Electrolyte, method for preparing electrolyte membrane, and lithium ion battery

Abstract

This application relates to the field of lithium-ion battery technology, and discloses an electrolyte comprising a lithium salt, an organic solvent, a polymer matrix, and temperature coefficient semiconductor particles dispersed in the polymer matrix; the temperature coefficient semiconductor particles are perovskite-structured ceramics with the general chemical formula Ba. 1‑x‑y Sr x Re y Ti 1‑z Nb z O3; where 0 ≤ x ≤ 0.20, 0

Description

Technical Field

[0001] This application relates to the field of lithium-ion battery technology, specifically to an electrolyte, a method for preparing an electrolyte membrane, and a lithium-ion battery. Background Technology

[0002] Currently, with the widespread application of lithium-ion batteries in new energy vehicles, energy storage systems, and portable electronic devices, the requirements for their energy density and rate performance are continuously increasing. In lithium-ion batteries, the overall performance can be improved by optimizing the positive electrode, negative electrode, or electrolyte system, such as by using a high-nickel ternary positive electrode, a high-capacity negative electrode, or a high-voltage electrolyte system.

[0003] As batteries improve in energy density and rate performance, the conflict between these improvements and safety requirements becomes more pronounced. Specifically, battery safety issues related to insufficient thermal stability become more prominent, necessitating further optimization in terms of performance and efficiency.

[0004] It should be noted that the information disclosed in the background section above is only used to enhance the understanding of the background of this application, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0005] Studies have shown that in lithium-ion batteries with the above-mentioned structure, the chemical properties of the materials and the corresponding interfacial side reactions may be partly responsible for the thermal stability issues. To address this, attempts have been made to add safety designs to the electrode or current collector side, such as coating the electrode particles with positive temperature coefficient (PTC) materials; constructing negative temperature coefficient (NTC) materials on the electrode particles; or introducing PTC materials into the current collector and the positive electrode undercoat.

[0006] In the process of developing the embodiments of this disclosure, a complex relationship was further discovered between the related technical means and the battery safety problem related to insufficient thermal stability. This creates a contradiction and constraint in optimizing battery safety related to insufficient thermal stability under high energy density and rate performance. Specifically, the safety design added by the above-mentioned methods will occupy a large amount of space of active material and increase interface impedance, thereby affecting energy density and rate performance. At the same time, during the charging and discharging process of lithium-ion batteries, it is difficult to actively control the current peak and local heat release due to the characteristics of the separator, which in turn affects the safety of the battery. Therefore, it is necessary to explore an optimal solution that achieves the best balance between the effects.

[0007] To provide a basic understanding of some aspects of the disclosed embodiments, a simple summary is given below. This summary is not a general review, nor is it intended to identify key / important elements or delineate the scope of protection of these embodiments. Instead, it serves as a preface to the detailed description that follows.

[0008] Embodiments of the present disclosure provide an electrolyte, a preparation method of an electrolyte membrane, and a lithium-ion battery. By optimizing the structure of the electrolyte, it is possible to achieve temperature-triggered differential regulation between electron conduction and ion conduction while ensuring rate performance and energy density, thereby ensuring the safety of the battery.

[0009] In some embodiments, the electrolyte includes a lithium salt, an organic solvent, a polymer matrix, and temperature coefficient semiconductor particles dispersed in the polymer matrix. Under the temperature condition of 25°C to 120°C, as the temperature increases, the electronic conductivity of the temperature coefficient semiconductor particles gradually decreases; the temperature coefficient semiconductor particles are perovskite-structured ceramics with a chemical general formula of Ba , , 50 , , , ,

[0013] , 90 ,

[0012] ,

[0016] ,

[0015] ,

[0014] Sr x Re y Ti 1-z Nb z O3;

[0010] Among them, 0 ≤ x ≤ 0.20, 0 < y ≤ 0.10, 0 < z ≤ 0.10, and Re is a rare earth element.

[0011] In some embodiments, in the solid medium of the electrolyte, the mass percentage of the lithium salt is 10% to 40%, the mass percentage of the polymer matrix is 2% to 60%, and the mass percentage of the temperature coefficient semiconductor particles is 2% to 25%.

[0012] In some embodiments, in the solid medium of the electrolyte, the volume percentage of the temperature coefficient semiconductor particles is 1% to 10%.

[0013] In some embodiments, the D 50 of the temperature coefficient semiconductor particles is 50 nm to 500 nm, and D 90 ≤ 1.5 μm. <000013​​​​​​In some embodiments, the organic solvent includes one or more combinations of ethylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethyl carbonate, fluorocarbonate, and phosphate ester.

[0017] In some embodiments, the thickness of the electrolyte film is 10 μm to 40 μm.

[0018] In some embodiments, at a first preset temperature, its ionic conductivity σ1 ≥ 5 × 10⁻⁶ -3 S / cm, electronic conductivity σ2≤1×10 -8 S / cm.

[0019] In some embodiments, at the second preset temperature, the electronic conductivity σ² is 1 × 10⁻⁶. -11 S / cm ~ 1×10 -9 S / cm; where the second preset temperature is greater than the first preset temperature.

[0020] In some embodiments, the method for preparing the electrolyte membrane includes the electrolyte described in the foregoing embodiments, and includes the following steps:

[0021] The polymer matrix is ​​dissolved in an organic solvent to obtain a polymer solution;

[0022] Temperature coefficient semiconductor particles and lithium salts were added to the polymer solution and mixed in a high-speed dispersion manner to obtain a gel precursor solution.

[0023] The gel precursor solution is coated on the surface of the substrate, and the organic solvent is evaporated by drying, so that the polymer matrix and the temperature coefficient semiconductor particles form a co-continuous phase to obtain an electrolyte membrane in thin film shape.

[0024] In some embodiments, the lithium-ion battery includes a positive electrode, a negative electrode, and an electrolyte membrane, wherein the electrolyte membrane is a thin film formed by the electrolyte described in the foregoing embodiments, or an electrolyte membrane prepared by the preparation method of the electrolyte membrane described in the foregoing embodiments.

[0025] In some embodiments, the compaction density of the negative electrode sheet is 1.2 g / cm³. 3 ~1.7g / cm 3 .

[0026] In some embodiments, the molecular formula of the positive electrode active material is Li a Ni b Co c Mn d M eO2; where 0.9 < a ​​< 1.2, 0.8 ≤ b ≤ 0.93, 0.1 ≤ c < 0.4, 0.05 ≤ d < 0.4, 0 ≤ e ≤ 0.1, and the M element includes one or more combinations of Zr, W, Ti, Al, Sr, La, B and Nd.

[0027] In some embodiments, the capacity ratio N / P of the negative electrode to the positive electrode is 1.02 to 1.20.

