A lithium-ion battery

Abstract

This invention provides a lithium-ion battery comprising a positive electrode active material, which includes lithium cobalt oxide particles doped with one or more elements selected from Al, Mg, Ti, Zr, Ni, Mn, Y, La, Sr, W, and Sc. At 0% SOC, the molar ratio of lithium to cobalt in the positive electrode active material is A; at 100% SOC, the molar ratio is B, where 0.62 ≤ A - B ≤ 0.655. The lithium-ion battery provided by this invention exhibits good cycle performance at high voltage.

Description

Technical Field

[0001] This invention relates to a lithium-ion battery and to the field of secondary battery technology. Background Technology

[0002] Since their commercialization, lithium-ion batteries have been widely used in digital devices such as laptops and mobile phones due to their high specific energy and good cycle performance. However, with the continuous improvement of human demand for electronic devices, higher requirements have been placed on the energy density of lithium-ion batteries. The energy density of lithium-ion batteries is closely related to their volume, discharge voltage plateau, and discharge capacity. Therefore, improving the discharge voltage plateau of lithium-ion batteries has become one of the effective means to increase energy density.

[0003] However, when a lithium-ion battery is charged to above 4.2V, lithium ions are released from the positive electrode active material LiCoO2 and form Li. 1-x When the charging voltage of LiCoO2 (0≤x≤0.5) is increased to above 4.4V, more lithium ions are extracted from the positive electrode active material. After the lithium ions are extracted, LiCoO2 continuously transforms from a hexagonal crystal system to a monoclinic crystal system. The transformed monoclinic LiCoO2 no longer has the ability to reversibly insert and extract lithium ions. At the same time, when the charging voltage of lithium-ion batteries reaches 4.4V and above, the side reactions between the positive electrode active material and the electrolyte will gradually intensify. Therefore, as the charging voltage continues to increase, the reversible capacity of the positive electrode active material continues to decrease, resulting in poor cycle performance of lithium-ion batteries and limiting their application. This is also one of the important reasons why the reversible capacity of lithium cobalt oxide, the positive electrode active material currently used in commercial applications, is much smaller than its theoretical capacity (274mAh / g). Therefore, how to improve the cycle performance of lithium-ion batteries at high voltages has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0004] This invention provides a lithium-ion battery for improving the cycle performance of lithium-ion batteries under high voltage.

[0005] This invention provides a lithium-ion battery, comprising a positive electrode active material, wherein the positive electrode active material comprises lithium cobalt oxide particles doped with one or more elements selected from Al, Mg, Ti, Zr, Ni, Mn, Y, La, Sr, W, and Sc; wherein at 0% SOC, the molar ratio of lithium to cobalt in the positive electrode active material is A; and at 100% SOC, the molar ratio of lithium to cobalt in the positive electrode active material is B, wherein 0.62 ≤ A ≤ 0.655.

[0006] This invention provides a lithium-ion battery comprising a positive electrode active material, wherein the positive electrode active material comprises lithium cobalt oxide particles doped with one or more elements selected from Al, Mg, Ti, Zr, Ni, Mn, Y, La, Sr, W, and Sc. Elemental doping of the lithium cobalt oxide particles helps improve the structural stability of the positive electrode active material. Simultaneously, the structural stability of the positive electrode active material is also affected by the charge-discharge regime. When a lithium-ion battery comprising the above-mentioned positive electrode active material is charged and discharged using a certain charge-discharge regime, at 0% SOC, the molar ratio of lithium to cobalt in the positive electrode active material is tested and denoted as A. At 10... At 0% SOC, the molar ratio of lithium to cobalt in the positive electrode active material is tested and denoted as B. When 0.62 ≤ AB ≤ 0.655, it indicates that the lithium-ion battery containing this positive electrode active material has good structural stability under this charge-discharge regime, and the lithium-ion battery containing this positive electrode active material has good cycle performance. Otherwise, the cycle performance of the lithium-ion battery cannot meet the usage requirements, and corresponding adjustments need to be made to the positive electrode active material or the charge-discharge regime to meet 0.62 ≤ AB ≤ 0.655. The high voltage referred to in this invention means that the charging cut-off voltage of the lithium-ion battery is above 4.4V. In summary, this invention provides a lithium-ion battery in which, when the lithium-ion battery is at 0% SOC and the molar ratio of lithium to cobalt in the positive electrode active material is A, and when the lithium-ion battery is at 100% SOC and the molar ratio of lithium to cobalt in the positive electrode active material is B, and 0.62 ≤ AB ≤ 0.655, it indicates that the lithium-ion battery has good cycle performance at high voltage.

[0007] In one specific embodiment, in order to improve the structural stability of the positive electrode active material, the positive electrode active material can also be coated. Specifically, the positive electrode active material further includes a coating layer covering at least part of the outer surface of the lithium cobalt oxide particles. The coating layer includes one or more of metal fluorides, metal oxides, metal borate compounds, and metal phosphate compounds.

