Battery and electric device

Abstract

The invention discloses a battery and a power utilization device, the battery comprises a positive plate and an electrolyte, the positive plate comprises a positive electrode material, the positive electrode material comprises a positive electrode active material, the positive electrode active material comprises lithium iron phosphate and an iron-containing lithium supplement agent, the lithium iron phosphate comprises an inner core and a carbon coating layer, the thickness of the carbon coating layer is b nm, and the thickness of the carbon coating layer is b nm. The ratio of the Fe < 3 + > peak area to the O1s peak area in the XPS map under the 210nm etching depth in the positive plate is a, the viscosity of the electrolyte under the condition of 25 DEG C is c mPa.s, and a, b and c meet the condition that a * c * b is more than or equal to 1.5 and less than or equal to 40. The invention can give consideration to both fast charging and long service life of the battery.

Description

TECHNICAL FIELD

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

[0002] Lithium ion battery is a kind of rechargeable secondary battery, which is mainly composed of positive electrode, negative electrode, separator and electrolyte; the electrolyte as lithium ion transmission medium is generally composed of lithium salt dissolved in organic solvent, and sometimes additives are added to improve the performance of the battery.

[0003] Lithium ion battery improves the lithium ion transmission rate by reducing the viscosity of electrolyte, that is, using low viscosity solvent to improve the fast charging performance of the battery, but after using low viscosity solvent, the side reaction between electrolyte and negative electrode increases, resulting in reduced battery life. SUMMARY

[0004] Therefore, the technical problem to be solved by the present application is to overcome the defect that the existing battery cannot well balance the battery life when using low viscosity solvent to improve the fast charging performance, thereby providing a battery and a power device to solve the above problems.

[0005] To achieve the above purpose, the present application provides a battery, comprising a positive electrode sheet and an electrolyte, the positive electrode sheet comprising a positive electrode material, the positive electrode material comprising a positive electrode active material, the positive electrode active material comprising lithium iron phosphate and a lithium supplementing agent containing iron, the lithium iron phosphate comprising a core and a carbon coating layer, the thickness of the carbon coating layer being b nm, the ratio of the peak area of Fe 3+ to the peak area of O1s in the XPS spectrum of the positive electrode sheet at an etching depth of 210 nm being a, and the viscosity of the electrolyte at 25 DEG C being c mPa.s, 1.5≤a×c×b≤40.

[0006] The present application provides a power device comprising the above-mentioned battery.

[0007] The beneficial effects of the present application are as follows: The battery disclosed in the present application optimizes the type of lithium supplementing agent, the ratio a of the peak area of Fe 3+ to the peak area of O1s in the XPS spectrum of the positive electrode sheet at an etching depth of 210 nm, the thickness b of the carbon coating layer of lithium iron phosphate, and the viscosity c of the electrolyte, and balances the fast charging performance and the battery life. DETAILED DESCRIPTION

[0008] The following examples are provided to better further understand the present application, and are not limited to the best mode of the present application, and do not limit the content and protection scope of the present application, and any person under the inspiration of the present application or the combination of the present application with other prior art features, any product same or similar to the present application, falls within the protection scope of the present application.

[0009] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0010] The "range" disclosed in this invention is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 50%-90% and 60%-80% are listed for specific parameters, it is expected that ranges of 50% to 80% and 60% to 90% are also included. Furthermore, if minimum range values ​​1 and 2 are listed, and maximum range values ​​3, 4, and 5 are listed, then the following ranges are all expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In this application, unless otherwise stated, the numerical range "a to b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0.5-4" means that all real numbers between "1-4" have been listed in this article, such as: 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, etc. "0.5-4" is just a shortened representation of these numerical combinations.

[0011] In lithium iron phosphate batteries, the insertion and extraction rates of lithium ions between the positive and negative electrodes are crucial to the fast-charging performance of lithium-ion batteries. Studies have found that using low-viscosity solvents can improve the transport rate of lithium ions in the electrolyte and enhance fast-charging performance. However, due to their smaller molecular weight, low-viscosity solvents are more reactive with the negative electrode active materials. They can more easily penetrate the pores or defects in the particulate material of the negative electrode SEI film (solid electrolyte interphase), directly contacting the exposed negative electrode active materials (such as graphite and silicon) and exacerbating side reactions. Furthermore, low-viscosity solvents may fail to form a dense SEI film in the early stages of formation, leading to continuous SEI film growth in the later stages (consuming active lithium). Moreover, low-viscosity solvents typically have higher reduction potentials, making them more easily reduced and decomposed on the negative electrode surface, generating gases (such as CO2 and CH4) or organolithium compounds (such as ROCO2Li), resulting in increased gas generation during formation and reduced cycle life.

[0012] This invention provides a battery comprising a positive electrode and an electrolyte. The positive electrode comprises a positive electrode material, which in turn comprises a positive electrode active material. The positive electrode active material comprises lithium iron phosphate and an iron-containing lithium supplement. The lithium iron phosphate comprises a core and a carbon coating layer, the carbon coating layer having a thickness of b nm. The XPS pattern of the positive electrode at a etching depth of 210 nm shows Fe... 3+The ratio of the peak area to the O1s peak area is a, the viscosity of the electrolyte at 25℃ is c mPa·s, and 1.5≤a×c×b≤40.

[0013] Fe in the X-ray photoelectron spectroscopy (XPS) spectrum of the positive electrode 3+ The ratio of the characteristic peak area to the O1s peak area is set as a, where Fe 3+ The characteristic peaks of the O1s element are located at 710.5–711.5 eV in X-ray photoelectron spectroscopy (XPS), while the O1s peak is located at 530–531 eV. O1s refers to the peak of oxygen. In XPS analysis, O is chosen as the benchmark to calculate the ratio 'a'. Its main advantage lies in effectively eliminating systematic errors of the instrument and sample through the "internal standard" function, thus improving the reliability and repeatability of data analysis. This ratio 'a' is related to the content of lithium replenishing agent in the positive electrode. By adding lithium replenishing agent to the positive electrode, an additional lithium source is provided before battery assembly or cycling, replenishing the irreversible active lithium consumed during the formation stage. Furthermore, during battery charging and discharging, the dynamic rupture / repair of the SEI film during cycling continuously consumes lithium. This invention addresses this by controlling the Fe... 3+ The ratio 'a' of the characteristic peak area to the peak area of ​​O1s replenishes the active lithium consumed during charging, discharging, and cycling, improving battery cycle performance while avoiding impact on battery capacity. This invention selects the Fe content measured after etching the positive electrode to a depth of 210 nm. 3+ The ratio α of the characteristic peak area to the peak area of ​​O1s is mainly determined by considering the presence of an interface protective film on the surface of the positive electrode active material layer. By controlling the etching depth of the positive electrode sheet to 210 nm, the detected α can better reflect the content of lithium supplement in the positive electrode active material layer.

