composition

Abstract

Provided herein are compositions having the general formula AX. In the formula, A = LieTif[c]d; [c] is a cation vacancy; 0 ≤ d ≤ 0.5; 0 ≤ e < 1; 0 < f ≤ 1. X = OpSqFlClk[a]m; [a] is an anion vacancy; 0 ≤ p ≤ 1; 0 ≤ q ≤ 1; 0 ≤ l ≤ 1; 0 ≤ k ≤ 1; 0 ≤ m ≤ 0.5. Also provided are methods of making the compositions, use of the compositions, and an electrode, electrochemical cell, or electrochemical energy storage devices comprising such compositions.

Description

[0001] COMPOSITION

[0002] BACKGROUND

[0003] Many currently available batteries use a lithium-containing composition in the electrodes, and as a consequence are known as lithium-ion batteries. Such compositions are assessed primarily on performance and cost. Research into new compositions balancing these properties is ongoing.

[0004] Graphite is known as an anode material. An emerging alternative electrode technology is niobium-based oxides, such as NbieWsOss. These show promise in terms of rate and capacity. The cost of Nb is roughly 5,300 times more expensive per tonne than titanium. Titanium is less toxic than niobium.

[0005] Lithium titanate and lithium titanate-based materials are also known, predominantly in the spinel form.

[0006] SUMMARY

[0007] In a first aspect, the present invention relates to compositions having a disordered rock salt structure that may be used in applications such as lithium-ion batteries. Compositions of the first aspect have the general formula:

[0008] AX wherein:

[0009] A = LieTif[c]d;

[0010] [c] is a cation vacancy;

[0011] 0 < d < 0.5; 0 < e < 1; 0 < f < 1; and wherein:

[0012] X = OPSqFiClk[a]m;

[0013] [a] is an anion vacancy;

[0014] 0 < p < 1; 0 < q < 1; 0 < l < 1; 0 < k < 1; 0 < m < 0.5.

[0015] An X-ray diffraction pattern of the composition using a CuKa radiation source may have peaks whose full-width half-maximum value is >1.20° 29. This FWHM value may usefully identify compositions having particularly desirable structural disorder and / or crystallite size. For example, an X-ray diffraction pattern of the composition using a CuKa radiation source may have peaks whose full-width half-maximum value is >1.25° 29, or >1.39° 29, >1.35° 29. Or >1.49° 29, >1.45° 29, >1.59° 29.

[0016] In some embodiments, an X-ray diffraction pattern of the composition using a CuKa radiation source may have peaks whose full-width half-maximum value is >1.0° 29.

[0017] It should be noted that A and X have a 1 : 1 stoichiometry. Thus, (e+f+d) = (p+q+l+k+m). Compositions of the first aspect necessarily comprise titanium.

[0018] When e > 0 and p > 0, the compositions of the first aspect may be described as lithium titanates. Lithium titanates can be less expensive, and less toxic, compared to niobium-based oxides.

[0019] Graphite as an electrode material may suffer from dendrite formation at a high charging rate due to its low potential. While traditional lithium titanate materials, such as Li4TisOi2 electrode materials operate at a higher potential than graphite, they can be comparatively poor electronic and ionic conductors. Efforts to address these materials in the past have focussed on reducing the size of the lithium titanate-based materials to increase porosity and specific surface area, or on carbon-coating the lithium titanate-based materials, to increase electronic conductivity. These approaches lead to the inclusion of a higher fraction of electrochemically inactive materials in the electrodes. Therefore, these electrodes have a lower gravimetric and volumetric energy densities. However, lithium titanate-based materials have the potential for a good cycle life, fast-charging capability, and high safety.

[0020] Thus, in some embodiments, compositions of the first aspect have e > 0 and p > 0. In some such embodiments, compositions of the first aspect have q=l=k=0.

[0021] In some embodiments, compositions of the first aspect may have a disordered rock salt structure having structural disorder. Such structural disorder may impart useful performance properties on the present materials. In some embodiments, the composition having a disordered rock salt structure having structural disorder has e=0.5, f=0.5, d=0, p=l, q=l=n=m. The present structures may be prepared by a process - described later - that is simpler e.g. by not requiring multiple steps, and which may be carried out at lower temperatures, when compared to the methods used to prepare other lithium titanate-based structures and corresponding structures.

[0022] In some embodiments, compositions of the first aspect have k = 0. Compositions having anions which include O, S and F may have more desirable properties than compositions comprising Cl as anion.

[0023] In some embodiments, compositions of the first aspect have p > 0. Such embodiments comprise O anions. In some embodiments, compositions of the first aspect have q > 0. Such embodiments comprise S anions. In some embodiments, compositions of the first aspect have p > 0 and q > 0. Such embodiments comprise O and S anions.

[0024] In some embodiments, 1 > 0. Such embodiments comprise F anions. In some embodiments, k = 0, p > 0 and 1 > 0. Such embodiments comprise O and F anions but do not comprise Cl anions. In some embodiments, k = 0, p > 0, 1 > 0 and q > 0. Such embodiments comprise O, F and S anions but do not comprise Cl anions.

[0025] In some embodiments, k = 0 and one or both of p > 0 and q > 0. That is, in some embodiments, the compositions do not comprise Cl anions but do comprise O and / or S anions.

[0026] In some embodiments, e > 0. Such compositions comprise Li cations. In some embodiments, d = 0. Such compositions do not comprise a cation vacancy. In such embodiments, (e+f) = (p+q+l+k+m). In some embodiments, m=0. Such compositions do not comprise an anion vacancy. In such embodiments, (e+f+d)=(p+q+l+k). In some embodiments, d =0 and m = 0. In such embodiments, (e+f) = (p+q+l+k). In some embodiments, e > 0 and one or both of d = 0 and m = 0.

[0027] In some embodiments, 0 < e < 2 / 3. In some embodiments, 0 < e < 2 / 3.

[0028] In some embodiments, in a charge-discharge curve of the composition, the integral of the second discharge is greater than 50% of the integral of the second charge. In some embodiments, discharge corresponds with lithiation and charge corresponds with delithiation. In some embodiments, the charge-discharge curve is produced in a cell using a lithium anode / reference electrode.

[0029] In some embodiments, the composition of the first aspect is in the form of a single phase. In some embodiments, there is no other crystalline phase identifiable in the XRD pattern in the range 30-70° 29.

[0030] In some embodiments, an XRD pattern of the composition using a CuKa radiation source has a peak at a 29 value of 37.4° ± 2.0°.

[0031] In some embodiments, an XRD pattern of the composition using a CuKa radiation source has a peak at a 29 value of 43.5° ± 2.0°.

[0032] In some embodiments, an XRD pattern of the composition using a CuKa radiation source has a peak at a 29 value of 63.3° ± 2.9°.

[0033] In some embodiments, an XRD pattern of the composition using a CuKa radiation source has peaks at a 29 value of 37.4° ± 2.9° and 43.5° ± 2.9°.

[0034] In some embodiments, an XRD pattern of the composition using a CuKa radiation source has peaks at a 29 value of 37.4° ± 2.9° and 63.3° ± 2.9°.

[0035] In some embodiments, an XRD pattern of the composition using a CuKa radiation source has peaks at a 29 value of 43.5° ± 2.9° and 63.3° ± 2.9°.

[0036] In some embodiments, an XRD pattern of the composition using a CuKa radiation source has peaks at a 29 value of 37.4° ± 2.9°, 43.5° ± 2.9°, and 63.3° ± 2.9°.

[0037] In some embodiments, an XRD pattern of the composition using a CuKa radiation source has an absence of peaks below a 29 value of 30°. In some embodiments, 0 < e < 2 / 3 and 1 / 3 < f < 1. In some embodiments, 0.05 < e < 2 / 3 and 1 / 3 < f < 0.95.

[0038] In some embodiments, 0.25 < e < 0.45; 0.55 < f < 0.75. In some embodiments, 0.55 < e < 0.60; 0.40 < f < 0.45.

[0039] In some embodiments, 0.25 < e < 2 / 3 and 0.35 < f < 0.75. In some embodiments, 0.25 < e < 0.6 and 0.4 < f < 0.75. In some embodiments, 0.25 < e < 0.53 and 0.47 < f < 0.75. In some embodiments, 0.25 < e < 0.45 and 0.55 < f < 0.75. In some embodiments, 0.55 < e < 0.6 and 0.45 < f < 0.4.

[0040] In some embodiments, e = 0.55 and f = 0.45. In some embodiments, e = 0.5 and f = 0.5. In some such embodiments, q = 1 = k = 0. Such compositions may show particularly good capacity Such compositions may be able to access comparatively low voltages. Such compositions may have good capacity retention.

[0041] In some embodiments of the compositions of the first aspect, q = 1 = k = 0. That is, the compositions of the first aspect may comprise O anions and / or anion vacancies but not S, F or Cl anions. In some such embodiments, p > 0.

[0042] In some embodiments, the composition comprises titanium in a single oxidation state. In some embodiments, such as LiTiCh, the composition may comprise titanium in an oxidation state of 3+. In some embodiments, such as TiCh, the composition may comprise titanium in an oxidation state of 4+. In some embodiments, the composition comprises titanium in a mixture of 2+ and +3, or 2+ and 4+, or 3+ and 4+, or 2+ and 3+ and 4+ oxidation states. In some embodiments, the composition comprises titanium in a mixture of 2+ and 3+ oxidation states. In some embodiments, the composition comprises titanium in a mixture of 2+ and 4+ oxidation states. In some embodiments, the composition comprises titanium in a mixture of 3+ and 4+ oxidation states. In some embodiments, the composition comprises titanium in a mixture of 2+, 3+ and 4+ oxidation states.

[0043] In some embodiments, compositions of the first aspect may have anion vacancies. In such embodiments, m > 0. In general, these vacancies are not expected to affect the overall structure of the compositions. Anion vacancies may affect properties such as, but not limited to, thermal stability - and therefore safety - as well as gas generation on cycling or electrochemical behaviour.

[0044] In some embodiments, compositions of the first aspect may have one or more cation vacancies. In such embodiments, d > 0. In general, such vacancies are not expected to affect the overall structure of the composition. Control over cation vacancies may also affect properties such as, but not limited to, thermal stability - and therefore safety - as well as gas generation on cycling or electrochemical behaviour In some embodiments, the cation vacancy may be or comprise the absence of a Li. In some embodiments, where e = 0, there are no lithium cations, thereby giving rise to cation vacancies. In some embodiments, the cation vacancy may be or comprise the absence of a Ti. In some embodiments, there may be an absence of a Li and a Ti in the compositions of the first aspect. It should be noted that titanium is always present in compositions of the first aspect. In some embodiments, there is an excess of Li. In some embodiments, there is an excess of Ti. The ratio Li:Ti may define whether there is an excess of Li or Ti. In some embodiments, the presence of cation vacancies can be controlled by appropriate choice of input ratio of Li and Ti during the preparation procedure, which may be a method as defined in the second or third aspects of the present invention. Alternatively or additionally, the presence of cation vacancies may be induced by a ball milling method, such as a ball milling method described herein, as a result of local imperfections in the resulting crystal.

[0045] In some embodiments, compositions of the first aspect may contain up to 20% of cation and / or up to 20% of anion vacancies. Such compositions may retain their original structure of a disordered rock salt structure having the indicated FWHM value.

