A lithium iron manganese phosphate battery

Abstract

The application provides a lithium iron manganese phosphate battery, which comprises a positive electrode sheet, a negative electrode sheet and a nonaqueous electrolyte; the positive electrode sheet comprises a positive electrode active material and a positive electrode active coating arranged on at least one surface of the positive electrode active material; the positive electrode active material comprises lithium iron manganese phosphate LiMn x Fe 1‑x PO4, wherein 0.5≤x≤0.8; the negative electrode sheet comprises a negative electrode active material and a negative electrode active coating arranged on at least one surface of the negative electrode active material; the battery satisfies the following relationship: 4.5≤(a / 20+d) / (b+c)≤12.8; a is the membrane sheet resistance of the positive electrode sheet after coating; b is the compactness of the positive electrode sheet; c is the mass percentage content of vinylene carbonate in the positive electrode slurry; and d is the mass percentage content of lithium bisfluorosulfonylimide in the nonaqueous electrolyte. Through optimization of the composition of the lithium ion battery, the low-temperature discharge performance of the battery is improved, and the high-temperature cycle performance is also considered.

Description

Technical Field

[0001] This application relates to the field of lithium battery technology, and in particular to a lithium manganese iron phosphate battery. Background Technology

[0002] Lithium-ion rechargeable batteries, as a highly promising new energy device, are developing rapidly, and their application areas are constantly expanding. Among the many types of lithium-ion batteries, lithium manganese iron phosphate batteries stand out in the lithium-ion battery market due to their outstanding safety and structural stability, occupying the largest share and becoming the preferred battery type in many fields. Their olivine-type structure gives them excellent thermal stability, making them less prone to dangerous situations such as thermal runaway under extreme conditions such as high temperatures or overcharging, greatly improving the safety during battery use. This stability makes lithium manganese iron phosphate batteries irreplaceable in applications with extremely high safety requirements, such as electric vehicles and energy storage power stations.

[0003] Lithium manganese iron phosphate (LFP) batteries inherently have low electrical conductivity, and their poor low-temperature performance is a significant disadvantage in practical applications. When the ambient temperature decreases, the rate of chemical reactions within the battery slows down, ion migration is hindered, leading to a substantial drop in discharge capacity and charge / discharge efficiency. To improve the low-temperature performance of LFP batteries, various strategies have been employed. For example, coating and doping strategies aim to improve the electronic conductivity of the material and promote ion transport by coating the surface of the LFP material with a layer of highly conductive material, such as carbon, or by doping it with metal ions, such as magnesium or aluminum ions. Changing the particle size of the material shortens the diffusion path of lithium ions within the material, thereby improving the battery's performance at low temperatures.

[0004] While existing coating strategies offer some optimization for improving the low-temperature performance of lithium manganese iron phosphate (LFP) batteries, the non-in-situ preparation process has significant drawbacks. Current non-in-situ preparation methods, which involve coating after material synthesis, cannot achieve complete and tight encapsulation of LFP due to process limitations. Incomplete coating in some areas significantly reduces the improvement in low-temperature discharge performance. More seriously, this preparation method introduces other defect sites on the material surface. These defect sites become active centers for electrolyte decomposition, further promoting electrolyte decomposition on the surface. Electrolyte decomposition not only consumes active materials, leading to rapid battery capacity decay, but also generates large amounts of gas and byproducts, severely degrading the battery's high-temperature cycling performance. Therefore, LFP batteries based on related technologies struggle to balance low-temperature discharge performance and high-temperature cycling performance, failing to meet the market's urgent demand for wide-temperature-range LFP batteries. Summary of the Invention

[0005] This application provides a lithium manganese iron phosphate battery to solve the problem that existing lithium manganese iron phosphate batteries cannot simultaneously achieve low-temperature discharge performance and high-temperature cycle performance.

[0006] This application provides a lithium manganese iron phosphate battery, which includes a positive electrode, a negative electrode, and a non-aqueous electrolyte; the positive electrode includes a positive active material and a positive active coating disposed on at least one surface of the positive active material; the positive active material includes lithium manganese iron phosphate (LiMn) coated with a carbon coating layer. x Fe 1-x PO4), where 0.5 ≤ x ≤ 0.8;

[0007] The negative electrode sheet includes a negative electrode active material and a negative electrode active coating disposed on at least one surface of the negative electrode active material; the non-aqueous electrolyte includes lithium bis(fluorosulfonyl)imide.

[0008] The battery described above satisfies the following relationship:

[0009] 4.5≤(a / 20+d) / (b+c)≤12.8;

[0010] a represents the film resistance after coating the positive electrode;

[0011] b is the compaction density of the positive electrode sheet;

[0012] c represents the mass percentage of vinylene carbonate in the cathode slurry;

[0013] d represents the mass percentage of lithium bis(fluorosulfonyl)imide in the non-aqueous electrolyte.

[0014] This application addresses the adjustment of the positive electrode composition in lithium manganese iron phosphate battery cells. Using lithium manganese iron phosphate as the positive electrode active material, it controls the amount of vinylene carbonate (VC) added to the positive electrode slurry, the film resistance of the positive electrode, and the compaction density. An appropriate amount of lithium bisfluorosulfonyl imide (LiFSI) is added to the non-aqueous electrolyte, and the battery composition is made to meet specific requirements. This fully leverages the synergistic effect between lithium bisfluorosulfonyl imide (LiFSI) and vinylene carbonate (VC) with the positive electrode active material, improving the battery's low-temperature discharge performance while also ensuring high-temperature cycle performance.

[0015] In some possible implementations, the positive electrode active coating includes a positive electrode active material, a conductive agent, a dispersant, and a binder, wherein the mass percentage of the conductive agent, dispersant, and binder is 1-2:c:1-2, the mass percentage of the positive electrode active material and the dispersant is in the range of 95-97, and the mass percentage of the positive electrode active material is (95-97)-c; the dispersant is vinylene carbonate.

[0016] In some possible implementations, the negative electrode active coating includes a negative electrode active material, a conductive agent, a thickener, an additive, and a binder, wherein the mass percentage of the negative electrode active material, conductive agent, thickener, additive, and binder is 95-97:1-2:0.1-0.5:0.1-0.8:1.5-2, and the additive is styrene-butadiene rubber.

[0017] In some possible implementations, the film resistance α after the positive electrode is coated is 200–500 mΩ.

[0018] In some possible implementations, the compaction density b of the positive electrode sheet is 2.4–2.7 g / cm³. 3 .

[0019] In some possible implementations, the mass percentage c of the vinylene carbonate in the cathode slurry is 0.1 to 0.5 wt%.

[0020] In some possible implementations, the mass percentage d of the lithium bis(fluorosulfonyl)imide in the non-aqueous electrolyte is 3 to 7 wt%.

[0021] In some possible implementations, the conductive agent includes one or more of Ketjen black, mesophase carbon microspheres, activated carbon, graphite, conductive carbon black, acetylene black, carbon fiber, carbon nanotubes, and graphene; the thickener includes one or more of carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, and casein; and the binder includes one or more of polyvinylidene fluoride, hexafluoropropylene, pentafluoropropylene, tetrafluoropropylene, trifluoropropylene, perfluorobutene, hexafluorobutadiene, hexafluoroisobutylene, trifluoroethylene, trifluorochloroethylene, and tetrafluoroethylene.