[0008] In specific implementation, those skilled in the art can choose to dope lithium cobalt oxide particles, or simultaneously dope and coat them. This invention mainly uses the doping and coating of lithium cobalt oxide particles as an example to elaborate on the positive electrode active material. Specifically, the positive electrode active material is prepared by the following preparation method:

[0009] The lithium cobalt oxide particles are doped with element M, wherein element M is one or more selected from Al, Mg, Ti, Zr, Ni, Mn, Y, La, Sr, W, and Sc;

[0010] The positive electrode active material is obtained by coating at least a portion of the surface of lithium cobalt oxide particles doped with element M with one or more of the following: metal fluoride, metal oxide, metal borate compound, and metal phosphate compound.

[0011] This invention provides a method for preparing a positive electrode active material. First, lithium cobalt oxide particles are doped with elements (M). Then, a suitable coating material is selected to coat the lithium cobalt oxide particles doped with element M to obtain the positive electrode active material. The preparation process is described in detail below:

[0012] Step 1, doping the lithium cobalt oxide particles with element M, specifically includes:

[0013] Step 1-1: Dissolve the cobalt source, complexing agent and soluble base containing carbonate in a solvent, mix and react to obtain cobalt carbonate;

[0014] Specifically, the cobalt source is selected from one or more of cobalt acetate, cobalt oxalate, cobalt nitrate, cobalt sulfate, cobalt chloride, and cobalt hydroxide. The complexing agent can be ammonia water with a concentration of 20%-25%. The carbonate-containing soluble base is selected from one or more of Na2CO3, NH4HCO3, and (NH4)2CO3. The solvent can be deionized water. The above materials are dissolved in water. The concentration of the cobalt source is 0.8-3.8 mol / L, and the concentration of the soluble base is 0.8-3.8 mol / L. Under the action of the complexing agent, the carbonate-containing soluble base reacts with the cobalt source to generate cobalt carbonate precipitate. The reaction temperature is 30-80℃, and the reaction time is 10-20 hours.

[0015] Steps 1-2: Calcine the cobalt carbonate to obtain the precursor;

[0016] The precursor is obtained by calcining cobalt carbonate at a high temperature of 920-1000℃ for 8-12 hours.

[0017] Steps 1-3: Mix and calcine the lithium source, precursor, and compound containing element M.

[0018] A lithium source, a precursor, and a compound containing element M are mixed and calcined to obtain lithium cobalt oxide particles doped with element M. The lithium source is selected from one or more of lithium hydroxide, lithium nitrate, lithium carbonate, lithium oxalate, lithium acetate, lithium oxide, and lithium citrate. The compound containing element M is one or more of oxides, chlorides, hydroxides, carbonates, sulfates, nitrates, oxalates, and acetates of element M.

[0019] The calcination temperature is 900-1050℃, and the calcination time is 8-12h.

[0020] Step 2: Coating at least a portion of the surface of lithium cobalt oxide particles doped with element M with one or more of the following: metal fluoride, metal oxide, metal borate compound, and metal phosphate compound.

[0021] One or more of metal fluorides, metal oxides, metal borate compounds, and metal phosphate compounds are mixed with lithium cobalt oxide particles doped with element M and calcined to coat at least a portion of the surface of the lithium cobalt oxide particles with the coating material, thereby obtaining the positive electrode active material.

[0022] Wherein, the metal fluoride is selected from one or more of AlF3, Li3F, and MgF; the metal oxide is selected from one or more of Al2O3, TiO2, ZrO2, and MgO; the metal borate compound is AlBO3; and the metal phosphate compound is selected from one or two of AlPO4 and Li3PO4.

[0023] The calcination temperature is 800-1000℃, and the calcination time is 6-9 hours.

[0024] To make the coating material more uniform, the coating material and lithium cobalt oxide particles doped with element M can be physically mixed before calcination. The physical mixing can be one or more of stirring, ball milling, and grinding, and the physical mixing time is 2-4 hours.

[0025] The thickness of the coating layer should not be too high, otherwise it will cause Li to degrade during charging and discharging. + The transport of the material is obstructed, thereby affecting the rate performance and low-temperature performance of the lithium-ion battery. Specifically, the thickness of the coating layer is no more than 50 nm. Those skilled in the art can control the amount of coating material added according to the requirements of the coating layer thickness. Specifically, the mass of the coating layer is no more than 1% of the total mass of the positive electrode active layer material.

[0026] The inventors discovered that Al helps improve the structural stability of the positive electrode active material. Therefore, in order to further improve the cycle performance of lithium-ion batteries, the positive electrode active material includes Al. As the doping amount of Al increases, the stability of the positive electrode active material also increases, and the AB decreases. Therefore, the doping amount of Al is not less than 3500ppm, that is, the content of Al / the total content of the positive electrode active material is ≥3500ppm.

[0027] The compound containing Al can be an aluminum salt and / or an aluminum oxide. For example, the compound containing Al can be one or more of Al2(SO4)3, AlCl3, and Al2O3, and the amount added can be adjusted according to the content of Al.

[0028] The positive electrode active material can be obtained by the above method. Since the final particle size distribution of the positive electrode active material affects the compaction of the positive electrode sheet and the performance of the lithium-ion battery, the average particle size of the positive electrode active material is 8.0-15.0 μm. Those skilled in the art can select the particle size of the raw material or grind the calcined positive electrode active material to meet the requirements of the final active material particle size.