[0014] By coating the surface of lithium iron phosphate cathode active material with a carbon coating layer and controlling the thickness b of the carbon coating layer, side reactions between the solvent and the cathode are reduced. This avoids the situation where, while lithium replenishment occurs, the solvent oxidizes and produces gas on the cathode side, affecting battery life. The present invention does not limit the method of adjusting the carbon layer thickness. Specifically, it can be adjusted by the selection of carbon source, the amount of carbon source added, and the coating method. The coating method of carbon source coating includes wet coating or dry coating.

[0015] The viscosity (c) of the electrolyte affects the transport performance of lithium ions in the electrolyte, thus affecting the fast charging performance of the battery.

[0016] This invention achieves comprehensive control of Fe at an etching depth of 210 nm on the positive electrode. 3+The relationship between the / O1s peak area ratio, electrolyte viscosity, and positive electrode carbon coating thickness should satisfy 1.5 ≤ a × c × b ≤ 40 to achieve a balance between lifespan and fast-charging performance. The formula values ​​should not be too large, as this slows lithium-ion transport rates and affects fast-charging performance; conversely, the values ​​should not be too small, as this increases side reactions in the electrolyte and negative electrode, impacting battery lifespan.

[0017] By further controlling the formula range to 5-20, the fast charging capability and battery life can be further improved.

[0018] In one optional setting, a is 0.1-1; And / or, the b nm is 3nm-10nm; And / or, the c mPa.s is 1 mPa.s-5 mPa.s.

[0019] In this process, by controlling the range of 'a', the content of iron-containing lithium supplement can be effectively controlled to achieve the purpose of lithium supplementation, thereby improving cycle performance. Controlling the value of 'a' can also effectively reduce the oxidation of the solvent by the positive electrode, avoid increasing gas production, and thus improve cycle performance and extend service life.

[0020] By controlling the range of b, the carbon coating layer on the surface of lithium iron phosphate can be used to protect the cathode material, reduce the oxidation of the solvent by the cathode, reduce gas production, and improve service life; at the same time, it also avoids the carbon layer being too thick, which would affect lithium-ion transport.

[0021] By controlling the range of c, we can avoid the electrolyte viscosity being too high, which would affect fast charging performance; and avoid the electrolyte viscosity being too low, which would increase side reactions with the positive and negative electrodes, increase gas production, and affect service life.

[0022] Furthermore, a is 0.4-0.9; And / or, the bnm is 4nm-8nm; And / or, the c mPa.s is 1.8 mPa.s-3 mPa.s.

[0023] In one optional configuration, the iron-containing lithium supplementer includes Li5FeO4, which generates LiFeO2 after performing its lithium supplementation function, meaning that the cathode material also includes LiFeO2.

[0024] In one optional configuration, the surface of the iron-containing lithium supplement is provided with a carbon layer, the carbon layer having a thickness of 10-30 nm.

[0025] Most lithium replenishers (such as Li₂CO₃, Li₂O, Li₅FeO₄, etc.) are ionic compounds or wide-bandgap semiconductors with a large band gap between their valence band and conduction band, resulting in extremely low free electron concentration and difficult electron migration. By depositing a carbon layer on the surface of the lithium replenisher, the conductivity of the replenisher can be improved, thus enhancing the lithium replenishment effect. However, if the carbon layer thickness is too large, it will affect ion transport, and an excessively thick carbon layer will prolong the diffusion path of Li⁺, reducing electrode reaction kinetics and leading to a decrease in rate performance. Therefore, in this invention, the carbon layer thickness is controlled to be 10-30 nm, which can improve both the lithium replenishment effect and the rate performance.

[0026] In one optional configuration, the iron-containing lithium supplement has a particle size range of 5-15 μm.

[0027] This invention improves the specific surface area of ​​the lithium replenishing agent by controlling the particle size within a suitable range, allowing for more thorough contact between the lithium replenishing agent and the electrode material, thereby enhancing the lithium replenishment effect.

[0028] In one optional configuration, the electrolyte includes a solvent, which includes a nitrile solvent, and the nitrile solvent accounts for 5% to 50% of the mass of the electrolyte.

[0029] By selecting nitrile solvents, the viscosity of the electrolyte can be reduced, thereby increasing the transport rate of lithium ions in the electrolyte. Furthermore, nitrile solvents possess the cyano group (-C≡N), a linear, highly symmetrical, and strongly polar group. Although the carbon atom in the cyano group is electron-deficient, the electron cloud of the entire functional group is firmly "locked" due to the extremely strong electronegativity of the nitrogen atom, resulting in very high reduction stability. Unlike the carbonyl group in esters, it does not easily gain electrons from the outside and undergo reductive decomposition. Therefore, at the working potential of the graphite anode (~0.1 V vs. Li), the reduction stability is significantly improved. + When using nitrile solvents (e.g., nitrile esters), nitrile solvent molecules are much more "inert" than carboxylic acid ester molecules, and the tendency and rate of reduction side reactions are significantly reduced. This means that the side reactions between nitrile solvents and electrolytes are reduced, which can improve battery life.

[0030] To further improve battery life, the nitrile solvent is a nitrile compound having 2 to 4 carbon atoms. Preferably, the nitrile solvent includes fluorinated nitrile solvents and / or non-fluorinated nitrile solvents; for example, the nitrile solvent is selected from acetonitrile, propionitrile, butyronitrile, isobutyronitrile, or one or more of their fluorinated derivatives. The fluorinated derivatives refer to fluorinated derivatives of acetonitrile, propionitrile, butyronitrile, and isobutyronitrile, such as fluorinated acetonitrile, fluorinated propionitrile, fluorinated butyronitrile, and fluorinated isobutyronitrile.

[0031] As a preferred configuration, the solvent includes acetonitrile and its fluorinated derivatives, with the mass percentage of acetonitrile and its fluorinated derivatives in the electrolyte being 15% to 35%. By further selecting acetonitrile solvents (acetonitrile and its fluorinated derivatives) and controlling the range of acetonitrile solvents, the viscosity of the electrolyte can be further reduced, thereby improving the fast-charging performance of the battery. Acetonitrile solvents have relatively low ignition points; therefore, the content of acetonitrile solvents should not be too high to avoid affecting the safety performance of the battery.

[0032] The solvent includes propionitrile and its fluorinated derivatives, with propionitrile and its fluorinated derivatives accounting for 15% to 50% of the mass of the electrolyte. By further controlling the content of propionitrile solvents (propionitrile and its fluorinated derivatives), the viscosity of the electrolyte can be further reduced, thereby improving the fast charging performance of the battery.