[0022] In some possible implementations, the battery further includes a separator and a housing, the separator separating the positive electrode and the negative electrode, and the housing encapsulating the positive electrode, the negative electrode, the separator, and the non-aqueous electrolyte; wherein the non-aqueous electrolyte includes ethylene carbonate, diethyl carbonate, methyl ethyl carbonate, and lithium bis(fluorosulfonyl)imide; and the ethylene carbonate, diethyl carbonate, and methyl ethyl carbonate are present in a mass percentage ratio of 1–2:1–2:1–2.

[0023] In some possible implementations, the method for preparing the lithium manganese iron phosphate battery includes:

[0024] A positive electrode slurry is prepared by weighing and mixing the positive electrode active material, conductive agent, dispersant and binder in a predetermined ratio; wherein the mass percentage of the positive electrode active material, conductive agent, dispersant and binder in the predetermined ratio is 95-97:1-2:0.1-0.5:1-2; the dispersant is vinylene carbonate;

[0025] The positive electrode slurry is coated onto the positive electrode active material to obtain a positive electrode sheet;

[0026] A negative electrode slurry and a non-aqueous electrolyte are prepared; the negative electrode slurry includes a negative electrode active material, a conductive agent, a thickener, an additive, and a binder, wherein the mass percentage of the negative electrode active material, conductive agent, thickener, additive, and binder is 95-97:1-2:0.1-0.5:0.1-0.8:1.5-2, and the additive is styrene-butadiene rubber;

[0027] The negative electrode slurry is coated onto the negative electrode active material to obtain a negative electrode sheet;

[0028] The positive electrode and the negative electrode are assembled, and then vacuum-sealed with a non-aqueous electrolyte to obtain a lithium manganese iron phosphate battery.

[0029] By optimizing the cathode composition and non-aqueous electrolyte composition of lithium manganese iron phosphate batteries, the capacity decay of lithium manganese iron phosphate batteries at low temperatures is effectively delayed, the cycle life of the batteries is improved, the internal resistance of the batteries is reduced, and the low-temperature performance of the batteries is enhanced, thereby obtaining a wide-temperature-range lithium manganese iron phosphate battery that can balance low-temperature discharge performance and high-temperature cycle performance.

[0030] As can be seen from the above, this application discloses a lithium manganese iron phosphate battery, which includes a positive electrode, a negative electrode, and a non-aqueous electrolyte; the positive electrode includes a positive active material and a positive active coating disposed on at least one surface of the positive active material; the positive active material includes lithium manganese iron phosphate (LiMn) coated with a carbon coating layer. x Fe 1-x PO4), wherein 0.5≤x≤0.8; the negative electrode sheet includes a negative electrode active material and a negative electrode active coating disposed on at least one surface of the negative electrode active material; the non-aqueous electrolyte includes lithium bis(fluorosulfonyl)imide; wherein the battery satisfies the following relationship: 4.5≤(a / 20+d) / (b+c)≤12.8; a is the film resistance after coating of the positive electrode sheet; b is the compaction density of the positive electrode sheet; c is the mass percentage content of vinylene carbonate in the positive electrode slurry; d is the mass percentage content of lithium bis(fluorosulfonyl)imide in the non-aqueous electrolyte. By optimizing the composition of lithium-ion batteries, using lithium manganese iron phosphate as the positive electrode active material, controlling the amount of VC added in the positive electrode slurry, the resistance of the positive electrode film, and the compaction density, and adding an appropriate amount of lithium bisfluorosulfonyl imide (LiFSI) to the non-aqueous electrolyte, and making the battery composition meet specific requirements, the synergistic effect between lithium bisfluorosulfonyl imide (LiFSI) and vinylene carbonate (VC) and the positive electrode active material can be fully utilized, so that the battery can improve the low-temperature discharge performance while taking into account the high-temperature cycle performance. Detailed Implementation

[0031] The embodiments described in the following examples do not represent all embodiments consistent with this application. They are merely examples of systems and methods consistent with some aspects of this application as detailed in the claims.

[0032] Lithium-ion rechargeable batteries, as a highly promising new energy device, are developing rapidly, and their application areas are constantly expanding. Among the many types of lithium-ion batteries, lithium manganese iron phosphate batteries stand out in the lithium-ion battery market due to their outstanding safety and structural stability, occupying the largest share and becoming the preferred battery type in many fields. Their olivine-type structure gives them excellent thermal stability, making them less prone to dangerous situations such as thermal runaway under extreme conditions such as high temperatures or overcharging, greatly improving the safety during battery use. This stability makes lithium manganese iron phosphate batteries irreplaceable in applications with extremely high safety requirements, such as electric vehicles and energy storage power stations.

[0033] Lithium manganese iron phosphate (LFP) batteries inherently have low electrical conductivity, and their poor low-temperature performance is a significant disadvantage in practical applications. When the ambient temperature decreases, the rate of chemical reactions within the battery slows down, ion migration is hindered, leading to a substantial drop in discharge capacity and charge / discharge efficiency. To improve the low-temperature performance of LFP batteries, various strategies have been employed. For example, coating and doping strategies aim to improve the electronic conductivity of the material and promote ion transport by coating the surface of the LFP material with a layer of highly conductive material, such as carbon, or by doping it with metal ions, such as magnesium or aluminum ions. Changing the particle size of the material shortens the diffusion path of lithium ions within the material, thereby improving the battery's performance at low temperatures.

[0034] While existing coating strategies offer some optimization for improving the low-temperature performance of lithium manganese iron phosphate (LFP) batteries, the non-in-situ preparation process has significant drawbacks. Current non-in-situ preparation methods, which involve coating after material synthesis, cannot achieve complete and tight encapsulation of LFP due to process limitations. Incomplete coating in some areas significantly reduces the improvement in low-temperature discharge performance. More seriously, this preparation method introduces other defect sites on the material surface. These defect sites become active centers for electrolyte decomposition, further promoting electrolyte decomposition on the surface. Electrolyte decomposition not only consumes active materials, leading to rapid battery capacity decay, but also generates large amounts of gas and byproducts, severely degrading the battery's high-temperature cycling performance. Therefore, LFP batteries based on related technologies struggle to balance low-temperature discharge performance and high-temperature cycling performance, failing to meet the market's urgent demand for wide-temperature-range LFP batteries.

[0035] Based on this, and addressing the problem that lithium manganese iron phosphate batteries in related technologies cannot simultaneously achieve low-temperature discharge performance and high-temperature cycle performance, this application provides a lithium manganese iron phosphate battery.

[0036] In some embodiments, this application provides a lithium manganese iron phosphate battery, the battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte; the positive electrode comprises a positive active material and a positive active coating disposed on at least one surface of the positive active material; the positive active material comprises lithium manganese iron phosphate (LiMn) coated with a carbon coating layer. x Fe 1-x PO4), where 0.5 ≤ x ≤ 0.8;

[0037] The negative electrode sheet includes a negative electrode active material and a negative electrode active coating disposed on at least one surface of the negative electrode active material; the non-aqueous electrolyte includes lithium bis(fluorosulfonyl)imide (LiFSI);

[0038] The battery described above satisfies the following relationship:

[0039] 4.5≤(a / 20+d) / (b+c)≤12.8;

[0040] a represents the film resistance after coating the positive electrode;

[0041] b is the compaction density of the positive electrode sheet;

[0042] c represents the mass percentage of vinylene carbonate in the cathode slurry;

[0043] d represents the mass percentage of lithium bis(fluorosulfonyl)imide in the non-aqueous electrolyte.

