Use of nickel in a lithium rich cathode material for suppressing gas evolution from the cathode material during a charge cycle and for increasing the charge capacity of the cathode material

Abstract

Use of nickel in a cathode material of the general formula Li (4/3-2x/3-y/3-z/3)Ni.sub.xCo.sub.yAl.sub.zMn(2/3-x/3-2y/3-2z/3)0.sub.2 wherein x is greater than 0.06 and equal to or less than 0.4; y is equal to or greater than 0 and equal to or less than 0.4; and z is equal to or greater than 0 and equal to or less than 0.05 for suppressing gas evolution during a charge cycle and/or increasing the charge capacity of the material.

Claims

1. A method comprising: suppressing gas evolution from a cathode material during a charge cycle by incorporating a nickel doped lithium rich cathode material of the general formula: ${\mathrm{Li}}_{\left(\frac{4}{3}-\frac{2x}{3}-\frac{y}{3}-\frac{z}{3}\right)}{\mathrm{Ni}}_x{\mathrm{Co}}_y{\mathrm{Al}}_z{\mathrm{Mn}}_{\left(\frac{2}{3}-\frac{x}{3}-\frac{2y}{3}-\frac{2z}{3}\right)}{O}_2$ wherein the cathode material is selected from one of Li.sub.1.15Co.sub.0.15Ni.sub.0.2Mn.sub.0.5O.sub.2Li.sub.1.15Ni.sub.0.2Co.sub.0.1Al.sub.0.05Mn.sub.0.5O.sub.2, or Li.sub.1.1333Ni.sub.0.2Co.sub.0.15Al.sub.0.05Mn.sub.0.4667O.sub.2.

2. The method of claim 1, wherein the gas is at least one of molecular oxygen and carbon dioxide.

3. A method comprising: suppressing gas evolution from a cathode material during a charge cycle by incorporating a nickel doped lithium rich cathode material of the general formula: ${\mathrm{Li}}_{\left(\frac{4}{3}-\frac{2x}{3}\right)}{\mathrm{Ni}}_x{\mathrm{Mn}}_{\left(\frac{2}{3}-\frac{x}{3}\right)}{O}_2$ wherein x is equal to or greater than 0.06 and equal to or less than 0.12.

4. A method comprising: suppressing gas evolution from a cathode material during a charge cycle by incorporating a nickel doped lithium rich cathode material, wherein the cathode material is Li.sub.1.066Ni.sub.0.4Mn.sub.0.533O.sub.2.

5. The method of claim 3, wherein the gas is at least one of molecular oxygen and carbon dioxide.

6. The method of claim 4, wherein the gas is at least one of molecular oxygen and carbon dioxide.

7. A method comprising: increasing the charge capacity of a cathode material by incorporating a nickel doped lithium rich cathode material of the general formula: ${\mathrm{Li}}_{\left(\frac{4}{3}-\frac{2x}{3}-\frac{y}{3}-\frac{z}{3}\right)}{\mathrm{Ni}}_x{\mathrm{Co}}_y{\mathrm{Al}}_z{\mathrm{Mn}}_{\left(\frac{2}{3}-\frac{x}{3}-\frac{2y}{3}-\frac{2z}{3}\right)}{O}_2$ wherein the cathode material is selected from one of Li.sub.1.15Co.sub.0.15Ni.sub.0.2Mn.sub.0.5O.sub.2Li.sub.1.15Ni.sub.0.2Co.sub.0.1Al.sub.0.05Mn.sub.0.5O.sub.2, or Li.sub.1.1333Ni.sub.0.2Co.sub.0.15Al.sub.0.05Mn.sub.0.4667O.sub.2.

8. A method comprising: increasing the charge capacity of a cathode material by incorporating a nickel doped lithium rich cathode material of the general formula: ${\mathrm{Li}}_{\left(\frac{4}{3}-\frac{2x}{3}\right)}{\mathrm{Ni}}_x{\mathrm{Mn}}_{\left(\frac{2}{3}-\frac{x}{3}\right)}{O}_2$ wherein x is greater than 0.06 and equal to or less than 0.2.

