A lithium-ion battery

Abstract

The application provides a lithium ion battery, which comprises a positive electrode sheet and a negative electrode sheet; a positive electrode active material of the positive electrode sheet comprises a lithium metal oxide shown in formula 1 or formula 2, the lithium metal oxide is a cubic crystal system Cmca space group, and has a 002 peak with 2θ of 17.9°-18.1° and a 131 peak with 2θ of 67.0°-67.5°; the negative electrode sheet comprises lithium metal, and a negative electrode current collector and a negative electrode active layer which are sequentially stacked; the thickness ratio of the negative electrode sheet and the positive electrode sheet is m1, and the area density ratio of the positive electrode sheet and the negative electrode sheet is m2, wherein m1 is greater than or equal to 1.4, and m2 is less than or equal to 1.9. The lithium ion battery has excellent specific capacity at high voltage and excellent cycle performance.

Description

TECHNICAL FIELD

[0001] The present application relates to a lithium ion battery, belonging to the technical field of secondary batteries. BACKGROUND

[0002] With the development and progress of lithium ion battery technology, higher and higher requirements are put forward for its capacity. In the composition of lithium ion batteries, the capacity of the positive active material plays a crucial role in the capacity of lithium ion batteries.

[0003] In order to improve the capacity of lithium ion batteries, the most commonly used method is to increase the charge and discharge voltage. However, with the increase of voltage, the crystal structure of the positive active material will collapse, which will lead to a series of problems such as rapid capacity decay and significant reduction of cycle performance of the battery.

[0004] Therefore, it is another urgent problem to develop a lithium ion battery with high specific capacity and good cycle performance. SUMMARY

[0005] The present application provides a lithium ion battery which has excellent specific capacity at high voltage and excellent cycle performance.

[0006] The present application provides a lithium ion battery, which comprises a positive electrode sheet and a negative electrode sheet.

[0007] The positive active material of the positive electrode sheet comprises a lithium metal oxide represented by formula 1 or formula 2, which is a cubic crystal system with a Cmca space group, and has a 002 peak with 2θ of 17.9°-18.1° and a 131 peak with 2θ of 67.0°-67.5° in XRD diffraction;

[0008] The negative electrode sheet comprises lithium metal, and a negative electrode current collector and a negative electrode active layer which are sequentially stacked;

[0009] The thickness ratio of the negative electrode sheet and the positive electrode sheet is m1, and the area density ratio of the positive electrode sheet and the negative electrode sheet is m2, wherein m1≥1.4 and m2≤1.9;

[0010] Li n1-y1 Na y1 Co 1-a1-b1 M1 b1 M2 a1 O2Formula 1

[0011] Li n2-y2-b2 Na y2 Co 1-a2 M1 b2 M2 a2 O2Formula 2

[0012] In formula 1, 0.6≤n1≤0.8, 0

[0013] In formula 2, 0.6≤n2≤0.8, 0

[0014] wherein M1 is selected from at least one of Te, W, Al, B, P and K; and M2 is a doping element different from M1.

[0015] The lithium ion battery as described above, wherein the lithium content in the negative electrode sheet is not less than 4000 ppm.

[0016] The lithium ion battery as described above, wherein the thickness of the positive electrode sheet is 50-120 μm; and / or the thickness of the negative electrode sheet is 70-168 μm.

[0017] The lithium ion battery as described above, wherein the area density of the positive electrode sheet is 8.6-23 mg / cm 2 ; and / or the area density of the negative electrode sheet is 4.7-11 mg / cm 2 .

[0018] The lithium ion battery as described above, wherein the area density of the lithium metal is 0.09 mg / cm 2 -3.5 mg / cm 2 .

[0019] The lithium ion battery as described above, wherein the peak intensity of the 002 peak is I1, the peak intensity of the 131 peak is I2, and I1 / I2≥3.

[0020] The lithium ion battery as described above, wherein the positive electrode active material comprises the lithium metal oxide and a coating layer covering at least part of the surface of the lithium metal oxide.

[0021] The lithium ion battery as described above, wherein when the cut-off voltage is 3.0-3.6 V and the SOC is zero, in the lithium metal oxide, 0.7≤n1, n2≤1.0.

[0022] The lithium ion battery as described above, wherein the median particle size Dv50 of the lithium metal oxide is 12 μm-20 μm.

[0023] The lithium ion battery as described above, wherein the half-cell comprising the lithium metal oxide has a first-stage discharge capacity proportion C1 / C0≥9% and a second-stage discharge capacity proportion C2 / C0≥25%.

[0024] Wherein, C0 is the discharge capacity of the half battery including the lithium metal oxide when the half battery is discharged at 3.0-4.55V voltage; in the discharge process, the capacity discharged when the half battery is discharged from the initial discharge voltage to 4.4V is defined as C1, and the capacity discharged when the half battery is discharged from 3.8V to 3.7V is defined as C2.

[0025] The lithium ion battery of the present application, by matching the chemical composition and related physical parameters of the positive and negative electrode sheets respectively, not only makes it exhibit higher initial efficiency under high voltage conditions, thereby improving the specific capacity of the lithium ion battery, but also reduces the capacity loss of the lithium ion battery during long-term charge and discharge application, and optimizes the cycle performance of the lithium ion battery. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is a structural schematic view of an embodiment of the negative electrode sheet of the lithium ion battery of the present application;

[0027] Figure 2 is a schematic view of the partial area of the negative electrode sheet after charge and discharge cycling of the lithium ion battery of the present application;

[0028] Figure 3 is a schematic view of the electrode sheet thickness detection site during detection of the thickness of the electrode sheet of the present application;

[0029] Figure 4 is an XRD diffraction pattern of lithium metal oxide 2# of the present application;

[0030] Figure 5 is the charge and discharge curve of the button cell including lithium metal oxide 1# of the present application. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical scheme and advantages of the present application clearer, the technical scheme in the embodiments of the present application will be described clearly and completely below in combination with the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0032] The first aspect of the present application provides a lithium ion battery, comprising a positive electrode sheet and a negative electrode sheet; a positive electrode active material of the positive electrode sheet comprises a lithium metal oxide shown in Formula 1 or Formula 2, the lithium metal oxide is a cubic system of Cmca space group, and has a 002 peak of 2θ of 17.9°-18.1° and a 131 peak of 2θ of 67.0°-67.5°; the negative electrode sheet comprises lithium metal, and a negative electrode current collector and a negative electrode active layer which are sequentially stacked; a thickness ratio of the positive electrode sheet and the negative electrode sheet is m1, and a surface density ratio of the negative electrode sheet and the positive electrode sheet is m2, wherein m1≥1.4 and m2≤1.9.

