WO2023221711A1 - 一种电池极片的改造方法 - Google Patents

一种电池极片的改造方法 Download PDF

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Publication number
WO2023221711A1
WO2023221711A1 PCT/CN2023/088834 CN2023088834W WO2023221711A1 WO 2023221711 A1 WO2023221711 A1 WO 2023221711A1 CN 2023088834 W CN2023088834 W CN 2023088834W WO 2023221711 A1 WO2023221711 A1 WO 2023221711A1
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Prior art keywords
battery
pptc
pole piece
positive electrode
lithium
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PCT/CN2023/088834
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English (en)
French (fr)
Inventor
冼剑光
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吉通科技（广州）有限公司
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Publication of WO2023221711A1 publication Critical patent/WO2023221711A1/zh

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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
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/60—Heating or cooling; Temperature control
    • H01M10/63—Control systems
    • H01M10/637—Control systems characterised by the use of reversible temperature-sensitive devices, e.g. NTC, PTC or bimetal devices; characterised by control of the internal current flowing through the cells, e.g. by switching
    • 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

Definitions

  • the invention relates to the field of battery technology applications, and in particular to a method for transforming battery pole pieces.
  • the present invention demonstrates a technical solution for preventing battery thermal runaway.
  • conductive materials such as carbon black (CB) and metal powder
  • CB carbon black
  • metal powder will produce a composite conductive material.
  • This material usually has a PTC effect (Positive Temperature Coefficient, positive temperature coefficient).
  • PPTC Polymeric Positive Temperature Coefficient
  • PPTC Polymeric Positive Temperature Coefficient
  • the present invention is based on an innovative discovery.
  • the present invention prefers the structure of the positive electrode sheet of the lithium battery to illustrate the core spirit of the present invention:
  • the existing lithium battery cathode sheet structure mainly includes active materials, conductive materials and polymer PVDF (polyvinylidene fluoride, polyvinylidene fluoride) adhesive, which actually includes the PPTC core structure, so there will be a PTC effect. , just because this effect is relatively weak and cannot give the battery enough protection.
  • PVDF polyvinylidene fluoride, polyvinylidene fluoride
  • the present invention is based on this discovery and strengthens the PPTC structure of the lithium battery cathode plate structure.
  • the strengthening measures are any combination or all of the following:
  • the polymer of the positive electrode sheet is a low melting point copolymer.
  • the structure of the positive electrode sheet of the lithium battery is transformed into a sufficiently strong PPTC. After forming the lithium battery, it can be imagined that the entire battery positive electrode is filled with PPTC units. All positive active materials are surrounded by PPTC units, thus providing better protection for the battery. Thermal runaway protection.
  • the core spirit of the present invention is mainly explained based on existing lithium-ion batteries. Those familiar with the technical field can understand that the core spirit of the present invention is applicable to lithium-ion batteries, lithium solid batteries, lithium metal batteries, fuel cells, etc. Various battery forms.
  • Figure 1 shows the structure of the positive electrode sheet in a lithium-ion battery.
  • 10 is the current collector
  • 11 is the cathode coating, including 101, 102 and 103
  • 101 is the cathode active material
  • 102 is the conductive particle
  • 103 is the polymer adhesive.
  • Figure 2 is a schematic diagram of batteries connected in series and parallel.
  • FIG. 2 shows that multiple battery cells in a lithium-ion battery are connected in series to form a battery string, and in parallel to form a battery pack.
  • 1, 2 and 3 in the figure represent a battery string composed of battery cells connected in series.
  • Battery cells 101, 102 and 103 constitute battery string 1
  • battery cells 201, 202 and 203 constitute battery string 2
  • battery cell 301 , 302 and 303 constitute battery string 3.
  • Battery string 1, battery string 2 and battery string 3 are connected in parallel to form a battery pack.
  • relay 110 is the relay of battery string 1. When the current of battery string 1 is too large, relay 110 will be cut off, thereby disconnecting the entire battery string 1.
  • the relay 210 is the relay of the battery string 2. When the battery string 2 has excessive current, the relay 210 will be cut off, thereby disconnecting the entire battery string 2.
  • the relay 310 is the relay of the battery string 3. When the battery string 3 has excessive current, the relay 310 will be cut off, thus disconnecting the entire battery string 3.
  • PPTC Polymeric Positive Temperature Coefficient
  • CB carbon black
  • PVDF polyvinylidene
  • BMS Battery Management System
  • Battery Management System for short, is an important component of the electric vehicle power battery system. Real-time monitoring of battery cells is carried out. When safety hazards are discovered, a safety warning is issued. When an abnormality occurs, the abnormal battery cells or battery strings (battery packs) are cut off and isolated.
  • PPTC unit In the positive electrode sheet structure, around each active material particle, there will be a microscopic PPTC structure connecting the active material particles and the current collector.
  • Lithium battery structure The main materials of lithium-ion batteries include electrolyte, isolation membrane, positive active material, positive conductive material, negative material, positive current collector and negative current collector. According to the different cathode active materials, the common lithium batteries currently on the market are divided into lithium iron phosphate batteries and ternary lithium batteries.
  • the positive active material of lithium iron phosphate battery is lithium iron phosphate.
  • Ternary lithium batteries are subdivided into NCM batteries and NCA batteries.
  • NCM means that the positive active material is lithium nickel cobalt manganese oxide, which is composed of three materials: nickel, cobalt and manganese in a certain proportion, while the positive electrode material of NCA is nickel cobalt aluminum oxide.
  • Lithium is composed of three materials, nickel, cobalt and aluminum, in a certain proportion. Each letter corresponds to the chemical initials of the relevant elements.
  • the conductive material of the positive electrode is usually carbon black (CB).
  • CB carbon black
  • the resistivity of the active material is generally very high, and conductive materials need to be added to reduce the on-resistance between it and the current collector.
  • the negative electrode material is usually graphite.
  • the positive current collector currently used in actual production is aluminum foil, with a thickness generally between 10 and 20um, and the negative current collector is copper foil, with a thickness generally between 4.5 and 10um.
  • the isolation membrane is a microporous and porous film, mainly made of PE (polyethylene, referred to as PE, polyethylene), PP (polypropylene, referred to as PP, polypropylene), placed between the positive and negative electrodes, and is mainly used to isolate the positive and negative electrodes.
  • PE polyethylene
  • PP polypropylene
  • the negative electrode prevents short circuits within the battery and has an important function of allowing electrolyte ions to pass through.
  • PTC effect of polymers Filling the polymer matrix with conductive fillers such as carbon black (CB) and metal powder will produce a composite conductive material, which usually has a PTC effect.
  • CB carbon black
  • metal powder will produce a composite conductive material, which usually has a PTC effect.
  • conductive fillers such as carbon black (CB) and metal powder
  • CB carbon black
  • metal powder will produce a composite conductive material, which usually has a PTC effect.
  • CB carbon black
  • PPTC Polymeric Positive Temperature Coefficient
  • resettable fuse or polymer fuse it is commonly known as self-restoring fuse or overcurrent protection sheet in China.
