USE OF COBALT IN A LITHIUM RICH CATHODE MATERIAL FOR INCREASING THE CHARGE CAPACITY OF THE CATHODE MATERIAL AND FOR SUPPRESSING GAS EVOLUTION FROM THE CATHODE MATERIAL DURING A CHARGE CYCLE

Abstract

Use of cobalt in a cathode material of the general formula: Li (4/3-2x/3-y/3) Ni.sub.xCo.sub.yMn(2/3- x/3-2y/3)O.sub.2 for increasing the charge capacity of the material and for suppressing gas evolution from the cathode material during a charge cycle.

Claims

1. A method comprising: increasing a charge capacity of a cathode material by incorporating cobalt in a lithium rich cathode material of the general formula: ${\mathrm{Li}}_{\left(\frac{4}{3}-\frac{2.Math.x}{3}-\frac{y}{3}\right)}.Math.{\mathrm{Ni}}_x.Math.{\mathrm{Co}}_y.Math.{\mathrm{Mn}}_{\left(\frac{2}{3}-\frac{x}{3}-\frac{2.Math.y}{3}\right)}.Math.O_2$

2. The method of claim 1, wherein x has a value equal to or greater than 0.175 and equal to or less than 0.275; and y has a value equal to or greater than 0.1 and equal to or less than 0.35

3. The method of claim 2, wherein the value of x+y is equal to or greater than 0.3.

4. The method of claim 2, wherein x and y both are greater than 0.13.

518. (canceled)

19. The method of claim 1, wherein the cathode material has a layered structure.

20. The method of claim 19, wherein the layered structure is expressed as the general formula:
(1-a-b)Li.sub.2MnO.sub.3.aLiCoO.sub.2.bLiNi.sub.0.5Mn.sub.0.5O.sub.2 wherein a=y and b=2x; and a is equal to or greater than 0.15 and equal to or less than 0.2; and b is 0.4.

21. The method of claim 20, wherein the material is 0.45Li.sub.2MnO.sub.3.0.15LiCoO.sub.2.0.4LiNi.sub.0.5Mn.sub.0.5O.sub.2.

22. The method of claim 20, wherein the material is 0.4Li.sub.2MnO.sub.3.0.2LiCoO.sub.2.0.4LiNi.sub.0.5Mn.sub.0.5O.sub.2.

23. A method comprising: increasing the charge capacity of a cathode material by incorporating cobalt in a lithium rich cathode material of the general formula: ${\mathrm{Li}}_{\left(\frac{4}{3}-\frac{y}{3}\right)}.Math.{\mathrm{Co}}_y.Math.{\mathrm{Mn}}_{\left(\frac{2}{3}-\frac{2.Math.y}{3}\right)}.Math.O_2$ wherein y has a value greater than 0.12 and equal to or less than 0.4.

24. The method of claim 23, wherein y has a value of equal to or greater than 0.2 and equal to or less than 0.3.

25. The method of claim 23, wherein y is equal to 0.2.

26. The method of claim 23, wherein y is equal to 0.3.

27. The method of claim 23, wherein the compound is a cathode material having a layered structure.

28. The method of claim 27, wherein the layered structure is expressed as the general formula:
aLi.sub.2MnO.sub.3.(1-a)LiCoO.sub.2 wherein a=y; and a is less than 0.88.

29. The method of claim 26, wherein a is equal or greater than 0.7 and equal to or less than 0.8.

30. The method of claim 26, wherein the material is 0.8Li.sub.2MnO.sub.3.0.2LiCoO.sub.2.

31. The method of claim 26, wherein the material is 0.7Li.sub.2MnO.sub.3.0.3LiCoO.sub.2.

32. A method comprising: suppressing gas evolution from a cathode material during a charge cycle by incorporating cobalt in a lithium rich cathode material of the general formula: ${\mathrm{Li}}_{\left(\frac{4}{3}-\frac{2.Math.x}{3}-\frac{y}{3}\right)}.Math.{\mathrm{Ni}}_x.Math.{\mathrm{Co}}_y.Math.{\mathrm{Mn}}_{\left(\frac{2}{3}-\frac{x}{3}-\frac{2.Math.y}{3}\right)}.Math.O_2$

33. The method of claim 32, wherein the gas is molecular oxygen and/or carbon dioxide.

34. The method of claim 32, wherein x has a value equal to or greater than 0.175 and equal to or less than 0.275; and y has a value equal to or greater than 0.1 and equal to or less than 0.35

