Battery and power consuming device

Abstract

This invention relates to the field of battery technology, specifically to a battery and an electrical device. The provided battery includes: a cell unit, the cell unit comprising a positive electrode sheet arranged sequentially; the positive electrode sheet comprising a positive electrode active material, the positive electrode active material comprising lithium iron phosphate; the battery satisfies: 6.0 ≤ Δt / (a×b) ≤ 25; where a is the median particle size D of the positive electrode active material. v50 The unit is μm; b is the volume content of CO2 in the cell at the first temperature, in mL; Δt is the time interval between the moment when the cell reaches a temperature rise rate of 3℃ / s during thermal runaway under full charge and the moment when the cell reaches its highest temperature, in seconds; the first temperature is less than the highest temperature, and the first temperature ranges from 110℃ to 200℃. The battery of this invention can effectively improve the battery's pass rate and give lithium iron phosphate batteries good safety performance.

Description

Technical Field

[0001] The present invention relates to the field of battery technology, and in particular, to a battery and an electric device. Background Art

[0002] After preparation, lithium iron phosphate batteries can only be put into normal use after passing qualification inspection. Currently, the national standard test for energy storage cells is generally performed as follows: a cell in a fully charged state is charged while being heated, and when a thermal runaway condition is reached, that is, when the temperature rise rate of the cell is greater than 3°C / s, the cell is considered qualified if it does not catch fire or explode within one hour.

[0003] Therefore, it is of great significance to improve the detection qualification rate of lithium iron phosphate batteries and enable them to have high safety performance. Summary of the Invention

[0004] In view of this, the present invention aims to solve one of the technical problems in the related art at least to a certain extent. Therefore, the present invention provides a battery and an electric device, which can effectively improve the detection qualification rate of the battery and endow the lithium iron phosphate battery with good safety performance.

[0005] To solve the above technical problem, the present invention is implemented as follows: According to one aspect of the present invention, the present invention provides a battery, comprising: a cell unit, wherein the cell unit comprises a positive electrode plate arranged in sequence; the positive electrode plate comprises a positive active material, and the positive active material comprises lithium iron phosphate; the battery satisfies: 6.0 ≤ Δt / (a×b) ≤ 25; wherein a is the median diameter D of the positive active material v50 , with a unit of μm; b is the volume content of CO₂ in the cell unit at a first temperature, with a unit of mL; Δt is the time interval between the moment when the temperature rise rate of the cell unit reaches 3°C / s during thermal runaway in the fully charged state and the moment when the cell unit reaches the maximum temperature, with a unit of s; the temperature value of the first temperature is less than the temperature value of the maximum temperature, and the temperature value of the first temperature is 110°C to 200°C.

[0006] According to another aspect of the present invention, the present invention provides an electric device, comprising the battery described in any of the above embodiments.

[0007] Implementing the technical solution of the present invention has at least the following beneficial effects: In this invention, by synergistically controlling the median particle size of the positive electrode active material, the volume content of carbon dioxide in the cell at the first temperature, and the time interval between the cell's heating rate reaching 3℃ / s and the cell reaching its maximum temperature during thermal runaway under full charge conditions, the parameters satisfy 6.0≤Δt / (a×b)≤25. This ensures that the cell generates a certain amount of carbon dioxide during thermal runaway, providing a flame-retardant effect and effectively extending the time for the cell to reach its maximum temperature during thermal runaway. At the same time, excessive carbon dioxide gas is prevented from being generated, thus avoiding excessive internal pressure and explosion of the cell, thereby improving the battery's pass rate and safety performance.

[0008] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Detailed Implementation

[0009] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0010] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges or individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0011] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0012] Unless otherwise specified, all technical features and optional technical features of this invention can be combined to form new technical solutions.

[0013] Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0014] Unless otherwise specified, the terms "comprise" and "include" mentioned in the present invention are open-ended and can also be closed-ended. For example, the said "comprise" and "include" can mean that other components not listed may also be included or comprised, or can mean that only the listed components are included or comprised.

[0015] At present, the positive electrode active materials commonly used in lithium-ion batteries include ternary materials (such as NCM), lithium iron phosphate, etc., among which the application of lithium iron phosphate is the most mature. However, when lithium iron phosphate batteries undergo thermal runaway, they are prone to cause fire, explosion and other accidents. Therefore, after the preparation of lithium iron phosphate batteries, they can only be used normally after passing the inspection.