[0046] In a second aspect, the present invention provides a method of preparing a composition of the first aspect, the method comprising the steps of:

[0047] (a) providing at least one lithium salt precursor and at least one titanium salt precursor, or providing at least one lithium titanium mixed salt precursor; and

[0048] (b) ball milling the at least one lithium salt precursor and at least one titanium salt precursor, or the at least one lithium titanium mixed salt precursor, for a period of time; wherein the salt of the at least one lithium salt precursor, at least one titanium salt precursor, and at least one lithium titanium mixed salt precursor is or comprises an oxide, a sulfide, a fluoride or a chloride.

[0049] Since this method involves at least one lithium salt precursor, it follows that the compositions produced will contain lithium i.e. e > 0.

[0050] The salt of the at least one lithium salt precursor, the at least one titanium salt precursor, and the at least one lithium titanium mixed salt precursor may be the same or different in each of the precursors. In some embodiments, the salt is or comprises an oxide. In some such embodiments, each salt is or comprises an oxide. In such embodiments, the composition produced will have p > 0. In embodiments where each salt is an oxide, the composition produced will have p > 0 and q = 1 = k = 0.

[0051] In some embodiments, the method further comprises delithiating the composition. Delithiation may be achieved by any method known in the art. In some embodiments, the method involves delithiation until the composition prepared has e = 0 i.e. complete delithiation may be achieved in some embodiments. In such embodiments, the space previously occupied by lithium cations may be cation vacancies.

[0052] In a third aspect, the present invention provides a method of preparing a composition of the first aspect, the method comprising the steps of:

[0053] (a) providing a composition having the general formula AX wherein:

[0054] A = LieTif[c]d;

[0055] [c] is a cation vacancy;

[0056] 0 < d < 0.5; 0 < e < 1; 0 < f < 1; and wherein:

[0057] X = OPSqFiClk[a]m;

[0058] [a] is an anion vacancy;

[0059] 0 < p < l; 0 < q < l; 0 < l < l; 0 < k < l; 0 < m < 0.5; and wherein the composition has a structure other than disordered rock salt structure; and

[0060] (b) ball milling the composition provided at (a) for a period of time. Accordingly, in the third aspect, ball milling is carried out on a composition having the corresponding formula to compositions of the first aspect, but which have a different structure to the compositions of the first aspect. Specifically, the third aspect involves ball milling a composition having such different structure for a period of time so as to produce a composition having a disordered rock salt structure as set out in the first aspect. In some embodiments, the structure other than disordered rock salt structure is a layered structure.

[0061] The ball milling methods of the second and third aspects are found to produce the compositions of the first aspect without showing evidence of the presence of precursors or contaminants. Thus, the methods may be particularly efficient at producing the compositions of the first aspect.

[0062] In general, the characteristics of the ball milling may apply to each of the methods of the second and third aspects.

[0063] In some embodiments, the period of time is Ih to 300h. In some embodiments, the ball milling speed is 150 rpm or more and / or 1000 rpm or less. In some embodiments, a weight ratio of milling media to powder is between 1 : 1 to 1 : 100, wherein the powder is the least one lithium salt precursor and at least one titanium salt precursor, or the at least one lithium titanium salt precursor, or the composition having the structure other than the disordered rock salt structure. In some embodiments, the ball milling is carried out in a milling jar which is ZrCb, stainless steel, agate (SiCh), SiC, or WC. Such methods are particularly useful in producing compositions according to the first aspect.

[0064] For each of the second and third aspects, the options set out for the first aspect apply.

[0065] In a fourth aspect, the present invention provides an electrode comprising the composition according to the first aspect, or the composition prepared by the methods of the second or third aspects. In some embodiments, the electrode comprises additives. In some embodiments, the electrode comprises a binder. In some embodiments, the electrode comprises additives and a binder. In some embodiments, the electrode is an anode.

[0066] In a fifth aspect, the present invention provides an electrochemical cell comprising the composition according to the first aspect, or the composition prepared by the method of the second or third aspects, or an electrode according to the fourth aspect.

[0067] In a sixth aspect, the present invention provides an electrochemical energy storage device comprising an electrochemical cell according to the fifth aspect.

[0068] In a seventh aspect, the present invention provides the use of a composition of the first aspect in an electrode, or in an electrochemical cell, or in an electrochemical storage device.

[0069] For each of the fourth to seventh aspects, the options set out for the first, second and third aspect apply.

[0070] BRIEF DESCRIPTION OF THE DRAWINGS

[0071] Figure 1 is a powder XRD pattern of a composition having the target formula LiTiO2 in accordance with the invention.

[0072] Figure 2 is a powder XRD pattern of a composition having the target formula Li1.1Tio.9O2 in accordance with the invention.

[0073] Figure 3 is an X-ray photoelectron spectroscopy (XPS) scan of a composition having the target formula Li1.1Tio.9O2 in accordance with the invention.

[0074] Figure 4 shows higher resolution scans of specific XPS regions of interest from Figure 3. Figure 4(a) shows the \2p region; Figure 4 (b) shows the Li7 region; and Figure 4(c) shows the 075 region.

[0075] Figures 5(a) and 5(b) show scanning electron microscope (SEM) images of a composition having the target formula Li1.1Tio.9O2 powder in accordance with the invention at different magnifications. The scale bar of Figure 5(a) is 100 pm and the scale bar of Figure 5(b) is 20 pm.

[0076] Figure 6(a) is an SEM image of a composition having the target formula Li1.1Tio.9O2 in accordance with the invention superimposed with energy-dispersive X-ray (EDX) mapping information. The scale bar is 200 pm. Figure 6(b) is EDX analysis of the composition of Figure 6(a). The peak labelled 1 is characteristic of carbon; the peak labelled 2 is characteristic of oxygen; and the peaks labelled 3 are characteristic of Ti.

[0077] Figure 7 shows the distribution of (a) titanium and (b) oxygen in the image of Figure 6(a).

[0078] The scale bars are both 200 pm. Lighter areas of the figure are indicative of the presence of the respective elements.

[0079] Figure 8 shows electrochemical performance of a composition having the target formula Li1.1Tio.9O2 within 1.5-4.8V window at 30°C. Figure 8(a) is a graph of voltage vs capacity; Figure 8(b) shows the evolution of the capacity over different cycles.

[0080] Figure 9 shows electrochemical performance of a composition having the target formula Li1.1Tio.9O2 within 0.5-4.8V window at 30°C. Figure 9(a) is a graph of voltage vs capacity; Figure 9(b) shows the evolution of the capacity over different cycles.

[0081] Figure 10 shows electrochemical performance of a composition having the target formula Li1.1Tio.9O2 within 0.5-3.5V window at 30°C. Figure 10(a) is a graph of voltage vs capacity; Figure 10(b) shows evolution of the capacity over different cycles.

[0082] Figure 11 shows electrochemical performance of a composition having the target formula Li1.1Tio.9O2 within 0.5-4.8V window at 45°C. Figure 11(a) is a graph of voltage vs capacity; Figure 11(b) shows the evolution of the capacity over different cycles.

[0083] Figure 12 shows electrochemical performance of a composition having the target formula LiTiCh within 0.5-3.5V window at 30°C. Figure 12(a) is a graph of voltage vs capacity; Figure 12(b) shows the evolution of the capacity over different cycles. Figure 13 is a schematic diagram showing pictorially the calculation of FWHM.

[0084] Figure 14(a) is a powder XRD pattern of a composition having the target formula Li1.07Ti0.9O2 in accordance with the invention. Figure 14(b) is a powder XRD pattern of a composition having the target formula Li1.2Tio.sO2 in accordance with the invention.

[0085] Figure 15(a) is a powder XRD pattern of a composition having the target formula Lio.5Ti2+i.25Ti4+o.2502 in accordance with the invention. Figure 15(b) is a powder XRD pattern of a composition having the target formula Lio.5Ti2+i.oTi3+o.502 in accordance with the invention.

[0086] Figure 16 is an XPS scan of a composition having the target formula LiTiO2 in accordance with the invention.

[0087] Figure 17 shows higher resolution scans of specific XPS regions of interest from Figure 16. Figure 17(a) shows the \2p region; Figure 17(b) shows the Tid.s and Li7 region; and Figure 4(c) shows the 075 region.

[0088] Figure 18 is an XPS scan of a composition having the target formula Lio.5Ti2+i.25Ti4+o.2502 in accordance with the invention.

[0089] Figure 19 shows higher resolution scans of specific XPS regions of interest from Figure 18. Figure 19(a) shows the \2p region; Figure 19(b) shows the TB and Li75 region; and Figure 19(c) shows the 075 region.

[0090] Figure 20 is an XPS scan of a composition having the target formula Lio.5Ti2+i.oTi3+o.502 in accordance with the invention.

[0091] Figure 21 shows higher resolution scans of specific XPS regions of interest from Figure 20. Figure 21(a) shows the \2p region; Figure 21(b) shows the Tid.s and Li75 region; and Figure 21(c) shows the 075 region. Figures 22(a) and 22(b) show scanning electron microscope (SEM) images of a composition having the target formula LiTiCb powder in accordance with the invention at different magnifications. The scale bar of Figure 22(a) is 150 pm and the scale bar of Figure 5(b) is 30 pm.

[0092] Figure 23 is an SEM image of a composition having the target formula LiTiCh in accordance with the invention superimposed with EDX mapping information. The scale bar is 50 pm.

[0093] Figure 24 shows the distribution of (a) oxygen and (b) titanium in the image of Figure 23. The scale bars are both 50 pm. Lighter areas are indicative of the presence of the respective elements.

[0094] Figures 25(a) and 25(b) show scanning electron microscope (SEM) images of a composition having the target formula Lio.5Ti2+i.25Ti4+o.2502 powder in accordance with the invention at different magnifications. The scale bar of Figure 25(a) is 150 pm and the scale bar of Figure 25(b) is 30 pm.

[0095] Figure 26(a) is an SEM image of a composition having the target formula Lio.5Ti2+i.25Ti4+o.2502 in accordance with the invention superimposed with energy-dispersive X-ray (EDX) mapping information. The scale bar is 50 pm. Figure 26(b) is EDX analysis of the composition of Figure 26(a). The peak labelled 1 is characteristic of carbon; the peak labelled 2 is characteristic of oxygen; and the peaks labelled 3 are characteristic of Ti.

[0096] Figure 27 shows the distribution of (a) oxygen and (b) titanium in the image of Figure 26(a). The scale bars are both 50 pm. Lighter areas are indicative of the presence of the respective elements.

[0097] Figures 28(a) and 28(b) show scanning electron microscope (SEM) images of a composition having the target formula Lio.5Ti2+i.oTi3+o.502 powder in accordance with the invention at different magnifications. The scale bar of Figure 28(a) is 150 pm and the scale bar of Figure 28(b) is 30 pm. Figure 29(a) is an SEM image of a composition having the target formula Lio.5Ti2+i.oTi3+o.502 in accordance with the invention superimposed with EDX mapping information. The scale bar is 50 pm. Figure 29(b) is EDX analysis of the composition of Figure 29(a). The peak labelled 1 is characteristic of carbon; the peak labelled 2 is characteristic of oxygen; and the peaks labelled 3 are characteristic of Ti.

