CN116799435A - Safety diaphragm, lithium ion battery and preparation method - Google Patents

Safety diaphragm, lithium ion battery and preparation method Download PDF

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Publication number
CN116799435A
CN116799435A CN202311017789.7A CN202311017789A CN116799435A CN 116799435 A CN116799435 A CN 116799435A CN 202311017789 A CN202311017789 A CN 202311017789A CN 116799435 A CN116799435 A CN 116799435A
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core
coating
battery
microspheres
shell
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请求不公布姓名
张传健
赵斌
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Anhui Deyi Energy Technology Co ltd
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Anhui Deyi Energy Technology Co ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/449—Separators, membranes or diaphragms characterised by the material having a layered structure
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/058—Construction or manufacture
    • H01M10/0583—Construction or manufacture of accumulators with folded construction elements except wound ones, i.e. folded positive or negative electrodes or separators, e.g. with "Z"-shaped electrodes or separators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/403—Manufacturing processes of separators, membranes or diaphragms
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/431—Inorganic material
    • H01M50/434—Ceramics
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/443—Particulate material

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Ceramic Engineering (AREA)
  • Inorganic Chemistry (AREA)
  • Materials Engineering (AREA)
  • Secondary Cells (AREA)
  • Battery Electrode And Active Subsutance (AREA)

Abstract

The invention discloses a safety diaphragm, a lithium ion battery and a preparation method, and belongs to the technical field of lithium ion batteries. The safety diaphragm is arranged between the positive pole piece and the negative pole piece; the safety diaphragm comprises a polyolefin base film, wherein the surface of the polyolefin base film is provided with a coating, and the coating is prepared from core-shell structure microspheres, ceramic oxide and a binder; the microsphere with the core-shell structure comprises a microsphere shell and a conductive core arranged in the shell, wherein the microsphere shell coats the conductive core. When the heated temperature of the battery rises, the microsphere shell is melted at a lower temperature, so that the diaphragm is closed, the anode and the cathode are isolated, meanwhile, the conductive core is exposed, and a micro short circuit is formed between the anode and the cathode, so that the battery slowly generates self-discharge, the charge quantity is reduced, and the safety of the battery at a high temperature is improved; the problem that the normal use of the battery is affected by thermal runaway or local internal short circuit easily occurring when the temperature of the existing battery is increased is solved.

Description

Safety diaphragm, lithium ion battery and preparation method
Technical Field
The invention relates to the technical field of lithium ion batteries, in particular to a safety diaphragm, a lithium ion battery and a preparation method.
Background
The statements herein merely provide background information related to the present disclosure and may not necessarily constitute prior art.
With the rapid development of the electric automobile industry, the technology of the lithium ion battery for the automobile gradually focuses on the direction of high energy density, wherein the positive electrode adopts high nickel ternary as a main mode for realizing high energy density. However, the most significant problem of the high nickel ternary material is poor thermal stability and unstable structure at high temperature, which greatly deteriorates intrinsic safety of the battery, and thus, improving the safety of the battery is an important task of current researches.
There are many ways to improve the safety of the battery, wherein the research on the safety diaphragm is particularly extensive, the safety diaphragm is mainly concentrated on the development of a high temperature resistant coating and a high temperature resistant base film, and on the basis, the safety of the battery is improved by regulating the closed pore and rupture temperature of the diaphragm.
In the invention patent publication No. CN113078414A, a composite membrane is provided in which polyethylene microspheres and a ceramic coating are coated on one side of a polypropylene-based membrane. The diaphragm can realize thermal closed pores at a lower temperature, and when the lithium ion battery is in thermal runaway, the low-melting-point polyethylene microspheres are heated and melted to be filled into the micropores of the polypropylene base film, so that the lithium ion transmission is blocked, and the safety performance of the lithium ion battery is improved. The mechanism of safety improvement is that the closed pores are realized at a lower temperature through the low-melting-point polyethylene microspheres, the anode and cathode active materials are isolated, and the heating safety is improved.