9. A method comprising: increasing the charge capacity of a cathode material by incorporating a nickel doped lithium rich cathode material, wherein the cathode material is Li.sub.1.066Ni.sub.0.4Mn.sub.0.533O.sub.2.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) 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:

(2) FIG. 1 shows powder X-ray Diffraction patterns of the synthesised materials according to Example 1a compared with the calculated patterns of the C12/m and R-3m symmetry lattice shown at the bottom and top of the figure respectively;

(3) FIGS. 2A-2B shows powder X-ray Diffraction patterns of the synthesised materials according to Example 1b;

(4) FIGS. 3A-3B shows powder X-ray Diffraction patterns of the synthesised materials according to Example 1c;

(5) FIG. 4 shows first cycle galvanostatic load curves for the synthesised materials according to Example 1a;

(6) FIGS. 5A-5B shows first cycle galvanostatic load curves for the synthesised materials according to Example 1b;

(7) FIGS. 6A-6B shows first cycle galvanostatic load curves for the synthesised materials according to Example 1c;

(8) FIGS. 7A-7C shows OEMS analysis of the nickel doped Li.sub.2MnO.sub.2 materials; and

(9) FIG. 8 shows OEMS analysis of one of the materials according to the Example 1c.

DETAILED DESCRIPTION OF THE DISCLOSURE

(10) The present invention will now be illustrated with reference to the following examples.

Example 1—Synthesis of the Nickel Substituted Lithium Rich Materials

(11) 1a) The Formaldehyde-Resorcinol sol gel synthetic route was employed to synthesise materials with general formula

(12) ${\mathrm{Li}}_{\left(\frac{4}{3}-\frac{2x}{3}\right)}{\mathrm{Ni}}_x{\mathrm{Mn}}_{\left(\frac{2}{3}-\frac{x}{3}\right)}{O}_2$
with x=0, 0.06, 0.12, 0.2, 0.3 and 0.4 all the reagents ratios were calculated in order to obtain 0.01 mol of the final product.

(13) Stoichiometric amounts of CH.sub.3COOLi.2H.sub.2O (98.0%, Sigma Aldrich®), (CH.sub.3COO).sub.2Mn.4H.sub.2O (>99.0%, Sigma Aldrich®) and (CH.sub.3COO).sub.2Ni.4H.sub.2O (99.0% Sigma Aldrich® were dissolved in 50 mL of water with 0.25 mmol of CH.sub.3COOLi.2H.sub.2O (99.0%, Sigma Aldrich®) 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®) was dissolved in 0.15 mol of formaldehyde (36.5% w/w solution in water, Fluka®). 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.

(14) 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.

(15) 1b) For cobalt-containing cathode material doped with nickel, The Formaldehyde-Resorcinol sol gel synthetic route was employed to synthesise materials with general formula

(16) ${\mathrm{Li}}_{\left(\frac{4}{3}-\frac{2x}{3}-\frac{y}{3}\right)}{\mathrm{Co}}_y{\mathrm{Ni}}_x{\mathrm{Mn}}_{\left(\frac{2}{3}-\frac{x}{3}-\frac{2y}{3}\right)}{O}_2$
with a composition where x=0.2 y=0.2 (composition in FIGS. 2A and 5A) and with a composition w here x=0.2 y=0.15 (composition in FIGS. 2B and 5B). All the reagents ratios were calculated in order to obtain 0.01 mol of the final product.

(17) Stoichiometric amounts of CH.sub.3COOLi.2H.sub.2O (98.0%, Sigma Aldrich®), (CH.sub.3COO).sub.2Mn.4H.sub.2O (>99.0%, Sigma Aldrich®) (CH.sub.3COO).sub.2Ni.4H.sub.2O (99.0% Sigma Aldrich® and (CH.sub.3COO).sub.2Co.4H.sub.2O (99.0% Sigma Aldrich®) were dissolved in 50 mL of water with 0.25 mmol of CH.sub.3COOLi.2H.sub.2O (99.0%, Sigma Aldrich®) 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®) was dissolved in 0.15 mol of formaldehyde (36.5% w/w solution in water, Fluka®). 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.

(18) 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.

(19) 1c) For cobalt-aluminium-containing cathode material doped with nickel, the Formaldehyde-Resorcinol sol gel synthetic route was employed to synthesise materials with general formula

(20) ${\mathrm{Li}}_{\left(\frac{4}{3}-\frac{2x}{3}-\frac{y}{3}-\frac{z}{3}\right)}{\mathrm{Ni}}_x{\mathrm{Co}}_y{\mathrm{Al}}_z{\mathrm{Mn}}_{\left(\frac{2}{3}-\frac{x}{3}-\frac{2y}{3}-\frac{2z}{3}\right)}{O}_2$
with a composition having x=0.2 y=0.15 z=0.05 (composition in FIGS. 3A and 6A); and with a composition having x=0.2 y=0.1 z=0.05 (composition in FIGS. 3B and 6B).

