of reduced mass (the transition metal oxide precursor compound).

[0157] The NMC oxide material was analysed using X-ray fluorescence (XRF), in order to determine the weight percentage of metals present in the material, which was used to calculate the amount of aluminium source required in the next step (for reaction with 5 g of the NMC oxide material).

[0158] The ratio of transition metals to lithium to aluminium was found to be 1 : 1.38 : 0.061. The elemental analysis of the transition metals was as shown in Table 1 below.

[0159] Table 1 - Transition metal elemental analysis of NMC oxide

[0160] In view of the target product formula of Li1.133Ni0.25Mn0.5i67Co0.05Al0.05O2, the number of moles of aluminium required for addition was calculated as 0.00413. Therefore, as the selected aluminium source, 1.301 g of hydrated aluminium sulfate (A12(SO4)3-16H2O) was used, being dissolved fully into 100 mL of deionised water, before being added slowly to a 300 mL dispersion of the 5 g of NMC oxide in deionised water. The mixture was left to stir at 150 rpm for 15 minutes, and then an aqueous solution of sodium hydroxide (0.495 g in 100 mL of deionised water) was added rapidly to the stirring mixture, which was left to stir at 150 rpm for a further 90 minutes at room temperature. The solution was then filtered using a Buchner funnel and washed with 200 mL of water. The solid material was collected and dried in a drying oven at 80 °C overnight, before being calcined at 240 °C for 5 hours.

[0161] The obtained material (comprising aluminium-containing pre-particles) was then characterised again using XRF analysis, in order to determine the amount of lithium source required in the next step. As the selected lithium source, 3.451 g of lithium carbonate (Li2CCh) was mixed with the material, using a Resodyn acoustic mixer. The resulting mixture was calcined by raising the temperature from 25 °C to 240 °C at a ramping rate of 0.5 °C / min, before holding the temperature for 5 hours at 240 °C (Ti), and then raising the temperature from 240 °C to 850 °C at a ramping rate of 1 °C / min, before holding the temperature for 15 hours at 850 °C (T2). The temperature was then allowed to drop to 100 °C at a rate of 2 °C / min.

[0162] A lithium transition metal oxide material comprising particles of the invention was thus obtained, having the formula Li1.133Ni0.25Mn0.5i67Co0.05Al0.05O2.

[0163] Example 2

[0164] A transition metal (TM) carbonate material was formed in a co-precipitation reaction, by dissolving NiSO4.6H2O and MnSOi.FLO in deionised water to give a 3.5 M solution, and then combining this solution with an aqueous sodium carbonate solution (3.5 M) and an aqueous ammonia solution (0.34 M) in a 1 L stirred tank reactor. 7.5 g of the TM carbonate material was then heated to 500 °C for 5 hours. This resulted in the evolution of carbon dioxide, forming a TM oxide of reduced mass (the transition metal oxide precursor compound).

[0165] The TM oxide material was analysed using X-ray fluorescence (XRF), in order to determine the weight percentage of metals present in the material, which was used to calculate the amount of aluminium source required in the next step (for reaction with 5 g of the transition metal oxide material).

[0166] The ratio of transition metals to lithium to aluminium was found to be 1 : 1.07 : 0.052. The elemental analysis of the transition metals was as shown in Table 2 below. Table 2 - Transition metal elemental analysis of TM oxide

[0167] In view of the target product formula of Lio.996Nio.4oiMno.53oAlo.o4s02, the number of moles of aluminium required for addition was calculated as 0.00326.

[0168] Therefore, as the selected aluminium source, 1.027 g of hydrated aluminium sulfate (A12(SO4)3-16H2O) was used, being dissolved fully into 100 mL of deionised water, before being added slowly to a 300 mL dispersion of the 5 g of TM oxide in deionised water. The mixture was left to stir at 150 rpm for 15 minutes, and then an aqueous solution of sodium hydroxide (0.495 g in 100 mL of deionised water) was added rapidly to the stirring mixture, which was left to stir at 150 rpm for a further 90 minutes at room temperature. The solution was then filtered using a Buchner funnel and washed with 200 mL of water. The solid material was collected and dried in a drying oven at 80 °C overnight, before being calcined at 240 °C for 5 hours.