Although the battery heating safety can be improved to a certain extent, the battery heating safety is limited, the low-melting-point polyethylene microspheres are melted when heated, the positive and negative electrode active layers are isolated, the occurrence of thermal runaway caused by large-area short circuit is avoided, but the negative electrode fully embedded with lithium and the positive electrode in a delithiated state are ignored, and the potential safety hazard of thermal runaway is easily caused even if the low-melting-point polyethylene microspheres are singly present in electrolyte at high temperature.
In the chinese patent publication No. CN115295959a, an isolation layer comprising inorganic ceramic, a binder and an NTC material is provided, and when the temperature increases, the NTC effect of the NTC material forms a conductive path in the isolation layer and generates a leakage current, thereby releasing the electric quantity of the electrochemical device, so as to improve the thermal stability of the whole electrochemical device and reduce the risk of further thermal runaway.
The method utilizes the characteristic that the internal resistance of the NTC material is reduced when the temperature is increased to enable the anode and the cathode to form micro short circuit to release electric quantity, but has the problems that insulation and conduction transition of the NTC material is only controlled by the temperature, when the temperature is increased sharply, the NTC material is instantly conductive, a large-area internal short circuit is easy to occur, potential safety hazards exist, meanwhile, the internal resistance of the NTC material is sensitive to the temperature, when the local temperature of a battery is high in normal use, the local internal short circuit is possibly caused, the normal use of the battery is influenced, and the reliability is reduced.
Disclosure of Invention
Aiming at the defects existing in the prior art, the embodiment of the invention aims to provide a safety diaphragm, a battery and a preparation method, wherein when the heated temperature of the battery rises, a microsphere shell is melted at a lower temperature, so that the diaphragm is closed, the anode and the cathode are isolated, meanwhile, a conductive inner core is exposed, and a micro short circuit is formed between the anode and the cathode, so that the battery slowly self-discharges, the charge quantity is reduced, and the safety of the battery at a high temperature is improved.
In order to achieve the above object, the present invention provides the following technical solutions:
in a first aspect, the invention provides a safety diaphragm, comprising a polyolefin base film, wherein the surface of the polyolefin base film is provided with a coating, and the coating is prepared from core-shell structure microspheres, ceramic oxide and a binder;
the microsphere with the core-shell structure comprises a microsphere shell and a conductive core arranged in the shell, wherein the microsphere shell covers the conductive core.
Further, the microsphere shell is made of polyethylene or polypropylene, and the conductive core is made of SP carbon particles or metal particles.
In a second aspect, the present invention provides a lithium ion battery;
the lithium ion battery comprises the safety diaphragm, the positive electrode plate and the negative electrode plate, wherein the safety diaphragm is arranged between the positive electrode plate and the negative electrode plate.
In a third aspect, the present invention provides a method of making a safety barrier;
a method of making a safety barrier comprising:
heating the low-melting-point microspheres to form molten liquid and diluting, dispersing conductive particles into the obtained diluted liquid, uniformly mixing, and performing spray drying treatment to obtain core-shell structure microspheres;
uniformly dispersing the core-shell structure microspheres, the ceramic oxide and the adhesive into deionized water to obtain slurry;
and coating the slurry on the polyolefin base film to form a coating, thereby obtaining the safety diaphragm.
Further, the mass ratio of the core-shell structure microsphere, the ceramic oxide and the adhesive is 1% -10%: 75% -95%: 5% -15%.
Further, the low melting point microspheres encapsulate the conductive particles.
Further, the low-melting-point microspheres are polyethylene microspheres or polypropylene microspheres, and the conductive particles are SP carbon particles or metal particles.