[0098] Figure 30 shows the distribution of (a) oxygen and (b) titanium in the image of Figure 29(a). The scale bars are both 50 pm. Lighter areas are indicative of the presence of the respective elements.

[0099] Figure 31(a) is a graph of voltage vs capacity showing electrochemical performance of LiTiCb within 3.0-0.1 V window at 30°C (delithiation first), and Figure 31(b) is a graph pf capacity vs number of cycles.

[0100] Figure 32 shows graphs of voltage vs capacity showing electrochemical performance of a composition having the target formula Lio.5Ti2+i.25Ti4+o.2502 within (a) 0.5-4.8 V window at 30°C and (b) 3-0. IV (delithiation first). The insets show capacity vs number of cycles.

[0101] Figure 33 shows graphs of voltage vs capacity showing electrochemical performance of a composition having the target formula Lio.5Ti2+i.oTi3+o.502 within (a) 0.5-4.8 V window at 30°C and (b) 3-0. IV (delithiation first). The insets show capacity vs number of cycles.

[0102] Figure 34(a) shows a thermogravimetric analysis (TGA) of a composition having the target formula LiTiCh (solid line) and a composition having the target formula Li1.1Tio.9O2 (dashed line) taken between 0-900°C, over 5 hours, in air. The mass change indicative of oxygen vacancies is indicated by the arrows. For the targeted LiTiO2 the mass change is 4.33 weight% (wt%) (m=0.115) and for the targeted Li1.1Tio.9O2 the mass change is 3.32 wt% (m=0.085). Figure 34 (b) shows a TGA analysis of a composition having the target formula Lio.5Ti2+i.25Ti4+o.2502 (solid line) and a composition having the target formula Lio.5Ti2+i.oTi3+o.502 (dashed line) taken between 0-900°C, over 5 hours, in air. The mass change indicative of oxygen vacancies is indicated by the arrows. For the targeted Lio.5Ti2+i.25Ti4+o.2502 the mass change is 5.58 wt% (m=0.175) for the targeted Lio.5Ti2+i.oTi3+o.502 the mass change is 4.35 wt% (m=0.135). In the figures, all XPS intensity values are normalised intensity values.

[0103] DETAILED DESCRIPTION

[0104] It is to be understood that any aspect of the invention may be combined with any other aspect of the invention unless the context demands otherwise. Any of the optional features of any aspect may be combined, either singly or in combination, with any aspect of the invention unless the context demands otherwise.

[0105] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. Methods and materials are described herein for use in the present disclosure; other, suitable methods and materials known in the art can also be used. The materials, methods, and examples are illustrative only and not intended to be limiting. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control.

[0106] Methods described herein usually employ ambient temperature of a typical laboratory, which is typically between 20 and 30°C, such as around 25°C, at atmospheric pressure, unless a different condition is defined herein or is more usually employed e.g. for a particular apparatus.

[0107] Unless indicated otherwise, “%” refers to “weight %”. Similarly, “wt%” denotes “weight%”.

[0108] According to a first aspect, the present invention relates to a composition having the general formula:

[0109] AX wherein:

[0110] A = LieTif[c]d;

[0111] [c] is a cation vacancy;

[0112] 0 < d < 0.5; 0 < e < 1; 0 < f < 1; and wherein:

[0113] X = OPSqFiClk[a]m;

[0114] [a] is an anion vacancy; 0 < p < 1; 0 < q < 1; 0 < l < 1; 0 < k < 1; 0 < m < 0.5.

[0115] The composition may have a disordered rock salt structure. An X-ray diffraction pattern of the composition using a CuKa radiation source may have peaks whose full-width half-maximum value is >1.20° 29.

[0116] In compositions of the first aspect, A comprises Ti. In some embodiments, A comprises Li. In some embodiments, A comprises [c]. In some embodiments, A comprises Ti and Li and m=0. In some embodiments, A comprises Ti and [c] and e=0. In some embodiments, A comprises Li and Ti and [c].

[0117] In some embodiments, the compositions of the first aspect may comprise [c] (d > 0) or [a] (m > 0) or may comprise both [c] and [a] i.e. have d > 0 and m > 0. In some embodiments, anion vacancies [a] may be introduced during preparation of the compositions, such as during a ball milling step discussed elsewhere herein. In some embodiments, anion vacancies [a] may be introduced during other stages e.g. during fast cooling (quenching) of the compositions following heating. In some embodiments, cation vacancies [c] may be introduced by delithiation, such as during use in a lithium-ion battery. In some embodiments, cation vacancies [c] may be introduced during preparation of the compositions, such as during a ball milling step discussed elsewhere herein. In some embodiments, vacancies [a] and [c] may be introduced by careful control of the starting materials. For example, if cation vacancies are desired, using a specific proportion of titanium salt precursor and lithium salt precursor may suitably be used in a method described elsewhere herein to introduce cation vacancies [c] .

[0118] In some embodiments, compositions of the first aspect may contain up to 20% [c] and / or up to 20% [a]. In some embodiments, such compositions may retain their original structure. In some embodiments, compositions of the first aspect may contain up to 18% [c], such as up to 15% [c], up to 12% [c] or up to 10% [c] . In some embodiments, compositions of the first aspect may contain up to 18% [a], such as up to 15% [a], up to 12% [a] or up to 10% [a]. In some embodiments, compositions of the first aspect may any combination of these ranges, for example up to 20% [a] and up to 10% [c], up to 10% [a] and up to 20% [c], up to 15% [a] and up to 15 [c], up to 12% [a] and up to 18% [c], or up to 10% [a] and up to 10% [c] . In some embodiments, e = 0. In some embodiments, e > 0, such as 0.005 or more, 0.01 or more,

[0119] 0.015 or more, 0.02 or more, 0.025 or more, 0.05 or more, 0.075 or more, 0.1 or more, 0.13 or more, or 0.15 or more such as 1 / 3 or more. In some embodiments, e is 0.25 or more, such as 0.27 or more, 0.3 or more, 0.33 or more, or 0.35 or more. In some embodiments, e is 2 / 3 or less, such as 0.65 or less, 0.63 or less, 0.6 or less, or 0.57 or less. Combinations of any of these values may be used to provide exemplary ranges for e. For example, e may be in the range of 0 < e < 2 / 3, or 0 < e < 0.63, or 0.005 < e < 2 / 3, or 0.01 < e < 0.63, or 0.015 < e < 0.6, or 0.02 < e < 0.65, or 0.025 < e < 0.065, or 0.05 < e < 0.6, or 0.075 < e < 0.65, or 0.1 < e < 0.63, or 0.13 < e < 0.65, or 0.15 < e < 0.63, or 0.25 < e < 0.57, or 0.27 < e < 0.65, or 0.3 < e < 0.6, or 0.33 < e < 0.65, or 0.35 < e < 0.57.

[0120] In some embodiments, 0.05 < e < 2 / 3.

[0121] In some embodiments, 0.25 < e < 2 / 3.

[0122] In some embodiments, 0.25 < e < 0.6.

[0123] In some embodiments, f =1. In some embodiment, f < 1, such as 0.99 or less, 0.98 or less, 0.97 or less, 0.96 or less, 0.95 or less, 0.94 or less, 0.93 or less, 0.9 or less, 0.88 or less, or 0.85 or less. In some embodiments, f is 0.75 or less, such as 0.73 or less, 0.7 or less, 0.68 or less, or 0.65 or less. In some embodiments, f is 1 / 3 or more, such as 0.35 or more, 0.38 or more, 0.4 or more, or 0.43 or more. Combinations of any of these values may be used to provide exemplary ranges for f. For example, f may be in the range of 1 / 3 < f < 1, or 1 / 3 < f <1, or 1 / 3 < f < 0.99, or 1 / 3 < f < 0.98, or 0.35 < f < 1, or 0.35 < f < 0.97, or 0.35 < f < 0.96, or 0.38 < f < 0.96, or 0.38 < f < 0.95, or 0.38 < f < 0.93, or 0.4 < f < 1, 0.4 < f < 0.95, 0.4 < f < 0.9, 0.4 < f < 0.88, 0.4 < f < 0.85, 0.43 < f < 1, or 0.43 < f < 0.85, or 0.43 < f < 0.75, or 1 / 3 < f < 0.75, or 0.4 < f < 0.73, or 1 / 3 < f < 0.7, or 1 / 3 < f < 0.68, or 0.38 < f < 0.68, or 0.43 < f < 0.68.

[0124] In some embodiments, 1 / 3 < f < 0.95. In some embodiments, 1 / 3 < f < 0.75. In some embodiments, 0.4 < f < 0.75. In some embodiments, where e is less than 0.5 and f is more than 0.5, the composition may be described as lithium-deficient or titanium-rich. In some embodiments, where e is more than 0.5 and f is less than 0.5, the composition may be described as lithium-rich or titanium-deficient.

[0125] Without wishing to be bound by theory, the inventors consider that the compositions of the first aspect of the present invention may contain titanium ions having more than one oxidation state. In some embodiments, the titanium is present in an oxidation state of 3+ and 4+. In some embodiments, the titanium is present in an oxidation state of 2+ and 4+. In some embodiments, the titanium is present in an oxidation state of 2+ and 3+. In some embodiments, the titanium is present in an oxidation state of 2+ and 3+ and 4+.

[0126] In some embodiments, a lithium rich composition may have titanium in both 3+ and 4+ oxidation states, and may be written as follows (assuming no cation vacancies):

[0127] Lii+bTi3+i-3bTi4+2bO2 where 0 < b < 1 / 3

[0128] In some embodiments, a lithium deficient composition may have titanium in both 2+ and 4+, or in 2+ and 3+ oxidation states, and may be written as follows (assuming no cation vacancies): Lii-bTi2+(3b+i) / 2Ti4+(i-b) / 2O2 where 0 < b < 1 Lii-bTi2+2bTi3+i-bO2 where 0 < b < 1

[0129] Compositions containing titanium in more than one oxidation state are considered to affect the size of the unit cell, due to the variation in size of the ions and consequently affect the performance characteristics of the materials.

[0130] In some embodiments, the composition of the first aspect comprises a cation vacancy.

[0131] In some embodiments, d = 0. Such embodiments do not have any cation vacancy. In some embodiments, d > 0, such as at least 0.01, at least 0.02, at least 0.03, at least 0.04, at least 0.05, or at least 0.08. In some embodiments, d = 0.5. In some embodiments, d < 0.5, such as up to 0.48, up to 0.45, up to 0.43 or up to 0.4. Combinations of any of these end-points may be combined to form a suitable range, such as 0 < d < 0.5, 0 < d < 0.5, 0 < d < 0.5, 0.01 < d < 0.48, 0.02 < d < 0.45, 0.02 < d < 0.43, 0.03 < d < 0.43, 0.05 < d < 0.48, 0.08 < d < 0.45, or 0.08 < d < 0.4. In some embodiments, X comprises O. In some embodiments, X comprises S. In some embodiments, X comprises F. In some embodiments, X comprises Cl. In some embodiments, X comprises O and S. In some embodiments, X comprises O and F. In some embodiments, X comprises O and Cl. In some embodiments, X comprises S and F. In some embodiments, X comprises S and Cl. In some embodiments, X comprises O, S and F. In some embodiments, X comprises O, S and Cl.

