Diaphragm, negative electrode sheet, method for manufacturing same, and battery

Abstract

A diaphragm, a negative electrode sheet and a battery, wherein the diaphragm comprises a base film and coated particles, the coated particles are loaded on the negative electrode side surface of the base film, the shell layer of the coated particles comprises a low-melting polymer material, the core material of the coated particles is a lithium-deficient material, when the temperature is greater than or equal to 60 DEG C, the low-melting polymer material changes in structure so that the lithium-deficient material can at least partially expose the surface of the shell layer, the exposed lithium-deficient material contacts the negative electrode and can extract lithium ions from the negative electrode, thereby reducing the state of charge of the negative electrode, improving the stability of the negative electrode and enhancing the safety of the battery.

Description

Technical Field

[0001] The present invention relates to the field of battery technology, and in particular to a separator, a negative electrode sheet, a method for preparing the same, and a battery. Background Technology

[0002] To meet the range requirements of new energy vehicles, lithium-ion power batteries are developing towards larger sizes and higher energy densities. The negative electrode, as a key component of the power battery, directly affects the battery's energy density and safety through its specific energy and thermal stability. However, the poor thermal stability of the negative electrode (it may undergo a heat-generating reaction above 60℃, causing self-heating or even thermal runaway) is one of the main shortcomings in the safety of power batteries.

[0003] To address the above problems, existing solutions include: (1) coating the surface of the negative electrode material and improving the preparation process; and (2) introducing additives into the electrolyte.

[0004] However, the improvement effect of scheme (1) is not obvious and cannot effectively improve the thermal stability of the negative electrode; the additives in scheme (2) are expensive and affect the performance of the battery, so the improvement effect is limited.

[0005] Therefore, how to effectively improve battery safety has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] The technical problem solved by the embodiments of the present invention is how to effectively improve battery safety.

[0007] To address the aforementioned problems, the present invention provides a separator comprising a base membrane and coated particles, wherein the coated particles are loaded on the negative electrode side surface of the base membrane, the shell of the coated particles comprises a low-melting-point polymer material, and the core material of the coated particles is a lithium-deficient material. When the temperature is ≥60℃, the structure of the low-melting-point polymer material changes so that at least part of the lithium-deficient material can be exposed on the shell surface.

[0008] Optionally, the shell of the coated particles may further include a conductive material.

[0009] Optionally, the lithium-deficient material is selected from elemental sulfur, elemental phosphorus, sulfur-phosphorus compounds, and Li. x Ni y Co z Mn (1-y-z) O2(0≤x<1,0≤y≤1,0≤z≤1,0≤y+z≤1), Li x Mn₂O₄ (0≤x<1), Li x Fe y Mn (1-y)PO4 (0≤x<1, 0≤y≤1), carbon, silicon, silicon-carbon, phosphorus-carbon, sulfur-carbon, phosphorus-silicon, and sulfur-silicon.

[0010] Optionally, the conductive material includes at least one of carbon black, carbon nanotubes, graphene, carbon fiber, polypyrrole, polythiophene, polyaniline, polyacetylene, and polyphenylacetylene.

[0011] Optionally, the polymer material includes at least one of polyvinyl chloride, polyethersulfone, polyamic acid, poly(m-phenylene isophthalamide), poly(p-phenylene terephthalamide), polysiloxane, polytetrafluoroethylene, polyethylene, polypropylene, polyethylene glycol, polyethylene oxide, polypropylene oxide, polyethyleneimine, polyvinylidene fluoride, polymethyl methacrylate, polyacrylic acid, carboxymethyl cellulose, chitosan, sodium alginate, polyvinyl alcohol, polyvinylpyrrolidone, and styrene-butadiene rubber latex.

[0012] Optionally, the diameter of the core is 50 nm-5 μm; and / or the thickness of the shell is 20 nm-1 μm.

[0013] Optionally, the lithium-deficient material is prepared by an electrochemical delithiation method.

[0014] Optionally, the loading amount of the coated particles ranges from 1 g / m³. 2 -6g / m 2 .

[0015] Optionally, the base membrane is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, poly(m-phenylene isophthalamide), poly(p-phenylene terephthalamide), polyethersulfone, polyimide, polyvinylidene fluoride, and polytetrafluoroethylene porous membranes.

[0016] In another aspect, the present invention provides a method for preparing a diaphragm, comprising the following steps:

[0017] 1) Provide lithium-deficient materials;

[0018] 2) The lithium-deficient material is dispersed in a coating solution and then atomized and dried to obtain coated particles;

[0019] 3) The coated particles are dispersed in a coating solution and then coated on the negative electrode side of the base membrane to obtain the separator.

[0020] Optionally, the coating liquid contains a coating agent, the material of which is selected from at least one of polyvinyl chloride, polyethersulfone, polyamic acid, poly(m-phenylene isophthalamide), poly(p-phenylene terephthalamide), polysiloxane, polytetrafluoroethylene, polyethylene, polypropylene, polyethylene glycol, polyethylene oxide, polypropylene oxide, polyethyleneimine, polyvinylidene fluoride, polymethyl methacrylate, polyacrylic acid, carboxymethyl cellulose, chitosan, sodium alginate, polyvinyl alcohol, polyvinylpyrrolidone, and styrene-butadiene rubber.

[0021] Optionally, the coating liquid contains a conductive agent, the material of which is selected from at least one of carbon black, carbon nanotubes, graphene, carbon fiber, polypyrrole, polythiophene, polyaniline, polyacetylene, and polyphenylacetylene.

[0022] Optionally, the lithium-deficient material is selected from elemental sulfur, elemental phosphorus, sulfur-phosphorus compounds, and Li. x Ni y Co z Mn (1-y-z) O2(0≤x<1,0≤y≤1,0≤z≤1,0≤y+z≤1), Li x Mn₂O₄ (0≤x<1), Li x Fe y Mn (1-y) PO4 (0≤x<1, 0≤y≤1), carbon, silicon, silicon-carbon, phosphorus-carbon, sulfur-carbon, phosphorus-silicon, and sulfur-silicon.

[0023] In another aspect, the present invention provides a negative electrode sheet, wherein coated particles are dispersed on the surface and / or within the negative electrode sheet, the shell of the coated particles comprises a low-melting-point polymer material, and the core material of the coated particles is a lithium-deficient material. When the temperature is ≥60°C, the structure of the low-melting-point polymer material changes so that at least part of the lithium-deficient material can be exposed from the shell.

[0024] Optionally, the shell of the coated particles may further include a conductive material.

[0025] Optionally, the lithium-deficient material is selected from elemental sulfur, elemental phosphorus, sulfur-phosphorus compounds, and Li. x Ni y Co z Mn (1-y-z) O2(0≤x<1,0≤y≤1,0≤z≤1,0≤y+z≤1), Li x Mn₂O₄ (0≤x<1), Li x Fe y Mn (1-y) PO4 (0≤x<1, 0≤y≤1), carbon, silicon, silicon-carbon, phosphorus-carbon, sulfur-carbon, phosphorus-silicon, and sulfur-silicon.

[0026] Optionally, the conductive material includes at least one of carbon black, carbon nanotubes, graphene, carbon fiber, polypyrrole, polythiophene, polyaniline, polyacetylene, and polyphenylacetylene.

[0027] Optionally, the polymer material includes at least one of polyvinyl chloride, polyethersulfone, polyamic acid, poly(m-phenylene isophthalamide), poly(p-phenylene terephthalamide), polysiloxane, polytetrafluoroethylene, polyethylene, polypropylene, polyethylene glycol, polyethylene oxide, polypropylene oxide, polyethyleneimine, polyvinylidene fluoride, polymethyl methacrylate, polyacrylic acid, carboxymethyl cellulose, chitosan, sodium alginate, polyvinyl alcohol, polyvinylpyrrolidone, and styrene-butadiene rubber latex.

