WO2023246704A1 - 一种锂离子电池极片及其制备方法 - Google Patents

一种锂离子电池极片及其制备方法 Download PDF

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Publication number
WO2023246704A1
WO2023246704A1 PCT/CN2023/101101 CN2023101101W WO2023246704A1 WO 2023246704 A1 WO2023246704 A1 WO 2023246704A1 CN 2023101101 W CN2023101101 W CN 2023101101W WO 2023246704 A1 WO2023246704 A1 WO 2023246704A1
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Prior art keywords
ion battery
lithium
active material
pole piece
battery pole
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PCT/CN2023/101101
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English (en)
French (fr)
Inventor
黄旭
魏小亮
谭远高
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惠州锂威新能源科技有限公司
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Publication of WO2023246704A1 publication Critical patent/WO2023246704A1/zh

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/621—Binders
    • H01M4/622—Binders being polymers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/621—Binders
    • H01M4/622—Binders being polymers
    • H01M4/623—Binders being polymers fluorinated polymers
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the invention belongs to the technical field of batteries, and specifically relates to a lithium ion battery pole piece and a preparation method thereof.
  • the heating rate of the battery is much greater than the heat dissipation rate, and thermal runaway occurs after reaching a certain critical temperature.
  • the thermal abuse test of the battery as heat continues to accumulate inside the battery, the battery temperature continues to rise. When it reaches the melting point of the separator, the separator begins to melt, causing the positive and negative electrodes to short-circuit, releasing more heat, and cannot Avoid thermal runaway. In overcharge and other electric abuse tests, there is a risk that the precipitated lithium dendrites will puncture the separator, eventually leading to thermal runaway of the battery.
  • the essence of battery abuse is that the battery undergoes internal short circuit under the action of various factors, which ultimately leads to thermal runaway of the battery.
  • One of the purposes of the present invention is to provide a lithium-ion battery pole piece in view of the shortcomings of the existing technology. By optimizing the structure of the pole piece, the probability of internal short circuit in the battery can be reduced, thereby improving the safety performance of the battery.
  • a lithium ion battery pole piece including a current collector; an active material layer coated on the surface of the current collector; a safety coating coated on the surface of the active material layer; the thickness of the safety coating is 1- 10 ⁇ m, including polyolefin latex particles, cross-linking agent and adhesive.
  • the polyolefin latex particles are 100 parts by mass, the cross-linking agent is 0.05-2 parts by mass, and the binder is 10-20 parts by mass.
  • the polyolefin latex particles are polyethylene, polypropylene, or ethylene-propylene graft and block copolymers.
  • the cross-linking agent is epoxy glycidyl ether, melamine hexamethoxymethylol melamine, and isocyanate toluene diisocyanate.
  • the adhesive is styrene-butadiene rubber, polyvinylidene fluoride, polytetrafluoroethylene or polyacrylic polymer material.
  • the active material layer includes a negative active material, a conductive agent and an adhesive.
  • the negative active material is at least one of graphite, lithium titanate and silicon negative electrode materials.
  • the conductive agent is conductive carbon black, At least one of carbon nanotubes and graphene, and the adhesive is styrene-butadiene rubber.
  • the graphite has a layered structure, and the lithium titanate is of spinel type.
  • the security coating is coated on the surface of the active material layer by gravure printing and spraying.
  • the thickness of the safety coating is 3-5 ⁇ m.
  • the second object of the present invention is to provide a method for preparing lithium-ion battery pole pieces, which includes:
  • Step 1 Mix polyolefin latex particles, cross-linking agent and binder in a preset proportion to obtain a safe coating slurry;
  • Step 2 Coat the slurry of the negative active material layer on the surface of the current collector, and then dry it at 80°C;
  • Step 3 Coat the safety coating slurry on the surface of the negative active material layer, dry it, roll it, and slit it to obtain a negative electrode sheet.
  • the beneficial effect of the present invention is that the present invention coats the surface of the active material layer with a safety coating.