[0132] In any of these embodiments, X can also comprise anion vacancy.

[0133] In some embodiments, X consists of O and optionally anion vacancy. In some embodiments, X consists of S and optionally anion vacancy. In some embodiments, X consists of F and optionally anion vacancy. In some embodiments, X consists of Cl and optionally anion vacancy. In some embodiments, X consists of O and S and optionally anion vacancy. In some embodiments, X consists of O and F and optionally anion vacancy. In some embodiments, X consists of O and Cl and optionally anion vacancy. In some embodiments, X consists of S and F and optionally anion vacancy. In some embodiments, X consists of S and Cl and optionally anion vacancy. In some embodiments, X consists of O, S and F and optionally anion vacancy. In some embodiments, X consists of O, S and Cl and optionally anion vacancy.

[0134] In some embodiments, p = 0. In some embodiments, p > 0, such as at least 0.01, at least 0.05, at least 0.1, at least 0.2 or at least 0.3. In some embodiments, p is 1. In some embodiments, p

[0135] < 1, such as 0.99 or less, 0.98 or less, 0.97 or less, 0.96 or less, or 0.95 or less. Combinations of these end-points may be combined to form any suitable range. For example, 0 < p < 1, or 0

[0136] < p < 0.99, or 0.01 < p < 0.99, or 0.05 < p < 0.99, or 0.1 < p < 0.98, or 0.2 < p < 0.98, or 0.3 < p < 0.95.

[0137] In some embodiments, q = 0. In some embodiments, q > 0 such as at least 0.01, at least 0.02, at least 0.03, at least 0.04 or at least 0.05. In some embodiments, q is 1. In some embodiments, q < 1, such as 0.9 or less, 0.5 or less, 0.4 or less, 0.2 or less, or 0.1 or less. Combinations of these end-points may be combined to form any suitable range. For example, 0 < q < 1, or 0 < q < 0.9, or 0.01 < q < 0.5, or 0.02 < q < 0.4, or 0.03 < q < 0.5, or 0.04 < q < 0.2, or 0.05 < q < 0.1. In some embodiments, 1 = 0. In some embodiments, 1 > 0, such as at least 0.01, at least 0.02, at least 0.03, at least 0.04 or at least 0.05. In some embodiments, 1 is 1. In some embodiments, 1 < 1, such as 0.9 or less, 0.5 or less, 0.4 or less, 0.2 or less, or 0.1 or less. Combinations of these end-points may be combined to form any suitable range. For example, 0 < 1 < 1, or 0 < 1 < 0.9, or 0.01 < 1 < 0.5, or 0.02 < 1 < 0.4, or 0.03 < 1 < 0.5, or 0.04 < 1 < 0.2, or 0.05 < 1 < 0.1.

[0138] In some embodiments, k = 0. In some embodiments, k > 0, such as at least 0.01, at least 0.02, at least 0.03, at least 0.04 or at least 0.05. In some embodiments, k is 1. In some embodiments, k < 1, such as 0.9 or less, 0.5 or less, 0.4 or less, 0.2 or less, or 0.1 or less. Combinations of these end-points may be combined to form any suitable range. For example, 0 < k < 1, or 0 < k < 0.9, or 0.01 < k < 0.5, or 0.02 < k < 0.4, or 0.03 < k < 0.5, or 0.04 < k < 0.2, or 0.05 < k < 0.1.

[0139] In some embodiments, the composition of the first aspect comprises an anion vacancy [a].

[0140] In some embodiments, m = 0. Such embodiments do not have any anion vacancy. In some embodiments, m > 0, such as at least 0.01, at least 0.02, at least 0.03, at least 0.04, at least 0.05, or at least 0.08. In some embodiments, m = 0.5. In some embodiments, m < 0.5, such as up to 0.48, up to 0.45, up to 0.43 or up to 0.4. Combinations of any of these end-points may be combined to form a suitable range, such as 0 < m < 0.5, 0 < m < 0.5, 0 < m < 0.5, 0.01 < m < 0.48, 0.02 < m < 0.45, 0.02 < m < 0.43, 0.03 < m < 0.43, 0.05 < m < 0.48, 0.08 < m < 0.45, or 0.08 < m < 0.4.

[0141] In some embodiments, the composition has a face centred cubic (FCC) structure. In such embodiments, the composition has a space group Fm-3m. In some embodiments, the composition has a unit cell having a dimension (length) of at least a=b=c=4.10 A, such as at least 4.11 A, or at least 4.12 A. In some embodiments, the composition has a unit cell dimension of no more than 4.20 A, no more than 4.18 A or no more than 4.17 A. Combinations of any of these values may be used to provide exemplary ranges. In these embodiments, a=P=y=90o. A skilled person will appreciate that disordered rock salt structures have a cubic unit cell size (i.e. a=b=c and a=P=y=90o). In some embodiments, any structural disorder will be averaged across the unit cell dimension. The crystalline structure of the compositions of the first aspect may be assessed using XRD techniques. Typically, the compositions of the present invention are in the form of a powder, rather than single crystals, and so the crystalline structure of the compositions may be assessed using powder XRD techniques. Accordingly, where X-ray diffraction or XRD is used herein, it may generally refer to powder X-ray diffraction or powder XRD.

[0142] The XRD pattern may be measured on any suitable diffractometer. Suitable diffractometers are typically used in reflection geometry. Suitable diffractometers may use CuKa radiation, with an x-ray wavelength of 1.54056A. Suitable diffractometers may operate at 40 kV and 40 mA. A measurement range may be 30-75° 29. Analysis may be performed by any suitable means, such as with appropriate software. For example, a suitable diffractometer may be an Aeris Benchtop X-ray diffractometer equipped with a PIXcel detector. Any suitable sample preparation method may be used.

[0143] In some embodiments, structural disorder refers to the variability of the position of an atom at its site in the overall structure. This may include, for example, local variation in the length of bonds or variables. In the present compositions, the structural disorder may be provided by one or more of the cations, by one or more of the anions, or by one or more of the cations and the anions, such as by each of the kinds of ions present.

[0144] A highly crystalline composition having disordered rock salt structure may be expected to contain intense, sharp peaks in an XRD pattern. Broadening of these peaks may be seen when introducing structural disorder or smaller crystallite size, for example. The width of a peak may be assessed using FWHM. The extent of structural disorder and / or crystallite size may therefore be assessed, in some embodiments, by considering the FWHM of the peaks produced in the XRD pattern of the composition. The FWHM may be expected to be the same for each peak in the XRD pattern.

[0145] Figure 13 shows a schematic diagram showing the principle of the method of measuring the FWHM of an XRD peak. The maximum intensity (Imax) of the peak is determined by identifying the peak position at 29 and reading the corresponding intensity value, then subtracting the value of the background. The half-maximum intensity (Imax / 2) can then be determined by dividing the maximum intensity by 2. The width of the peak at this halfmaximum value is the FWHM value. Typically, this calculation can be done using appropriate software and performing a Rietveld refinement according to standard methods. The reader is directed to e.g. H.M. Rietveld, J. Appl. Cryst. (1969) 2, 65-71.

[0146] In general, the inventors believe the FWHM values of the peaks of the present compositions are larger than those of more ordered structures, especially known lithium titanates having other crystallographic structures, such as layered or spinel phases.

[0147] The FWHM of the present compositions is at least 1.20° 29, such as at least 1.21° 29 or at least 1.22° 29. In some embodiments, the FWHM of a composition of the first aspect is at least 1.23° 29, at least 1.24° 29, at least 1.25° 29, at least 1.26° 29, or at least 1.27° 29.

[0148] In some embodiments, the FWHM is at least 1.39° 29, such as at least 1.31° 29, at least 1.32° 29, at least 1.33° 29, at least 1.34° 29, at least 1.35° 29, at least 1.36° 29, or at least 1.37° 29.

[0149] In some embodiments, the FWHM is at least 1.59° 29, such as at least 1.55° 29, at least 1.69° 29, at least 1.65° 29 or at least 1.79° 29.

[0150] In some embodiments, the FWHM is at least 1.89° 29, such as at least 1.81° 29, at least 1.82° 29, or at least 1.83° 29.

[0151] In some embodiments, the XRD pattern shows a signature of a cubic phase associated with peaks at indicated positions.

[0152] In some embodiments, an XRD pattern of the composition using a CuKa radiation source has a peak at a 29 value of 37.4° ± 2.9°. In some embodiments, an XRD pattern of the composition using a CuKa radiation source has a peak at a 29 value of 37.4° ± 1.9°. In some embodiments, an XRD pattern of the composition using a CuKa radiation source has a peak at a 29 value of 37.4° ± 9.5°. In some embodiments, an XRD pattern of the composition using a CuKa radiation source has a peak at a 29 value of 37.4° ± 9.4°. In some embodiments, an XRD pattern of the composition using a CuKa radiation source has a peak at a 29 value of 43.5° ± 2.9°. In some embodiments, an XRD pattern of the composition using a CuKa radiation source has a peak at a 29 value of 43.5° ± 1.9°. In some embodiments, an XRD pattern of the composition using a CuKa radiation source has a peak at a 29 value of 43.5° ± 9.5°. In some embodiments, an XRD pattern of the composition using a CuKa radiation source has a peak at a 29 value of 43.5° ± 9.4°.

[0153] In some embodiments, an XRD pattern of the composition using a CuKa radiation source has a peak at a 29 value of 63.3° ± 2.9°. In some embodiments, an XRD pattern of the composition using a CuKa radiation source has a peak at a 29 value of 63.3° ± 1.9°. In some embodiments, an XRD pattern of the composition using a CuKa radiation source has a peak at a 29 value of 63.3° ± 9.5°. In some embodiments, an XRD pattern of the composition using a CuKa radiation source has a peak at a 29 value of 63.3° ± 9.4°.

[0154] In some embodiments, an XRD pattern of the composition using a CuKa radiation source has peaks at a 29 value of 37.4° ± 2.9° and 43.5° ± 2.9°. In some embodiments, an XRD pattern of the composition using a CuKa radiation source has peaks at a 29 value of 37.4° ± 1.9° and 43.5° ± 1.9°. In some embodiments, an XRD pattern of the composition using a CuKa radiation source has peaks at a 29 value of 37.4° ± 9.5° and 43.5° ± 9.5°. In some embodiments, an XRD pattern of the composition using a CuKa radiation source has peaks at a 29 value of 37.4° ± 9.4° and 43.5° ± 9.4°.

[0155] In some embodiments, an XRD pattern of the composition using a CuKa radiation source has peaks at a 29 value of 37.4° ± 2.9° and 63.3° ± 2.9°. In some embodiments, an XRD pattern of the composition using a CuKa radiation source has peaks at a 29 value of 37.4° ± 1.9° and 63.3° ± 1.9°. In some embodiments, an XRD pattern of the composition using a CuKa radiation source has peaks at a 29 value of 37.4° ± 9.5° and 63.3° ± 9.5°. In some embodiments, an XRD pattern of the composition using a CuKa radiation source has peaks at a 29 value of 37.4° ± 9.4° and 63.3° ± 9.4°.