[0028] Optionally, the lithium-deficient material is prepared by an electrochemical delithiation method.

[0029] The present invention also provides a coated particle, wherein the shell of the coated particle is a low-melting-point polymer material and the core of the coated particle is a lithium-deficient material, wherein when the temperature is ≥60°C, the lithium-deficient material can at least partially expose the shell.

[0030] Optionally, the shell may also include a conductive material.

[0031] Optionally, the lithium-deficient material is selected from elemental sulfur, elemental phosphorus, sulfur-phosphorus compounds, and Li. x Ni y Co z Mn (1-y-z) O2(0≤x<1,0≤y≤1,0≤z≤1,0≤y+z≤1), Li x Mn₂O₄ (0≤x<1), Li x Fe y Mn (1-y) PO4 (0≤x<1, 0≤y≤1), carbon, silicon, silicon-carbon, phosphorus-carbon, sulfur-carbon, phosphorus-silicon, and sulfur-silicon.

[0032] Optionally, the conductive material includes at least one of carbon black, carbon nanotubes, graphene, carbon fiber, polypyrrole, polythiophene, polyaniline, polyacetylene, and polyphenylacetylene.

[0033] Optionally, the polymer material includes at least one of polyvinyl chloride, polyethersulfone, polyamic acid, poly(m-phenylene isophthalamide), poly(p-phenylene terephthalamide), polysiloxane, polytetrafluoroethylene, polyethylene, polypropylene, polyethylene glycol, polyethylene oxide, polypropylene oxide, polyethyleneimine, polyvinylidene fluoride, polymethyl methacrylate, polyacrylic acid, carboxymethyl cellulose, chitosan, sodium alginate, polyvinyl alcohol, polyvinylpyrrolidone, and styrene-butadiene rubber latex.

[0034] Optionally, the diameter of the core is 50 nm-5 μm; and / or the thickness of the shell is 20 nm-1 μm.

[0035] Optionally, the lithium-deficient material is prepared by an electrochemical delithiation method.

[0036] Optionally, the coated particles are prepared by the following steps:

[0037] 1) Provide lithium-deficient materials;

[0038] 2) The lithium-deficient material is dispersed in a coating solution and then atomized and dried to obtain coated particles with a core-shell structure.

[0039] This invention also provides a method for preparing a negative electrode, comprising the following steps:

[0040] 1) Provide a negative electrode substrate;

[0041] 2) Disperse the above-mentioned coated particles in the coating solution, and after surface coating, obtain the negative electrode sheet.

[0042] In another aspect, the present invention provides a method for preparing a negative electrode, comprising the following steps:

[0043] The aforementioned coated particles are dispersed in the negative electrode slurry, and after surface coating, the negative electrode sheet is obtained.

[0044] The present invention also provides a diaphragm comprising the aforementioned coated particles.

[0045] The present invention also provides a battery comprising the aforementioned separator.

[0046] The present invention also provides a battery comprising the aforementioned negative electrode.

[0047] Compared with the prior art, the technical solution of the embodiments of the present invention has the following advantages:

[0048] The separator provided in this invention can perform its basic functions under normal temperature conditions (below 60°C) to ensure the normal operation of the battery. Furthermore, when the battery is in an overheated environment (above 60°C), the shell layer (low-melting-point polymer) of the coating particles on the separator surface undergoes a structural transformation. The exposed lithium-deficient material acts as a lithium-deficient agent and comes into contact with the negative electrode, allowing it to capture lithium ions from the negative electrode. Lithium ions in the lithium-intercalated state of the negative electrode migrate to the lithium vacancies in the lithium-deficient material, reducing the degree to which lithium ions are intercalated into the negative electrode during charging. This reduces the state of charge of the negative electrode, improves its stability, and enhances battery safety. The shell melts and enters the pores of the base film under capillary force, sealing the channels and preventing material shuttle, thus effectively suppressing thermal runaway. Furthermore, the lithium-deficient material particles adhere to the separator surface, improving the separator's temperature resistance and suppressing thermal shrinkage, thereby enhancing battery safety. Detailed Implementation

[0049] As can be seen from the background technology, the current anode materials have poor thermal stability, which means that the safety performance of lithium batteries needs to be improved.

[0050] To better understand the technical solution of this invention, we will first analyze the reasons for the poor thermal stability of current anode materials.

[0051] Lithium-ion batteries are secondary batteries that use lithium-intercalation compounds as positive and negative electrode materials. During charging and discharging, lithium ions repeatedly intercalate and deintercalate between the two electrodes. Currently, the negative electrode material of lithium-ion power batteries is basically graphite-based carbon material. When the battery is charged, lithium ions intercalate into the graphite. After being fully charged, the graphite C material becomes a LiC6 compound, which itself has poor heat resistance.

[0052] Current efforts to improve the temperature resistance of anode materials mainly focus on surface modification through coating of graphite-based carbon anode materials. For example, coating the surface of anode material particles, improving particle size, or adding heat-resistant materials between particles (e.g., coating the surface of LiC6 compounds) are all methods to improve temperature resistance at the material level, but these methods are not very effective.

[0053] To address the aforementioned problems, embodiments of the present invention provide a separator that, when the battery is in an overheated environment (above 60°C), allows the lithium-deficient material in the coated particles loaded on the separator to acquire lithium ions from the LiC6 compound generated from the negative electrode material, thereby reducing the number of lithium ions in the negative electrode material (e.g., the LiC6 compound transforms into LiC). 12 (Compounds, etc.), thereby reducing the charge on the negative electrode, improving the stability of the negative electrode, and increasing the safety of the battery.

[0054] Reference will now be made to detailed embodiments of the present invention, one or more of which are described below. Each example is provided for explanation and not for limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made to the invention without departing from its scope or spirit. For example, features described or illustrated as part of one embodiment may be used in another embodiment to produce further embodiments.

[0055] Therefore, this invention is intended to cover such modifications and variations falling within the scope of the appended claims and their equivalents. Other objects, features, and aspects of the invention are disclosed in or will be apparent from the following detailed description. It will be understood by those skilled in the art that this discussion is merely a description of exemplary embodiments and is not intended to limit the broader aspects of the invention.

[0056] To address the aforementioned issues, this invention provides a separator comprising a base membrane and coated particles. The coated particles are loaded onto the negative electrode side surface of the base membrane. The shell of the coated particles comprises a low-melting-point polymer material, and the core material of the coated particles is a lithium-deficient material. When the temperature is ≥60°C, the structure of the low-melting-point polymer material changes, allowing at least a portion of the lithium-deficient material to be exposed on the shell surface.

[0057] The base membrane is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, poly(m-phenylene isophthalamide), poly(p-phenylene terephthalamide), polyethersulfone, polyimide, polyvinylidene fluoride, and polytetrafluoroethylene porous membranes.

[0058] It should be noted that the negative electrode side surface of the base film refers to the side of the separator closer to the negative electrode in the thickness direction after it is assembled into a battery.

[0059] It should be noted that when the temperature is ≥60℃, at least a portion of the lithium-deficient material can be exposed in the shell layer. This means that after the coated particles are assembled into a battery, when the battery temperature rises above 60℃, the structure of the polymer material in the shell layer changes, and the thermal contraction causes some of the lithium-deficient material to be exposed on the shell layer surface. The degree to which the lithium-deficient material is exposed in the shell layer is related to the battery temperature and the melting point of the polymer material.