In a fourth aspect, the invention provides a lithium ion battery preparation method;
a method for preparing a lithium ion battery, comprising:
preparing a positive pole piece and a negative pole piece;
heating the low-melting-point microspheres to form molten liquid and diluting, dispersing conductive particles into the obtained diluted liquid, uniformly mixing, and performing spray drying treatment to obtain core-shell structure microspheres; uniformly dispersing the core-shell structure microspheres, the ceramic oxide and the adhesive into an organic solvent to obtain slurry; coating the slurry on a polyolefin base film to form a coating, thereby obtaining a safety diaphragm;
and placing the safety diaphragm between the positive pole piece and the negative pole piece, performing Z-shaped stacking to obtain a battery cell, placing the battery cell in a packaging shell, and injecting electrolyte to obtain the lithium ion battery.
Further, the preparation of the positive electrode sheet specifically comprises: sequentially adding polyvinylidene fluoride, a conductive agent and a positive electrode material into N-methyl pyrrolidone, and uniformly stirring to obtain coating slurry; and coating the coating slurry on an aluminum foil current collector, and sequentially drying, cold pressing and punching to obtain the positive electrode plate.
Further, the mass ratio of the polyvinylidene fluoride, the conductive agent and the positive electrode material is 0.5% -2%: 0.5% -2%: 96% -99%.
Further, the preparation of the negative electrode plate comprises the following steps: sequentially adding sodium carboxymethyl cellulose, styrene-butadiene rubber emulsion, a conductive agent and graphite into deionized water, uniformly stirring to obtain coating slurry, coating the coating slurry on a copper foil current collector, and sequentially drying, cold pressing and punching to obtain the negative electrode plate.
Further, the mass ratio of the sodium carboxymethyl cellulose to the styrene-butadiene rubber emulsion to the conductive agent to the graphite is 0.5% -2%: 0.5% -2.5%: 1.5%:94.5 to 97.5 percent.
The technical scheme provided by the invention has at least the following technical effects or advantages:
1. according to the technical scheme provided by the invention, the microsphere with the core-shell structure has the characteristics of local conductivity, the core of the microsphere is conductive, the shell of the microsphere has the characteristic of low melting point, the material is an insulator at the conventional temperature, the low melting point material of the shell is molten at the high temperature, the core conductive material is exposed, and a micro short circuit is formed between the anode and the cathode, so that the self-discharge of the battery is slowly generated, the charge quantity is reduced, and the safety of the battery at the high temperature is improved.
2. According to the technical scheme provided by the invention, the safety diaphragm is prepared by using the core-shell structure microsphere, so that the battery can be normally used under the conventional condition, the large-surface isolation of the anode and the cathode can be realized under the high-temperature environment, and the local micro short circuit can be realized, so that the battery is self-discharged, and the system energy is reduced; and the core-shell structure microsphere is only added when the diaphragm coating slurry is mixed, no extra working procedure is needed, no change is needed to the diaphragm structure, no new coating is needed, and the process is simple.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention.
Fig. 1 is a schematic diagram of the principle provided by an embodiment of the present invention.
The mutual spacing or dimensions are exaggerated for the purpose of showing the positions of the various parts, and the schematic illustrations are used for illustration only.
Detailed Description
It should be noted that the following detailed description is illustrative and is intended to provide further explanation of the invention. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.
As shown in fig. 1, as described in the background art, the lithium ion battery in the prior art has the risk of thermal runaway and large-area internal short circuit, and in order to solve the technical problems as described above, the invention provides a safety diaphragm, a lithium ion battery and a preparation method.
As shown in fig. 1, the present invention describes a safety diaphragm comprising a polyolefin-based film, the surface of which is coated with a coating layer made of core-shell structure microspheres, ceramic oxide and a binder; the microsphere with the core-shell structure comprises a microsphere shell and a conductive core arranged in the shell, wherein the microsphere shell coats the conductive core.
The safety diaphragm is added with core-shell structure microsphere, the shell of the microsphere has lower melting point, and in the embodiment, the melting point is controlled between 100 ℃ and 130 ℃.
As one implementation mode, the microsphere shell is made of polyethylene, and the conductive core is made of SP carbon particles or metal particles.
The invention also provides a lithium ion battery, which comprises a safety diaphragm, a positive pole piece and a negative pole piece, wherein the safety diaphragm is arranged between the positive pole piece and the negative pole piece.
