Lithium ion battery separator and lithium ion battery

Abstract

The present application discloses a lithium ion battery separator and a lithium ion battery. The lithium ion battery separator comprises a base membrane; at least one surface of the base membrane is provided with a functional coating; the functional coating contains negative temperature coefficient (NTC) material particles and ceramic particles; based on the functional coating, the mass content of the NTC material particles is 30-80 wt%; the base membrane is a base membrane having a low rupture temperature; and the rupture temperature of the base membrane is not higher than 180°C. According to the present application, a base membrane having a low rupture temperature is used in combination with an NTC material, so that in the early stage of a thermal safety test (before failure), micro short circuit points are formed by the base membrane having a low rupture temperature, and then large-area micro self-discharge is achieved by a combined coating of the NTC material and ceramic particles; by means of the cooperation of the base membrane having a low rupture temperature and the NTC material within a certain range, a controllable self-discharge rate can be achieved, the SOC of the battery can be quickly reduced, and the thermal safety performance of the battery can be improved.

Description

Lithium-ion battery separator, lithium-ion battery Technical Field

[0001] The present application relates to the technical field of lithium-ion batteries, and in particular to a lithium-ion battery separator and a lithium-ion battery. Background Art

[0002] At present, in order to pursue high energy density batteries, high voltage system cathode lithium cobalt oxide is usually used. When fully charged, the amount of lithium delithiation of the lithium cobalt oxide in the cathode is large, its structure is unstable, and the cathode side has strong oxidizing properties. The electrolyte under the fast charging system usually uses a low viscosity, high dielectric constant electrolyte, and the boiling point and flash point of the electrolyte are also lower, which puts higher requirements on the thermal safety performance of the battery.

[0003] In order to improve the thermal safety performance of batteries, existing technical means include cathode primer coating (STS technology) and anode ceramic coating (CCA technology). On the one hand, these technologies will increase the thickness of the battery cell and cause the energy density of the battery cell to decrease. On the other hand, both STS technology and CCA technology will affect the fast charging performance of the battery.

[0004] Summary of the Invention

[0005] In view of this, the present application provides a lithium-ion battery separator and a lithium-ion battery to improve the thermal safety performance of the battery while taking into account the energy density and rate performance of the battery.

[0006] In a first aspect, the present application provides a lithium-ion battery separator, comprising a base membrane, wherein at least one surface of the base membrane is provided with a functional coating, wherein the functional coating comprises NTC material particles and ceramic particles, wherein the mass content of the NTC material particles is 30-80 wt% based on the functional coating, and the base membrane has a low rupture temperature, wherein the rupture temperature of the base membrane is not higher than 180°C. Preferably, the rupture temperature of the base membrane is 135-180°C.

[0007] Lithium cobalt oxide (Li xWhen the lithium delithiation amount of lithium cobalt oxide (CoO2) is high (0.5>x>0.45) and the charging voltage is about 4.2V, it transforms from hexagonal H-2 to monoclinic M, belonging to the P12 / m1 space group. This process is accompanied by irregular changes in the unit cell parameters. For example, as shown in Figure 1, it can be seen from Figure 1 that when the lithium delithiation amount of lithium cobalt oxide enters the O1 phase from the H1-3 phase, there will be a discharge platform. The lithium cobalt oxide in the O1 phase is unstable at high temperature (thermal safety test environment). The reason for this phenomenon may be that the spatial law of lithium ions and lithium vacancies changes, showing an ordered-disordered-ordered change law, resulting in poor thermal stability of high-delithiation lithium cobalt oxide materials, which is prone to thermal runaway and is not conducive to improving battery safety performance. In order to improve the safety performance of the battery, this application selects a base film with a rupture temperature of 135-180 ° C, and combines it with a functional coating containing an appropriate amount of NTC material particles and ceramic particles. Through the synergy of the base film with a low rupture temperature and the functional coating, the self-discharge of the battery cell can be promoted, resulting in the back insertion of lithium ions into the extremely lithium-deficient Li X CoO2 (at this time X <0.1), thereby stabilizing the structure, so as to accelerate the self-discharge of the battery at high temperature in the early stage of the thermal safety test, which is beneficial to the improvement of the thermal stability of the battery positive electrode material, especially high-voltage lithium cobalt oxide, and can significantly improve the pass rate of the battery's thermal safety test; it should be noted that the early stage of the thermal safety test refers to the early stage of the hot box test, including the stage of rising from room temperature to the preset test temperature and the stage of maintaining the preset test temperature to the first third of the total test time, which is the early stage of the thermal safety test.