[0060] It is readily understood by those skilled in the art that when the separator is assembled into a battery, due to the battery's weight and the application of external pressure, the lithium-deficient material exposed on the shell surface of the positive and negative electrode sheets will come into contact with the negative electrode sheet under its own weight. The lithium-deficient material being at least partially exposed means that after the structure of the polymer material of the shell changes under temperature rise, the lithium material can come into contact with the negative electrode material in any local area of ​​the negative electrode sheet cross-section, thus enabling the acquisition of lithium ions from the negative electrode.

[0061] The low-melting-point polymer material in the embodiments of the present invention refers to a polymer material that can undergo deformation in the temperature range of 60°C to 150°C, such as an oligomer with a melting point or softening point of around 100°C.

[0062] Polymer materials are used as coating agents to coat lithium-deficient materials, which can ensure the normal operation of the battery at room temperature, and can also deform at high temperature to expose the lithium-deficient materials.

[0063] The polymer materials include at least one of the following: polyvinyl chloride, polyethersulfone, polyamic acid, poly(m-phenylene isophthalamide), poly(p-phenylene terephthalamide), polysiloxane, polytetrafluoroethylene, polyethylene, polypropylene, polyethylene glycol, polyethylene oxide, polypropylene oxide, polyethyleneimine, polyvinylidene fluoride, polymethyl methacrylate, polyacrylic acid, carboxymethyl cellulose, chitosan, sodium alginate, polyvinyl alcohol, polyvinylpyrrolidone, and styrene-butadiene rubber.

[0064] It's easy to understand that when the temperature reaches the polymer's melting point, the polymer is already in a fully fluid, viscous flow state. Therefore, as the temperature rises, near the melting point, the small molecules begin to flow, and the shell as a whole exhibits good plasticity and can deform. Under the influence of gravity and capillary forces between particles, lithium-deficient materials can detach from the shell.

[0065] The lithium-intercalated negative electrode has a low potential. If the lithium-deficient material is exposed after the shell layer is exposed and comes into contact with the negative electrode, the lithium-deficient material acts as a lithium-deficient agent. Lithium ions will migrate from the negative electrode to the lithium-deficient material under the drive of the potential, and are used to store the lithium ions provided by the negative electrode.

[0066] In one specific embodiment, the lithium-deficient material is selected from elemental sulfur, elemental phosphorus, sulfur-phosphorus compounds, and Li. x Ni y Co z Mn (1-y-z) O2(0≤x<1,0≤y≤1,0≤z≤1,0≤y+z≤1), Li x Mn₂O₄ (0≤x<1), Li x Fe y Mn (1-y) PO4 (0≤x<1, 0≤y≤1), carbon, silicon, silicon-carbon, phosphorus-carbon, sulfur-carbon, phosphorus-silicon, and sulfur-silicon.

[0067] Lithium-deficient materials exhibit higher stability after lithium absorption compared to their anodes. The specific compound formed after lithium absorption in lithium-deficient materials depends on the amount of lithium intercalation. For example, elemental sulfur can form Li₂S compounds after lithium ion absorption, while elemental phosphorus can form Li₃P compounds.

[0068] In one specific embodiment, the lithium-deficient material is prepared by an electrochemical delithiation method.

[0069] It should be noted that the particle size of the lithium-deficient material, as the core of the core-shell structure, cannot be too large or too small. If the particle size of the lithium-deficient material is too large, on the one hand, when the coated particles are loaded onto the base film as a battery separator, the loading of lithium-deficient material on the base film will be too small, which is not conducive to its role in replenishing lithium to the positive electrode; on the other hand, excessively large particle size can easily puncture the battery. If the particle size of the lithium-deficient material is too small, the coated particles piled on the base film will be too dense, which is not conducive to lithium-ion transport under normal battery operation. Therefore, in a specific embodiment, the diameter of the core can be 50nm-5μm. Specifically, the diameter of the core can be 60nm, 100nm, 300nm, 500nm, 0.1μm, 1μm, 2μm, etc.

[0070] It should be noted that the core diameter of the coated particles does not have to be a single size; that is, the coated particles can contain both nanometer-sized and micrometer-sized lithium-deficient materials. The particle size of the material can be uniform or non-uniform, and the particle size of the lithium-deficient material is related to the lithium-deficient material selected. Several lithium-deficient materials with different particle sizes can be used simultaneously as lithium-deficient agents.

[0071] Similarly, the thickness of the shell layer cannot be too thick or too thin. If the shell layer is too thick, the lithium-deficient material will not easily be exposed, which is not conducive to the extraction of lithium from the negative electrode; if the shell layer is too thin, the lithium-deficient material will be unevenly coated, and the lithium-deficient material may come into contact with the positive electrode at room temperature, causing a short circuit between the positive and negative electrodes and affecting battery performance. Therefore, in a specific embodiment, the thickness of the shell layer can be 20nm-1μm. Specifically, the thickness of the shell layer can be 30nm, 50nm, 100nm, 300nm, 500nm, 1μm, etc.

[0072] The loading of the coated particles should not be too low or too high. If the loading is too low, the lithium-deficient material will struggle to store excessive lithium ions at the negative electrode, resulting in a minimal decrease in the negative electrode's state of charge and difficulty in improving stability. If the loading is too high, it will increase unnecessary costs. Therefore, in one specific embodiment, the loading of the coated particles is in the range of 1 g / m³. 2 -6g / m 2 For example, 2g / / m 2 3g / m 2 5g / m 2 .

[0073] It is easy to understand that two transport paths are formed when a battery is charging: a lithium-ion transport channel and an electron transport channel. In one specific embodiment, the coating of the particles also includes a conductive material. When the battery is fully charged, if the temperature is too high, the negative electrode replenishes lithium ions to the lithium-deficient material, and at the same time, corresponding electrons are generated. Adding conductive material can improve the smoothness of the electron transport path, thereby reducing the degree of lithium intercalation in the negative electrode, further reducing the state of charge of the negative electrode, and improving the battery safety performance.

[0074] It should be noted that lithium-deficient materials inherently possess both electronic and ionic conductivity. Since the coated particles on the base film surface are in direct contact with the negative electrode, lithium ions can be transported, and the surface lithium-deficient material can also form electronic pathways. Adding conductive materials to open these electronic pathways allows for the formation of electronic pathways both on the surface and inside the lithium-deficient material, thereby improving the smoothness of the electron transport path and further ensuring its integrity.

[0075] The conductive material may include at least one of carbon black, carbon nanotubes, graphene, carbon fiber, polypyrrole, polythiophene, polyaniline, polyacetylene, and polyphenylacetylene.

[0076] The separator provided in this invention can perform its basic functions under normal temperature conditions (below 60°C), ensuring the normal operation of the battery. Furthermore, when the battery is in an overheated environment (above 60°C), the shell layer (coating agent) of the core-shell structure of the coating particles on the separator surface undergoes a structural transformation. The exposed lithium-deficient material acts as a lithium-deficient agent and comes into contact with the negative electrode, allowing it to capture lithium ions from the negative electrode. Lithium ions in the lithium-intercalated state of the negative electrode migrate to the lithium vacancies in the lithium-deficient material, reducing the degree to which lithium ions are intercalated into the negative electrode during charging. This reduces the state of charge of the negative electrode, improves its stability, and enhances battery safety. The shell melts and enters the pores of the base film under capillary force, sealing the channels and preventing material shuttle, thus effectively suppressing thermal runaway. Furthermore, the lithium-deficient material particles adhere to the surface of the base film, improving the separator's temperature resistance and suppressing thermal shrinkage, thereby enhancing battery safety.