[0169] The obtained material (comprising aluminium-containing pre-particles) was then characterised again using XRF analysis, in order to determine the amount of lithium source required in the next step. As the selected lithium source, 2.90 g of lithium carbonate (LhCCh) was mixed with the material, using a Resodyn acoustic mixer. The resulting mixture was calcined by raising the temperature from 25 °C to 240 °C at a ramping rate of 0.5 °C / min, before holding the temperature for 5 hours at 240 °C (Ti), and then raising the temperature from 240 °C to 850 °C at a ramping rate of 1 °C / min, before holding the temperature for 15 hours at 850 °C (T2). The temperature was then allowed to drop to 100 °C at a rate of 2 °C / min. A lithium transition metal oxide material comprising particles of the invention was thus obtained, having the formula Lio.996Nio.4oiMno.53oAlo.o4s02.

[0170] Example 3

[0171] An NMC carbonate material was formed in a co-precipitation reaction, by dissolving NiSO4.6H2O, MnSCU.EEO and COSO4.6H2O in deionised water to give a 3.5 M solution, and then combining this solution with an aqueous sodium carbonate solution (3.5 M) and an aqueous ammonia solution (0.34 M) in a 1 L stirred tank reactor. 7.5 g of the NMC carbonate material was then heated to 500 °C for 5 hours. This resulted in the evolution of carbon dioxide, forming an NMC oxide of reduced mass (the transition metal oxide precursor compound).

[0172] The NMC oxide material was analysed using X-ray fluorescence (XRF), in order to determine the weight percentage of metals present in the material, which was used to calculate the amount of aluminium source required in the next step (for reaction with 5 g of the NMC oxide material).

[0173] The ratio of transition metals to lithium to aluminium was found to be 1 : 1.30 : 0.006. The elemental analysis of the transition metals was as shown in Table 3 below.

[0174] Table 3 - Transition metal elemental analysis of NMC oxide

[0175] In view of the target product formula of Lii.i26Nio.269Mno.53sCoo.o56Alo.oo502, the number of moles of aluminium required for addition was calculated as 0.000364. Therefore, as the selected aluminium source, 0.115 g of hydrated aluminium sulfate (A12(SO4)3-16H2O) was used, being dissolved fully into 100 mL of deionised water, before being added slowly to a 300 mL dispersion of the 5 g of NMC oxide in deionised water. The mixture was left to stir at 150 rpm for 15 minutes, and then an aqueous solution of sodium hydroxide (0.495 g in 100 mL of deionised water) was added rapidly to the stirring mixture, which was left to stir at 150 rpm for a further 90 minutes at room temperature. The solution was then filtered using a Buchner funnel and washed with 200 mL of water. The solid material was collected and dried in a drying oven at 80 °C overnight, before being calcined at 240 °C for 5 hours.

[0176] The obtained material (comprising aluminium-containing pre-particles) was then characterised again using XRF analysis, in order to determine the amount of lithium source required in the next step. As the selected lithium source, 2.99 g of lithium carbonate (Li2CCh) was mixed with the material, using a Resodyn acoustic mixer. The resulting mixture was calcined by raising the temperature from 25 °C to 240 °C at a ramping rate of 0.5 °C / min, before holding the temperature for 5 hours at 240 °C (Ti), and then raising the temperature from 240 °C to 850 °C at a ramping rate of 1 °C / min, before holding the temperature for 15 hours at 850 °C (T2). The temperature was then allowed to drop to 100 °C at a rate of 2 °C / min.

[0177] A lithium transition metal oxide material comprising particles of the invention was thus obtained, having the formula Lii.i26Nio.269Mno.538Coo.o56Alo.oo502.

[0178] Figures 1 and 2 each show (in respective image (a)) a scanning electron microscope (SEM) image of two transition metal oxide materials according to Example 1 of the invention, where the materials were separately prepared according to the above method for Example 1. The SEM images show cross-sections of individual particles (obtained using an ion beam polisher). EDS elemental maps of the SEM images are also provided for carbon (map (b)), oxygen (map (c)), aluminium (map (d)), manganese (map (e)), cobalt (map (f)) and nickel (map (g)).

