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CN-122025540-A - Positive electrode plate, preparation method thereof, lithium ion battery and electric equipment

CN122025540ACN 122025540 ACN122025540 ACN 122025540ACN-122025540-A

Abstract

The invention discloses a positive pole piece, a preparation method thereof, a lithium ion battery and electric equipment, and relates to the technical field of lithium ion batteries. The positive temperature coefficient functional layer is introduced between the positive electrode current collector and the positive electrode active coating, and has the characteristic that the ratio of the resistivity at the temperature of more than 80 ℃ to the resistivity at the temperature of 25 ℃ is more than 400%. The positive temperature coefficient functional layer can maintain a stable electronic conduction state at normal temperature, and controllable volume expansion occurs when the temperature exceeds about 80 ℃, so that the conductive network is destroyed, thereby obviously increasing the resistivity, realizing active interruption of an electronic transmission path, restraining occurrence of thermal runaway from the source and improving the safety performance of the battery.

Inventors

  • WANG KAI
  • CHEN FEIFAN

Assignees

  • 江苏睿恩新能源科技有限公司

Dates

Publication Date
20260512
Application Date
20260226

Claims (10)

  1. 1. The positive electrode plate is characterized by comprising a positive electrode current collector, wherein a positive temperature coefficient functional layer and a positive electrode active material layer are arranged on at least one side surface of the positive electrode current collector, the positive temperature coefficient functional layer is positioned between the positive electrode current collector and the positive electrode active material layer, and the ratio of the resistivity of the positive temperature coefficient functional layer at the temperature of more than 80 ℃ to the resistivity of the positive electrode active material layer at the temperature of 25 ℃ is more than 400%.
  2. 2. The positive electrode sheet according to claim 1, wherein the positive temperature coefficient functional layer contains 30% -40% of carbon-coated lithium iron phosphate, 50% -60% of a first binder and 5% -15% of a first conductive agent in terms of mass fraction.
  3. 3. The positive electrode sheet according to claim 2, wherein the first binder is selected from at least one of polyvinylidene fluoride, polyacrylic acid, and polyimide; and/or the first conductive agent is selected from at least one of conductive carbon black, carbon nanotubes and conductive graphene; and/or the thickness of the carbon layer in the carbon-coated lithium iron phosphate is 2.5nm-5.0nm, and the average particle diameter of the carbon-coated lithium iron phosphate particles is 100nm-500nm; And/or the positive temperature coefficient functional layer has a thickness of 1 μm to 3 μm.
  4. 4. The positive electrode sheet according to claim 1, wherein the positive electrode active material in the positive electrode active material layer is selected from at least one of lithium nickel cobalt manganate, lithium cobalt oxide, and lithium nickel cobalt aluminate; and/or, the positive electrode active material layer contains 95-97% of positive electrode active material, 1-3% of second binder and 1-3% of second conductive agent by mass fraction, preferably, the second conductive agent comprises conductive carbon black and carbon nano tube, the mass ratio of the conductive carbon black to the carbon nano tube is 1 (0.5-1.5), preferably, the second binder is at least one of polyvinylidene fluoride and polyacrylic acid.
  5. 5. The positive electrode sheet according to claim 1 or 4, wherein the positive electrode active material layer has a thickness of 40 μm to 80 μm; And/or the thickness of the positive electrode current collector is 3-10 μm; And/or the material of the positive electrode current collector is aluminum.
  6. 6. A method for preparing a positive electrode sheet according to any one of claims 1 to 5, comprising sequentially forming the positive temperature coefficient functional layer and the positive electrode active material layer on the positive electrode current collector.
  7. 7. The preparation method of the positive temperature coefficient functional layer according to claim 6, wherein the preparation process of the positive temperature coefficient functional layer comprises the steps of coating carbon-coated lithium iron phosphate, a first binder, a first conductive agent and a solvent to obtain functional layer slurry, coating the functional layer slurry on the positive electrode current collector, and drying, wherein the solid content of the functional layer slurry is preferably 25-35 wt%, and the drying temperature is preferably controlled to be 90-110 ℃ and the drying time is preferably 1-3 h when the positive temperature coefficient functional layer is prepared; And/or, before the positive temperature coefficient functional layer is prepared, carrying out surface cleaning on the positive electrode current collector, wherein the surface cleaning preferably comprises alkali cleaning, acid cleaning, water cleaning and drying in sequence, and more preferably, the alkali cleaning is carried out by using a sodium hydroxide solution, and the acid cleaning is carried out by using a nitric acid solution.
  8. 8. The method according to claim 6, wherein the positive electrode active material layer is prepared by coating positive electrode slurry on the positive temperature coefficient functional layer, drying, rolling, and controlling the compaction density to 3.3mg/cm 3 -3.8mg/cm 3 ; preferably, the preparation process of the positive electrode slurry includes mixing a positive electrode active material, a second binder, a second conductive agent, and a solvent.
  9. 9. A lithium ion battery, characterized by comprising the positive electrode sheet according to any one of claims 1 to 5 or the positive electrode sheet prepared by the preparation method according to any one of claims 6 to 8; preferably, the lithium ion battery further comprises a negative electrode plate, a diaphragm and electrolyte, wherein the electrolyte contains a flame retardant; more preferably, the flame retardant is at least one selected from triethyl phosphate, dimethyl methylphosphonate and ammonium trifluorophosphate, and the mass fraction of the flame retardant in the electrolyte is 1.0% -3.0%; preferably, the lithium ion battery is subjected to needling test, no fire or explosion phenomenon occurs under the conditions that the diameter of a steel nail is 3mm and the piercing speed is 10mm/s, and the highest surface temperature is less than or equal to 110 ℃; preferably, in the 70% deformation extrusion test, the battery does not generate fire or explosion phenomena, and the highest surface temperature is less than or equal to 100 ℃.
  10. 10. A powered device comprising the lithium-ion battery of claim 9.