[0077] To address the above problems, embodiments of the present invention provide a method for preparing a diaphragm, comprising the following steps:

[0078] 1) Provide lithium-deficient materials;

[0079] 2) The lithium-deficient material is dispersed in a coating solution and then atomized and dried to obtain coated particles;

[0080] 3) The coated particles are dispersed in a coating solution and then coated on the negative electrode side of the base membrane to obtain the separator.

[0081] In one specific embodiment, the lithium-deficient material is selected from elemental sulfur, elemental phosphorus, sulfur-phosphorus compounds, and Li. x Ni y Co z Mn (1-y-z) O2(0≤x<1,0≤y≤1,0≤z≤1,0≤y+z≤1), Li x Mn₂O₄ (0≤x<1), Li x Fe y Mn (1-y) PO4 (0≤x<1, 0≤y≤1), carbon, silicon, silicon-carbon, phosphorus-carbon, sulfur-carbon, phosphorus-silicon, and sulfur-silicon.

[0082] The coating liquid contains a coating agent, the material of which is selected from at least one of polyvinyl chloride, polyethersulfone, polyamic acid, poly(m-phenylene isophthalamide), poly(p-phenylene terephthalamide), polysiloxane, polytetrafluoroethylene, polyethylene, polypropylene, polyethylene glycol, polyethylene oxide, polypropylene oxide, polyethyleneimine, polyvinylidene fluoride, polymethyl methacrylate, polyacrylic acid, carboxymethyl cellulose, chitosan, sodium alginate, polyvinyl alcohol, polyvinylpyrrolidone, and styrene-butadiene rubber.

[0083] The coating liquid contains a conductive agent, the material of which is selected from at least one of carbon black, carbon nanotubes, graphene, carbon fiber, polypyrrole, polythiophene, polyaniline, polyacetylene, and polyphenylacetylene.

[0084] The base membrane is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, poly(m-phenylene isophthalamide), poly(p-phenylene terephthalamide), polyethersulfone, polyimide, polyvinylidene fluoride, and polytetrafluoroethylene porous membrane.

[0085] The coating liquid contains a surfactant and a binder. The surfactant is used to disperse the particles uniformly, and the binder is used to adhere the particles to the base film. The surfactant is selected from at least one of glyceryl monostearate and sodium dioctyl succinate sulfonate.

[0086] The membrane preparation method provided in this invention is simple to operate. The prepared membrane can perform its basic functions under normal conditions, ensuring the normal operation of the battery. Furthermore, when the battery is in an overheated environment (above 60°C), the shell structure of the coating particles on the membrane surface undergoes a structural transformation. The lithium-deficient material comes into contact with the negative electrode material, and lithium ions from the lithium-intercalated negative electrode can migrate to the lithium vacancies in the lithium-deficient material, reducing the charge state of the negative electrode and thus enhancing its thermal stability and improving battery safety. Further, the lithium-deficient material particles adhere to the base membrane surface, improving the membrane's temperature resistance and suppressing thermal shrinkage, thereby enhancing battery safety.

[0087] To address the aforementioned issues, this invention provides a negative electrode sheet, wherein coated particles are dispersed on the surface and / or within the negative electrode sheet. The shell of the coated particles comprises a low-melting-point polymer material, and the core material of the coated particles is a lithium-deficient material. When the temperature is ≥60℃, the structure of the low-melting-point polymer material changes, allowing at least a portion of the lithium-deficient material to be exposed from the shell.

[0088] The lithium-deficient material is selected from elemental sulfur, elemental phosphorus, sulfur-phosphorus compounds, and Li. x Ni y Co z Mn (1-y-z) O2(0≤x<1,0≤y≤1,0≤z≤1,0≤y+z≤1), Li x Mn₂O₄ (0≤x<1), Li x Fe y Mn (1-y) PO4 (0≤x<1, 0≤y≤1), carbon, silicon, silicon-carbon, phosphorus-carbon, sulfur-carbon, phosphorus-silicon, and sulfur-silicon.

[0089] The shell of the coated particles also includes a conductive material, which includes at least one of carbon black, carbon nanotubes, graphene, carbon fiber, polypyrrole, polythiophene, polyaniline, polyacetylene, and polyphenylacetylene.

[0090] The polymer material includes at least one of the following: polyvinyl chloride, polyethersulfone, polyamic acid, poly(m-phenylene isophthalamide), poly(p-phenylene terephthalamide), polysiloxane, polytetrafluoroethylene, polyethylene, polypropylene, polyethylene glycol, polyethylene oxide, polypropylene oxide, polyethyleneimine, polyvinylidene fluoride, polymethyl methacrylate, polyacrylic acid, carboxymethyl cellulose, chitosan, sodium alginate, polyvinyl alcohol, polyvinylpyrrolidone, and styrene-butadiene rubber latex.

[0091] The negative electrode sheet provided in this embodiment of the invention, when assembled into a battery, when the temperature is below 60°C, the lithium-deficient material is covered by the shell layer, and the negative electrode material and the lithium-deficient material do not come into contact, and the battery works normally; when the lithium-intercalated state of the negative electrode becomes unstable during battery charging, if the battery temperature gradually increases (above 60°C), the shell layer gradually deforms or even melts due to heat, and the exposed lithium-deficient material comes into contact with the negative electrode material, which can capture lithium ions from the negative electrode. The lithium ions in the lithium-intercalated state of the negative electrode migrate to the lithium vacancies in the lithium-deficient material, thereby reducing the degree of lithium ion intercalation into the negative electrode due to charging, thereby reducing the state of charge of the negative electrode and improving the stability of the negative electrode. As can be seen, the negative electrode sheet provided in this embodiment of the invention can ensure the cycle performance and power performance of the battery under normal (below 60°C) conditions. When the battery is in an overheated environment (above 60°C), the shell layer of the coated particles undergoes a structural transformation. The exposed lithium-deficient material comes into contact with the negative electrode material. Lithium ions in the lithium-intercalated state of the negative electrode migrate to the lithium vacancies in the lithium-deficient material to reduce the state of charge of the negative electrode, thereby enhancing the thermal stability of the negative electrode and increasing the safety of battery use.

[0092] To address the aforementioned problems, this invention provides a coated particle, wherein the shell of the coated particle is a low-melting-point polymer material, and the core of the coated particle is a lithium-deficient material. When the temperature is ≥60°C, the lithium-deficient material can at least partially expose the shell.

[0093] It should be noted that when the temperature is ≥60℃, the lithium-deficient material can at least partially expose the shell layer. This means that after the coated particles are assembled into a battery, when the battery temperature rises above 60℃, the structure of the polymer material in the shell layer changes, and the thermal contraction causes some of the lithium-deficient material to be exposed on the shell layer surface. The degree to which the lithium-deficient material is exposed in the shell layer is related to the battery temperature and the melting point of the polymer material.

[0094] It will be readily understood by those skilled in the art that when the coated particles are assembled into a battery, due to the battery's weight and the application of external pressure, the lithium-deficient material exposed on the shell surface will come into contact with the negative electrode under its own weight. The fact that at least a portion of the lithium-deficient material can be exposed from the shell means that after the structure of the polymer material in the shell changes under temperature rise, the lithium-deficient material can come into contact with the negative electrode material in any local area of ​​the negative electrode cross-section, thus enabling it to acquire lithium ions from the negative electrode.

[0095] The low-melting-point polymer material in the embodiments of the present invention refers to a polymer material that can undergo deformation in the temperature range of 60°C to 150°C, such as an oligomer with a melting point or softening point of around 100°C.