  • polymer switch Poly Switch
  • Public information shows that PPTC was invented by the American company Raychem (now merged into Tyco Electronics) in 1981. It is mainly used in over-current protection of various electronic products such as batteries, computers, motors, and communications industries.
  • PPTC is a very mature and reliable application, and the current global annual market size is approximately US$400 million.
  • PPTC currently on the market is mainly used as separate components.
  • Publicly available information shows that PPTC applications using PVDF as a polymer are also very common, and the PTC effect is also significant, which means that it is economically feasible to strengthen the PPTC structure of the existing lithium battery cathode sheet structure.
  • the PTC tripping temperature When the temperature reaches the tripping temperature, the resistance of the PTC increases sharply and the current becomes smaller, protecting the battery safety.
  • the main determinants of the tripping temperature include the melting point of the polymer and the doping concentration of the conductive particles. As the doping concentration of conductive particles decreases, the tripping temperature gradually moves toward low temperatures, below the melting point of the polymer.
  • the magnitude of the resistance trip of the PPTC unit After the temperature exceeds the PTC tripping temperature, the highest resistance reached by the PPTC unit is often several orders of magnitude greater than the resistance value at room temperature of 25°C.
  • the magnitude of the resistance jump is 7, which means that the above-mentioned highest resistance is 10 7 times the resistance value at room temperature of 25°C, that is, 10 to the 7th power.
  • NTC effect of PPTC unit The resistivity of PPTC unit increases with the increase of temperature. When the temperature rises to near the melting point of the polymer, the resistivity increases sharply, showing an obvious PTC effect. After the resistance reaches its peak value, as the As the temperature further increases, it begins to drop sharply, showing the NTC (Negative Temperature Coefficient, negative temperature coefficient) resistance effect.
  • the reason for the NTC effect is that after the polymer reaches the melting point, the polymer becomes soft and can even flow, and the conductive filler moves and agglomerates. The NTC effect reduces the stability and reliability of PPTC. Methods to eliminate NTC effect: 1. Limit the movement and agglomeration of conductive particles through cross-linking; 2.
  • the polymer with the lowest melting point will have a PTC effect when it reaches its melting point, but the matrix will undergo double percolation behavior due to the presence of higher melting point components.
  • the entire matrix will not melt; 3.
  • Cross-linking High molecular polymers are bonded and cross-linked to each other to form a three-dimensional network structure. This reaction converts linear or lightly branched macromolecules into a three-dimensional network structure, thereby improving strength, heat resistance, and wear resistance. properties, solvent resistance, etc. Irradiation cross-linking refers to the use of electron beams generated by electron accelerators or cobalt 60 gamma rays to cause cross-linking reactions in polymers.
  • the internal temperature of the battery needs to be strictly controlled and limited to a certain temperature value. Usually this temperature needs to be controlled below the melting point of the isolation film.
  • the melting point is about 130°C.
  • the isolation film is made of PP material, the melting point is about 160°C. After the isolation film melts, the positive and negative electrodes will lose isolation and cause a short circuit. Therefore, when the isolation film is made of PE material, the maximum safe temperature of the battery needs to be below 130°C. Therefore, when the isolation film is made of PP material, the maximum safe temperature of the battery needs to be below 160°C.
  • the PTC trip temperature is lower than the maximum safe temperature of the battery.
  • Lithium batteries are divided into cylindrical batteries, prismatic batteries and soft pack batteries according to their appearance. There are certain differences in the production processes. However, the overall lithium battery manufacturing process can be divided into the front-end process (pole piece manufacturing) and the middle process (battery cells). Synthesis), back-end process (formation).
  • the main processes in the front-end process include
  • Material preparation material preparation and material preprocessing.
  • Pulping Mix the positive and negative battery materials evenly and stir into a slurry.
  • Coating and drying Place the wet film obtained by coating in an oven for heating and drying. Drying technology includes hot air drying and infrared ray drying. Drying, microwave drying, etc.
  • the dried electrode sheets are compacted by a roller press.
  • the thickness of the treated positive electrode sheets is more uniform, the surface is flat and smooth, and the bonding between the coating material and the current collector is strengthened.
  • the main processes of the middle process of square and cylindrical batteries are:
  • Liquid injection Inject the battery's electrolyte quantitatively into the battery core.
  • Packaging Put the battery core into the battery shell.
  • the main processes in the middle process of soft pack battery are:
  • Liquid injection Inject the battery’s electrolyte quantitatively into the battery core.
  • Packaging Put the battery core into the battery shell.
  • the main processes in the back-end process include
  • the first charge activates the battery core.
  • an effective passivation film SEI film, Solid Electrolyte Interphase
  • SEI film Solid Electrolyte Interphase
  • Capacity classification that is, analyzing the capacity, charging and discharging the formed battery core according to the design standards to measure the capacity of the battery core.
  • the core of the invention is to strengthen the PPTC structure of the lithium battery pole piece structure.
  • the present invention prefers the structure of the positive electrode sheet of a lithium battery to illustrate the core spirit of the present invention. Those familiar with the technical field can understand that the core spirit of the present invention is also applicable to the negative electrode of lithium batteries.
  • the existing lithium battery cathode structure actually contains the PPTC core structure. Therefore, there will be a PTC effect.
  • the reasons for this weak effect include:
  • the NTC effect of the PPTC unit occurs. When the battery undergoes thermal runaway, the temperature rises very rapidly, so it quickly crosses the PTC effect temperature range and enters the NTC effect temperature range, so the protective effect of PTC is greatly weakened.
  • the resistance jump magnitude of the PPTC unit is not large enough, and the thermal protection effect is insufficient.
  • the positive electrode adhesive of existing lithium batteries generally uses PVDF (polyvinylidene fluoride, polyvinylidene fluoride), whose melting point is 170°C.
  • the isolation film of existing lithium batteries is usually PE/PP. When the isolation film is made of PE material, the melting point It is about 130°C. When the isolation film is made of PP material, the melting point is about 160°C. At 170°C, the battery's isolation film has melted, causing a short circuit between the positive and negative electrodes, exacerbating the thermal runaway process. At the same time, some internal components have begun to decompose and generate heat.
  • the melting point of the positive electrode adhesive is preferably 100°C to 130°C, which is lower than the melting point of the isolation film and the decomposition temperature of the materials inside the battery, which is beneficial to the stability of the battery.
  • the manufacturing process of the positive electrode currently does not consider PPTC.
  • the high molecular polymer in PPTC can form a good crystal state through thermal annealing treatment.
  • the crystal state directly affects various indicators of the PPTC unit.
  • Preparation Prepare the positive active material, positive conductive material and positive binder.
  • the mass ratio is usually optional (90 ⁇ 98): (0.5 ⁇ 5): (1 ⁇ 5);
  • the solvent is usually any one or a mixture of at least two of N-methylpyrrolidone NMP, dimethylformamide DMF or dimethylacetamide DMAC. Solvent. Pulse the mixture through a blender.
  • Coating Coat the above slurry on one or both sides of the positive electrode current collector through a coating machine.