[0029] In addition, in order to balance the high and low temperature performance of lithium-ion batteries and the compaction of the positive electrode sheet, the positive electrode active material can be obtained by gradation of large and small particles. Large particles refer to particles with an average particle size of 8.0-18.0 μm, and small particles refer to particles with an average particle size of 2.0-6.0 μm.

[0030] Based on the preparation of the positive electrode active material, the positive electrode active material, conductive agent and binder are dispersed in a solvent to prepare a positive electrode active layer slurry, which is then uniformly coated on the surface of the positive electrode current collector to obtain a positive electrode sheet. Specifically, the positive electrode active layer slurry includes 70-99 wt.% positive electrode active material, 0.5-15 wt.% conductive agent and 0.5-15 wt.% binder by mass percentage; further, the positive electrode active layer slurry includes 80-98 wt.% positive electrode active material, 1-10 wt.% conductive agent and 1-10 wt.% binder by mass percentage.

[0031] The conductive agent is selected from one or more of conductive carbon black, acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, carbon nanotubes, metal powder, and carbon fiber; the binder is selected from one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and lithium polyacrylate (PAALi).

[0032] The lithium-ion battery also includes a negative electrode sheet, a separator, and an electrolyte. Specifically, the negative electrode sheet includes a negative current collector and a negative active layer. The negative active layer includes a negative active material, a conductive agent, and a binder. The preparation method of the negative active layer is the same as that of the positive active layer. The negative active layer slurry includes 70-99 wt.% of negative active material, 0.5-15 wt.% of conductive agent, and 0.5-15 wt.% of binder by mass percentage. Further, the negative active layer slurry includes 80-98 wt.% of negative active material, 1-10 wt.% of conductive agent, and 1-10 wt.% of binder by mass percentage.

[0033] The selection of conductive agent and binder is the same as that of positive electrode sheet, and the negative electrode active material is selected from one or more of artificial graphite, natural graphite, hard carbon, mesophase carbon microspheres, lithium titanate, silicon carbide, and silicon suboxide.

[0034] The electrolyte comprises a non-aqueous solvent, a conductive lithium salt, and additives. The non-aqueous solvent is a mixture of at least one of cyclic carbonates and linear carbonates and linear carboxylic acid esters in any proportion. The cyclic carbonate is selected from ethylene carbonate and / or propylene carbonate; the linear carbonate is selected from one or more of dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate; and the linear carboxylic acid ester is selected from one or more of ethyl propionate, propyl propionate, and propyl acetate. The conductive lithium salt is selected from one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide. The additives include one or more of nitrile compounds, vinylene carbonate, and 1,3-propenesulfonyl lactone.

[0035] Based on a total volume of 100 vol% for non-aqueous organic solvents, the volume fraction of the cyclic carbonate is 20-40 vol%, and the volume fraction of the linear carbonate and / or linear carboxylic acid ester is 60-80 vol%.

[0036] The diaphragm is a polypropylene film, or at least one polypropylene film with a ceramic coating on its surface.

[0037] A lithium-ion battery is obtained by preparing a cell using a stacking or winding process for the positive electrode, separator, and negative electrode, and then encapsulating it and injecting electrolyte. This process can be performed by those skilled in the art using conventional techniques. Subsequently, the charge-discharge regime of the lithium-ion battery can be explored. The inventors have discovered that during the charge-discharge process of a lithium-ion battery, the charging cut-off voltage, charging cut-off current, and charge-discharge temperature are important factors affecting the AB (charge-to-discharge ratio). For example, as the charging cut-off voltage increases, AB gradually increases; as the charging cut-off current increases, AB gradually decreases; and as the charge-discharge temperature continuously increases, AB continuously increases. Therefore, when charging and discharging a lithium-ion battery, the charging cut-off voltage should be less than 4.5V; the charging cut-off current should be not less than 0.02C; and the charge-discharge temperature should be less than 45℃.

[0038] After determining a suitable charge-discharge regime, the lithium-ion battery is charged and discharged according to that regime. When the molar ratio of lithium to cobalt in the positive electrode active material is A at 0% SOC and B at 100% SOC, and 0.62≤AB≤0.655, it indicates that the lithium-ion battery containing this positive electrode active material has good cycle performance under this charge-discharge regime. Otherwise, the doping amount in the positive electrode active material and / or the charge-discharge regime need to be adjusted to meet the requirement of 0.62≤AB≤0.655.

[0039] The molar ratio of lithium to cobalt in the positive electrode active material of a lithium-ion battery at 0% SOC and 100% SOC can be obtained by ICP testing.

[0040] In summary, the present invention provides a lithium-ion battery in which the molar ratio of lithium to cobalt in the positive electrode active material is A when the lithium-ion battery is at 0% SOC, and the molar ratio of lithium to cobalt in the positive electrode active material is B when the lithium-ion battery is at 100% SOC, and 0.62≤AB≤0.655, the lithium-ion battery has good cycle performance. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0042] Example 1

[0043] This embodiment provides a lithium-ion battery, including a positive electrode, a separator, a negative electrode, and an electrolyte. The positive electrode includes aluminum foil and a positive active layer, and the positive active layer includes a positive active material. The negative electrode includes copper foil and a negative active layer. Specifically:

[0044] The positive electrode active layer includes positive electrode active material, which includes lithium cobalt oxide particles doped with Al, Mg and Ti, and a coating layer, which includes magnesium oxide and titanium oxide.