[0028] The electrolyte, the method for preparing the electrolyte membrane, and the lithium-ion battery provided in this disclosure can achieve the following technical effects:

[0029] By dispersing temperature coefficient semiconductor particles in a polymer matrix, the Sr element in the temperature coefficient semiconductor particles can adjust the lattice and phase transition temperature, making the PTC response window closer to the early temperature of abnormal cell heating (100℃~120℃). The Re and Nb elements can control the carrier concentration and grain boundary barrier, adjust the degree of n-type semiconductorization and the height of the grain boundary barrier inside the grain, so that the electronic conductivity at 25℃ is maintained in a "moderate and low" range, thereby avoiding a significant increase in the electronic leakage current of the gel electrolyte. At the same time, the Re element also affects the lattice and grain boundary structure, thereby affecting the PTC jump temperature and peak shape.

[0030] Therefore, under temperature conditions ranging from 25℃ to 120℃, the electronic conductivity of temperature coefficient semiconductor particles gradually decreases as the temperature increases, i.e., the resistivity increases. This allows for the construction of a temperature-dependent electron current-limiting network, achieving pre-current limiting, i.e., the PTC effect. Simultaneously, the polymer matrix and organic solvent can form a highly efficient ion pathway. Since the temperature coefficient semiconductor particles primarily regulate "electron channels" rather than "ion channels," this electrolyte can reduce electronic conductivity while ensuring efficient lithium-ion conduction within the room temperature and normal operating temperature range, thus meeting the requirements for high rate performance and high energy density.

[0031] Furthermore, in the event of abnormal temperature rise in a localized area of ​​the battery cell, the electronic conductivity of the temperature coefficient semiconductor particles gradually decreases, resulting in a significant increase in resistance. This leads to a more pronounced slope / transition near the Curie point, which can reduce the electronic bypass current during localized abnormal temperature rise and suppress the exothermic side reaction, thereby improving thermal safety. This effectively suppresses the peak values ​​of short-circuit current and side reaction current, reduces the risk of thermal runaway, and ultimately ensures the safety of the battery.

[0032] The above general description and the description below are exemplary and illustrative only and are not intended to limit this application. Attached Figure Description

[0033] One or more embodiments are illustrated by way of example with reference to the accompanying drawings. These illustrations and drawings do not constitute a limitation on the embodiments. Elements having the same reference numerals in the drawings are shown as similar elements. The drawings are not to be scaled. And wherein:

[0034] Figure 1 This is a schematic diagram of the structure of a lithium-ion battery provided in an embodiment of this disclosure;

[0035] Figure 2 This is a schematic diagram of the structure of a lithium-ion battery provided in an embodiment of this disclosure;

[0036] Figure 3 This is a schematic diagram of a lithium-ion battery provided in an embodiment of this disclosure;

[0037] Figure 4 This is a temperature versus resistivity curve of a lithium-ion battery provided in an embodiment of this disclosure;

[0038] Figure 5 This is a temperature versus resistivity curve of a lithium-ion battery provided in an embodiment of this disclosure.

[0039] Figure label:

[0040] 1-Positive terminal; 10-Cell; 11-Positive terminal post; 12-Negative terminal; 2-Shell; 3-Negative electrode; 4-Electrolyte membrane; 5-Positive electrode. Detailed Implementation

[0041] To provide a more detailed understanding of the features and technical content of the embodiments of this disclosure, the implementation of the embodiments of this disclosure will be described in detail below with reference to the accompanying drawings. The accompanying drawings are for illustrative purposes only and are not intended to limit the embodiments of this disclosure. In the following technical description, for ease of explanation, several details are used to provide a full understanding of the disclosed embodiments. However, one or more embodiments may still be implemented without these details. In other cases, well-known structures and devices may be simplified in their depiction to simplify the drawings.

[0042] The terms "first," "second," etc., used in the specification, claims, and accompanying drawings of this disclosure are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate for the embodiments of this disclosure described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion.

[0043] In the embodiments of the present disclosure, the orientation or positional relationship indicated by terms such as "upper", "lower", "inner", "middle", "outer", "front", "rear", etc. is based on the orientation or positional relationship shown in the drawings. These terms are mainly used to better describe the embodiments of the present disclosure and their examples, and are not used to limit that the indicated device, element or component must have a specific orientation, or be constructed and operated in a specific orientation. Moreover, in addition to being used to represent the orientation or positional relationship, some of the above terms may also be used to represent other meanings. For example, the term "upper" may also be used to represent a certain attachment relationship or connection relationship in some cases. For those of ordinary skill in the art, the specific meanings of these terms in the embodiments of the present disclosure can be understood according to specific circumstances.

[0044] In addition, the terms "arranged", "connected", "fixed" should be understood in a broad sense. For example, "connected" can be a fixed connection, a detachable connection, or an integral structure; it can be a mechanical connection or an electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, or there is internal communication between two devices, elements or components. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present disclosure can be understood according to specific circumstances.

[0045] Unless otherwise specified, the term "plural" means two or more.

[0046] In the embodiments of the present disclosure, the character " / " indicates that the objects before and after are in an "or" relationship. For example, A / B means: A or B.

[0047] The term "and / or" is a description of the associated relationship of an object, indicating that there can be three relationships. For example, A and / or B means: A or B, or, A and B these three relationships.

[0048] It should be noted that, without conflict, the embodiments in the embodiments of the present disclosure and the features in the embodiments can be combined with each other.

[0049] The embodiments of the present disclosure provide an electrolyte, including a lithium salt, an organic solvent, a polymer matrix, and temperature coefficient semiconductor particles dispersed in the polymer matrix. Under the temperature condition of 25°C to 120°C, as the temperature increases, the electronic conductivity of the temperature coefficient semiconductor particles gradually decreases; the temperature coefficient semiconductor particles are perovskite structure ceramics, and their chemical general formula is Ba 1-x-y Sr x Re y Ti 1-z Nb z O3;

[0050] Where 0 ≤ x ≤ 0.20, 0 < y ≤ 0.10, 0 < z ≤ 0.10, and Re is a rare earth element.

[0051] Using the electrolyte provided in this embodiment, temperature coefficient semiconductor particles are dispersed and doped in a polymer matrix. Here, the Sr element in the temperature coefficient semiconductor particles can adjust the lattice and electrical phase transition temperature, making the PTC response window closer to the early temperature of abnormal cell temperature rise (100℃~120℃). The Re and Nb elements can control the carrier concentration and grain boundary barrier, adjust the degree of n-type semiconductorization and the height of the grain boundary barrier inside the grain, so that the electronic conductivity at 25℃ is maintained in a "moderate and low" range, thereby avoiding a significant increase in the electronic leakage current of the gel electrolyte. At the same time, the Re element also affects the lattice and grain boundary structure, thereby affecting the PTC jump temperature and peak shape.

[0052] Therefore, under temperature conditions ranging from 25℃ to 120℃, the electronic conductivity of temperature coefficient semiconductor particles gradually decreases with increasing temperature, while the resistivity increases. This allows for the construction of a temperature-dependent electron current-limiting network, achieving pre-current limiting, i.e., the PTC effect. Simultaneously, the polymer matrix and organic solvent can form a highly efficient ion pathway. Since the temperature coefficient semiconductor particles primarily regulate "electron channels" rather than "ion channels," the electrolyte can reduce electronic conductivity while ensuring efficient lithium-ion conduction within the room temperature and normal operating temperature range, thus meeting the requirements for high rate performance and high energy density.