[0033] Li n1-y1 Na y1 Co 1-a1-b1 M1 b1 M2 a1 O2Formula 1

[0034] Li n2-y2-b2 Na y2 Co 1-a2 M1 b2 M2 a2 O2Formula 2

[0035] In Formula 1, 0.6≤n1≤0.8, 0

[0036] In Formula 2, 0.6≤n2≤0.8, 0

[0037] M1 is selected from at least one of Te, W, Al, B, P and K; M2 is a doping element different from M1.

[0038] The present application does not limit the specific structure of the lithium ion battery, for example, it can be a square shell battery, a cylindrical battery, etc.

[0039] The positive electrode sheet of the lithium ion battery comprises a current collector and a positive electrode active layer arranged on at least one functional surface (two surfaces with the largest area and arranged oppositely in the current collector) of the positive electrode current collector, the positive electrode active layer at least comprises a positive electrode active material, a conductive agent and a binder. Exemplarily, the positive electrode active layer comprises 70-99 wt% of the positive electrode active material, 0.5-15 wt% of the conductive agent and 0.5-15 wt% of the binder in terms of mass percentage, further, 80-98 wt% of the positive electrode active material, 1-10 wt% of the conductive agent and 1-10 wt% of the binder. The selection of the conductive agent and the binder in the positive electrode sheet is not special and can be the conventional selection in the art. For example, the conductive agent is selected from at least one of conductive carbon black, acetylene black, ketjen black, conductive graphite, conductive carbon fiber, carbon nanotube, single-walled carbon nanotube, multi-armed carbon nanotube and carbon fiber, and the binder is selected from at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE) and lithium polyacrylate (PAALi).

[0040] Further, in order to improve the safety performance, a safety layer can also be arranged between the positive electrode active layer and the positive electrode current collector. The material of the safety layer is generally a non-conductive safety material, such as iron-containing compounds (such as lithium iron phosphate, lithium phosphate, etc.), aluminum-containing compounds (such as ceramic aluminum oxide) and the like. Of course, the safety layer also comprises a binder, and the proportion of the binder and the safety material can be further determined according to specific requirements.

[0041] The positive electrode active material in the positive electrode sheet comprises a lithium metal oxide shown in Formula 1 or Formula 2, which is a compound with a T2 phase stacking structure, specifically an oxide comprising at least lithium, sodium and cobalt. Further, it can also be doped with M1 and / or M2, and the specific selection of M2 is not limited in the present application and can be the common doping element in the art. For example, it can be at least one of Mg, Ti, Mn, Al, Te, W, Ni, Nb, Zr, La, F, Ce, Sr, Y, K, B and P elements.

[0042] The present application does not make too many limitations on y1, y2, a1, a2, b1, b2 and the like within the above defined range.

[0043] For example, in Formula 1, y1 is 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.010, 0.012, 0.015, 0.018, 0.020, 0.022, 0.024, 0.025, 0.026, 0.028, 0.03, 0.04, or 0.05; a1 is 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.010, 0.012, 0.015, 0.018, 0.020, 0.022, 0.024, 0.025, 0.026, 0.028, 0.030, 0.032, 0.034, 0.035, 0.04, 0.045, 0.05, 0.055, 0.06, 0.065, 0.07, 0.075, 0.08, 0.085, 0.09, or 0.095; b1 is 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.010, 0.012, 0.015, 0.018, 0.020, 0.022, 0.024, 0.025, 0.026, 0.028, 0.030, 0.032, 0.034, 0.035, 0.04, 0.045, 0.05, 0.055, 0.06, 0.065, 0.07, 0.075, 0.08, 0.085, 0.09, or 0.095; and b1 / 1-a1-b1 is 0.005, 0.01, 0.02, 0.03, 0.04, 0.06, 0.08, 0.09, 0.095, or 0.1.

[0044] In formula 2, y2 is 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.010, 0.012, 0.015, 0.018, 0.020, 0.022, 0.024, 0.025, 0.026, 0.028, 0.03, 0.04, or 0.05; a2 is 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.010, 0.012, 0.015, 0.018, 0.020, 0.022, 0.024, 0.025, 0.026, 0.028, 0.030, 0.032, 0.034, 0.035, 0.04, 0.045, 0.05, 0.055, 0.06, 0.065, 0.07, 0.075, 0.08, 0.085, 0.09, or 0.095; b2 is 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.010, 0.012, 0.015, 0.018, 0.02.

[0045] It is emphasized that n1 and n2 above are parameters related to the lithium content in the positive active material without any charge-discharge treatment. It can be understood that, after the positive active material is applied in a lithium ion battery for any charge-discharge treatment, the molar amount of lithium in a unit of molar lithium metal oxide is different under different charge-discharge mechanisms and charge-discharge nodes, and thus n1 and n2 also change, and even are not within the above defined range.

[0046] The negative electrode sheet of the present application comprises lithium metal and a negative electrode current collector and a negative electrode active layer which are sequentially stacked. Specifically, the negative electrode active layer comprises a negative electrode active material, a conductive agent and a binder. In one specific embodiment, the negative electrode active layer comprises 70-99 wt% of the negative electrode active material, 0.5-15 wt% of the conductive agent and 0.5-15 wt% of the binder, further comprising 80-98 wt% of the negative electrode active material, 1-10 wt% of the conductive agent and 1-10 wt% of the binder. The negative electrode active material, the conductive agent and the binder can be selected from the conventional ones in the art. For example, the negative electrode active material is selected from one or more of artificial graphite, natural graphite, hard carbon, mesocarbon microbeads, lithium titanate, silicon-carbon, and silicon monoxide; the conductive agent is selected from at least one of carbon black, acetylene black, ketjen black, and carbon fiber; and the binder is selected from at least one of carboxymethyl cellulose, styrene butadiene rubber, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, oxirane-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate. Further, the negative electrode active material comprises graphite and silicon material, wherein the mass of the silicon material is ≤20% of the mass of the graphite, so as to be more suitable for the negative electrode sheet comprising lithium metal.