[0045] The method for preparing the positive electrode active material provided in this embodiment includes the following steps:

[0046] Step 1-1: Dissolve CoCl2 in an aqueous solution to prepare Co 2+A 1.25 mol / L cobalt salt solution was prepared. Concentrated ammonia and distilled water were mixed at a volume ratio of 1:10 to prepare a complexing agent solution (concentration 2-2.5%). Sodium carbonate was dissolved in an aqueous solution to prepare a 1.2 mol / L sodium carbonate solution. One-third of the sodium carbonate solution was injected into the reactor. Under strong stirring and inert gas protection, the cobalt salt solution, complexing agent solution, and the remaining two-thirds of the sodium carbonate solution were continuously injected into the reactor in a parallel flow controlled manner. The flow rate was controlled to not exceed 200 L / h, while stirring was performed at a speed not exceeding 200 rpm. The pH of the reaction system was controlled to be 6-12, and the temperature of the reactor was controlled to be 70-80℃ during the reaction. The liquid phase ion concentration of Co in the reaction system was monitored in real time during the reaction. After repeated crystallization three times, the mixture was centrifuged and filtered to obtain cobalt carbonate CoCO3.

[0047] Steps 1-2: The cobalt carbonate CoCO3 was placed in a muffle furnace and calcined at 930°C for 10 hours. The calcined product was then pulverized to obtain a precursor Co3O4 with uniform particle distribution.

[0048] Steps 1-3: Mix the prepared precursors Co3O4, Li2CO3, Al2(SO4)3, MgSO4, and TiO2, wherein Co:Al:Mg:Ti = 0.9935:0.0045:0.001:0.001, and the molar ratio of Li to Co is 100:99.6. After the above substances are physically mixed, they are placed in a muffle furnace for calcination at a temperature of 1035℃ for 11 hours. Then, the calcined product is pulverized to obtain lithium cobalt oxide particles with uniform particle distribution and doped with M element.

[0049] Step 2: Weigh magnesium oxide, titanium oxide and lithium cobalt oxide particles doped with element M according to the molar ratio Mg:Ti:M-doped lithium cobalt oxide particles = 0.5:0.5:99.5, stir and mix evenly, then place in a muffle furnace for calcination at 950℃ for 8 hours. Then pulverize the calcined product to obtain the positive electrode active material.

[0050] The average particle size of the positive electrode active material is 14.5 μm.

[0051] A positive electrode active layer slurry was prepared by dispersing 97 parts by mass of positive electrode active material, 1.5 parts by mass of conductive agent Super-P, and 1.5 parts by mass of binder polyvinylidene fluoride (PVDF) in N-methylpyrrolidone (NMP). The slurry was uniformly coated onto the surface of aluminum foil, baked in a five-stage oven at temperatures of 70°C, 80°C, 95°C, 120°C, and 120°C, and then rolled up. The current collector coated with the positive electrode active layer slurry was then placed in an oven at 100°C for 8 hours to allow the solvent in the slurry to evaporate completely before rolling and compaction to a density of 4.1 g / cm³. 3 The positive electrode sheet was thus produced.

[0052] A negative electrode active layer slurry was prepared by dispersing 96 parts by mass of artificial graphite (average particle size: 13±1μm, graphitization degree 94±0.5%, a mixture of secondary and single particles, with secondary particles accounting for 50% by mass), 1 part by mass of superconducting carbon black (Super-P), 1.5 parts by mass of sodium carboxymethyl cellulose (CMC), and 1.5 parts by mass of styrene-butadiene rubber (SBR) in a solvent. The negative electrode active layer slurry was coated onto an 8μm copper foil and dried at 100℃ for 4 hours. After drying, the slurry was rolled to obtain a compaction density of 1.68 g / cm³. 3 The negative electrode plate.

[0053] The diaphragm is a single-sided ceramic + double-sided oil-based LBG coated diaphragm;

[0054] The electrolyte comprises a non-aqueous organic solvent, a lithium salt, and additives. The non-aqueous organic solvent comprises ethylene carbonate (EC), propylene carbonate (PC), and dimethyl carbonate (DMC) in a mass ratio of 1:1:1. The lithium salt is LiPF6. The additives include 4 wt.% of 1,3-propenesulfonyl lactone, 6 wt.% of vinylene carbonate, 1 wt.% of succinic anionyl nitrile, and 2 wt.% of adiponitrile.

[0055] The positive electrode, negative electrode, and separator are wound together to form a battery cell, which is then packaged with an aluminum-plastic film. The cell is baked in a nitrogen-protected oven at 120°C for 36 hours. Electrolyte is then injected, and the cell undergoes processes such as chemical composition and sorting to finally obtain a soft-pack lithium-ion battery with a capacity of 5Ah.