[0053] Furthermore, in the event of abnormal temperature rise in a localized area of ​​the battery cell, the electronic conductivity of the temperature coefficient semiconductor particles gradually decreases, resulting in a significant increase in resistance. This leads to a more pronounced slope / transition near the Curie point, which can reduce the electronic bypass current during localized abnormal temperature rise and suppress the exothermic side reaction, thereby improving thermal safety. This effectively suppresses the peak values ​​of short-circuit current and side reaction current, reduces the risk of thermal runaway, and ultimately ensures the safety of the battery.

[0054] In some embodiments, in the solid medium of the electrolyte, the mass percentage of lithium salt is 10% to 40%, the mass percentage of polymer matrix is ​​20% to 60%, and the mass percentage of temperature coefficient semiconductor particles is 2% to 25%.

[0055] In this embodiment of the disclosure, lithium salt, organic solvent, polymer matrix and temperature coefficient semiconductor particles constitute the solid medium of the electrolyte.

[0056] In some embodiments, the volume percentage of temperature coefficient semiconductor particles in the solid medium of the electrolyte is 1% to 10%.

[0057] In this embodiment of the disclosure, the correspondence between the volume percentage and mass percentage of the temperature coefficient semiconductor particles is determined by the true density of each solid phase component.

[0058] Specifically, the conversion is performed using the following formula:

[0059] w=

[0060] Where w represents the temperature coefficient and the mass percentage of the semiconductor particles. ρ is the volume percentage of the temperature coefficient semiconductor particles. p ρ is the true density of the temperature coefficient semiconductor particles (particulate phase). m It is the equivalent true density of the solid medium (matrix phase).

[0061] In some embodiments, the D of the temperature coefficient semiconductor particle 50 For 50nm~500nm, and D 90 ≤1.5μm.

[0062] In some embodiments, the Re element is one or more combinations of La, Ce, Pr, and Nd.

[0063] In this embodiment, Re is La. Specifically, the doped titanate ceramic is a ceramic powder with BaTiO3 as the matrix and simultaneously doped with Sr, La and Nb. The ceramic powder is obtained by calcining a mixture of BaCO3, SrO, TiO2, La2O3 and Nb2O5 in air at 900℃~1350℃ for 2h~6h, followed by cooling and pulverization.

[0064] In this embodiment, the temperature coefficient semiconductor particle is a BaTiO3-based perovskite ceramic. + Able to replace part of Ba² + Nb 5+ Able to replace some Ti 4+ These factors work together to regulate the carrier concentration within the grains and modulate the barrier structure at the grain boundaries. When the material temperature approaches the Curie temperature, changes in dielectric properties modulate the grain boundary barrier, resulting in a significant increase in resistivity with increasing temperature, characteristic of the PTC (Potentially Transient Charge) feature. Based on this, Sr²... + Able to replace part of Ba² + By adjusting the lattice constant and phase transition characteristics, the Curie temperature position and the width of the phase transition range can be adjusted, thereby achieving designable control of the PTC response window.

[0065] In some embodiments, the polymer matrix includes one or more combinations of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyacrylonitrile, polyethylene oxide, and polymethyl methacrylate.

[0066] In some embodiments, the organic solvent includes one or more combinations of ethylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethyl carbonate, fluorocarbonate, and phosphate ester.

[0067] In some embodiments, the thickness of the electrolyte film is 10 μm to 40 μm.

[0068] In some embodiments, at a first preset temperature, its ionic conductivity σ1 ≥ 5 × 10⁻⁶ -3 S / cm, electronic conductivity σ2≤1×10 -8 S / cm.

[0069] In some embodiments, at the second preset temperature, the electronic conductivity σ² is 1 × 10⁻⁶. -11 S / cm ~ 1×10 -9 S / cm; where the second preset temperature is greater than the first preset temperature.

[0070] In this embodiment of the disclosure, the first preset temperature is 25°C, and the second preset temperature is 80°C to 130°C.

[0071] This disclosure also provides a method for preparing an electrolyte membrane, comprising the following steps:

[0072] S101. Dissolve the polymer matrix in an organic solvent to obtain a polymer solution; wherein the solid content of the polymer solution is 5wt%~20wt%.

[0073] S102. Temperature coefficient semiconductor particles and lithium salt are added to the polymer solution separately and mixed by high-speed dispersion to obtain a gel precursor solution; wherein, the particle size D of the temperature coefficient semiconductor particles in the polymer solution is... 50 The range is 50nm to 500nm.

[0074] S103. The gel precursor solution is coated onto the surface of a substrate, and the organic solvent is evaporated by drying, allowing the polymer matrix and temperature coefficient semiconductor particles to form a co-continuous phase to obtain an electrolyte membrane. The wet film thickness of the gel precursor solution coated onto the substrate surface is 20 μm to 100 μm; the drying temperature is 40℃ to 100℃; and the thin film thickness of the electrolyte membrane is 10 μm to 40 μm.

[0075] This disclosure also provides a lithium-ion battery, including a positive electrode, a negative electrode, and an electrolyte membrane, wherein the electrolyte membrane is a thin film formed by the electrolyte described in the foregoing embodiments, or an electrolyte membrane prepared by the preparation method of the electrolyte membrane described in the foregoing embodiments.

[0076] The specific structure and parameters of the electrolyte or electrolyte membrane are as described in the above embodiments. Since this lithium-ion battery adopts all the technical solutions of all the above embodiments, it has at least all the technical effects brought about by the technical solutions of the above embodiments, and will not be described in detail here.

[0077] In some embodiments, the compaction density of the negative electrode sheet is 1.2 g / cm³. 3 ~1.7g / cm 3 .

[0078] In some embodiments, the molecular formula of the positive electrode active material is Li a Ni b Co c Mn d M e O2; where 0.9 < a ​​< 1.2, 0.8 ≤ b ≤ 0.93, 0.1 ≤ c < 0.4, 0.05 ≤ d < 0.4, 0 ≤ e ≤ 0.1, and the M element includes one or more combinations of Zr, W, Ti, Al, Sr, La, B and Nd.

[0079] In some embodiments, the capacity ratio N / P of the negative electrode to the positive electrode is 1.02 to 1.20.