  • the positive electrode current collector is aluminum foil, and the thickness is usually 15 microns.
  • the undried slurry coating obtained through the coating process is also called "wet film”.
  • Coating and drying Place the wet film obtained by coating in an oven for heating and drying. Drying techniques include hot air drying, infrared drying, microwave drying, etc.
  • the dried positive electrode sheets are compacted by a roller press.
  • the thickness of the treated positive electrode sheets is more uniform, the surface is flat and smooth, and the bonding between the coating material and the current collector is strengthened.
  • Cross-link the positive electrode to improve the thermal stability of the positive electrode polymer and eliminate the NTC effect. It is preferred to use electron beam cross-linking, with electron beam energy of 2 to 10 Mev, electron beam current of 5 to 20 mA, and irradiation dose of 100 to 300 kGy. After cross-linking treatment, the polymer of the positive electrode will form a three-dimensional network structure to improve strength and heat resistance and eliminate the NTC effect.
  • the cross-linking treatment is preferably performed after the 6th step of winding (or the 9th step of lamination) in the main manufacturing process of the above-mentioned lithium battery, because the mechanical processing performance of the polymer decreases after cross-linking, and it can be done after the winding. Or cross-linking after lamination.
  • Another additional benefit of cross-linking after winding or lamination is that the separator material is also cross-linked at the same time, and its strength and heat resistance will be improved to a certain extent.
  • the cross-linking process of the separator material Can be done individually.
  • Those skilled in the art can perform cross-linking treatment at any appropriate step after coating in the main manufacturing process of the above-mentioned lithium battery according to actual needs, and adjust the parameters of electron beam irradiation according to actual applications.
  • the principle of selecting parameters is to completely eliminate NTC effect, but not excessive, causing the polymer to harden and affecting mechanical indicators.
  • the interval between the melting points is preferably above 30°C, and both of them are preferably soluble in solvents.
  • the solvents are usually N-methylpyrrolidone NMP, dimethyl Any one of DMF or dimethylacetamide DMAC or a mixed solvent of at least two.
  • PVDF-HFP Polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinylidene fluoride-hexafluoropropylene copolymer
  • Copolymers with melting points between 100°C and 130°C are preferred and mixed with PVDF with a melting point of 170°C in a certain mass ratio.
  • conductive particles with low resistivity including but not limited to the following materials, or a combination of the following materials: conductive carbon black or nanoscale carbon nanotubes, metal powder, powder of known metal materials, such as nickel, Copper, aluminum, tin, zinc, silver, gold, etc., carbide metal powder, including titanium carbide, tungsten carbide, titanium silicon carbide, titanium aluminum carbide or titanium tin carbide, etc. This reduces the room temperature resistance and increases the resistance jump magnitude of the PPTC unit. Because the positive electrode needs to be immersed in the electrolyte, the stability of the conductive particles in the electrolyte will affect the long-term reliability of the battery. Those skilled in the art need to comprehensively consider the implementation process. This part belongs to the material preparation steps of the above-mentioned positive electrode sheet manufacturing process, and the conductive particles belong to the positive electrode conductive materials described in the process.
  • the main considerations for the mass ratio of various materials for the existing lithium battery cathode are to improve the efficiency of the active material and reduce the resistivity.
  • the polymer used as the binder can be as little as possible while meeting the adhesion indicators. .
  • the mass ratio may not be appropriate and needs to be considered comprehensively and adjusted.
  • This part belongs to the material preparation steps of the above-mentioned positive electrode sheet manufacturing process.
  • the positive electrode adhesive of the lithium battery uses a polymer with a lower melting point, preferably PVDF-HFP (Polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinylidene fluoride-hexafluoropropylene copolymer), with a melting point between 100°C and 130°C. copolymer between.
  • PVDF-HFP Polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinylidene fluoride-hexafluoropropylene copolymer
  • This part belongs to the material preparation steps of the above-mentioned positive electrode sheet manufacturing process, and the high molecular polymer belongs to the positive electrode binder described in the process.
  • Thermal annealing treatment can eliminate internal stress and make the crystals of polymers continue to improve.
  • PVDF is preferably annealed at 120°C.
  • the coated wet film needs to be coated and dried, and the drying temperature can be as high as 200°C. Rolling is often heated to high temperatures.
  • the thermal annealing treatment is preferably performed after the coating, drying or rolling in the above-mentioned positive electrode sheet manufacturing process.
  • Example 1 Apply the above solution 1 to strengthen the PPTC structure of the lithium battery cathode sheet structure.
  • Example 2 Apply the above solution 2 to strengthen the PPTC structure of the lithium battery cathode sheet structure.
  • Example 3 Apply the above solutions 1 and 4 to strengthen the PPTC structure of the lithium battery cathode sheet structure.
  • Example 4 Apply the above solutions 1 and 3 to strengthen the PPTC structure of the lithium battery cathode sheet structure.
  • Example 5 Apply the above solutions 1, 3 and 4 to strengthen the PPTC structure of the lithium battery cathode sheet structure.
  • Example 6 Apply the above solutions 1, 3, 4 and 5 to strengthen the PPTC structure of the lithium battery cathode sheet structure.
  • Example 7 Apply the above solutions 1, 3, 4, 5 and 6 to strengthen the PPTC structure of the lithium battery cathode sheet structure.
  • the core of the invention is to strengthen the PPTC structure of the battery pole piece structure.
  • the present invention prefers the structure of the positive electrode sheet of a lithium battery to illustrate the core spirit of the present invention.
  • Those familiar with the technical field can understand that the core spirit of the present invention is also applicable to the negative electrode of lithium batteries.
  • Filling the polymer matrix with conductive materials will result in a composite conductive material.
  • This material usually has a PTC effect (Positive Temperature Coefficient, positive temperature coefficient).
  • the existing lithium battery negative electrode structure mainly includes active materials,
  • the adhesive between conductive materials and polymers actually contains the core structure of PPTC. Therefore, there will be a PTC effect.
  • the PPTC structure can also be strengthened. , which is the core spirit of the present invention.
  • the core of the invention is to strengthen the PPTC structure of the battery pole piece structure.
  • the preferred positive electrode sheet structure of the lithium battery of the present invention To illustrate the core spirit of the present invention, those familiar with the technical field can understand that the core spirit of the present invention is also applicable to batteries with any other active materials, such as batteries using sodium as the active material, that is, the batteries of the present invention. Materials include but are not limited to lithium, sodium and other materials.
  • cross-linking of electrode polymers is a very important method, and electron beam cross-linking is preferably used.
  • the structure of the electron accelerator can be improved and the Its working area and power enable parallel cross-linking processing of large-format battery pole pieces.
  • PVDF is used as the adhesive for the positive electrode.
  • the core spirit of the present invention can be applied to any other adhesives and any new adhesives, because the present invention explains that it is applicable to any Under the guidance of the general rules of polymers, those in the technical field can smoothly implement various replacements, changes and modified versions within the scope of patent protection.
  • the positive electrode sheet after the above-mentioned PPTC structure strengthening treatment is formed into a lithium battery: it can be imagined that the entire positive electrode of the battery is filled with PPTC units, and all positive active materials are surrounded by PPTC units.