[0008] If the proportion of the NTC material particles is too small (<30%), the self-discharge rate will be too low, and it will not be possible to achieve rapid discharge in the early stage of the thermal safety test to reduce the battery SOC. If the proportion of the NTC material particles is too high (>80%), on the one hand, it will cause the heat generation of the battery during the self-discharge process to be uncontrollable, which is not conducive to the improvement of thermal safety performance. On the other hand, it will inevitably lead to the proportion of ceramic particles being too low. At this time, there is a lack of ceramic particles to play a supporting and barrier role. At high temperatures (ambient temperatures above 120°C, high temperatures below refer to above 120°C), it is difficult for ceramic particles to play a "skeleton" role to support the base film, which in turn leads to an excessively large self-discharge rate, uncontrollable self-discharge rate, and may even cause thermal runaway.

[0009] In some embodiments, the NTC material particles are selected from at least one of metal oxide particles having a spinel structure or metal oxide particles having a perovskite structure. Negative temperature coefficient inorganic materials are made of metal oxides such as manganese, cobalt, nickel and copper as the main materials, and are manufactured using a ceramic process and have semiconductor properties. When the temperature is low (≤100°C), the number of carriers (electrons and holes) of these metal oxide particles is small, resulting in a higher resistance value. However, as the temperature increases (>100°C), the number of carriers increases and the resistance value decreases. When the temperature rises to above 120°C, the anode and cathode are turned on, reducing the overall potential of the battery cell.

[0010] Metal oxide particles with a spinel structure or metal oxide particles with a perovskite structure are more conducive to cooperating with a base film with a low rupture temperature to produce local micro-short-circuit points at high temperatures to achieve controllable self-discharge, which is beneficial to improving the thermal safety performance of the battery. It should be noted that the perovskite-type NTC materials mainly include Re(Cr,Mn)O3 system, BaTiO3 system, etc. This type can exert thermosensitive properties. The thermosensitive properties refer to the material maintaining insulation under the formation and storage environment, but as the temperature rises (above 100°C), the material changes from an insulator to a semiconductor and conductor, achieving conduction between the anode and cathode, and achieving self-discharge at high temperatures. For example, the typical rare earth perovskite structure YCrO3 material, but the structure of this material after high-temperature sintering is loose and porous, and its anti-aging ability is poor. After doping modification, Y 1-x Ca x CrO3, YCr 1-x Mn x O3、YCo 1-x Mn x O3, Y 0.9 Ca 0.1 Cr 1-x Mn x O3, etc. The thermal sensitivity of the material can be adjusted within a certain range, and the density pore structure after sintering is also improved to a certain extent.

[0011] In some embodiments, the NTC material particles are metal oxide particles having a spinel structure, wherein the spinel structure is preferably a Mn-based spinel structure, and the Mn-based spinel structure NTC material particles contain Mn elements, O elements, and T elements, wherein the T element is selected from at least one of Ni elements, Fe elements, Cu elements, Co elements, and Zn elements. In the Mn-based spinel structure NTC material particles, the molar amount of the Mn element is recorded as n Mn , the molar amount of the T element is recorded as n T , satisfying: 0.76≤n Mn / n T≤6.5. Mn-based spinel NTC materials doped with different metal ions have different thermal sensitivity characteristics. Among them, Mn-based spinel NTC materials doped with quaternary or more metal elements have the best thermal sensitivity characteristics, which are more conducive to achieving controllable self-discharge in conjunction with the base film with low rupture temperature. For example, Cu 0.2 Ni 0.5 Zn 1.0 Mn 1.3 O4, this thermosensitive ceramic has a small particle size and a large specific surface area, and its thermal sensitivity is most controllable between -60°C and 300°C. The conductive mechanism of spinel-structured materials is that metal cations exist in multiple valence states. These variable-valence metals occupy different crystallographic positions, causing electrons to jump between ions of different valence states. This electron hopping phenomenon is affected by external conditions. In spinel NTC materials, electron hopping intensifies with increasing temperature, which, combined with a base film with a low rupture temperature, allows for controllable self-discharge at high temperatures.

[0012] In some embodiments, the functional coating comprises 50-80 wt% of the NTC material particles, 15-45 wt% of the ceramic particles, and the remaining components comprise a dispersant, a binder, and a wetting agent. This allows for a suitable self-discharge rate at high temperatures, facilitating a rapid voltage drop in the early stages of thermal safety testing while also ensuring thermal safety, helping the battery safely pass hot box testing.