[0044] This application achieves higher cycle life and service life in lithium manganese iron phosphate batteries by controlling the design of the positive electrode and the amount of vinylene carbonate (VC) added. Specifically, this application discloses a positive electrode design for a lithium manganese iron phosphate battery, employing a lower compaction density to ensure a more complete structure of the positive electrode material and a higher liquid retention. By reducing the film resistance of the positive electrode, the low-temperature discharge capability of the cell can be improved. Excessive VC content in the positive electrode slurry can affect cycle life; therefore, VC should be controlled within a reasonable range. By controlling the amount of VC added to the positive electrode slurry, the film resistance of the positive electrode, and the compaction density, and by adding an appropriate amount of lithium bisfluorosulfonyl imide (LiFSI) to the non-aqueous electrolyte, the cell meets specific relationship requirements, reducing the cell film resistance and thus improving the battery's high and low temperature performance.

[0045] By controlling the ratio in the above formula between 4.5 and 12.8, it is helpful to balance the battery's internal resistance with the distribution and characteristics of its internal materials. A lower film resistance 'a' after coating of the positive electrode, combined with an appropriate mass percentage 'd' of lithium bis(fluorosulfonyl)imide (LiFSI), can significantly improve the overall conductivity of the battery. When this ratio is within a reasonable range, it can effectively reduce energy loss during charging and discharging, and improve the battery's charging and discharging efficiency. For example, in practical applications, it can reduce charging time, while allowing the battery to output a more stable and stronger current during discharge, thus improving the performance of the device.

[0046] In some embodiments, the positive electrode active coating comprises a positive electrode active material, a conductive agent, a dispersant, and a binder, wherein the mass percentage of the positive electrode active material, conductive agent, dispersant, and binder is (95-97)-c:1-2:c:1-2, wherein the sum of the mass percentages of the positive electrode active material and vinylene carbonate (VC) is greater than or equal to 95 and less than or equal to 97. The conductive agent includes one or more of Ketjen black, mesophase carbon microspheres, activated carbon, graphite, conductive carbon black, acetylene black, carbon fiber, carbon nanotubes, and graphene; the binder includes one or more of vinylidene fluoride, hexafluoropropylene, pentafluoropropylene, tetrafluoropropylene, trifluoropropylene, perfluorobutene, hexafluorobutadiene, hexafluoroisobutylene, trifluoroethylene, trifluorochloroethylene, and tetrafluoroethylene; and the dispersant is vinylene carbonate (VC). Vinylene carbonate (VC) can effectively reduce the agglomeration of positive electrode active material particles, making the active material more uniformly dispersed in the coating. The addition of vinylene carbonate (VC) helps to increase the contact area between the active material and the non-aqueous electrolyte, improve the insertion and extraction efficiency of lithium ions during the charging and discharging process, and thus enhance the charging and discharging performance and rate performance of the battery.

[0047] During the initial charge and discharge of the battery, vinylene carbonate (VC) decomposes on the electrode surface, forming a stable solid electrolyte interphase (SEI) film. This SEI film possesses excellent ionic conductivity and electronic insulation, effectively preventing further reactions between the non-aqueous electrolyte and the electrode materials, reducing side reactions, and improving the battery's coulombic efficiency and cycle life. The formed SEI film helps reduce the impedance of the electrode surface, especially at low temperatures, increasing the migration rate of lithium ions and reducing polarization, thereby improving the battery's low-temperature discharge performance and enabling the battery to maintain good capacity output and rate performance even at low temperatures.

[0048] In some embodiments, the positive electrode active material is a carbon-coated lithium manganese iron phosphate active material (LiMn). x Fe 1-x PO4), where 0.5≤x≤0.8.

[0049] Lithium manganese iron phosphate (LMP) itself has low electronic conductivity, while carbon has excellent electrical conductivity. The presence of a carbon coating layer provides a good channel for electron transport, greatly improving the overall electronic conductivity of the material. The carbon coating layer can optimize the surface properties of LMP particles, reduce the diffusion resistance of lithium ions on the particle surface, and also inhibit the growth of LMP grains to a certain extent, shortening the lithium ion diffusion path and thus improving the lithium ion diffusion coefficient. The carbon coating layer can protect the active material of LMP, preventing it from directly contacting the electrolyte and causing side reactions, reducing the loss of active material; and during charging and discharging, it can alleviate the volume changes caused by lithium ion insertion and extraction, maintaining the stability of the electrode structure. Carbon materials themselves have a certain degree of thermal stability; after coating the surface of LMP, it can improve the overall thermal stability of the cathode material to a certain extent, and can also prevent adverse reactions between LMP and the electrolyte at high temperatures. In some embodiments, the thickness of the carbon coating layer is 2–20 nm.

[0050] By using carbon-coated lithium manganese iron phosphate active material as the positive electrode active material, electrons can be transferred more quickly between the positive electrode active materials during charging and discharging, thereby improving the battery's rate performance. This allows the battery to charge and discharge at high current densities, meeting the high-power output requirements of applications such as electric vehicles. Furthermore, the carbon-coated lithium manganese iron phosphate active material also enhances the battery's safety and performance stability under high-temperature environments, reducing safety hazards such as battery bulging and combustion caused by high temperatures, and widening the battery's operating temperature range, enabling it to operate more stably under various environmental temperature conditions.

[0051] Manganese has a higher electrochemical potential than iron. Appropriately increasing the proportion of manganese can enhance the overall electrochemical potential of lithium manganese iron phosphate (LFP) materials, thereby increasing the battery's output voltage. With the battery volume and mass remaining constant, the increased output voltage means the battery can store and release more electrical energy, effectively improving its energy density and meeting the high energy density requirements of electronic devices. When the proportion of Mn in the active material of LFP is within the range of 0.5 ≤ x ≤ 0.8, the crystal structure of the material becomes more stable. During battery charging and discharging, it better resists structural distortion and damage, reducing the loss of active material and the increase in internal resistance caused by structural changes, thus contributing to improved cycle performance and lifespan. This proportion range also helps optimize the electronic structure of LFP materials, making electron transport within the material smoother and improving electronic conductivity. Good electronic conductivity can reduce polarization during charging and discharging, improving charging and discharging efficiency, reducing energy loss, and also enhancing rate performance, allowing the battery to maintain good performance even under high-current charging and discharging conditions.

