A lithium battery and a powered vehicle

Abstract

This application provides a lithium battery and a power vehicle. The lithium battery combines lithium transition metal oxide with LiFe... 1‑a Mn a PO4 material is used as the positive electrode active material, and LiFe is added. 1‑a Mn a The mass ratio of PO4 material is related to the content of vinylene carbonate in the battery electrolyte, the discharge capacity and DC internal resistance of the battery at 0.33C discharge at 25℃, and the content of Fe dissolved into the negative electrode material after high-temperature cycling. These factors are then made to meet certain conditions to ensure that the battery can achieve both good low-temperature rate performance at 0℃ and high-temperature cycling performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a lithium battery and a power vehicle. BACKGROUND

[0002] Lithium ion batteries have been widely used in portable electronic devices (such as mobile phones, tablets, etc.), new energy vehicles and other fields. Among them, positive active materials such as lithium iron phosphate (LFP) and lithium manganese iron phosphate (LMFP) are more widely used in new energy vehicles due to their high safety and low cost.

[0003] However, in the actual preparation and long cycle process of the battery, a certain amount of moisture will inevitably exist in the electrolyte, which will cause the hydrolysis of fluorine-containing lithium salt in the electrolyte to generate HF, and HF will attack the solid electrolyte interface (SEI film) on the surface of the negative electrode, as well as LFP, LMFP, etc., so that the self-discharge degree of the battery is high and the high-temperature cycle performance is reduced. Most of the existing technologies are to increase the concentration of negative electrode film-forming additives in the electrolyte to ensure that there is enough film-forming additive to repair the damaged SEI film, thereby prolonging the cycle life, but excessive increase of the concentration of film-forming additives will cause the internal resistance of the battery to rise, resulting in poor low-temperature rate performance of the battery.

[0004] Therefore, how to control the battery to simultaneously consider good high-temperature cycle performance and low-temperature rate performance is a problem to be solved at present. SUMMARY

[0005] In view of this, the present application mixes lithium transition metal oxide with LiFe 1-a Mn a PO4 material, and establishes a connection with the VC content in the electrolyte, the direct current internal resistance of the battery, the Fe content in the negative electrode material after a certain number of high-temperature cycles, and controls them to meet certain conditions to ensure that the battery considers good high-temperature cycle performance and 0℃ low-temperature rate performance.

[0006] In a first aspect, the present application provides a lithium battery, comprising a positive electrode sheet, a negative electrode sheet and an electrolyte, the positive electrode sheet comprising a positive electrode current collector and a positive electrode material layer arranged on at least one side surface of the positive electrode current collector, wherein the positive electrode active material contained in the positive electrode material layer comprises LiFe 1-a Mn a PO4 material and lithium transition metal oxide, the mass of the LiFe 1-a Mn a PO4 material accounts for the mass of the LiFe 1-a Mn aX1% of the sum of the mass of the LiFePO4 material and the lithium transition metal oxide, 0X1<100, 0≤a≤0.8; the electrolyte contains vinylene carbonate (VC) with a mass percentage of A%;

[0007] The lithium battery satisfies: 0<100α / X1≤600, 0≤DCIR×C0×A×X1≤30;

[0008] Wherein, C0 is the discharge capacity of the lithium battery at 25°C under 0.33C discharge, with the unit of Ah; DCIR is the direct current internal resistance of the lithium battery measured based on the C0, with the unit of Ω; α is the Fe content in the negative electrode material of the negative electrode sheet of the lithium battery after 500 cycles at 1C0 at 45°C, with the unit of ppm.