  • the temperature of the PPTC unit there rises.
  • the resistance of the PPTC unit rises, which reversely suppresses the rise in current and reduces the current heating, thus suppressing the temperature rise. Continue to rise.
  • the capacity of a single battery cell does not exceed a certain safety threshold. In this way, when an internal short circuit occurs in a battery cell, the current of many PPTC units will eventually be quickly controlled within the rated range, and the current of the entire cell will converge to Internal short circuit, but since the capacity of a single battery cell is within the safety threshold and the heat generated by current convergence is within the safe range, thermal runaway will not occur at this internal short circuit.
  • FIG 2 is a schematic diagram of a series and parallel connection of batteries.
  • battery cells 101, 102 and 103 belong to battery string 1.
  • the battery management system monitors the current of each battery string in real time. When the current flowing through the battery string 1 exceeds the safety threshold, the battery management system will immediately turn off the relay 110 to isolate the battery string 1 from other circuits and record it in the system to remind that a short circuit has occurred.
  • Another situation is that the battery cell 101 has an internal short circuit and the current flowing through the battery string 1 has not exceeded the safety threshold.
  • the relay 110 is not cut off. However, because the battery cell 101 has an internal short circuit, the battery string 1 and other strings are not connected. The total voltage between them is unbalanced, which is detrimental to the operation of the entire battery pack.
  • the battery management system monitors the voltage of each battery cell in real time. As the short-circuit discharge proceeds, the voltage of the battery cell 101 will continue to drop. When the discharge is completed, the voltage will drop to nearly 0.
  • the battery management system can monitor the voltage of each battery cell in real time. When this situation is monitored, the relay 110 will be turned off, thereby isolating the battery string 1 from other circuits, and recording in the system to remind that a short circuit has occurred.
  • the battery cell 101 does not have a battery cell directly connected in parallel with it, so there is no need to consider monitoring and turning off the battery cells connected in parallel with it, which is relatively simple.
  • battery cell 101 is connected in series with battery cells 102 and 103 to form battery string 1, and then connected in parallel with other battery strings.
  • the characteristic of the series circuit is the current between battery cell 101 and battery cells 102 and 103. are the same, so when an internal short circuit occurs in the battery cell 101, as long as the battery cells 102 and 103 do not have a short circuit, the PPTC units in the battery cells 102 and 103 will limit the current, so that the current of the current string 1 Eventually it will be quickly controlled within the rated range, so this series-parallel structure has better stability.
  • FIG. 2 is only used as an exemplary example to illustrate the core spirit of the present invention, and is not intended to limit the present invention. In actual implementation, any suitable combination of battery cells may be used.
  • the battery cell (or even the entire battery string) can be physically examined again, so that More secure until all results are normal.
  • the battery needs regular physical examination.