[0052] In some embodiments, the film resistance α after coating the positive electrode is 200–500 mΩ. At low temperatures, the ion diffusion rate and electron conduction rate of the lithium manganese iron phosphate battery itself decrease significantly. If the film resistance after coating the positive electrode is high, it will further hinder the transport of electrons and lithium ions. Electrons have difficulty smoothly conducting from the positive electrode active material to the active material, and the insertion and extraction processes of lithium ions also become more difficult. This significantly reduces the amount of active material participating in the discharge reaction, leading to a sharp decrease in the cell's discharge capacity. Under low-temperature conditions, it cannot release the amount of electricity it should have at room temperature, severely affecting the battery's usage time and range in low-temperature scenarios. When the film resistance is low, although the low-temperature environment still inhibits the transport of electrons and lithium ions, the relatively small film resistance can alleviate this obstacle to some extent. Electrons and lithium ions can move relatively smoothly, allowing more positive electrode active material to participate in the discharge reaction. Therefore, compared to the case of high film resistance, a higher discharge capacity can be retained, improving the cell's usable power and range performance in low-temperature environments. The film resistance α after coating the positive electrode can be 320mΩ, 362mΩ, 371mΩ, 373mΩ, 374mΩ, 375mΩ, 399mΩ, 403mΩ, 409mΩ, 410mΩ, 412mΩ, 416mΩ, 421mΩ, 420mΩ, 430mΩ, 444mΩ, 464mΩ, 487mΩ, or 498mΩ.

[0053] In some embodiments, the compaction density b of the positive electrode sheet is 2.4–2.7 g / cm³. 3 The higher the compaction density of the positive electrode sheet, the higher the content of the positive electrode active material. Setting a certain compaction density for the positive electrode sheet ensures it possesses both energy and sufficient porosity to facilitate the insertion / extraction of active ions and improve ion mobility. The compaction density b of the positive electrode sheet can be 2.4 g / cm³. 3 2.5g / cm 3 2.55g / cm 3 2.6g / cm 3 2.65g / cm 3 2.7g / cm 3 .

[0054] The compaction density (b) of the positive electrode sheet has a significant impact on battery performance. A reasonable compaction density optimizes the packing state of the electrode materials and improves the volumetric energy density of the electrode. If the compaction density is too high, it may lead to poor contact between material particles, increasing resistance; if it is too low, it wastes space and reduces the overall energy storage capacity of the battery. The relationship between b and other parameters ensures that b is within the range that optimizes battery performance, guarantees a good ion transport channel between the positive electrode active material and the non-aqueous electrolyte, and maintains stable battery operation.

[0055] In this application, the important film-forming additive vinylene carbonate (VC) is mixed into the cathode material in advance, allowing it to fully contact the lithium manganese iron phosphate material. During electrolyte injection, the principle of "like dissolves like" promotes the wetting of the cathode material by the non-aqueous electrolyte and ensures the dispersion of the film-forming additive in different thickness layers of the cathode material. This facilitates comprehensive coverage of the cathode material at different thicknesses on the electrode sheet. In the early stage of cell film formation, a protective film can be quickly formed on the surface of the lithium manganese iron phosphate material, which not only increases the contact area between lithium manganese iron phosphate materials and with the active material, but also avoids the oxidative decomposition of components with high film-forming resistance in the non-aqueous electrolyte at that location. This reduces the initial resistance and resistance growth rate of the cell, thereby improving the low-temperature discharge performance and high-temperature cycle performance of the battery.

[0056] In some embodiments, the mass percentage c of vinylene carbonate (VC) in the cathode slurry is 0.1–0.5 wt%. Specifically, the mass percentage c of vinylene carbonate (VC) in the cathode slurry can be 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, or 0.5 wt%.

[0057] The mass percentage (c) of vinylene carbonate (VC) in the positive electrode slurry acts as a film-forming additive in the battery. An appropriate amount of vinylene carbonate (VC) can form a stable solid electrolyte interphase (SEI) film on the positive electrode surface. When the formula defines a suitable proportion of c, this film can effectively prevent further decomposition of the non-aqueous electrolyte, protect the positive electrode active materials, and improve the battery's cycle stability. After multiple charge-discharge cycles, the rate of battery capacity decay slows down, thereby extending the battery's lifespan.

[0058] The fluoride ions in lithium fluorosulfonylimide (LiFSI) exhibit strong electron-withdrawing properties, weakening the coordination between cations and anions in lithium salts. This results in highly mobile lithium ions with high thermal and electrochemical stability, virtually eliminating side reactions and suppressing swelling. In this application, adding an appropriate amount of lithium fluorosulfonylimide (LiFSI) to the non-aqueous electrolyte of lithium manganese iron phosphate batteries significantly improves the conductivity of the non-aqueous electrolyte, thereby enhancing the low-temperature discharge performance of the cell. Furthermore, lithium fluorosulfonylimide (LiFSI) can further modify the composition of the positive and negative electrode films, reducing the cell's film-forming impedance and thus improving the cell's high and low temperature performance.

[0059] In some embodiments, the mass percentage d of lithium bisfluorosulfonylimide (LiFSI) in the non-aqueous electrolyte is 3–7 wt%. Specifically, the mass percentage d of lithium bisfluorosulfonylimide (LiFSI) in the non-aqueous electrolyte can be 3 wt%, 4 wt%, 5 wt%, 6 wt%, or 7 wt%. The mass percentage d of lithium bisfluorosulfonylimide (LiFSI) in the non-aqueous electrolyte not only affects the conductivity of the non-aqueous electrolyte but also plays an important role in the high and low temperature performance of the battery. A suitable d value, combined with other parameters in the formula, can improve the ion transport capability of the battery in low-temperature environments and alleviate the problem of poor low-temperature performance of lithium manganese iron phosphate batteries. At low temperatures, the battery can maintain a relatively high discharge capacity and charge-discharge efficiency, reducing performance degradation caused by low temperatures. At the same time, in high-temperature environments, it also helps maintain the internal chemical balance of the battery, avoiding excessive reactions of the non-aqueous electrolyte caused by temperature rise, and improving the high-temperature stability of the battery.

[0060] In some embodiments, the negative electrode active coating includes a negative electrode active material, a conductive agent, a thickener, and a binder. In this application, the negative electrode active coating further includes styrene-butadiene rubber (SBR). The mass percentage of the negative electrode active material, conductive agent, thickener, SBR, and binder is 95-97:1-2:0.1-0.5:0.1-0.8:1.5-2. The conductive agent includes one or more of Ketjen black, mesophase carbon microspheres, activated carbon, graphite, conductive carbon black, acetylene black, carbon fiber, carbon nanotubes, and graphene. The thickener includes one or more of carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, and casein. The binder includes one or more of polyvinylidene fluoride, hexafluoropropylene, pentafluoropropylene, tetrafluoropropylene, trifluoropropylene, perfluorobutene, hexafluorobutadiene, hexafluoroisobutylene, trifluoroethylene, trifluorochloroethylene, and tetrafluoroethylene.

[0061] In some embodiments, the battery further includes a separator and a housing. The separator separates the positive electrode and the negative electrode, and the housing encapsulates the positive electrode, the negative electrode, the separator, and the non-aqueous electrolyte. The separator can be any material suitable for lithium-ion battery separators in the art, including, but not limited to, one or more combinations of polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester, and natural fibers. In some embodiments, the housing is made of stainless steel or aluminum-plastic film.

