Lithium-ion battery and electric device

Abstract

A lithium-ion battery and an electric device. Positive electrode active substances of the lithium-ion battery comprise a lithium nickel cobalt manganese oxide and a manganese iron lithium oxide, and a positive electrode sheet satisfies the relationship as show in the following formula: 0.5≤R＝10×ω×PD / ln(H)≤4, wherein ω is the weight proportion of the manganese iron lithium oxide in the positive electrode active substances; PD g / cm3 is the compaction density of the positive electrode sheet; and H J / g is the enthalpy of the positive electrode sheet.

Description

Lithium ion battery and power-consuming device

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese invention patent application CN202310787285.7 filed on June 29, 2023, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present application relates to the field of battery technology, and in particular to a lithium-ion battery and an electrical device. Background Art

[0004] Lithium-ion batteries have become the preferred powertrain for electric vehicles due to their high energy density, high operating voltage, and excellent cycle performance. Lithium-ion batteries based on nickel-cobalt-manganese ternary cathode materials have higher gram capacity and plateau voltage than lithium iron phosphate (LiFePO4) batteries, resulting in higher energy density and longer battery life for electric vehicles.

[0005] However, as nickel content continues to increase, the thermal stability of nickel-cobalt-manganese ternary materials continues to decline, making high-nickel ternary batteries more susceptible to thermal runaway and posing a risk of heat spread to the battery module. Thermal runaway is prone to occur when heated to >130°C in a hot box, resulting in fire and smoke. The battery's thermal stability needs to be improved.

[0006] Summary of the Invention

[0007] In order to solve the problem that the thermal stability of existing lithium-ion batteries still needs to be improved, the present application provides a lithium-ion battery with excellent thermal stability. The present application mixes lithium iron manganese oxide with lithium nickel cobalt manganese oxide, and reasonably matches the doping amount of lithium iron manganese oxide, the compaction density of the positive electrode sheet (PD g / cm 3 ) and the thermal enthalpy (HJ / g) of the positive electrode sheet, so that it is within a suitable range, significantly improving the thermal stability and safety of lithium-ion batteries.

[0008] To achieve the above objectives, in a first aspect, the present application provides a lithium-ion battery, comprising a positive electrode sheet and a negative electrode sheet, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode active layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode active layer comprises a positive electrode active material, wherein the positive electrode active material comprises lithium nickel cobalt manganese oxide and lithium manganese iron oxide, and wherein the positive electrode sheet satisfies the following conditions: 0.5≤R≤4;

[0009] Where R = 10 × ω × PD / ln (H),

[0010] ω is the weight ratio of manganese iron lithium oxide in the positive electrode active material;

[0011] PD g / cm 3 is the compaction density of the positive electrode sheet;

[0012] HJ / g is the thermal enthalpy of the positive electrode sheet at 100% state of charge (SOC) of the battery, measured using differential scanning calorimetry (DSC) and calculated by calculating the peak area of ​​the DSC curve.

[0013] In some embodiments, the positive electrode plate satisfies: 1≤R≤3.

[0014] In some embodiments, the weight ratio ω of manganese iron lithium oxide in the positive electrode active material is 20% to 50%.

[0015] In some embodiments, the compacted density of the positive electrode sheet is PD g / cm 3 2.6~3.0g / cm 3 .

[0016] In some embodiments, the thermal enthalpy HJ / g of the positive electrode sheet at 100% SOC of the battery is 500 to 1000 J / g.

[0017] In some embodiments, in the lithium nickel cobalt manganese oxide, based on the molar amount of the metal elements other than lithium, the molar percentage of the nickel element is n1%, and n1≥80 is satisfied.

[0018] In some embodiments, in the manganese iron lithium oxide, the molar percentage of manganese element in the total amount of metal elements excluding lithium is n2%, satisfying 50≤n2≤90.

[0019] In some embodiments, the D of the lithium nickel cobalt manganese oxide is v50 Greater than the D of the manganese iron lithium oxide v50 .

[0020] In some embodiments, at least a portion of the lithium nickel cobalt manganese oxide is a single crystalline particle.