(21) All the reagents ratios were calculated in order to obtain 0.01 mol of the final product.

(22) Stoichiometric amounts of CH.sub.3COOLi.2H.sub.2O (98.0%, Sigma Aldrich®), (CH.sub.3COO).sub.2Mn.4H.sub.2O (>99.0%, Sigma Aldrich®), (CH.sub.3COO).sub.2Co.4H.sub.2O (99.0% Sigma Aldrich®), Al.sub.2(SO.sub.4).sub.3.4H.sub.2O (Sigma Aldrich®) and (CH.sub.3COO).sub.2Ni.4H.sub.2O (99.0% Sigma Aldrich®) were dissolved in 50 mL of water with 0.25 mmol of CH.sub.3COOLi.2H.sub.2O (99.0%, Sigma Aldrich®) 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®) was dissolved in 0.15 mol of formaldehyde (36.5% w/w solution in water, Fluka®). Once all the reagents were completely dissolved in their respective solvents, the two solutions were mixed and the mixture was vigorously stirred for 1 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.

(23) 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 Nickel Substituted Lithium Rich Materials

(24) The materials according to Example 1a-c were examined with Powder X-Ray Diffraction (PXRD) which was carried out utilising a Rigaku® SmartLab equipped with a 9 kW Cu rotating anode; and MAS-NMR spectra were collected on the materials with a Bruker Avance III 400WD magnet.

(25) FIGS. 1 (nickel doped Li.sub.2MnO.sub.2), 2A and 2B (nickel doped cobalt compositions 1 and 2, respectively) and 3A and 3B (nickel doped aluminum cobalt 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 Å), Ni.sup.+2 (0.69 Å) and Mn.sup.4+ (0.83 Å) 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 Nickel Substituted Lithium Rich Materials

(26) The materials according to Example 1a-c 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-1. The electrolyte employed was LP30 (a 1M solution of LiPF.sub.6 in 1;1 w/w ratio of EC;DMC).

(27) FIGS. 4, 5A-5B, and 6A-6B show the potential curves during the charge and subsequent discharge of the first cycle for each material according to Example 1.

(28) FIG. 4 shows the potential curves during the charge and subsequent discharge of the first cycle for each material according to Example 1a. All of the samples present a high voltage plateau of different lengths centred on 4.5 V vs. Li.sup.+/Li.sup.0, whereas the presence of a sloped region at the beginning of the charge progressively increases in length with the amount of nickel doping. The extension of this region may be attributed to the oxidation of nickel from Ni.sup.+2 toward Ni.sup.+4. appears to be in good agreement with the amount of lithium (i.e. charge) that would be extracted accounting for solely the nickel redox activity. Hence, as expected, Li.sub.2MnO.sub.3 does not show any pre-plateau region whilst the

(29) ${\mathrm{Li}}_{\left(\frac{4}{3}-\frac{2x}{3}\right)}{\mathrm{Ni}}_x{\mathrm{Mn}}_{\left(\frac{2}{3}-\frac{x}{3}\right)}{O}_{2}x=0.3$
doped oxide presents more than 150 mAhg.sup.−1.

(30) During the first discharge, none of the materials show 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.

(31) For all the material according to Example 1a 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 60-70%, to values higher than 98% within the first five cycles. However, with this regard Li.sub.2MnO.sub.3 and

(32) ${\mathrm{Li}}_{\left(\frac{4}{3}-\frac{2x}{3}\right)}{\mathrm{Ni}}_x{\mathrm{Mn}}_{\left(\frac{2}{3}-\frac{x}{3}\right)}{O}_2$
with x=0.06 are an exception, showing an initial loss in efficiency. When the nickel substitution increases such that x=0.12 a significant improvement in the electrochemical performance is seen, indicating that there is a change in the nature of the charge storage mechanism.

(33) FIGS. 5A-5B (nickel doped cobalt cathode materials) show the potential curves during the charge and subsequent discharge of the first cycle for materials according to Example 1b. 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.

(34) 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.

(35) For the materials of Example 1b 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.