[0080] In this embodiment of the disclosure, the lithium-ion battery further includes a casing, in which a positive electrode and a negative electrode are encapsulated. Figures 1 to 3 As shown, the lithium-ion battery specifically includes a cylindrical casing 2, which houses the battery cells. The top is the positive terminal 1, and the bottom is the negative terminal 12. A positive electrode post 11 is disposed on the positive terminal 1. Specifically, Figure 2 A schematic diagram of the lithium-ion battery structure in this application is shown. Figure 3 A schematic diagram of the lithium-ion battery described in this application is shown. The positive electrode 5, negative electrode 3, and electrolyte membrane 4 are shown as follows: Figure 3 The layers are stacked and then wound to form... Figure 2 The cylindrical battery cell 10 shown is initially wound to the electrode end at the cylindrical axis, and ends to the electrode end on the outer surface of the cylinder after winding. The positive electrode 5 includes a strip-shaped positive electrode foil, a positive electrode coating on the surface of the strip-shaped positive electrode foil, and a first empty foil area. The negative electrode 3 includes a strip-shaped negative electrode foil, a negative electrode coating on the surface of the strip-shaped negative electrode foil, and a second empty foil area. The first and second empty foil areas are perpendicular to the winding direction and are formed into the top or bottom end face of the lithium-ion battery by methods such as flattening or folding.

[0081] Based on this, the present disclosure provides a method for preparing a lithium-ion battery, comprising:

[0082] Preparation of positive electrode sheet: Mix positive electrode slurry, coat it on both sides of the positive electrode current collector, and obtain positive electrode sheet after drying and cold pressing;

[0083] Preparation of negative electrode sheet: Mix negative electrode slurry, coat it on both sides of the negative electrode current collector, and obtain negative electrode sheet after drying and cold pressing;

[0084] Battery cell preparation: The positive and negative electrode sheets are rolled and slit respectively, and then wound together with the electrolyte membrane to obtain the battery cell;

[0085] Assembling lithium-ion batteries: The tabs of the lithium-ion battery are welded to the electrical connectors, installed into the battery casing, and electrolyte is injected, sealed, and formed to obtain the lithium-ion battery.

[0086] Furthermore, embodiments of this disclosure provide an electrical device including a lithium-ion battery for providing power as described in this application.

[0087] The present invention will be further explained and illustrated below with reference to embodiments.

[0088] Example 1

[0089] Preparation of positive electrode sheet: Select positive electrode active material, carbon black (Super P), carbon nanotubes (CNT) and polyvinylidene fluoride (PVDF), and mix them thoroughly in an N-methylpyrrolidone solvent system at a mass ratio of 96:1:1:2 to obtain positive electrode slurry; then coat the positive electrode slurry onto a 12.0 μm aluminum foil, and after drying, cold pressing, slitting and cutting, obtain positive electrode sheet.

[0090] Preparation of the negative electrode sheet: Silicon carbide, graphite, negative electrode conductive agent, carbon black, thickener sodium carboxymethyl cellulose, binder polyacrylic acid (PAA), and binder styrene-butadiene rubber (SBR) were selected and thoroughly mixed in deionized water at a mass ratio of 20:76:0.75:0.75:1:0.75:0.75 to obtain a negative electrode slurry. The negative electrode slurry was then coated onto copper foil, and after drying, cold pressing, slitting, and cutting, a compacted density of 1.5 g / cm³ was obtained. 3 The negative electrode sheet.

[0091] Preparation of electrolyte membrane: This includes the preparation of PTC ceramic powder, using BaTiO3 as the matrix, and simultaneously doping with La, Sr, and Nb to achieve the target composition including Ba. 0.97 Sr 0.01 La 0.02 Ti 0.98 Nb 0.02 O3, i.e., 1 mol% Sr 2+ Replace part of Ba 2+ 2 mol% La 3+ Replace part of Ba 2+ 2 mol% Nb 5+ Partially replaces Ti 4+ .

[0092] The following were selected as precursors:

[0093] BaCO3 (analytical grade, ≥99%), SrO (≥99%), TiO2 (anatase, ≥99%), La2O3 (≥99%), Nb2O5 (≥99%). To synthesize 1 mol Ba... 0.97 Sr 0.01 La 0.02 Ti 0.98 Nb 0.02 Taking O3 as an example, its theoretical molar dosage is:

[0094] Ba is 0.97 mol (from BaCO3), Sr is 0.01 mol (from SrO), La is 0.02 mol (from La2O3), Ti is 0.98 mol (from TiO2), and Nb is 0.02 mol (from Nb2O5).

[0095] The amounts of each precursor are as follows:

[0096] The amount of BaCO3 used is approximately 0.97 mol × 197.34 g / mol ≈ 191.4 g;

[0097] The amount of TiO2 used is 0.98mol × 79.8 g / mol ≈ 78.3 g;

[0098] The amount of SrO used is 0.01mol × 103.62 g / mol ≈ 1.04 g;

[0099] The amount of La2O3 used is 0.01mol × 325.8g / mol ≈ 3.26g (one molecule contains 2mol of La);

[0100] The amount of Nb₂O₅ used is 0.01mol × 265.8g / mol ≈ 2.66g (one molecule contains 2 mol of Nb);

[0101] The mass ratio of BaCO3:TiO2:SrO:La2O3:Nb2O5 is 191.4:78.3:1:3.3:2.7.

[0102] Mixing and pre-firing

[0103] Weigh out BaCO3, SrO, TiO2, La2O3 and Nb2O5 and add them to a ball mill jar; add anhydrous ethanol as the ball milling medium to make the slurry solid content 60wt%; add zirconia balls and control the ball-to-material ratio (mass ratio) to 5:1.

[0104] Ball milling was performed at 200 rpm to 250 rpm for 12 hours to fully mix and initially refine the powder.

[0105] After ball milling, the slurry is poured out, stirred at low speed to remove bubbles, and placed in a hot air oven at 80 ℃ to dry until the ethanol is completely evaporated, resulting in a dry mixed powder.

[0106] High-temperature solid-state synthesis

[0107] The dried mixed powder is passed through a 200-mesh sieve and loosely packed into an alumina crucible; the packing height is less than 2 / 3 of the height of the alumina crucible.

[0108] Place the alumina crucible in a box-type electric furnace with an ambient air environment, and control the temperature as follows:

[0109] The temperature was increased from room temperature to 900℃ at a rate of 3℃ / min and held for 4 hours; this pre-burning process removed CO2 and promoted the precursor reaction.

[0110] The temperature is increased from 900℃ to 1250℃ at a rate of 3℃ / min, and held for 4 hours; in this way, the solid-phase reaction is completed, and the PTC ceramic main phase is formed.

[0111] The temperature was naturally cooled from 1250°C to room temperature. After cooling, the block ceramic sintered body was removed and mechanically crushed into coarse powder.

[0112] Crushing and Grading

[0113] The coarse powder is added to an air jet mill for air jet milling at a pressure of 0.6 MPa to 0.8 MPa.

[0114] Adjust the classifier rotation speed to 5000 rpm to 7000 rpm to achieve the desired median particle size D of the resulting powder. 50 Controlled at around 200nm;

[0115] Particle size distribution was determined by laser particle size analyzer to confirm D. 50 =200±20nm、D 90 After reaching ≤500nm, the powder is used as PTC ceramic powder for future use.