[0062] In some embodiments, the non-aqueous electrolyte can be various materials suitable for lithium-ion battery electrolytes in the art, such as, but not limited to, combinations of ethylene carbonate (EC), diethyl carbonate (DMC), ethyl methyl carbonate (EMC), lithium bis(fluorosulfonyl)imide (LiFSI), lithium hexafluorophosphate (LiPF6), etc. In some embodiments, the ethylene carbonate (EC), diethyl carbonate (DMC), and ethyl methyl carbonate (EMC) are present in a mass percentage ratio of 1–2:1–2:1–2.

[0063] In some embodiments, the method for preparing the lithium manganese iron phosphate battery in the above embodiments provided in this application includes:

[0064] A positive electrode slurry is prepared by weighing and mixing the positive electrode active material, conductive agent, dispersant and binder in a predetermined ratio; wherein the mass percentage of the positive electrode active material, conductive agent, dispersant and binder in the predetermined ratio is 95-97:1-2:0.1-0.5:1-2; the dispersant is vinylene carbonate;

[0065] A positive electrode sheet is obtained by coating the positive electrode slurry onto the positive electrode active material;

[0066] A negative electrode slurry and a non-aqueous electrolyte are prepared. The negative electrode slurry includes a negative electrode active material, a conductive agent, a thickener, an additive, and a binder. The mass percentage of the negative electrode active material, conductive agent, thickener, additive, and binder is 95-97:1-2:0.1-0.5:0.1-0.8:1.5-2. The additive is styrene-butadiene rubber.

[0067] A negative electrode sheet is obtained by coating the negative electrode slurry onto the negative electrode active material;

[0068] The positive electrode and the negative electrode are assembled, and then vacuum-sealed with a non-aqueous electrolyte to obtain a lithium manganese iron phosphate battery.

[0069] In order to enable lithium manganese iron phosphate batteries to achieve both low-temperature discharge performance and high-temperature cycle performance, it is necessary to limit the film resistance after coating the positive electrode. Specifically, the film resistance after coating the positive electrode is 200-500mΩ. Electrode sheets with a film resistance value less than or equal to the preset value after coating are selected as positive electrode sheets, thereby improving the low-temperature discharge capability of the cell.

[0070] This application optimizes the positive electrode composition and non-aqueous electrolyte composition of lithium manganese iron phosphate batteries, effectively delaying capacity decay at low temperatures, improving cycle life, reducing internal resistance, and enhancing low-temperature performance, thereby obtaining a wide-temperature-range lithium manganese iron phosphate battery that can balance low-temperature discharge performance and high-temperature cycle performance.

[0071] Example 1:

[0072] 1) Preparation of positive electrode sheet

[0073] Step 1: Mix the binder polyvinylidene fluoride (PVDF) and the positive electrode active material lithium manganese iron phosphate (LMFP) powder to obtain a mixed powder.

[0074] Step 2: Stir and mix the solvent N-methyl-2-pyrrolidone (NMP), the conductive agent carbon nanotubes (CNT), and the vinylene carbonate (VC) compound to obtain a mixed liquid.

[0075] Step 3: Add the mixed liquid to the mixed powder, disperse at high speed, and stir evenly to obtain the positive electrode slurry. The mass percentage of the positive electrode active material, conductive agent carbon nanotubes (CNTs), vinylene carbonate (VC), and positive electrode binder polyvinylidene fluoride (PVDF) is 96.4 - c:1.4:c:2.2. The positive electrode active material is lithium manganese iron phosphate (LiMn) coated with a carbon coating layer. 0.6 Fe 0.4 PO4) active material, c = 0.1%.

[0076] Step 4: The prepared positive electrode slurry is uniformly coated onto the positive electrode active material (e.g., aluminum foil), and then the resistance of the electrode sheet is measured using a film resistivity meter. The film resistivity is 403 mΩ, and the compaction density is 2.5 g / cm³. 3 .

[0077] Step 5: Obtain the positive electrode sheet through drying, rolling, die cutting or slitting.

[0078] 2) Preparation of negative electrode sheet

[0079] Step 1: Weigh out the negative electrode material according to the mass percentage ratio of graphite: conductive carbon (superP): carboxymethyl cellulose (CMC): styrene-butadiene rubber (SBR): binder = 96.4:1.0:0.3:0.5:1.8.

[0080] Step 2: First, stir and premix the graphite, conductive carbon (superP), and carboxymethyl cellulose (CMC), then add pure water and stir thoroughly.

[0081] Step 3: Add binder to the mixed slurry, mix thoroughly, then add styrene-butadiene rubber (SBR) to finally obtain the negative electrode slurry.

[0082] Step 4: The prepared negative electrode slurry is evenly coated on copper foil, and then dried, rolled, die-cut or slit to obtain the negative electrode sheet.

[0083] 3) Preparation of non-aqueous electrolyte

[0084] Ethylene carbonate (EC), diethyl carbonate (DMC), and methyl ethyl carbonate (EMC) were mixed in a mass percentage ratio of EC:DMC:EMC = 1:1:1. 3% lithium bis(fluorosulfonyl)imide (LiFSI) was added, followed by the addition of lithium hexafluorophosphate (LiPF6) to a molar concentration of 0.9 mol / L. The numerical value of the above formula is 8.90.

[0085] 4) Lithium-ion cell manufacturing

[0086] The prepared positive electrode sheet and the prepared negative electrode sheet are assembled into a stacked soft-pack battery cell.

[0087] 5) Electrolyte injection and formation of battery cells

[0088] In an environment where the dew point is controlled below -40°C, the non-aqueous electrolyte prepared above is injected into the cell, vacuum-sealed, and left to stand for 72 hours. Then, the first charge is performed according to the following steps: 0.05C constant current charging for 180 minutes, 0.1C constant current charging for 120 minutes, 0.2C constant current charging for 120 minutes, followed by a second vacuum sealing, and then a full charge at 0.2C (100% SOC). After being left to stand at room temperature for 72 hours, it is fully discharged at 0.2C (0% SOC).

[0089] Example 2:

[0090] The preparation method of the lithium manganese iron phosphate battery in this embodiment is the same as that in Example 1, but the film resistance of the positive electrode is 444 mΩ and the compaction density of the positive electrode is 2.55 g / cm³. 3 The content of vinylene carbonate is 0.2 wt%, and the content of lithium bis(fluorosulfonyl)imide is 4 wt%.

[0091] Example 3:

[0092] The preparation method of the lithium manganese iron phosphate battery in this embodiment is the same as that in Example 1, but the film resistance of the positive electrode is 487mΩ and the compaction density of the positive electrode is 2.65g / cm³. 3 The content of vinylene carbonate is 0.2 wt%, and the content of lithium bis(fluorosulfonyl)imide is 3 wt%.

[0093] Example 4:

[0094] The preparation method of the lithium manganese iron phosphate battery in this embodiment is the same as that in Example 1, but the film resistance of the positive electrode is 412 mΩ and the compaction density of the positive electrode is 2.5 g / cm³. 3 The content of vinylene carbonate is 0.2 wt%, and the content of lithium bis(fluorosulfonyl)imide is 3 wt%.

[0095] Example 5:

[0096] The preparation method of the lithium manganese iron phosphate battery in this embodiment is the same as that in Example 1, but the film resistance of the positive electrode is 498 mΩ and the compaction density of the positive electrode is 2.6 g / cm³. 3 The content of vinylene carbonate is 0.2 wt%, and the content of lithium bis(fluorosulfonyl)imide is 6 wt%.