[0016] The national standard test for energy storage cells is usually as follows: when the cell is in a fully charged state, it is heated while being charged. When the thermal runaway condition is reached, that is, the temperature rise rate of the cell is greater than 3°C / s, if the cell does not catch fire or explode within one hour, the test is qualified.

[0017] In view of this, how to improve the inspection pass rate of lithium iron phosphate batteries and enable them to have high safety performance has become an important research topic.

[0018] The technical solution of the present invention is specifically as follows: <Battery> In some embodiments of the present invention, a battery is provided, comprising: a cell unit, wherein the cell unit comprises a positive electrode plate arranged in sequence; the positive electrode plate comprises a positive electrode active material, and the positive electrode active material comprises lithium iron phosphate; the battery satisfies: 6.0 ≤ Δt / (a×b) ≤ 25.

[0019] Wherein, a is the median particle diameter D of the positive electrode active material v50 , unit: μm; b is the volume content of CO₂ in the cell unit at a first temperature, unit: mL; Δt is the time interval from the moment when the temperature rise rate of the cell unit reaches 3°C / s during thermal runaway to the moment when the cell unit reaches the maximum temperature when the cell is in a fully charged state, unit: s; the temperature value of the first temperature is lower than the temperature value of the maximum temperature, and the temperature value of the first temperature is 110°C to 200°C.

[0020] As an example, the positive electrode in the battery cell includes a current collector and a positive electrode coating on the current collector. The positive electrode coating includes a positive electrode active material, which includes lithium iron phosphate. The battery cell also includes a negative electrode and a separator. The negative electrode includes a current collector and a negative electrode coating on the current collector. The negative electrode coating includes a negative electrode active material, which includes, but is not limited to, one or more of graphite, soft carbon, and silicon-based materials. It is understood that the current collectors in the positive and negative electrode are made of metal materials such as aluminum foil, copper foil, and aluminum alloy foil. The materials of the current collectors in the positive and negative electrode can be the same or different. The separator in the battery cell unit can be made of polymer materials such as polyethylene, polypropylene, and polyvinylidene fluoride. This invention does not specifically limit the use of such materials. It is also understood that the battery cell unit also includes an electrolyte, which includes lithium salts and solvents. The solvents include, but are not limited to, one or more of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). The lithium salts include, but are not limited to, lithium hexafluorophosphate and lithium difluorosulfonylimide.

[0021] Furthermore, to prevent lithium iron phosphate batteries from catching fire or exploding during thermal runaway, and to improve the pass rate and safety performance of lithium iron phosphate batteries, a small amount of lithium supplementer, such as lithium carbonate, is usually added to the positive electrode. This allows the battery to produce flame-retardant carbon dioxide gas during thermal runaway, which can prevent fire to some extent. However, during thermal runaway, the lithium supplementer undergoes an electrochemical reaction within the battery, and the decomposition temperature of this reaction is much lower than the reaction temperature in the normal environment. Moreover, due to the complexity of the internal chemical reactions of the battery, the type and amount of lithium supplementer added are highly dependent on the subsequent thermal runaway test pass rate, making it difficult to guarantee the pass rate of lithium iron phosphate batteries. Through in-depth research, the researchers of this invention have discovered that the thermal runaway fire and explosion of lithium iron phosphate batteries are mainly related to the median particle size of the positive electrode active material, the volume content of carbon dioxide in the cell at the first temperature, and the time interval between the cell's temperature rise rate reaching 3°C / s and the cell reaching its maximum temperature under full charge conditions. For example, if the median particle size of the positive electrode active material is too small, the reaction within the cell during thermal runaway will be too intense, leading to an excessively rapid instantaneous gas production rate and a rapid increase in pressure within the cell, which can easily cause a battery explosion. Furthermore, if the volume content of carbon dioxide at the first temperature is too low, it will not be able to... Effective flame retardancy can easily lead to fire when the battery cell experiences thermal runaway. If the carbon dioxide volume content is too high, it will increase the internal pressure of the battery cell, which can easily cause the battery cell to explode. It is understandable that the first temperature is the temperature at which the lithium replenisher reacts and decomposes inside the battery cell. Because an electrochemical reaction occurs inside the battery, the reaction and decomposition temperature of the lithium replenisher will be lower than under normal conditions. For example, under full charge conditions, if the time interval between the battery cell's temperature rise rate of 3℃ / s and the battery cell reaching its maximum temperature during thermal runaway is too short, it indicates that the reaction inside the battery cell is relatively intense, which can easily cause the battery to catch fire or explode.