[0096] Polymer materials are used as coating agents to coat lithium-deficient materials, which can ensure the normal operation of the battery at room temperature, and can also deform at high temperature to expose the lithium-deficient materials.

[0097] The polymer materials include at least one of the following: polyvinyl chloride, polyethersulfone, polyamic acid, poly(m-phenylene isophthalamide), poly(p-phenylene terephthalamide), polysiloxane, polytetrafluoroethylene, polyethylene, polypropylene, polyethylene glycol, polyethylene oxide, polypropylene oxide, polyethyleneimine, polyvinylidene fluoride, polymethyl methacrylate, polyacrylic acid, carboxymethyl cellulose, chitosan, sodium alginate, polyvinyl alcohol, polyvinylpyrrolidone, and styrene-butadiene rubber.

[0098] It's easy to understand that when the temperature reaches the polymer's melting point, the polymer is already in a fully fluid, viscous flow state. Therefore, as the temperature rises, near the melting point, the small molecules begin to flow, and the shell as a whole exhibits good plasticity and can deform. Under the influence of gravity and capillary forces between particles, lithium-deficient materials can detach from the shell.

[0099] The lithium-intercalated negative electrode has a low potential. If the lithium-deficient material is exposed after the shell layer is exposed and comes into contact with the negative electrode, the lithium-deficient material acts as a lithium-deficient agent. Lithium ions will migrate from the negative electrode to the lithium-deficient material under the drive of the potential, and are used to store the lithium ions provided by the negative electrode.

[0100] In one specific embodiment, the lithium-deficient material is selected from elemental sulfur, elemental phosphorus, sulfur-phosphorus compounds, and Li. x Ni y Co z Mn (1-y-z) O2(0≤x<1,0≤y≤1,0≤z≤1,0≤y+z≤1), Li x Mn₂O₄ (0≤x<1), Li x Fe y Mn (1-y) PO4 (0≤x<1, 0≤y≤1), carbon, silicon, silicon-carbon, phosphorus-carbon, sulfur-carbon, phosphorus-silicon, and sulfur-silicon.

[0101] In one specific embodiment, the lithium-deficient material is prepared by an electrochemical delithiation method.

[0102] In one specific embodiment, the diameter of the core can be 50nm-5μm. Specifically, the diameter of the core can be 60nm, 100nm, 300nm, 500nm, 0.1μm, 1μm, 2μm, 3μm, 4μm, etc.

[0103] In one specific embodiment, the thickness of the shell layer can be 20nm-1μm. Specifically, the thickness of the shell layer can be 30nm, 50nm, 100nm, 300nm, 500nm, 800nm, 1μm, etc.

[0104] The coated particles provided in this embodiment of the invention use lithium-deficient materials as lithium-deficient agents, and the shell layer includes a polymer material with a melting point of 60°C to 150°C as a coating agent. When the temperature exceeds 60°C, the polymer material in the shell layer of the coated particles undergoes a thermal structural change, thereby exposing the lithium-deficient materials. It can be seen that the coated particles provided in this embodiment of the invention provide a foundation for increasing the safety of battery use.

[0105] In order to form electronic pathways both on the surface and inside of lithium-deficient materials, thereby improving the smoothness of electron transport paths and further ensuring electron transport, the shell may also contain conductive materials.

[0106] The conductive material may include at least one of carbon black, carbon nanotubes, graphene, carbon fiber, polypyrrole, polythiophene, polyaniline, polyacetylene, and polyphenylacetylene.

[0107] Coated particles can be prepared through the following steps:

[0108] 1) Provide lithium-deficient materials;

[0109] 2) The lithium-deficient material is dispersed in a coating solution and then atomized and dried to obtain the coated particles.

[0110] Lithium-deficient materials are selected from elemental sulfur, elemental phosphorus, sulfur-phosphorus complexes, and Li. x Ni y Co z Mn (1-y-z) O2(0≤x<1,0≤y≤1,0≤z≤1,0≤y+z≤1), Li x Mn₂O₄ (0≤x<1), Li x Fe y Mn (1-y) PO4 (0≤x<1, 0≤y≤1), carbon, silicon, silicon-carbon, phosphorus-carbon, sulfur-carbon, phosphorus-silicon, and sulfur-silicon.

[0111] The coating liquid contains a coating agent, the material of which is selected from at least one of polyvinyl chloride, polyethersulfone, polyamic acid, poly(m-phenylene isophthalamide), poly(p-phenylene terephthalamide), polysiloxane, polytetrafluoroethylene, polyethylene, polypropylene, polyethylene glycol, polyethylene oxide, polypropylene oxide, polyethyleneimine, polyvinylidene fluoride, polymethyl methacrylate, polyacrylic acid, carboxymethyl cellulose, chitosan, sodium alginate, polyvinyl alcohol, polyvinylpyrrolidone, and styrene-butadiene rubber.

[0112] The coating solvent of the coating solution is selected from at least one of acetonitrile, methanol, ethanol, 1,4-dioxane, toluene, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, dichloromethane, 1,2-dichloroethane, chloroform, tetrahydrofuran, acetone, and ethyl acetate.

[0113] The coating liquid also includes a conductive agent. When the battery is fully charged, if the temperature is too high, the lithium-deficient material will take away lithium ions from the negative electrode. At the same time, the negative electrode will generate corresponding electrons. Adding a conductive material can improve the smoothness of the electron transport path, thereby reducing the degree of lithium replenishment by the negative electrode during charging, further reducing the state of charge of the negative electrode, and improving the battery safety performance.

[0114] The conductive agent is selected from at least one of carbon black, carbon nanotubes, graphene, carbon fiber, polypyrrole, polythiophene, polyaniline, polyacetylene, and polyphenylacetylene.

[0115] The coated particles prepared by the preparation method provided in the embodiments of the present invention are more likely to form spherical particles because they are dried by atomization and are in a rotating state with the airflow in the equipment. The particle morphology and particle size distribution are easier to control, thereby improving the coating effect of the coated particles.

[0116] To address the aforementioned problems, embodiments of the present invention also provide a diaphragm comprising the aforementioned coated particles.

[0117] By dispersing the coated particles in a coating solution and then coating and drying them, a self-supporting membrane is obtained, which is the separator. Placing it between the positive and negative electrode plates enhances battery safety.

[0118] It is understandable that the membrane prepared by coating particles as a separate film can be used as a separate membrane. Of course, in order to further improve the strength of the membrane, in one specific embodiment, the coated particles can be used in combination with commercial battery membranes.

[0119] To address the above problems, this invention also provides a method for preparing a negative electrode, comprising the following steps:

[0120] 1) Provide a negative electrode substrate;

[0121] 2) The aforementioned coated particles are dispersed in a coating solution and then coated on the surface to obtain a negative electrode sheet.

[0122] The coating liquid contains surfactants and binders;

[0123] The surfactant is selected from at least one of glyceryl monostearate and sodium dioctyl succinate sulfonate.

[0124] The negative electrode material of the negative electrode substrate can be selected from graphite, lithium metal, silicon-carbon, phosphorus-carbon; or at least one of silicon and phosphorus.

[0125] To address the above problems, this invention also provides a method for preparing a negative electrode, comprising the following steps:

[0126] 1) The aforementioned coated particles are dispersed in the negative electrode slurry and then coated on the surface to obtain the negative electrode sheet.

[0127] The content of coated particles ranges from 4 wt% to 12 wt%.

[0128] Coating methods include scraping, gravure roller coating, dip coating, narrow coating, or spraying.