  • the car also needs regular maintenance, usually once a year.
  • the battery of the electric vehicle can be physically examined at the same time.
  • the battery management system can be connected to the vehicle management system of the electric vehicle. The battery management system manages the physical examination. When the time is over and the physical examination is not done, a reminder will be issued. The longer the delay, the level of the reminder can be increased to cause Attention electric vehicle users.
  • the battery management system itself monitors each battery cell in real time, the above-mentioned maintenance facilities can be added to the battery management system. In order to reduce costs, separate maintenance facilities can also be set up, so that when users do maintenance, the maintenance shop provides separate maintenance facilities.
  • the battery management system can provide corresponding hardware and software interfaces to facilitate separate maintenance facilities for physical examinations. .
  • Each battery, each battery string, and each cell can have a unique identification code.
  • each battery, each battery string, and each cell is stored in detail: 1. Factory date . 2. Factory identification code, model, voltage, current, capacity and other parameters. 3. Maintenance records, at what time, which maintenance master was employed, and what maintenance operations were performed, with detailed records. 4. Physical examination records, at what time, which maintenance master was employed, and what maintenance operations were performed, with detailed records.
  • the present invention discovers the hidden PPTC structure in the existing positive electrode structure, unearths it and strengthens it.
  • the advantage of the present invention is that it is compatible with the existing lithium battery production process, so that only minimal modification costs are required. Enhance the safety performance of lithium batteries. With the popularity of electric cars, users are paying more and more attention to the problem of spontaneous combustion of electric car batteries. Users expect that electric car batteries can achieve zero risk of spontaneous combustion. The present invention will help achieve this goal.

Abstract

一种电池极片的改造方法，本发明基于一个创新性的发现，即现有的锂电池正极片结构，主要有活性材料、导电材料和高分子聚合物的PVDF(聚偏氟乙烯)胶粘剂，这其实就包含了PPTC(高分子聚合物正温度系数)核心结构，因此，就会有PTC(正温度系数)效应，只是因为这个效应比较弱，不能给电池足够的保护。本发明正是基于这一发现，对锂电池正极片结构进行PPTC结构强化，将锂电池正极片结构改造为足够强的PPTC，组成锂电池后，可以想象为整个电池正极，充满了PPTC单元，所有正极活性材料，都被PPTC单元包围着，从而能够对电池提供更好的热失控保护。

Description

一种电池极片的改造方法 所属技术领域
本发明涉及电池技术应用领域，特别涉及一种电池极片的改造方法。
背景技术
近年，电动小汽车着火的事件时不时会发生，起火原因主要是源于电动小汽车所装载的电池，其中锂离子电池占了很大比例，锂离子电池起火的重要原因是电池内部过热而造成的热失控，这种过热在电池充放电过程中最容易发生。由于锂离子电池自身具有一定的内阻，在充放电的同时会出现一定的热量，使得自身温度变高，当温度持续升高并超出安全阈值后，引发热失控，最终导致电池自燃、爆炸。
电池着火和爆炸直接威胁到用户的安全，急需找到有效的预防和应对方案。
发明内容
本发明展示了电池热失控预防的技术方案。
以炭黑(CB)、金属粉末等导电材料填充到高分子聚合物基体，会得到复合的导电材料，这一材料通常具有PTC效应(Positive Temperature Coefficient，正的温度系数)，这样制作的元件就是PPTC(Polymeric Positive Temperature Coefficient)，即高分子聚合物正温度系数元件。当温度到达特定的温度转折点时，电阻增大几个数量级，从而导致通过的电流急剧减小，因此PPTC能提供有效的过热保护，在许多领域都得到广泛应用。
本发明基于一个创新性的发现，本发明优选锂电池的正极片结构以阐述本发明的核心精神：
现有的锂电池正极片结构，主要有活性材料、导电材料和高分子聚合物的PVDF(polyvinylidene fluoride，聚偏氟乙烯)胶粘剂，这其实就包含了PPTC核心结构，因此，就会有PTC效应，只是因为这个效应比较弱，不能给电池足够的保护。
本发明正是基于这一发现，对锂电池正极片结构进行PPTC结构强化，强化措施是以下所列的任意部分组合或者全部：
1.对正极片的高分子聚合物进行交联处理。
2.以两种以上不同熔点的高分子聚合物代替单一高分子聚合物作为正极片胶粘剂，组成正极的高分子基体，其中熔点最低的聚合物在到达其熔点时，基体因为存在更高熔点的组成物，发生双渗逾行为，整个基体不会熔解。
3.添加电阻率低的导电颗粒，包括纳米级碳纳米管，金属粉，碳化金属粉末等等。
4.调整正极片各种物质的比例。
5.正极片的高分子聚合物采用低熔点共聚物。
6.对正极片进行热退火处理。
将锂电池正极片结构改造为足够强的PPTC，组成锂电池后，可以想象为整个电池正极，充满了PPTC单元，所有正极活性材料，都被PPTC单元包围着，从而能够对电池提供更好的热失控保护。