[0056] The battery prepared above was charged and discharged at 25°C. It was discharged to 3.0V at a rate of 0.7C. The cell was disassembled to test its Li and Co content and A was calculated. It was then charged to 4.45V at a constant current rate of 0.7C, followed by constant voltage charging with a cutoff current of 0.1C. The cell under this condition was disassembled to test its Li and Co content and B was calculated.

[0057] The lithium-ion battery was subjected to cycle testing using the above charge-discharge regime, namely 0.7C / 0.7C, 0.1C cutoff, voltage range 3.0-4.45V, temperature 25℃, and capacity retention was tested after 500T cycles.

[0058] ICP testing was performed on the positive electrode active material, and the results showed that the total content of Al in the positive electrode active material was 4500 ppm, the total content of Mg was 1500 ppm, and the total content of Ti was 1500 ppm.

[0059] The ICP testing method specifically includes the following steps:

[0060] 1. Disassemble the lithium-ion battery prepared above, retain the disassembled positive electrode sheet, immerse the positive electrode sheet in a dimethyl carbonate (DMC) solution for 30 minutes, remove it, and dry it in a 120℃ oven for 6 hours.

[0061] 2. Place the dried positive electrode sheet in a tube furnace and sinter it at high temperature. Set the tube furnace sintering temperature to 300℃ and the sintering time to 4 hours. After sintering, allow it to cool naturally and then place it in a sealed glass bottle.

[0062] 3. Place the glass bottle containing the positive electrode in an ultrasonic machine and sonicate for 15 minutes. After sonicating, remove the bottle and gently rub the powder to obtain the positive electrode powder.

[0063] 4. The above-mentioned positive electrode powder was tested using atomic absorption spectrometry (ICP) to obtain the content values ​​of each element. The spectral lines of each element are shown in Table 1.

[0064] Table 1. Spectral lines of various elements in the positive electrode active material

[0065] element Li Co Al Mg Ti Spectral lines (nm) 670.784 228.616 396.15 279.553 323.5 STD1 0 0 0 0 0 STD2 1 10 1 1 1 STD3 3 30 2 2 2 STD4 10 100 5 5 5

[0066] Example 2

[0067] The lithium-ion battery provided in this embodiment is the same as that in Embodiment 1, except that the charging and discharging system is different. Specifically, at 25°C, the cell is discharged to 3.0V at a rate of 0.7C, the cell is disassembled and its Li and Co content is tested, and A is calculated. The cell is then charged to 4.45V at a constant current rate of 0.7C, followed by constant voltage charging with a cutoff current of 0.05C. The cell under this condition is disassembled and its Li and Co content is tested, and B is calculated.

[0068] The lithium-ion battery was subjected to cycle testing using the above charge-discharge regime, namely 0.7C / 0.7C, 0.05C cutoff, voltage range of 3.0-4.45V, temperature of 25℃, and capacity retention was tested after 500T cycles.

[0069] Example 3

[0070] The lithium-ion battery provided in this embodiment is the same as that in Embodiment 1, except that the charging and discharging system is different. Specifically, at 25°C, the cell is discharged to 3.0V at a rate of 0.7C, the cell is disassembled and its Li and Co content is tested, and A is calculated. The cell is then charged to 4.45V at a constant current rate of 0.7C, followed by constant voltage charging with a cutoff current of 0.02C. The cell under this condition is disassembled and its Li and Co content is tested, and B is calculated.

[0071] The lithium-ion battery was subjected to cycle testing using the above charge-discharge regime, namely 0.7C / 0.7C, 0.02C cutoff, voltage range of 3.0-4.45V, temperature of 25℃, and capacity retention was tested after 500T cycles.

[0072] Example 4

[0073] The lithium-ion battery provided in this embodiment is the same as that in Embodiment 1, except that the charging and discharging system is different. Specifically, at 25°C, the cell is discharged to 3.0V at a rate of 0.7C, the cell is disassembled and its Li and Co content is tested, and A is calculated. The cell is then charged to 4.4V at a constant current rate of 0.7C, followed by constant voltage charging with a cutoff current of 0.05C. The cell under this condition is disassembled and its Li and Co content is tested, and B is calculated.

[0074] The lithium-ion battery was subjected to cycle testing using the above charge-discharge regime, namely 0.7C / 0.7C, 0.05C cutoff, voltage range of 3.0-4.4V, temperature of 25℃, and capacity retention was tested after 500T cycles.

[0075] Example 5

[0076] The lithium-ion battery provided in this embodiment is the same as that in Embodiment 1, except that the charging and discharging system is different. Specifically, at 25°C, the cell is discharged to 3.0V at a rate of 0.7C, the cell is disassembled and its Li and Co content is tested, and A is calculated. The cell is then charged to 4.48V at a constant current rate of 0.7C, followed by constant voltage charging with a cutoff current of 0.05C. The cell under this condition is disassembled and its Li and Co content is tested, and B is calculated.

[0077] The lithium-ion battery was subjected to cycle testing using the above charge-discharge regime, namely 0.7C / 0.7C, 0.05C cutoff, voltage range of 3.0-4.48V, temperature of 25℃, and capacity retention was tested after 500T cycles.