[0116] The main reaction equations include:

[0117] Solid-state reaction of barium titanate matrix: BaCO3 + TiO2 → BaTiO3 + CO2↑;

[0118] Co-doped system: (1) x y)BaCO3+xSrO+y / 2Re2O3+(1 z)TiO2+z / 2Nb2O5→

[0119] Ba1 x y Sr x Re y Ti1 z Nb z O3+(1 x y)CO2↑+(y+z) / 4O2↑;

[0120] x=0.01, y=0.02, z=0.02; Re=La;

[0121] Thus, we obtain Ba 0.97 Sr 0.01 La 0.02 Ti 0.98 Nb 0.02 O3.

[0122] It also includes the preparation of gel precursor solutions. Taking the preparation of a gel electrolyte containing 100g of solids as an example, the target solid mass ratio includes: 30wt% lithium salt LiPF6 (30g), 50wt% polymer matrix PVDF-HFP (50g), 10wt% PTC ceramic powder (10g), and 10wt% other additives (such as film-forming aids, stabilizers, etc., totaling 10g); the organic solvent includes a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7.

[0123] To prepare the polymer solution, 350g of EC and EMC mixed solvent with a volume ratio of 3:7 was added to a mixing tank; 50g of PVDF-HFP was slowly added, and the solution was dissolved by mechanical stirring at 300rpm~500rpm for 3h~4h under oil bath conditions at 60℃, to obtain a homogeneous transparent or semi-transparent polymer solution with a solid content of 12wt%~15wt%.

[0124] Add 30g of LiPF6 in batches to the above polymer solution, keeping the temperature between 40℃ and 50℃, and stir continuously for 2 hours until completely dissolved, avoiding the introduction of water.

[0125] Add 10g of other additives, specifically 2g LiDFOB, 2g LiFSI, and 6g LiPO2F2, and continue stirring for 2 hours. The final overall solid content is between 12wt% and 18wt%, yielding a polymer mixed solution.

[0126] Take 440g of polymer mixture solution and control the temperature between 40℃ and 50℃;

[0127] 10g of PTC ceramic powder was dried at 120℃ for 2 hours to remove adsorbed water; then, 10g of PTC ceramic powder was slowly added in batches under a high-speed disperser at a speed of 1000rpm~1500rpm to make it evenly wetted.

[0128] Maintain high-speed dispersion for 30-60 minutes to keep the PTC ceramic powder particle size in the solution at D. 50 The mixture is uniformly dispersed at 200 nm; the stirring speed is reduced to 400 rpm to 600 rpm, and stirring is continued for 30 min to complete homogenization, thus obtaining the gel precursor solution.

[0129] The gel precursor solution was transferred to a vacuum degassing tank. Degas for 30 minutes at 0.08 MPa to remove any mixed microbubbles.

[0130] Polytetrafluoroethylene release film was selected as the substrate;

[0131] Using a doctor blade coating device, the degassed gel precursor liquid is poured onto the leading edge of the substrate. By adjusting the doctor blade gap, the wet film thickness is made to be approximately 60 μm.

[0132] The coated wet film is then placed in a multi-stage constant temperature oven and dried as follows:

[0133] First drying stage: Dry at 40℃ for 1 hour to allow the solvent to evaporate slowly;

[0134] Second drying stage: Dry at 60℃ for 1 hour to continue evaporating the solvent and promote the formation of the polymer and PTC network structure;

[0135] The third drying stage: Dry at 80℃ for 0.5h~1h to reduce the residual solvent to the target range.

[0136] After cooling to room temperature, the dry film thickness was measured to be 25 μm.

[0137] The dry membrane was peeled off from the substrate as a whole to obtain a self-supporting gel electrolyte membrane;

[0138] The prepared electrolyte membrane can be used for corresponding tests. In the solid composition of the electrolyte membrane, the mass fraction of PTC particles is 10%, polymer is 50%, lithium salt is 30%, and other additives are 10%.

[0139] Lithium-ion battery assembly:

[0140] By rolling and slitting the positive and negative electrode sheets respectively, and then winding them together with the electrolyte membrane, a cylindrical battery core is obtained. The battery core is then welded to the electrical connectors and installed into the battery casing. After completing the electrolyte injection, sealing, and formation processes, the lithium-ion battery of Example 1 is obtained. The casing of this lithium-ion battery is cylindrical, with dimensions of 21.0 mm in diameter and 70.0 mm in length.

[0141] Example 2

[0142] Example 2 provides an electrolyte membrane and a lithium-ion battery. The difference between this example and Example 1 is that the PTC ceramic powder is 6 wt%, while the rest is the same as in Example 1.

[0143] Example 3

[0144] Example 3 provides an electrolyte membrane and a lithium-ion battery. The difference between this example and Example 1 is that the PTC ceramic powder is 18 wt%, while the rest is the same as in Example 1.

[0145] Comparative Example 1

[0146] Comparative Example 1 provides an electrolyte membrane and a lithium-ion battery. The difference between this comparative example and Example 1 is that the PTC ceramic powder is 1 wt%, while all other aspects are the same as in Example 1.

[0147] Example 4

[0148] Example 4 provides an electrolyte membrane and a lithium-ion battery. The difference between this example and Example 1 is that the D of the PTC ceramic powder... 50 The wavelength is 100nm, and everything else is the same as in Example 1.

[0149] Example 5

[0150] Example 5 provides an electrolyte membrane and a lithium-ion battery. The difference between this example and Example 1 is that the D of the PTC ceramic powder... 50 The wavelength is 350nm, and everything else is the same as in Example 1.

[0151] Comparative Example 2

[0152] Comparative Example 2 provides an electrolyte membrane and a lithium-ion battery. The difference between this comparative example and Example 1 is that the D of the PTC ceramic powder... 50 The wavelength is 800nm, and everything else is the same as in Example 1.

[0153] Example 6

[0154] Example 6 provides an electrolyte membrane and a lithium-ion battery. The difference between this example and Example 1 is that the polymer matrix is ​​35 wt%, while everything else is the same as in Example 1.

[0155] Example 7

[0156] Example 7 provides an electrolyte membrane and a lithium-ion battery. The difference between this example and Example 1 is that the polymer matrix is ​​60 wt%, while all other aspects are the same as in Example 1.

[0157] Comparative Example 3

[0158] Comparative Example 3 provides an electrolyte membrane and a lithium-ion battery. The difference between this comparative example and Example 1 is that the polymer matrix is ​​20 wt%, while everything else is the same as in Example 1.

[0159] Example 8

[0160] Example 8 provides an electrolyte membrane and a lithium-ion battery. The difference between this example and Example 1 is that the wet film thickness is reduced so that the dry film thickness is 15 μm. All other aspects are the same as in Example 1.

[0161] Example 9

[0162] Example 9 provides an electrolyte membrane and a lithium-ion battery. The difference between this example and Example 1 is that the wet film thickness is increased so that the dry film thickness is 35 μm. All other aspects are the same as in Example 1.