[0097] Example 6:

[0098] The preparation method of the lithium manganese iron phosphate battery in this embodiment is the same as that in Example 1, but the film resistance of the positive electrode is 464 mΩ and the compaction density of the positive electrode is 2.6 g / cm³. 3 The content of vinylene carbonate is 0.2 wt%, and the content of lithium bis(fluorosulfonyl)imide is 6 wt%.

[0099] Example 7:

[0100] The preparation method of the lithium manganese iron phosphate battery in this embodiment is the same as that in Example 1, but the film resistance of the positive electrode is 399 mΩ and the compaction density of the positive electrode is 2.6 g / cm³. 3 The content of vinylene carbonate is 0.1 wt%, and the content of lithium bis(fluorosulfonyl)imide is 4 wt%.

[0101] Example 8:

[0102] The preparation method of the lithium manganese iron phosphate battery in this embodiment is the same as that in Example 1, but the film resistance of the positive electrode is 320mΩ and the compaction density of the positive electrode is 2.6g / cm³. 3 The content of vinylene carbonate is 0.2 wt%, and the content of lithium bis(fluorosulfonyl)imide is 4 wt%.

[0103] Example 9:

[0104] The preparation method of the lithium manganese iron phosphate battery in this embodiment is the same as that in Example 1, but the film resistance of the positive electrode is 362 mΩ and the compaction density of the positive electrode is 2.6 g / cm³. 3 The content of vinylene carbonate is 0.2 wt%, and the content of lithium bis(fluorosulfonyl)imide is 4 wt%.

[0105] Example 10:

[0106] The preparation method of the lithium manganese iron phosphate battery in this embodiment is the same as that in Example 1, but the film resistance of the positive electrode is 410 mΩ and the compaction density of the positive electrode is 2.6 g / cm³. 3 The content of vinylene carbonate is 0.2 wt%, and the content of lithium bis(fluorosulfonyl)imide is 4 wt%.

[0107] Example 11:

[0108] The preparation method of the lithium manganese iron phosphate battery in this embodiment is the same as that in Example 1, but the film resistance of the positive electrode is 371 mΩ and the compaction density of the positive electrode is 2.6 g / cm³. 3 The content of vinylene carbonate is 0.1 wt%, and the content of lithium bis(fluorosulfonyl)imide is 3 wt%.

[0109] Example 12:

[0110] The preparation method of the lithium manganese iron phosphate battery in this embodiment is the same as that in Example 1, but the film resistance of the positive electrode is 375mΩ and the compaction density of the positive electrode is 2.6g / cm³. 3 The content of vinylene carbonate is 0.1 wt%, and the content of lithium bis(fluorosulfonyl)imide is 4 wt%.

[0111] Example 13:

[0112] The preparation method of the lithium manganese iron phosphate battery in this embodiment is the same as that in Example 1, but the film resistance of the positive electrode is 374 mΩ and the compaction density of the positive electrode is 2.6 g / cm³. 3 The content of vinylene carbonate is 0.1 wt%, and the content of lithium bis(fluorosulfonyl)imide is 5 wt%.

[0113] Example 14:

[0114] The preparation method of the lithium manganese iron phosphate battery in this embodiment is the same as that in Example 1, but the film resistance of the positive electrode is 373 mΩ and the compaction density of the positive electrode is 2.6 g / cm³. 3 The content of vinylene carbonate is 0.1 wt%, and the content of lithium bis(fluorosulfonyl)imide is 7 wt%.

[0115] Example 15:

[0116] The preparation method of the lithium manganese iron phosphate battery in this embodiment is the same as that in Example 1, but the film resistance of the positive electrode is 416 mΩ and the compaction density of the positive electrode is 2.4 g / cm³. 3 The content of vinylene carbonate is 0.1 wt%, and the content of lithium bis(fluorosulfonyl)imide is 4 wt%.

[0117] Example 16:

[0118] The preparation method of the lithium manganese iron phosphate battery in this embodiment is the same as that in Example 1, but the film resistance of the positive electrode is 409 mΩ and the compaction density of the positive electrode is 2.5 g / cm³. 3 The content of vinylene carbonate is 0.1 wt%, and the content of lithium bis(fluorosulfonyl)imide is 4 wt%.

[0119] Example 17:

[0120] The preparation method of the lithium manganese iron phosphate battery in this embodiment is the same as that in Example 1, but the film resistance of the positive electrode is 421 mΩ and the compaction density of the positive electrode is 2.6 g / cm³. 3 The content of vinylene carbonate is 0.1 wt%, and the content of lithium bis(fluorosulfonyl)imide is 4 wt%.

[0121] Example 18:

[0122] The preparation method of the lithium manganese iron phosphate battery in this embodiment is the same as that in Example 1, but the film resistance of the positive electrode is 430 mΩ and the compaction density of the positive electrode is 2.6 g / cm³. 3 The content of vinylene carbonate is 0.1 wt%, and the content of lithium bis(fluorosulfonyl)imide is 4 wt%.

[0123] Example 19:

[0124] The preparation method of the lithium manganese iron phosphate battery in this embodiment is the same as that in Example 1, but the film resistance of the positive electrode is 420 mΩ and the compaction density of the positive electrode is 2.6 g / cm³. 3 The content of vinylene carbonate is 0.2 wt%, and the content of lithium bis(fluorosulfonyl)imide is 4 wt%.

[0125] Comparative Example 1

[0126] The preparation method of this comparative lithium manganese iron phosphate battery is the same as that in Example 1, but the film resistance of the positive electrode is 389 mΩ and the compaction density of the positive electrode is 2.5 g / cm³. 3 The content of vinylene carbonate is 0 wt%, and the content of lithium bis(fluorosulfonyl)imide is 3 wt%.

[0127] Comparative Example 2

[0128] The preparation method of this comparative lithium manganese iron phosphate battery is the same as that in Example 1, but the film resistance of the positive electrode is 467 mΩ and the compaction density of the positive electrode is 2.5 g / cm³.3 The content of vinylene carbonate is 0.5 wt%, and the content of lithium bis(fluorosulfonyl)imide is 3 wt%.

[0129] Comparative Example 3

[0130] The preparation method of this comparative lithium manganese iron phosphate battery is the same as that in Example 1, but the film resistance of the positive electrode is 596 mΩ and the compaction density of the positive electrode is 2.5 g / cm³. 3 The content of vinylene carbonate is 0.2 wt%, and the content of lithium bis(fluorosulfonyl)imide is 3 wt%.

[0131] Comparative Example 4

[0132] The preparation method of this comparative lithium manganese iron phosphate battery is the same as that in Example 1, but the film resistance of the positive electrode is 598 mΩ and the compaction density of the positive electrode is 2.2 g / cm³. 3 The content of vinylene carbonate is 0 wt%, and the content of lithium bis(fluorosulfonyl)imide is 10 wt%.

[0133] Comparative Example 5

[0134] The preparation method of this comparative lithium manganese iron phosphate battery is the same as that in Example 1, but the film resistance of the positive electrode is 553 mΩ and the compaction density of the positive electrode is 2.3 g / cm³. 3 The content of vinylene carbonate is 0.2 wt%, and the content of lithium bis(fluorosulfonyl)imide is 5 wt%.