  • a safety coating Under normal operation of the battery, there are certain gaps between the polyolefin latex particles coated on the surface of the active material layer, which can conduct electricity. Lithium ions do not affect the normal operation of the battery; when the battery is abused and the temperature reaches a certain preset threshold, the polyolefin latex particles melt, and the cross-linking agent decomposes to generate free radicals, which triggers the cross-linking of the polyolefin latex particles. Forming a dense film that blocks the transmission of lithium ions, that is, forming an insulating layer, can cut off short-circuit current and prevent thermal runaway of the battery.
  • the existence of the safety coating helps to reduce the probability of direct contact between the positive electrode current collector aluminum foil and the negative electrode active material, and forms a double protective effect with the separator, reducing the probability of internal short circuit in the battery and improving the safety performance of the
  • Figure 1 is a schematic diagram of a safety coating containing polyethylene latex particles according to the present invention.
  • Figure 2 is a schematic diagram of the safety coating cross-linked under the action of high temperature and cross-linking agent according to the present invention.
  • connection In the invention, unless otherwise clearly stated and limited, the terms “installation”, “connection”, “connection”, “fixing” and other terms should be understood in a broad sense. For example, it can be a fixed connection or a detachable connection. Or integrally connected; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be an internal connection between two components.
  • connection connection
  • fixing and other terms should be understood in a broad sense. For example, it can be a fixed connection or a detachable connection. Or integrally connected; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be an internal connection between two components.
  • the specific meanings of the above terms in the present invention can be understood according to specific circumstances.
  • a lithium-ion battery pole piece including:
  • the polyolefin latex particles 4 coated on the surface of the active material layer 2 which can conduct lithium ions without affecting the normal operation of the battery; when the battery is abused, and the temperature reach one
  • the preset threshold is set, the polyolefin latex particles 4 melt, and the cross-linking agent 5 decomposes to generate free radicals, which triggers the cross-linking of the polyolefin latex particles 4, forming a dense film that blocks the transmission of lithium ions, that is, forming an insulating layer, which can Cut off the short-circuit current to avoid thermal runaway of the battery.
  • the existence of the safety coating helps to reduce the probability of direct contact between the positive electrode current collector aluminum foil and the negative electrode active material, and forms a double protective effect with the separator, reducing the probability of internal short circuit in the battery and improving the safety performance of the battery.
  • the polyolefin latex particles 4 in the safety coating are cross-linked to form a dense film that blocks the transmission of lithium ions, allowing the lithium-ion battery to pass through acupuncture, unilateral extrusion, foreign body extrusion, and hot box Abuse tests such as overcharging and overcharging can help improve the quality of the battery.
  • the thickness of the safety coating 3 is preferably 3-5 ⁇ m.
  • the polyolefin latex particles 4 can expand and the gaps can be reduced, exerting a PTC-like effect.
  • the functional groups on the surface can be activated by the initiator under the action of the initiator. , cross-linking occurs, forming an insulating film that blocks current.
  • the polyolefin latex particles 4 are 100 parts by mass
  • the cross-linking agent 5 is 0.05-2 parts by mass
  • the binder is 10-20 parts by mass.
  • the fluid is in contact with the negative active material, if the content of the cross-linking agent 5 is too high, there will still be unconsumed cross-linking agent 5 after the polymer matrix is fully cross-linked, resulting in an increase in production costs.
  • the polyolefin latex particles 4 are graft and block copolymers of polyethylene, polypropylene, and ethylene-propylene.
  • the polyolefin latex particles 4 are water-based polyolefin latex, polyethylene (Polmer materials such as PE), polypropylene (PP), ethylene-propylene graft and block copolymers, considering the production cost, the organic acid is preferably maleic acid or its anhydride.
  • the cross-linking agent 5 can be an organic small molecule with a functionality of not less than two, preferably an epoxy-based glycidyl ether or a melamine-based hexamethoxyhydroxymethylmelamine. , isocyanates such as toluene diisocyanate, etc.
  • Cross-linking agent 5 decomposes above 80°C to produce free groups, initiating the cross-linking of polyolefin latex particles 4.
  • the binder is styrene-butadiene rubber, polyvinylidene fluoride, polytetrafluoroethylene or polyacrylic polymer material, and styrene-butadiene rubber (SBR) water-based bonding is preferably used agent.
  • SBR styrene-butadiene rubber
  • the safety coating 3 is coated on the surface of the active material layer 2 by gravure printing and spraying.