[0013] In some embodiments, the self-discharge rate of the lithium-ion battery separator at an ambient temperature above 120° C. is 120 to 260 mV / h. Preferably, the self-discharge rate of the lithium-ion battery separator at an ambient temperature above 120° C. is 180 to 220 mV / h.

[0014] In some embodiments, the average particle size of the NTC material particles is recorded as D1, and the average particle size of the ceramic particles is recorded as D2, satisfying: 1≤D1 / D2≤25. At this time, further limiting the particle size ratio of the NTC material particles can better suppress the thermal shrinkage of the base film and make the coating denser, which is conducive to improving the fast charging performance. Preferably, D1 is 0.5-2μm, and D2 is 0.1-0.5μm. More preferably, D1 is 0.5-1.5μm, and D2 is 0.3-0.5μm.

[0015] In some embodiments, the base film has a thickness of 3 to 6 μm. This thickness facilitates localized membrane rupture at high temperatures, facilitates coordination with the functional coating, and enables controlled self-discharge. Furthermore, it improves the volumetric energy density of the battery.

[0016] In some embodiments, the thickness of the functional coating is 2 to 8 μm. The combination of an appropriate coating thickness and a suitable base film thickness is more conducive to improving the battery energy density, while also taking into account the thermal shrinkage performance of the separator and better realizing the NTC material's function of reducing the potential.

[0017] In the second aspect, the present application provides a lithium-ion battery comprising a positive electrode sheet, a negative electrode sheet, a diaphragm and an electrolyte, wherein the diaphragm is arranged between the positive electrode sheet and the negative electrode sheet, and the diaphragm is the lithium-ion battery diaphragm described in any one of the above items, and the positive electrode sheet contains a lithium cobalt oxide positive electrode material.

[0018] The beneficial effects brought about by the technical solutions provided by some embodiments of the present application include at least the following: the lithium-ion battery separator described in the present application can fundamentally improve the thermal safety of the battery cell, by using a base film with a low rupture temperature in combination with a negative temperature coefficient material, so that in the early stage of the thermal safety test (before failure), a micro-short-circuit point is formed by the base film with a low rupture temperature, and then a large-area micro-self-discharge is achieved by the combined coating of the NTC material and ceramic particles, which can reduce the overall voltage of the battery cell, promote the delithiation of the fully charged anode, and the reinsertion of lithium ions into the cathode, so that the stability of the cathode structure is improved while reducing the cathode oxidation, and reducing the heat generated by the side reaction of the cathode oxidation electrolyte. Through the synergy of the base film with a low rupture temperature and the appropriate amount of NTC material, a controllable self-discharge rate can be achieved, so that the battery cell can form a high-temperature self-discharge of the entire electrode in the early stage of the test, reducing the SOC of the test battery, and the battery with a low SOC is more conducive to passing the thermal safety test. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without paying any creative work.

[0020] FIG1 is a schematic diagram of the structural transformation of lithium cobalt oxide materials;

[0021] FIG2 is a schematic structural diagram of the lithium-ion battery separator described in this application;

[0022] FIG3 is a SEM image of the NTC material in Example 1 of the present application;

[0023] FIG4 is a temperature-resistance curve of the NTC material shown in FIG3 ;

[0024] FIG5 is a graph showing voltage variation of batteries containing different contents of NTC materials at high temperature. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solutions and advantages of this application more clearly understood, the present application is further described in detail below with reference to the accompanying drawings, embodiments and comparative examples. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0026] lithium-ion batteries

[0027] An embodiment of the present application provides a lithium-ion battery, including a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte.

[0028] diaphragm

[0029] The diaphragm includes a base film, at least one surface of which is provided with a functional coating, wherein the functional coating contains NTC material particles and ceramic particles. Based on the functional coating, the mass content of the NTC material particles is 30 to 80 wt %. The base film has a low rupture temperature, and the rupture temperature of the base film is not higher than 180°C. The schematic structure of the diaphragm is shown in FIG2 . The base film with a low rupture temperature ruptures under a heated environment. The isolation of the ceramic layer allows the NTC material to exert controllable self-discharge between the ruptured film and the conductive anode and cathode to reduce the cathode potential and transform the lithium cobalt oxide phase of the 4.45V / 4.48V / 4.50V system from the unstable H1-3 phase to the relatively stable monoclinic system M, corresponding to a voltage of 4.4V and a high-temperature self-discharge rate of 120 to 260 mV / h.

[0030] Illustratively, the mass content of the NTC material particles is 30 wt%, 40 wt%, 50 wt%, 60 wt%, 70 wt%, 80 wt% or a range consisting of any two of the above values.