[0021] In a second aspect of the present application, an electrical device comprising a lithium-ion battery is provided.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] In this application, lithium nickel cobalt manganese oxide is mixed with lithium manganese iron oxide in the positive electrode material, and the content of lithium nickel cobalt manganese oxide and lithium manganese iron oxide is reasonably matched, and the compaction density (PD g / cm 3 ) and the thermal enthalpy (HJ / g) of the positive electrode sheet so that they meet a specific relationship, which can significantly improve the thermal stability of lithium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] FIG1 is a morphology diagram of the positive electrode active material on the surface of the positive electrode sheet in Example 1;

[0025] FIG2 is a hot box test curve diagram of the lithium ion battery of Example 6;

[0026] FIG3 is a hot box test curve diagram of the lithium ion battery of Comparative Example 1. DETAILED DESCRIPTION

[0027] To better illustrate the purpose, technical solutions and advantages of the present application, the present application will be further described below in conjunction with specific examples and accompanying drawings, but the examples do not limit the present application in any form. Unless otherwise specified, the reagents, methods and equipment used in this application are conventional reagents, methods and equipment in the art. Unless otherwise specified, the reagents and materials used in this application are commercially available.

[0028] An embodiment of the present application provides a lithium-ion battery, comprising a positive electrode sheet and a negative electrode sheet, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode active layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode active layer comprises a positive electrode active material, wherein the positive electrode active material comprises lithium nickel cobalt manganese oxide and lithium manganese iron oxide, and wherein the positive electrode sheet satisfies the following conditions: 0.5≤R≤4;

[0029] Where R = 10 × ω × PD / ln (H),

[0030] ω is the weight ratio of manganese iron lithium oxide in the positive electrode active material;

[0031] PD g / cm 3 is the compaction density of the positive electrode sheet;

[0032] HJ / g is the enthalpy value of the positive electrode sheet at 100% SOC of the battery, obtained by DSC testing, and its value is the same as the peak area value of the DSC curve.

[0033] In this application, lithium nickel cobalt manganese oxide is mixed with manganese iron lithium oxide, and the content of lithium nickel cobalt manganese oxide and manganese iron lithium oxide, the compaction density of the positive electrode sheet (PD g / cm 3 ) and the thermal enthalpy (HJ / g) of the positive electrode sheet so that they are within a suitable range can significantly improve the thermal stability of the battery.

[0034] By adding manganese iron lithium oxide to the lithium nickel cobalt manganese oxide slurry of lithium-ion batteries and controlling the content and preparation process of manganese iron lithium oxide, the manganese iron lithium oxide particles are filled in the gaps between the lithium nickel cobalt manganese oxide particles during the subsequent electrode compaction process, thereby improving its thermal stability and preventing thermal runaway in high-temperature environments. The possible reasons for the reduction in thermal runaway are as follows:

[0035] Manganese iron lithium oxide is mixed with lithium nickel cobalt manganese oxide, and manganese iron lithium oxide is filled into the gaps of lithium nickel cobalt manganese oxide, so that the thermal decomposition temperature of the prepared positive electrode plate is increased. The oxygen release amount is low during the use of the battery, which can effectively increase the thermal decomposition temperature of the positive electrode and reduce the release of gas. At the same time, it can increase the diaphragm resistance of the positive electrode plate to a certain extent. When the diaphragm in the battery fails at high temperature, the short-circuit current formed by the contact between the positive and negative electrodes will decrease, further reducing the heat release rate and avoiding the occurrence of thermal runaway. In addition, the operating voltage of manganese iron lithium oxide and lithium nickel cobalt manganese oxide is matched, so that the overall performance of the lithium-ion battery is improved.

[0036] It should be noted that the enthalpy value (HJ / g) of the positive electrode is represented by the peak area of ​​the differential scanning calorimetry (DSC) curve of the fully charged (100% SOC) delithiated positive electrode in a DSC test. In some embodiments, the DSC test conditions are in the range of 25-400°C, with a heating rate of 5°C / min. The weight percentage of manganese iron lithium oxide in the positive electrode active material can be determined by elemental analysis (e.g., analysis of Fe content).

[0037] In some embodiments, the positive electrode sheet satisfies: 1≤R≤3. When the R value of the positive electrode sheet is within this range, in addition to having excellent thermal stability and high safety performance, the prepared lithium-ion battery also has better cycle stability.

[0038] positive electrode active material

[0039] The positive electrode active material includes lithium nickel cobalt manganese oxide and lithium manganese iron oxide. In some embodiments, the D v50 Greater than the D of the manganese iron lithium oxide v50 . D v50 The particle size corresponding to the cumulative volume percentage of the positive electrode active material (lithium manganese iron oxide and lithium nickel cobalt manganese oxide) reaches 50%, and the unit is μm.

[0040] In the positive electrode active material in the positive electrode plate of the present application, since the particle size of lithium manganese iron oxide is much smaller than that of lithium nickel cobalt manganese oxide, it can fill the gaps between the lithium nickel cobalt manganese oxide particles, making the contact between the particles closer and reducing the ion diffusion path; and it also allows the lithium manganese iron oxide to effectively wrap the lithium nickel cobalt manganese oxide particles (see Figure 1), reducing the contact between the lithium nickel cobalt manganese oxide positive electrode active material and the electrolyte.