  • Gravure printing or spraying has high precision and good stability, and can obtain a coating with smaller area density and thinner thickness. Therefore, gravure printing or spraying is used to apply the slurry of safety coating 3 to the active material layer of the negative electrode sheet. 2 surface.
  • the negative electrode material active material layer mainly includes negative electrode active materials, conductive agents, and adhesives.
  • the negative electrode active materials are mainly one or more of layered graphite, spinel lithium titanate, and high-capacity silicon negative electrode materials.
  • Conductive agents It mainly includes one or more types of conductive carbon black, carbon nanotubes, and graphene, and the adhesive is styrene-butadiene rubber (SBR).
  • the maleic anhydride modified polyethylene latex particles, the binder styrene-butadiene rubber and the cross-linking agent glycidyl ether are mixed in a weight ratio of 100:15:0.1 to obtain a safety coating slurry.
  • the surface of the polyethylene microspheres coated with the active material layer 2 has cross-linkable functional groups introduced. As shown in Figure 2, cross-linking can occur under high temperature under the trigger of the cross-linking agent 5 to form a layer of Dense membrane.
  • LiPF6 lithium hexafluorophosphate
  • DMC dimethyl carbonate
  • EC ethylene carbonate
  • EMC ethyl methyl carbonate
  • the above-mentioned positive electrode sheet, negative electrode sheet with safety coating 3 and separator are wound into an electric core.
  • the separator is located between the adjacent positive electrode sheets and negative electrode sheets.
  • the positive electrode is led out by spot welding with aluminum tabs, and the negative electrode is spot welded with nickel tabs. Take it out, then place the battery core in an aluminum-plastic packaging bag, inject the above-mentioned electrolyte after baking, and go through processes such as packaging, formation, and volume separation, and finally make a polymer lithium-ion battery with a capacity of about 5Ah.
  • Example 1 The difference from Example 1 is that the proportion of cross-linking agent glycidyl ether in safety coating 3 is 0.05 parts.
  • Example 1 The difference from Example 1 is that the active material surface layer of the negative electrode sheet does not contain safety coating 3.
  • Example 1 The difference from Example 1 is that the negative electrode safety coating is 100 parts by mass of ordinary polyethylene microspheres and 15 parts by mass of styrene-butadiene rubber. It does not contain cross-linking agent 5 and can only melt under the action of high temperature to form a Layer a lower-strength film to block short-circuit current.
  • the battery core prepared in Example 1-2 has a higher pass rate in the abuse tests of acupuncture, unilateral extrusion, foreign body extrusion, hot box and overcharging, and is overall better than Comparative Example 1- 2.
  • the pass rate of each test in Example 1 is 100%, indicating that the safety coating used in the present invention has excellent safety performance.
  • the polyolefin latex particles 4 melt, and the cross-linking agent 5 decomposes to generate free radicals, which triggers the cross-linking of the polyolefin latex particles 4 and forms a dense layer that blocks the transmission of lithium ions.
  • the film forms an insulating layer, which can cut off short-circuit current and prevent thermal runaway of the battery.