[0033] As an optional configuration, the solvent further includes at least one of ethylene carbonate, ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, diethyl sulfone, ethylene glycol dimethyl ether, propylene glycol dimethyl ether, and tetrahydrofuran.

[0034] Preferably, the solvent in the electrolyte includes ethylene carbonate (EC), ethyl methyl carbonate (EMC), and acetonitrile (AcN), wherein the mass ratio of ethylene carbonate:ethyl methyl carbonate:acetonitrile is (20-40):(40-60):(20-40). This ratio range ensures a low viscosity in the electrolyte while reducing solvent decomposition and gas production, thus extending battery life. Specifically, EC is a solid at room temperature with a high dielectric constant, enabling complete dissociation of lithium salts. Higher lithium salt content requires more EC for dissociation, but its viscosity is also high; higher content leads to even higher viscosity. EMC, as a low-viscosity diluent, reduces the high viscosity introduced by EC, while acetonitrile, as an even lower viscosity solvent, further reduces electrolyte viscosity. Therefore, the combination of these three components improves electrolyte viscosity, increases the lithium-ion transport rate in the electrolyte, enhances battery fast-charging performance, and improves lithium salt dissociation capability, while simultaneously reducing side reactions of the solvent and negative electrode, thus balancing battery life.

[0035] Furthermore, the electrolyte also includes additives; by adding additives to the electrolyte, films are formed on the positive and negative electrodes, reducing side reactions with the electrolyte and improving battery life.

[0036] The additive is selected from at least one of vinylene carbonate (VC), fluoroethylene carbonate (FEC), ethylene ethylene carbonate (VEC), and succinic anhydride (SA); and / or, the additive accounts for 0.5% to 14% of the electrolyte by mass. More specifically, the additive accounts for 1.5% to 8% of the electrolyte by mass.

[0037] Preferably, the additives include 1 wt%-5 wt% vinylene carbonate (VC) and 0.5 wt%-2 wt% fluoroethylene carbonate (FEC) in the electrolyte. Further optimization of the types and amounts of these additives can better achieve electrolyte film formation at both the positive and negative electrodes, thereby reducing side reactions in the electrolyte and improving battery life.

[0038] In one optional configuration, the electrolyte further includes a lithium salt; The lithium salt is selected from at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and lithium difluorophosphate (LiPO2F2); and / or, the lithium salt accounts for 8%-20% of the mass of the electrolyte.

[0039] This invention improves the lithium-ion transport rate and enhances the fast-charging performance of batteries by controlling the lithium salt content. Preferably, the electrolyte includes 12%-18% lithium hexafluorophosphate (LiPF6) by mass.

[0040] In one optional configuration, the negative electrode sheet includes a negative current collector and a negative active layer attached to at least one side of the negative current collector. The negative active layer includes a negative active material, and the volumetric cumulative distribution particle size Dv50 of the negative active material is 5~25 micrometers, preferably 6~15 micrometers.

[0041] The volumetric cumulative distribution particle size Dv50 of the negative electrode active material of the present invention can be confirmed by, but is not limited to, the following methods: the secondary battery is discharged to the lower limit of 2.5V at a rate of 0.33C for discharge treatment, the negative electrode sheet of the secondary battery is disassembled and soaked in DMC for 2 hours, dried, the negative electrode active material layer is scraped off, and the resulting powder is measured using a laser particle size distribution measuring instrument (Mastersizer 3000) according to the particle size distribution laser diffraction method (specific steps refer to GB / T19077-2016). The particle size corresponding to the volumetric cumulative distribution percentage reaching 50% is Dv50.

[0042] This invention further controls the negative electrode particle size range, avoiding excessively large particle sizes that would affect lithium-ion transport, and also avoiding excessively small particle sizes that would increase the specific surface area and lead to excessive electrolyte side reactions, thus affecting battery life. In a preferred embodiment, the negative electrode sheet comprises primary particles and secondary particles; the particle size Dn50 of the primary particles is 5-14 μm; and the particle size Dn50 of the secondary particles is 15-25 μm.

[0043] Primary particles typically refer to small, independent sheet-like or spherical graphite crystals; secondary particles refer to agglomerations of multiple (three or more) primary particles. Smaller primary particles have a larger specific surface area, resulting in more side reactions and better initial kinetics, improving fast charging. However, the increased side reactions at high temperatures worsen cell lifespan. Secondary particles generally have larger particle sizes than primary particles, extending ion transport paths and deteriorating initial DCR / kinetics, impacting fast charging. However, their significantly reduced specific surface area decreases side reactions at high temperatures, improving cycle life. By controlling the particle sizes of the blended primary and secondary particles, it is possible to avoid both excessively small particle sizes leading to intensified electrolyte side reactions and excessively large particle sizes affecting kinetics and thus deteriorating fast charging performance, achieving a balance between kinetic performance and cycle life. Furthermore, the addition of primary particles optimizes current distribution, preventing lithium plating problems caused by excessive local embedding / extraction of lithium ions on the secondary particle surface. This makes the lithiation / delithiation process more uniform, reduces structural stress in the particles, and helps further extend overall cycle life.

[0044] The average particle size of both primary and secondary particles can be determined by electron microscopy. The specific testing method is as follows: The secondary battery is discharged to the lower limit of 2.5V at 0.33C for venting treatment, and then disassembled. The resulting negative electrode sheet is soaked in dimethyl carbonate (DMC) at 25℃ for 2 hours and dried. The active material layer of the negative electrode is then scraped off as a sample. The sample is fixed with conductive adhesive, polished with CP argon ion, and coated with a conductive film. It is then placed on a sample stage and observed under a scanning electron microscope (SEM). The image is taken at a magnification of 5Kx. The size of the SEM image is then measured using MEARSURE NANO software. The particle size is collected using the diagonal tracing method. The particle size of particles in three regions is counted. A total of 100 particles are counted. The particle size corresponding to the cumulative number of particles in each region reaching 50% of the baseline distribution is calculated. The average value of the three regions is calculated to obtain the corresponding Dn50.

[0045] The lithium iron phosphate comprises a first particle and a second particle; the particle size of the first particle is greater than or equal to 0.85 μm, and the particle size of the second particle is less than 0.85 μm; preferably, the particle size Dn50 of the first particle is 0.9-2 μm, and / or the particle size Dn50 of the second particle is 0.2-0.8 μm.