[0041] It should be noted that the particle size (D v50), the battery needs to be disassembled, the electrodes are disassembled and baked, and the positive electrode active material powder on the positive electrode is scraped off. The positive electrode active material powder is analyzed using a scanning electron microscope (SEM) and a particle size distribution tester:

[0042] Energy dispersive spectrum analysis (EDS) scanning is performed on the selected visible area through SEM to distinguish between manganese iron lithium oxide and lithium nickel cobalt manganese oxide. At this time, the proportion of manganese iron lithium oxide and lithium nickel cobalt manganese oxide in the positive electrode active material powder can be determined; then the powder of the positive electrode active material is tested for particle size distribution using a particle size distribution tester. Two characteristic peaks will be displayed in the particle size distribution graph, and the peak area represents the content of the substance. Combined with the proportion of manganese iron lithium oxide and lithium nickel cobalt manganese oxide determined by SEM, the particle size shown in the corresponding curve can be corresponded to manganese iron lithium oxide and lithium nickel cobalt manganese oxide, and the particle size of manganese iron lithium oxide and lithium nickel cobalt manganese oxide in the positive electrode active material in the finished battery can be determined.

[0043] In some embodiments, the D of the manganese iron lithium oxide is v50 The range is 0.15 to 10 μm. For example, it can be any one of 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm, 0.45 μm, 0.5 μm, 0.8 μm, 1 μm, 3 μm, 5 μm, 7 μm, and 10 μm, or a range consisting of any two of these values.

[0044] In some embodiments, the D of the manganese iron lithium oxide is v50 0.2~5μm.

[0045] In some embodiments, the D of the manganese iron lithium oxide is v50 It is 0.22~0.9μm.

[0046] In some embodiments, the D of the manganese iron lithium oxide is v50 0.2~0.6μm.

[0047] In some embodiments, the D of the lithium nickel cobalt manganese oxide is v50 The thickness may be 1 to 20 μm. For example, it may be any one of 1 μm, 3 μm, 5 μm, 5.5 μm, 6 μm, 7 μm, 7.3 μm, 7.8 μm, 8 μm, 8.2 μm, 8.7 μm, 9 μm, 9.3 μm, 9.6 μm, 10 μm, 12 μm, 14 μm, 15 μm, 18 μm, and 20 μm, or a range consisting of any two of these values.

[0048] In some embodiments, the D of the lithium nickel cobalt manganese oxide is v50 6~12μm.

[0049] In some embodiments, the D of the lithium nickel cobalt manganese oxide v50 is 6.8 - 10 μm.

[0050] In some embodiments, the D of the lithium nickel cobalt manganese oxide v50 is 6.7 - 9.3 μm.

[0051] In some embodiments, the ratio of D of the lithium nickel cobalt manganese oxide v50 to D of the lithium manganese iron oxide v50 is greater than or equal to 20.

[0052] In some embodiments, the weight percentage ω of the lithium manganese iron oxide in the positive active material is 20 - 50%. If the incorporation amount of the lithium manganese iron oxide is too low, the lithium manganese iron oxide cannot effectively wrap the lithium nickel cobalt manganese oxide, resulting in ineffective improvement of the thermal stability of the manufactured lithium-ion battery; and due to the poor conductivity of the lithium manganese iron oxide itself, too high incorporation amount will reduce the energy density of the manufactured lithium-ion battery. At the same time, with the decrease of the compaction density, the cycle stability of the obtained lithium-ion battery will decline. When the weight percentage of the lithium manganese iron oxide is within this range, the thermal stability, safety and cycle stability of the lithium-ion battery can be taken into account.

[0053] In some embodiments, based on the molar amount of metal elements except lithium, the molar percentage content of nickel element in the lithium nickel cobalt manganese oxide is n1%, satisfying n1 ≥ 80 (that is, the lithium nickel cobalt manganese oxide in the present application belongs to the high-nickel ternary cathode material). The most important role of nickel element is to improve the energy density and enhance the battery's endurance. In some embodiments, the chemical formula of the lithium nickel cobalt manganese oxide satisfies Li 0.95～1.05 Ni x Co y Mn z M 1-x-y-z O 2-m A m , 0.8 ≤ x ≤ 0.9, 0.8 < x + y + z ≤ 1, 0 ≤ m < 2, where M and A are doping elements, M includes at least one of Mg, Ti, Zn, Zr, Nb, Sr, Y, Al, and A includes at least one of N, F, S, Cl.