[0156] In some embodiments, an XRD pattern of the composition using a CuKa radiation source has peaks at a 29 value of 43.5° ± 2.0° and 63.3° ± 2.0°. In some embodiments, an XRD pattern of the composition using a CuKa radiation source has peaks at a 29 value of 43.5° ± 1.9° and 63.3° ± 1.0°. In some embodiments, an XRD pattern of the composition using a CuKa radiation source has peaks at a 29 value of 43.5° ± 9.5° and 63.3° ± 9.5°. In some embodiments, an XRD pattern of the composition using a CuKa radiation source has peaks at a 29 value of 43.5° ± 9.4° and 63.3° ± 9.4°.

[0157] In some embodiments, an XRD pattern of the composition using a CuKa radiation source has peaks at a 29 value of 37.4° ± 2.9°, 43.5° ± 2.9°, and 63.3° ± 2.9°. In some embodiments, an XRD pattern of the composition using a CuKa radiation source has peaks at a 29 value of 37.4° ± 1.9°, 43.3° ± 1.9°, and 63.3° ± 1.9°. In some embodiments, an XRD pattern of the composition using a CuKa radiation source has peaks at a 29 value of 37.4° ± 9.5°, 43.3° ± 9.5°, and 63.3° ± 9.5°. In some embodiments, an XRD pattern of the composition using a CuKa radiation source has peaks at a 29 value of 37.4° ± 9.4°, 43.3° ± 9.4°, and 63.3° ± 9.4°.

[0158] By “± 2.9°” we mean that the peaks describing the XRD pattern may differ by up to 2.9° 29 from the values mentioned. In some embodiments, one or more of the peaks, such as all of the peaks, may differ by up to 1.9° 29. In some embodiments, one or two of the peaks, may differ by up to 9.5° 29 from the mentioned values. In some embodiments, one or two of the peaks, may differ by up to 9.4° 29 from the mentioned values.

[0159] In some embodiments, an XRD pattern of the composition using a CuKa radiation source has three peaks at 29 = 37.4°, 43.4° and 63.3°.

[0160] In some embodiments, an XRD pattern of the composition using a CuKa radiation source has three peaks at 29 = 37.5°, 43.6° and 63.3°.

[0161] In some embodiments, an XRD pattern of the composition using a CuKa radiation source has three peaks at 29 = 37.2°, 43.2° and 63.9°.

[0162] In some embodiments, an XRD pattern of the composition using a CuKa radiation source has three peaks at 29 = 37.7°, 43.8° and 63.7°.

[0163] In some embodiments, an XRD pattern of the composition using a CuKa radiation source has an absence of peaks below a 29 value of 30°. In some embodiments, the characteristic XRD pattern has an absence of peaks below a 29 value of 31°, or below a 29 value of 32°, or below a 29 value of 33°, or below a 29 value of 34°, or below a 29 value of 35°.

[0164] In some embodiments, the characteristic XRD pattern is substantially similar to, or the same as, the XRD pattern shown in any of Figures 1, 2. 14(a), 14(b). 15(a) or 15(b).

[0165] In some embodiments, the peaks of the characteristic peak XRD pattern with the range 30 to 70° 29 can be indexed to the Miller indices (a) (111); (b) (020) and (c) (022).

[0166] In some embodiments, compositions of the first aspect may contain a single phase. That is, the compositions of the present invention may form a disordered rock salt structure, without any other crystalline phases, such as remaining precursor materials and no identifiable XRD peak below 30 °29. In some embodiments, the compositions are 100% disordered rock salt structure having the indicated FWHM value.

[0167] In some embodiments, the electrochemical properties of the material may be measured. Such measurements may be carried out in a non-aqueous electrolyte containing a Li salt with a Li metal counter / reference electrode. Application of a positive / negative current may be applied and the resulting changes in potential vs Li metal recorded. These measurements may be measured using a cell, such as a coin type cell, assembled in an area containing inert gas, such as argon. Galvanostatic tests may be performed on an appropriate machine, such as a MACCOR, at a desired current density and within a desired voltage range, at any desired temperature and suitable pressure. A suitable pressure may be 101 kPa. Electrodes may be prepared according to any suitable method, and counter electrodes and electrolytes chosen appropriately. These measurements may permit understanding of the electronic structure within the material as a function of the Li content. The resulting voltage vs charge plots may be thought of as correlating to a measurement of the Fermi level within a material as a function of the Li content. These measurements can be used to infer how this material may perform in a practical Li ion cell. These measurements may be considered characteristic of the material and provide a signature which is unique for a given composition and structure. In the Galvanostatic testing of the composition, the integral of the second negative current hold may be approximately 81% of the integral of the second positive current hold vs Li. Without wishing to be bound by theory and considering that there is some variation in the potentials during the negative and positive current holds resulting from cell resistances, this may indicate that the electronic structure of the material at a specific degree of lithiation during the negative current hold is very similar as the electronic structure of the material at a specific degree of lithiation during the positive current hold. This may give a characteristic signature of this material.

[0168] In some embodiments, in a charge-discharge curve of the composition, the integral of the second discharge is greater than 50%, such as greater than 55%, greater than 60% or greater than 70% of the integral of the second charge.

[0169] Also provided as second and third aspects of the invention are methods of preparing the composition of the first aspect. The methods may be described as mechanochemical synthesis methods because they use a mechanical method to cause a chemical reaction. The methods of the second and third aspects may use a ball milling process to achieve the mechanochemical synthesis, and not only a mechanical mixing of precursors.

[0170] In a second aspect, the present invention provides a method of preparing a composition of the first aspect wherein e > 0 i.e. wherein the composition comprises Li. The method of the second aspect comprises the steps of:

[0171] (a) providing at least one lithium salt precursor and at least one titanium salt precursor, or providing at least one lithium titanium mixed salt precursor; and

[0172] (b) ball milling the at least one lithium salt precursor and at least one titanium salt precursor, or the at least one lithium titanium mixed salt precursor, for a period of time; wherein the salt of the at least one lithium salt precursor, at least one titanium salt precursor, and at least one lithium titanium mixed salt precursor is oxide, sulfide, fluoride or chloride.

[0173] In some embodiments wherein more than one precursor is used, the salt may be the same or different among the precursors. In some embodiments, at least one salt is oxide. In some embodiments, at least one salt comprises sulfide. In some embodiments, at least one salt comprises fluoride. In some embodiments, at least one salt comprises chloride.

[0174] In some embodiments, the lithium salt precursor may be or comprise Li2O.

[0175] In some embodiments, the lithium salt precursor may be or comprise I 2S, LiF and / or LiCl.

[0176] In some embodiments, the titanium salt precursor may be or comprise one or more selected from TiO, TiiCh and TiCh. In some embodiments, the titanium salt precursor may be or comprise one or more selected from TiS, TnSs and TiS2, or TiF2 or TiCh.

[0177] In some embodiments, only one titanium salt precursor is used. In some embodiments, two titanium salt precursors are used. In some embodiments, three titanium salt precursors are used. Where the method uses more than one titanium salt precursor, any suitable proportion may be chosen.

[0178] In some embodiments, the titanium salt precursors may be TiO and Ti2O3, or may be TiO and TiO2; or may be Ti2O3 and TiO2 or TiO, Ti2O3 and TiO2. In some embodiments, the titanium salt precursor may be or comprise corresponding S, F and / or Cl containing precursors.

[0179] In a third aspect, the present invention provides a method of preparing a composition according to the first aspect, the method comprising the steps of:

[0180] (a) providing a composition having the general formula AX wherein:

[0181] A = LieTif[c]d;

[0182] [c] is a cation vacancy;

[0183] 0 < d < 0.5; 0 < e < 1; 0 < f < 1; and wherein:

[0184] X = OPSqFiClk[a]m;

[0185] [a] is an anion vacancy;

[0186] 0 < p < l; 0 < q < l; 0 < l < l; 0 < k < l; 0 < m < 0.5; and wherein the composition has a structure other than disordered rock salt structure; and

[0187] (b) ball milling the composition provided at (a) for a period of time. In the method of the third aspect, the step (b) corresponds with the step (b) of the method of the second aspect. The method of the third aspect differs from the method of the second aspect at least by the precursor provided in step (a) i.e. the precursor of step (a) of the third aspect corresponds with the desired composition, except that it does not have the disordered rock salt structure of the compositions of the first aspect. In some embodiments, it has a layered structure.

[0188] In some embodiments of the method of the second or third aspect where the third aspect uses a composition having a structure other than disordered rock salt structure in which e >0, the method further comprises delithiating the composition obtained after step (b). In some embodiments, delithiating the composition comprises applying a potential difference to an electrode comprising a composition of the first aspect, so as to cause delithiation of the composition originally produced following step (b). In some embodiments, delithiation can be achieved using chemical means, such as with iodine.

[0189] In some embodiments, the delithiating comprises reducing the amount of lithium in the composition. In some embodiments, the delithiating is carried out until e=0. In some embodiments, the delithiating is carried out until the amount of lithium is reduced, but e > 0.

[0190] In the following, references to step (b) refer to the step (b) of the methods of both the second and third aspects.

[0191] In some embodiments, in step (b), the period of time is measured in hours (h). In some embodiments, in step (b), the period of time is at least 1 h, such as at least 3 h, at least 5 h, at least 7 h, or at least 10 h.

[0192] In some embodiments, in step (b), the period of time is up to 300 h, such as up to 280 h, up to 250 h, up to 220 h, up to 200 h, or up to 150 h.

[0193] Combinations of any of these values may be used to provide exemplary ranges for the period of time. For example, the period of time may be between 1 h and 300 h, between 3 h and 280 h, between 3 h and 250 h, between 7 h and 200 h, or between 10 h and 150 h. In some embodiments, in step (b), the period of time corresponds with a time at which no crystalline precursor peaks can be observed in a product of the ball milling, the crystalline precursor peaks being determined by taking an XRD pattern using a CuKa radiation source as described elsewhere herein. In some embodiments, reference to the precursor here intends the at least one lithium salt precursor, the at least one titanium salt precursor, the at least one lithium titanium mixed salt precursor, and the composition having the general formula AX wherein: A = LieTif[c]d; [c] is a cation vacancy; 0 < d < 0.5; 0 < e < l; 0 < f < l; and wherein: X = OpSqFiClk[a]m; [a] is an anion vacancy; 0 < p < l; 0 < q < l; 0 < l < l; 0 < k < l; 0 < [a] < 0.5; and wherein the composition has a structure other than disordered rock salt structure.

[0194] In some embodiments, the ball milling of step (b) is carried out in cycles. For example, ball milling may be performed for a certain time, then paused, to form a single cycle. In some embodiments, the period of time may correspond to the total milling time taken for a particular number of such cycles, excluding any pauses. In some embodiments, there is no pause.

[0195] In some embodiments, in step (b), the ball milling is carried out at a speed of 150 revolutions per minute (rpm) or more, such as 250 rpm or more, 350 rpm or more, 450 rpm or more, or 500 rpm or more such as 550 rpm.

[0196] In some embodiments, in step (b), the ball milling is carried out at a speed of 1000 rpm or less, such as 950 rpm or less, 900 rpm or less, 850 rpm or less, or 800 rpm or less.