[0078] Example 6

[0079] The lithium-ion battery provided in this embodiment is the same as that in Embodiment 1, except that the charging and discharging system is different. Specifically, at 25°C, the cell is discharged to 3.0V at a rate of 0.7C, the cell is disassembled and its Li and Co content is tested, and A is calculated. At 10°C, it is charged to 4.45V at a constant current rate of 0.7C, and then charged at a constant voltage with a cutoff current of 0.05C. The cell under this condition is disassembled and its Li and Co content is tested, and B is calculated.

[0080] The lithium-ion battery was subjected to cycle testing using the above charge-discharge regime, namely 0.7C / 0.7C, 0.05C cutoff, voltage range of 3.0-4.45V, temperature of 10℃, and capacity retention was tested after 500T cycles.

[0081] Example 7

[0082] The lithium-ion battery provided in this embodiment is the same as that in Embodiment 1, except that the charging and discharging system is different. Specifically, at 25°C, the cell is discharged to 3.0V at a rate of 0.7C, the cell is disassembled and its Li and Co content is tested, and A is calculated. At 35°C, it is charged to 4.45V at a constant current rate of 0.7C, and then charged at a constant voltage with a cutoff current of 0.05C. The cell under this condition is disassembled and its Li and Co content is tested, and B is calculated.

[0083] The lithium-ion battery was subjected to cycle testing using the above charge-discharge regime, namely 0.7C / 0.7C, 0.05C cutoff, voltage range of 3.0-4.45V, temperature of 35℃, and capacity retention was tested after 500T cycles.

[0084] Example 8

[0085] The lithium-ion battery provided in this embodiment can be referred to in Embodiment 2, except that the total content of Al in the positive electrode active material is 3500ppm, the total content of Mg is 1500ppm, and the total content of Ti is 1500ppm.

[0086] The lithium-ion battery was charged and discharged using the charge and discharge regime provided in Example 2, and the capacity retention rate was tested.

[0087] Example 9

[0088] The lithium-ion battery provided in this embodiment can be referred to in Embodiment 2, except that the total content of Al in the positive electrode active material is 4000ppm, the total content of Mg is 1500ppm, and the total content of Ti is 1500ppm.

[0089] The lithium-ion battery was charged and discharged using the charge and discharge regime provided in Example 2, and the capacity retention rate was tested.

[0090] Example 10

[0091] The lithium-ion battery provided in this embodiment can be referred to in Embodiment 2, except that the total content of Al in the positive electrode active material is 5000ppm, the total content of Mg is 1500ppm, and the total content of Ti is 1500ppm.

[0092] The lithium-ion battery was charged and discharged using the charge and discharge regime provided in Example 2, and the capacity retention rate was tested.

[0093] Example 11

[0094] The lithium-ion battery provided in this embodiment can be referred to in Embodiment 2, except that the total content of Al in the positive electrode active material is 5500ppm, the total content of Mg is 1500ppm, and the total content of Ti is 1500ppm.

[0095] The lithium-ion battery was charged and discharged using the charge and discharge regime provided in Example 2, and the capacity retention rate was tested.

[0096] Example 12

[0097] The lithium-ion battery provided in this embodiment can be referred to in Embodiment 2, except that the total content of Al in the positive electrode active material is 6000ppm, the total content of Mg is 1500ppm, and the total content of Ti is 1500ppm.

[0098] The lithium-ion battery was charged and discharged using the charge and discharge regime provided in Example 2, and the capacity retention rate was tested.

[0099] Example 13

[0100] The lithium-ion battery provided in this embodiment can be referred to in Embodiment 2, except that the total content of Al in the positive electrode active material is 7000ppm, the total content of Mg is 1500ppm, and the total content of Ti is 1500ppm.

[0101] The lithium-ion battery was charged and discharged using the charge and discharge regime provided in Example 2, and the capacity retention rate was tested.

[0102] Comparative Example 1

[0103] The positive electrode active material provided in this comparative example is lithium cobalt oxide. The preparation of the lithium-ion battery and the charge-discharge regime can be referred to Example 2.

[0104] The preparation method of the positive electrode active material provided in this comparative example includes the following preparation steps:

[0105] Step 1: Dissolve CoCl2 in an aqueous solution to prepare Co 2+A solution with a concentration of 1.25 mol / L was mixed with an ammonia solution (concentrated ammonia and distilled water were prepared at a volume ratio of 1:10) and a sodium carbonate solution (1.2 mol / L) to carry out a complex precipitation reaction. The reaction was repeated three times and then centrifuged and filtered to obtain cobalt carbonate CoCO3.

[0106] Step 2: Place the cobalt carbonate in a muffle furnace for calcination at a temperature of 930℃ for 10 hours. Then, pulverize the calcined product to obtain a precursor Co3O4 with uniform particle distribution.

[0107] Step 3: The prepared precursors Co3O4 and Li2CO3 were mixed by high-speed ball milling at a ratio of Li:Co = 100:99.6, and then calcined in a muffle furnace at a temperature of 1035℃ for 11 hours. The calcined product was then pulverized to obtain LiCoO2.