[0054] The lithium nickel cobalt manganese oxide can be single crystal particles, polycrystalline particles, or a mixture thereof. Among them, polycrystalline particle materials have better ion diffusion performance and thus better cycle stability; while single crystal particle materials have higher voltage and better safety performance. In some embodiments, the lithium nickel cobalt manganese oxide is at least one of 8-series polycrystalline ternary materials, 8-series single crystal ternary materials, 9-series polycrystalline ternary materials or 9-series single crystal ternary materials.

[0055] In some embodiments, at least a portion of the lithium nickel cobalt manganese oxide is a single crystalline particle.

[0056] In the manganese iron lithium oxide, the increase of manganese (Mn) content can make the material's charge and discharge platform higher and its energy density higher. However, in the charged state, Mn3+ will produce strong electron lattice interaction (Jiang-Taylor effect), which will reduce the stability of its crystal structure and reduce its safety performance. On the other hand, Mn 3+ Easy to undergo disproportionation to generate Mn 2+ ions, generated Mn 2+ It is very easy to dissolve in the electrolyte and react with the electrolyte to generate heat; and Mn 2+ It will diffuse to the surface of the negative electrode and be reduced to Mn metal, reducing the negative electrode lithium insertion sites, increasing the risk of diaphragm puncture, and increasing the short circuit rate of the battery in the hot box test. In some embodiments, the molar percentage of manganese content in the manganese iron lithium oxide to the total amount of metal elements other than lithium is n2%, satisfying 50≤n2≤90. In some embodiments, the chemical formula of the manganese iron lithium oxide satisfies Li 0.9～1.1 MnaFe 1-a PO4, where 0.5≤a≤0.9.

[0057] Positive electrode

[0058] The positive electrode sheet in the present application includes a positive electrode active material (lithium nickel cobalt manganese oxide and lithium manganese iron oxide), as well as a binder and a conductive agent. The positive electrode sheet of the present application is prepared by mixing the positive electrode active material, binder, and conductive agent in a solvent to form a positive electrode active slurry, which is then coated on a positive electrode current collector and dried, compacted, slit, and die-cut. In some embodiments, the weight ratio of the components in the positive electrode active slurry is positive electrode active material: binder: conductive agent = (95-99): (1-2): (1.5-2.5).

[0059] Because the particle size of lithium iron manganese oxide is smaller than that of lithium nickel cobalt manganese oxide, the higher the amount of lithium iron manganese oxide incorporated, the higher the amount of binder (such as polyvinylidene fluoride, or PVDF) required in the positive electrode slurry. In some embodiments, the amount of binder in the positive electrode active slurry is 1.0-2.0 wt%.

[0060] Conventional binders, conductive agents, and solvents in the art can be used in this application. In some embodiments, the binder includes commonly used PVDF; the conductive agent includes at least one of conductive carbon black or carbon nanotubes; and the solvent includes NMP (N-methylpyrrolidone).

[0061] In some embodiments, the compacted density of the positive electrode sheet is PD g / cm 3 2.3~3.5g / cm3 range, for example, 2.3 g / cm 3 , 2.4g / cm 3 , 2.5g / cm 3 , 2.6g / cm 3 , 2.7g / cm 3 , 2.8g / cm 3 , 3.0g / cm 3 、3.2g / cm 3 , 3.5g / cm 3 Any value or any two values ​​thereof. Further, it can be 2.6 to 3.0 g / cm 3 The lower the electrode's compaction density, the higher the reactivity between the cathode active material and the electrolyte in the lithium-ion battery, and the lower the safety. On the other hand, if the electrode's compaction density is too high, the electrolyte may not be able to effectively penetrate the cathode, causing cycling problems such as cycling dips. Within this range, the resulting lithium-ion battery exhibits both excellent safety and cycling performance.

[0062] In some embodiments, the compaction density of the positive electrode sheet is calculated by the following formula:

[0063] Positive electrode sheet compaction density = positive electrode sheet surface density / (positive electrode sheet thickness after rolling) positive electrode current collector thickness, unit is g / cm 3 .

[0064] In some embodiments, the compaction density is tested by a compaction density meter, and the testing process can refer to the national standard GB / T24533 2019.

[0065] In some embodiments, the thermal enthalpy value HJ / g of the positive electrode plate is in the range of 240 to 1300 J / g, for example, it can be any value of 240 J / g, 260 J / g, 280 J / g, 300 J / g, 400 J / g, 450 J / g, 500 J / g, 600 J / g, 650 J / g, 700 J / g, 800 J / g, 850 J / g, 900 J / g, 980 J / g, 1000 J / g, or a range consisting of any two of these values. It can further be 500 to 1000 J / g. The thermal enthalpy value reflects the heat released by the plate at high temperature. The higher the value, the lower the thermal stability of the plate. It can be understood that the thermal enthalpy value of the positive electrode plate is related to the composition, compaction density and homogenization process of the positive electrode active material. The thermal enthalpy value can be controlled within the above range by regulating the composition, compaction density and homogenization process of the positive electrode active material in the plate.