[0197] Combinations of any of these values may be used to provide exemplary ranges for the ball milling speed. For example, ball milling may be carried out at a speed of between 150 rpm and 1000 rpm, or between 250 rpm and 950 rpm, or between 350 rpm and 900 rpm, or between 450 rpm and 850 rpm, or between 550 rpm and 800 rpm.

[0198] In some embodiments, in step (b), a speed of the ball milling may be varied over the period of time. For example, ball milling may be carried out at 350 rpm for part of the period of time and increased to one or more higher speeds for the remainder of the period of time. In some embodiments, in step (b), a milling media is used to assist or cause the mechanochemical reaction. The milling media may comprise beads and / or balls. The milling media may be placed inside the ball mill to affect, cause or enhance the mechanochemical reaction. In some embodiments, the milling media has a diameter of 2-20 mm, such as between 3-10 mm, such as 4-7 mm. Any suitable known milling media may be used, for example yttrium stabilized ZrCb (YSZ).

[0199] In some embodiments, in step (b), a weight ratio of the milling media to the at least one lithium oxide precursor and the at least one titanium oxide precursor is at least 1 : 1, such as at least 1 :2, at least 1 :4, at least 1 :5, at least 1 :6, or at least 1 :7. The ratio refers to the sum of the weight of the precursors (i.e. the sum of the at least one lithium salt precursor and the at least one titanium salt precursor, or the sum of the at least one mixed lithium titanium salt precursor). Accordingly, in embodiments using, for example, one lithium salt precursor and two titanium salt precursors, the ratio may refer to the sum of the weights of (the one lithium salt precursor + first titanium salt precursor + second titanium salt precursor).

[0200] In some embodiments, in step (b), the weight ratio of milling media to at least one lithium salt precursor and at least one titanium salt precursor, or at least one lithium titanium mixed salt precursor, or composition having the structure other than disordered rock salt structure, is up to 1 : 100, up to 1 :50, up to 1 :20, or up to 1 : 10.

[0201] Combinations of any of these values may be used to provide exemplary ranges for the weight ratio. For example, the weight ratio may be 1 : 1 to 1 : 100, 1 :2 to 1 : 100, 1 :4 to 1 :50, 1 :5 to 1 :20 or 1 :7 to 1 : 10.

[0202] In some embodiments, in step (b), the ball milling is carried out in a milling jar which is ZrCh, stainless steel, agate (SiCh), SiC, or WC. Such milling jars are considered to be capable of achieving the mechanochemical reaction while not causing unwanted contamination. In some embodiments, a hard and / or dense material is chosen for the jar material. In some embodiments, the milling jar is ZrCb or stainless steel. In some embodiments, the milling jar is ZrCh.

[0203] In some embodiments, the milling jar has a volume of at least 20 mL, at least 45 mL, at least 50 mL, at least 80 mL or at least 100 mL. In some embodiments, the milling jar has a volume or at least 250 mL or at least 500 mL. In some embodiments, a larger milling jar may allow a lower rpm to be used to achieve the mechanochemical synthesis.

[0204] In some embodiments, variation of the ball milling conditions in step (b) may provide the compositions of the first aspect with one or more anion vacancies. In some embodiments, one or more anion vacancies can be introduced by considering aspects of the ball milling conditions of step (b) such as the period of time or speed of ball milling.

[0205] In some embodiments, the amount of anion vacancies can be measured using TGA or XPS. In some embodiments, the amount of anion vacancies can be measured using TGA. In some such embodiments, the composition may be heated in air at any appropriate heating rate. In principle, any anion vacancies are filled by oxide anions from air during the heating process. Therefore, a mass increase recorded by the TGA in the region 0 to 450°C may be ascribed to the filling of anion vacancies, and thus the amount of vacant anion sites may be calculated. In some embodiments, the mass increase is the maximum mass increase, which may be identified by a peak position in that region. In some embodiments, other subsequent mass changes may be ascribed to thermal decomposition processes, such as mass changes occurring above 450°C or above 500°C. In some embodiments, the mass change is calculated from the peak position, or the largest mass change observed in the region 0 to 450°C. In some embodiments, the amount of anion vacancies that can be measured using TGA is the amount of oxygen anion vacancies. In some embodiments, induced oxygen deficiency may be calculated from TGA. In some embodiments, the calculation of induced oxygen deficiency may involve converting the wt% mass change to O2 (g), and using oxygen deficiency = (O2 mass x 2) / (mol[AX] x molecular mass [AX]). Corresponding calculations may be done for F, S and Cl.

[0206] In some embodiments, TGA analysis records a mass increase in the range (temperature range) of up to 10 wt%, such as up to 9 wt%, up to 8 wt%, up to 7 wt% or up to 6wt%.

[0207] Also provided as a fourth aspect of the invention is an electrode comprising a composition as described herein, or a composition as prepared by a method as described herein. In some embodiments, the composition is a composition of the first aspect. In some embodiments, the composition is a composition as prepared by a method of the second or third aspects. In some embodiments, the electrode is an anode. It will be understood that the composition should be present in the electrode in an amount which is sufficient to achieve the desired electronic conductivity. In some embodiments, the composition will be present in the electrode in an amount of at least 60 weight%, based on the total mass of the electrode (the total mass of the electrode being 100 weight%), for example at least 65 weight%, at least 70 weight% or at least 75 weight%. In some embodiments, the composition is present in an electrode in an amount of up to 96 weight%, based on the total mass of the electrode, for example up to 95 weight%, up to 94 weight%, up to 93 weight%, up to 92 weight% up to 91 weight% or up to 90 weight%. Combinations of any of these values may be used to provide exemplary ranges. For example, in some embodiments the composition is present in the electrode in an amount of between 60-96 weight%, such as 65-95 weight%, 65-94 weight%, 70-93 weight%, 70-92 weight%, 70-91 weight%, or 75-90 weight%.

[0208] In some embodiments, the electrode comprises one or more kinds of composition of the first aspect. In such cases, the amounts provided above refer to the total amount of composition of the first aspect.

[0209] In some embodiments, the electrode comprises a binder. In some embodiments, the binder may be a solvent. In some embodiments, the binder may be a plasticiser. In some embodiments, the binder may be a polymeric binder.

[0210] In some embodiments, the binder may comprise or consist of one or more selected from the group of poly(vinylidene difluoride) (PVDF), poly(methyl methacrylate) (PMMA), carboxymethyl cellulose (CMC), poly(ethylene oxide) (PEO), or polytetrafluoroethylene (PTFE).

[0211] In some embodiments, the binder may be present in an amount of at least 1 weight%, based on the total mass of the electrode (the total mass of the electrode being 100 weight%), for example at least 2 weight%, at least 3 weight%, or at least 4 weight%. In some embodiments, the binder may be present in an amount of up to 20 weight%, based on the total mass of the electrode, such as up to 15 weight%, or up to 12 weight%. Combinations of any of these values may be used to provide exemplary ranges. For example, in some embodiments the binder is present in the electrode in an amount of between 1-20 weight%, such as 1-12 weight%, 2-15 weight%, 2- 15 weight%, 3-15 weight%, 4-20 weight%, or 4-12 weight%.

[0212] In some embodiments, the electrode comprises an additive. In some embodiments, the additive is a conductive additive. In some embodiments, the conductive additive includes a conductive carbon. In some embodiments, the conductive additive may be particulate.

[0213] In some embodiments, the additive may be a high surface area carbon compound, such as carbon black or carbon nanotubes. In some embodiments, the conductive additive comprises or consists of one or more of carbon black, carbon nanotubes, graphene and graphite. In some embodiments, the conductive additive comprises or consists of carbon black or graphite. Examples of commercially available carbon black include Ketjen Black and Super C65.

[0214] In some embodiments, the additive may be present in an amount of at least 1 weight%, based on the total mass of the electrode (the total mass of the electrode being 100 weight%), for example at least 2 weight%, at least 3 weight%, or at least 4 weight%. In some embodiments, the additive may be present in an amount of up to 20 weight%, based on the total mass of the electrode, such as up to 15 weight%, or up to 12 weight%. Combinations of any of these values may be used to provide exemplary ranges. For example, in some embodiments the additive is present in the electrode in an amount of between 1-20 weight%, such as 1-12 weight%, 2-15 weight%, 2-15 weight%, 3-15 weight%, 4-20 weight%, or 4-12 weight%.

[0215] In some embodiments, the binder and additive are included in the electrode in roughly equal amounts.

[0216] In some embodiments, the electrode may contain one or more other known electrode active materials in addition to the composition of the present invention. In some embodiments, no electrode active material is used in the electrode, other than the composition of the present invention. Where other known electrode active materials are present, they will typically replace some of the composition of the invention i.e. the amounts described above are total amounts of electroactive material, meaning the sum of the composition of the present invention and any other known electrode active materials. The present compositions may find utility in an electrode prepared by any appropriate method.

[0217] Also provided as a fifth aspect of the invention is an electrochemical secondary cell comprising such electrode. The cell may be a lithium-ion secondary cell.

[0218] In some embodiments the electrochemical secondary cell comprises a first electrode according to the invention, wherein the first electrode is an anode, and a second electrode which is a cathode. In some embodiments, the electrochemical secondary cell may also comprise an electrolyte between the cathode and the anode. In some embodiments, the electrolyte is a liquid electrolyte. In some embodiments, the liquid electrolyte comprises or is a solution comprising an alkali metal salt.

[0219] In some embodiments the electrochemical secondary cell comprises an electrode according to the invention laminated with a current collector, for example a metallic foil.

[0220] Also provided herein as a sixth aspect of the invention is an electrochemical energy storage device comprising an electrochemical secondary cell of the invention. In some embodiments, the electrochemical energy storage device is a battery. In some embodiments, the electrochemical energy storage device is a lithium-ion battery.

[0221] Also provided herein as a seventh aspect of the invention is a use of the compositions described and prepared herein in an electrode, or in an electrochemical cell, or in an electrochemical energy storage device. In some embodiments, the composition is used in an anode.

[0222] In some embodiments, the electrodes, electrochemical secondary cells and / or electrochemical energy storage devices described herein may find applications in electronics, especially high- power electronics, or in the automotive industry.

[0223] EXAMPLES

[0224] The present invention will now be described by way of examples, which are intended to be illustrative and not limiting on the present invention. The following compositions were synthesized using ball milling at around 700 rpm for around 30 h, with ZrCb 20 mL milling jars and media (5 mm) and a milling media : precursor ratio of 1 :8. Milling was performed in a Fristch Pulversiette 7. Sampling was carried out every 5h, and the milling was carried out in a cyclic manner with 75 mins milling with 15 mins break.

[0225] XRD patterns were measured with an Aeris Benchtop X-ray diffractometer equipped with a PIXcel detector in reflection geometry using CuKa radiation, with an x-ray wavelength of 1.54056A, operating at 40 kV and 40 mA. The measurement range was 30-75° 29.

[0226] For XPS measurements, the composition was pressed into a pellet to form an approximately flat surface. The prepared pellet was transferred to the XPS via airless transfer. XPS of was performed on an ESCALAB QXi XPS from Thermofisher Scientific, as a survey scan over 1350 - 30 eV. Higher resolution scans were then performed over regions of interest, such as Lils, Ti2p, Ti3s, Ols etc.