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
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Abstract

本发明属于电池的技术领域，具体涉及一种锂离子电池极片，包括集流体；活性物质层，涂覆在所述集流体表面；安全涂层，涂覆在所述活性物质层的表面；所述安全涂层的厚度为1-10μm，包括聚烯烃乳胶粒子、交联剂和粘结剂。本发明通过优化极片的结构，能够降低电池发生内短路的概率，从而提高电池的安全性能。此外，本发明还公开了一种锂离子电池极片的制备方法。

Description

一种锂离子电池极片及其制备方法 技术领域
本发明属于电池的技术领域，具体涉及一种锂离子电池极片及其制备方法。
背景技术
随着移动电话、笔记本电脑、电动汽车和电动工具等应用的不断增加，所用锂离子电池的能量密度也越来越高，一旦发生滥用将会造成非常可怕的后果，其安全性也越来越受到人们的重视。锂离子电池的滥用测试通常包括机械滥用、热滥用和电滥用。一般来说，机械滥用是指电池或电池组在外部的机械作用下发生形变，进而发生起火、爆炸。实验室中通常采用针刺和单边挤压等，来测试电池的机械滥用性能，测试时电池内隔膜发生破裂，阴阳极片直接接触发生内短路，大量能量在极短的时间内被释放，电池的升温速率远大于散热速率，达到某个临界温度后发生热失控。而在电池的热滥用测试中，随着热量在电池内部不断累积，电池温度不断上升，当达到隔膜的熔点后，隔膜开始融化，导致正负极片短接，释放出更多的热量，不可避免的发生热失控。而在过充等电滥用测试中，则存在析出的锂枝晶刺破隔膜的风险，最后导致电池的热失控。电池滥用的实质是电池在各种因素的作用下发生内短路，最终导致电池的热失控。
现有改善电池滥用性能的方法包括使用正温度系数热敏电阻，当电池的温度达到PTC元件的居里温度时，其电阻快速增加，从而切断电路，阻止进一步的热失控。但该方法也存在缺点，由于传热速率的限制，PTC元件对温度的响应存在滞后性，其发生作用时电池内部的温度通常高于其居里点，当电池发生热失控时，这种滞后性可能造成非常严重的后果。另外，也可以采用在隔膜表面涂覆陶瓷的方法，但这种做法成本较高，且陶瓷在电池循环使用过程中有脱 落的风险。
发明内容
本发明的目的之一在于：针对现有技术的不足，提供一种锂离子电池极片，通过优化极片的结构，能够降低电池发生内短路的概率，从而提高电池的安全性能。
为了实现上述目的，本发明采用如下技术方案：
一种锂离子电池极片，包括集流体；活性物质层，涂覆在所述集流体表面；安全涂层，涂覆在所述活性物质层的表面；所述安全涂层的厚度为1-10μm，包括聚烯烃乳胶粒子、交联剂和粘结剂。
优选的，所述聚烯烃乳胶粒子为100质量份，所述交联剂为0.05～2质量份，所述粘结剂为10～20质量份。
优选的，所述聚烯烃乳胶粒子为聚乙烯、聚丙烯、乙烯-丙烯的接枝及嵌段共聚物。
优选的，所述交联剂为环氧类的缩水甘油醚、三聚氰胺类的六甲氧基羟甲基三聚氰胺、异氰酸酯类的甲苯二异氰酸酯。
优选的，所述粘结剂为丁苯橡胶、聚偏氟乙烯、聚四氟乙烯或聚丙烯酸类高分子材料。
优选的，所述活性物质层包括负极活性物质、导电剂和粘接剂，所述负极活性物质为石墨、钛酸锂和硅负极材料中的至少一种，所述导电剂为导电炭黑、碳纳米管和石墨烯中的至少一种，所述粘接剂为丁苯橡胶。
优选的，所述石墨为层状结构，所述钛酸锂为尖晶石型。
优选的，所述安全涂层通过凹版印刷和喷涂的方式涂布于所述活性物质层的表面。
优选的，所述安全涂层的厚度为3-5μm。
本发明的目的之二在于提供一种锂离子电池极片的制备方法，包括：
步骤一、将聚烯烃乳胶粒子、交联剂和粘结剂按预设比例混合，得到安全涂层浆料；