[0066] In some embodiments, the positive electrode current collector is aluminum foil. The thickness of the aluminum foil is 10 to 15 μm. Thinner aluminum foil can increase the energy density of lithium-ion batteries, while thinner foil can easily cause processing problems such as wrinkling and curling.

[0067] lithium-ion batteries

[0068] The lithium-ion battery of the present application is assembled by winding the positive electrode sheet, separator, and negative electrode sheet. After assembly, the tabs are welded and then placed in an aluminum-plastic film. The electrolyte is injected into the casing, and then the battery is finally formed through processes such as packaging, static, formation, aging, and shaping.

[0069] Conventional lithium-ion negative electrode sheets, separators, electrolytes, and assembly processes can all be used in this application.

[0070] The negative electrode plate includes a negative electrode active material and a negative electrode current collector. The negative electrode active material includes graphite. The negative electrode current collector is a copper foil, which can be 5 to 8 μm thick.

[0071] The separator includes but is not limited to at least one of polyethylene, polypropylene or polyvinylidene fluoride.

[0072] The electrolyte includes an electrolyte salt and an organic solvent: the electrolyte salt includes but is not limited to at least one of lithium hexafluorophosphate, organic lithium borate, lithium perchlorate, and sulfonimide lithium salts; the organic solvent includes but is not limited to at least one of cyclic carbonate, chain carbonate, and carboxylate.

[0073] The present application provides the following examples to facilitate understanding of the present application. These examples are not intended to limit the scope of the claims.

[0074] Example 1

[0075] This embodiment provides a lithium-ion battery, and the specific preparation process is as follows:

[0076] Preparation of positive electrode

[0077] The chemical formula of lithium manganese iron oxide (LMFP) used in this embodiment is LiMn 0.6 Fe 0.4 PO4, D v50 The lithium nickel cobalt manganese oxide used in this embodiment is an 8-series polycrystalline material with a molar percentage of nickel of 83%, and the chemical formula is LiNi 0.83 Co 0.1 Mn 0.07 O2, D v50 It is 8.3μm.

[0078] S1. Preparation of positive electrode active slurry

[0079] Lithium nickel cobalt manganese oxide, conductive carbon black and adhesive PVDF were added to a mixing tank and pre-mixed for 20 minutes using a planetary mixer. Then, lithium manganese iron oxide was added and stirred for 20 minutes. Then, solvent NMP and carbon nanotubes were added and pre-mixed for 30 minutes, pre-dispersed for 5 minutes, and dispersed for 240 minutes. Finally, the viscosity of the slurry was adjusted to 4000 cps by adding NMP. Finally, the slurry was stored in a vacuum to eliminate bubbles to obtain a positive electrode active slurry.

[0080] Among them, lithium nickel cobalt manganese oxide and lithium manganese iron oxide are positive electrode active materials, and the weight ratio of lithium nickel cobalt manganese oxide and lithium manganese iron oxide is 2:8, that is, the weight proportion of lithium manganese iron oxide in the positive electrode active material is 80%; the weight ratio of each raw material in the positive electrode active slurry is positive electrode active material: conductive carbon black: carbon nanotubes: binder PVDF = 96.5:1.7:0.5:1.3.

[0081] S2. Preparation of positive electrode sheet

[0082] The positive electrode active slurry prepared in step S1 was sieved through a 150-mesh double-layer filter cloth, and then coated on both sides of a 12 μm aluminum foil by transfer coating, and then heated and dried in an oven; the dried electrode was then cold pressed (the compaction density after cold pressing is shown in Table 1), slit, and die-cut to obtain the positive electrode sheet.

[0083] Preparation of negative electrode sheet

[0084] S1. Preparation of negative electrode active slurry

[0085] The negative electrode active material graphite and conductive carbon black were added to a mixing tank and pre-stirred for 15 minutes using a planetary mixer. Deionized water was added and pre-stirred for 10 minutes to knead. After checking the kneading state, full dispersion was performed for 60 minutes. Then, dispersant CMC (carboxymethyl cellulose) and deionized water were added and pre-stirred for 5 minutes, and full dispersion was performed for 60 minutes. Deionized water was added to adjust the slurry viscosity to 3500cps according to the viscosity of the pot. Then, binder SBR (styrene-butadiene rubber) was added and stirred for 15 minutes. After that, deionized water was added to adjust the slurry viscosity to 5000cps according to the viscosity of the pot. Finally, vacuum storage was performed to eliminate bubbles to prepare the negative electrode active slurry.