And (3) carrying out Z-shaped stacking on the safety diaphragm, the positive electrode plate and the negative electrode plate to obtain a battery core to be injected with the electrolyte, and then, after baking, injecting the electrolyte to obtain the lithium ion battery.
The invention also provides a preparation method of the safety diaphragm, which comprises the following steps:
heating the low-melting-point microspheres to form molten liquid and diluting, dispersing conductive particles into the obtained diluted liquid, uniformly mixing, and drying to obtain core-shell structure microspheres;
uniformly dispersing the core-shell structure microspheres, the ceramic oxide and the adhesive into deionized water to obtain slurry;
and coating the slurry on the polyolefin base film to form a coating, thereby obtaining the safety diaphragm.
As an embodiment, the mass ratio of the core-shell structure microsphere, the ceramic oxide and the adhesive is 2%:85%:13%.
At normal temperature, the low-melting-point microspheres and the conductive particles can be compounded in any mass ratio under the condition of ensuring that the low-melting-point microspheres completely wrap the conductive particles. As one embodiment, the low melting point microspheres are polyethylene microspheres and the conductive particles are SP carbon particles.
The safety mechanism is improved in two aspects, on one hand, the low-melting-point material is heated and melted to block the contact between the anode and the cathode; on the other hand, the conductive agent is exposed, so that micro short circuit appears at the local parts of the positive electrode and the negative electrode, the discharge is slow, the charge quantity of the battery is reduced, and the aim of improving safety is fulfilled.
The invention also provides a preparation method of the lithium ion battery, which comprises the following steps:
preparing a positive pole piece and a negative pole piece;
heating the low-melting-point microspheres to form molten liquid and diluting, dispersing conductive particles into the obtained diluted liquid, uniformly mixing, and performing spray drying treatment to obtain core-shell structure microspheres; uniformly dispersing the core-shell structure microspheres, the ceramic oxide and the adhesive into an organic solvent to obtain slurry; coating the slurry on a polyolefin base film to form a coating, thereby obtaining a safety diaphragm;
and placing the safety diaphragm between the positive pole piece and the negative pole piece, performing Z-shaped stacking to obtain a battery cell, placing the battery cell in a packaging shell, and injecting electrolyte to obtain the lithium ion battery.
As an embodiment, the preparation of the positive electrode sheet specifically includes: sequentially adding polyvinylidene fluoride, a conductive agent and a positive electrode material into N-methyl pyrrolidone, and uniformly stirring to obtain coating slurry; and coating the coating slurry on an aluminum foil current collector, and sequentially drying, cold pressing and punching to obtain the positive electrode plate.
As one embodiment, the mass ratio of polyvinylidene fluoride, conductive agent and positive electrode material is 0.5% -2%: 0.5% -2%: 96% -99%.
As an embodiment, the preparation of the negative electrode sheet specifically comprises: sequentially adding sodium carboxymethyl cellulose, styrene-butadiene rubber emulsion, a conductive agent and graphite into deionized water, uniformly stirring to obtain coating slurry, coating the coating slurry on a copper foil current collector, and sequentially drying, cold pressing and punching to obtain the negative electrode plate.
As one embodiment, the mass ratio of the sodium carboxymethyl cellulose, the styrene-butadiene rubber emulsion, the conductive agent and the graphite is 0.5% -2%: 0.5% -2.5%: 0.5 to 1.5 percent: 94.5 to 97.5 percent.
The present invention is described in further detail below with reference to specific examples, but is not intended to limit the scope of the present invention.
Example 1
(1) Preparing microspheres with core-shell structures: and heating the polyethylene microspheres to form a melt, diluting the melt into polyethylene diluent with a certain concentration, dispersing conductive carbon particles SP into the polyethylene diluent, uniformly mixing, and then carrying out spray drying to obtain the microsphere material with the core-shell structure. And separating and washing the reaction product from the solution to obtain the SP@ polyethylene microsphere core-shell structure material.