本发明中，主要基于现有的锂离子电池阐述本发明的核心精神，熟悉本技术领域的人员可以理解，本发明核心精神适用于锂离子电池、锂固体电池、锂金属电池、燃料电池等各种各样的电池形式。
下面结合附图和实施例对本发明进一步说明。
附图说明
图1是锂离子电池中正极片结构。
图1中，10是集流体，11是正极涂层，包含101、102和103，101是正极活性材料，102是导电颗粒，103是高分子胶粘剂。
图2是电池串并联的示意图。
图2中，展示了锂离子电池中多个电池单体通过串联构成电池串，通过并联构成电池组。图中1、2和3代表了由串联的电池单体组成的电池串，电池单体101、102和103构成电池串1，电池单体201、202和203构成电池串2，电池单体301、302和303构成电池串3。电池串1、电池串2和电池串3通过并联构成电池组。
110是电池串1的继电器，当电池串1发生电流过大时，继电器110将被切断，从而断开整个电池串1。
210是电池串2的继电器，当电池串2发生电流过大时，继电器210将被切断，从而断开整个电池串2。
310是电池串3的继电器，当电池串3发生电流过大时，继电器310将被切断，从而断开整个电池串3。
具体实施方式
现在结合上述附图详细介绍本发明的具体实施过程：
一些名词的解释：
PPTC结构：本发明中，PPTC(Polymeric Positive Temperature Coefficient)是指正极形成的高分子聚合物正温度系数结构，包括正极活性材料、炭黑(CB)等导电颗粒和高分子聚合物的PVDF(polyvinylidene fluoride)胶粘剂。
电池管理系统：简称BMS(Battery Management System)，是电动汽车动力电池系统的重要组成。对电池单体进行实时监测，当发现安全隐患时，发出安全预警，当出现异常时，切断隔离异常的电池单体或者电池串(电池组)。
PPTC单元：在正极片结构中，围绕每一个活性材料颗粒，将会有一个微观上的PPTC结构连接活性材料颗粒和集流体。
已有技术的解释：
锂电池结构：锂离子电池的主要构成材料包括电解液、隔离膜、正极活性材料、正极导电材料、负极材料、正极集流体和负极集流体等。按照正极活性材料的不同，目前市场上常见的锂电池分为磷酸铁锂电池和三元锂电池。磷酸铁锂电池的正极活性材料为磷酸铁锂。三元锂电池细分为NCM电池和NCA电池，NCM是指正极活性材料是镍钴锰酸锂，由镍钴锰三种材料由一定比例组合而成，而NCA的正极材料是镍钴铝酸锂，由镍钴铝三种材料由一定比例组合而成，每个字母对应的都是相关元素的化学首字母。正极导电材料通常为炭黑(CB)，活性材料的电阻率一般都很高，需要添加导电材料，以减少其与集流体的导通电阻。目前市场上常见的锂电池，负极材料通常为石墨。目前运用于实际生产的正极集流体为铝箔，厚度一般在10到20um，负极集流体为铜箔，厚度一般在4.5到10um。隔离膜为微孔性及多孔性薄膜，材质以PE(polyethylene，简称PE，聚乙烯)、PP(polypropylene，简称PP，聚丙烯)为主，置于正负极之间，主要用作隔离正负电极，防止电池内部短路，此外一项重要功能是使电解质离子通过。
聚合物的PTC效应：以炭黑(CB)、金属粉末等导电填料填充到高分子聚合物基体，会得到复合的导电材料，这一材料通常具有PTC效应。关于PTC效应产生的原因，已有很多探索。一种合理的解释是，在常温下，导电粒子在高分子聚合物基体内形成导电链，电阻率较低，随着温度升高，由于导电粒子的热膨胀系数远低于高分子聚合物基体的热膨胀系数，膨胀程度的差异引起导电粒子间的距离增大，使导电粒子形成的通电通路断开，从而导致电阻率增加。在高分子聚合物基体的熔点附近，复合导电材料的体积膨胀急剧增加，电阻率急剧上升。复合导电材料的体积膨胀曲线与其电阻率变化曲线的形状非常相似，电阻率变化曲线和体积膨胀曲线的转折温度基本一致，这表明PTC特性与体积膨胀确实存在着内在的联系。
PPTC(Polymeric Positive Temperature Coefficient)，即高分子聚合物正系数温度元件。又称可恢复保险丝(Resettable Fuse)或聚合物保险丝(Poly Fuse)，在国内俗称自恢复保险丝或过流保护片。在国外多称为高分子开关(Poly Switch)。公开的资料显示，PPTC是美商Raychem(现已经并入Tyco Electronics)在1981年发明，主要应用于电池、计算机、电机、通讯行业等各种电子产品的过电流保护。PPTC是一个很成熟可靠的应用，当前全球的年市场规模大约为4亿美元。当前市场上的PPTC主要以单独元件进行应用。公开的资料显示，以PVDF作为高分子聚合物的PPTC应用也很常见，而且PTC效应也很显著，这就意味着，对现有锂电池正极片结构进行PPTC结构强化存在经济上可行性。
PTC跳闸温度：当温度到达跳闸温度时，PTC的电阻急剧增加，电流急剧变小，保护电池安全。跳闸温度主要决定因素包括高分子聚合物的熔点，导电颗粒的掺杂浓度。随着导电颗粒的掺杂浓度减小，跳闸温度逐渐移向低温，低于聚合物的熔点。
PPTC单元的电阻跳变数量级：温度越过PTC跳闸温度后，PPTC单元达到的最高电阻往往比室温25℃时的电阻值大了几个数量级。电阻跳变数量级是7，就代表上述最高电阻是室温25℃时电阻值的107倍，即10的7次方。
PPTC单元的NTC效应：PPTC单元电阻率随着温度的升高而增加，当温度升而到高分子聚合物的熔点附近时，电阻率急剧增大，呈现出明显的PTC效应。电阻达到峰值后，随着 温度的进一步升高又开始急剧地下降，呈现出NTC(Negative Temperature Coefficient，负温度系数)电阻效应。NTC效应的原因是，高分子聚合物到达熔点后，高分子聚合物变软甚至可以流动，导电填料发生移动和团聚，NTC效应降低了PPTC的稳定可靠性。消除NTC效应的方法：1。通过交联限制导电粒子的移动和团聚；2。以两种以上不同熔点的聚合物代替单一聚合物作为基体，其中熔点最低的聚合物在到达其熔点时，会有PTC效应，但基体因为存在更高熔点的组成物，发生双渗逾行为，整个基体不会熔解；3。导电粒子的表面处理，如炭黑氧化、高温处理等，改善导电粒子的表面性质，从而改善导电粒子与聚合物的相容性。
交联：高分子聚合物相互键合交联成三维网络结构，这种反应使线型或轻度支链型的大分子转变成三维网状结构，以此提高强度、耐热性、耐磨性、耐溶剂性等性能。辐照交联是指利用电子加速器产生的电子束或者钴60γ射线照射，使高分子聚合物产生交联反应。
电池最高安全温度：为了保证电池的使用安全，电池的内部温度需要严密控制并限制在一定温度值以下。通常这一温度需要控制在隔离膜的熔点以下，当隔离膜为PE材料时，熔点约在130℃，当隔离膜为PP材料时，熔点约在160℃。隔离膜熔化后，正负极将失去隔离而导致短路。所以当隔离膜为PE材料时，电池最高安全温度需要在130℃以下。所以当隔离膜为PP材料时，电池最高安全温度需要在160℃以下。
所以PTC跳闸温度要比电池最高安全温度低。
锂电池按照外观形态分为圆柱电池、方形电池和软包电池等，其生产工艺之间存在一定差异，但整体上锂电池制造流程可划分为前段工序(极片制造)、中段工序(电芯合成)、后段工序(化成)。
现有锂电池的主要制造流程如下：
前段工序的主要流程有
1.备料：材料准备和材料预处理。
2.制浆：将正、负极电池材料混合均匀后搅拌成浆状。
3.涂布：搅拌后的浆料均匀涂覆在金属箔片上。
4.涂布烘干：将涂布所得湿膜置于烘箱进行加热烘干，烘干技术包括热风干燥、红外线 干燥、微波干燥等。
5.辊压：将干燥后的极片通过辊压机压实，处理后的正极片厚度更加均匀，表面平整光滑，涂层材料与集流体的结合得到加强。
方形、圆柱电池的中段工序主要流程有
6.卷绕：将前段工序制作的正负极片和隔膜材料一起卷绕成锂电池的电芯。
7.注液：将电池的电解液定量注入电芯中。
8.封装：将电芯放入电芯外壳中。
软包电池的中段工序主要流程有
9.叠片：将前段工序制作的正负极片和隔膜材料叠成锂离子电池的电芯。
10.注液：将电池的电解液定量注入电芯中。
11.封装：将电芯放入电芯外壳中。
后段工序主要流程有
12.化成：第一次充电使电芯激活，在此过程中负极表面生成有效钝化膜(SEI膜，Solid Electrolyte Interphase)。
13.分容：即分析容量，将化成后的电芯按照设计标准进行充放电，以测量电芯的容量。
14.检测：根据检测结果对化成、分容后的电池按一定标准进行分类。