步骤二、将负极活性物质层的浆料涂布在集流体的表面，然后在80℃下烘干；
步骤三、将安全涂层的浆料涂布在负极活性物质层的表面，干燥后进行辊压、分条，得到负极片。
本发明的有益效果在于，本发明在活性物质层的表面涂覆安全涂层，在电池正常工作情况下，涂覆于活性物质层表面的聚烯烃乳胶粒子之间存在一定的空隙，能够导通锂离子，不影响电池的正常工作；在电池发生滥用时，且温度达到一定预设阈值，聚烯烃乳胶粒子发生融化，而交联剂发生分解产生自由基，引发聚烯烃乳胶粒子的交联，形成阻断锂离子传输的致密膜，即形成绝缘层，能够切断短路电流，避免电池的发生热失控。安全涂层的存在有助于降低正极集流体铝箔与负极活性物质直接接触的概率，并与隔膜形成双重保护作用，降低电池发生内短路的概率，提高电池的安全性能。
附图说明
下面将参考附图来描述本发明示例性实施方式的特征、优点和技术效果。
图1为本发明所述包含聚乙烯乳胶粒子的安全涂层示意图。
图2为本发明所述在高温和交联剂作用下发生交联的安全涂层示意图。
其中，附图标记说明如下：
1-集流体；
2-活性物质层；
3-安全涂层；
4-聚烯烃乳胶粒子；
5-交联剂。
具体实施方式
如在说明书及权利要求当中使用了某些词汇来指称特定组件。本领域技术人员应可理解，硬件制造商可能会用不同名词来称呼同一个组件。本说明书及权利要求并不以名称的差异来作为区分组件的方式，而是以组件在功能上的差异来作为区分的准则。如在通篇说明书及权利要求当中所提及的“包含”为一开放式用语，故应解释成“包含但不限定于”。“大致”是指在可接受的误差范围内，本领域技术人员能够在一定误差范围内解决技术问题，基本达到技术效果。
此外，术语“第一”、“第二”等仅用于描述目的，而不能理解为指示或暗示相对重要性。
在发明中，除非另有明确的规定和限定，术语“安装”、“相连”、“连接”、“固定”等术语应做广义理解，例如，可以是固定连接，也可以是可拆卸连接，或一体地连接；可以是机械连接，也可以是电连接；可以是直接相连，也可以通过中间媒介间接相连，可以是两个元件内部的连通。对于本领域的普通技术人员而言，可以根据具体情况理解上述术语在本发明中的具体含义。
以下结合附图1对本发明作进一步详细说明，但不作为对本发明的限定。
一种锂离子电池极片，包括：
集流体1；活性物质层2，涂覆在集流体1表面；安全涂层3，涂覆在活性物质层2的表面；安全涂层3的厚度为1-10μm，包括聚烯烃乳胶粒子4、交联剂5和粘结剂。
由于传热速率的限制，PTC元件对温度的响应存在滞后性，其发生作用时电池内部的温度通常高于其居里点，当电池发生热失控时，这种滞后性可能造成非常严重的后果。另外，也可以采用在隔膜表面涂覆陶瓷的方法，但这种做法成本较高，且陶瓷在电池循环使用过程中有脱落的风险。因此，可通过在活性物质层2的表面涂覆安全涂层3的方式来提高电池的滥用性能。在电池正常工作情况下，涂覆于活性物质层2的表面的聚烯烃乳胶粒子4之间存在一定的空隙，能够导通锂离子，不影响电池的正常工作；在电池发生滥用时，且温度达到一 定预设阈值，聚烯烃乳胶粒子4发生融化，而交联剂5发生分解产生自由基，引发聚烯烃乳胶粒子4的交联，形成阻断锂离子传输的致密膜，即形成绝缘层，能够切断短路电流，避免电池的发生热失控。安全涂层的存在有助于降低正极集流体铝箔与负极活性物质直接接触的概率，并与与隔膜形成双重保护作用，降低电池发生内短路的概率，提高电池的安全性能。
在电池发生滥用时，安全涂层中的聚烯烃乳胶粒子4的交联，形成阻断锂离子传输的致密膜，使锂离子电池能通过针刺、单边挤压、异物挤压、热箱和过充等滥用测试，有助于提高电池的质量，优选安全涂层3的厚度为3-5μm。此外，聚烯烃乳胶粒子4在温度较低时，可发生膨胀，间隙减小，发挥类似PTC效应，在温度进一步升高，达到一定预设阈值时，其表面的官能团可在引发剂的作用下，发生交联，形成阻隔电流的绝缘膜。