[0022] Therefore, further research by the inventors revealed that by synergistically controlling the median particle size of the positive electrode active material, the volumetric carbon dioxide content within the cell at the first temperature, and the time interval between the cell's heating rate reaching 3°C / s and the cell reaching its maximum temperature during thermal runaway under full charge conditions, the parameters of these three parameters can satisfy 6.0 ≤ Δt / (a×b) ≤ 25, i.e., when Δt / (a×b) takes the values ​​of 6.0, 6.1, 6.2, 6.3, 6.5, 6.8, 8, 8.5, 9, 10, 1... When any one of the values ​​1, 12, 13, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, or 25, or any value between any two, is selected, a certain amount of carbon dioxide can be generated in the cell unit when thermal runaway occurs. This has a flame-retardant effect and effectively prolongs the time it takes for the cell unit to heat up to its maximum temperature during thermal runaway. At the same time, excessive carbon dioxide gas will not be generated, which could lead to excessive internal pressure and explosion of the cell unit. This improves the pass rate of lithium iron phosphate batteries and gives the batteries excellent safety performance. If the above relationship is not met, the carbon dioxide gas production may be too low, failing to provide effective flame retardancy. During thermal runaway, the time interval between the cell's heating rate reaching 3℃ / s and the cell reaching its maximum temperature may be too short, easily leading to cell fire and explosion. If the median particle size of the positive electrode active material is too small, the reaction within the cell during thermal runaway may be too violent. Even with sufficient carbon dioxide gas for flame retardancy, the total gas content inside the cell may be too high, causing the cell casing to rupture and explode. In summary, when the above range is met, lithium iron phosphate batteries exhibit a high pass rate and good safety performance. The first temperature value can be any one of 110℃, 120℃, 130℃, 150℃, 170℃, 190℃, or 200℃, or any point between any two.

[0023] In some embodiments, the value of a ranges from 0.8 μm to 1.1 μm.

[0024] For example, the median particle size D of the positive electrode active material v50That is, the value of 'a' can be any one of 0.81μm, 0.82μm, 0.83μm, 0.84μm, 0.85μm, 0.88μm, 0.9μm, 0.92μm, 0.95μm, 0.98μm, 1μm, 1.02μm, 1.05μm, 1.08μm, or 1.1μm, or any point value between any two of them; limiting the median particle size range of the above positive electrode active material can effectively control the intensity of the reaction during thermal runaway of the cell unit, preventing the internal reaction of the cell unit from being too violent, while reducing the side reactions between the positive electrode active particles and the electrolyte, so that the cell unit can react and release more carbon dioxide gas more slowly during thermal runaway, thereby slowly increasing the gas pressure inside the cell unit, ensuring that the cell unit casing will not crack and explode, opening the explosion-proof valve to release pressure, and improving the safety performance of the battery. If the particle size exceeds the above range, it will affect the transport of lithium ions on the active particles, prolonging the ion transport path and impacting the battery's cycle and rate performance. The median particle size mentioned above can be measured using methods such as laser diffraction and electron microscopy (SEM / TEM + image analysis). It is understood that the median particle size D... v50 This refers to the particle size value corresponding to a cumulative volume percentage of 50% on the cumulative particle size distribution curve; that is, 50% of the particles in the sample have a volume smaller than this particle size, and the other 50% have a volume larger than this particle size.

[0025] In some embodiments, the SPAN value of the positive electrode active material is set as x, which is dimensionless; wherein the value of x ranges from 0.8 to x < 1.2.