[0031] Illustratively, the rupture temperature of the base film is 135°C, 140°C, 145°C, 150°C, 155°C, 160°C, 165°C, 170°C, 175°C, 180°C or a range consisting of any two of the above values.

[0032] In some embodiments, the NTC material particles are selected from at least one of metal oxide particles having a spinel structure or metal oxide particles having a perovskite structure.

[0033] Specifically, in some examples, the NTC material particles are metal oxide particles having a spinel structure, in other examples, the NTC material particles are metal oxide particles having a perovskite structure, or in other examples, the NTC material particles include metal oxide particles having a spinel structure and also include metal oxide particles having a perovskite structure.

[0034] In some embodiments, the average particle size of the NTC material particles is recorded as D1, and the average particle size of the ceramic particles is recorded as D2, satisfying: 1≤D1 / D2≤25.

[0035] Illustratively, the ratio of D1 / D2 is 1, 5, 10, 15, 20, 25, or a range consisting of any two of the above values.

[0036] In some embodiments, the NTC material particles are metal oxide particles having a spinel structure, wherein the metal oxide particles having a spinel structure contain Mn element, O element, and optionally T element, wherein the T element is selected from at least one of Ni element, Fe element, Cu element, and Zn element. In the metal oxide particles having a spinel structure, the molar amount of the Mn element is recorded as n Mn , the molar amount of the T element is recorded as n T , satisfying: 0.76≤n Mn / n T ≤6.5.

[0037] Specifically, in some examples, the metal oxide particles having a spinel structure contain Mn and O elements. In other examples, the metal oxide particles having a spinel structure contain T elements in addition to Mn and O elements.

[0038] For example, n Mn / n T The ratio is 0.76, 0.8, 1.0, 1.2, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5 or a range consisting of any two of the above values.

[0039] In some embodiments, in the functional coating, the mass content of the NTC material particles is 50-80 wt %, the mass content of the ceramic particles is in the range of 15-45 wt %, and the remaining components are dispersant, binder and wetting agent.

[0040] The binder is selected from at least one of polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR) or polyacrylic acid (PAA).

[0041] The dispersant is selected from at least one of sodium polyacrylate (SPA) and hydroxypropyl methylcellulose (HPMC).

[0042] The wetting agent is selected from at least one of polyoxyethylene alkylphenol ether, polyoxyethylene fatty alcohol ether or polyoxyethylene polyoxypropylene block ester.

[0043] Illustratively, the mass content of the NTC material particles is 50 wt%, 60 wt%, 70 wt%, 80 wt% or a range consisting of any two of the above values.

[0044] Illustratively, the mass content of the ceramic particles is 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt% or a range consisting of any two of the above values.

[0045] In some embodiments, the average particle size D1 of the NTC material particles is 0.5 to 2 μm. Preferably, the average particle size D1 of the NTC material particles is 0.5 to 1.5 μm.

[0046] Illustratively, the average particle size D1 of the NTC material particles is 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 1.3 μm, 1.5 μm, 1.8 μm, 2 μm, or a range consisting of any two of the above values.

[0047] In some embodiments, the average particle size D2 of the ceramic particles is 0.1 to 0.5 μm. Preferably, the average particle size D2 of the ceramic particles is 0.3 to 0.5 μm.

[0048] Illustratively, the average particle size D2 of the ceramic particles is 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, or a range consisting of any two of the above values.

[0049] In some embodiments, the self-discharge rate of the lithium-ion battery separator at an ambient temperature above 120° C. is 120 to 260 mV / h. Preferably, the self-discharge rate of the lithium-ion battery separator at an ambient temperature above 120° C. is 180 to 220 mV / h.

[0050] Exemplarily, the self-discharge rate of the lithium-ion battery separator at an ambient temperature above 120°C is 120mV / h, 140mV / h, 160mV / h, 180mV / h, 190mV / h, 200mV / h, 210mV / h, 220mV / h, 240mV / h, 260mV / h or a range consisting of any two of the above values.

[0051] In some embodiments, the base film has a thickness of 3 to 6 μm.

[0052] Illustratively, the thickness of the low-breakage base film is 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, or a range consisting of any two of the above values.

[0053] In some embodiments, the functional coating has a thickness of 2 to 8 μm.

[0054] Illustratively, the thickness of the functional coating is 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, or a range consisting of any two of the above values.