[0086] The weight ratio of the raw materials in the negative electrode active slurry is negative electrode active material: conductive carbon black: dispersant CMC: binder SBR = 96.5:0.7:1.0:1.8.

[0087] S2. Preparation of negative electrode sheet

[0088] The negative electrode active slurry prepared in step S1 is sieved through a 150-mesh double-layer filter cloth and then transfer-coated on both sides of a 6-μm copper foil. During the coating process, it is heated and dried in an oven. The dried electrode is then cold-pressed, striped, and die-cut to obtain the electrode.

[0089] Lithium-ion battery assembly

[0090] The prepared positive electrode sheets, separators and negative electrode sheets are assembled by stacking, and the tabs are welded after assembly, and then placed in an aluminum-plastic film; the electrolyte is injected into the shell, and then the battery is formed through packaging, standing, formation, aging, shaping and other processes.

[0091] In this example, the diaphragm model is Enjie BP129B, and its composition is a 7μm base film, a 3μm ceramic coating on one side, and a 5μm organic coating on one side. The ceramic coating increases the mechanical strength of the diaphragm, improving the battery's high-temperature resistance and needle puncture resistance. The organic coating, which faces the positive electrode during battery manufacturing, strengthens the adhesion between the positive electrode and the diaphragm, reducing gas escape and reducing electrolyte at the interface.

[0092] In the electrolyte of this embodiment, the organic solvent is ethylene carbonate, the electrolyte is lithium hexafluorophosphate, and the electrolyte concentration is 1M.

[0093] Example 2

[0094] This embodiment provides a lithium-ion battery, which is prepared according to the method of Example 1. The difference from Example 1 is that in the positive electrode active material, the weight ratio of lithium nickel cobalt manganese oxide and lithium manganese iron oxide is 4:6.

[0095] Example 3

[0096] This embodiment provides a lithium-ion battery, which is prepared according to the method of Example 1. The difference from Example 1 is that in the positive electrode active material, the weight ratio of lithium nickel cobalt manganese oxide and lithium manganese iron oxide is 5:5.

[0097] Example 4

[0098] This embodiment provides a lithium-ion battery, which is prepared according to the method of Example 1. The difference from Example 1 is that the weight ratio of lithium nickel cobalt manganese oxide to lithium manganese iron oxide is 6:4.

[0099] Example 5

[0100] This embodiment provides a lithium-ion battery, which is prepared according to the method of Example 1. The difference from Example 1 is that the weight ratio of lithium nickel cobalt manganese oxide to lithium manganese iron oxide is 7:3.

[0101] Example 6

[0102] This embodiment provides a lithium-ion battery, which is prepared according to the method of Example 1. The difference from Example 1 is that the weight ratio of lithium nickel cobalt manganese oxide to lithium manganese iron oxide is 8:2.

[0103] Example 7

[0104] This embodiment provides a lithium ion battery, which is prepared according to the method of embodiment 1. The difference from embodiment 1 is that the chemical formula of lithium manganese iron oxide (LMFP) is LiMn 0.5 Fe 0.5 PO4, D v50 It is 0.29μm.

[0105] Example 8

[0106] This embodiment provides a lithium ion battery, which is prepared according to the method of embodiment 1. The difference from embodiment 1 is that the chemical formula of lithium manganese iron oxide (LMFP) is LiMn 0.9 Fe 0.1 PO4, D v50 It is 0.29μm.

[0107] Example 9

[0108] This embodiment provides a lithium ion battery, which is prepared according to the method of embodiment 1. The difference from embodiment 1 is that the chemical formula of lithium manganese iron oxide (LMFP) is LiMn 0.4 Fe 0.6 PO4, D v50 It is 0.29μm.

[0109] Example 10

[0110] This embodiment provides a lithium ion battery, which is prepared according to the method of embodiment 1. The difference from embodiment 1 is that the lithium nickel cobalt manganese oxide is an 8 series single crystal material, D v50 It is 8.3μm.

[0111] Example 11

[0112] This embodiment provides a lithium-ion battery, which is prepared according to the method of Example 1. The difference from Example 1 is that the lithium nickel cobalt manganese oxide is a mixed lithium nickel cobalt manganese oxide obtained by mixing 8 series single crystal material (the same material as Example 10) and 8 series polycrystalline material (the same as Example 1) in a weight ratio of 1:1.