[0009] The present application takes LiFePO4 material and lithium transition metal oxide as the positive electrode active material of the lithium battery. 1-a Mn a The LiFePO4 material and the lithium transition metal oxide are used together as the positive electrode active material of the lithium battery, and the residual moisture of the electrolyte can be pre-absorbed by the good water absorption of the lithium transition metal oxide, so as to reduce the damage probability of the SEI film, and the LiFePO4 material and the lithium transition metal oxide can be used together. 1-a Mn a The LiFePO4 material and the lithium transition metal oxide are used together as the positive electrode active material of the lithium battery, and the residual moisture of the electrolyte can be pre-absorbed by the good water absorption of the lithium transition metal oxide, so as to reduce the damage probability of the SEI film, and the LiFePO4 material and the lithium transition metal oxide can be used together. 1-a Mn a The mass percentage X1% of the LiFePO4 material and the lithium transition metal oxide, the mass content A% of the VC in the electrolyte, the discharge capacity C0 of the battery at 25°C under 0.33C discharge, the direct current internal resistance DCIR of the battery, and the Fe content α in the negative electrode material of the battery after 500 cycles at 1C0 at 45°C are related, 100α / X1 is controlled in the range of (0, 600], and DCIR×C0×A×X1 is controlled in the range of [0, 30], so as to ensure that the battery has good high-temperature 45°C cycle performance and low-temperature rate performance at 0°C.

[0010] In the second aspect, the present application further provides a power vehicle with the lithium battery of the first aspect of the present application.

[0011] Since the above lithium battery can have good high-temperature cycle performance and low-temperature rate performance at 0°C, the market competitiveness of the power vehicle is outstanding. DETAILED DESCRIPTION

[0012] The present application provides a lithium battery, which comprises a positive electrode sheet, a negative electrode sheet and an electrolyte, the positive electrode sheet comprises a positive electrode current collector and a positive electrode material layer arranged on at least one side surface of the positive electrode current collector, wherein the positive electrode active material contained in the positive electrode material layer comprises LiFePO4 material and lithium transition metal oxide. 1-a Mn a PO4 material and lithium transition metal oxide, LiFe1- a Mn a PO4 material accounts for the mass of the LiFe 1-a Mn a PO4 material and the lithium transition metal oxide is X1%, 0X1<100, 0≤a≤0.8; the electrolyte contains vinylene carbonate (VC) with a mass percentage of A%;

[0013] The lithium battery satisfies: 0<100α / X1≤600, 0≤DCIR×C0×A×X1≤30,

[0014] Wherein, C0 is the discharge capacity of the lithium battery at 25°C with 0.33C discharge, unit: Ah; DCIR is the direct current resistance of the lithium battery measured based on C0, unit: Ω; α is the Fe content in the negative electrode material of the negative electrode sheet after the lithium battery is cycled at 1C0 for 500 times at 45°C, unit: ppm.

[0015] The lithium transition metal oxide and the LiFe 1-a Mn a PO4 material are used together as the positive electrode active material of the lithium battery. Firstly, the lithium transition metal oxide is alkaline and has good water absorption, which can absorb the residual water in the electrolyte, reduce the chance of hydrolysis of the fluorine-containing electrolyte salt in the electrolyte to produce HF, and make the LiFe 1-a Mn a PO4 material and the SEI film less likely to be attacked by HF, thereby reducing the self-discharge degree of the battery cell and improving the high-temperature cycle performance. Secondly, the mass percentage of the lithium transition metal oxide in the sum of the LiFe 1-a Mn a PO4 material and the lithium transition metal oxide is indirectly related to the mass content A% of VC in the electrolyte, the discharge capacity C0 and the direct current resistance DCIR of the battery at 0.33C discharge, and the Fe content in the negative electrode material after the battery is cycled at 45°C for a certain number of times, and controls 100α / X1 in the range of (0, 600] and DCIR×C0×A×X1 in the range of 0-30, so as to ensure that the battery has good high-temperature cycle performance and low-temperature rate performance at 0°C.

[0016] For the convenience of expression, 100α / X1 is represented by the letter X and DCIR×C0×A×X1 is represented by the letter Y. Wherein, X=α / (X1 / 100), X reflects the comprehensive influence of the addition of lithium transition metal oxide to the positive electrode of the battery on the high-temperature cycle performance of the battery. Wherein, controlling X not to exceed 600 can to some extent reflect that the negative electrode of the battery forms a SEI film with complete structure, and ensure that the high-temperature cycle life of the battery will not be too low.