[0047] The present application does not limit the form of lithium metal in the negative electrode sheet. Preferably, during the preparation process, the lithium metal layer can be arranged on the surface of the negative electrode active layer away from the current collector. Figure 1 The negative electrode sheet in the present application comprises a negative electrode current collector 101, a negative electrode active layer 20 and a lithium metal layer 30 which are sequentially stacked. Figure 1 The negative electrode sheet in the present application is arranged on both sides, of course, it can also be arranged on one side of the negative electrode current collector 101. When the above-mentioned negative electrode sheet comprising a lithium metal layer is assembled with a positive electrode sheet and the like to obtain a lithium ion battery, after any charge-discharge cycle including formation, at least part of the lithium metal in the lithium metal layer of the negative electrode sheet will migrate and be embedded into the positive electrode. For the lithium ion battery which has experienced charge-discharge cycle, when at least part of the lithium metal in the lithium metal layer migrates and is embedded into the positive electrode sheet, the surface of the negative electrode active layer of the negative electrode sheet will be dispersed with residual lithium metal. Generally, it can be disassembled and the surface morphology SEM of the negative electrode sheet is observed to determine that, when the SEM magnification of the electrode sheet is ≤100, if the electrode sheet presents a lithium metal-rich region 40 and a small amount of lithium metal region 50 with different contrasts as shown in the figure, it is proved that the negative electrode of the lithium ion battery comprises a lithium metal layer during the preparation process. Figure 2

[0048] ​The thickness of the positive and negative electrode plates mentioned in this invention refers to the total thickness of the positive and negative electrode plates after disassembling the lithium-ion battery of this invention. It is important to emphasize that before measuring the thickness of the positive and negative electrode plates, the lithium-ion battery must be in a stage after formation treatment but without further charge-discharge cycles, or in a stage after formation treatment and having undergone no more than 5 charge-discharge cycles. The specific thickness measurement method includes: disassembling the lithium-ion battery in one of the above two stages after discharging it at 0.2C to 3.0V, such as... Figure 3 As shown, 10 first point-like regions A are taken on one side of the electrode, and 10 second point-like regions corresponding to the first point-like regions A are taken on the other side of the electrode. The thickness between the corresponding first point-like regions and second point-like regions is measured using a thickness measuring instrument, and 10 sets of lithium-ion battery thickness data are obtained. The average value of the 10 sets of thickness data is the thickness of the electrode.

[0049] The areal density of the positive and negative electrode mentioned in this invention refers to the areal density of the positive and negative electrode sheets after the lithium ions of this invention have been disassembled. Similarly, the disassembled battery must also be in one of the two stages mentioned above. The specific method for detecting areal density includes: after disassembling a lithium-ion battery in one of the two aforementioned stages, taking 10 first point-like regions on one side of the electrode, and simultaneously taking 10 second point-like regions corresponding to the 10 first point-like regions on the other side of the electrode. Using a circular electrode punch with a diameter of 15mm, the electrode between the corresponding first and second point-like regions is punched to obtain 10 small discs. The 10 small discs are weighed, and the average value is taken as Ma (mg). Simultaneously, 10 current collector discs are punched from the current collector without active material coating on the electrode using the same method, and the 10 current collector discs are weighed, and the average value is taken as Mb (mg). The areal density of the electrode is calculated as (Ma - Mb) / (π * 1.5 * 1.5 / 4), with units of mg / cm³. 2 .

[0050] According to the above scheme provided by the present application, the initial efficiency, specific capacity and cycle performance of the lithium ion battery of the present application are all excellent, and the relevant electrical properties of the lithium ion battery will not deteriorate even under high voltage working conditions. Based on this phenomenon, the inventors believe that: on the one hand, the lithium metal oxide with the above crystal characteristics not only has a more perfect layered crystal structure, so as to reduce or inhibit the occurrence of internal mixed arrangement of the crystal phase, and further enable the lithium ions to be smoothly deintercalated, and the lithium ion battery including the above thickness ratio and surface density ratio can exhibit excellent initial efficiency, and further realize the significant improvement of the specific capacity; on the other hand, the structural stability of the lithium metal oxide conforming to formula 1 or formula 2 is improved to a certain extent, so that the lithium metal oxide with stable structure is more helpful to improve the efficiency of lithium ion deintercalation, and promote the improvement of the cycle performance and specific capacity of the lithium ion battery.

[0051] As described above, for the lithium ion battery of the present application which has experienced charge and discharge cycles, most of the lithium metal in the lithium metal layer will migrate and intercalate into the positive electrode sheet. At this time, the residual lithium content dispersed on the surface of the negative electrode active layer is not less than 4000 ppm. Specifically, after the lithium ion battery is disassembled, the negative electrode sheet can be detected by ICP.

[0052] In a specific embodiment, during the preparation process, the surface density of lithium metal in the negative electrode sheet is 0.09 mg / cm 2 ~ 3.5 mg / cm 2 .

[0053] In a specific embodiment, after the lithium ion battery is disassembled, the thickness of the positive electrode sheet is 50 ~ 120 μm; and / or, the thickness of the negative electrode sheet is 70 ~ 168 μm. Further, the thickness of the positive electrode sheet is 65 ~ 100 μm, and the thickness of the negative electrode sheet is 86 ~ 125 μm. In addition, after the lithium ion battery is disassembled, the surface density of the positive electrode sheet is 8.6 ~ 23 mg / cm 2 ; and / or, the surface density of the negative electrode sheet is 4.7 ~ 11 mg / cm 2 . At this time, the specific capacity of the lithium ion battery is more excellent.

[0054] In an embodiment, in the lithium metal oxide, the peak intensity of the 002 peak is I1, the peak intensity of the 131 peak is I2, and I1 / I2≥3. At this time, the internal crystal structure of the lithium metal oxide is more perfect, and thus helps to improve the cycle performance of the battery. Further, I1 / I2≥4, and more further, I1 / I2≥6.