本发明实施例：
本发明的核心是对锂电池极片结构进行PPTC结构强化。本发明优选锂电池的正极片结构以阐述本发明的核心精神，熟悉本技术领域的人员可以理解，本发明核心精神也适用于锂电池负极。
现有的锂电池正极片结构其实就包含了PPTC核心结构，因此，就会有PTC效应，这个效应比较弱的原因包括：
1.发生了PPTC单元的NTC效应，电池发生热失控时，温度上升很迅猛，因而很快越过PTC效应温度区间，进入NTC效应温度区间，因而PTC的保护效果被大幅削弱。
2.PPTC单元的电阻跳变数量级没有足够的大，热保护的效果不足够。
3.正极各种材料的质量配比目前没有考虑PPTC，直接影响PPTC单元的各项指标。
4.现有锂电池的正极胶粘剂一般用PVDF(polyvinylidene fluoride，聚偏氟乙烯)，其熔点为170℃，现有锂电池的隔离膜通常为PE/PP，当隔离膜为PE材料时，熔点约在130℃，当隔离膜为PP材料时，熔点约在160℃。在170℃，电池的隔离膜已经熔解，引起正负极短路，加剧了热失控过程，同时内部一些组成物质已经开始分解发热。正极胶粘剂的熔点优选为100℃至130℃，低于隔离膜的熔点，低于电池内部物质的分解温度，有利于电池的稳定。
5.正极的制造流程目前没有考虑PPTC，PPTC中的高分子聚合物通过热退火处理可以形成好的晶体状态，晶体状态直接影响PPTC单元的各项指标。
现有锂电池的正极片制作工艺：
1.备料：准备正极活性材料、正极导电材料和正极粘结剂，质量比通常可选(90～98):(0.5～5):(1～5)；
2.制浆：将上述准备好的材料与正极溶剂混合，溶剂通常为N-甲基吡咯烷酮NMP、二甲基甲酰胺DMF或二甲基乙酰胺DMAC中的任意一种或至少两种的混合溶剂。将混合物通过搅拌机进行搅拌制浆。
3.涂布：将上述浆料通过涂布机在正极集流体的单面或者双面进行涂布，正极集流体为铝箔，厚度通常为15微米。经过涂布工艺得到的未经干燥浆料涂膜也称为“湿膜”。
4.涂布烘干：将涂布所得湿膜置于烘箱进行加热烘干，烘干技术包括热风干燥、红外线干燥、微波干燥等。
5.辊压：将干燥后的正极片通过辊压机压实，处理后的正极片厚度更加均匀，表面平整光滑，涂层材料与集流体的结合得到加强。
本发明的解决方法：
1.对正极进行交联处理，提高正极高分子聚合物的热稳定性，消除NTC效应。优选采用电子束交联，电子束能量2～10Mev，电子束流5～20mA，辐照剂量为100～300kGy。交联处理后，正极的高分子聚合物将会形成三维网状结构，以此提高强度、耐热性，消除NTC效应。交联处理优选地置于上述锂电池的主要制造流程的第6步卷绕(或者第9步叠片)之后进行，因为高分子聚合物交联后机械加工性能下降，可以在卷绕 或者叠片之后再交联。在卷绕或者叠片之后交联的另一个额外的好处是，隔膜材料也同时得到交联处理，其强度和耐热性会有一定的提高，另外需要强调的是，隔膜材料的交联处理可以单独地进行。本领域技术人员可以根据实际需要，在上述锂电池的主要制造流程的涂布之后任意合适的步骤进行交联处理，并按实际应用，调整电子束辐照的参数，参数的选择原则在于完全消除NTC效应，但又不会过度，引起高分子聚合物发硬，影响机械性指标。
2.以2种以上不同熔点的高分子聚合物混合代替一种，熔点之间的间隔优选在30℃以上，并且优选地均能溶解于溶剂，溶剂通常为N-甲基吡咯烷酮NMP、二甲基甲酰胺DMF或二甲基乙酰胺DMAC中的任意一种或至少两种的混合溶剂。优选PVDF-HFP(Polyvinylidene fluoride-hexafluoropropylene copolymer，聚偏氟乙烯-六氟丙烯共聚物)，优先选择熔点在100℃至130℃之间的共聚物，与熔点为170℃的PVDF按一定质量比混合，这样在PVDF-HFP的熔点会有PTC效应，但因为存在更高熔点的PVDF，混合物就不会熔解，因而能经受更高温度。本发明展示了这种核心精神，本领域技术人员可以在这一指引下，将其应用到任何适合的高分子聚合物搭配上。本部分属于上述正极片制作工艺的备料步骤，所述高分子聚合物属于工艺中所述的正极粘结剂。
3.添加电阻率低的导电颗粒，包括但不限于以下材料，或者是以下材料之间的组合物：导电炭黑或者纳米级碳纳米管，金属粉，已知金属材料的粉末，如镍、铜、铝、锡、锌、银、金等等，碳化金属粉末，包括碳化钛、碳化钨、碳化钛硅、碳化钛铝或碳化钛锡等等。这样就降低室温电阻，提高PPTC单元的电阻跳变数量级。正极因为需要浸泡在电解质中，导电颗粒在电解质中的稳定性会影响电池的长期可靠性，本领域技术人员实施过程需要综合考虑。本部分属于上述正极片制作工艺的备料步骤，所述导电颗粒属于工艺中所述的正极导电材料。
4.现有锂电池正极各种材料的质量配比主要考虑点是提高活性物质的效率和降低电阻率，作为粘结剂的高分子聚合物则在满足粘合的指标下，能少则少。而当要考虑PPTC时，质量配比未必合适，需要综合考虑并做出调整。正极活性材料、正极导电材料和正极粘结剂；现有锂电池工艺，正极活性材料、正极导电材料和正极粘结剂的质量比优选为(90～98):(0.5～5):(1～5)，当考虑PPTC时，粘结剂所占质量比需要做出调整，其质量占比可以为1～50。当粘结剂的质量比较大，不能很好溶解在溶剂中，这种情况甚至需要在混料时加热到熔融温度，以更好地混合。特别注明的是，质量比需 要考虑的要素较多，本领域技术人员可以根据实际需要进行选择。本部分属于上述正极片制作工艺的备料步骤。
5.锂电池的正极胶粘剂采用更低熔点的高分子聚合物，优选PVDF-HFP(Polyvinylidene fluoride-hexafluoropropylene copolymer，聚偏氟乙烯-六氟丙烯共聚物)，优先选择熔点在100℃至130℃之间的共聚物。本部分属于上述正极片制作工艺的备料步骤，所述高分子聚合物属于工艺中所述的正极粘结剂。
6.热退火处理可以消除内应力，使高分子聚合物的晶体不断趋于完善。PVDF优选在120℃进行退火处理。现有锂电池正极片制作工艺中，正极片涂布完成后，涂布后的湿膜要进行涂布烘干处理，烘干的温度会高达200℃。辊压往往也有加热到高温的。热退火处理优选地置于上述正极片制作工艺的涂布烘干或者辊压之后进行。
实施例1：应用上述的解决方法1，对锂电池正极片结构进行PPTC结构强化。
实施例2：应用上述的解决方法2，对锂电池正极片结构进行PPTC结构强化。
实施例3：应用上述的解决方法1和4，对锂电池正极片结构进行PPTC结构强化。
实施例4：应用上述的解决方法1和3，对锂电池正极片结构进行PPTC结构强化。
实施例5：应用上述的解决方法1、3和4，对锂电池正极片结构进行PPTC结构强化。
实施例6：应用上述的解决方法1、3、4和5，对锂电池正极片结构进行PPTC结构强化。
实施例7：应用上述的解决方法1、3、4、5和6，对锂电池正极片结构进行PPTC结构强化。
本领域技术人员可以根据实际需要，选择上述解决方法之间的任意组合作为实施例。
本发明的核心是对电池极片结构进行PPTC结构强化。本发明优选锂电池的正极片结构以阐述本发明的核心精神，熟悉本技术领域的人员可以理解，本发明核心精神也适用于锂电池负极。以导电材料填充到高分子聚合物基体，会得到复合的导电材料，这一材料通常具有PTC效应(Positive Temperature Coefficient，正的温度系数)，现有的锂电池负极片结构，主要有活性材料、导电材料和高分子聚合物的胶粘剂，这其实就包含了PPTC核心结构，因此，就会有PTC效应，只是因为这个效应比较弱，不能给电池足够的保护，因此也可以对其进行PPTC结构强化，这是本发明的核心精神。
本发明的核心是对电池极片结构进行PPTC结构强化。本发明优选锂电池的正极片结构 以阐述本发明的核心精神，熟悉本技术领域的人员可以理解，本发明核心精神也适用于任何其他活性材料的电池，如以钠为活性材料的电池，即本发明所述的电池，其活性材料包括但不限于锂、钠等材料。
本发明的阐述中，对电极高分子聚合物进行交联处理是一个很重要方法，优选采用电子束交联，在实际生产中，为了提高劳动生产率，可以对电子加速器的结构进行改进，加大其工作面积和功率，使得能够对大幅面的电池极片进行并行的交联处理。
本发明的阐述中，以PVDF作为正极的胶粘剂，熟悉本技术领域的人员可以理解，本发明的核心精神可以适用于任何其他的胶粘剂，适用于任何新的胶粘剂，因为本发明阐述了适用于任何高分子聚合物的通用规律，本技术领域的人员在这一规律指引下，其专利保护范围内所进行的各种更换、变动和修改后的版本均可顺利实施。