[0108] Comparative Example 2

[0109] The lithium-ion battery provided in this comparative example is the same as that in Example 1, except that the charge and discharge regime is different. Specifically, at 25°C, the cell is discharged to 3.0V at a rate of 0.7C, the cell is disassembled and its Li and Co content is tested, and A is calculated. The cell is then charged to 4.45V at a constant current rate of 0.7C, followed by constant voltage charging with a cutoff current of 0.01C. The cell under this condition is disassembled and its Li and Co content is tested, and B is calculated.

[0110] The lithium-ion battery was subjected to cycle testing using the above charge-discharge regime, namely 0.7C / 0.7C, 0.01C cutoff, voltage range of 3.0-4.45V, temperature of 25℃, and capacity retention was tested after 500T cycles.

[0111] Comparative Example 3

[0112] The lithium-ion battery provided in this comparative example is the same as that in Example 1, except that the charge and discharge regime is different. Specifically, at 25°C, the cell is discharged to 3.0V at a rate of 0.7C, the cell is disassembled and its Li and Co content is tested, and A is calculated. At the same time, the cell of the same scheme is charged to 4.5V at a constant current rate of 0.7C, and then constant voltage charging is performed with a cutoff current of 0.05C. The cell under this state is disassembled and its Li and Co content is tested, and B is calculated.

[0113] The lithium-ion battery was subjected to cycle testing using the above charge-discharge regime, namely 0.7C / 0.7C, 0.05C cutoff, voltage range of 3.0-4.5V, temperature of 25℃, and capacity retention was tested after 500T cycles.

[0114] Comparative Example 4

[0115] The lithium-ion battery provided in this comparative example is the same as that in Example 1, except that the charge and discharge regime is different. Specifically, at 25°C, the cell is discharged to 3.0V at a rate of 0.7C, the cell is disassembled and its Li and Co content is tested, and A is calculated. The cell is then charged to 4.55V at a constant current rate of 0.7C, followed by constant voltage charging with a cutoff current of 0.05C. The cell under this condition is disassembled and its Li and Co content is tested, and B is calculated.

[0116] The lithium-ion battery was subjected to cycle testing using the above charge-discharge regime, namely 0.7C / 0.7C, 0.05C cutoff, voltage range of 3.0-4.55V, temperature of 25℃, and capacity retention was tested after 500T cycles.

[0117] Comparative Example 5

[0118] The lithium-ion battery provided in this comparative example is the same as that in Example 1, except that the charge and discharge regime is different. Specifically, at 25°C, the cell is discharged to 3.0V at a rate of 0.7C, the cell is disassembled and its Li and Co content is tested, and A is calculated. At 45°C, it is charged to 4.45V at a constant current rate of 0.7C, and then charged at a constant voltage with a cutoff current of 0.05C. The cell under this condition is disassembled and its Li and Co content is tested, and B is calculated.

[0119] The lithium-ion battery was subjected to cycle testing using the above charge-discharge regime, namely 0.7C / 0.7C, 0.05C cutoff, voltage range of 3.0-4.45V, temperature of 45℃, and capacity retention was tested after 500T cycles.

[0120] Comparative Example 6

[0121] The lithium-ion battery provided in this comparative example is the same as that in Example 1, except that the charge and discharge regime is different. Specifically, at 25°C, the cell is discharged to 3.0V at a rate of 0.7C, the cell is disassembled and its Li and Co content is tested, and A is calculated. At 55°C, it is charged to 4.45V at a constant current rate of 0.7C, and then charged at a constant voltage with a cutoff current of 0.05C. The cell under this condition is disassembled and its Li and Co content is tested, and B is calculated.

[0122] The lithium-ion battery was subjected to cycle testing using the above charge-discharge regime, namely 0.7C / 0.7C, 0.05C cutoff, voltage range of 3.0-4.45V, temperature of 55℃, and capacity retention was tested after 500T cycles.

[0123] Tables 2-5 provide a list of the positive electrode active materials and charge / discharge regimes provided in Examples 1-13 and Comparative Examples 1-6, and show the capacity retention rates of the lithium-ion batteries provided in Examples 1-13 and Comparative Examples 1-6, so as to make the differences and effects of the embodiments provided by the present invention more intuitive.

[0124] Table 2 shows the AB and capacity retention rates of the lithium-ion batteries provided in Examples 1-3 and Comparative Examples 1-2.

[0125] A B AB Capacity retention Charging cutoff current Example 1 0.926 0.301 0.625 93.01％ 0.1C Example 2 0.926 0.287 0.639 91.46％ 0.05C Example 3 0.926 0.280 0.646 88.44％ 0.02C Comparative Example 1 0.913 0.253 0.660 86.74％ 0.05C Comparative Example 2 0.926 0.269 0.657 87.76％ 0.01C

[0126] The lithium-ion battery was cycled at 25°C within a voltage range of 3.0-4.45V to ensure a consistent charge / discharge rate. The charging cut-off current was adjusted to 0.1C, 0.05C, 0.02C, and 0.01C. According to the data provided in Examples 1-3 and Comparative Example 2, as the charging cut-off current decreases, AB increases, the capacity retention rate decreases, and the cycle performance deteriorates.