[0055] In addition to the above positive promotion of the lithium metal oxide on the battery-related electrical performance, when the at least part of the surface of the lithium metal oxide is covered by the coating layer, the performance of the battery is further improved. By setting the coating layer, the positive active material is a core-shell structure including the inner core of the lithium metal oxide and the coating layer covering the inner core. The coating layer helps to reduce or inhibit the side reaction of the lithium metal oxide and the electrolyte, so that a stable interface between the positive active material and the electrolyte can still be formed even when the battery works in a high pressure environment, and the cycle performance of the battery is improved by avoiding the transition of metal ions in the positive active ion and avoiding the lack of liquid phenomenon. At the same time, the inhibition or reduction of the side reaction can also reduce the gas production in the battery, thereby also ensuring the safety performance of the battery.

[0056] The present application does not limit the selection of the coating layer material, as long as it can inhibit the side reaction and ensure the normal migration of lithium ions. In order to further improve the lithium ion conductivity, the coating layer can be selected from materials such as carbon-containing compounds and fast ion conductors.

[0057] As described above, in the lithium metal oxide which has not been subjected to any charge and discharge treatment, n1 and n2 are between 0.6 and 0.8. After the lithium ion battery is subjected to charge and discharge, when the remaining capacity SOC of the lithium ion battery is 0 (i.e. in a fully discharged state) and the discharge cutoff voltage is 3.0-3.6V, n1 and n2 of the lithium metal oxide are between 0.7 and 1.0. It should be noted that "after the lithium ion battery is subjected to charge and discharge" herein refers to the number of charge and discharge cycles of the lithium ion battery after formation being within 10. Specifically, after the lithium metal oxide satisfying the above formula 1 or formula 2 is subjected to charge and discharge, the composition thereof changes, and in particular, the molar amount of lithium increases significantly. The reason is that the lithium metal oxide having the above crystal structure has partial vacancies, so when the lithium ion battery is subjected to charge and discharge treatment (e.g. formation), the number of deintercalation between the positive and negative electrodes having the above thickness ratio and surface density ratio is further increased, and more vacancies of the positive electrode sheet can accept more lithium atoms from the negative electrode sheet, thereby increasing the molar amount of lithium ions compared to before the charge and discharge application. This property helps to further improve the cycle performance and specific capacity of the battery.

[0058] The detection of n1 and n2 can be performed by ICP. Specifically, the battery after discharge is disassembled and the positive electrode sheet is taken out. After soaking in dimethyl carbonate (DMC) for 1-3h or DMC leaching, natural drying in a drying room, placing in a muffle furnace at 300-600°C for 2-5h, and sieving with 200 mesh, the powder to be detected is obtained, and then the metal elements in the powder to be detected are detected by ICP to calculate n1 and n2.

[0059] The positive electrode active material in the positive electrode sheet of the lithium ion battery can be single crystal morphology or polycrystal morphology, and the specific morphology is related to the selection and proportion of the doped elements. Specifically, when it is polycrystal morphology, it is spherical or spherical-like particles; when it is single crystal morphology, it can be whisker-like, flake-like, or any other irregular shape.

[0060] Further, the median particle size Dv50 of the positive electrode active material is 12-20 μm, for example, 3 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm or 20 μm. The inventors found that when the median particle size of the positive electrode active material meets the above requirements, on the one hand, its corresponding specific surface area can meet the deintercalation of more lithium ions; on the other hand, the agglomeration phenomenon between the positive electrode active materials is effectively controlled, so that it can be stably dispersed in the slurry during the slurry preparation process. For example, the median particle size Dv50 can be detected by a laser particle size analyzer.

[0061] It should be explained that the positive electrode active material with the above morphology or median particle size refers to the lithium metal oxide meeting formula 1 or formula 2, or the positive electrode active material with a coating layer coated on at least part of the surface of the lithium metal oxide meeting formula 1 or formula 2.

[0062] The inventors found that when the lithium metal oxide meets the doping of specific elements and the doping proportion, the multiple small discharge platforms in the charge-discharge process of the half-cell including the lithium metal oxide all exhibit excellent discharge capacity.

[0063] In a specific embodiment, the half-cell including the lithium metal oxide has a first stage discharge capacity ratio C1 / C0≥9% and a second stage discharge capacity ratio C2 / C0≥25%; wherein C0 is the discharge capacity of the half-cell including the lithium metal oxide when the half-cell is discharged at a voltage of 3.0-4.55 V; in the discharge process, the capacity discharged by the half-cell from the initial discharge voltage to 4.4 V is defined as C1, and the capacity discharged by the half-cell from 3.8 V to 3.7 V is defined as C2. Further, C1 / C0≥11%, and the second stage discharge capacity ratio C2 / C0≥28%.

[0064] It should be explained that the above discharge capacity is carried out under a special discharge mechanism. Specifically, the half-cell composed of the positive electrode sheet including the lithium metal oxide and the lithium metal negative electrode is charged to 100% SOC (without special limitation on the charging mechanism), and then discharged at 0.1C in the range of 3.0-4.55V. Among them, when discharged from 4.55V to 4.4V at 0.1C, the released electric quantity is C1, when continuously discharged from 3.8V to 3.7V, the released electric quantity of the voltage drop stage is C2, and when continuously discharged to 3.0V (at this time, the SOC is 0), the total electric quantity released from the initial self-discharge is C0.

[0065] It is obvious that in the discharge treatment under high voltage environment, both the first stage discharge capacity ratio and the second stage discharge capacity ratio are excellent. Therefore, the positive electrode active material including the lithium metal oxide of the present application has strong voltage resistance, so that the specific capacity of the lithium ion battery can be improved by voltage boosting treatment.

[0066] The present application does not limit the preparation method of the above-mentioned lithium metal oxide. In a specific embodiment, the lithium metal oxide of the present application can be prepared by mixing a sodium metal oxide represented by formula 1a or 2a with a lithium compound and ion-exchanging.