35. The method of claim 34, wherein the value of x+y is equal to or greater than 0.3.

36. The method of claim 34, wherein x and y both are greater than 0.13.

37-49. (canceled)

50. The method of claim 34, wherein when y is 0.35, x has a value equal to 0.175.

51. The method of claim 32, wherein the cathode material has a layered structure.

52. The method of claim 51, wherein the layered structure is expressed as the general formula:
(1-a-b)Li.sub.2MnO.sub.3.aLiCoO.sub.2.bLiNi.sub.0.5Mn.sub.0.5O2 wherein a=y and b=2x; and a is equal to or greater than 0.15 and equal to or less than 0.2; and b is 0.4.

53. The method of claim 52, wherein the material is 0.45Li.sub.2MnO.sub.3.0.15LiCoO.sub.0.0.4LiNi.sub.0.5Mn.sub.0.5O.sub.2.

54. The method of claim 52, wherein the material is 0.4Li.sub.2MnO.sub.3.0.2LiCoO.sub.2.0.4LiNi.sub.0.5Mn.sub.0.5O.sub.2.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0014] In order that the present invention may be more readily understood, an embodiment of the invention will now be described, by way of example, with reference to the accompanying Figures, in which:

[0015] FIG. 1 shows powder X-ray Diffraction patterns of synthesised materials in accordance with Example 1;

[0016] FIG. 2 shows first cycle galvanostatic load curves for the synthesised materials in accordance with Example 1;

[0017] FIGS. 3A-3B show additional powder X-ray Diffraction patterns of alternative synthesised materials in accordance with Example 1; and

[0018] FIG. 4 shows first cycle galvanostatic load curves for alternative synthesised materials in accordance with Example 1, and capacity measurements over a number of cycles;

[0019] FIG. 5 shows ternary contour plots capacity and energy maps during discharge for materials of the present invention at 30 C., C/10, 2-4.8 V vs. Li/Li.sup.+;

[0020] FIG. 6 shows ternary contour plots capacity and energy maps during discharge for materials of the present invention at 55 C., C/10, 2-4.8 V vs. Li/Li.sup.+; and

[0021] FIG. 7 shows ternary contour plots gas loss maps during discharge for materials of the present invention at 30 C., C/10, 2-4.8 V vs. Li/Li.sup.+.

DETAILED DESCRIPTION OF THE DISCLOSURE

[0022] The present invention will now be illustrated with reference to the following examples.

EXAMPLE 1

Synthesis of the Cobalt and Cobalt-Nickel Substituted Lithium Rich Materials

[0023] For material doped with cobalt only (i.e. x=0) the Formaldehyde-Resorcinol sol gel synthetic route was employed to synthesise materials with general formula

[00003]${\mathrm{Li}}_{\left(\frac{4}{3}-\frac{y}{3}\right)}.Math.{\mathrm{Co}}_y.Math.{\mathrm{Mn}}_{\left(\frac{2}{3}-\frac{2.Math.y}{3}\right)}.Math.O_2$

with y=0, 0.06, 0.12, 0.2 and 0.3 all the reagents ratios were calculated in order to obtain 0.01 mol of the final product.

[0024] Stoichiometric amounts of CH.sub.3COOLi.2H.sub.2O (98.0%, Sigma Aldrich (RTM)), (CH.sub.3COO).sub.2Mn.4H.sub.2O (>99.0%, Sigma Aldrich (RTM)) and (CH.sub.3COO).sub.2Co.4H.sub.2O (99.0% Sigma Aldrich (RTM)) were dissolved in 50 mL of water with 0.25 mmol of CH.sub.3COOLi.2H.sub.2O (99.0%, Sigma Aldrich (RTM)) corresponding to 5% moles of lithium with respect to the 0.01 moles of synthesized material. At the same time 0.1 mol of resorcinol (99.0%, Sigma Aldrich (RTM)) was dissolved in 0.15 mol of formaldehyde (36.5% w/w solution in water, Fluka (RTM)). Once all the reagents were completely dissolved in their respective solvents, the two solutions were mixed and the mixture was vigorously stirred for one hour. The resulting solution, containing 5% molar excess of lithium, was subsequently heated in an oil bath at 80 C. until the formation of a homogeneous white gel.

[0025] The gel was finally dried at 90 C. overnight and then heat treated at 500 C. for 15 hours and 800 C. for 20 hours.