[0113] Example 12

[0114] This embodiment provides a lithium ion battery, which is prepared according to the method of Example 1. The difference from Example 1 is that the D of lithium manganese iron oxide (LMFP) is v50 0.6μm; D of lithium nickel cobalt manganese oxide v50 9μm.

[0115] Example 13

[0116] This embodiment provides a lithium ion battery, which is prepared according to the method of Example 1. The difference from Example 1 is that the D of lithium manganese iron oxide (LMFP) is v50 0.6μm; D of lithium nickel cobalt manganese oxide v50 is 12μm.

[0117] Example 14

[0118] This embodiment provides a lithium ion battery, which is prepared according to the method of Example 1. The difference from Example 1 is that the D of lithium manganese iron oxide (LMFP) is v50 0.2μm; D of lithium nickel cobalt manganese oxide v50 6μm.

[0119] Comparative Example 1

[0120] This comparative example provides a lithium-ion battery prepared according to the method of Example 1. The difference from Example 1 is that in the positive electrode active material, an equal amount of manganese iron lithium oxide is replaced by lithium nickel cobalt manganese oxide, that is, the positive electrode active material is only lithium nickel cobalt manganese oxide.

[0121] Comparative Example 2

[0122] This comparative example provides a lithium-ion battery, which is prepared according to the method of Example 1. The difference from Example 1 is that the weight ratio of lithium nickel cobalt manganese oxide to lithium manganese iron oxide is 9:1.

[0123] Comparative Example 3

[0124] This comparative example provides a lithium-ion battery, which is prepared according to the method of Example 1. The difference from Example 1 is that the weight ratio of lithium nickel cobalt manganese oxide to lithium manganese iron oxide is 1:9.

[0125] Comparative Example 4

[0126] This comparative example provides a lithium ion battery, which is prepared according to the method of Example 1. The difference from Example 1 is that the compaction density is different. For details, see Table 1.

[0127] The performance of the positive electrode active materials, positive electrode sheets, and lithium-ion batteries obtained in the above examples and comparative examples were tested. The specific test items, test methods, and results are as follows:

[0128] 1) The morphology of the positive electrode active material on the surface of the positive electrode plate was observed using a scanning electron microscope (SEM). Figure 1 shows the surface morphology of the positive electrode plate in the lithium-ion battery of Example 1. As can be seen from Figure 1, manganese iron lithium oxide fills the gaps between the lithium nickel cobalt manganese oxide particles, making the contact between the particles closer.

[0129] 2) Thermal stability and safety test of lithium-ion batteries - hot box test:

[0130] The lithium-ion battery is fully charged to 4.25V at a 0.33C rate and then placed in a hot box for testing. The hot box is heated from room temperature to 50°C at a heating rate of 5°C / min, and then continues to heat at the same heating rate in 5°C gradient intervals until the temperature reaches 200°C. The temperature is maintained at a constant temperature for 30 minutes at each step ambient temperature. The hot box test in this application can be stopped if the following conditions occur: a. The ambient temperature reaches the upper limit temperature of 200°C or above (no destructive events occur); b. A destructive event occurs, such as: battery fire, explosion, etc.

[0131] In the test of this application, a discharge voltage of ≤4V is considered a battery short circuit. When the battery voltage reaches 4V, the hot box heating temperature is the battery short circuit temperature T2 (the higher T2, the better the thermal stability of the battery and the lower the short circuit rate); and when the battery is short-circuited until the end of the test, the highest temperature monitored in the battery is the peak temperature T1 after the battery short circuit (T1 indicates whether thermal runaway has occurred. If thermal runaway occurs, the battery temperature will suddenly increase to over 200°C).

[0132] 3) Cycling stability: Cycling test was conducted at 25°C with a charge / discharge current of 1C / 1C and a charge / discharge voltage range of 2.8-4.25V. Before cycling, the discharge capacity (C1) was measured at a charge / discharge current of 0.33C / 0.33C. Cycling was performed under these conditions, with the discharge capacity after t cycles being recorded as Ct. The capacity retention (%) of the battery after t cycles was calculated as Ct / C1*100%. The maximum number of cycles at which the capacity retention remained above 80% was recorded.

[0133] In the lithium-ion batteries of the above embodiments and comparative examples of this application, the relevant performance parameters of the lithium-ion batteries are shown in Table 1:

[0134] Table 1 Relevant performance parameters of lithium-ion batteries

[0135] From the above results we can see that:

[0136] Comparison of the thermal abuse curves of Example 6 (Figure 2) and Comparative Example 1 (Figure 3) shows that the 8-series ternary battery without manganese iron lithium oxide (Comparative Example 1) experienced thermal runaway at around 152°C, with a sharp rise in battery temperature and fire. At this point, the R value was less than 0.5. In contrast, the battery with only 20% manganese iron lithium oxide (Example 6) did not experience thermal runaway even up to 200°C. This demonstrates that the incorporation of manganese iron lithium oxide can effectively enhance the thermal stability of high-nickel 8-series ternary cathode materials and prevent thermal runaway.