[0055] An exemplary method for preparing the base film with a low rupture temperature is as follows: by adding a low rupture temperature component to the raw materials for preparing the base film. For example, by adding a certain weight ratio of 0-20% PE to the PP film, the rupture temperature of the PP film can be reduced as a whole while also improving the tensile properties. For the PE base film, the molecular weight of the polyethylene can be adjusted to 300,000 to 2,000,000 molecular weight, and preferably to 400,000 to 600,000 molecular weight to ensure processing performance and mechanical properties, with a narrow molecular weight distribution, PDI = M W When / Mn=6-8, the base film rupture temperature can be adjusted to 135-180°C. The parameter representing the rupture temperature is the rupture temperature T, which can be measured. The specific operation process of the base film with a low rupture temperature can refer to conventional technical means in the prior art and will not be repeated in this application.

[0056] The slurry is coated on one side or both sides of the base film, and after the ceramic layer (functional coating) is coated, the adhesive layer is coated on the ceramic layer as usual to obtain the lithium ion battery separator.

[0057] other

[0058] Positive electrode

[0059] The invention comprises a positive electrode current collector and a positive electrode active material layer arranged on at least one surface of the positive electrode current collector. The positive electrode active material layer can selectively contain a lithium cobalt oxide positive electrode material.

[0060] For example, the positive electrode current collector may be made of a metal foil or a porous metal plate, for example, a foil or a porous plate made of a metal such as aluminum, copper, nickel, titanium, or iron, or an alloy thereof, such as Al (aluminum) foil.

[0061] The positive electrode sheet can be prepared according to conventional methods in the art.

[0062] Negative electrode

[0063] The negative electrode current collector includes a negative electrode active layer disposed on the surface of the negative electrode current collector, the negative electrode active layer comprising a negative electrode active material. The present application does not particularly limit the thickness of the negative electrode active layer, as long as the objectives of the present application are achieved. For example, the thickness of the negative electrode active layer is 30 μm to 120 μm. In some embodiments, the negative electrode active material may include at least one of a carbon material or a silicon-based material. In some embodiments, the carbon material includes, but is not limited to, at least one of natural graphite, artificial graphite, mesophase microcarbon beads, hard carbon, or soft carbon. In some embodiments, the silicon-based material includes, but is not limited to, at least one of silicon, a silicon-oxygen composite, or a silicon-carbon composite. The present application does not particularly limit the thickness of the negative electrode current collector, as long as the objectives of the present application are achieved. For example, it may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or a composite current collector (e.g., a composite current collector with a metal layer disposed on the surface of a polymer layer). The present application does not particularly limit the thickness of the negative electrode current collector, as long as the objectives of the present application are achieved. For example, the thickness of the negative electrode current collector is 5 μm to 12 μm. The negative electrode active layer may also include a binder and a thickener. This application does not specifically limit the types of binder and thickener, as long as they can achieve the objectives of this application. For example, the binder may include, but is not limited to, at least one of polyvinyl alcohol, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, styrene-butadiene rubber, or acrylated styrene-butadiene rubber; the thickener may include, but is not limited to, at least one of sodium carboxymethyl cellulose or lithium carboxymethyl cellulose. The negative electrode active layer may also include a conductive agent. This application does not specifically limit the type of conductive agent, as long as it can achieve the objectives of this application. For example, the conductive agent may include, but is not limited to, at least one of conductive carbon black, carbon nanotubes (CNTs), carbon fibers, Ketjen black, graphene, a metallic material, or a conductive polymer. This application does not specifically limit the mass ratio of the negative electrode active material, conductive agent, binder, and thickener in the negative electrode active layer. Those skilled in the art may select the ratio based on actual needs, as long as it can achieve the objectives of this application. Optionally, the negative electrode plate may also include a conductive layer, which is located between the negative electrode current collector and the negative electrode active layer. The present application does not particularly limit the composition of the conductive layer, and it may be any conductive layer commonly used in the art. For example, the conductive layer may include a conductive agent and a binder. The present application does not particularly limit the conductive agent and binder in the conductive layer, and for example, it may be at least one of the conductive agent and binder used in the negative electrode active layer described above.