[0026] For material doped with cobalt-nickel, The Formaldehyde-Resorcinol sol gel synthetic route was employed to synthesise materials with general formula

[00004]${\mathrm{Li}}_{\left(\frac{4}{3}-\frac{2.Math.x}{3}-\frac{y}{3}\right)}.Math.{\mathrm{Co}}_y.Math.{\mathrm{Ni}}_x.Math.{\mathrm{Mn}}_{\left(\frac{2}{3}-\frac{x}{3}-\frac{2.Math.y}{3}\right)}.Math.O_2$

where x=0.2 y=0.15. All the reagents ratios were calculated in order to obtain 0.01 mol of the final product.

[0027] Stoichiometric amounts of CH.sub.3COOLi.2H.sub.2O (98.0%, Sigma Aldrich (RTM)), (CH.sub.3COO).sub.2Mn.4H.sub.2O (>99.0%, Sigma Aldrich (RTM)) (CH.sub.3COO).sub.2Ni.4H.sub.2O (99.0% Sigma Aldrich (RTM) and (CH.sub.3COO).sub.2Co.4H.sub.2O (99.0% Sigma Aldrich (RTM)) were dissolved in 50 mL of water with 0.25 mmol of CH.sub.3COOLi.2H.sub.2O (99.0%, Sigma Aldrich (RTM)) corresponding to 5% moles of lithium with respect to the 0.01 moles of synthesized material. At the same time 0.1 mol of resorcinol (99.0%, Sigma Aldrich (RTM)) was dissolved in 0.15 mol of formaldehyde (36.5% w/w solution in water, Fluka (RTM)). Once all the reagents were completely dissolved in their respective solvents, the two solutions were mixed and the mixture was vigorously stirred for one hour. The resulting solution, containing 5% molar excess of lithium, was subsequently heated in an oil bath at 80 C. until the formation of a homogeneous white gel.

[0028] The gel was finally dried at 90 C. overnight and then heat treated at 500 C. for 15 hours and 800 C. for 20 hours.

EXAMPLE 2

Structural Analysis and Characterisation of the Cobalt and Cobalt-Nickel Substituted Lithium Rich Materials

[0029] The materials according to Example 1 were examined with Powder X-Ray Diffraction (PXRD) which was carried out utilising a Rigaku (RTM) SmartLab equipped with a 9 kW Cu rotating anode.

[0030] FIGS. 1 (cobalt doped) and 3A and 3B (nickel-cobalt doped compositions 1 and 2, respectively) show Powder X-ray Diffraction patterns of the synthesized materials. These are characteristic of layered materials with some cation ordering in the transition layer. All of the patterns appear to show the major peaks consistent with a close-packed layered structure such as LiTMO.sub.2 with a R-3m space group. Additional peaks are observed in the range 20-30 2Theta degrees which cannot be assigned to the R-3m space. The order derives from the atomic radii and charge density differences between Li.sup.+(0.59 ), Ni.sup.+2 (0.69 ) and Mn.sup.4+ (0.83 ) and appears the strongest in the structures of the low nickel doped oxides. The peaks are not as strong as in materials where a perfect order exists as in Li.sub.2MnO.sub.3. No presence of extra-peaks due to impurities was observed.

EXAMPLE 3

Electrochemical Analysis of the Cobalt and Cobalt-Nickel Substituted Lithium Rich Materials

[0031] The materials according to Example 1 were characterised electrochemically through galvanostatic cycling performed with a BioLogic VMP3 and a Maccor 4600 series potentiostats. All the samples were assembled into stainless steel coincells against metallic lithium and cycled between 2 and 4.8 V vs. Li.sup.+/Li for 100 cycles at a current rate of 50 mAg.sup.1. The electrolyte employed was LP30 (a 1M solution of LiPF.sub.6 in 1;1 w/w ratio of EC;DMC).

[0032] FIGS. 2 (cobalt doped) and 4 (nickel-cobalt doped compositions 1 and 2, respectively) show the potential curves during the charge and subsequent discharge of the first cycle for materials according to Example 1. Both samples present a high voltage plateau of different lengths centered on 4.5 V vs. Li.sup.+/Li.sup.0, and a sloped region at the beginning of the charge. The length of this region may be attributed to the oxidation of nickel from Ni.sup.+2 toward Ni.sup.+4 and Co.sup.+3 toward Co.sup.+4 and appears to be in good agreement with the amount of lithium (i.e. charge) that would be extracted accounting for solely the transition metal redox activity.