[0129] The negative electrode slurry contains negative electrode material, coated particles, binder, and solvent.

[0130] The negative electrode material can be selected from at least one of graphite, lithium metal, silicon-carbon, phosphorus-carbon, silicon, and phosphorus.

[0131] To address the aforementioned problems, embodiments of the present invention provide a battery including the aforementioned separator.

[0132] The negative electrode material of the battery can be selected from at least one of graphite, lithium metal, silicon-carbon, phosphorus-carbon, silicon, and phosphorus.

[0133] The positive electrode material of the battery can be selected from at least one of lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, nickel-cobalt-manganese ternary materials, and lithium-rich layered materials.

[0134] The battery provided in this embodiment of the invention, because it includes the aforementioned separator, can ensure normal operation of the battery at normal temperatures (below 60°C). On the other hand, when the battery is in an overheated environment (above 60°C), the shell layer of the coating particles on the surface of the separator undergoes a structural transformation, and the exposed lithium-deficient material comes into contact with the negative electrode material. Lithium ions in the lithium-intercalated state of the negative electrode migrate into the lithium vacancies of the lithium-deficient material, thereby reducing the degree to which lithium ions are intercalated into the negative electrode during charging, thus reducing the state of charge of the negative electrode, thereby enhancing the thermal stability of the negative electrode and improving the safety of the battery. Furthermore, the lithium-deficient material particles adhere to the surface of the separator, improving the temperature resistance of the separator, suppressing the thermal shrinkage of the separator, and thus enhancing the safety of the battery.

[0135] To address the aforementioned problems, embodiments of the present invention provide a battery comprising the aforementioned negative electrode sheet.

[0136] The negative electrode material of the battery can be selected from at least one of graphite, lithium metal, silicon-carbon, phosphorus-carbon, silicon, and phosphorus.

[0137] The battery provided in this embodiment of the invention includes the aforementioned negative electrode sheet, thus ensuring normal operation of the battery at normal temperatures (below 60°C). On the other hand, when the battery is in an overheated environment (above 60°C), the shell layer in the coated particles on the negative electrode sheet undergoes a structural transformation, and the exposed lithium-deficient material comes into contact with the negative electrode material. Lithium ions in the lithium-intercalated state of the negative electrode migrate to the lithium vacancies in the lithium-deficient material, thereby reducing the degree to which lithium ions are intercalated into the negative electrode during charging, thereby reducing the state of charge of the negative electrode, and thus enhancing the thermal stability of the positive electrode and improving the safety of the battery.

[0138] The following detailed description of the battery separator, its preparation method, and the battery of the present invention, in conjunction with specific embodiments and comparative examples, provides further details.

[0139] Example 1

[0140] The coated particles are prepared by the following steps:

[0141] 1) Li 0.1 Ni 0.8 Co 0.1 Mn 0.1 O2 is dispersed in a coating solution and then atomized and dried to obtain coated particles with a core-shell structure.

[0142] 2) The coated particles are dispersed in a coating solution and then surface coated onto the negative electrode side surface of the base membrane to obtain the separator.

[0143] The lithium-deficient material was prepared by an electrochemical delithiation method;

[0144] The coating liquid contains a coating agent, a coating solvent, and a conductive agent;

[0145] The coating agent is selected from a composition of polymethyl methacrylate, polyacrylic acid, and carboxymethyl cellulose, with a mass ratio of polymethyl methacrylate / polyacrylic acid / carboxymethyl cellulose of 2 / 1 / 3.

[0146] The coating solvent is selected from a combination of N,N-dimethylacetamide and dimethyl sulfoxide, with a volume ratio of N,N-dimethylacetamide / dimethyl sulfoxide of 1 / 2;

[0147] The conductive agent is selected from a composition of carbon black, graphene, and polypyrrole, with a mass ratio of carbon black / graphene / polypyrrole of 5 / 2 / 2.

[0148] The solid content of the coating solution is 11.5 wt%, and the mass ratio of the lithium-deficient material to the coating solution is 2 / 8. The two are mechanically stirred at 65°C for 10 h.

[0149] The atomization drying temperature is 80℃ and the flow rate is 40ml / min, thus obtaining coated particles with a core-shell structure;

[0150] The coating liquid has a solid content of 15.5 wt%, and the mass ratio of the coated particles to the coating liquid is 2 / 8.

[0151] The base film is selected from polyethylene terephthalate nonwoven fabric;

[0152] The coated particles are loaded onto the negative electrode side surface of the base film by a scraping method, with a loading rate of 4.5 g / m³. 2 The diaphragm sample was prepared, and its basic performance parameters are shown in Table 1.

[0153] Battery assembly: Using lithium iron phosphate (LFP) as the positive electrode and natural graphite Gr as the negative electrode, with the sample from Example 1 as the separator, and the lithium-deficient material surface facing the negative electrode side, an LFP / Gr battery with a capacity of 60Ah was assembled.

[0154] Performance testing:

[0155] The initial coulombic efficiency and discharge capacity (2.6-3.7V) of the battery were tested at 0.1C, and the test results are shown in Table 2.

[0156] The battery sample from Example 1 was charged to full charge (3.7V) at 0.1C and then left to stand for 10 hours at 25°C, 45°C, 45°C, and 150°C, respectively. The lowest voltage V was monitored. min and the highest temperature T max The test results are shown in Table 3.

[0157] The battery sample from Example 1 was charged to a fully charged state (3.7V) at 0.1C, and its minimum voltage V was monitored using an accelerating calorimeter within the range of room temperature to 200°C. min and the highest temperature t max and the maximum rate of temperature rise R max The test results are shown in Table 4.

[0158] Example 2

[0159] The coated particles are prepared by the following steps:

[0160] 1) Li 0.2 Mn2O4, Li 0.05 Ni 0.9 Co 0.05 Mn 0.05 A mixture of O2 (mass ratio 1:1) is dispersed in a coating solution and then atomized and dried to obtain coated particles with a core-shell structure.

[0161] 2) The coated particles are dispersed in a coating solution and then surface coated onto the negative electrode side surface of the base membrane to obtain the separator.

[0162] The coating liquid contains a coating agent and a coating solvent;

[0163] The coating agent is selected from a composition of polyvinylidene fluoride and carboxymethyl fiber in a mass ratio of 2 / 1;

[0164] The coating solvent is selected from N,N-dimethylacetamide;

[0165] The solid content of the coating solution is 10.5 wt%, and the mass ratio of the lithium-deficient material to the coating solution is 2 / 8. The two are mechanically stirred at 65°C for 10 h.

[0166] The atomization drying temperature is 80℃ and the flow rate is 40ml / min, thus obtaining coated particles with a core-shell structure;

[0167] The coating liquid contains surfactants and binders;

[0168] The coating liquid has a solid content of 15.5 wt%, and the mass ratio of the coated particles to the coating liquid is 2 / 8.

[0169] The base film is selected from polyethylene terephthalate nonwoven fabric;

[0170] The coated particles were loaded onto the negative electrode side surface of the base membrane by a scraping method, with a loading amount of 4.5 g / m2, to obtain the membrane sample. The basic performance parameters are shown in Table 1.

[0171] Battery assembly: Using lithium iron phosphate (LFP) as the positive electrode and natural graphite Gr as the negative electrode, with the sample from Example 2 as the separator, and the lithium-deficient material surface facing the negative electrode side, an LFP / Gr battery with a capacity of 60Ah was assembled.

[0172] Performance testing

[0173] Its initial coulombic efficiency and discharge capacity (2.6-3.7V) were tested at 0.1C, and the test results are shown in Table 2.