(2) Preparing a positive electrode plate: polyvinylidene fluoride (PVDF), a conductive agent (SP) and a positive electrode material (NCM 811) are mixed according to the mass ratio of 2 percent: 1.5%:96.5 percent of the aluminum foil is sequentially added into N-methyl pyrrolidone (NMP), fully stirred and uniformly mixed, the slurry is coated on the aluminum foil current collector, and the positive electrode plate is prepared by drying, cold pressing and punching.
(3) Preparing a negative electrode plate: sodium carboxymethylcellulose (CMC), styrene butadiene rubber emulsion (SBR), a conductive agent and graphite are mixed according to the mass ratio of 1.7 percent: 1.8%:1.5%:95% of the material is added into deionized water in sequence, fully stirred and uniformly mixed, the slurry is coated on a copper foil current collector, and the negative electrode plate is prepared through drying, cold pressing and punching.
(4) The preparation method of the membrane containing the core-shell microsphere structural material comprises the following steps: the base film adopts the currently commercialized polyethylene diaphragm, the microsphere with the core-shell structure, the ceramic oxide and the binder are uniformly dispersed into deionized water, the uniform slurry is obtained after uniform stirring, and then the slurry is coated on the surface of the polyethylene diaphragm to obtain the diaphragm with the coating.
(5) And (3) stacking the diaphragm prepared in the step (4) with the positive electrode plate and the negative electrode plate in a Z shape, packaging by adopting an aluminum plastic film to obtain a battery core to be injected with the electrolyte, and injecting the electrolyte after baking to obtain the lithium ion battery with the nominal capacity of 3Ah to be tested.
Comparative example 1
(1) Preparing a positive electrode plate: polyvinylidene fluoride (PVDF), a conductive agent (SP) and a positive electrode material (NCM 811) are mixed according to the mass ratio of 2 percent: 1.5%:96.5 percent of the aluminum foil is sequentially added into N-methyl pyrrolidone (NMP), fully stirred and uniformly mixed, the slurry is coated on the aluminum foil current collector, and the positive electrode plate is prepared by drying, cold pressing and punching.
(2) Preparing a negative electrode plate: sodium carboxymethylcellulose (CMC), styrene butadiene rubber emulsion (SBR), a conductive agent and graphite are mixed according to the mass ratio of 1.7 percent: 1.8%:1.5%:95% of the material is added into deionized water in sequence, fully stirred and uniformly mixed, the slurry is coated on a copper foil current collector, and the negative electrode plate is prepared through drying, cold pressing and punching.
(3) The conventional preparation method of the diaphragm comprises the following steps: the base film adopts the currently commercialized polyethylene diaphragm, ceramic oxide and binder are uniformly dispersed into deionized water, the mixture is uniformly stirred to obtain uniform slurry, and then the slurry is coated on the surface of the polyethylene diaphragm to obtain the diaphragm with the coating.
(4) And (3) stacking the diaphragm prepared in the step (3) with the positive electrode plate and the negative electrode plate in a Z shape, packaging by adopting an aluminum plastic film to obtain a battery core to be injected with the electrolyte, and injecting the electrolyte after baking to obtain the lithium ion battery with the nominal capacity of 3Ah to be tested.
Comparative example 2
(1) Preparing a positive electrode plate: polyvinylidene fluoride (PVDF), a conductive agent (SP) and a positive electrode material (NCM 811) are mixed according to the mass ratio of 2 percent: 1.5%:96.5 percent of the aluminum foil is sequentially added into N-methyl pyrrolidone (NMP), fully stirred and uniformly mixed, the slurry is coated on the aluminum foil current collector, and the positive electrode plate is prepared by drying, cold pressing and punching.
(2) Preparing a negative electrode plate: sodium carboxymethylcellulose (CMC), styrene butadiene rubber emulsion (SBR), a conductive agent and graphite are mixed according to the mass ratio of 1.7 percent: 1.8%:1.5%:95% of the material is added into deionized water in sequence, fully stirred and uniformly mixed, the slurry is coated on a copper foil current collector, and the negative electrode plate is prepared through drying, cold pressing and punching.