[0067] Na x1 Co 1-a1-b1 M1 b1 M2 a1 O2Formula 1a Na x2 Co 1-a2 M1 b2 M2 a1 O2Formula 2a

[0068] In formula 1a, 0.68

[0069] The ion exchange treatment is a heat treatment process, specifically referring to mixing the sodium metal oxide and the lithium compound and then heat treating at 80-300°C for no more than 10h. After ion exchange treatment, the ion-exchanged system is washed and dried to finally obtain the lithium metal oxide. The drying temperature is 80-180°C, and the time is at least 10h. The equipment for ion exchange treatment and the drying equipment are not limited, for example, the equipment for ion exchange treatment can be a closed container equipment with closed function and stirring capacity, such as wet coating reaction equipment, coprecipitation reaction equipment, etc.; the drying equipment can be a blast oven, a vacuum drying oven, a rotary kiln, a disc dryer, an oven, etc.

[0070] The lithium compound can be at least one of lithium carbonate, lithium chloride, lithium bromide, lithium iodide, lithium nitrate, lithium hydroxide, lithium fluoride, which are commonly used in the art as lithium source compounds. In the ion exchange treatment, the mass ratio of the lithium compound to the sodium metal oxide is not less than 1:1, and preferably (1-3):1.

[0071] Further, when a positive electrode active material coated with a coating layer on a lithium metal oxide is to be prepared, a coating layer raw material needs to be added in addition to the raw materials of the sodium metal oxide and the lithium compound in the ion exchange treatment.

[0072] For the sodium metal compound represented by Formula 1a and Formula 2a, exemplarily, it can be prepared by a method comprising the following processes:

[0073] The cobalt source, the sodium source, the M1 source and the M2 source are mixed in a target ratio and then subjected to a calcination treatment to obtain the sodium metal compound represented by Formula 1a and Formula 2a.

[0074] Specifically, the calcination treatment is performed at a temperature of 700-900°C for 8-50h, and can be performed in an oxygen or air atmosphere. The calcination treatment can be performed by using a high-temperature sintering device such as a muffle furnace, a tunnel furnace, a roller kiln, a tube furnace, etc.

[0075] The mixing of the above-mentioned sources can be performed by using a high-speed mixing device, a sand milling device, a ball milling device, a ploughshare mixing device, an inclined mixing device, etc. It should be noted that, if a sand milling device or a ball milling device is used and a solvent (water, ethanol or other solvent medium) is added during the sand milling or ball milling, the mixed system needs to be dried after the mixing treatment. Generally, the mixing time is not more than 4h.

[0076] The present application does not limit the specific selection of the cobalt source, the sodium source, the M1 source and the M2 source. Exemplarily, the cobalt source is selected from one or more of cobalt hydroxide, tricobalt tetroxide, doped tricobalt tetroxide, cobalt suboxide, cobalt hydroxide oxide, cobalt nitrate, cobalt sulfate, etc.; the sodium source is selected from one or more of sodium carbonate, sodium nitrate, sodium hydroxide, sodium bicarbonate, sodium sulfate, etc.; the M1 source can be an oxide of M1, for example, when M1 is W, the M1 source is tungstic acid and / or sodium tungstate, etc.; when M1 is Te, the M1 source is telluric acid and / or sodium tellurate, etc.; when M1 is Al, the M1 source is one or more of aluminum sulfate, aluminum nitrate, aluminum hydroxide, etc.; when M1 is B, the M1 source is boric acid and / or sodium borate, etc.; when M1 is P, the M1 source is phosphoric acid and / or sodium phosphate, etc.; when M1 is K, the M1 source is one or more of potassium carbonate, potassium nitrate, potassium hydroxide, potassium bicarbonate, potassium sulfate, etc.; the M2 source can be an oxide of M2, for example, one or more of basic magnesium carbonate, magnesium hydroxide, zirconium oxide, yttrium oxide, lanthanum oxide, lanthanum fluoride, nickel oxide, niobium oxide, etc.

[0077] In addition to the positive and negative electrode sheets, the lithium ion battery of the present application further comprises a separator and an electrolyte.

[0078] Exemplarily, the electrolyte is a conventional electrolyte known in the art comprising a lithium salt and a solvent, the solvent containing ethylene carbonate (abbreviated as EC), diethyl carbonate (abbreviated as DEC), propylene carbonate (abbreviated as PC), fluoroethylene carbonate (abbreviated as FEC). Further, an additive shown in formula T is further included, the mass percentage content of which in the electrolyte is 0.1-10%, etc.

[0079]

[0080] Exemplarily, the separator is a material with polypropylene as a base material, or a coated separator coated with ceramic on one side or both sides.

[0081] The lithium ion battery of the present application is suitable for a high-voltage system, and in particular, has excellent energy density and cycle performance at a voltage of ≥4.50V. Therefore, the lithium ion battery of the present application has good cycle stability and higher gram capacity at a voltage of 4.50V or higher, and can meet the use requirements of high-end digital products for light and thin.

[0082] Hereinafter, the lithium ion battery of the present application will be described in detail through specific examples.

[0083] Lithium metal oxide 1#

[0084] The preparation method of the lithium metal oxide 1# comprises the following steps:

[0085] 1) Weigh 36.56 kg of sodium carbonate powder and 291.05 kg of cobalt nitrate hexahydrate powder, and put them into a high-speed mixing device, set the mixing program, mix at 300 rpm for 3 minutes, then mix at 500 rpm for 5 minutes, and then mix at 1000 rpm for 10 minutes. After taking out the mixed material, it is considered that the mixing is uniform after confirming that there is no white sodium carbonate small white spot in the mixed material;

[0086] 2) Take about 30 kg of the uniformly mixed material, and uniformly load it into a ceramic crucible in batches, and use a VBF-1200X type pit furnace to perform high-temperature sintering. The sintering temperature curve is 5℃ / min, and the temperature is raised to 750℃ for isothermal sintering for 10h. After sintering, the sample is taken out after natural cooling to room temperature, and a sintered cobalt and sodium-containing compound Na 0.69 CoO2;

[0087] 3) Take a reaction container, weigh 1.049 kg of lithium hydroxide monohydrate and 34.47 kg of lithium nitrate particles, and add the two lithium compounds into the reaction container, weigh 10 kg of Na0 .69 CoO2, pour into the reaction container, mix preliminarily, ion exchange at 280℃ for 0.4h, and obtain the crude product;

[0088] 4) After the crude product is washed by deionized water for 3 times, dry at 90℃ for 8h, obtain lithium metal oxide 1#, the chemical composition is Li 0.715 Na 0.02 CoO2.