[0064] electrolyte

[0065] The invention comprises an organic solvent and a lithium salt; the organic solvent comprises a carbonate solvent, a carboxylate solvent, or a combination thereof; wherein the carbonate solvent comprises at least one of diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), ethylmethyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), or butylene carbonate (BC); and the carboxylate solvent comprises at least one of ethyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl butyrate, ethyl difluoroacetate, difluoroethyl acetate, ethyl trifluoroacetate, trifluoroethyl acetate, or methyl trifluoropropionate. The lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium bis(oxalatoborate) (LiB(C2O4)2, LiBOB), lithium difluorooxalatoborate (LiBF2(C2O4), LiDFOB), lithium tetrafluoroborate (LiBF4), lithium bis(fluorosulfonyl)imide (LiFSI), or lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The above-mentioned electrolyte may further include an electrolyte additive, and the electrolyte additive may include but is not limited to at least one of fluoroethylene carbonate (FEC), vinyl ethylene carbonate (VC), or 1,3-propane sultone (PS).

[0066] The following examples and comparative examples are given to illustrate the embodiments of the present application in more detail. Unless otherwise stated, the parts, percentages and ratios listed below are all based on weight, and the raw materials used are commercially available or synthesized according to conventional methods.

[0067] Example 1

[0068] Preparation of lithium-ion battery separators

[0069] A base film with a rupture temperature of 135°C was selected, and a coating slurry containing the NTC material particles, the ceramic particles, and other components was applied to one side of the base film. The other components included a dispersant (SPA), a binder (PVDF), and a wetting agent (polyoxyethylene alkylphenol ether). Specific parameters are shown in Table 1. A SEM image of the NTC material particles in Example 1 is shown in Figure 3, and its temperature resistance curve is shown in Figure 4.

[0070] As can be seen from Figure 3, the NTC material particles are spinel structures;

[0071] As can be seen from Figure 4, within a certain temperature range, the resistance change rate of the NTC material particles gradually decreases as the temperature increases. The resistance change rate refers to the difference in resistance change when the temperature changes by 1°C.

[0072] Compared with Example 1, Examples 2 to 5 are different in that the content of NTC material particles and the content of ceramic particles are further adjusted in Examples 2 to 5, as shown in Table 1 for details.

[0073] The difference between Example 6 and Example 1 is that Example 6 uses base films with different film breaking temperatures, as shown in Table 1.

[0074] Examples 7 and 8 use NTC material particles different from those of Examples 1 to 6. Example 7 is also a spinel-structured manganese-based quaternary NTC particle, but the molar ratio of its elements is not within the appropriate range of the present application. Example 8 is a spinel-structured manganese-based non-quaternary NTC particle, as shown in Table 1.

[0075] Compared with Example 1, Examples 9 and 10 differ in that Example 9 uses NTC particles with a perovskite structure, and Example 10 uses NTC particles with neither a perovskite structure nor a spinel structure, as shown in Table 1.

[0076] Compared with Example 1, Example 11 is different in that the content of ceramic particles in Example 11 is not within the appropriate range, as shown in Table 1.

[0077] Compared with Example 1, Example 12 is different in that Example 12 adopts the method of coating the coating slurry on both sides of the base film.

[0078] The difference between Example 13 and Example 1 is that the film breaking temperature of the base film adopted in Example 13 is 130°C.

[0079] Compared with Example 1, Comparative Examples 1 to 3 differ in that Comparative Examples 1 and 2 contain only one of the NTC material particles and the ceramic particles, and the remaining content is other components. In Comparative Example 3, the content of the NTC material particles and the ceramic particles is not within the appropriate range, as shown in Table 1.

[0080] Compared with Example 4, Examples 14 to 20 are different in that the average particle size D1 of the NTC material particles and the average particle size D2 of the ceramic particles are further adjusted in Examples 14 to 20, as shown in Table 2 for details.

[0081] Compared with Example 17, Examples 21 to 23 differ in that the base film thickness and the coating thickness are changed in Examples 21 to 23, as shown in Table 2 for details.

[0082] Preparation of positive electrode

[0083] The positive electrode active material - lithium cobalt oxide active material LiCoO2 (4.5V), conductive carbon black Super-P, and binder PVDF are added to the N-methylpyrrolidone NMP solvent system in a weight ratio of 97.6:1.3:1.1, and are fully stirred by a vacuum mixer to obtain a positive electrode slurry; the positive electrode slurry is coated on both surfaces of a 9μm Al foil substrate with a coating weight of 280mg, and then dried, cold pressed, slit, and cut to obtain a positive electrode sheet. The thickness of the positive electrode sheet after cold pressing is 95μm.