[0026] For example, the SPAN value, i.e., x, of the positive electrode material can be any one of 0.8, 0.9, 1.0, 1.05, 1.1, 1.15, or 1.2, or any value between any two; wherein, the SPAN value (particle size distribution width index) refers to a dimensionless parameter characterizing the degree of dispersion of particle size distribution; its calculation formula can be (|D v90 -D v10 |) / D v50 ;D v90 D v50 and D v10 Volume distribution can be calculated using GB / T19077–2016 "Particle Size Distribution - Laser Diffraction Method". By limiting the range of the SPAN value of the aforementioned positive electrode sheet material, the particle size of lithium iron phosphate can be made more uniform, and the uniformity of lithium iron phosphate particles can be higher. This, in turn, can balance the reaction rate of the entire cell unit, preventing the reaction rate at any location within the cell unit from becoming too fast, leading to excessive gas production or a high gas production rate, which could easily cause the cell unit to catch fire or explode. It is understandable that D... v10This refers to the particle size value corresponding to a cumulative volume percentage of 10% on the cumulative volume distribution curve; that is, the particle volume of 10% of the sample is ≤D. v10 The remaining 90% of the particles have a volume greater than D. v10 D v90 This refers to the particle size value corresponding to a cumulative volume percentage of 90% on the cumulative volume distribution curve, i.e., 90% of the particle volume in the sample is ≤D. v90 The remaining 10% of particles have a volume greater than D. v90 .

[0027] In some embodiments, when the capacity of the battery cell is 1Ah to 3Ah, the value of b ranges from 80mL to 300mL; preferably, when the capacity of the battery cell is 2Ah, the value of b ranges from 160mL to 200mL.

[0028] As an example, when the capacity of the battery cell is 1Ah~3Ah, at the first temperature, the volume content of CO2 in the battery cell, i.e., b, can be any one of 80mL, 100mL, 120mL, 150mL, 160mL, 161mL, 162mL, 163mL, 164mL, 165mL, 170mL, 175mL, 180mL, 185mL, 190mL, 195mL, 200mL, 220mL, 250mL, 280mL, or 300mL, or any point between any two. Limiting the range of CO2 volume content in the battery cell at the first temperature can give the battery cell a good flame-retardant effect in the event of thermal runaway. At the same time, a higher volume content of carbon dioxide can cause the gas pressure inside the battery cell to rise more slowly, thereby allowing the explosion-proof valve to open in time to release gas and pressure, so that the battery will not catch fire or explode in the event of thermal runaway. If the volumetric CO2 content in the cell is too low at the first temperature, the lack of carbon dioxide gas will hinder its flame-retardant effect, potentially leading to open flames and reduced battery safety. It's understandable that limiting the range of the first temperature ensures that additives react and decompose to produce carbon dioxide gas. If the temperature is too low, the battery may not experience thermal runaway due to the heat generated during charging and discharging, allowing the additives to react and activate the explosion-proof valve. Conversely, if the temperature is too high, thermal runaway may occur, preventing the additives from reacting and thus failing to provide flame retardant effects. The volumetric CO2 content in the cell at the first temperature can be measured using an accelerated calorimeter (ARC) combined with gas chromatography / mass spectrometry (GC / MS). The ARC collects the gas, and then GC is used to analyze the gas composition and volume percentage.

[0029] In some embodiments, the value of Δt ranges from 1500s to 1600s.

[0030] As an example, under full charge, the time interval Δt between the moment T1 when the cell temperature rises to 3℃ / s during thermal runaway and the moment T2 when the cell reaches its highest temperature can be any one of 1500s, 1510s, 1520s, 1530s, 1540s, 1550s, 1560s, 1570s, 1580s, 1590s, 1595s, or 1600s, or any point between any two. By limiting the time interval between T1 and T2, the internal reaction of the cell during thermal runaway can be kept relatively mild, resulting in a slower temperature rise rate and a slower internal voltage rise rate, thus reducing the likelihood of casing cracking. If the time interval is less than the above range, the internal temperature rise rate of the cell during thermal runaway may be too fast, leading to a faster voltage rise rate, which could easily cause casing cracking and explosion, seriously affecting the battery's safety performance. The Δt measurement method can monitor the cell temperature during thermal runaway overcharge testing with a sampling interval of 0.1s / 1s. After the test is completed, the time T1 (temperature rise rate reaches 3℃ / s) and T2 (the highest temperature during thermal runaway) are found, and Δt is calculated.

[0031] In some embodiments, the thickness of the cell unit is set to h, and h is greater than 0, in mm; wherein, the cell unit satisfies: 1.6≤b / h≤60.