Description

Positive electrode plate, preparation method thereof, lithium ion battery and electric equipment Technical Field The invention relates to the technical field of lithium ion batteries, in particular to a positive pole piece, a preparation method thereof, a lithium ion battery and electric equipment. Background With the wide application of lithium ion batteries in electric vehicles, portable electronic devices and energy storage systems, the energy density of the lithium ion batteries is continuously improved, and the thermal safety problems of the batteries under abnormal working conditions such as overcharging, internal short circuit, mechanical damage, local overheating and the like are increasingly prominent. The existing safety strategies mainly depend on a diaphragm thermal shutdown, an electrolyte flame retardant additive or an external thermal management system, but most of the schemes belong to passive response or external regulation, so that local abnormal heat sources inside the pole piece are difficult to suppress in time, and particularly active cutting of an electronic conduction path cannot be realized at the early stage of a battery cell, so that further amplification of thermal runaway is prevented. The existing positive electrode plate is generally formed by directly compounding an aluminum current collector and a positive electrode active material layer, and still maintains a continuous conductive state when the temperature is abnormally increased, so that abnormal current is easy to continuously flow and heat accumulation is aggravated. Although PTC elements have been used for circuit level protection, they are typically located outside the cell or at the module level, are difficult to precisely couple with the thermal evolution process at the pole piece scale, and have problems of response delay, difficulty in integration, etc. Therefore, there is a need to develop functional structures that can rapidly and actively trigger resistance transitions and interrupt electron channels under high temperature conditions to achieve suppression of thermal runaway sources from material and structure levels. In view of this, the present invention has been made. Disclosure of Invention The invention aims to provide a positive electrode plate, a preparation method thereof, a lithium ion battery and electric equipment, and aims to provide a functional structure for rapidly and actively triggering resistance to jump and interrupt an electronic channel so as to inhibit occurrence of thermal runaway from the source and improve the safety performance of the battery. The invention is realized in the following way: in a first aspect, the invention provides a positive electrode plate, which comprises a positive electrode current collector, wherein a positive temperature coefficient functional layer and a positive electrode active material layer are arranged on at least one side surface of the positive electrode current collector, the positive temperature coefficient functional layer is positioned between the positive electrode current collector and the positive electrode active material layer, and the ratio of the resistivity of the positive temperature coefficient functional layer at a temperature of more than 80 ℃ to the resistivity of the positive electrode active material layer at a temperature of 25 ℃ is more than 400%. In an alternative embodiment, the positive temperature coefficient functional layer contains 30% -40% of carbon-coated lithium iron phosphate, 50% -60% of a first binder and 5% -15% of a first conductive agent according to mass fraction. In an alternative embodiment, the first binder is selected from at least one of polyvinylidene fluoride, polyacrylic acid, and polyimide; And/or the first conductive agent is selected from at least one of conductive carbon black, carbon nanotubes and conductive graphene; and/or the thickness of the carbon layer in the carbon-coated lithium iron phosphate is 2.5nm-5.0nm, and the average particle diameter of the carbon-coated lithium iron phosphate particles is 100nm-500nm; and/or the positive temperature coefficient functional layer has a thickness of 1 μm to 3 μm. In an alternative embodiment, the positive electrode active material in the positive electrode active material layer is selected from at least one of lithium nickel cobalt manganese oxide, lithium cobalt oxide, and lithium nickel cobalt aluminate; and/or the positive electrode active material layer contains 95-97% of positive electrode active material, 1-3% of second binder and 1-3% of second conductive agent according to mass fraction, wherein the second conductive agent preferably comprises conductive carbon black and carbon nano tubes, the mass ratio of the conductive carbon black to the carbon nano tubes is 1 (0.5-1.5), and the second binder preferably is at least one of polyvinylidene fluoride and polyacrylic acid. In an alternative embodiment, the thickness of the positive electrode active m