[0046] Lithium iron phosphate (LFP) batteries employ a combination of large and small particle sizes. Smaller particles shorten the lithium-ion transport path, improving fast-charging performance. Simultaneously, larger particles prevent excessively large specific surface areas of the cathode, which could increase electrolyte side reactions and thus affect battery life. Further optimization of the particle size of the first and second particles enhances fast-charging performance and improves the cell's low-temperature discharge capacity. Simultaneously, it alleviates the problem of iron leaching from the cathode material at high temperatures, improving high-temperature cycle performance and achieving a balance between high and low-temperature performance.

[0047] The particle sizes of the first and second particles mentioned above can be determined by electron microscopy. The specific testing method is as follows: The secondary battery is discharged to the lower limit of 2.5V at 0.33C for depletion treatment. In the depletion state, it is disassembled, and the obtained positive electrode sheet is soaked in dimethyl carbonate (DMC) at 25°C for 2 hours and dried. Then, the positive electrode active material layer is scraped off as a sample. The sample is fixed with conductive adhesive and polished with CP argon ion, coated with a conductive film, placed on the sample stage and observed under a scanning electron microscope (SEM). The magnification is adjusted to 10Kx, and three areas are selected for photography. Then, the size of the SEM images is measured using MEARSURE NANO software. The particle size is collected by the diagonal line method. The particle size of the particles in the three areas is counted. A total of 100 particles are counted. The particle size corresponding to the cumulative number of particles in each area reaches 50% of the baseline distribution is calculated, and the corresponding Dn50 is obtained.

[0048] In one optional configuration, the lithium iron phosphate further includes a first metal element M, which includes, but is not limited to, one or more of Ti, V, Mn, Ni, Co, Cr, Cu, Bi, and Sb. The content of the first metal element M in the lithium iron phosphate is 100-10000 ppm. The lithium iron phosphate in this invention further includes the first metal element M, and the addition of the first metal element M can improve conductivity and enhance fast-charging performance.

[0049] The following describes a specific embodiment of a battery and power-consuming device according to the present invention, but unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid making the following description unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the following description is provided to enable those skilled in the art to fully understand this application and is not intended to limit the subject matter described in the present invention.

[0050] [Battery] The battery in this invention, also known as a rechargeable battery or storage battery, refers to a battery that can be used again after being discharged by recharging to activate the active materials.

[0051] Typically, a battery consists of a positive electrode, a negative electrode, a separator, and an electrolyte. During charging and discharging, active ions (such as lithium ions) repeatedly insert and extract between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing active ions to pass through. The electrolyte, also positioned between the positive and negative electrodes, mainly serves to conduct active ions.

[0052] As an example, the battery manufacturing process is as follows: the positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. Then, the electrodes are wound or stacked to obtain a bare cell. The bare cell is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, the battery is obtained.

[0053] [Positive electrode tablets] A positive electrode typically includes a positive current collector and a positive active layer disposed on at least one side of the positive current collector. The positive active layer includes a positive electrode material, which comprises a positive active material, a binder, a conductive agent, and any other components (e.g., a dispersant). Specifically, the positive active material comprises 89%–98% (including lithium iron phosphate and iron-containing lithium supplementers), the binder 0.01%–5%, the conductive agent 0.01%–3%, and the dispersant 0.01%–3%.

[0054] In some embodiments, the positive electrode sheet can be prepared by dispersing the components used to prepare the positive electrode sheet, such as the positive electrode active material (lithium iron phosphate + iron-containing lithium supplementer), conductive agent, binder, and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto a positive electrode current collector, and then performing processes such as drying, rolling, and cutting to obtain the positive electrode sheet. The solid content of the positive electrode slurry is 35%~60%; the areal density of the positive electrode sheet is 200~390 g / m². 2 The compacted density is 2.3~2.7 g / m³. 3 .

[0055] The positive electrode active material in the positive electrode sheet of this invention is lithium iron phosphate and an iron-containing lithium supplement. Lithium iron phosphate (LFP) is a positive electrode active material with an olivine-type crystal structure, possessing advantages such as low cost and high safety. The general chemical formula of lithium iron phosphate can be Li... a FeMPO4; wherein 0.9≤a≤1.2, M in the positive electrode active material is a first metallic element, which is selected from one or more of Ti, V, Mn, Ni, Co, Cr, Cu, Bi, and Sb, and the content of the first metallic element M in lithium iron phosphate is 100-10000ppm. A carbon layer is also disposed on the surface of the positive electrode active material, and the thickness b of the carbon layer is 3-10nm.

[0056] Lithium iron phosphate (LFP) is a carbon-coated LFP particle. Its preparation process includes: uniformly mixing lithium, iron, and phosphorus sources to obtain a mixture; dispersing the mixture in an organic solvent and ball milling it; then spray drying it; calcining the resulting powder; and finally pulverizing it to obtain carbon-coated LFP particles. The carbon source forming the carbon coating layer can be added together with the lithium, iron, and phosphorus sources (the amount of carbon source added is 2-10% of the total amount of lithium, iron, and phosphorus sources), corresponding to method one; or it can be added after spray drying (the amount of carbon source added is 2-10% of the mass of the spray-dried powder), corresponding to method two.

[0057] In some embodiments, the lithium source includes at least one selected from lithium carbonate, lithium hydroxide, lithium carbonate, lithium nitrate, lithium oxalate, lithium dihydrogen phosphate, lithium citrate, and lithium acetate; the phosphorus source includes at least one selected from ammonium dihydrogen phosphate, lithium dihydrogen phosphate, and ammonium phosphate; more preferably, the phosphorus source and the lithium source can be the same, such as lithium dihydrogen phosphate. The iron source includes at least one selected from ferrous oxalate, ferric hydroxide, ferrous hydroxide, ferric phosphate, ferrous phosphate, ferric acetate, ferrous acetate, ferric carbonate, ferrous carbonate, ferric oxide, magnetite, and ferric oxalate; the carbon source includes at least one selected from glucose, sucrose, microcrystalline sugar, and organic polymers. The organic polymers include one or more selected from polypropylene (PP), polyvinyl alcohol (PVA), polyaniline (PANI), and asphalt.

[0058] In some embodiments, the grinding process takes 1 to 3.5 hours and rotates at 400 to 600 r / min. In some embodiments, the spray drying process uses a pressure of 0.4 to 0.7 MPa, an inlet temperature of 200 to 290°C, and an outlet temperature of 80 to 120°C. In some embodiments, the calcination process uses a temperature of 720 to 850°C, a heating rate of 3 to 5°C / min, and a calcination time of 4 to 12 hours. In some embodiments, the pulverization is performed using airflow milling.

[0059] This invention does not limit the preparation method of the lithium supplement. Specifically, the preparation of Li5FeO4 can be used as an example, as follows: 1) Mix lithium source and iron source according to stoichiometric ratio, with lithium source in excess to compensate for high-temperature lithium volatilization, and grind evenly.