[0089] Lithium metal oxide 2#

[0090] The preparation method of lithium metal oxide 2# includes the following steps:

[0091] The preparation method of the positive electrode active material of the embodiment is basically the same as that of lithium metal oxide 1#, except for step 1. Specifically, in step 1), weigh 36.56 kg of sodium carbonate powder, 0.21 kg of potassium carbonate powder, 282.31 kg of cobalt nitrate hexahydrate powder and 1.21 kg of nano magnesium oxide powder, put them into a high-speed mixing device, set the mixing program, mix at 300 rpm for 3 minutes, then mix at 500 rpm for 5 minutes, and then mix at 1000 rpm for 10 minutes, take out the mixture, and confirm that there is no white sodium carbonate small white spot in the mixture, and then consider that the mixture is uniform.

[0092] The chemical composition of lithium metal oxide 2# is Li 0.715 Na 0.015 K 0.003 Co 0.97 Mg 0.03 O2. Figure 4 The XRD diffraction pattern of lithium metal oxide 2# of the present application. As can be seen from the figure, the lithium metal oxide of the present application is a cubic crystal system with Cmca space group, and the XRD diffraction has a 002 peak at 2θ of 17.9°-18.1°, and a 131 peak at 2θ of 67.0°-67.5°.

[0093] Lithium metal oxide 3#

[0094] The preparation method of lithium metal oxide 3# includes the following steps:

[0095] The preparation method of the positive active material of the present embodiment is basically the same as that of the lithium metal oxide 1#, except for step 1. Specifically, in step 1), 36.56 kg of sodium carbonate powder, 0.21 kg of potassium carbonate powder, and 291.05 kg of cobalt nitrate hexahydrate powder are weighed, put into a high-speed mixing device, and set to a mixing program. After mixing at 300 rpm for 3 minutes, mixing at 500 rpm for 5 minutes, and mixing at 1000 rpm for 10 minutes, the mixture is taken out. After confirming that there are no white sodium carbonate spots in the mixture, it is considered that the mixture is uniformly mixed.

[0096] The chemical composition of the lithium metal oxide 3# is Li 0.715 Na 0.015 K 0.003 CoO2.

[0097] Example 1

[0098] The preparation method of the lithium ion battery of the present embodiment includes the following steps:

[0099] 1) The lithium metal oxide 1# is mixed with conductive carbon black and PVDF at a weight ratio of 97.6%:1.2%:1.2%, respectively, to obtain a positive electrode slurry by dispersion. The positive electrode slurry is coated on a 9 μm aluminum foil current collector, and after roll drying, a positive electrode sheet with a positive electrode slurry coating surface density of 11.52 mg / cm 2 and a compacted density of 4.15 g / cm 3 is obtained;

[0100] 2) The commercially available artificial graphite 1 with a specific capacity of 355 mAh / g, styrene diene rubber (SBR), and carboxymethyl cellulose sodium, and conductive carbon black are mixed at a weight ratio of 96.9%:1.3%:1.3%:0.5%, and the mixture is dispersed in water by double planetary mixing to obtain a negative electrode slurry. The negative electrode slurry is coated on a 6 μm copper current collector, and after roll drying (roll pressure is 38 tons), a copper foil-negative active layer laminated body with a negative electrode slurry coating surface density of 7.16 mg / cm 2 and a compacted density of 1.7 g / cm 3 is obtained;

[0101] Then, a lithium foil with a surface density of 0.1302 mg / cm 2 is stacked on the surface of the negative active layer by rolling, and finally a negative electrode sheet containing lithium metal is obtained.

[0102] 3) Then the positive electrode sheet, the negative electrode sheet and the separator are assembled into a lithium ion battery, and a non-aqueous electrolyte 7.1 g is injected. The electrolyte is mixed according to the mass ratio of ethylene carbonate (abbreviated as EC): diethyl carbonate (abbreviated as DEC): propylene carbonate (abbreviated as PC) = 2:5:3, 5% of fluoroethylene carbonate (abbreviated as FEC) in the total mass of the electrolyte is added, 13% of lithium hexafluorophosphate (abbreviated as LiPF6) in the total mass of the electrolyte is added, and the additive shown in formula T is added, and the additive content accounts for 2% of the total content of the electrolyte.

[0103] 4) After the final aging, formation and sorting, a lithium ion battery with a capacity average of 3403 mAh is obtained.

[0104] Example 2

[0105] The preparation method of the lithium ion battery of the present embodiment is basically the same as that of Example 1, except for steps 2) and 4).

[0106] Specifically, the negative electrode slurry coating surface density of the negative electrode sheet in step 2) is 7.2 mg / cm 2 ; the capacity of the lithium ion battery in step 4) is 3419 mAh.

[0107] Example 3

[0108] The preparation method of the lithium ion battery of the present embodiment is basically the same as that of Example 2, except for steps 1), 2) and 4).

[0109] Specifically, the positive electrode active material in step 1) is replaced by lithium metal oxide 2#, and the coating surface density of the positive electrode slurry is 11.42 mg / cm 2 ; the surface density of the lithium foil in step 2) is 0.1408 mg / cm 2 ; the capacity of the lithium ion battery in step 4) is 3410 mAh.

[0110] Example 4

[0111] The preparation method of the lithium ion battery of the present embodiment is basically the same as that of Example 3, except for steps 2) and 4).

[0112] Specifically, the negative electrode active material in step 2) is replaced by graphite 2 with a specific capacity of 360 mAh / g, and the coating surface density of the negative electrode slurry of the negative electrode sheet is 7.06 mg / cm 2 ; the capacity of the lithium ion battery in step 4) is 3408 mAh.

[0113] Example 5

[0114] The preparation method of the lithium ion battery of the present embodiment is basically the same as that of Embodiment 3, except for steps 2) and 4).