[0227] SEM and EDX was performed on a Phenom XL G2 Desktop SEM from Thermofisher Scientific.

[0228] For electrochemical testing, the prepared compositions were mixed inside a glovebox with a carbon conductive additive and PTFE as binder in a weight ratio of 80: 10: 10. The chargedischarge curve was measured from a standard CR 2032 coin type cell assembled in an argon filled glove box (H2O content < Ippm). The charge-discharge cycle tests were performed at a current density of 30 mA / g cycled between 0.5 and 3 V vs. Li / Li+ on a MACCOR. A I M LiPFe solution obtained by dissolving in a mixture of EC and DMC in a volume ratio of 1 :1 was used as electrolyte. Electrodes were prepared by combining the composition comprising lithium and titanium, acetylene black and PTFE in a weight ratio of 8: 1 : 1 into a pellet. Metallic lithium was used as the counter electrode. The charge-discharge cycle tests were performed at 30°C (303 K) unless stated otherwise, and ambient pressure (101 kPa).

[0229] Example 1

[0230] To target a composition of LiTiCh, the precursors Li2O (0.8605 g) and Ti2Ch (4.140 g) were loaded into the ball milling jars in an argon filled glovebox, to ensure an inert environment. They were then sealed and removed from the glovebox for milling to be performed. The jars were returned to the glovebox for sampling of the material.

[0231] Figure 1 shows a powder XRD pattern of the composition prepared according to the present invention.

[0232] Three peaks were observed, at 29 = 37.3906°, 43.4452° and 63.1206°. These peaks were indexed (h,k,T) as (1,1,1), (2,0,0), and (2,2,0), respectively. Rietveld refinement analysis was used to calculate the FWHM and unit cell values. The FWHM was calculated to be 1.331° 29. The unit cell length was calculated to be 4.163 A. No evidence of crystalline precursors was observed.

[0233] XPS of Figure 1 is shown in Figure 16. The survey scan shows no evidence of contaminates or other elements present.

[0234] Higher resolution scans at Ti2 / ?, Li7 and Ti3 , and Ols XPS regions are shown in Figures 17(a), 17(b) and 17(c), respectively. The T2p region (Figure 17(a)) at around 475 - 450 eV indicates the presence of both Ti3+(455.7-456.0 eV) and Ti4+(457.8-125.4 eV). This was expected within the LiTiCh structure. A peak at 529.2-529.37 eV assigned to bulk in the Ols region (Figure 17(c)) reflects that a of metal oxide material. -OH and adventitious carbon species at 531.0-531.4 eV are loosely bound at the surface. The Li7 peak is recorded at 54.5 eV (Figure 17(b)).

[0235] Figures 22(a) and 22(b) each show SEM images of the powder composition. These indicate that the composition is a particulate material, i.e. a material made up of a plurality of discrete particles. The particles may comprise primary particles and / or secondary particles formed from the agglomeration of a plurality of primary particles. See also e.g. Figure 23.

[0236] Figures 24(a) and 24(b) show the location of the elements oxygen (Figure 24(a)) and titanium (Figure 24(b)) in the composition shown in Figure 23. These elements are uniformly distributed across the sample. Electrochemical testing between 0.5 - 3.5 V at 30°C (Figure 12) accessed a capacity of 210 mAh / g (Figure 12(a)). The observed low initial Coulombic efficiency (Figure 12(b)) is attributed to the formation of a solid electrolyte interphase (SEI) layer, which is a known behaviour seen for anode type materials.

[0237] Electrochemical testing between 3.5 - 0.1 V at 30°C (Figure 31) showed an improvement over Li1.1Tio.9O2 (see Example 2) by accessing a capacity of 210 mAh / h. Furthermore, performing the discharge first on cycling between 3.0-0.1 V, the material shows analogous behaviour to that shown in Figure 12.

[0238] The mass change recorded by TGA analysis (Figure 34(a)) indicated that the composition contained anion vacancies and the projected formula is LiTiOi.77 so that in terms of AX the composition has e=0.5,Ti=0.5,d=0,p=0.885,q=l=k=0 and m=0.115.

[0239] Example 2

[0240] To target a composition of Li1.1Tio.9O2, the precursors Li2O (0.993 g), Ti2Ch (3.042 g) and TiO2 (0.966 g), were loaded into the ball milling jars in an argon filled glovebox, to ensure an inert environment. They were then sealed and removed from the glovebox for milling to be performed. The jars were returned to the glovebox for sampling of the material.

[0241] Figure 2 shows a powder XRD pattern of the composition prepared according to the present invention.

[0242] Three peaks were observed, at 29 = 37.5242°, 43.5842° and 63.2777°. These peaks were indexed (h,k,T) as (1,1,1), (2,0,0), and (2,2,0), respectively. Rietveld refinement analysis was used to calculate the FWHM and unit cell values. The FWHM was calculated to be 1.272 °29. The unit cell length was calculated to be 4.159 A. No evidence of crystalline precursors was observed.

[0243] XPS of Figure 2 is shown in Figure 3. The survey scan shows no evidence of contaminants or other elements present. Higher resolution scans at Li7 , T\2p and Ols XPS regions are shown in Figures 4(a), 4(b) and 4(c), respectively. The T\2p region (Figure 4(a)) at 475 - 450 eV indicates the presence of both Ti3+(456.0 eV) and Ti4+(458.4 eV). This was expected within the Li1.1Tio.9O2 structure. A peak at 529.7 eV assigned to bulk in the Ols region (Figure 4(c)) reflects that a of metal oxide material. Loosely bound -OH and adventitous carbon species at 531.4 eV were indicated to be present at the surface. The Li7 peak is recorded at 54.5 eV (Figure 4(b)).

[0244] Figures 5(a) and 5(b) each show SEM images of the powder composition of Figure 2. These indicate that the composition is a particulate material, i.e. a material made up of a plurality of discrete particles. The particles may comprise primary particles and / or secondary particles formed from the agglomeration of a plurality of primary particles. See also e.g. Figures 6(a), 7(a) and 7(b).

[0245] Figure 6(b) shows an EDX spectrum of the composition of Figure 6(a). This shows three main peaks, at positions characteristic of carbon (peak labelled 1), oxygen (peak labelled 2) and titanium (peaks labelled 3 and 4). The carbon peak is considered to arise because the sample is analysed on a carbon (tape) substrate i.e. the carbon is not believed to derive from the sample itself. No lithium peak is observed, which is expected due to the very low molecular weight and level of energy of the electron shell. No other peaks are identified, indicating that the composition does not contain other elements or contaminants.

[0246] Figures 7(a) and 7(b) show the location of the elements oxygen (Figure 7(a)) and titanium (Figure 7(b)) in the composition shown in Figure 6(a). It can be seen that these elements are uniformly distributed across the sample.

[0247] A variety of electrochemical testing was performed on the synthesised composition. The observed low initial Coulombic efficiency observed in each test (shown in Figures 8(b), 9(b), 10(b) and 11(b), respectively) is attributed to the formation of a solid electrolyte interphase (SEI) layer. After the first cycle this material is able to access capacities of 95 mAh / g (Figure 8(a)) with a voltage window of 1.5 - 4.8 V at 30°C, 160 - 325 mAh / g (Figure 9(a)) between 0.5 - 4.8 V at 30°C, 145 mAh / g (Figure 10(a)) between 0.5 - 3.5 V at 30°C and 180 mAh / g (Figure 11(a)) between 0.5 - 4.8 V at 45°C. The mass change recorded by TGA analysis (Figure 34(a)) indicated that the composition contained anion vacancies and the projected formula is Li1.1Tio.9O1.s3 so that in terms of AX the composition has e=9.55, Ti=9.45, d=0, p=0.915, q=l=k=9 and m=9.985.

[0248] A second target composition of Li1.1Tio.9O2 according to the present invention was prepared. Three peaks were observed, at 29 = 37.2578, 43.3318, and 63.0792. These peaks were indexed as (1,1,1), (2,0,0), and (2,2,0), respectively. The FWHM was calculated to be 1.3912° 29. The unit cell length was calculated to be 4.159 A. No evidence of crystalline precursors was observed.

[0249] Example 3

[0250] To target a composition of Li1.07Ti0.93O2, the precursors, Li2O (0.947 g), Ti2O3 (3.149 g) and TiO2 (0.633 g), were loaded into the ball milling jars in an argon filled glovebox, to ensure an inert environment. They were then sealed and removed from the glovebox for milling to be performed. The jars were returned to the glovebox for sampling of the material.

[0251] Using a corresponding method to that of Examples 1 and 2 except with different ratios of precursors noted above, a composition according to the present invention was obtained as shown in Figure 14(a). A powder XRD pattern was obtained, and three peaks were observed at 29 = 37.175°, 43.24°, and 62.9556°. These peaks were indexed (h,k,I) as (1,1,1), (2,9,9), and (2,2,9), respectively.

[0252] Rietveld refinement analysis was used to calculate the FWHM and unit cell values. The FWHM was calculated to be 1.832° 29. The unit cell length was calculated to be 4.169 A. No evidence of crystalline precursors was observed.

[0253] Example 4

[0254] To target a composition of Li1.2Tio.sO2, the precursors, Li2O (1.14 g), Ti2O3 (1.829 g) and TiO2 (2.932 g), were loaded into the ball milling jars in an argon filled glovebox, to ensure an inert environment. They were then sealed and removed from the glovebox for milling to be performed. The jars were returned to the glovebox for sampling of the material. Using a corresponding method to that of Examples 1 and 2 except with different ratios of precursors noted above, a composition of Li1.2Tio.sO2 according to the present invention was obtained as shown in Figure 14(b). A powder XRD pattern was obtained, and three peaks were observed at 29 = 37.6151°, 43.7399°, and 63.67°. These peaks were indexed as (1,1,1), (2,0,0), and (2,2,0), respectively.

[0255] Rietveld refinement analysis was used to calculate the FWHM and unit cell values. The FWHM was calculated to be 1.865° 29. The unit cell length was calculated to be 4.124 A. No evidence of crystalline precursors was observed.

[0256] Example 5

[0257] To target a composition of Lio.5Ti2+i.25Ti4+o.2502, the precursors, Li2O (0.348 g), TiO (3.721 g) and TiO2 (0.620 g), were loaded into the ball milling jars in an argon filled glovebox, to ensure an inert environment. They were then sealed and removed from the glovebox for milling to be performed. The jars were returned to the glovebox for sampling of the material.

[0258] Using a corresponding method to that of Examples 1 and 2 except with different ratios of precursors noted above, a composition of Lio.5Ti2+i.25Ti4+o.2502 according to the present invention was obtained as shown in Figure 15(a). A powder XRD pattern was obtained, and three peaks were observed at 29 = 37.27°, 43.33° and 63.93°. These peaks were indexed (h,k,I) as (1,1,1), (2,9,9), and (2,2,9), respectively.

[0259] Rietveld refinement analysis was used to calculate the FWHM and unit cell values. The FWHM was calculated to be 1.237° 29. The unit cell length was calculated to be 4.162 A. No evidence of crystalline precursors was observed.

[0260] XPS of Figure 15(a) is shown in Figure 18. The survey scan shows no evidence of contaminates or other elements present.