[0060] 2) Pre-cook at 300–400°C in air or an inert atmosphere to remove moisture or organic matter.

[0061] 3) React at 600–800℃ (inert atmosphere or air) for 2–5 hours to generate Li5FeO4 (LFO).

[0062] 4) The synthesized LFO was mixed with an organic carbon source solution and dried to form a precursor.

[0063] 5) Pyrolysis at 300–500℃ in an inert atmosphere (Ar / N2) decomposes the carbon source to form carbon-coated LFO particles; the coating amount of the carbon layer is 3–10 wt%.

[0064] Lithium source: Li2CO3, LiOH or LiNO3.

[0065] Iron source: Fe2O3 or Fe3O4.

[0066] Carbon source: Organic carbon sources such as glucose, sucrose, citric acid, or polyacrylonitrile (PAN), or conductive carbon black (such as SuperP). In this invention, the binder is used to improve the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the current collector. The binder in this invention can be a conventional choice in the battery field. Specifically, the binder can be at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl alcohol (PVA), styrene-butadiene rubber (SBR), polyacrylonitrile (PAN), polyimide (PI), polyacrylic acid (PAA), polyacrylate, polyolefin, sodium carboxymethyl cellulose (CMC), or sodium alginate.

[0067] In this invention, the iron-containing lithium supplement is Li5FeO4 (lithium ferrite), which generates LiFeO2 after exerting its lithium supplementing effect.

[0068] In this invention, there is no specific limitation on the type of conductive agent. In some embodiments, as an example, the conductive agent can be one or more of conventional conductive agents such as conductive carbon black, acetylene black, and carbon nanotubes.

[0069] In this invention, there are no specific limitations on the types of binders and dispersants. For example, the dispersant can be selected from one or more of acrylics, acrylates, polyether esters, phosphate esters, small molecule alkanolamines, polyurethanes, modified styrene / maleic anhydride, HNBR, PVP, and polyethylene glycol (PEG).

[0070] The present invention does not impose any particular restrictions on the positive electrode current collector, as long as it is conductive and will not cause adverse chemical changes in the battery, and can be made of, for example: stainless steel, aluminum, nickel, titanium, sintered carbon; or aluminum or stainless steel that has been surface treated with one of carbon, nickel, titanium, silver, etc.

[0071] [Negative electrode plate] The negative electrode includes a negative current collector and a negative active layer disposed on at least one side of the negative current collector, the negative active layer comprising a negative active material. As an example, the negative active material includes one or more of natural graphite, artificial graphite, mesophase carbon microspheres, hard carbon, soft carbon, silicon, SiOx, and silicon-carbon.

[0072] In some embodiments, the negative electrode active layer may optionally include a conductive agent, a binder, or any other additives (such as dispersants).

[0073] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder, and any other additives, in a solvent (e.g., water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and obtaining the negative electrode sheet after drying, rolling, cutting, and other processes; wherein the mass percentage of the negative electrode active material is 90%-98%, the mass percentage of the conductive agent is 0%-5%, the mass percentage of the binder is 1.5%-5%, and the mass percentage of the dispersant is 0.3%-1.5%.

[0074] This invention does not impose specific limitations on the type of negative electrode conductive agent. As an example, the negative electrode conductive agent can be one or more of conventional negative electrode conductive agents such as acetylene black and carbon nanotubes. This invention also does not impose specific limitations on the type of negative electrode binder. As an example, the binder can be one or more of conventional negative electrode binders such as styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polyacrylic acid (PAA), and sodium carboxymethyl cellulose (CMC).

[0075] This invention does not impose specific limitations on the type of negative electrode current collector. As an example, the negative electrode current collector can be one of the conventional negative electrode current collectors such as copper foil.

[0076] Electrolyte The electrolyte acts as a conductor of ions between the positive and negative electrodes. The electrolyte of this invention comprises a lithium salt, a solvent, and additives. The electrolyte of this invention can be any electrolyte suitable for electrochemical energy storage devices in the art.

[0077] Electrolytes consist of solvents, additives, and lithium salts.

[0078] The solvent includes nitrile solvents, and further includes at least one of the following: ethylene carbonate, ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone, ethylene glycol dimethyl ether (DME), propylene glycol dimethyl ether (PGME), and tetrahydrofuran.

[0079] The additives in the electrolyte of this invention include one or more of VC, fluoroethylene carbonate (FEC), ethylene ethylene carbonate (VEC), and succinic anhydride (SA).

[0080] The lithium salt of the present invention includes at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and lithium difluorophosphate (LiPO2F2).

[0081] As an example, the solvent includes nitrile solvents having 2-4 carbon atoms; for example, acetonitrile, propionitrile, butyronitrile, isobutyl, or one or more of their fluorinated nitrile derivatives. The solvent may also include other types of solvents, such as ethylene carbonate (EC) and ethyl methyl carbonate (EMC).

[0082] [Isolation membrane] In some embodiments, the battery also includes a separator. The present invention does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0083] In some embodiments, the diaphragm includes a base membrane and a coating, the coating being selected from alumina, osmium oxide, etc.; an adhesive layer is also provided on the surface of the coating; the base membrane can be one of PP, PE, PP / PF; as an example: polyethylene (PE) is used as the base membrane, and an Al2O3 coating is provided on the surface of the base membrane, wherein the thickness of the coating is 1-5 μm, the thickness of the base membrane is 6-15 μm, and the thickness of the adhesive layer is 1-3 μm. Example 1 A battery includes a positive electrode, a negative electrode, a separator, and an electrolyte. The manufacturing process of this battery is as follows: Preparation of iron-containing lithium supplement Li5FeO4 (LFO): Lithium source (Li2CO3) and iron source (Fe2O3) were mixed in stoichiometric ratio and ground uniformly. The mixture was pre-calcined at 3350℃ in an inert atmosphere (N2) at a heating rate of 5℃ / min to remove moisture and organic matter. The pre-calcined material was then reacted at 700℃ (inert atmosphere (N2)) to generate Li5FeO4. The generated Li5FeO4 was mixed with a glucose solution, dried, and used to form a precursor. This precursor was then pyrolyzed at 400℃ in an inert atmosphere (N2), resulting in the decomposition of the carbon source to form carbon-coated LFO particles. The thickness of the carbon coating and the particle size of the carbon-coated LFO particles are shown in Table 2.