[0115] Specifically, the negative active material in step 2) is replaced by artificial graphite 2 with a gram capacity of 360 mAh / g, and the coating area density of the negative electrode slurry of the negative electrode sheet is 7.06 mg / cm 2 , the compaction density is 1.8 g / cm 3 , and the rolling pressure is 60 tons; the capacity of the lithium ion battery in step 4) is 3406 mAh.

[0116] Embodiment 6

[0117] The battery preparation and assembly method of the present embodiment 6 is basically the same as that of Embodiment 5, except for steps 2) and 4).

[0118] Specifically, the rolling pressure in step 2) is 70 tons; the capacity of the lithium ion battery in step 4) is 3409 mAh.

[0119] Embodiment 7

[0120] The battery preparation and assembly method of the present embodiment 7 is basically the same as that of Embodiment 5, except for steps 2) and 4).

[0121] Specifically, the rolling pressure in step 2) is 45 tons; the capacity of the lithium ion battery in step 4) is 3407 mAh.

[0122] Embodiment 8

[0123] The preparation method of the lithium ion battery of the present embodiment is basically the same as that of Embodiment 5, except for steps 2) and 4).

[0124] Specifically, the negative active material in step 2) is replaced by a mixture of 97 wt% graphite 3 and 3 wt% silicon dioxide, with a final gram capacity of 395 mAh / g, and the coating area density of the negative electrode slurry of the negative electrode sheet is 6.44 mg / cm 2 , the compaction density is 1.7 g / cm 3 , and the rolling pressure is 38 tons; the capacity of the lithium ion battery in step 4) is 3412 mAh.

[0125] Embodiment 9

[0126] The preparation method of the lithium ion battery of the present embodiment is basically the same as that of Embodiment 5, except for steps 2) and 4).

[0127] Specifically, the negative active material in step 2) is replaced by a mixture of 95wt% of graphite 2 and 5wt% of silicon dioxide, the final gravimetric capacity is 420mAh / g, and the coating area density of the negative electrode slurry of the negative electrode sheet is 6.05mg / cm 2 , the compaction density is 1.7g / cm 3 , the rolling pressure is 38 tons; the capacity of the lithium ion battery in step 4) is 3417mAh.

[0128] Example 10

[0129] The preparation method of the lithium ion battery of the present example is basically the same as that of Example 4, except for steps 1), 2) and 4).

[0130] Specifically, the positive active material in step 1) is replaced by lithium metal oxide 3#, and the coating area density of the positive electrode slurry of the positive electrode sheet is 11.31mg / cm 2 ; the area density of the lithium foil in step 2) is 0.1495mg / cm 2 ; the capacity of the lithium ion battery in step 4) is 3420mAh.

[0131] Comparative Example 1

[0132] The preparation method of the lithium ion battery of the present example is basically the same as that of Example 1, except for steps 1) and 4).

[0133] Specifically, the positive active material in step 1) is replaced by 4.5V high-voltage lithium cobaltate 1, which has a gravimetric capacity of 186mAh / g, and the coating area density of the positive electrode slurry of the positive electrode sheet is 13.5mg / cm 2 ; the capacity of the lithium ion battery in step 4) is 3406mAh.

[0134] Comparative Example 2

[0135] The preparation method of the lithium ion battery of the present example is basically the same as that of Example 1, except for steps 1), 2) and 4).

[0136] Specifically, the positive active material in step 1) is replaced by 4.5V high-voltage lithium cobaltate 1, which has a gravimetric capacity of 186mAh / g, and the coating area density of the positive electrode slurry of the positive electrode sheet is 13.5mg / cm 2 ; the coating area density of the negative electrode slurry in step 2) is 7.45mg / cm 2 , and no lithium foil is superimposed; the capacity of the lithium ion battery in step 4) is 3415mAh.

[0137] Comparative Example 3

[0138] The preparation method of the lithium ion battery of the present example is basically the same as that of Example 1, except for steps 2) and 4).

[0139] Specifically, no lithium foil is superimposed in step 2), and the copper foil-negative active layer stack is the negative electrode sheet of the present comparative example; the capacity of the lithium ion battery in step 4) is 2660 mAh.

[0140] Comparative Example 4

[0141] The preparation method of the lithium ion battery of the present example is basically the same as that of Example 1, except for steps 2) and 4).

[0142] Specifically, the coating area density of the negative electrode slurry in step 2) is 5.70 mg / cm 2 ; the capacity of the lithium ion battery in step 4) is 2720 mAh.

[0143] Test Example 1

[0144] The positive electrode active materials (lithium metal oxide 1#, lithium metal oxide 2#, lithium metal oxide 3#, 4.5V high-voltage lithium cobalt oxide 1) in all examples and comparative examples are respectively prepared as positive electrode sheets, and then assembled with negative electrode sheets, electrolyte and separators to obtain button cells according to the following method. The method comprises:

[0145] The positive electrode active materials in the examples and comparative examples are respectively mixed with conductive carbon black (SP) and PVDF at a weight ratio of 80%:10%:10%, and a positive electrode slurry is obtained by dispersion. The slurry is coated on an aluminum foil current collector, rolled to prepare a positive electrode sheet, and then the positive electrode sheet is punched into small round sheets with a film diameter of 12 mm, dried and weighed, and then assembled into a button cell in an Ar protective atmosphere glove box using a 2025 button cell shell, a Li metal round sheet as a negative electrode, and a conventional high-voltage lithium cobalt oxide electrolyte.

[0146] After the obtained button cells are placed in a conventional environment for 4h, the first charge-discharge capacity test is carried out, and the test conditions are as follows: 0.1C charging to 4.55V, constant voltage charging to 0.025C cutoff, standing for 3min, and then 0.1C discharging to 3.0V. During the discharging process, the first discharge full capacity C0, the first charge capacity, the discharge capacity C1 of 4.4-4.55V, the discharge capacity C2 of 3.7-3.8V are recorded respectively, and the first efficiency, the first stage discharge capacity ratio C1 / C0 and the second stage discharge capacity ratio C2 / C0 are calculated. The results are shown in Table 1. Figure 5 is the charge-discharge curve of the button cell of the present application including lithium metal oxide 1#. It can be seen from Figure 3 that the lithium metal oxide 1# of the present application has a first efficiency of more than 100%.