[0017] Y=DCIRxC0xA*X1, Y represents the comprehensive influence degree of the lithium transition metal oxide on the low-temperature rate performance of the lithium battery (especially the 0°C low-temperature discharge rate). Wherein, Y is in the range of 0-30, which can ensure that the internal resistance of the battery at 0°C is low, so that the discharge capacity at 0°C is high and the rate performance is good.

[0018] The above lithium battery provided by the embodiments of the present application can balance the good high-temperature cycle performance and the 0°C low-temperature rate performance when meeting the above requirements, and can provide a quantitative controllable means for manufacturing a battery with excellent comprehensive performance.

[0019] In some embodiments of the present application, X can be in the range of 1-590, and further can be in the range of 20-540. In this way, the high-temperature cycle life of the battery can be ensured to be higher, while the 0°C low-temperature rate performance of the battery is better, and the safety performance is better. Specifically, X can be 25, 30, 40, 50, 70, 80, 100, 120, 150, 180, 200, 250, 300, 350, 380, 400, 450, 480, 500, 520 or 530, etc. In some embodiments, X can be in the range of 50-530, and further can be in the range of 70-500.

[0020] Specifically, the above Y can be 0.01, 0.05, 0.1, 0.2, 0.5, 1, 2, 3, 5, 8, 9, 10, 15, 20, 23, 25, 28 or 29, etc. When Y is greater than 0, it is more conducive to ensuring that the 0°C low-temperature internal resistance of the battery is low. In some embodiments of the present application, Y can be in the range of 0.01-24, and further Y can be in the range of 0.1-24. In other embodiments, Y is in the range of 0.5-24. In this case, the 0°C low-temperature rate performance of the lithium battery is more excellent.

[0021] In the embodiments of the present application, the product of the above DCIR and C0 (i.e. DCIRxC0) is less than or equal to 0.22Ω Ah. In this way, the 0°C low-temperature rate performance of the above lithium battery can be better ensured, for example, the ratio of the discharge capacity of the battery at 0°C after 3 times of 0.33C charge-discharge to the discharge capacity at 25°C after 3 times of 0.33C charge-discharge can be above 81%, preferably above 83%.

[0022] In the embodiments of the present application, the capacity retention rate of the above lithium battery after 500 times of 1C0 cycle at 45°C can be above 85%, and further can be above 90%.

[0023] Among the above parameters, C0, DCIR, and A are measured for a lithium battery in a full package form. The lithium battery has no particular limitation on shape, and can be square, cylindrical, etc. Among them, the above C0 can specifically refer to the discharge capacity of the lithium battery at 25°C at 0.33C discharge, and C0 can be referred to as the rated discharge capacity of the lithium battery at normal temperature. The specific test method of C0, DCIR, and A can be referred to the description hereinafter of the present application.

[0024] The mass percentage A% of VC in the electrolyte of the lithium battery can be obtained by analyzing and determining the composition of the electrolyte after disassembling the lithium battery. In some embodiments of the present application, the above A can be in the range of 0-2. A lower content of A helps to maintain the better 0°C low-temperature rate performance of the above battery. In some embodiments, A can be 0.01-2, for example, specifically 0.05, 0.1, 0.2, 0.3, 0.5, 1.0, 1.2, 1.5, 1.6, 1.8, or 1.9, etc.

[0025] LiFe 1-a Mn a PO4 material. The above mass percentage X1% of the LiFe

[0026] In the present application, the LiFe 1-a Mn a PO4 material. The mass percentage X1% of the LiFe 1-a Mn a PO4 material and the lithium transition metal oxide is the sum of the mass of the LiFe 1-a Mn a PO4 material and the lithium transition metal oxide is the sum of the mass of the LiFe 1- a Mn a PO4 material, the lithium transition metal oxide, and other active materials.