经过上述PPTC结构强化处理后的正极片组成锂电池后：可以想象为整个电池正极，充满了PPTC单元，所有正极活性材料，都被PPTC单元包围着。当电池内部发生局部的温度失控时，该处的PPTC单元温度升高，当温度升高时，PPTC单元的电阻升高，反向抑制电流的上升，电流发热得以变小，从而抑制了温度的继续升高。
当电池内部或者外部发生短路时，电流会急剧上升，使得正极结构中众多PPTC单元温度急剧升高，当温度升高到PTC跳闸温度，PPTC单元的电阻会急剧上升，升幅可达几个数量级，在如此的反馈控制下，PPTC单元的电流最终会迅速地被控制在额定的范围内。当短路故障点在电池内部时，以下问题需要得到妥善处理：
1.在发生内部短路的电池单体，即便PPTC单元的电流最终会迅速地被控制在额定的范围内，但整个单体的电流会汇聚到内部短路处，要确保在该内部短路处不发生热失控。
2.在发生内部短路的电池单体，即便PPTC单元的电流最终会迅速地被控制在额定的范围内，但在实际应用中，多个电池单体往往是串并联在一起的，其他电池单体的电流会向内部短路处汇聚，要确保在该内部短路处不发生热失控。
解决方法：
1.单个电池单体的容量不超过一定的安全阈值，这样在发生内部短路的电池单体，众多PPTC单元的电流最终会迅速地被控制在额定的范围内，整个单体的电流会汇聚到内部短路处，但由于单个电池单体的容量在安全阈值内，电流汇聚产生的热量在安全范围内，该内部短路处不会发生热失控。
2.这需要电池管理系统的协调管理来解决这个问题。目前一辆电动车有几千个电池单体，这些电池单体会以串并联的方式组合工作，图2是电池一种串并联的示意图。图2中，电池单体101、102和103属于电池串1，电池单体101发生内部短路时，其他串的电池会向电池串1汇聚，电池管理系统实时监控每一路电池串的电流，当流经电池串1的电流超过安全阈值时，电池管理系统将会立即关断继电器110，从而将电池串1与其他电路隔离开来，并且在系统中记录，提醒发生了短路。另一种情况是电池单体101发生内部短路，而流经电池串1的电流还没有超过安全阈值时，继电器110没有被切断，但因为电池单体101发生内部短路，电池串1与其他串之间的总电压是不平衡的，对整个电池组运行是不利的。电池管理系统实时监控每个电池单体的电压，随着短路放电的进行，电池单体101的电压将会一直下降，当其放电完毕时，电压将会降到近乎0，电池管理系统可以实时监控到这个情况，将关断继电器110，从而将电池串1与其他电路隔离开来，并且在系统中记录，提醒发生了短路。图2中，电池单体101没有与其直接并联的电池单体，所以不需要考虑监控并关断与其并联的电池单体，比较简单。图2中，电池单体101是与电池单体102和103串联成为电池串1后，与其他电池串再进行并联的，串联电路的特点是电池单体101与电池单体102和103的电流是一样的，这样电池单体101发生内部短路时，只要电池单体102和103不发生短路，电池单体102和103中的PPTC单元就会对电流进行限流，从而使得电流串1的电流最终会迅速地被控制在额定的范围内，因而这种串并联结构稳定性比较好。图2只是作为一个示范例子阐述本发明的核心精神，而不是对本发明的限制，实际实施中，可以采用任何合适的电池单体组合形式。
电池制造好以后，需要定期的维护保养，以确保其能持续可靠工作。
维护保养方法：对每一个电池单体，在极短时间内接通一个电阻值很低的负载，时间极短是为了减少对电池的消耗和冲击，然后实时监控负载的电压电流值，如果电池单体的PPTC结构功能正常，则负载的电流值应该会迅速被稳定在额定的范围内，如果电池单体的PPTC 结构功能失效，则负载的电流值就不会迅速被稳定在额定的范围内。通过分析负载的电压电流值，就可以判断电池单体的PPTC结构功能是否正常。这就相当于给电池做体检，不正常的电池单体(甚至整个电池串)就可以进行更换，更换好后还可以对该电池单体(甚至所在的整个电池串)再体检一次，这样就更稳妥了，直到所有结果都正常。电池需要定期进行体检，对于电动车，车子也需要定期保养，通常是每年一次，在车子保养的时候，同时就可以对电动车的电池进行体检。电池管理系统可以与电动车的整车管理系统连通，电池管理系统对体检进行管理，到过了时间而没做体检，就会发出提醒，拖延的时间越长，提醒的级别可以提高，以引起电动车用户的注意。
因为电池管理系统本身就对每一个电池单体进行实时监控，所以可以在电池管理系统中添加上述的维护保养设施。为了降低成本，也可以设立单独的维护保养设施，这样用户去做保养时，保养维修店提供单独的维护保养设施，电池管理系统可以提供相应的硬件和软件接口，方便单独的维护保养设施进行体检。
云端数据库：每个电池，每个电池串，每个单体可以有唯一的标识码，在联网的数据库中，详细保存每个电池，每个电池串，每个单体的：1.出厂日期。2.出厂时标识码、型号、电压、电流、容量等参数。3.维修记录，在哪个时间，有哪个维修师傅，做了什么维修操作，具体记录。4.体检记录，在哪个时间，有哪个维修师傅，做了什么保养操作，具体记录。
有了这样详细的质量追溯管控记录，就可以进行对电池进行终生跟踪管理。
本发明在现有正极结构中发现了隐藏着的PPTC结构，将其发掘出来并加以强化，本发明的优点是与现有锂电池的生产工艺兼容，这样只需要极小的改动成本，就可以增强锂电池的安全性能。随着电动小汽车的普及，用户越来越关注电动小汽车电池自燃的问题，用户期待电动小汽车电池可以实现零自燃风险，本发明将会有助于实现这一目标。
上面结合附图和实施例描述了发明的方法以及具体实施例，熟悉本技术领域的人员可以理解，本发明可以有许多不同的实施方式。因此，应该理解，本发明并不局限于所描述的优选实施例，正如随附权利要求书所给出的本发明的精神实质，本发明包括其专利保护范围内所进行的各种更换、变动和修改。

Claims (10)

  1. 一种电池极片的改造方法，其特征在于，对电池的极片结构进行PPTC(Polymeric Positive Temperature Coefficient)结构强化的措施。
  2. 根据权利要求1所述的措施，强化措施是以下所列的任意部分组合或者全部：
    a)对极片的高分子聚合物进行交联处理。
    b)以两种以上不同熔点的高分子聚合物代替单一高分子聚合物作为极片胶粘剂。
    c)添加电阻率低的导电颗粒。
    d)调整极片各种物质的比例。
    e)极片的高分子聚合物采用低熔点共聚物。
    f)对极片进行热退火处理。
  3. 根据权利要求2所述的a)对极片的高分子聚合物进行交联处理，优选采用电子束交联。
  4. 根据权利要求2所述的b)以两种以上不同熔点的高分子聚合物代替单一高分子聚合物作为极片胶粘剂，优选采用PVDF-HFP(Polyvinylidene fluoride-hexafluoropropylene copolymer，聚偏氟乙烯-六氟丙烯共聚物)和PVDF(polyvinylidene fluoride，聚偏氟乙烯)。
  5. 根据权利要求2所述的c)添加电阻率低的导电颗粒，包括但不限于以下材料，或者是以下材料之间的组合物：导电炭黑或者纳米级碳纳米管，金属粉，已知金属材料的粉末，如镍、铜、铝、锡、锌、银、金等等，碳化金属粉末，包括碳化钛、碳化钨、碳化钛硅、碳化钛铝或碳化钛锡等等。
  6. 根据权利要求2所述的e)极片的高分子聚合物采用低熔点共聚物，优选PVDF-HFP(Polyvinylidene fluoride-hexafluoropropylene copolymer，聚偏氟乙烯-六氟丙烯共聚物)，优先选择熔点在100℃至130℃之间的共聚物。
  7. 根据权利要求1所述的电池极片，其所属的电池的活性材料包括但不限于锂、钠。
  8. 根据权利要求1所述的电池极片，其所属的电池类型包括但不限于锂离子电池、锂固体电池、锂金属电池、燃料电池等各种各样的电池形式。
  9. 根据权利要求1所述的电池极片，可以是正极片，也可以是负极片。
  10. 一种电池，其特征在于，所述电池极片是包含权利要求1～8项的任意部分组合或者全部方法制备得到的。
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CN115133029A (zh) * 2021-03-24 2022-09-30 詹馥微 一种锂电池极片的改造方法和锂电池

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