[0032] For example, at the first temperature, the ratio of the volumetric CO2 content in the cell to the cell volume, i.e., b / h, can be any one of 1.6, 1.7, 1.8, 2, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 56, 57, 58, 59, or 60, or any value between any two. Limiting the range of the ratio of the volumetric CO2 content in the cell to the cell volume at the first temperature allows for better control of the safety performance of cell volumes with different capacities. Since a thicker cell has a larger capacity, it needs to generate more carbon dioxide flame-retardant gas during thermal runaway to prevent it from igniting an open flame and exploding. If the ratio is less than the above range, the battery may face risks of fire or explosion during thermal runaway. It is understood that the thickness of the cell can be measured using calipers or a micrometer.

[0033] In some embodiments, the positive electrode also includes additives, which include at least one of lithium source and carbon source; the lithium source includes, but is not limited to, one or several of lithium oxalate, lithium carbonate, lithium citrate and lithium formate in any mass ratio or molar ratio; the carbon source includes, but is not limited to, one or several of sucrose, glucose, citric acid and succinic acid in any mass ratio or molar ratio.

[0034] In some embodiments, the mass percentage of the additive is set as c, which is dimensionless, based on the mass of the positive electrode active material; wherein, the value of c ranges from 0.01% to 2%. For example, the mass percentage of the additive, i.e., the value of c, can be any one or any point between any two of 0.01%, 0.02%, 0.03%, 0.05%, 0.08%, 0.1%, 0.2%, 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, or 2%. If it is less than the above range, the carbon dioxide production may be insufficient during thermal runaway of the battery cell, thus failing to effectively achieve the flame-retardant effect; if it is greater than the above range, the reaction may be too violent during thermal runaway of the battery cell, causing a sudden increase in pressure inside the battery cell, which may easily lead to the battery cell exploding.

[0035] Optionally, c / b satisfies: 3.3 × 10 -7 ≤c / b≤2.5×10 -4 The value of c / b can be 3.3 × 10⁻⁶. -7 4×10 -7 5×10 -7 8×10 -7 4.0×10 -6 5.0×10 -6 8.0×10 -6 1.0×10 -5 1.1×10 -5 1.2×10 -5 1.3×10 -5 5×10 -5 8×10 -5 1×10 -4 2×10 -4 Or 2.5×10 -4 The ratio range can be defined by any one of the values ​​or any point between any two of the values. This can effectively control the CO2 content in the battery cell, thereby giving the battery cell good safety performance, making it less prone to ignition, and preventing the generation of excessive CO2 that could cause the battery cell to crack.

[0036] In some embodiments, the positive electrode sheet also includes a conductive agent and a binder: the conductive agent includes, but is not limited to, one or several of carbon black and carbon nanotubes in any proportion (mass ratio or molar ratio).

[0037] In some embodiments, the binder includes, but is not limited to, polyvinylidene fluoride.

[0038] In some embodiments, the conductive agent accounts for 0.4% to 1% of the mass of the positive electrode active material; for example, the conductive agent accounts for any one or any value between any two of 0.4%, 0.5%, 0.6%, 0.7%, 0.9% or 1% of the mass of the positive electrode active material.

[0039] In some embodiments, the binder accounts for 1% to 2% of the mass of the positive electrode active material; for example, the binder accounts for any one of 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.7%, 1.8%, 1.9%, 2% or any point value between any two.

[0040] In some embodiments, the negative electrode sheet includes a negative electrode active material, which includes, but is not limited to, one or several of graphite, soft carbon, hard carbon and silicon-based materials in any proportion (mass ratio or molar ratio).

[0041] <Electrical Equipment> In some embodiments of the present invention, an electrical device is provided, including: the battery in any of the above embodiments.

[0042] Optionally, the aforementioned electrical equipment can be vehicles, mobile phones, portable devices, laptops, ships, spacecraft, electric toys, power tools, energy storage devices, amusement equipment, elevators and lifting equipment, etc. Electric toys include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, or electric airplane toys, etc.; power tools include metal cutting power tools, grinding power tools, assembly power tools, and railway power tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers, etc.; energy storage devices can be energy storage walls, base station energy storage, container energy storage, etc.; amusement equipment can be carousels, drop towers, etc. The aforementioned vehicles can be fuel-powered vehicles, natural gas vehicles, or new energy vehicles. New energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc. A battery is installed inside the vehicle, and the battery can be located at the bottom, front, or rear of the vehicle. The battery can be used to power the vehicle; for example, the battery can serve as the vehicle's operating power source. The vehicle may also include a controller and a motor. The controller controls the battery's power supply to the motor, for example, to meet the vehicle's power needs during starting, navigation, and driving. The battery can serve not only as the vehicle's operating power source but also as its driving power source, replacing or partially replacing fuel or natural gas to provide propulsion.