(3) The preparation method of the diaphragm containing the polyethylene microsphere structural material comprises the following steps: the base film adopts the currently commercialized polyethylene diaphragm, low-melting point polyethylene microspheres, ceramic oxide and binder are uniformly dispersed into deionized water, and are uniformly stirred to obtain uniform slurry, and then the slurry is coated on the surface of the polyethylene diaphragm to obtain the safety diaphragm with the coating.
(4) And (3) stacking the safety diaphragm prepared in the step (3) with the positive pole piece and the negative pole piece in a Z shape, packaging by adopting an aluminum plastic film to obtain a battery core to be injected with the electrolyte, and injecting the electrolyte after baking to obtain the lithium ion battery with the nominal capacity of 3Ah to be tested.
Testing of lithium ion batteries:
and (3) testing the internal resistance of the battery: testing the resistance of the battery by using a battery internal resistance tester to obtain direct current internal resistance data of the battery;
capacity test: charging and discharging the battery by using 0.33C and 1C respectively to obtain capacity data of the battery 0.33C and 1C;
and (3) hot box test: and (3) placing the fully charged battery in an explosion-proof oven, heating to 150 ℃ at a speed of 5 ℃ per minute from 25 ℃, keeping for 60 minutes, and recording the temperature rise and the voltage change of the battery.
Table 1, internal resistance of battery, capacity of battery, pressure drop of battery at 130 ℃ in hot box and maximum temperature data of battery at 150 ℃ in hot box
As can be seen from the data in table 1, the batteries prepared in example 1, comparative example 1 and comparative example 2 have similar internal resistances and capacity ratios of 1C/0.33C, which indicates that the separator containing the core-shell structure microspheres, the conventional separator and the separator containing the polyethylene microspheres have no obvious influence on the internal resistances and capacities of the batteries, i.e., the electrical properties of the batteries can be normally exerted when the batteries are used under the conventional conditions.
In the hot box test process, we monitor the voltage drop of the battery at 130 ℃, and it can be seen that in the embodiment 1, the battery uses the microsphere separator with core-shell structure, the voltage drop is obviously reduced, and the voltage drop reaches 0.12V, because in the hot box test process, when the temperature reaches the melting point of the microsphere with core-shell structure, the shell material is melted, the core material with internal conduction is exposed, a micro short circuit is formed inside the battery, the battery discharges slowly, and the voltage is reduced. Therefore, when the battery fails at 150 ℃, the highest temperature is only 183 ℃, because the battery is slowly self-discharged, the charge quantity is reduced, the thermal stability of the whole battery system is improved, and the energy is reduced.
In comparative example 1, a conventional separator was used for the fabricated battery, the voltage drop of the battery was small at 130 ℃ and the positive and negative electrodes were still in an off state, and in comparative example 2, a conventional base film polyethylene microsphere was used for the separator, and at 130 ℃, the polyethylene microsphere was melted to close the pores of the separator, and the positive and negative electrodes were well disconnected, thus exhibiting minimal voltage drop. In terms of the highest temperature, both comparative examples 1 and 2 exhibited higher temperatures than example 1 because the battery in the full state had poor high temperature stability and released a large amount of energy upon failure. Comparative examples 1 and 2 are compared, and it can be seen that the battery of comparative example 2 contains a polyethylene microsphere separator, completely insulates the anode and the cathode, and can reduce the reaction intensity to some extent, so that comparative example 2 shows relatively lower temperature rise compared with comparative example 1.
In summary, the membrane containing the core-shell structure microsphere is applied to a battery, the electrical property of the membrane is basically consistent with that of a conventional membrane, but the safety aspect can be obviously improved, and the membrane is particularly characterized in that when the battery fails at high temperature, the charge of the battery is reduced, and the temperature rise generated by the energy released by the battery is obviously reduced.