[0084] The preparation of lithium iron phosphate (LiFePO4) (LFP) adopts method 1, which specifically includes: dispersing lithium carbonate, iron phosphate, and carbon source in pure water according to stoichiometric ratio, controlling the solid content of the resulting slurry to be 45%, mixing and stirring for 1 hour, then circulating the mixed slurry into a sand mill and milling it at a rate of 500 rpm / min for 2 hours, followed by spray drying (inlet air temperature 220℃, outlet air temperature 75℃, pressure 0.5MPa), and calcining the resulting spherical raw material at 800℃ for 10 hours under a nitrogen atmosphere at a rate of 5℃ / min to remove magnetism, and then performing air jet milling to obtain carbon-coated LFP particles with a carbon coating thickness of 4.3 nm; the carbon-coated LFP particles include first particles and second particles, and the types of carbon sources for the carbon-coated LFP particles are shown in Table 2.

[0085] 1. Preparation of positive electrode sheet The specific preparation process of the positive electrode sheet is as follows: Positive electrode active materials (carbon-coated LFP particles + carbon-coated LFO particles), binder (PVDF), conductive agent (conductive carbon black Super-P), and dispersant (PVP) are mixed uniformly in a mass ratio of 96.4%:1.5%:1.1%:1%. The amount of lithium supplementer carbon-coated LFO particles added is 0.62% of the total amount of positive electrode active materials + binder + conductive agent + dispersant. Solvent NMP is added, and the mixture is stirred under vacuum until the system is homogeneous, obtaining a positive electrode slurry with a solid content of 50%. This positive electrode slurry is coated onto aluminum foil to obtain a double-sided coated positive electrode sheet. After rolling and cutting, the positive electrode sheet is obtained. The surface density of the positive electrode sheet is 380 g / m². 2 The compaction density is 2.5 g / m³. 3 .

[0086] 2. Preparation of negative electrode sheet The specific preparation process is as follows: The negative electrode active material (graphite), conductive agent (conductive carbon black Super-P), and binder (polyacrylic acid PAA + styrene-butadiene rubber SBR) are mixed uniformly at a mass ratio of 96.4%:0.6%:3%, wherein the mass ratio of polyacrylic acid PAA to styrene-butadiene rubber SBR is 1:2. This mixture is dispersed in deionized water to obtain a negative electrode slurry. This negative electrode slurry is then coated onto one side of a copper foil surface. Afterwards, it is rolled and cut to obtain a negative electrode sheet. The areal density of the negative electrode sheet is 165 g / m³. 2 The compacted density is 1.6 g / cm³. 3 The negative electrode consists of primary particles and secondary particles. The primary particles have a particle size of 10 μm, and the secondary particles have a particle size of 20 μm.

[0087] 3. Acquisition of the separating membrane In this embodiment, the separator is a conventional base film with a coating. PP is selected as the base film, Al2O3 is selected as the coating, the base film thickness is 9µm, the coating thickness is 3µm, and PVDF adhesive layers with a thickness of 2µm are provided on both sides.

[0088] 4. Preparation of electrolyte EC, EMC, and nitrile solvents were mixed to obtain an organic solvent. Thoroughly dried lithium salt (LiPF6) was dissolved in the mixed organic solvent and allowed to stand in a refrigerator for 0.5 hours. Additives vinylene carbonate (VC) and fluoroethylene carbonate (FEC) were then added to prepare the electrolyte. The contents of EC, nitrile solvents, vinylene carbonate, fluoroethylene carbonate, and lithium salt are shown in Table 3. The total mass of EMC, EC, and nitrile solvents was 100%.

[0089] 5. Assembly of secondary batteries The specific process is as follows: the positive electrode sheet, separator, and negative electrode sheet are stacked in sequence, with the separator between the positive and negative electrode sheets to provide isolation. Then, they are wound to obtain a bare cell. The bare cell is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a lithium-ion battery is obtained.

[0090] The batteries prepared above were tested using the following specific testing methods: 1. Fe at an etching depth of 210 nm in the positive electrode 3+ The ratio a of the peak area to the O1s peak area: 1) Pretreatment: Discharge the battery at 0.33C to the lower limit voltage of 2.5V, take out the empty battery, disassemble the electrode, soak the electrode in dimethyl carbonate (DMC) solution for 4 hours, and then air dry; 2) XPS etching peak intensity: The sample is fixed in a suitable position, such as on conductive tape on a copper sheet, and then sent into the analysis chamber through a rapid sample introduction chamber. A 120W monochromatic Al Kα X-ray source is used; the energy resolution is less than or equal to 0.48 eV; the test beam spot size is 400 micrometers, and the instrument automatically supplements the test pass range according to the element to be measured; etching conditions: Ar ions are used for etching, and the etching depth is controlled to reach 210 nm by adjusting the etching rate or etching time. Combined with the obtained XPS spectrum and software, the Fe in the XPS spectrum is obtained. 3+ Peak area at corresponding position, peak area unit CPS.eV, where Fe 3+ The corresponding peak position is 710.5-711.5 eV, and the O1s peak area is obtained at the same time. The position of the O1s peak is around 530-531 eV.

[0091] Ratio a = Fe 3+ Peak area / O1s peak area.

[0092] 2. Test method for carbon coating thickness b: The battery was discharged to 2.5V at 0.33C. The positive electrode of the lithium-ion battery in its empty state was taken and soaked in dimethyl carbonate (DMC) solution at room temperature for 4 hours. After soaking, the positive electrode was taken out and dried in a vacuum environment. The powder on the surface of the positive electrode was scraped off with a ceramic knife. The scraped powder was evenly dispersed in ethanol and subjected to TEM (transmission electron microscopy) test. In the TEM observation field, the thickness of the outer coating of the core was measured at three different positions on a single particle and the average value was calculated to obtain the thickness of the carbon coating of lithium iron phosphate in the positive electrode.

[0093] 3. Test method for electrolyte viscosity c: 1) Electrolyte Collection: The secondary battery under test is discharged using a battery charge / discharge device. Discharge conditions: current 0.3C, cutoff lower limit voltage 2.5V. The battery is disassembled and the electrolyte collected in a glove box (H2O≤0.1ppm, O2≤0.1ppm). There are three methods for collecting the electrolyte: After removing the battery cover, ① if there is free electrolyte, collect it into a 5mL sample tube using a pipette and seal it with sealing tape to prevent leakage. ② if there is no free electrolyte, a hydraulic press (Beijing Heng'ao Technology Co., Ltd.'s FY-30 hydraulic press) can be used to continuously pressurize until free electrolyte appears. Collect the electrolyte into a sample tube and seal it. ③ Add an appropriate amount of dichloromethane extractant to the battery and record the dichloromethane content. After adding dichloromethane, put the battery into an aluminum-plastic bag and seal it with a heat sealer. Transfer it to an ultrasonic oscillator and oscillate for 12 hours to allow the electrolyte in the electrode to mix thoroughly with the dichloromethane. Then, use a pipette to draw the mixture of dichloromethane and electrolyte into a 5mL sample tube and seal the sample tube with sealing glue. 2) Measurement using a Vicolab 400 viscometer: ① Clean the probe and measuring chamber with ethanol, and dry them with a clean sponge swab; fill the measuring chamber with the electrolyte to be tested, then remove some to rinse the chamber, and add another 2 ml of the electrolyte to the measuring chamber. Use a magnetic pen to draw the probe and place it into the measuring chamber, ensuring the probe is completely immersed in the sample; ② Press the "Enter" button to select "Operate", then press "Enter" again to select "Measure Uiscosity" to begin measurement. When the U value is within ±1% and the T value is within ±0.2℃, record the current U value, which is the viscosity (mPa.s). If the measuring chamber temperature is 25±0.2℃, the test data is valid; otherwise, continue the constant temperature circulating water bath in the measuring chamber until the temperature meets the requirements.