[0043] Since the battery provided in this embodiment of the invention adopts all the technical solutions of the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, and will not be described in detail here.

[0044] The present invention will be specifically described below with reference to examples, but the implementation and protection of the present invention are not limited thereto. The following embodiments are only some embodiments of the present invention and are not intended to limit the present invention.

[0045] Example 1 1. Battery manufacturing (1) Preparation of positive electrode sheet: Lithium iron phosphate, SP (conductive agent) and polyvinylidene fluoride are added to the solvent NMP (N-methylpyrrolidone) in a mass ratio of 96.5%:0.8%:1.5%, and an additive (1% lithium oxalate) is added to make a positive electrode slurry. The positive electrode slurry is coated onto aluminum foil and dried to obtain a positive electrode sheet.

[0046] (2) Preparation of negative electrode sheet: The negative electrode active material, SP and SBR (styrene-butadiene rubber) are added to the solvent in a mass ratio of 96%:0.5%:1% to make a negative electrode slurry. The negative electrode slurry is coated onto copper foil and dried to obtain a negative electrode sheet.

[0047] (3) Electrolyte: Lithium salt-LiPF6; solvent is EC (ethylene carbonate): EMC (methyl ethyl carbonate) = 3:7.

[0048] (4) Separator: PE7 + double-sided adhesive + single-sided ceramic.

[0049] (5) Battery assembly: In a dry environment, stack the cells alternately in the order of separator → negative electrode → separator → positive electrode → separator. The negative electrode must completely cover the edge of the positive electrode. The separator should be free of wrinkles and damage. The tabs should be in opposite directions. Finally, use tape to fix the bare cells. The main process is stacking → welding of tabs / connecting pieces → casing → laser welding of cover plate → liquid injection → formation → degassing → capacity testing.

[0050] Example 2 The only difference between Example 2 and Example 1 is that lithium citrate is used instead of lithium oxalate in the positive electrode.

[0051] Example 3 The only difference between Example 2 and Example 1 is that glucose is used instead of lithium oxalate in the positive electrode.

[0052] Example 4 The only difference between Example 2 and Example 1 is that sucrose is used instead of lithium oxalate in the positive electrode.

[0053] Example 5 The only difference between Example 5 and Example 1 is that lithium carbonate is used instead of lithium oxalate in the positive electrode sheet.

[0054] Example 6 The only difference between Example 6 and Example 1 is that the mass percentage of lithium oxalate in the positive electrode is 0.1%.

[0055] Example 7 The only difference between Example 6 and Example 1 is that the mass percentage of lithium oxalate in the positive electrode is 1.5%.

[0056] Example 8 The only difference between Example 6 and Example 1 is that the mass percentage of lithium oxalate in the positive electrode is 2%.

[0057] Comparative Example 1 The only difference between Example 6 and Example 1 is that the mass percentage of lithium oxalate in the positive electrode is 0.

[0058] Comparative Example 2 The only difference between Example 6 and Example 1 is that the mass percentage of lithium oxalate in the positive electrode is 2.6%.

[0059] Performance testing (1) Median particle size of positive electrode active material: obtained by particle size analyzer, with the core process being preheating → background calibration → sample dispersion → concentration adjustment → measurement → data processing → cleaning and shutdown.

[0060] (2) SPAN value: Based on particle size distribution, SPAN value = (D v0.9 -D v0.1 ) / D v0.5 .

[0061] (3) Carbon dioxide content at the first temperature: ARC (accelerated calorimeter) + gas chromatography / mass spectrometry. ARC captures the temperature / pressure / heat release rate of thermal runaway under adiabatic conditions and collects the generated gas simultaneously; GC-MS performs qualitative and quantitative analysis on the generated gas.