(36) The materials according to Example 1c 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-1. The electrolyte employed was LP30 (a 1M solution of LiPF6 in 1;1 w/w ratio of EC;DMC).

(37) FIGS. 6A-6B show the potential curves during the charge and subsequent discharge of the first cycle for each material according to Example 1c. 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.

(38) 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.

(39) For both materials according to Example 1c 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.

Example 4—Gas Evolution During the First Cycle of the Nickel Substituted Lithium Rich Materials

(40) One pellet of material according to Example 1a was assembled into a Swagelok® test cell specifically machined to carry out an Operando Electrochemical Mass Spectrometry (OEMS) measurement. The mass spectrometry measurement involved in the OEMS experiment was performed with a Thermo-Fisher quadrupolar mass spectrometer. OEMS was performed on the set of materials in order to get an insight on the origin of the extra-capacity that is observed during the first cycle.

(41) FIGS. 7A-7C show OEMS analysis of the nickel doped

(42) ${\mathrm{Li}}_{\left(\frac{4}{3}-\frac{2}{3x}\right)}{\mathrm{Ni}}_x{\mathrm{Mn}}_{\left(\frac{2}{3}-\frac{1}{3x}\right)}{O}_2$
for x=0.2, 0.3 and 0.4, respectively. Each graph shows the galvanostatic curve during the first two cycles (top lines in each graph), the oxygen trace, and the carbon dioxide trace for each material. The right y-axis represents the electrode potential while the left y-axis the gas release rate expressed as moles of gas per minute per mole of active material, both axis reported as function of lithium equivalents. Argon was used as carrier gas with a flux rate of 0.7 mL/min and the electrode was cycled against metallic lithium at a rate of 15 mAg.sup.−1 between 2 and 4.8 V vs. Li.sup.+/Li.sup.0 for all the materials. The electrolyte employed was a 1M solution of LiPF.sub.6 in propylene carbonate.

(43) CO.sub.2 and O.sub.2 were the only gaseous species detected for all the samples and a clear trend appears from FIG. 4, with a progressively lower amount of gas released as the amount of dopant nickel increases.

(44) CO.sub.2 is detected first in all cases, peaking at the beginning of the high potential plateau (around 4.5 V vs. Li.sup.+/Li.sup.0) region and progressively decreasing until the end of charge.

(45) The amount of CO.sub.2 decreases in line with the increase in nickel in content but is never eliminated. On the other hand, molecular oxygen appears to be released in a spike-like fashion that reaches its maximum towards the end of charge for the materials of the present invention. In the case of the high Ni substitution where x=0.4 it has been shown that there is almost complete suppression of O.sub.2 and a strong reduction in the amount of detected CO.sub.2 (FIG. 7C) This result is suggestive of the important role played by nickel as in stabilizing the oxide structures at high potentials by reducing the oxygen loss process.

(46) One pellet of Composition 1 Li.sub.1.333Co.sub.0.15Al.sub.0.5Ni.sub.0.2Mn.sub.0.4667O.sub.2 (a composition from Example 1c) was assembled into a Swagelok® test cell specifically machined to carry out an Operando Electrochemical Mass Spectrometry (OEMS) measurement. The mass spectrometry measurement involved in the OEMS experiment was performed with a Thermo-Fisher quadrupolar mass spectrometer. OEMS was performed on the set of materials in order to get an insight on the origin of the extra-capacity that is observed during the first cycle.

(47) FIG. 8 shows OEMS analysis of the nickel doped Li.sub.1.1333Co.sub.0.15Al.sub.0.05Ni.sub.0.2Mn.sub.0.4667O.sub.2 respectively. The graph shows the galvanostatic curve during the first two cycles (top graph), the oxygen trace, and the carbon dioxide trace for each material(bottom graph). Argon was used as carrier gas with a flux rate of 0.7 mL/min and the electrode was cycled against metallic lithium at a rate of 15 mAg-1 between 2 and 4.8 V vs. Li.sup.+/Li.sup.0 for all the materials. The electrolyte employed was a 1M solution of LiPF.sub.6 in propylene carbonate.

(48) CO.sub.2 was the only gaseous species detected for all the samples and a progressively lower amount of gas released as the amount of dopant nickel increases. CO.sub.2 peaks at the beginning of the high potential plateau (around 4.5 V vs. Li.sup.+/Li.sup.0) region and progressively decreasing until the end of charge.