[0179] In each of Figures 1(d) and 2(d), it can be seen from the consistency over the entire crosssection of the particle in the elemental map, that aluminium is evenly distributed, indicating a successful and uniform insertion of aluminium for each sample. Figure 3 also shows (in image (a)) an SEM image of a cross-section of a different particle in the material of Figure 2. EDS elemental point analysis was performed at various points on this cross-section. Graphs (b), (c) and (d) show the elemental point analysis at three different points (as shown by the added star symbols on image (a)), which demonstrate the presence of 1.1 wt% aluminium at each of these points. This further establishes the uniform distribution of aluminium in the particles.

[0180] Figures 4 and 5 show an analysis on a comparative example. The lithium transition metal oxide material of this comparative example was produced by a traditional route, involving the addition of aluminium together with lithium to a co-precipitated transition metal carbonate precursor via ball milling and subsequent thermal treatment. Here, the desired reaction is of lithium carbonate with aluminium-coated transition metal carbonate to form the lithium aluminium transition metal oxide material (on heating, with the evolution of carbon dioxide). However, this is in competition with a reaction that forms lithium aluminate (LiAlCh) on the surface of the material, due to the lower formation energy of LiAlCh.

[0181] Figure 4 shows (in image (a)) an SEM image of the lithium transition metal oxide material of the first comparative example, showing a cross-section of a particle (obtained using an ion beam polisher). EDS elemental maps of the SEM images are also provided for oxygen (map (b)), carbon (map (c)), manganese (map (d)), nickel (map (e)), and aluminium (map (f))-

[0182] It can be seen from Figure 4(f), from the lack of any consistency over the entire crosssection of the particle in the elemental map, that aluminium is not evenly distributed, indicating that aluminium is not successfully uniformly inserted in the particle.

[0183] Furthermore, EDS elemental point analysis was performed at various points on the crosssection of the particle. The graph of Figure 5 depicts the elemental point analysis at one such particular point, in which aluminium was not shown to be present, demonstrating its unsuccessful insertion in the particle. Figure 6 shows an EDS elemental line scanning analysis of a transition metal oxide material according to Example 1 of the invention, prepared according to the method described above for Example 1. In Figure 6, image (a) is an SEM image of a cross-section of the material, with an arrow added to show the position and direction of the line scan taken across a particle. The average atomic and weight percentages of the elements in the particle across the line scan are shown in Table 4 below (FW: 49 pm; Mode: 5 kV - image; Detector: BSD Full).

[0184] Table 4 - Elemental analysis of particle of Figure 6 (average across line scan)

[0185] The weight concentration data obtained from the line scan were normalised and plotted, as shown in graphs (b), (c), (d) and (e), which are the normalised line scans for aluminium, carbon, nickel and oxygen respectively. The data were normalised by using the Exponential Smoothing function in Microsoft Excel (with a damping factor in the range of from 0.1 to 0.9) and then normalising by the maximum value of each data set. Thus, as the person skilled in the art will appreciate, the normalised weight concentrations are different from the non-normalised (actual) weight concentrations.

[0186] Meanwhile, graph (f) approximately superimposes the aluminium line scan of graph (b) on the SEM image for the particle in question, and graph (g) approximately superimposes the carbon line scan of graph (c) on the SEM image of the particle in question. It can be seen from graphs (b) and (f) that the aluminium is uniformly distributed through the bulk of the particle. Indeed, it was found that the aluminium was present in at least 0.6 wt% (non-normalised figure) along at least 90% of the line scan across the cross-section of the particle (believed to be along any part of the line scan corresponding to the material of the particle). It can also be seen from graphs (c) and (g) that the carbon is predominantly present outside the particle.

[0187] Meanwhile, Figure 7 shows an EDS elemental line scanning analysis of a further comparative example transition metal oxide material (produced in the same way as the comparative example of Figures 4 and 5). In Figure 7, image (a) is an SEM image of a cross-section of the material, with a broken line added to show the position of the line scan taken across a particle. The particle has essentially the same composition as the particle of Figure 6. However, while the particle of Figure 6 has its aluminium uniformly distributed through the bulk of the particle, the particle of Figure 7 has its aluminium predominantly located on the surface of the particle (chiefly as lithium aluminate). This is shown in graph (b) of Figure 7, which depicts the line scan for aluminium for this comparative example, simultaneously superimposing the line scan on the SEM image for the particle in question.