[0062] (4) Δt: During the thermal runaway test, the cell temperature is monitored at an interval of 0.1s / 1s. After the test is completed, the times T1 and T2 are found and Δt is calculated. T1 is the temperature rise rate reaching 3℃ / s during the thermal runaway process, and T2 is the highest temperature of the cell during the thermal runaway process; (5) Volumetric CO2 content in the cell at the first temperature: This can be directly obtained through the GC-MS test in the third step above.

[0063] (6) Inspection pass rate: Number of cells that pass / Total number of cells tested.

[0064] The test results are shown in Table 1.

[0065] Table 1 As can be seen from Table 1 above, when the lithium iron phosphate battery satisfies the relationship 6.0≤Δt / (a×b)≤25, the pass rate of lithium iron phosphate battery testing can be effectively improved, thereby improving the safety performance of the battery.

[0066] The parts of this invention not described in detail are techniques known to those skilled in the art.

[0067] The basic principles of the present invention have been described above with reference to specific embodiments. However, it should be noted that the advantages, benefits, and effects mentioned in the present invention are merely examples and not limitations, and should not be considered as essential features of each embodiment of the present invention. Furthermore, the specific details disclosed above are for illustrative and facilitative purposes only, and are not limitations. These details do not limit the present invention to the necessity of employing the aforementioned specific details.

[0068] It should be noted that the terms "and / or" or " / " used herein are merely descriptions of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. The singular forms "a," "described," and "the" used in the embodiments of the invention and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0069] In the detailed description and claims, a list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements.

[0070] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A battery, characterized in that, include: The battery cell unit includes a positive electrode plate; The positive electrode sheet includes a positive active material, and the positive active material includes lithium iron phosphate; the battery satisfies: 6.0≤Δt / (a×b)≤25; Where a is the median particle size D of the positive electrode active material. v50 Unit: μm; b represents the volumetric CO2 content in the cell at the first temperature, in mL; Δt represents the time interval between the moment when the cell reaches a heating rate of 3°C / s during thermal runaway under full charge and the moment when the cell reaches its highest temperature during thermal runaway, in s; the first temperature is less than the highest temperature, and the first temperature is between 110°C and 200°C.

2. The battery according to claim 1, characterized in that, The value of 'a' ranges from 0.8 μm to 1.1 μm.

3. The battery according to claim 1 or 2, characterized in that, The SPAN value of the positive electrode active material is set as x, which is dimensionless. The value of x is in the range of 0.8 < x < 1.

2.

4. The battery according to claim 1, characterized in that, When the capacity of the battery cell is 1Ah to 3Ah, the value of b ranges from 80mL to 300mL. Preferably, when the capacity of the battery cell is 2Ah, the value of b ranges from 160mL to 200mL.

5. The battery according to claim 1, characterized in that, The value of Δt ranges from 1500s to 1600s.

6. The battery according to claim 1, characterized in that, The thickness of the battery cell unit is set as h, and h is greater than 0, with the unit being mm; The battery cell unit satisfies the following condition: 1.6 ≤ b / h ≤ 60.

7. The battery according to claim 1, characterized in that, The positive electrode also includes additives, which include at least one of lithium source and carbon source; The lithium source includes at least one of lithium oxalate, lithium carbonate, lithium citrate, and lithium formate. The carbon source includes at least one of sucrose, glucose, citric acid, and succinic acid.

8. The battery according to claim 6, characterized in that, Based on the mass of the positive electrode active material, the mass ratio of the additive is set as c, which is dimensionless. The value of c ranges from 0.01% to 2%.

9. The battery according to claim 8, characterized in that, The c / b ratio satisfies: 3.33 × 10 -7 ≤c / b≤2.5×10 -4 .

10. The battery according to any one of claims 1 or 4 to 9, characterized in that, The positive electrode sheet also includes a conductive agent and a binder: The conductive agent includes at least one of SuperP and carbon nanotubes; And / or, the adhesive comprises polyvinylidene fluoride; And / or, the conductive agent accounts for 0.4% to 1% of the mass of the positive electrode active material; And / or, the binder accounts for 1% to 2% of the mass of the positive electrode active material.

11. The battery according to claim 1, characterized in that, The negative electrode sheet includes a negative electrode active material, which includes at least one of graphite, soft carbon, hard carbon, and silicon-based materials.

12. An electrical appliance, characterized in that, include: The battery according to any one of claims 1 to 10.

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