[0174] The battery sample from Example 2 was charged to a fully charged state (3.7V) at 0.1C, and its minimum voltage V was monitored using an accelerating calorimeter within the range of room temperature to 200°C. min and the highest temperature t max and the maximum rate of temperature rise R max The test results are shown in Table 4.

[0175] Example 3

[0176] The coated particles are prepared by the following steps:

[0177] 1) Using lithium-deficient materials Li 0.05 Ni 0.9 Co 0.08 Mn 0.02A mixture of O2 and S (mass ratio 8 / 2) is dispersed in a coating solution and then atomized and dried to obtain coated particles with a core-shell structure.

[0178] 2) The coated particles are dispersed in a coating solution and then surface coated onto the negative electrode side of the base membrane to obtain the separator.

[0179] The coating liquid contains a coating agent, a coating solvent, and a conductive agent;

[0180] The coating agent is selected from a composition of polymethyl methacrylate and polyvinylidene fluoride-hexafluoropropylene (mass ratio 1 / 1);

[0181] The coating solvent is selected from a composition of dimethyl sulfoxide / acetone, with a volume ratio of 3 / 1;

[0182] The conductive agent is selected from carbon nanotubes, carbon black, graphene, and a combination thereof, with a mass ratio of 1 / 7 / 2.

[0183] The solid content of the coating solution is 13.5 wt%, and the mass ratio of the lithium-deficient material to the coating solution is 2 / 8. The two are mechanically stirred at 65°C for 10 h.

[0184] The atomization drying temperature is 80℃ and the flow rate is 40ml / min, thus obtaining coated particles with a core-shell structure;

[0185] The coating liquid contains surfactants and binders;

[0186] The coating liquid has a solid content of 14.5 wt%, and the mass ratio of the coated particles to the coating liquid is 2 / 8.

[0187] The base film is selected from polyethylene terephthalate nonwoven fabric;

[0188] The coated particles are loaded onto the negative electrode side surface of the base film by a scraping method, with a loading rate of 3.5 g / m³. 2 The diaphragm sample was prepared, and its basic performance parameters are shown in Table 1.

[0189] Battery assembly: Using lithium iron phosphate (LFP) as the positive electrode and natural graphite Gr as the negative electrode, with the sample of Example 11 as the separator, and the lithium-deficient material surface facing the positive electrode side surface, an LFP / Gr battery with a capacity of 60Ah was assembled.

[0190] Performance testing

[0191] Its initial coulombic efficiency and discharge capacity (2.6-3.7V) were tested at 0.1C, and the test results are shown in Table 2.

[0192] The battery sample from Example 3 was charged to a fully charged state (3.7V) at 0.1C, and its minimum voltage V was monitored using an accelerating calorimeter within the range of room temperature to 200°C. min and the highest temperature t max and the maximum rate of temperature rise R max The test results are shown in Table 4.

[0193] Example 4

[0194] 1) Provides a natural graphite Gr anode substrate;

[0195] 2) The coated particles from Example 3 were dispersed in a coating solution and loaded onto the surface of a natural graphite Gr anode substrate by a scraping method, with a loading amount of 4.2 g / m³. 2 A graphite anode sheet containing lithium-deficient materials was prepared.

[0196] Battery assembly

[0197] Using lithium iron phosphate (LFP) electrodes as the positive electrode, commercial polyethylene as the separator, and a graphite negative electrode containing lithium-deficient material as the negative electrode, with the surface of the negative electrode containing lithium-deficient material facing the separator, an LFP / Gr battery with a capacity of 60Ah is assembled.

[0198] Performance testing

[0199] Its initial coulombic efficiency and discharge capacity (2.6-3.7V) were tested at 0.1C, and the test results are shown in Table 2.

[0200] The battery sample from Example 4 was charged to a fully charged state (3.7V) at 0.1C, and its minimum voltage V was monitored using an accelerating calorimeter within the range of room temperature to 200°C. min and the highest temperature t max and the maximum rate of temperature rise R max The test results are shown in Table 4.

[0201] Example 5

[0202] Using the core-shell structured coated particles prepared in Example 4 as an additive, they were added to natural graphite (8 wt% coated particles). A commercial lithium iron phosphate (LFP) battery was assembled with commercial polyethylene as the separator and natural graphite Gr containing coated particles as the negative electrode, using LFP / Gr as the positive electrode.

[0203] Performance testing

[0204] Its initial coulombic efficiency and discharge capacity (2.6-3.7V) were tested at 0.1C, and the test results are shown in Table 2.

[0205] The battery sample from Example 5 was charged to a fully charged state (3.7V) at 0.1C, and its minimum voltage V was monitored using an accelerating calorimeter in the range of room temperature to 200°C. min and the highest temperature t max and the maximum rate of temperature rise R max The test results are shown in Table 4.

[0206] Example 6

[0207] 1) Using lithium-deficient materials Li 0.05 Ni 0.9 Co 0.08 Mn 0.02 A mixture of O2 and P (mass ratio 8 / 2) is dispersed in a coating solution and then atomized and dried to obtain coated particles with a core-shell structure.

[0208] 2) The coated particles are dispersed in a coating solution, coated and dried to obtain a self-supporting membrane of coated particles with a core-shell structure, which is the membrane.

[0209] The coating liquid contains a coating agent, a coating solvent, and a conductive agent;

[0210] The coating agent is selected from a combination of polyethylene oxide and polyvinyl alcohol in a mass ratio of 1 / 1;

[0211] The coating solvent is selected from dimethyl sulfoxide / acetone, with a volume ratio of 3 / 1;

[0212] The conductive agent is selected from carbon nanotubes / carbon black, with a mass ratio of 1 / 7;

[0213] The solid content of the coating solution is 11.5 wt%, and the mass ratio of the lithium-deficient material to the coating solution is 2 / 8. The two are mechanically stirred at 65°C for 10 h.

[0214] The atomization drying temperature is 80℃ and the flow rate is 40ml / min, thus obtaining coated particles with a core-shell structure;

[0215] The coating liquid contains a polyvinylidene fluoride binder;

[0216] The coating liquid has a solid content of 14.5 wt%, and the mass ratio of the coated particles to the coating liquid is 2 / 8.

[0217] The coated particles were coated by scraping and dried at 60°C to form a film, and the sample was obtained. The basic performance parameters are shown in Table 1.

[0218] Battery assembly

[0219] Using lithium iron phosphate (LFP) as the positive electrode and natural graphite Gr as the negative electrode, with the sample of Example 6 as the separator and the surface containing lithium-deficient material facing the negative electrode side, an LFP / Gr battery with a capacity of 60Ah was assembled.

[0220] Performance testing

[0221] Its initial coulombic efficiency and discharge capacity (2.6-3.7V) were tested at 0.1C, and the test results are shown in Table 2.

[0222] The battery sample from Example 6 was charged to a fully charged state (3.7V) at 0.1C, and its minimum voltage V was monitored using an accelerating calorimeter within the range of room temperature to 200°C. min and the highest temperature t max and the maximum rate of temperature rise R max The test results are shown in Table 4.

[0223] Comparative Example 1

[0224] Commercial ceramic-coated polyethylene diaphragm was used as the sample for Comparative Example 1. The basic performance parameters are shown in Table 1.

[0225] Battery assembly: Using lithium iron phosphate (LFP) as the positive electrode, natural graphite Gr as the negative electrode, and the sample of Comparative Example 1 as the separator, an LFP / Gr battery with a capacity of 60Ah was assembled.

[0226] Performance testing

[0227] Its initial coulombic efficiency and discharge capacity (2.6-3.7V) were tested at 0.1C, and the test results are shown in Table 2.