[0135] Comparative Example 6

[0136] The preparation method of this comparative lithium manganese iron phosphate battery is the same as that in Example 1, but the film resistance of the positive electrode is 374 mΩ and the compaction density of the positive electrode is 2.6 g / cm³. 3 The content of vinylene carbonate is 0.1 wt%, and the content of lithium bis(fluorosulfonyl)imide is 0 wt%.

[0137] Comparative Example 7

[0138] The preparation method of this comparative lithium manganese iron phosphate battery is the same as that in Example 1, but the film resistance of the positive electrode is 373 mΩ and the compaction density of the positive electrode is 2.6 g / cm³. 3 The content of vinylene carbonate is 0.1 wt%, and the content of lithium bis(fluorosulfonyl)imide is 10 wt%.

[0139] Comparative Example 8

[0140] The preparation method of this comparative lithium manganese iron phosphate battery is the same as that in Example 1, but the film resistance of the positive electrode is 412 mΩ and the compaction density of the positive electrode is 2.5 g / cm³. 3The proportion of vinylene carbonate is 0.2 wt%, and the proportion of lithium bis(trifluoromethanesulfonate)imide is 3 wt%. In this comparative example, lithium bis(trifluoromethanesulfonate)imide (LiTFSI) is used instead of lithium bis(fluorosulfonate)imide.

[0141] Comparative Example 9

[0142] The preparation method of this comparative lithium manganese iron phosphate battery is the same as that in Example 1, but the film resistance of the positive electrode is 412 mΩ and the compaction density of the positive electrode is 2.5 g / cm³. 3 The proportion of fluoroethylene carbonate is 0.2 wt%, and the proportion of lithium difluorosulfonyl imide is 3 wt%. In this comparative example, fluoroethylene carbonate (FEC) is used instead of vinylene carbonate.

[0143] Table 1 records the formula values ​​corresponding to Examples 1-19 and Comparative Examples 1-9.

[0144] Table 1

[0145]

[0146]

[0147] Charging performance tests were conducted on Examples 1-19 and Comparative Examples 1-9.

[0148] 1. Diaphragm resistance test

[0149] The resistance of the fabricated positive electrode was measured using an electrode resistance tester to obtain the film resistance.

[0150] DCIR test at 2.25℃

[0151] The lithium-ion battery was placed in a constant temperature environment of 25°C and charged at a constant current of 0.5C to the cutoff voltage of 3.65V. Then it was charged at a constant voltage until the current dropped to 0.05C. Subsequently, it was discharged at a constant current of 1 / 3C to 2.0V, and the discharge capacity was recorded. The battery was then fully charged again and discharged at a constant current of 0.5C to 50% of its SOC. After resting for 30 minutes, it was discharged at a constant current of 2C for 10 seconds. The DCIR of the cell was calculated.

[0152] Calculate the DCIR of the battery cell using the following formula:

[0153] DCIR = (Voltage after 30 minutes of rest - Voltage after 2C constant current discharge) / 2C discharge current.

[0154] 3. Low-temperature discharge test at -20℃

[0155] The lithium-ion battery was placed in a constant temperature environment of 25℃ and charged at a constant current of 0.5C to the cutoff voltage of 3.65V. Then it was charged at a constant voltage until the current dropped to 0.05C. Subsequently, it was discharged at a constant current of 1 / 3C to 2.0V. The discharge capacity at room temperature was recorded. The charging steps were repeated to fully charge the lithium battery. Then it was placed in a constant temperature environment of -20℃ and left to stand for 6 hours. Then it was discharged at a constant current of 1 / 3C to 2.0V. The discharge capacity at -20℃ was recorded, and the proportion of low temperature discharge capacity was calculated.

[0156] Calculate the capacity retention rate during the cycle using the following formula:

[0157] Low-temperature discharge capacity percentage (%) = -20℃ low-temperature discharge capacity / room temperature discharge capacity × 100%.

[0158] 4. High-temperature cycling performance test

[0159] The lithium-ion battery was placed in a constant temperature environment of 45°C and charged at a constant current of 1C to 3.65V. Then it was charged at a constant voltage until the current dropped to 0.05C. The internal resistance of the battery was tested. Then it was discharged at a constant current of 1C to 2.0V. This cycle was repeated 1000 times. The discharge capacity of the first cycle and the discharge capacity of the last cycle, as well as the internal resistance of the battery after the first full charge and the battery after the last full charge, were recorded.

[0160] Calculate the capacity retention rate and internal resistance growth rate during the cycle using the following formula:

[0161] Capacity retention rate (%) = Last discharge capacity / First discharge capacity × 100%;

[0162] Internal resistance growth rate (%) = (internal resistance of the battery after the last full charge - internal resistance of the battery after the first full charge) / internal resistance of the battery after the first full charge × 100%.

[0163] The results of charging performance tests for Examples 1-19 and Comparative Examples 1-9 are shown in Table 2.

[0164] Table 2

[0165]

[0166]

[0167] Through Examples 1 to 7, the formula values ​​are within the defined range, all parameters are within the defined range, and the performance fluctuation is small. Appropriate matching of parameters can achieve the optimal matching Example 2, which has low cell impedance and good high and low temperature performance. In contrast, in Comparative Examples 4 and 5, some or all of the parameters a, b, c, and d in the formula exceed the defined range, which will lead to a decrease in cell performance due to their inherent relationship. In Comparative Examples 8 and 9, lithium bis(trifluoromethanesulfonate)imide (LiTFSI) and fluoroethylene carbonate (FEC) are used to replace lithium bis(fluorosulfonylimide) (LiFSI) and ethylene carbonate (VC). The former will reduce cell impedance but will seriously degrade high-temperature cycling performance, while the latter will cause a significant increase in impedance and serious deterioration of high and low temperature performance.

[0168] Through Examples 8 to 10, by adjusting the diaphragm resistance values, the aim was to investigate the impact of the diaphragm resistance range on battery performance. In each example, the formula values ​​were within the defined range, and all parameters were within the limits, resulting in minimal performance fluctuations. However, it was observed that a decrease in diaphragm resistance improved the cell's low-temperature discharge capability. In contrast, in Comparative Example 3, the formula values ​​exceeded the defined range, leading to significant performance degradation, and the diaphragm resistance severely exceeded the upper limit, resulting in increased cell impedance and deteriorated low-temperature discharge capability.

[0169] Examples 11 to 14 investigated the effect of lithium bis(fluorosulfonyl)imide (LiFSI) addition on battery performance by adjusting the amount of LiFSI added. The formula values ​​in each example were within the specified range, and all parameters were within the limits, with minimal performance fluctuations. As the LiFSI content increased, the impedance decreased, and low-temperature discharge performance improved, but high-temperature cycling performance decreased. Compared to Comparative Examples 6 and 7, excessively low LiFSI content led to increased cell impedance and deteriorated low-temperature discharge performance, while excessively high LiFSI content also caused increased cell impedance and deteriorated high-temperature cycling performance.