[0127] Table 3 shows the AB and capacity retention rates of the lithium-ion batteries provided in Examples 2, 4, 5, and Comparative Examples 1-4.

[0128]

[0129] The lithium-ion battery was charged and discharged at 25°C at a rate of 0.7C / 0.7C, with a charging cut-off current of 0.05C. The cut-off voltages were adjusted to 4.4V, 4.45V, 4.48V, 4.5V, and 4.55V, respectively. According to the data provided in Examples 2, 4-5 and Comparative Examples 3-4, as the charging cut-off voltage increases, AB increases, the capacity retention decreases, and the cycle performance deteriorates.

[0130] Table 4 shows the AB and capacity retention rates of the lithium-ion batteries provided in Examples 2, 6-7 and Comparative Examples 1, 5, and 6.

[0131] A B AB Capacity retention Circulation temperature Example 2 0.926 0.287 0.639 95.08％ 25℃ Example 6 0.926 0.310 0.615 96.44％ 10℃ Example 7 0.926 0.279 0.646 92.69％ 35℃ Comparative Example 1 0.913 0.253 0.660 91.62％ 25℃ Comparative Example 5 0.926 0.245 0.681 90.48％ 45℃ Comparative Example 6 0.926 0.205 0.721 85.25％ 55℃

[0132] The lithium-ion battery was charged and discharged at 10, 25, 35, 45, and 55°C with a voltage of 3.0-4.45V, a voltage of 0.7C / 0.7C, and a cutoff current of 0.05C. According to the data provided in Examples 2, 6-7, and Comparative Examples 5-6, as the cycle temperature increases, AB increases, the capacity retention decreases, and the cycle performance deteriorates.

[0133] Table 5 shows the AB and capacity retention rates of the lithium-ion batteries provided in Examples 2, 8-13, and Comparative Example 1.

[0134]

[0135]

[0136] The doping amount of Al in the positive electrode active material was adjusted to 3500, 4000, 4500, 5000, 5500, 6000, and 7000 ppm, and the lithium-ion battery containing the above positive electrode active material was subjected to charge-discharge cycles under the same conditions. According to the data provided in Examples 2 and 8-13, as the doping amount of Al in the positive electrode active material increases, AB decreases, capacity retention increases, and cycle performance improves.

[0137] In summary, when the molar ratio of lithium to cobalt in the positive electrode active material is A at 0% SOC and B at 100% SOC, and 0.62≤AB≤0.655, the lithium-ion battery exhibits good cycle performance.

[0138] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A lithium-ion battery, characterized in that, The lithium-ion battery includes a positive electrode active material, which comprises lithium cobalt oxide particles doped with Al, Mg, and Ti. The lithium cobalt oxide particles are further doped with one or more elements selected from Zr, Ni, Mn, Y, La, Sr, W, and Sc. The positive electrode active material also includes a coating layer covering at least a portion of the outer surface of the lithium cobalt oxide particles, the thickness of which is not greater than 50 nm. The average particle size of the positive electrode active material is 8.0-15.0 μm. The positive electrode active material includes Al, and the Al content is not less than 3500 ppm. At 0% SOC, the molar ratio of lithium to cobalt in the positive electrode active material is A; at 100% SOC, the molar ratio of lithium to cobalt in the positive electrode active material is B, where 0.62 ≤ A ≤ 0.

655. The lithium-ion battery further includes a negative electrode active material, which includes artificial graphite, and also includes one or more of natural graphite, hard carbon, mesophase carbon microspheres, lithium titanate, silicon carbide, and silicon suboxide; wherein the artificial graphite is a mixture of secondary particles and single particles.

2. The lithium-ion battery according to claim 1, characterized in that, The coating layer includes one or more of the following: metal fluorides, metal oxides, metal borate compounds, and metal phosphate compounds.

3. The lithium-ion battery according to claim 2, characterized in that, The metal fluoride is selected from one or more of AlF3, Li3F, and MgF; And / or, the metal oxide is selected from one or more of Al2O3, TiO2, ZrO2, and MgO; And / or, the metal borate compound is AlBO3; And / or, the metal phosphate compound is selected from one or both of AlPO4 and Li3PO4.

4. The lithium-ion battery according to claim 2, characterized in that, The mass of the coating layer is no more than 1% of the total mass of the positive electrode active material.

5. The lithium-ion battery according to claim 2, characterized in that, The positive electrode active material is prepared by the following method: The lithium cobalt oxide particles are doped with element M, wherein element M is one or more selected from Al, Mg, Ti, Zr, Ni, Mn, Y, La, Sr, W, and Sc; The positive electrode active material is obtained by coating at least a portion of the surface of lithium cobalt oxide particles doped with element M with one or more of the following: metal fluoride, metal oxide, metal borate compound, and metal phosphate compound.

6. The lithium-ion battery according to any one of claims 1-5, characterized in that, The charging cutoff voltage of the lithium-ion battery is less than 4.5V.

7. The lithium-ion battery according to any one of claims 1-5, characterized in that, The charging cutoff current of the lithium-ion battery is not less than 0.02C.

8. The lithium-ion battery according to any one of claims 1-5, characterized in that, The charge / discharge temperature of the lithium-ion battery is less than 45°C.

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