[0163] Comparative Example 4

[0164] Comparative Example 4 provides an electrolyte membrane and a lithium-ion battery. The difference between this comparative example and Example 1 is that the wet film thickness is increased, resulting in a dry film thickness of 50 μm. Everything else is the same as in Example 1.

[0165] Example 10

[0166] Example 10 provides an electrolyte membrane and a lithium-ion battery. The difference between this example and Example 1 is that, in the preparation of the PTC ceramic powder, Sr is 0.01 mol, La is 0.03 mol, and Nb is 0.03 mol, resulting in a target composition of Ba. 0.96 Sr 0.01 La 0.03 Ti 0.97 Nb 0.03 O3, and everything else is the same as in Example 1.

[0167] Example 11

[0168] Example 11 provides an electrolyte membrane and a lithium-ion battery. The difference between this example and Example 1 is that, in the preparation of the PTC ceramic powder, La is 0.01 mol and Nb is 0.01 mol, resulting in a target composition of Ba. 0.99 La 0.01 Ti 0.99 Nb 0.01 O3, and everything else is the same as in Example 1.

[0169] Example 12

[0170] Example 12 provides an electrolyte membrane and a lithium-ion battery. The difference between this example and Example 1 is that, in the preparation of the PTC ceramic powder, La is 0.03 mol and Nb is 0.03 mol, resulting in a target composition of Ba. 0.97 La 0.03 Ti 0.97 Nb 0.03 O3, and everything else is the same as in Example 1.

[0171] Comparative Example 5

[0172] Comparative Example 5 provides an electrolyte membrane and a lithium-ion battery. The difference between this comparative example and Example 1 is that the BaTiO3 in the PTC ceramic powder is not doped with Sr, La and Nb, while the rest is the same as in Example 1.

[0173] The electrolyte membranes and lithium-ion batteries of Examples 1 to 12, and Comparative Examples 1 to 5 were tested accordingly.

[0174] This disclosure provides a method for testing the ionic conductivity of an electrolyte membrane using a blocking electrode (stainless steel SS electrode) and electrochemical impedance spectroscopy (EIS). The obtained electrolyte membrane is sandwiched between two blocking electrodes, a small AC voltage signal is applied, and its impedance is measured. The test environment temperature is 25°C. Specifically, the test is performed as follows:

[0175] Take two stainless steel circular electrodes, each with a diameter of 16mm, from the glove box;

[0176] The stainless steel electrode, electrolyte membrane, and stainless steel electrode are stacked sequentially.

[0177] Place it in a button cell casing or a special fixture, apply moderate pressure to ensure that the electrolyte membrane is fully adhered to the two stainless steel electrodes and to avoid air gaps;

[0178] By encapsulating button cells, SS|Gel|SS symmetrical cells (test cells) are obtained.

[0179] Perform AC impedance (EIS) testing on the test battery:

[0180] Connect the test cell to the electrochemical workstation and set the EIS parameters, including an initial voltage of 0 V (open circuit voltage); an AC disturbance amplitude of 5mV to 10mV; and a frequency range from high frequency to low frequency, i.e., 1MHz to 0.1Hz.

[0181] Perform operational tests to obtain impedance spectra, i.e., Nyquist plots;

[0182] Record the Nyquist plot, with the imaginary part Z'' opposite to the real part Z', and read the resistance value at the intersection of the high-frequency end and the real axis in the Nyquist plot, which is the bulk resistance R of the electrolyte membrane. b ;

[0183] The ionic conductivity is obtained from the electrolyte membrane thickness and the area A of the stainless steel disc electrode. The ionic conductivity σ1 is then calculated using the following formula:

[0184] σ1=

[0185] Where L is the thickness of the electrolyte membrane and A is the area of ​​the stainless steel disc electrode.

[0186] This embodiment also provides a method for testing the electronic conductivity of an electrolyte membrane, using an RM2610 resistance testing system to determine the interfacial resistance of the electrolyte membrane. The resistance testing system has 45 probes arranged in a square matrix, with one probe serving as a ground probe.

[0187] The testing method includes the following steps:

[0188] The vacuum-dried electrolyte membrane was divided into 40 square grids of 1.0 cm × 1.0 cm to ensure a smooth sample surface;

[0189] The electrolyte membrane was placed on the testing apparatus, and the pressure applied by the probe was adjusted using a pressure gauge to ensure good contact between the probe and the electrolyte membrane, with a contact area of ​​0.01 cm². 2 ;

[0190] During the test, a constant current is applied to the 20 outer probes, allowing the current to flow through the electrolyte membrane, while the 25 middle probes measure the voltage change in real time.

[0191] The resistance and conductivity of the electrolyte membrane were calculated using Ohm's law and fitting analysis methods.

[0192] Subsequently, another nine square grids were randomly selected using the above method for measurement. By calculating the average value of the above values, the actual electronic conductivity of the electrolyte membrane was obtained, so as to comprehensively evaluate the safety characteristics of the electrolyte membrane at different temperatures.

[0193] This disclosure also provides a method for testing the rate performance of a lithium-ion battery, wherein the lithium-ion battery to be tested is placed in a 45°C constant temperature chamber for 6 hours, and the test is performed as follows:

[0194] First round of constant current and constant voltage charging: Under the condition of 0.1C charging rate, constant current charging is carried out to 4.25V, and then constant voltage charging is carried out until the current drops to 0.01C, and then left to stand for 30 minutes;

[0195] Perform constant current discharge: under a discharge rate of 0.5C, discharge to 2.5V and record the reference capacity C1.

[0196] Charge and discharge process: Under a charging rate of 0.1C, constant current charging is performed to 4.25V, then constant voltage charging is performed until the current drops to 0.1C, and the charge is left to stand for 30 minutes.

[0197] Under a 5C discharge rate, the system was constantly discharged to 2.5V, the reference capacity C2 was recorded, and the system was left to stand for 30 minutes.

[0198] The rate performance of a lithium-ion battery is determined by C1 and C2. Here, the formula for rate capacity retention is C2 / C1*100%.

[0199] This disclosure also provides a method for testing the safety performance of lithium-ion batteries, wherein the test environment temperature is 25°C; specifically, the test is performed in the following manner:

[0200] A K-type thermocouple is attached to the outside of the middle of the lithium-ion battery;

[0201] A steel nail with a diameter of 3 mm was pierced through the middle of the lithium-ion battery at a speed of 25 mm / s, and the highest temperature of the lithium-ion battery casing was recorded.

[0202] This disclosure also provides a method for testing the long-term storage performance of a lithium-ion battery. Specifically, a lithium-ion battery with a reference capacity of C3 is placed in a constant temperature chamber at 60°C and stored for 30 days. After the lithium-ion battery is removed, its capacity is measured at a charge-discharge rate of 0.5C to C4 under the condition that the temperature returns to 25°C.

[0203] The long-term storage performance of lithium-ion batteries is determined by C3 and C4. Here, the formula for storage capacity retention rate is C4 / C3*100%.