[0188] Figure 8 shows the X-ray diffraction (XRD) spectrum for a comparative example transition metal oxide material (produced in the same way as the comparative example of Figure 7), with an XRD spectrum for pure lithium aluminate superimposed. By comparing the diffraction patterns (as shown at the circled parts of the spectra), the presence of lithium aluminate in the comparative example is evident.

[0189] Conversely, Figure 9 shows the XRD spectrum for a transition metal oxide material according to Example 1 of the invention, prepared according to the method described above for Example 1. As shown at the circled part of this spectrum, the characteristic peaks for lithium aluminate are absent, indicating that the presence of lithium aluminate is diminished in the inventive material.

[0190] The improvements in electrochemical performance achieved by a lithium transition metal oxide material having particles with uniform distribution of Al is shown in Figures 10 and 11. Galvanostatic cycling was performed (at C / 10, 2.0-4.8 V vs Li / Li+) on the inventive material of Figure 9 and also on a comparative material that is the same but does not comprise any aluminium. Cycling data were obtained from a half cell coin cell using 1 g of material. Both materials were observed to cycle well, but the Al-containing inventive material according to Example 1 exhibited increased reversibility and higher coulombic efficiency. As depicted in Figure 10, the inventive material according to Example 1 (solid line) generally has a greater capacity at a given voltage than the comparative material (broken line). Meanwhile, Figure 11 shows that the capacity retention over a number of cycles is greater for the inventive material according to Example 1 (dark black line) than for the comparative material (lighter grey line) - in particular, after 20 cycles, the capacity retention for the inventive material according to Example 1 is approximately 98%, while the capacity retention for the comparative material is slightly below 95%. The inventive material according to Example 1 was cycled at C / 10 for 25 cycles with a 10-hour OCV step prior.

[0191] Additional EDS elemental line scanning analysis was performed across cross-sections of further particles of a transition metal oxide material according to Example 1 of the invention, prepared according to the method described above for Example 1. The average atomic and weight percentages of the elements observed in the EDS line scans are shown in Tables 5 to 7, which correspond to different particles, with some minor variation in the scanning conditions as detailed below. In each case, it was found that aluminium was present in at least 0.6 wt% (non-normalised figure) along at least 90% of the line scan across the cross-section of the particle (believed to be along any part of the line scan corresponding to the material of the particle).

[0192] Figure 12(a) shows a scanning electron microscope (SEM) image of a transition metal oxide material according to Example 2 of the invention, prepared according to the method described above for Example 2. The SEM image shows cross-sections of individual particles (obtained using an ion beam polisher). Figures 12(b) to (d) show EDS elemental aluminium maps of the SEM images for three different individual particles of the material according to Example 2 of the invention having different porosities. The consistency over the entire cross-section of each of the particles in their elemental aluminium maps shows that aluminium is evenly distributed, indicating a successful and uniform insertion of aluminium for each of the particles, regardless of their porosity.

[0193] Figure 13 shows an EDS elemental line scanning analysis of a transition metal oxide material according to Example 2 of the invention. Figure 13(a) is an SEM image of a cross-section of a particle of the material, with a line added to show the position of the line scan taken across the particle. Figure 13(b) is a line scan for aluminium, which shows that the aluminium is uniformly distributed through the bulk of the particle.

[0194] The uniform presence of aluminium throughout particles of the material according to Example 3 was confirmed by point EDS elemental point analysis performed at various points on the cross-section of several particles.

Claims

CLAIMS1. A particle having a composition according to the general formula:wherein 0.2 < x < 0.55,0 < y < 0.325, and0.005 < z < 0.075; wherein the aluminium (Al) is uniformly distributed through the bulk of the particle.

2. The particle according to claim 1, wherein 0.025 < z < 0.075.

3. The particle according to claim 1 or claim 2, wherein, in an EDS elemental line scan taken across a cross-section of the particle, there is at least 0.6 wt% of Al along at least 80% of the line scan.