[0027] In some embodiments of the present application, the above X1 is in the range of 50-95. Correspondingly, X2 is in the range of 5-50. The introduction of the lithium transition metal oxide in an appropriate proportion can ensure that the LiFe 1-a Mn a PO4 material. In the case that the residual moisture in the battery electrolyte of the LiFe

[0028] In the present application, when a = 0, the general formula is LiFe 1-a Mn aThe material of LiFePO4 is specifically lithium iron phosphate material (abbreviated as LFP); when a>0, the material is specifically lithium manganese iron phosphate material (abbreviated as LMFP), where a≤0.8, which is beneficial to ensure the stability of the structure of the lithium manganese iron phosphate material. Generally, LiFePO4 1-a Mn a The particle size of the LiFePO4 material is smaller than that of the ternary material. In addition, the LiFePO4 1-a Mn a The LiFePO4 material can also contain a doping element (for example, at least one of Ti, Zr, V, Cr, Al) to improve its rate performance. Further, the LiFePO4 1-a Mn a The surface of the LiFePO4 material can also have a conductive coating layer (such as a conductive carbon layer) to improve its conductivity.

[0029] In this application, the lithium transition metal oxide is an oxide containing lithium element and transition metal element. The type of transition metal element contained in the lithium transition metal oxide can be one or more. In addition, the lithium transition metal oxide can also include other metal elements (such as main group metal elements) in addition to transition metal elements.

[0030] In some embodiments of the present application, the lithium transition metal oxide includes LiNi x Co y M 3 z O2, where x≥0, y≥0, z≥0, x+y+z=1; M 3 Mn, Al, Mg, Sr, V, Fe, Cr, Ni, Cu, Zn, Zr, Ti, Y, and W, and when M 3 When M is at least one of main group metal elements Al, Mg, and Sr, x and y are not both 0. Preferably, 0 3 Mn, and Al.

[0031] In the present application, the positive electrode material layer can be disposed on one side surface or opposite two side surfaces of the positive electrode current collector. The positive electrode material layer contains, in addition to the positive electrode active material, a binder and a conductive agent. Among them, the types and contents of the binder and the conductive agent are conventional choices in the battery field. Exemplarily, the binder can be selected from one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl alcohol (PVA), polyacrylonitrile (PAN), polyimide (PI), polyacrylic acid (PAA), polyacrylate, polyolefins (such as polyethylene, polypropylene, polystyrene), styrene butadiene rubber (SBR), sodium carboxymethyl cellulose (CMC), sodium alginate, etc. The conductive agent can be selected from at least one of conductive carbon black (such as acetylene black, ketjen black), carbon nanotubes (CNT), graphene, carbon fiber, graphite, etc., but is not limited thereto. In addition, the positive electrode current collector can include, but is not limited to, a metal film material, a foamed metal mesh, etc., and for example, can be specifically an aluminum foil, an aluminum foil with a conductive layer on the surface (carbon-coated aluminum foil), etc. The solvent in the positive electrode slurry used to form the positive electrode material layer can be selected from one or more of N-methyl pyrrolidone (NMP), dimethylformamide (DMF), diethylformamide (DEF), water, and alcohols, and preferably, the solvent includes NMP. The content of the solvent in the positive electrode slurry is not particularly limited, and can be sufficient to satisfy the flowability and uniformity of the positive electrode slurry coating.

[0032] The present application does not limit the area density and compaction of the above-mentioned positive electrode sheet, and can be designed according to the specific electrochemical system. In some embodiments, the positive electrode sheet of the present application is a double-sided positive electrode sheet with an area density of 300-500 g / m 2 , and the compaction density thereof can be 2.40-3.3 g / cm 3 .