[0204] After conducting the above tests on Examples 1 to 12 and Comparative Examples 1 to 5, the corresponding data were obtained.

[0205] The ionic conductivity, electronic conductivity, thermal safety performance (puncture safety temperature), rate performance (rate capacity retention), and long-term high-temperature storage performance (storage capacity retention) measured according to Examples 1 to 3 and Comparative Example 1 are shown in Table 1 below:

[0206]

[0207] Table 1

[0208] Table 1 shows that by comparing Examples 1 to 3 and Comparative Example 1, the content of PTC ceramic powder in the electrolyte solid directly determines whether the PTC network is interconnected and the degree of occupancy for ion conduction.

[0209] Here, when the PTC ceramic powder is in the intermediate range of 6 wt% in Example 1 and 18 wt% in Example 3, the volume fraction of the PTC material exceeds the percolation threshold, combined with Figure 4 and Figure 5 As shown, the network is continuous but not excessively dense, providing a significant resistance jump between 80℃ and 120℃, effectively limiting current at high temperatures; at the same time, it does not significantly compress the lithium-ion migration channels provided by the solvent and polymer. Ionic conductivity and high-rate discharge remain at high levels at 25℃.

[0210] In Example 2, the content of PTC ceramic powder was reduced, the high-temperature flow limiting ability began to weaken, and the puncture safety temperature increased.

[0211] In Comparative Example 1, the content of PTC ceramic powder continued to decrease, combined with Figure 5 As shown, the PTC network is almost discontinuous, resulting in limited changes in high-temperature electronic conductivity, loss of effective current limiting performance, and significant deterioration in thermal safety and high-temperature storage performance.

[0212] The ionic conductivity, electronic conductivity, thermal safety performance (puncture safety temperature), rate performance (rate capacity retention), and long-term high-temperature storage performance (storage capacity retention) measured according to Examples 1, 4, 5, and Comparative Example 2 are shown in Table 2 below:

[0213]

[0214] Table 2

[0215] Table 2 shows that by comparing Example 1, Example 4, Example 5 and Comparative Example 2, the particle size of PTC ceramic powder controls its dispersion uniformity and specific surface area in the polymer matrix, thereby affecting the three-dimensional percolation network and gel microporous structure of PTC material.

[0216] In Example 4, the D of PTC ceramic powder 50The smaller particle size makes it easier to form a uniform and dense network in the gel system, which increases the resistance at high temperatures and makes it more uniform in the thickness direction. At the same time, the local current concentration is significantly reduced, the puncture safety temperature is slightly lower, the high-temperature storage performance is slightly reduced, and the interference of the 100-nanometer-sized particles on the ion channels formed by the solvent and lithium salt is limited.

[0217] In Example 5, after increasing the particle size to 300 nm, some particles showed a tendency to agglomerate, local PTC ceramic powder was enriched while other areas were depleted, resulting in spatial non-uniformity of high-temperature limiting flow behavior, increased puncture safety temperature, increased tortuosity of ion migration path, and slight decrease in ionic conductivity.

[0218] In Comparative Example 2, when using near-micron coarse particles, the PTC material is distributed in an island-like pattern, which makes it difficult to form a continuous resistance switching network and severely disrupts the gel pore structure. This results in insufficient high-temperature current limiting effect, significantly deterioration of thermal safety performance and high-temperature storage performance, and a significant decrease in room temperature ion conduction due to channel blockage.

[0219] The ionic conductivity, electronic conductivity, thermal safety performance (puncture safety temperature), rate performance (rate capacity retention), and long-term high-temperature storage performance (storage capacity retention) measured according to Examples 1, 6, 7, and Comparative Example 3 are shown in Table 3 below:

[0220]

[0221] Table 3

[0222] Table 3 shows that by comparing Examples 1, 6, 7 and Comparative Example 3, the content of the polymer matrix is ​​a key balance parameter between the supporting skeleton and the free volume fraction of the solvent in the electrolyte.

[0223] Here, when the polymer matrix is ​​about 50 wt%, the polymer chains can form a continuous three-dimensional skeleton, which provides sufficient mechanical strength and morphological stability, while retaining a high proportion of flowable solvent phase and lithium salt dissolution space. This allows the ionic conductivity and high-rate performance at 25°C to remain at a high level, and at the same time, it can provide stable fixation sites for PTC particles, which is beneficial to the maintenance of the current-limiting network at high temperatures.

[0224] In Example 6, when the polymer matrix content decreased, the backbone became thinner, the gel tended to be more solvent-rich, the short-range ion migration resistance decreased, and the ionic conductivity increased slightly, but the dimensional stability and deformation resistance of the film deteriorated. Figure 4 As shown, PTC materials are more prone to displacement under high temperature conditions, resulting in a decrease in high-temperature current limiting and high-temperature storage performance.

[0225] In Example 7, when the content of polymer matrix is ​​increased, the skeleton is more compact, the thermomechanical stability and PTC network fixation effect are better, and the thermal safety performance and high temperature storage performance are enhanced. However, the free solvent and effective ion channels are reduced, resulting in a decrease in ionic conductivity and increased polarization at high rates.

[0226] In Comparative Example 3, when the polymer matrix content was very low, the system approached a "high solvent, low framework" state, resulting in a film prone to cracking and shrinkage, uncontrollable structure, and poor bonding. Figure 4 and Figure 5 As shown, both high-temperature current limiting and long-term high-temperature storage are clearly ineffective, resulting in extremely poor overall reliability.

[0227] The ionic conductivity, electronic conductivity, thermal safety performance (puncture safety temperature), rate performance (rate capacity retention), and long-term high-temperature storage performance (storage capacity retention) measured according to Examples 1, 8, 9, and Comparative Example 4 are shown in Table 4 below:

[0228]

[0229] Table 4

[0230] Table 4 shows that by comparing Examples 1, 8, 9 and Comparative Example 4, the thickness of the electrolyte membrane can affect the ion migration distance between the positive and negative electrodes and the effective resistance ramp-up length of the PTC functional layer in the thickness direction.

[0231] In Example 1, the dry film thickness of the electrolyte membrane is 25 μm, which can ensure a sufficiently short ion transport path at room temperature, keeping the internal resistance and polarization within a reasonable range, while providing a certain resistance growth space at high temperatures, so that the PTC network can form an effective current limiter throughout the entire film thickness direction.

[0232] In Example 8, the dry film thickness of the electrolyte membrane was 15 μm, the ion path was further shortened, the ion conductivity was slightly increased, and the high-rate performance was slightly improved. However, the longitudinal resistance ramp-up length of the PTC functional layer was insufficient, the current limiting ability at high temperature was weakened, the puncture safety temperature was increased, and the current density regulation ability during high-temperature storage was reduced.

[0233] In Example 9, the dry film thickness of the electrolyte membrane was 35 μm. At high temperatures, the resistance increased significantly, and the local short-circuit current was more effectively reduced, resulting in optimal thermal safety and high-temperature storage performance. However, the increased thickness led to a significant increase in ion migration distance. Figure 4 As shown, the internal resistance increases at room temperature, limiting high-rate discharge.