[0261] Higher resolutions of the scan at Tv2p, Li7 and TiJ , and Ols regions are shown in Figures 19(a), 19(b) and 19(c), respectively. The Ti2p region (Figure 19(a)) at around 475 - 459 eV indicates the presence of Ti2+(455.1 eV), and Ti4+(458.7 eV) species. This was expected within the Lio.5Ti2+i.25Ti4+o.2502 structure. A peak at 529.2-529.7 eV assigned to bulk in the Ols region (Figure 19(c)) reflects that a of metal oxide material. The Li7 peak is recorded at 54.5 eV and the Ti 3s is centred around 62.0 eV (Figure 19(b)).

[0262] Figures 26(a) and 26(b) each show SEM images of the powder composition. These indicate that the composition is a particulate material, i.e. a material made up of a plurality of discrete particles. The particles may comprise primary particles and / or secondary particles formed from the agglomeration of a plurality of primary particles. See also e.g. Figure 26(a).

[0263] Figure 26(b) shows an EDX spectrum of the composition of Figure 26(a). This shows three main peaks, at positions characteristic of carbon (peak labelled 1), oxygen (peak labelled 2) and titanium (peaks labelled 3 and 4). The carbon peak is considered to arise because the sample is analysed on a carbon (tape) substrate i.e. the carbon is not believed to derive from the sample itself. No lithium peak is observed, which is due to the very low molecular weight and level of energy of the electron shell. No other peaks are identified, indicating that the composition does not contain other elements or contaminants.

[0264] Figures 27(a) and 27(b) show the location of the elements oxygen (Figure 27(a)) and titanium (Figure 27(b)) in the composition shown in Figure 27(a). It can be seen that these elements are uniformly distributed across the sample.

[0265] Electrochemical testing between 0.5 - 4.8 V at 30°C (Figure 32) where observed low initial Coulombic efficiency observed is attributed to the formation of a solid electrolyte interphase (SEI) layer. After the first cycle this material is able to access capacities of -105 mAh / g. This is comparable to the theoretical expected Li capacity for these compositions of 124 mAh / g (Example 7). Next, performing the discharge first on cycling between 3.0 - 0.1 V showed the materials are able to access 90 mAh / g.

[0266] The mass change recorded by TGA analysis (Figure 34(b)) indicated that the composition contained anion vacancies and the projected formula is Lio.5Ti1.5O1.65 so that in terms of AX the composition has e=0.25, Ti=0.75, d=0, p=0.825, q=l=k=0 and m=0.175. Example 6

[0267] To target a composition of Lio.5Ti2+i.oTi3+o.502,_the precursors, Li2O (0.348 g), TiO (2.977 g) and Ti2Ch (1.675 g), were loaded into the ball milling jars in an argon filled glovebox, to ensure an inert environment. They were then sealed and removed from the glovebox for milling to be performed. The jars were returned to the glovebox for sampling of the material.

[0268] Using a corresponding method to that of Examples 1 and 2, a composition according to the present invention was obtained as shown in Figure 15(b). A powder XRD pattern was obtained, and three peaks were observed at 29 = 36.76°, 42.93° and 62.66°.

[0269] Rietveld refinement analysis was used to calculate the FWHM and unit cell values. The FWHM was calculated to be 1.229° 29. The unit cell length was calculated to be 4.161 A. No evidence of crystalline precursors was observed.

[0270] XPS of Figure 15(b) is shown in Figure 29. The survey scan shows no evidence of contaminates or other elements present.

[0271] Higher resolution scans of the \2p, Li7 and Ti3 , and 075 XPS regions are shown in Figures 21(a), 21(b) and 21(c), respectively. The Ti2 / > region (Figure 21(a)) at around 475 - 459 eV indicates the presence of Ti2+(455.1 eV) and Ti3+(457.8 eV). This was expected within the Lio.5Ti2+i.oTi3+o.502 structure. A peak at 529.2-529.7 eV assigned to bulk in the ls region (Figure 21(c)) reflects that a of metal oxide material. The Li75 peak is recorded at 54.5 eV and the Tid.s peak is centred around 62.9 eV (Figure 21(b)).

[0272] Figures 28(a) and 28(b) each show SEM images of a powder composition. These indicate that the composition is a particulate material, i.e. a material made up of a plurality of discrete particles. The particles may comprise primary particles and / or secondary particles formed from the agglomeration of a plurality of primary particles. See also e.g. Figure 28(a).

[0273] Figure 29(b) shows an EDX spectrum of the composition of Figure 29(a). This shows three main peaks, at positions characteristic of carbon (peak labelled 1), oxygen (peak labelled 2) and titanium (peaks labelled 3 and 4). The carbon peak is considered to arise because the sample is analysed on a carbon (tape) substrate i.e. the carbon is not believed to derive from the sample itself. No lithium peak is observed, which is expected due to the very low molecular weight and level of energy of the electron shell. No other peaks are identified, indicating that the composition does not contain other elements or contaminants.

[0274] Figures 30(a) and 30(b) show the location of the elements oxygen (Figure 30(a)) and titanium (Figure 30(b)) in the composition shown in Figure 30(a). These elements are uniformly distributed across the sample.

[0275] Electrochemical testing between 0.5 - 4.8 V at 30°C (Figure 33) where observed low initial Coulombic efficiency observed is attributed to the formation of a solid electrolyte interphase (SEI) layer. After the first cycle this material is able to access capacities of -105 mAh / g. This is comparable to the theoretical expected Li capacity for these compositions of 124 mAh / g (Example 7). Next, performing the discharge first on cycling between 3.0 - 0.1 V showed the materials can access 90 mAh / g.

[0276] The mass change recorded by TGA analysis (Figure 34(b)) indicated that the composition contained anion vacancies and the projected formula is Lio.5Ti1.5O1.73 so that in terms of AX the composition has e=0.25, Ti=0.75, d=0, p=0.865, q=l=k=0 and m=0.135.

Claims

CLAIMS1. A composition having the general formula:AX wherein:A = LieTif[c]d;[c] is a cation vacancy;0 < d < 0.5; 0 < e < 1; 0 < f < 1; and wherein:X = OPSqFiClk[a]m;[a] is an anion vacancy;0 < p < 1; 0 < q < 1; 0 < l < 1; 0 < k < 1; 0 < m < 0.5.

2. A composition according to claim 1, wherein the composition has a disordered rock salt structure, wherein an X-ray diffraction pattern of the composition using a CuKa radiation source has peaks whose full-width half-maximum (FWHM) value is >1.20° 29.

3. A composition according to claim 1 or 2, wherein:(i) k = 0; and / or(ii) p and / or q > 0; and / or(iii) wherein p > 0; and / or(iv) wherein 1 > 0.

4. A composition according to any one of the preceding claims, wherein in a chargedischarge curve of the composition, the integral of the second discharge is greater than 50% of the integral of the second charge.

5. A composition according to any one of the preceding claims, wherein:(i) e > 0; and / or(ii) d and / or m = 0.

6. A composition according to any one of the preceding claims, wherein 0 < e < 2 / 3.

7. A composition according to any one of the preceding claims, wherein the composition has a disordered rock salt structure having structural disorder, optionally wherein the composition having a disordered rock salt structure having structural disorder has e=0.5, f=0.5, d=0, p=l, q=l=n=m.

8. A composition according to any one of the preceding claims, wherein the composition is in the form of a single phase.

9. A composition according to any one of the preceding claims, wherein an X-ray diffraction pattern of the composition using a CuKa radiation source has a peak at a 29 value of at least one of, and optionally each of, (a) to (c):(a) 37.4° ± 2.0°(b) 43.5° ± 2.0°(c) 63.3° ± 2.0°.

10. A composition according to any one of the preceding claims, wherein an X-ray diffraction pattern of the composition using a CuKa radiation source has an absence of peaks below a 29 value of 30°.

11. A composition according to any one of the preceding claims, wherein 0 < e < 2 / 3; 1 / 3 < f < 1; and optionally q = 1 = k = 9.

12. A composition according to any one of the preceding claims, wherein 9.95 < e < 2 / 3; 1 / 3 < f < 9.95; and optionally q = 1 = k = 9.

13. A composition according to any one of the preceding claims, wherein(i) 9.25 < e < 9.45; 9.55 < f < 9.75; or(ii) 9.55 < e < 9.69; 9.49 < f < 9.45; and optionally for (i) and (ii) q = 1 = k = 9.

14. A composition according to any one of the preceding claims, comprising titanium in an oxidation state of 3+, an oxidation state of 4+, or in a mixture of 2+ and 3+, or 2+ and 4+, or 3+ and 4+, or 2+, 3+ and 4+ oxidation states.

15. A method of preparing a composition according to any one of claims 1 to 14 wherein e > 0, the method comprising the steps of:(a) providing at least one lithium salt precursor and at least one titanium salt precursor, or providing at least one lithium titanium mixed salt precursor; and(b) ball milling the at least one lithium salt precursor and at least one titanium salt precursor, or the at least one lithium titanium mixed salt precursor, for a period of time; wherein the salt of the at least one lithium salt precursor, at least one titanium salt precursor, and at least one lithium titanium mixed salt precursor is or comprises an oxide, a sulfide, a fluoride or a chloride.

16. A method according to claim 15, wherein:(i) at least one salt is or comprises an oxide; and / or(ii) the method comprises delithiating the composition; and optionally for (i) or (ii) the method prepares a composition having e = 0.

17. A method of preparing a composition according to any one of claims 1 to 14, the method comprising the steps of:(a) providing a composition having the general formula AX wherein:A = LieTif[c]d;[c] is a cation vacancy;0 < d < 0.5; 0 < e < 1; 0 < f < 1; and wherein:X = OPSqFiClk[a]m;[a] is an anion vacancy;0 < p < l; 0 < q < l; 0 < l < l; 0 < k < l; 0 < m < 0.5; and wherein the composition has a structure other than disordered rock salt structure; and(b) ball milling the at composition provided at (a) for a period of time.

18. A method according to any one of claims 15 to 17, wherein the period of time is Ih to300h.

19. A method according to any one of claims 15 to 18, wherein ball milling is carried out at a speed of 150 rpm or more and / or 1000 rpm or less.

20. A method according to any one of claims 15 to 19, wherein a weight ratio of milling media to at least one lithium salt precursor and at least one titanium salt precursor, or at least one lithium titanium mixed salt precursor, or composition having the structure other than disordered rock salt structure, is between 1 : 1 to 1 :100.

21. A method according to any one of claims 15 to 20, wherein the ball milling is carried out in a milling jar which is ZrCh, stainless steel, agate (SiCh), SiC, or WC.

22. An electrode comprising the composition according to any one of claims 1 to 14, or the composition prepared by the method of any one of claims 15 to 21.

23. An electrode according to claim 22, wherein the electrode comprises additives and / or a binder; and / or wherein the electrode is an anode.

24. An electrochemical cell comprising the composition according to any one of claims 1 to 14, or comprising a composition prepared by the method of any one of claims 15 to 21, or an electrode according to any one of claims 22 to 23.

25. An electrochemical energy storage device comprising an electrochemical cell according to claim 24.

26. Use of a composition according to any one of claims 1 to 14 in an electrode, or in an electrochemical cell, or in an electrochemical energy storage device.

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