[0147] Test Example 2

[0148] The capacity retention of the lithium ion batteries in all examples and comparative examples was tested according to the following method: at 25°C, constant current charging to 4.50V at a charge rate of 1C, then constant voltage charging to 4.50V at a charge rate of 0.05C, then discharging to 3.0V at a discharge rate of 1C, repeating this cycle of charging and discharging 500 times, measuring the discharge capacity at the first cycle and the discharge capacity at the 500th cycle, and calculating the capacity retention after 500 cycles according to the following formula: the results are shown in Table 2.

[0149] Capacity retention Q = (discharge capacity at the 500th cycle) / (discharge capacity at the first cycle) * 100%

[0150] Test Example 3

[0151] After discharging the lithium ion batteries in the examples and comparative examples to 3.0V at a current of 1 / 5 of the rated capacity, the voltage was tested and found to be 3.0-3.6V. Then the lithium ion batteries were disassembled, the positive and negative electrode sheets were removed, soaked in dimethyl carbonate (DMC) for 3h, and then naturally dried in a drying room. After being placed in a blast oven at 100°C for 2h, the positive and negative electrode sheets were removed and the thickness and surface density of the electrode sheets were measured according to the aforementioned method. The test results are shown in Table 2.

[0152] Test Example 4

[0153] After discharging the lithium ion batteries in all examples and comparative examples to 3.0V at a current of 1 / 10 of the rated capacity, the voltage was tested and found to be 3.0-3.6V. Then the lithium ion batteries were disassembled, the positive electrode sheets were removed, and soaked in dimethyl carbonate (DMC) for 3h or washed with DMC. After naturally drying in a drying room, the positive electrode sheets were placed in a muffle furnace at 300°C for 3h, and then sieved through a 200 mesh sieve to obtain sample powder. The content of each element in the sample powder was tested using ICP, and n (n1 or n2) was calculated based on the detection values of Li, Na and other elements. The results are shown in Table 1.

[0154] Test Example 5

[0155] After discharging the lithium ion batteries in all examples and comparative examples to 3.0V at a current of 1 / 10 of the rated capacity, the voltage was tested and found to be 3.0-3.6V. Then the lithium ion batteries were disassembled, the negative electrode sheets were removed, and soaked in dimethyl carbonate (DMC) for 3h or washed with DMC. The negative electrode sheets were then dissolved and soaked in water, and the negative electrode powder that fell off into the water was collected and dried at 80°C to obtain negative electrode sample powder. The content of Li element in the negative electrode sample powder was tested using ICP. The results are shown in Table 2.

[0156] Table 1

[0157]

[0158] Table 2

[0159]

[0160] From Table 1, it can be seen that the lithium ion battery of the present application has a first efficiency of more than 100%, more excellent gram capacity and cycle performance.

[0161] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit the present application; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that the technical solutions recorded in the foregoing embodiments can still be modified, or some or all of the technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A lithium-ion battery, characterized by, The lithium ion battery comprises a positive electrode sheet and a negative electrode sheet; The positive electrode active material of the positive electrode sheet comprises a lithium metal oxide shown in Formula 1 or Formula 2, the lithium metal oxide is a cubic crystal system of Cmca space group, and XRD diffraction has a 002 peak with 2θ of 17.9°-18.1° and a 131 peak with 2θ of 67.0°-67.5°; The negative electrode sheet comprises lithium metal, and a negative electrode current collector and a negative electrode active layer which are sequentially stacked; The thickness ratio of the negative electrode sheet and the positive electrode sheet is m1, and the area density ratio of the positive electrode sheet and the negative electrode sheet is m2, wherein m1≥1.4 and m2≤1.9; The thickness and area density of the negative electrode sheet and the positive electrode sheet are measured after the lithium ion battery is subjected to formation processing, then discharged and disassembled; Li n1-y1 Na y1 Co 1-a1-b1 M1 b1 M2 a1 O2 Formula 1 Li n2-y2-b2 Na y2 Co 1-a2 M1 b2 M2 a2 O2Formula 2 In Formula 1, 0.6≤n1≤0.8, 0 In Formula 2, 0.6≤n2≤0.8, 0 M1 is selected from at least one of Te, W, Al, B, P and K; M2 is a doping element different from M1; The thickness of the positive electrode sheet is 50-120 μm; the thickness of the negative electrode sheet is 70-168 μm; the area density of the positive electrode sheet is 8.6-23 mg / cm 2 ; the area density of the negative electrode sheet is 4.7-11 mg / cm 2 .

2. The lithium-ion battery of claim 1, wherein, The lithium content in the negative electrode sheet is not less than 4000 ppm.

3. The lithium-ion battery according to claim 1 or 2, characterized in that The areal density of the lithium metal is 0.09 mg / cm 2 ~ 3.5 mg / cm 2 .

4. The lithium-ion battery of claim 1, wherein, The peak intensity of the 002 peak is I1, the peak intensity of the 131 peak is I2, and I1 / I2≥3.

5. The lithium-ion battery of claim 1 or 4, wherein, The positive electrode active material comprises the lithium metal oxide and a coating layer on at least part of the surface of the lithium metal oxide.

6. The lithium-ion battery of claim 1, wherein, When the cutoff voltage is 3.0-3.6 V and the SOC is zero, in the lithium metal oxide of the lithium ion battery, 0.7≤n1, n2≤1.

0.

7. The lithium-ion battery of claim 5, wherein, The median particle size Dv50 of the lithium metal oxide is 12 μm-20 μm.

8. The lithium ion battery of any one of claims 1, 6-7, wherein, The half-cell comprising the lithium metal oxide has a first-stage discharge capacity proportion C1 / C0≥9% and a second-stage discharge capacity proportion C2 / C0≥25%; C0 is the discharge capacity of the half-cell comprising the lithium metal oxide when the half-cell is subjected to discharge processing at a voltage of 3.0-4.55 V; in the discharge processing, the capacity discharged when the half-cell is discharged from an initial discharge voltage to 4.4 V is defined as C1, and the capacity discharged when the half-cell is discharged from 3.8 V to 3.7 V is defined as C2.

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