在根据本发明的一种锂离子电池极片中，聚烯烃乳胶粒子4为100质量份，交联剂5为0.05～2质量份，粘结剂为10～20质量份。限定交联剂5的质量份，避免交联剂5的含量过低，导致安全涂层3对温度的响应的灵敏度降低，且高分子基体不能充分交联，使得安全涂层3无法阻隔正极集流体与负极活性材料的接触，若交联剂5的含量过高，使得高分子基体在充分交联后还存在未消耗完的交联剂5，导致生产成本上升。
在根据本发明的一种锂离子电池极片中，聚烯烃乳胶粒子4为聚乙烯、聚丙烯、乙烯-丙烯的接枝及嵌段共聚物。具体的，聚烯烃乳胶粒子4为水系聚烯烃乳胶，经过马来酸、对苯二甲酸、己二酸和富马酸等官能度不小于二的有机酸或其酸酐改性处理的聚乙烯(PE)，聚丙烯(PP)，乙烯-丙烯的接枝及嵌段共聚物等高分子材料，考虑到生产成本，有机酸优选为马来酸或其酸酐。
在根据本发明的一种锂离子电池极片中，交联剂5可以为官能度不小于二的有机小分子，优选为环氧类的缩水甘油醚、三聚氰胺类的六甲氧基羟甲基三聚氰胺、异氰酸酯类的甲苯二异氰酸酯等，交联剂5在80℃以上发生分解产生自由 基，引发聚烯烃乳胶粒子4的交联。
在根据本发明的一种锂离子电池极片中，粘结剂为丁苯橡胶、聚偏氟乙烯、聚四氟乙烯或聚丙烯酸类高分子材料，优选采用丁苯橡胶(SBR)水性粘结剂。
在根据本发明的一种锂离子电池极片中，安全涂层3通过凹版印刷和喷涂的方式涂布于活性物质层2的表面。凹版印刷或喷涂精度高，稳定性好，可以得到面密度更小、厚度更薄的涂层，故采用凹版印刷或喷涂的方式将安全涂层3的浆料涂覆于负极片的活性物质层2的表面。
负极材料活性物质层，主要包括负极活性物质、导电剂和粘接剂，负极活性物质主要为层状石墨、尖晶石型钛酸锂、高容量硅负极材料的一种或多种，导电剂主要包括导电炭黑、碳纳米管、石墨烯中一种或多种，粘接剂为丁苯橡胶(SBR)。
实施例1：
(1)负极安全涂层浆料制备：
将马来酸酐改性聚乙烯乳胶粒子、粘结剂丁苯橡胶和交联剂缩水甘油醚，按照重量比100:15:0.1的比例混合后得到安全涂层浆料。
(2)负极片制备：
将石墨、增稠剂、粘结剂丁苯橡胶，按质量比97.7：1.1：1.2混合均匀制成具有预设粘度的锂离子电池负极浆料，涂布在铜箔集流体一表面上，并在80℃下烘干收卷，然后在铜箔的另一面进行负极浆料涂布和干燥，得到双面均涂覆有活性物质的负极片，将安全涂层浆料采用凹版印刷或喷涂的方式涂覆于负极片活性物质层的表面，涂层的厚度为3μm，干燥后进行辊压、分条，得到活性物质表层带有安全涂层3的负极片；
如图1所示，活性物质层2涂覆的聚乙烯微球表面引入了可交联的官能团，如图2所示，高温下可在交联剂5的引发下发生交联，形成一层致密膜。
(3)正极片的制备：
将正极活性物质、导电剂超导碳和碳管、粘结剂聚偏氟乙烯按质量比97.6:0.6:0.5:1.3混合均匀制成正极浆料，将正极浆料涂布在集流体铝箔的一表面上，在85℃下烘干收卷，然后在铝箔的另一面进行正极浆料涂布和干燥，然后将双面涂有正极活性物质层的正极片进行冷压处理；之后进行切边、裁片、分条，制成锂离子电池正极片。
(4)电解液的制备：
将六氟磷酸锂(LiPF6)溶解于碳酸二甲酯(DMC)、碳酸乙烯酯(EC)、碳酸甲乙酯(EMC)混合溶剂中，三者的质量比为3:5:2，得到电解液。
(5)电池的制备：
将上述正极片、带安全涂层3的负极片和隔膜卷绕成电芯，隔膜位于相邻的正极片和负极片之间，正极以铝极耳点焊引出，负极以镍极耳点焊引出，然后将电芯置于铝塑包装袋中，烘烤后注入上述电解液，经封装、化成、分容等工序，最后制成容量约为5Ah聚合物锂离子电池。
实施例2：