[0033] During the first discharge, neither material shows the presence of a reversible plateau, indicating a difference in the thermodynamic pathways followed during the extraction (charge) and insertion (discharge) of lithium ions from/in the lattice of each sample.

[0034] For the materials of Example 1 the first cycle presents the lowest coulombic efficiency value due to the presence of the high potential plateau which is not reversible. The coulombic efficiencies appear to quickly improve from the first cycle values, around 60-80%, to values higher than 98% within the first five cycles.

[0035] Compositions demonstrating the technical benefits in accordance with the Examples and the present invention are detailed below.

TABLE-US-00001 Compo- sition Li Mn Co Ni O 1 1.15 0.55 0.05 0.25 2 2 1.15 0.525 0.1 0.225 2 3 1.15 0.5 0.15 0.2 2 4 1.15 0.475 0.2 0.175 2 5 1.133333 0.541667 0.05 0.275 2 6 1.133333 0.516667 0.1 0.25 2 7 1.133333 0.491667 0.15 0.225 2 8 1.133333 0.466667 0.2 0.2 2 9 1.133333 0.441667 0.25 0.175 2 10 1.116667 0.533333 0.05 0.3 2 11 1.116667 0.508333 0.1 0.275 2 12 1.116667 0.483333 0.15 0.25 2 13 1.116667 0.458333 0.2 0.225 2 14 1.116667 0.433333 0.25 0.2 2 15 1.116667 0.408333 0.3 0.175 2 16 1.1 0.525 0.05 0.325 2 17 1.1 0.5 0.1 0.3 2 18 1.1 0.475 0.15 0.275 2 19 1.1 0.45 0.2 0.25 2 20 1.1 0.425 0.25 0.225 2 21 1.1 0.4 0.3 0.2 2 22 1.1 0.375 0.35 0.175 2

[0036] Compositions demonstrating higher levels of the technical benefits in accordance with the Examples and the present invention are detailed below.

TABLE-US-00002 Compo- sition Li Mn Co Ni O 1 1.15 0.525 0.1 0.225 2 2 1.15 0.5 0.15 0.2 2 3 1.15 0.475 0.2 0.175 2 4 1.133333 0.516667 0.1 0.25 2 5 1.133333 0.491667 0.15 0.225 2 6 1.133333 0.466667 0.2 0.2 2 7 1.133333 0.441667 0.25 0.175 2 8 1.116667 0.483333 0.15 0.25 2 9 1.116667 0.458333 0.2 0.225 2 10 1.116667 0.433333 0.25 0.2 2 11 1.116667 0.408333 0.3 0.175 2 12 1.1 0.475 0.15 0.275 2 13 1.1 0.45 0.2 0.25 2 14 1.1 0.425 0.25 0.225 2 15 1.1 0.4 0.3 0.2 2 16 1.1 0.375 0.35 0.175 2

[0037] These materials were tested in accordance with the method above, and the results are shown in FIGS. 5 and 6 as ternary contour plots capacity and energy maps during discharge for materials of the present invention at 30 C. and 55 C. C/10, 2-4.8 V vs. Li/Li.sup.+.

EXAMPLE 4

Gas Evolution During the First Cycle of the Nickel-Cobalt Substituted Lithium Rich Materials

[0038] One pellet of each material according to the present invention was assembled into a EL-Cell PAT-Cell-Press (RTM) single cell. All the samples were assembled versus metallic lithium and cycled from OCV to 4.8 V vs. Li+/Li and then discharged to 2V at a current rate of 50 mAg-1. The electrolyte employed was LP30 (a 1M solution of LiPF6 in 1;1 w/w ratio of EC;DMC). This cell was specifically designed to record the pressure changes within the headspace, this could then be related to the mols of gas evolved from the cathode. The pressure sensor in the cell was connected via a controller box which was linked to a computer via a USB link. This was then logged via the Datalogger and EC-Link Software provided by EL-Cell (RTM). The data was logged as Voltage, Current, time and pressure. These values could be combined through the ideal gas law to calculate the number of mols of gas evolved on cycling which could be used to calculate the volume of gas evolved under ambient conditions. The total gas loss for each material during charge was calculated and a contour plot generated as FIG. 7 which shows gas loss as a function of composition within the ternary space.