[0033] In the present application, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one side surface of the negative electrode current collector, and the negative electrode active material layer contains a negative electrode active material, a binder, and optionally a conductive agent. Among them, the negative electrode active material can include, but is not limited to, one or more of carbon materials, silicon-based materials, tin-based materials, and lithium titanate. Among them, the carbon material includes one or more of soft carbon, hard carbon, graphitized carbon microspheres, and graphite (such as natural graphite or artificial graphite). The silicon-based material can include one or more of elemental silicon, silicon alloy, silicon oxide, silicon-carbon composite material, and silicon carbide. The tin-based material can include one or more of elemental tin, tin oxide, tin-based alloy, and tin-carbon compound. In some embodiments, the negative electrode active material includes graphite, and specifically can be natural graphite or artificial graphite. Similarly, the binder and the conductive agent in the negative electrode active material layer can be selected from the ranges described above for the positive electrode sheet. The negative electrode current collector can include, but is not limited to, a metal film material, a foamed metal mesh, etc., and for example, can be specifically a copper foil, a carbon-coated copper foil, etc.

[0034] The electrolyte of the present application contains electrolyte lithium salt, organic solvent and film-forming additive. The film-forming additive at least includes vinylene carbonate (VC). In some embodiments, the film-forming additive can also include at least one of vinyl ethylene carbonate (VEC), phenyl ethylene carbonate (PhEC), phenyl vinyl carbonate (PhVC), fluoroethylene carbonate (FEC) and the like. The organic solvent can include one or more of carbonate solvents, carboxylate solvents. The carboxylate solvent can include cyclic carbonate and / or linear carbonate. The specific composition of the electrolyte in the present application is not limited, which can be the conventional selection in the field of batteries. Generally, the injection coefficient of the electrolyte is generally 2.0-4.5 g / Ah.

[0035] The separator is used to separate the positive electrode sheet and the negative electrode sheet to maintain the insulation and liquid retention properties between the two; the separator and the positive electrode sheet and the negative electrode sheet together constitute the battery cell, which is accommodated in the battery shell (such as aluminum plastic film), and the electrolyte is injected into the battery shell. The separator of the present application is not particularly limited, which can be various separators commonly used in lithium batteries, including but not limited to single-layer PP (polypropylene) film, single-layer PE (polyethylene) film, double-layer PP / PE, double-layer PP / PP and triple-layer PP / PE / PP and the like.

[0036] The present application also provides a power vehicle which can be provided with the above-mentioned lithium battery of the present application. Since the above-mentioned lithium battery is used, it can provide the power vehicle with persistent power at low temperature, so that the vehicle has long endurance mileage and high safety.

[0037] Since the power vehicle uses the above-mentioned lithium battery which can balance good high-temperature cycle performance and low-temperature rate performance, the battery can provide the power vehicle with persistent power at high temperature and low temperature, so that the power vehicle has long endurance mileage, good charge-discharge resistance and high safety, and the market competitiveness of the power vehicle is outstanding.

[0038] The technical solutions of the present application will be further described below in combination with a plurality of specific embodiments.

[0039] Embodiment 1

[0040] A preparation method of a lithium battery, comprising:

[0041] (1) preparing a positive electrode sheet:

[0042] Preparation of the positive electrode slurry: the positive electrode active material, carbon nanotube CNT conductive agent and carbon black SP conductive agent, binder PVDF and solvent NMP were mixed in a mass ratio of 100:12:0.3:2.5:55, and after uniform dispersion, the positive electrode slurry was obtained. Among them, the positive electrode active material is specifically a mixture of lithium iron phosphate (LiFePO4, abbreviated as LFP) and lithium transition metal oxide (specifically single-crystal lithium nickel cobalt manganese oxide, abbreviated as NCM, and its structure general formula is LiNi 0.7 Co 0.1 Mn 0.2 O2); wherein the particle size D50 of the LFP is 0.8-1.4 μm, and the gram capacity is 142 mAh / g; the particle size D50 of the NCM is 3.5-5 μm, and the gram capacity is 189 mAh / g.

[0043] The aluminum foil with a thickness of 12 μm was used as the positive electrode current collector, and the above-mentioned positive electrode slurry was coated on one side surface of the aluminum foil, and after drying, a positive electrode material layer was formed; then, in the same way, the positive electrode slurry was coated on the other side surface of the aluminum foil to form a positive electrode material layer, and a double-sided positive electrode sheet was obtained; and the double-sided positive electrode sheet was rolled, cut and die-cut to obtain a to-be-used positive electrode sheet with a double-sided area density of about 400 g / m 2 .