[0170] Analysis of Examples 15 to 17 shows that by adjusting the compaction density, the aim is to explore the effect of the compaction density range on battery performance. The formula values ​​of each example are within the specified range, and all parameters are within the specified range, with small performance fluctuations. However, the increase in positive electrode compaction density will lead to a decrease in cell impedance and optimize low-temperature performance, but the effect on high-temperature cycling performance is not linear.

[0171] Examples 18 and 19 investigated the effect of vinylene carbonate (VC) content on battery performance by adjusting the amount of VC added. The numerical values ​​in the formulas for each example were within the defined range, and all parameters were within their limits, resulting in minimal performance fluctuations. Appropriately increasing the VC content led to increased impedance, decreased low-temperature performance, and optimized high-temperature cycling capability. Compared to Comparative Examples 1 and 2, excessively decreasing or increasing the VC content both resulted in a significant decrease in high-temperature performance.

[0172] As can be seen from the above embodiments, this application discloses a lithium manganese iron phosphate battery, which includes a positive electrode, a negative electrode, and a non-aqueous electrolyte; the positive electrode includes a positive active material and a positive active coating disposed on at least one surface of the positive active material; the positive active material includes lithium manganese iron phosphate (LiMn) coated with a carbon coating layer. x Fe 1-x PO4, wherein 0.5≤x≤0.8; the negative electrode sheet includes a negative electrode active material and a negative electrode active coating disposed on at least one surface of the negative electrode active material; the non-aqueous electrolyte includes lithium bis(fluorosulfonyl)imide; wherein the battery satisfies the following relationship: 4.5≤(a / 20+d) / (b+c)≤12.8; a is the film resistance of the positive electrode sheet after coating; b is the compaction density of the positive electrode sheet; c is the mass percentage content of vinylene carbonate in the positive electrode slurry; d is the mass percentage content of lithium bis(fluorosulfonyl)imide in the non-aqueous electrolyte. By optimizing the composition of lithium-ion batteries, using lithium manganese iron phosphate as the positive electrode active material, controlling the amount of vinylene carbonate (VC) added to the positive electrode slurry, the resistance of the positive electrode film, and the compaction density, and adding an appropriate amount of lithium bisfluorosulfonyl imide (LiFSI) to the non-aqueous electrolyte, and making the battery composition meet specific requirements, the synergistic effect between lithium bisfluorosulfonyl imide (LiFSI) and vinylene carbonate (VC) and the positive electrode active material can be fully utilized, so that the battery can improve the low-temperature discharge performance while taking into account the high-temperature cycle performance.

[0173] Similar parts between the embodiments provided in this application can be referred to mutually. The specific implementation methods provided above are only a few examples under the overall concept of this application and do not constitute a limitation on the scope of protection of this application. For those skilled in the art, any other implementation methods extended from the solution of this application without creative effort shall fall within the scope of protection of this application.

Claims

1. A lithium manganese iron phosphate battery, characterized in that, The battery includes a positive electrode, a negative electrode, and a non-aqueous electrolyte; the positive electrode includes a positive active material and a positive active coating disposed on at least one surface of the positive active material; the positive active material includes lithium manganese iron phosphate (LiMn) coated with a carbon coating layer. x Fe 1-x PO4, where 0.5 ≤ x ≤ 0.8; The negative electrode sheet includes a negative electrode active material and a negative electrode active coating disposed on at least one surface of the negative electrode active material; the non-aqueous electrolyte includes lithium bis(fluorosulfonyl)imide. The battery described above satisfies the following relationship: 4.5≤(a / 20+d) / (b+c)≤12.8; a represents the film resistance after coating the positive electrode; b is the compaction density of the positive electrode sheet; c represents the mass percentage of vinylene carbonate in the cathode slurry; d represents the mass percentage of lithium bis(fluorosulfonyl)imide in the non-aqueous electrolyte; The resistivity (a) of the coated positive electrode sheet is 200~500mΩ, and the compaction density (b) of the positive electrode sheet is 2.4~2.7g / cm³. 3 The mass percentage c of the vinylene carbonate in the positive electrode slurry is 0.1~0.4wt%, and the mass percentage d of the lithium bis(fluorosulfonyl)imide in the non-aqueous electrolyte is 3~7wt%.

2. The lithium manganese iron phosphate battery according to claim 1, characterized in that, The positive electrode active coating comprises a positive electrode active material, a conductive agent, a dispersant, and a binder. The mass percentage of the conductive agent, dispersant, and binder is 1~2:c:1~2, and the mass percentage of the positive electrode active material and the dispersant ranges from 95 to 97%. The dispersant is vinylene carbonate.

3. The lithium manganese iron phosphate battery according to claim 2, characterized in that, The negative electrode active coating comprises a negative electrode active material, a conductive agent, a thickener, an additive, and a binder, wherein the mass percentage of the negative electrode active material, conductive agent, thickener, additive, and binder is 95~97: 1~2: 0.1~0.5: 0.1~0.8: 1.5~2, and the additive is styrene-butadiene rubber.

4. The lithium manganese iron phosphate battery according to claim 3, characterized in that, The conductive agent includes one or more of Ketjen black, mesophase carbon microspheres, activated carbon, graphite, conductive carbon black, acetylene black, carbon fiber, carbon nanotubes, and graphene; the thickener includes one or more of carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, and casein; the binder includes one or more of polyvinylidene fluoride, hexafluoropropylene, pentafluoropropylene, tetrafluoropropylene, trifluoropropylene, perfluorobutene, hexafluorobutadiene, hexafluoroisobutylene, trifluoroethylene, trifluorochloroethylene, and tetrafluoroethylene.

5. The lithium manganese iron phosphate battery according to claim 1, characterized in that, The battery further includes a separator and a housing. The separator separates the positive electrode and the negative electrode, and the housing encapsulates the positive electrode, the negative electrode, the separator, and the non-aqueous electrolyte. The non-aqueous electrolyte includes ethylene carbonate, diethyl carbonate, methyl ethyl carbonate, and lithium bis(fluorosulfonyl)imide. The ethylene carbonate, diethyl carbonate, and methyl ethyl carbonate are present in a mass percentage ratio of 1~2:1~2:1~2.

6. The lithium manganese iron phosphate battery according to claim 1, characterized in that, The preparation method of the lithium manganese iron phosphate battery includes: A positive electrode slurry is prepared by weighing and mixing a pre-prepared ratio of positive electrode active material, conductive agent, dispersant and binder; wherein the mass percentage of the pre-prepared ratio of positive electrode active material, conductive agent, dispersant and binder is 95~97:1~2:0.1~0.5:1~2; the dispersant is vinylene carbonate; The positive electrode slurry is coated onto the positive electrode active material to obtain a positive electrode sheet; A negative electrode slurry and a non-aqueous electrolyte are prepared; the negative electrode slurry includes a negative electrode active material, a conductive agent, a thickener, an additive, and a binder, wherein the mass percentage of the negative electrode active material, conductive agent, thickener, additive, and binder is 95~97: 1~2: 0.1~0.5: 0.1~0.8: 1.5~2, and the additive is styrene-butadiene rubber; The negative electrode slurry is coated onto the negative electrode active material to obtain a negative electrode sheet; The positive electrode and the negative electrode are assembled, and then vacuum-sealed with a non-aqueous electrolyte to obtain a lithium manganese iron phosphate battery.

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