[0234] In Comparative Example 4, further increasing the dry film thickness of the electrolyte membrane slightly improved the thermal safety index, but the ion migration path was too long, resulting in a severe decrease in power density and volumetric energy density.

[0235] The ionic conductivity, electronic conductivity, thermal safety performance (puncture safety temperature), rate performance (rate capacity retention), and long-term high-temperature storage performance (storage capacity retention) measured according to Examples 1, 10, 11, 12, and Comparative Example 5 are shown in Table 5 below:

[0236]

[0237] Table 5

[0238] Table 5 shows that, by comparing Example 1, Examples 10 to 12, and Comparative Example 5, La³ + Replace Ba² + With Nb 5+ Replace Ti 4+ It belongs to co-doping, and its core function is to adjust the carrier concentration inside the grain and cooperate with the barrier structure at the grain boundary, thereby determining the modulation intensity of the grain boundary barrier by the change in dielectric properties near the Curie point, so that the PTC network exhibits temperature-sensitive current-limiting characteristics in the target temperature range, with the electronic conductivity decreasing as the temperature increases.

[0239] In Example 11, when the La and Nb elements were reduced to 0.01 mol, the degree of crystal semiconductorization was relatively weak and the effective barrier modulation was insufficient, resulting in a smaller resistance transition amplitude in the 100°C to 120°C range. The current limiting effect intensity decreased after heating, thus weakening the current suppression ability in the early stage of thermal runaway. However, its room temperature baseline resistance was often lower, and the disturbance to the ionic conduction network of the gel electrolyte was smaller, so the high-rate polarization was relatively mild.

[0240] In Example 12, when the amount of La and Nb was increased to 0.03 mol, the defect chemistry and lattice distortion were enhanced, resulting in a larger temperature coefficient of resistance near the Curie point, a steeper PTC effect transition, and a more significant decrease in electronic conductivity at high temperatures. This was beneficial for more quickly weakening local short-circuit current and exothermic interfacial side reactions. However, excessive doping may also increase the bulk resistance and increase the transport resistance of the composite system. Combined with the perturbation of the polymer continuous phase by the particles, this resulted in a certain sacrifice in high-rate performance.

[0241] In Example 1, based on the equivalent substitution of Sr by 0.01 mol, the Curie temperature position was anchored to a more suitable response window by adjusting the lattice constant and phase transition temperature. With 0.02 mol each of La and Nb, the current can be effectively limited in the early stage of thermal runaway. At the same time, the bulk resistance at room temperature is kept at a moderate level, which does not significantly increase the overall electron leakage of the gel, nor significantly weaken the ionic conductive network. It balances room temperature electron leakage suppression and high temperature current limiting strength, so the overall performance is more balanced.

[0242] In Example 10, while maintaining a strong PTC effect switching strength, the phase transition temperature and phase transition range can be adjusted by using the Sr element, so that the PTC response window is closer to the early stage of abnormal cell temperature rise, thereby more effectively limiting the electronic bypass current in the early stage of thermal runaway.

[0243] In contrast, BaTiO3 in Comparative Example 5, which is undoped with Sr, La and Nb, has a certain dielectric response, but the grain electrical properties and grain boundary barrier structure make it difficult to form a "semiconductor grain-barrier grain boundary" combination. This results in a weak PTC effect and an uncontrollable temperature range. As the temperature increases, the decrease in electronic conductivity is insufficient, making it difficult to provide considerable forward current limiting and safety gain.

[0244] The foregoing description and accompanying drawings fully illustrate embodiments of the present disclosure to enable those skilled in the art to practice them. Other embodiments may include structural and other changes. The embodiments represent only possible variations. Individual components and functions are optional unless explicitly required, and the order of operation may vary. Parts and features of some embodiments may be included or substituted for parts and features of other embodiments. Embodiments of the present disclosure are not limited to the structures described above and shown in the accompanying drawings, and various modifications and changes may be made without departing from its scope. The scope of the present disclosure is limited only by the appended claims.

Claims

1. An electrolyte, characterized in that, It includes lithium salt, organic solvent, polymer matrix, and temperature coefficient semiconductor particles dispersed in the polymer matrix. The temperature coefficient semiconductor particles are perovskite-structured ceramics with the general chemical formula Ba. 1-x- y Sr x Re y Ti 1-z Nb z O3; Among them, 0 ≤ x ≤ 0.20, 0 < y ≤ 0.10, 0 < z ≤ 0.10, and Re is a rare earth element; Under the temperature condition of 25°C to 120°C, for the temperature coefficient semiconductor particles, as the temperature increases, their electronic conductivity gradually decreases, that is, the resistivity increases.

2. The electrolyte according to claim 1, characterized in that, In the solid medium of the electrolyte, the mass percentage of the lithium salt is 10% - 40%, the mass percentage of the polymer matrix is 20% - 60%, and the mass percentage of the temperature coefficient semiconductor particles is 2% - 25%.

3. The electrolyte according to claim 2, characterized in that, In the solid medium of the electrolyte, the volume percentage of the temperature coefficient semiconductor particles is 1% - 10%.

4. The electrolyte according to any one of claims 1 to 3, characterized in that, D of temperature coefficient semiconductor particles 50 For 50nm~500nm, and D 90 ≤1.5μm.

5. The electrolyte according to any one of claims 1 to 3, characterized in that, The Re element is one or a combination of more than one of La, Ce, Pr, and Nd.

6. The electrolyte according to any one of claims 1 to 3, characterized in that, The thickness of the thin film formed by the electrolyte is 10 μm - 40 μm.

7. The electrolyte according to claim 6, characterized in that, At the first preset temperature, its ionic conductivity σ1 ≥ 5 × 10 -3 S / cm, electronic conductivity σ2≤1×10 -8 S / cm.

8. The electrolyte according to claim 7, characterized in that, At the second preset temperature, the electronic conductivity σ² is 1×10⁻⁶. -11 S / cm ~ 1×10 -9 S / cm; where the second preset temperature is greater than the first preset temperature.

9. A method for preparing an electrolyte membrane, characterized in that, Including the electrolyte according to any one of claims 1 to 8, comprising the following steps: Dissolve the polymer matrix in an organic solvent to obtain a polymer solution; Respectively add the temperature coefficient semiconductor particles and the lithium salt into the polymer solution and mix them in a high-speed dispersion manner to obtain a gel precursor solution; Coat the gel precursor solution on the surface of the substrate, and by drying, volatilize the organic solvent and make the polymer matrix and the temperature coefficient semiconductor particles form a co-continuous phase to obtain an electrolyte film in the shape of a thin film.

10. A lithium-ion battery, characterized in that, Including a positive electrode sheet, a negative electrode sheet, and an electrolyte film, the electrolyte film is a thin film formed by the electrolyte according to any one of claims 1 to 8, or an electrolyte film prepared by the preparation method of the electrolyte film according to claim 9.

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