[0044] (2) Preparation of the negative electrode sheet:

[0045] The natural graphite with a first gram capacity of 355 mAh / g was mixed with the binder CMC, the binder SBR and water in a mass ratio of 100:1.5:3:130 to obtain a negative electrode slurry; the negative electrode slurry was uniformly coated on both side surfaces of a copper foil with a thickness of 8 μm, and after baking at 110°C to remove water, a negative electrode active material layer was formed on both sides of the copper foil, and then the negative electrode sheet was rolled, cut and die-cut to obtain a double-sided negative electrode sheet.

[0046] (3) Assembly of the full battery:

[0047] The above-mentioned double-sided positive electrode sheet, PP separator and negative electrode sheet were stacked in a Z-shaped manner to form a one-directional cell, and the cell after heat pressing was accommodated in a battery shell, and a VC-containing electrolyte (the electrolyte contained common lithium salt LiPF6, common organic solvent and VC, and the initial VC content in the electrolyte was as shown in Table 1) was injected into the cell under vacuum according to an injection coefficient of 3.5 g / Ah, and then the shell was sealed, and after high-temperature aging, formation, aging and capacity grading, a square soft package battery with a length of 80 mm, a width of 60 mm and a height of 7 mm was obtained.

[0048] The full battery of Example 1 was subjected to the following performance tests. The related results are also summarized in Table 1 below.

[0049] a) Discharge capacity test of the battery at 25 °C at 0.33C: at 25 °C, the full battery is charged at 0.33C constant current and constant voltage to 4.2V, and after 30min of rest; then discharged at 0.33C constant current to 2.0V, and after 30min of rest; repeat the above charge and discharge steps for 3 times, and the capacity discharged in the 3rd time is recorded as C0, unit is Ah.

[0050] b) DCIR test: at 25 °C, charge to 0.5C0 cutoff current, and record the battery voltage V1 at the end of the rest; then discharge at 1.5C0 for 30s, and record the battery voltage V2 at the end of the discharge, wherein DCIR = (V1-V2) / 1.5C0, unit is Ω. Then DCIRxC0 = (V1-V2) / 1.5, unit is Ω Ah.

[0051] c) High temperature 45 °C cycle performance test: at 45 °C, the battery is charged at 1C0 constant current and constant voltage to 4.2V, and the cutoff current is 0.05C0, and then rests for 30min; then discharged at 1C0 constant current to 2.0V, and then rests for 30min. The above steps are cycled for 500 times, and the ratio of the capacity after 500 cycles at 45 °C to the first discharge capacity at 45 °C is the cycle capacity retention rate β.

[0052] d) 0 °C low temperature discharge ratio test: after the battery is rested at 0 °C for 4h, it is charged and discharged at 0.33C for 3 times, voltage range 2.0-4.2V, and the battery is rested for 30min during the charging and discharging process. The ratio of the 3rd discharge capacity C’ to the aforementioned C0 is the 0 °C low temperature discharge ratio γ of the battery. In other words, γ is the ratio of the discharge capacity of the lithium battery after 3 times of charging and discharging at 0 °C at 0.33C to the discharge capacity after 3 times of charging and discharging at 25 °C at 0.33C.

[0053] e) Test method of negative electrode Fe content: at 45 °C, the battery is charged at 1C0 constant current and constant voltage to 4.2V, and the cutoff current is 0.05C0, and then rests for 30min; then discharged at 1C0 constant current to 2.0V, and then rests for 30min. The above steps are cycled for 500 times, and the battery is disassembled and the negative electrode sheet is taken out, which is immersed in solvent dimethyl carbonate (DMC) for 10 minutes, repeated twice, and then the powder is scraped off after the negative electrode sheet is dried. The collected powder material is measured for Fe content by inductively coupled plasma spectrometer (ICP) to obtain the Fe content in the negative electrode material of the negative electrode sheet as α ppm.