[0084] Preparation of negative electrode sheet

[0085] The negative electrode graphite active material - silicon oxide material (graphite and silicon-based material silicon oxide SiO X The negative electrode slurry is prepared by mixing a thickener (sodium carboxymethyl cellulose (CMC) in a mass ratio of 90%:10%) and a binder (styrene-butadiene rubber) in a mass ratio of 96:2:2. The mixture is thoroughly stirred and uniformly mixed to obtain a negative electrode slurry. The average particle size of the silicon-based material is 7μm. The negative electrode slurry is evenly coated on a 12μm-thick copper foil for the negative electrode current collector and dried at 120°C to obtain a negative electrode sheet coated on one side with a negative electrode active material layer. The above steps are then repeated on the other side of the copper foil to obtain a negative electrode sheet coated on both sides with a negative electrode active material layer. The negative electrode sheets are then compacted and slit.

[0086] Preparation of electrolyte

[0087] In a dry argon atmosphere glove box, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a mass ratio of EC:EMC:DEC = 30:50:20. Lithium salt LiPF6 was added and mixed to obtain an electrolyte solution. The mass percentage of LiPF6 was 12.5% ​​based on the mass of the electrolyte solution. The viscosity of the electrolyte solution was 3 to 6 MPa.s.

[0088] Preparation of lithium-ion batteries

[0089] The positive electrode sheet, the lithium-ion battery separator, and the negative electrode sheet are stacked in sequence, with the lithium-ion battery separator acting as an insulator between the positive electrode sheet and the negative electrode sheet. The cells are then wound into bare cells, which are then enclosed in an aluminum-plastic film, injected with electrolyte, and sealed. The cells are then placed in a standing position, subjected to formation, and shaped to obtain a lithium-ion battery. The formation process is as follows: The first cycle of charge and discharge is performed at 45°C, with the following flow: first, charging at a constant current rate of 0.1C for 10 minutes, then charging at a constant current rate of 0.5C to a specified voltage of 4.6V, then charging at a constant voltage until the current is less than or equal to 0.05C, and then discharging at a constant current rate of 0.5C to 3.0V.

[0090] Test method:

[0091] (1) Hot box test

[0092] Step 1: Charge the prepared battery at a constant current of 0.5C to a cut-off voltage of 4.5V, then charge it at a constant voltage to a cut-off current of 200mA, and then let it stand for 5 minutes;

[0093] Step 2: Attach the temperature-sensing wire to the fully charged battery between the two tabs, connect the two tabs to monitor the voltage, and hang the battery cell vertically in the box;

[0094] Step 3: Heat the box to 130°C at a rate of 5°C and maintain for 60 minutes.

[0095] Judging criteria: The battery passes if it does not catch fire or explode.

[0096] (2) Self-discharge rate test

[0097] The voltage of the battery just after hanging in step 2 of the hot box test is recorded as V1. After heating to 130℃ and maintaining it for 30 minutes, the voltage is recorded as V2.

[0098] Self-discharge rate = 2(V1-V2).

[0099] (3) Thermal shrinkage test

[0100] The prepared separator was cut into pieces of 72.5 mm in the MD direction and 54.2 mm in the TD direction. The four corners were fixed to paper sheets with tape. The sample was placed in a 130°C oven and baked for 1 hour. The MD and TD lengths I1 and l2 were measured.

[0101] MD direction thermal shrinkage = (72.5-I1) / 72.5;

[0102] Thermal shrinkage in TD direction = (54.2-l2) / 54.2.

[0103] (4) Rate performance test

[0104] The lithium-ion battery was placed at 25°C for 10 minutes, then charged to 3V at a rate of 0.2C, placed for 10 minutes, and then charged to 4.5V at a rate of 0.7C. It was charged at a constant voltage of 4.5V to a cutoff current of 0.05C, placed for 10 minutes, and finally discharged to 3V at different rates. The capacity of the discharge rate of 0.7C, 1.1C, 2C, and 3C was tested respectively, and the capacity retention rate was calculated as follows: discharge capacity at different rates / discharge capacity at 0.7C rate * 100%.

[0105] Table 1

[0106] Comparing Comparative Examples 1 to 2 with Example 1, it can be seen that when the functional coating of the base film contains both NTC material particles and ceramic particles, and the contents of the NTC material particles and the ceramic particles are within an appropriate range, thermal shrinkage can be significantly suppressed. At the same time, the pass rate of the hot box test is also significantly improved.

[0107] Compared with Example 1, Example 3, and Example 5, it can be seen from Example 2 and Example 4 that further adjusting the content of the NTC material particles within the range of 50% to 80% can achieve both fast discharge and greater safety. In particular, in Example 5, when the content of the NTC material particles is 60%, the self-discharge rate is as high as 220mV / h, and the hot box test pass rate can reach 100%.