While the foregoing description of the embodiments of the present invention has been presented in conjunction with the drawings, it should be understood that it is not intended to limit the scope of the invention, but rather, it is intended to cover all modifications or variations within the scope of the invention as defined by the claims of the present invention.

Claims (10)

1. The safety diaphragm is characterized by comprising a polyolefin base film, wherein the surface of the polyolefin base film is provided with a coating, and the coating is prepared from core-shell structure microspheres, ceramic oxide and a binder;
the microsphere with the core-shell structure comprises a microsphere shell and a conductive core arranged in the shell, wherein the microsphere shell covers the conductive core.
2. The rupture disc according to claim 1, wherein said microsphere shell is polyethylene and said conductive core is SP carbon particles or metal particles.
3. A lithium ion battery comprising the safety diaphragm, the positive electrode plate and the negative electrode plate according to any one of claims 1-2, wherein the safety diaphragm is arranged between the positive electrode plate and the negative electrode plate.
4. A method of making a safety barrier comprising:
heating the low-melting-point microspheres to form molten liquid and diluting, dispersing conductive particles into the obtained diluted liquid, uniformly mixing, and performing spray drying treatment to obtain core-shell structure microspheres;
uniformly dispersing the core-shell structure microspheres, the ceramic oxide and the adhesive into deionized water to obtain slurry;
and coating the slurry on the polyolefin base film to form a coating, thereby obtaining the safety diaphragm.
5. The method for preparing a safety diaphragm according to claim 4, wherein the mass ratio of the core-shell structure microsphere, the ceramic oxide and the adhesive is 1% -10: 75% -95%: 5% -15%.
6. The method of making a safety barrier of claim 4, wherein said low melting microspheres encapsulate said conductive particles.
7. The method of preparing a safety barrier according to claim 4, wherein the low-melting microspheres are polyethylene microspheres or polypropylene microspheres, and the conductive particles are SP carbon particles or metal particles.
8. A method for preparing a lithium ion battery, comprising:
preparing a positive pole piece and a negative pole piece;
heating the low-melting-point microspheres to form molten liquid and diluting, dispersing conductive particles into the obtained diluted liquid, uniformly mixing, and performing spray drying treatment to obtain core-shell structure microspheres; uniformly dispersing the core-shell structure microspheres, the ceramic oxide and the adhesive into an organic solvent to obtain slurry; coating the slurry on a polyolefin base film to form a coating, thereby obtaining a safety diaphragm;
and placing the safety diaphragm between the positive pole piece and the negative pole piece, performing Z-shaped stacking to obtain a battery cell, placing the battery cell in a packaging shell, and injecting electrolyte to obtain the lithium ion battery.
9. The method for preparing a lithium ion battery according to claim 8, wherein the preparation of the positive electrode sheet comprises the following steps: sequentially adding polyvinylidene fluoride, a conductive agent and a positive electrode material into N-methyl pyrrolidone, and uniformly stirring to obtain coating slurry; coating the coating slurry on an aluminum foil current collector, and sequentially drying, cold pressing and punching to obtain a positive electrode plate;
further, the mass ratio of the polyvinylidene fluoride, the conductive agent and the positive electrode material is 0.5% -2%: 0.5% -2%: 96% -99%.
10. The method for preparing a battery according to claim 8, wherein the preparation of the negative electrode sheet comprises: sequentially adding sodium carboxymethylcellulose, styrene-butadiene rubber emulsion, a conductive agent and graphite into deionized water, uniformly stirring to obtain coating slurry, coating the coating slurry on a copper foil current collector, and sequentially drying, cold pressing and punching to obtain a negative electrode plate;
further, the mass ratio of the sodium carboxymethyl cellulose to the styrene-butadiene rubber emulsion to the conductive agent to the graphite is 0.5% -2%: 0.5% -2.5%: 0.5 to 1.5 percent: 94.5 to 97.5 percent.
CN202311017789.7A 2023-08-10 2023-08-10 Safety diaphragm, lithium ion battery and preparation method Pending CN116799435A (en)

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