[0228] The battery sample of Comparative Example 1 was charged to full charge (3.7V) at 0.1C and then left to stand for 10 hours at 25℃, 45℃, 80℃, and 150℃ respectively. The lowest voltage V was monitored. min and the highest temperature T max The test results are shown in Table 3.

[0229] The battery sample of Comparative Example 1 was charged to a fully charged state (3.7V) at 0.1C, and its minimum voltage V was monitored using an accelerating calorimeter in the range of room temperature to 200°C. min and the highest temperature t max and the maximum rate of temperature rise R max The test results are shown in Table 4.

[0230] Table 1. Basic performance parameters of different diaphragm samples

[0231] Example 1 14 115 49 176 1.3 Example 2 13 112 45 195 1.1 Example 3 14 116 42 188 1.2 Example 6 15 102 41 221 1.1 Comparative Example 1 14 125 47 173 1.2

[0232] The results in Table 1 show that the basic performance parameters of the separator samples prepared in this invention are consistent with those of commercial separator samples, which can ensure the normal performance of the battery.

[0233] Table 2 Performance of 60Ah LFP / Gr batteries with different separator assemblies

[0234]

[0235]

[0236] The results in Table 2 show that the basic performance parameters of the example samples prepared in this invention are consistent with those of commercial samples, which can ensure the normal performance of the battery.

[0237] Table 3. Test results of a fully charged 60Ah LFP / Gr battery after being left to stand at different temperatures for 10 hours.

[0238]

[0239] The results in Table 3 show that the sample prepared in this invention can reduce the state of charge of the positive electrode at temperatures of 80°C and above, thereby improving battery safety.

[0240] Table 4. Accelerated calorimeter test results of 5Ah batteries assembled using different separators / electrodes containing coated particles.

[0241]

[0242]

[0243] The results in Table 4 show that the sample prepared in this invention can reduce the state of charge of the negative electrode in an overheated environment, thereby improving battery safety.

[0244] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0245] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

[0246] While the embodiments of the present invention have been disclosed above, the present invention is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the present invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A diaphragm, characterized in that, The system comprises a base film and coated particles. The coated particles are loaded on the negative electrode side surface of the base film. The shell of the coated particles comprises a low-melting-point polymer material, and the core material of the coated particles is a lithium-deficient material. When the temperature is ≥60℃, the structure of the low-melting-point polymer material changes, allowing at least a portion of the lithium-deficient material to be exposed on the shell surface. The lithium-deficient material is prepared by an electrochemical delithiation method. The lithium-deficient material is selected from Li. x Ni y Co z Mn 1-y-z O2, where 0≤x<1, 0≤y≤1, 0≤z≤1, 0≤y+z≤1; or Li x Mn₂O₄, where 0 ≤ x < 1; or Li x Fe y Mn 1-y PO4, where at least one of 0 ≤ x < 1 and 0 ≤ y ≤ 1.

2. The diaphragm as described in claim 1, characterized in that, The shell of the coated particles also includes a conductive material.

3. The diaphragm as described in claim 2, characterized in that, The conductive material includes at least one of carbon black, carbon nanotubes, graphene, carbon fiber, polypyrrole, polythiophene, polyaniline, polyacetylene, and polyphenylacetylene.

4. The diaphragm as described in claim 1 or 2, characterized in that, The polymer material includes at least one of polyvinyl chloride, polyethersulfone, polyamic acid, poly(m-phenylene isophthalamide), poly(p-phenylene terephthalamide), polytetrafluoroethylene, polyethylene, polypropylene, polyethylene oxide, polyvinylidene fluoride, polymethyl methacrylate, polyacrylic acid, chitosan, sodium alginate, polyvinyl alcohol, and polyvinylpyrrolidone.

5. The diaphragm as described in claim 1 or 2, characterized in that, The diameter of the core is 50 nm-5 μm; and / or the thickness of the shell is 20 nm-1 μm.

6. The diaphragm as described in claim 1 or 2, characterized in that, The loading rate of the coated particles is in the range of 1 g / m³. 2 -6g / m 2 .

7. The diaphragm as described in claim 1 or 2, characterized in that, The base membrane is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, poly(m-phenylene isophthalamide), poly(p-phenylene terephthalamide), polyethersulfone, polyimide, polyvinylidene fluoride, and polytetrafluoroethylene porous membranes.

8. The method for preparing the diaphragm according to claim 1, characterized in that, Includes the following steps: 1) Provide lithium-deficient materials, which are prepared by an electrochemical delithiation method; 2) The lithium-deficient material is dispersed in a coating solution and then atomized and dried to obtain coated particles, wherein the coating solution contains a coating agent; 3) The coated particles are dispersed in a coating solution and then coated on the negative electrode side of the base membrane to obtain the separator.

9. The method for preparing the diaphragm as described in claim 8, characterized in that, The coating agent is selected from at least one of polyvinyl chloride, polyethersulfone, polyamic acid, poly(m-phenylene isophthalamide), poly(p-phenylene terephthalamide), polytetrafluoroethylene, polyethylene, polypropylene, polyethylene oxide, polyvinylidene fluoride, polymethyl methacrylate, polyacrylic acid, chitosan, sodium alginate, polyvinyl alcohol, and polyvinylpyrrolidone.

10. The method for preparing the diaphragm as described in claim 8, characterized in that, The coating liquid contains a conductive agent, the material of which is selected from at least one of carbon black, carbon nanotubes, graphene, carbon fiber, polypyrrole, polythiophene, polyaniline, polyacetylene, and polyphenylacetylene.

11. A negative electrode sheet, characterized in that, The negative electrode sheet has coated particles dispersed on its surface and / or within it. The shell of the coated particles comprises a low-melting-point polymer material, and the core material of the coated particles is a lithium-deficient material. When the temperature is ≥60℃, the structure of the low-melting-point polymer material changes, allowing at least a portion of the lithium-deficient material to be exposed from the shell. The lithium-deficient material is selected from Li. x Ni y Co z Mn 1-y-z O2, where 0≤x<1, 0≤y≤1, 0≤z≤1, 0≤y+z≤1; or Li x Mn₂O₄, where 0 ≤ x < 1; or Li x Fe y Mn 1-y PO4, where at least one of 0 ≤ x < 1 and 0 ≤ y ≤ 1.

12. The negative electrode sheet as described in claim 11, characterized in that, The shell of the coated particles also includes a conductive material.

13. The negative electrode sheet as described in claim 12, characterized in that, The conductive material includes at least one of carbon black, carbon nanotubes, graphene, carbon fiber, polypyrrole, polythiophene, polyaniline, polyacetylene, and polyphenylacetylene.

14. The negative electrode sheet as described in claim 11, characterized in that, The polymer material includes at least one of polyvinyl chloride, polyethersulfone, polyamic acid, poly(m-phenylene isophthalamide), poly(p-phenylene terephthalamide), polytetrafluoroethylene, polyethylene, polypropylene, polyethylene oxide, polyvinylidene fluoride, polymethyl methacrylate, polyacrylic acid, chitosan, sodium alginate, polyvinyl alcohol, and polyvinylpyrrolidone.

15. The negative electrode sheet as described in claim 13 or 14, characterized in that, The negative electrode material of the negative electrode sheet is selected from at least one of graphite, lithium metal, silicon-carbon, phosphorus-carbon, silicon, and phosphorus.

16. A battery, characterized in that, Includes the diaphragm as described in any one of claims 1-7.

17. A battery, characterized in that, Includes the negative electrode as described in claim 11.

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