[0054] f) Test the composition of the positive active material in the positive electrode tab of the disassembled battery: disassemble the above-mentioned batteries and take out the positive electrode tab, scrape off the powder, and use inductively coupled plasma spectrometer (ICP) to analyze the composition of the collected powder material, and it is found that the positive active material in the positive electrode tab is a mixture of LFP with a mass ratio of X1% and lithium transition metal oxide with a mass ratio of X2%. Wherein X1+X2=100, the specific value of X1 is listed in Table 1.

[0055] g) The content of VC in the electrolyte measured from the disassembled battery: at 25°C, inject a suitable solvent (in this application, EP (specifically ethyl propionate)) into the battery cell; seal the battery cell after injecting EP, then shake it on a swing instrument for 24h to fully soak the electrode tab, then disassemble the battery cell, take out the liquid and test it using gas chromatography-mass spectrometry (GC-MS) to measure the composition and content of the solvent and additives in the electrolyte. Among them, the mass ratio of VC in the electrolyte is A%.

[0056] In addition, according to the parameters listed in Table 1, the positive electrode tab and lithium battery of the remaining examples and comparative examples are prepared, and the relevant test results are also summarized in Table 1 below. Among them, the lithium transition metal oxide in examples 2-13 and comparative examples 4-6 is NCM, which is the same as example 1. The lithium transition metal oxide used in example 14 is lithium nickelate (LiNiO2, abbreviated as LNO), and the lithium transition metal oxide used in example 15 is lithium cobaltate (LiCoO2, abbreviated as LCO).

[0057] Table 1: Partial parameters and test results of each example and comparative example

[0058]

[0059] As can be seen by comparing Examples 1-4 with Comparative Example 1 in Table 1, the VC contents in the electrolytes of these disassembled batteries are close and are all low, and the DCIRxC0 values are close and are low. Since the positive electrode active materials in Comparative Example 1 are all LFP materials with poor low-temperature performance (i.e., X2 is 0), although the Y value is within the range of [0, 30] claimed in the present application, the low-temperature discharge ratio γ of the battery at 0°C is still lower than that of Examples 1-4. In addition, since the X value of Comparative Example 1 is not within the range of (0, 600] claimed in the present application, the capacity retention β of the battery of Comparative Example 1 after 500 cycles at high temperature 45°C is significantly lower than that of Examples 1-4. Although the positive electrode of Comparative Example 6 also contains alkaline NCM, and the Y value of the battery is within the range of [0, 30] claimed in the present application, the X value is greater than 600, which is outside the range claimed in the present application, so the low-temperature discharge ratio and high-temperature cycle performance of the battery are still lower than those of Examples 1-4. Similarly, the comparison of Comparative Example 2 with Examples 5, 9, and 14, which have close DCIRxC0 values, also has similar results as the comparison between Examples 1-4 and Comparative Example 1 described above. In addition, the low-temperature performance of the battery of Comparative Example 3, which has an X value within the range claimed in the present application and a Y value not within the range claimed in the present application, is very poor, and cannot balance good 0°C low-temperature discharge performance and high-temperature cycle performance.

[0060] As can be seen by comparing Examples 3, 5, and 10 with Comparative Example 5, in the case where the above-mentioned mass ratio X2 of alkaline NCM in the positive electrode active material is the same, the X value of the battery of Comparative Example 5 is within the range of (0, 600] claimed in the present application, but the Y value does not satisfy not more than 30, and thus the 0°C low-temperature discharge ratio γ of the battery is low. The comparison between Example 1 and Comparative Example 4, which have the same X2, also has similar results. The comparison between Example 13 and Comparative Example 6, which have the same X2, also has similar results.

[0061] In addition, as can be seen by comparing Examples 1 and 6, in the case where the above-mentioned mass ratio X2 of NCM is the same, the VC concentration in the electrolyte of the battery of Example 6 is lower than that of Example 1, and is as low as 0, but the X and Y values of Example 6 are still within the range claimed in the present application, the 45°C cycle capacity retention of the battery can still be maintained near 90%, and the low-temperature discharge capacity is slightly improved, so the comprehensive performance of the battery is still good. In addition, the comparison of Examples 6 and 7 with Example 1 can also show that when Y is within the range of 0.11 to 24, the 45°C cycle performance and 0°C low-temperature discharge performance of the lithium battery are more excellent.