[0094] The test results for a, b, and c above are shown in Table 1.

[0095] Examples 2-25 and Comparative Examples 1-3 The difference from Example 1 is that the values ​​of a, b, and c, the type of carbon source in LFP, the particle size of the lithium supplement, the thickness of the carbon layer of the lithium supplement, the type and content of the electrolyte solvent, and the types and contents of lithium salt and additives are different. The specific corresponding parameter conditions are shown in Tables 1-3 below.

[0096] Table 1

[0097] Table 2

[0098] Table 3

[0099] In Examples 3-5, 7-8, and 10-14, the carbon-coated LFP particles were prepared using Method 2. The specific preparation process of Method 2 is as follows: Lithium carbonate and iron phosphate were dispersed in pure water, and the solid content of the resulting slurry was controlled to be 45%. After mixing and stirring for 1 hour, the mixed slurry was pumped into a sand mill and milled at a rate of 500 rpm / min for 2 hours. Then, it was spray-dried (inlet air temperature 220℃, outlet air temperature 75℃, pressure 0.5MPa). The resulting spherical raw material was coated with a carbon source. After coating, it was calcined at 800℃ for 10 hours under a nitrogen atmosphere at a rate of 5℃ / min to remove magnetism. Then, it was air-jet pulverized to obtain carbon-coated LFP particles with a carbon coating thickness of 4.3 nm. The carbon-coated LFP particles include a first particle and a second particle. The types of carbon sources for the carbon-coated LFP particles are shown in Table 2.

[0100] In Examples 2-25 and Comparative Examples 1-3, all parameters and conditions are the same as in Example 1, except for those in Tables 1-3 above.

[0101] Experimental example: Performance tests were conducted on the batteries of the embodiments and comparative examples under the above parameter conditions. The test methods are as follows: 1. Fast charging performance testing method: 1) Obtaining a three-electrode soft-pack battery. Preparation of the three-electrode copper wire: Wrap the copper wire around the fixed copper foil surface, ensuring both ends of the wire are evenly adhered to the foil. Preparation: First, with the copper foil end (the neatly cut end of the double-sided tape) facing down, roll it into a semi-circle and place it in a 500mL beaker. Then add concentrated sulfuric acid (a 1:1 solution of pure water and concentrated sulfuric acid) to immerse the foil, ensuring the immersion depth exceeds the top of the double-sided tape by 10-15mm. Immerse in the concentrated sulfuric acid for 4 hours, then remove it. Next, clean the bottom immersed area with anhydrous ethanol and let it stand for 5 minutes before proceeding with further processing. Prepare 1.2mol / L dilute hydrochloric acid (currently, concentrated hydrochloric acid is 37wt%, diluted 10 times with deionized water). Immerse the copper foil with the attached copper wire in the dilute hydrochloric acid and acid-wash for 15 minutes. Remove the acid-washed copper wire and place it in anhydrous ethanol, then clean it in an ultrasonic cleaner for 10-15 minutes. Transfer the copper wire to a room with humidity less than 1.2% for later use. Assembly and Formation: Prepare the required positive and negative electrode sheets and copper wires. Stack the electrode sheets in the following order: negative electrode sheet, separator, copper wire, separator, positive electrode sheet, separator, negative electrode sheet. The positive electrode sheet should be placed in the center of the negative electrode sheets, and the negative electrode sheets should be completely aligned. After stacking, peel off the outermost negative electrode sheet. Arrange the ends of the copper wires (processed ends) at a distance of 32±5 mm from the top edge and 40.5±5 mm from the left and right sides from the center of the cell. Then add another 81×81 mm layer. 2After placing the separator and negative electrode plate, arrange the copper wires, ensuring they are 11.5mm from each side of the electrode tab. The separator will automatically wind one and a half turns before being rolled up and glued to secure the cell separator. The outermost separator should be tightly wrapped without significant looseness, and at least 110mm of copper wire should be exposed. Use a soldering iron to transfer the copper wires (soldering temperature 300℃, time 5-10s). During ultrasonic soldering, handle the cell gently to prevent the copper wires from breaking during transport. The final product is a bare cell with a positive electrode size of 75mm×75mm and a negative electrode size of 80mm×80mm. The bare cell is placed in an outer packaging shell, dried to a satisfactory condition, and then injected with electrolyte. After vacuum sealing, standing, and formation (0.05C rate, constant current charging for 120min, standing for 10min, then 0.33C charging for 120min, then 0.33C charging to 3.65V, and 0.2C charging to 4.2V), the lithium replenishing agent is oxidized and replenished at a sufficiently high voltage. Then it is discharged at 0.2C to 3.4V, and cycled between 3.4V and 4.2V 3 times to ensure that the lithium replenishing agent is fully oxidized. Finally, it is charged at 0.2C to 3.65V to obtain a fully charged lithium-ion battery after formation. The battery is specially designed with copper wire as a reference electrode. After normalization and calibration, the battery is charged to 0% SOC (discharged at 0.33C to the lower limit voltage of 2.5V). Then, lithium is plated on the copper wire of the three electrodes at a rate of 0.01C for 10 hours on the positive side. After lithium plating, a three-electrode soft-pack battery for fast charging test is obtained.

[0102] 2) Fast charging test: The battery is first left to stand for 10 minutes, then discharged at 1C to 2.5V; left to stand for 10 minutes; charged at 0.33C to 10% SOC, then charged at 0.4C in descending order, charged at 4C, 3.6C, 3.2C...0.4C respectively, with the charging cutoff condition at each rate, reaching the upper limit voltage of 3.65V or the auxiliary voltage of 0V; calculate the charging time from 10% SOC to 80% SOC.