4. The particle according to claim 3, wherein there is at least 0.6 wt% of Al along at least 90% of the line scan.

5. The particle according to either claim 3 or claim 4, wherein there is at least 0.6 wt% of Al along any part of the line scan corresponding to the material of the particle.

6. The particle according to any one of claims 3 to 5, wherein there is from 0.6 wt% to 3.0 wt% of Al along either at least 80%, or along at least 90% of the line scan, or along any part of the line scan corresponding to the material of the particle.

7. The particle according to any one of claims 3 to 6, wherein the cross-section passes through a core region of the particle, wherein the core region is defined as a spherical volume having a 1 pm radius and a centre that is the centre-of-mass of the particle;optionally wherein the line scan is taken from a first boundary region of the cross-section passing through the core region to a second boundary region of the cross-section.

8. The particle according to any one of claims 3 to 7, wherein, in EDS elemental mapping of a surface of the cross-section of the particle, at least 80% of the surface shows at least 0.6 wt% of Al present and optionally at most 3 wt% of Al present.

9. The particle according to any one of claims 3 to 8, wherein, in EDS elemental mapping of a surface of the cross-section of the particle, any point of the cross-section corresponding to the material of the particle shows at least 0.6 wt% Al present and optionally at most 3 wt% of Al present.

10. The particle according to any one of claims 1 to 9, wherein the particle has a shape which is approximately spherical, approximately ovoid, or potato-like.

11. The particle according to any one of claims 1 to 10, wherein the particle has a diameter of greater than 4 pm.

12. The particle according to any one of claims 1 to 11, wherein x + y + z is equal to or greater than 0.3 and equal to or less than 0.6.

13. The particle according to any one of claims 1 to 12, wherein 0.2 < x < 0.4, optionally wherein 0.025 < y < 0.1 and 0.025 < z < 0.075.

14. The particle according to any one of claims 1 to 13, wherein the particle is manufactured by a method which includes formation of a transition metal oxide precursor compound by calcination of a transition metal carbonate compound, followed by reaction of the transition metal oxide precursor compound with an aluminium source and calcination, followed by reaction with a lithium source and further calcination to form the particle.

15. The particle according to claim 14, wherein the reaction with the aluminium source comprises precipitation of aluminium hydroxide on the transition metal oxide precursor compound.

16. A lithium transition metal oxide material comprising a plurality of particles according to any one of claims 1 to 15.

17. The lithium transition metal oxide material according to claim 16, wherein in the range of from 0 to 500 ppm lithium aluminate is present on a surface of the material.

18. The lithium transition metal oxide material according to either claim 16 or claim 17, having an intra-particle porosity of from 3% to 20%, as determined by mercury intrusion porosimetry.

19. An electrode comprising the material according to any one of claims 16 to 18.

20. An electrochemical secondary cell or battery comprising the electrode according to claim 19.

21. An electrical device or a vehicle comprising the cell or battery according to claim 20.

22. A method of manufacturing the particle according to any one of claims 1 to 15, the method comprising: forming a transition metal oxide precursor compound by calcining a transition metal carbonate compound, optionally at a temperature of in the range of from 400 °C to 600 °C; adding an aluminium source to the transition metal oxide precursor compound, and calcining to form an aluminium-containing pre-particle; and adding a lithium source to the aluminium-containing pre-particle, and calcining the mixture of the lithium source and the aluminium-containing pre-particle to form the particle.

23. The method according to claim 22, wherein the step of adding the aluminium source comprises precipitating aluminium hydroxide on the transition metal oxide precursor compound, optionally in a stirred tank reactor.

24. The method according to claim 23, wherein the aluminium hydroxide is formed by adding a metal hydroxide to aluminium sulfate in the presence of the transition metal oxide precursor compound.

25. The method according to any one of claims 22 to 24, wherein the lithium source is selected from lithium carbonate, lithium hydroxide and lithium nitrate.

26. The method according to any one of claims 22 to 25, wherein calcining the mixture of the lithium source and the aluminium-containing pre-particle comprises a first step at a temperature Ti in the range of from 200 °C to 600 °C, and a second step at a temperature T2 in the range of from 800 °C to 1000 °C, wherein heating to Ti and heating from Ti to T2 are each performed at a ramping rate in the range of from 0.5 to 10 °C / min.

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