[0062] The lithium batteries of other Examples 8-13 of the present application, which have different X and Y values, can also balance good 45°C high-temperature cycle performance and 0°C low-temperature rate performance, and in particular, the 0°C low-temperature discharge performance of these batteries is better than that of Comparative Examples 1-6. The batteries of Examples 14-15, in which the type of lithium transition metal oxide is changed, can also balance the above-mentioned high-temperature cycle performance and 0°C low-temperature rate performance well.

[0063] From the above analysis, the lithium battery provided by the embodiment of the present application introduces lithium transition metal oxide as a supplement of lithium-containing phosphate positive electrode material, and controls the mass ratio of lithium transition metal oxide and the VC content in the electrolyte to establish a connection, so that the aforementioned defined parameters X are in the range of (0, 600] and Y are in the range of [0, 30], which can ensure that the battery has good high-temperature cycle performance and 0℃ low-temperature rate performance.

[0064] The above-described embodiments only express several embodiments of the present application, which are described in detail and specifically, but should not be understood as a limitation on the scope of the patent of the present application. It should be pointed out that for ordinary skilled persons in the art, several modifications and improvements can be made without departing from the concept of the present application, which all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A lithium battery comprising a positive electrode sheet, a negative electrode sheet, and an electrolyte, the positive electrode sheet comprising a positive electrode current collector and a positive electrode material layer provided on at least one side surface of the positive electrode current collector, characterized in that, The positive electrode active material contained in the positive electrode material layer includes LiFe 1-a Mn a PO4 material and a lithium transition metal oxide, the mass of the LiFe 1-a Mn a PO4 material accounts for X1% of the total mass of the LiFe 1-a Mn a PO4 material and the lithium transition metal oxide, 0X1<100, 0≤a≤0.8; the electrolyte contains vinylene carbonate with a mass ratio of A%; The lithium battery satisfies: 0 < 100a / X1≤ 600, 0≤ DCIR×C0×A×X1≤ 30, Wherein, C0 is the discharge capacity of the lithium battery at 25℃ with 0.33C discharge, unit Ah; DCIR is the direct current internal resistance of the lithium battery measured based on the C0, unit Ω; a is the Fe content in the negative electrode material of the negative electrode sheet of the lithium battery after 500 times of 1C0 cycle at 45℃, unit ppm.

2. The lithium battery of claim 1, wherein, 0.01≤ DCIR×C0×A×X1≤ 24.

3. The lithium battery of claim 1, wherein the lithium metal anode is a lithium foil anode. 20≤100α / X1≤540。 4. The lithium battery of claim 1, wherein the lithium metal anode is a lithium foil anode. The A is in the range of 0-2.

5. The lithium battery of claim 1, wherein the lithium metal anode is a lithium foil anode. The product of the DCIR and the C0 is less than or equal to 0.22Ω Ah.

6. The lithium battery of claim 1, wherein, The X1 is in the range of 50-95.

7. The lithium battery according to any one of claims 1-6, characterized in that, The LiFe 1-a Mn a The surface of the LiFePO4 material also has a conductive coating layer.

8. The lithium battery according to any one of claims 1-6, characterized in that, LiNi x Co y M 3 z O2, wherein x > 0, y > 0, z > 0, x + y + z = 1; M 3 is selected from one or more of Mn, Al, Mg, Sr, V, Fe, Cr, Ni, Cu, Zn, Zr, Ti, Y, and W, and when M 3 x and y are not simultaneously 0 when M is Al, Mg, Sr.

9. The lithium battery of claim 8, wherein the lithium metal anode is a lithium foil anode. 0.33≤ x≤ 0.98, 0 < y < 1.

10. A powered vehicle characterized by The power vehicle is provided with the lithium battery as claimed in any one of claims 1-9.

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