[0103] 2. Cyclic performance testing method: After formation, the lithium-ion battery is charged at 60°C with a constant current of 0.33C to the upper limit voltage of 3.65V, then charged at a constant voltage to the 0.05C cutoff current, and finally discharged at a constant current of 0.33C to the lower limit voltage of 2.5V. This process is repeated three times to obtain the discharge capacity Q1 of the third charge-discharge cycle, which is taken as the fixed capacity. Then, the battery is charged at a constant voltage of 0.5C to the upper limit voltage of 3.65V, then charged at a constant voltage to the cutoff current, and finally discharged at a constant current of 0.5C to the lower limit voltage of 2.5V. This process is repeated a certain number of times. The discharge capacity Q2 of the battery on the 100th cycle is recorded. The capacity retention rate is calculated as Q2 / Q1 × 100%.

[0104] The test results of the above performance tests are shown in Table 4 below.

[0105] Table 4

[0106] As shown in Table 4 above, by adjusting the values ​​of a×c×b within the range of 1.5-40, both fast charging performance and cycle life can be balanced. When the fast charging time is less than 17 minutes, the capacity retention rate can reach more than 94%. Further adjusting the values ​​of a×c×b within the range of 5-20 can ensure that the capacity retention rate reaches more than 96% when the fast charging time is less than 15 minutes, which is a significant effect.

[0107] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A battery, characterized in that, The electrode comprises a positive electrode sheet and an electrolyte. The positive electrode sheet includes a positive electrode material, which in turn includes a positive electrode active material. The positive electrode active material includes lithium iron phosphate and an iron-containing lithium supplement. The lithium iron phosphate comprises a core and a carbon coating layer with a thickness of b nm. The XPS pattern of the positive electrode sheet at an etching depth of 210 nm shows Fe. 3+ The ratio of the peak area to the O1s peak area is a, the viscosity of the electrolyte at 25℃ is c mPa·s, and 1.5≤a×c×b≤40.

2. The battery according to claim 1, characterized in that, 5≤a×c×b≤20.

3. The battery according to claim 1 or 2, characterized in that, The value of 'a' is 0.1-1; And / or, the b nm is 3nm-10nm; And / or, the c mpa.s is 1 mpa.s-5 mpa.s.

4. The battery according to claim 3, characterized in that, a is 0.4-0.9; And / or, the b nm is 4nm-8nm; And / or, the c mpa.s is 1.8 mpa.s-3 mpa.s.

5. The battery according to claim 1 or 2, characterized in that, The cathode material includes LiFeO2.

6. The battery according to claim 1 or 2, characterized in that, The diameter of the core of the lithium iron phosphate is 0.15-4 μm.

7. The battery according to claim 6, characterized in that, The lithium replenishing agent has a carbon layer on its surface, and the carbon layer thickness is 10-30 nm. And / or, the particle size range of the lithium supplement is 5-15 μm.

8. The battery according to claim 1 or 2, characterized in that, The electrolyte includes a solvent, which includes nitrile solvents, and the mass percentage of the nitrile solvent in the electrolyte is 5% to 50%.

9. The battery according to claim 8, characterized in that, The nitrile solvent is a nitrile compound having 2 to 4 carbon atoms.

10. The battery according to claim 9, characterized in that, The nitrile solvent is selected from one or more of acetonitrile, propionitrile, butyronitrile, isobutyronitrile, or their fluorinated derivatives.

11. The battery according to claim 10, characterized in that, The solvent includes acetonitrile and its fluorinated derivatives, and the mass percentage of acetonitrile and its fluorinated derivatives in the electrolyte is 15% to 35%. And / or, the solvent includes propionitrile and its fluorinated derivatives, wherein the mass percentage of propionitrile and its fluorinated derivatives in the electrolyte is 15% to 50%.

12. The battery according to claim 8, characterized in that, The solvent also includes at least one of the following: ethylene carbonate, ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, diethyl sulfone, ethylene glycol dimethyl ether, propylene glycol dimethyl ether, and tetrahydrofuran.

13. The battery according to claim 12, characterized in that, The solvent in the electrolyte includes ethylene carbonate, methyl ethyl carbonate and acetonitrile, wherein the mass ratio of ethylene carbonate: methyl ethyl carbonate: acetonitrile is (20-40):(40-60):(20-40).

14. The battery according to claim 1 or 2, characterized in that, The electrolyte also includes additives; The additive is selected from at least one of vinylene carbonate, fluoroethylene carbonate, and succinic anhydride.

15. The battery according to claim 14, characterized in that, The additive accounts for 0.5% to 14% of the mass of the electrolyte.

16. The battery according to claim 15, characterized in that, The additive accounts for 1.5% to 8% of the mass of the electrolyte.

17. The battery according to claim 16, characterized in that, The additives include vinylene carbonate and fluoroethylene carbonate, wherein the mass percentage of vinylene carbonate in the electrolyte is 1 wt%-5 wt%, and the mass percentage of fluoroethylene carbonate in the electrolyte is 0.5 wt%-2 wt%.

18. The battery according to claim 1 or 2, characterized in that, The electrolyte also includes lithium salt; The lithium salt is selected from at least one of LiPF6, LiFSI, LiBF4, LiTFSI, and LiBO2F2; and / or, the lithium salt accounts for 8%-20% of the mass of the electrolyte.

19. The battery according to claim 1 or 2, characterized in that, The negative electrode sheet in the battery includes a negative electrode current collector and a negative electrode active layer attached to at least one side of the negative electrode current collector. The negative electrode active layer includes a negative electrode active material, and the volumetric cumulative distribution particle size Dv50 of the negative electrode active material is 5-25 micrometers.

20. The battery according to claim 19, characterized in that, The negative electrode sheet comprises primary particles and secondary particles; the particle size Dn50 of the primary particles is 5-14 μm; the particle size Dn50 of the secondary particles is 15-25 μm.

21. The battery according to claim 1 or 2, characterized in that, The lithium iron phosphate comprises a first particle and a second particle, wherein the particle size of the first particle is greater than or equal to 0.85 μm and the particle size of the second particle is less than 0.85 μm.

22. The battery according to claim 21, characterized in that, The particle size Dn50 of the first particle is 0.9-2 μm, and / or the particle size Dn50 of the second particle is 0.2-0.8 μm.

23. The battery according to claim 1 or 2, characterized in that, The lithium iron phosphate also includes a first metal element M, which is selected from one or more of Ti, V, Mn, Ni, Co, Cr, Cu, Bi, and Sb, and the content of the first metal element M in the lithium iron phosphate is 100-10000 ppm.

24. An electrical appliance, characterized in that, It includes the battery as described in any one of claims 1-23.

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