[0108] Compared with Example 6, Example 7 and Example 8 also have spinel-structured manganese-based quaternary NTC particles, but the element molar ratio n is Mn / n T Not within the scope of this application, Example 8 is a spinel structured manganese-based non-quaternary NTC particle, but its element molar ratio n Mn / n T It is within the range of 0.76 to 6.5. As can be seen from Table 1, the degree of thermal shrinkage inhibition of Examples 7 and 8 is reduced, and the self-discharge rate is also reduced to 170 mV / h. At the same time, the pass rate of the hot box test is significantly reduced.

[0109] Compared with Example 6, Examples 9 and 10 used different types of NTC material particles, and their corresponding thermal safety performance was significantly reduced compared with Example 6. Compared with Example 1, the base film rupture temperature in Example 13 was not within the appropriate range of this application. Too low a rupture temperature would lead to a decrease in the thermal safety performance of the battery.

[0110] Compared with Example 1, Comparative Example 3 has the same type of NTC material particles as Example 1, but the content of the NTC material particles in Comparative Example 3 is too low, which results in it being unable to achieve a suitable self-discharge rate at high temperature, which is not conducive to reducing the voltage in the early stage of the thermal safety test, thereby resulting in its poor thermal safety performance.

[0111] Table 2

[0112] Compared with Examples 16 to 18, it can be seen from Examples 4, 14 to 15, and 19 to 20 that further adjusting the average particle size D1 of the NTC material particles and the average particle size D2 of the ceramic particles within an appropriate range is beneficial to improving the rate performance.

[0113] Compared with Example 17, Examples 21 to 23 show that the thickness of the base film and the coating is appropriate, which is more conducive to the improvement of energy density.

[0114] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

1. A lithium ion battery separator, characterized in that: including basement membrane; At least one surface of the base film is provided with a functional coating; The functional coating contains NTC material particles and ceramic particles; Based on the functional coating, the mass content of the NTC material particles is 30-80wt%; The film breaking temperature of the base film is not higher than 180°C.

2. The lithium-ion battery separator according to claim 1, characterized in that At least one of the following conditions is met: Condition I: The NTC material particles are selected from at least one of metal oxide particles having a spinel structure or metal oxide particles having a perovskite structure; Condition II: The average particle size of the NTC material particles is recorded as D1, and the average particle size of the ceramic particles is recorded as D2, satisfying: 1≤D1 / D2≤25; Condition III: The film breaking temperature of the base film is 135-180°C.

3. The lithium ion battery separator according to claim 2, characterized in that: The NTC material particles are metal oxide particles with a spinel structure; The metal oxide particles having a spinel structure contain Mn element, O element and T element, and the T element is selected from at least one of Ni element, Fe element, Cu element, Co element and Zn element; Wherein, the molar amount of the Mn element is recorded as n Mn , the molar amount of the T element is recorded as n T , satisfying: 0.76≤n Mn / n T ≤6.

5.

4. The lithium ion battery separator according to claim 2, characterized in that: The mass content of the NTC material particles is 50-80wt%; The mass content of the ceramic particles is in the range of 15 to 45 wt %.

5. The lithium ion battery separator according to claim 4, characterized in that: At least one of the following conditions is met: Condition A: The average particle size D1 of the NTC material particles is 0.5 to 2 μm; Condition B: The average particle size D2 of the ceramic particles is 0.1 to 0.5 μm.

6. The lithium-ion battery separator according to claim 5, characterized in that: At least one of the following conditions is met: Condition a: The average particle size D1 of the NTC material particles is 0.5 to 1.5 μm; Condition b: The average particle size D2 of the ceramic particles is 0.3 to 0.5 μm.

7. The lithium-ion battery separator according to claim 1, characterized in that: The self-discharge rate of the lithium-ion battery separator at an ambient temperature above 120° C. is 120 to 260 mV / h.

8. The lithium-ion battery separator according to claim 7, characterized in that: The self-discharge rate of the lithium-ion battery separator at an ambient temperature above 120° C. is 180 to 220 mV / h.

9. The lithium-ion battery separator according to claim 1, characterized in that: At least one of the following conditions is met: Condition 1: The thickness of the base film is 3 to 6 μm; Condition 2: The thickness of the functional coating is 2 to 8 μm.

10. A lithium ion battery, characterized in that: Including positive electrode sheet, negative electrode sheet, separator and electrolyte; The separator is arranged between the positive electrode sheet and the negative electrode sheet; The separator is a lithium-ion battery separator according to any one of claims 1 to 9; The positive electrode plate contains lithium cobalt oxide positive electrode material.

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