与实施例1不同的是：安全涂层3中交联剂缩水甘油醚的比例为0.05份。
其他方法与实施1相同，这里不再赘述。
对比例1：
与实施例1不同的是：负极片活性物质表层不含安全涂层3。
其他方法与实施1相同，这里不再赘述。
对比例2：
与实施例1不同的是：负极安全涂层为100质量份的普通的聚乙烯微球和15质量份的丁苯橡胶，不含交联剂5，仅能在高温的作用下发生融化形成一层强度较低的膜来阻断短路电流。
其他方法与实施1相同，这里不再赘述。
表1、实施例的电芯和对比例的电芯安全测试结果
从上表可以看出，实施例1-2制得的电芯在针刺、单边挤压、异物挤压、热箱和过充的滥用测试通过率较高，全面优于对比例1-2，特别的，实施例1各项测试的通过率为100％，说明本发明所用的安全涂层的安全性能优异。由以上测试结果可推测，在电池发生滥用时，聚烯烃乳胶粒子4发生融化，而交联剂5发生分解产生自由基，引发聚烯烃乳胶粒子4的交联，形成阻断锂离子传输的致密膜，即形成绝缘层，能够切断短路电流，避免电池的发生热失控。
根据上述说明书的揭示和教导，本发明所属领域的技术人员还能够对上述实施方式进行变更和修改。因此，本发明并不局限于上述的具体实施方式，凡是本领域技术人员在本发明的基础上所作出的任何显而易见的改进、替换或变型均属于本发明的保护范围。此外，尽管本说明书中使用了一些特定的术语，但这些术语只是为了方便说明，并不对本发明构成任何限制。

Claims (10)

  1. 一种锂离子电池极片，其特征在于，包括：
    集流体(1)；
    活性物质层(2)，涂覆在所述集流体(1)的表面；
    安全涂层(3)，涂覆在所述活性物质层(2)的表面；
    所述安全涂层(3)的厚度为1-10μm，包括聚烯烃乳胶粒子(4)、交联剂(5)和粘结剂。
  2. 如权利要求1所述的一种锂离子电池极片，其特征在于：所述聚烯烃乳胶粒子(4)为100质量份，所述交联剂(5)为0.05～2质量份，所述粘结剂为10～20质量份。
  3. 如权利要求1所述的一种锂离子电池极片，其特征在于：所述聚烯烃乳胶粒子(4)为聚乙烯、聚丙烯、乙烯-丙烯的接枝及嵌段共聚物。
  4. 如权利要求1所述的一种锂离子电池极片，其特征在于：所述交联剂(5)为环氧类的缩水甘油醚、三聚氰胺类的六甲氧基羟甲基三聚氰胺、异氰酸酯类的甲苯二异氰酸酯。
  5. 如权利要求1所述的一种锂离子电池极片，其特征在于：所述粘结剂为丁苯橡胶、聚偏氟乙烯、聚四氟乙烯或聚丙烯酸类高分子材料。
  6. 如权利要求1所述的一种锂离子电池极片，其特征在于：所述活性物质层(2)包括负极活性物质、导电剂和粘接剂，所述负极活性物质为石墨、钛酸锂和硅负极材料中的至少一种，所述导电剂为导电炭黑、碳纳米管和石墨烯中的至少一种，所述粘接剂为丁苯橡胶。
  7. 如权利要求6所述的一种锂离子电池极片，其特征在于：所述石墨为层状结构，所述钛酸锂为尖晶石型。
  8. 如权利要求1所述的一种锂离子电池极片，其特征在于：所述安全涂层(3) 通过凹版印刷和喷涂的方式涂布于所述活性物质层(2)的表面。
  9. 如权利要求1所述的一种锂离子电池极片，其特征在于：所述安全涂层(3)的厚度为3-5μm。
  10. 一种锂离子电池极片的制备方法，其特征在于，包括：
    步骤一、将聚烯烃乳胶粒子(4)、交联剂(5)和粘结剂按预设比例混合，得到安全涂层(3)的浆料；
    步骤二、将负极活性物质层(2)的浆料涂布在集流体的表面，然后在80℃下烘干；
    步骤三、将安全涂层(3)的浆料涂布在负极的活性物质层(2)的表面，干燥后进行辊压、分条，得到负极片。
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