[0137] The results of Examples 1-14 and Comparative Examples 1-4 of the present application also show that when the R value is in the range of 0.5 to 4, it can be ensured that the lithium-ion battery will not experience thermal runaway in the hot box (at least within 200°C), and a higher content of manganese iron lithium oxide can be mixed and doped in the high-nickel ternary positive electrode material.

[0138] 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 scope of protection of the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present application.

Claims

1. A lithium-ion battery, comprising a positive electrode sheet and a negative electrode sheet, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode active layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode active layer comprises a positive electrode active material, characterized in that: The positive electrode active material includes lithium nickel cobalt manganese oxide and lithium manganese iron oxide, and the positive electrode plate satisfies: 0.5≤R≤4; Where R = 10 × ω × PD / ln (H), ω is the weight ratio of manganese iron lithium oxide in the positive electrode active material; PD g / cm 3 is the compaction density of the positive electrode sheet; HJ / g is the thermal enthalpy value of the positive electrode plate at 100% state of charge (SOC) of the battery.

2. The lithium ion battery according to claim 1, wherein The positive electrode plate satisfies: 1≤R≤3.

3. The lithium ion battery according to claim 1, wherein The weight proportion ω of manganese iron lithium oxide in the positive electrode active material is 20% to 80%.

4. The lithium ion battery according to claim 3, wherein: The weight proportion ω of manganese iron lithium oxide in the positive electrode active material is 20% to 50%.

5. The lithium ion battery according to claim 1, wherein: The compaction density of the positive electrode sheet is PD g / cm 3 2.3~3.5g / cm 3 .

6. The lithium ion battery according to claim 5, wherein: The compaction density of the positive electrode sheet is PD g / cm 3 2.6~3.0g / cm 3 .

7. The lithium ion battery according to claim 1, wherein: The thermal enthalpy value HJ / g of the positive electrode plate at 100% SOC of the battery is 240 to 1300 J / g.

8. The lithium ion battery according to claim 7, wherein: The thermal enthalpy value HJ / g of the positive electrode plate at 100% SOC of the battery is 500-1000 J / g.

9. The lithium ion battery according to any one of claims 1 to 8, wherein: In the lithium nickel cobalt manganese oxide, based on the molar amount of metal elements other than lithium, the molar percentage of the nickel element is n1%, and n1≥80 is satisfied.

10. The lithium ion battery according to any one of claims 1 to 8, wherein: In the manganese iron lithium oxide, the molar percentage of manganese element in the total amount of metal elements except lithium is n2%, satisfying 50≤n2≤90.

11. The lithium ion battery according to any one of claims 1 to 8, wherein: The lithium nickel cobalt manganese oxide D v50 Greater than the D of the manganese iron lithium oxide v50 .

12. The lithium ion battery according to any one of claims 1 to 8, wherein: At least a portion of the lithium nickel cobalt manganese oxide is a single crystal particle.

13. The lithium ion battery according to any one of claims 1 to 8, wherein: The lithium nickel cobalt manganese oxide includes single crystal particles, polycrystalline particles, or a mixture thereof.

14. The lithium ion battery according to claim 11, wherein: The D v50 is 0.15 to 10 μm, and the D v50 1~20μm.

15. The lithium ion battery according to claim 11, wherein: The lithium nickel cobalt manganese oxide D v50 With the manganese iron lithium oxide D v50 The ratio is greater than or equal to 20.

16. The lithium ion battery according to any one of claims 1 to 8, wherein: The chemical formula of the lithium nickel cobalt manganese oxide satisfies Li 0.95～1.05 Ni x Co y Mn z M 1-x-y-z O 2-m A m , 0.8 ≤ x ≤ 0.9, 0.8 < x + y + z ≤ 1, 0 ≤ m < 2, where M includes at least one of Mg, Ti, Zn, Zr, Nb, Sr, Y, Al, and A includes at least one of N, F, S, Cl.

17. The lithium ion battery according to any one of claims 1 to 8, wherein: The chemical formula of the manganese iron lithium oxide satisfies Li 0.9～1.1 Mn a Fe 1-a PO4, where 0.5≤a≤0.

9.

18. An electrical device comprising the lithium ion battery according to any one of claims 1 to 17.

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