Current collector with safety protection mechanism

Abstract

The invention discloses a current collector with a safety protection mechanism, and relates to the technical field of lithium batteries. Comprising a macromolecular base membrane, an aluminum chloride layer and a metal aluminum layer, the aluminum chloride layer is arranged between the macromolecular base membrane and the metal aluminum layer; the surface of the current collector is provided with a polymer film layer, and the polymer film layer is composed of carbon nanotubes and poly (3-dodecyl thiophene); when the temperature of the battery is abnormal, the aluminum chloride reacts with the metal aluminum layer, and the resistance is increased, and when the temperature continuously rises, the aluminum chloride further reacts with the metal aluminum layer, and electron transmission is blocked, so that the current collector loses the conductive effect, and spontaneous combustion and explosion of the battery caused by temperature rise are prevented.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and specifically to a current collector with a safety protection mechanism. Background Art

[0002] The main reasons for the spontaneous combustion of lithium batteries include overcharging, short circuit, external force damage, and manufacturing defects. Overcharging can cause lithium ions to accumulate at the negative electrode, forming lithium dendrites, which may pierce the separator, resulting in internal short circuit and fire. A short circuit may be caused by external factors that lead to too high a battery temperature, damage the battery separator, cause internal heat accumulation, and thus trigger combustion. External force damage such as extrusion or puncture will directly damage the battery structure, resulting in short circuit and fire. In addition, impurities or uneven electrode coatings during the manufacturing process may also cause internal short circuit, increasing the fire risk. To prevent the spontaneous combustion of lithium batteries, it is recommended to avoid overcharging and over-discharging, keep the battery working at an appropriate temperature, and avoid external force damage to the battery. In addition, choosing reliable batteries and charging devices is also an important measure to ensure safety.

[0003] In existing lithium batteries, "thermal runaway" of the battery is caused by too high a battery internal temperature. When the battery temperature is too high, the separator is damaged, resulting in a short circuit, and the probability of lithium dendrite growth increases. The battery short circuit will further generate a large amount of heat, the electrolyte decomposes, generating combustible organic substances and gases, greatly increasing the risk of battery combustion and explosion. The specific inducements are as follows:

[0004] 1. Long-term overcharging of the battery cell: Under a long charging state, overcharging and overcurrent will also lead to high temperature and high pressure, posing potential hazards. Lithium batteries may instantaneously discharge to generate a large amount of current under special temperature, humidity, and poor contact conditions, resulting in spontaneous combustion or explosion.

[0005] 2. Battery short circuit: When the mobile phone is in a high temperature state, or is subjected to impacts, metal friction, etc., it may cause a battery short circuit and explosion.

[0006] 3. Charging causing battery explosion: Playing with the mobile phone while charging will cause the charging time to become longer. Long-time charging will cause the mobile phone temperature to rise and is more likely to explode.

[0007] 4. Mismatch between the charger and the battery: Chargers with incorrect models are likely to cause battery accidents.

[0008] 5. Too high temperature: Too high temperature means that the internal heat of the battery reaches the limit. Long-time charging, high temperature irradiation, and baking are all likely to cause the battery temperature to be too high.

[0009] 6. Thermal runaway: The reason why lithium-ion batteries are at risk of explosion is due to a process called "thermal runaway" in the internal reaction of the battery.

[0010] Therefore, for thermal runaway, we add a safety protection mechanism on the current collector to prevent the current conduction when the lithium-ion battery is in danger, so that it cannot undergo thermal runaway, thereby improving the safety of the lithium battery. Summary of the Invention

[0011] The purpose of the present invention is to provide a current collector with a safety protection mechanism to solve the problems raised in the prior art.

[0012] To achieve the above purpose, the present invention provides the following technical solutions:

[0013] A current collector with a safety protection mechanism includes a polymer-based film, an aluminum chloride layer, and a metallic aluminum layer; the aluminum chloride layer is disposed between the polymer-based film and the metallic aluminum layer.

[0014] Furthermore, the thickness of the aluminum chloride layer is 1 - 3 μm; the polymer-based film is any one of a polypropylene film and a polyester film, with a thickness of 1 - 10 μm; the aluminum content of the metallic aluminum layer > 99%, and the thickness is 0.5 - 3 μm;

[0015] The preparation method of the above current collector with a safety protection mechanism includes the following preparation steps:

[0016] Step 1: Select a polymer-based film, and use evaporation coating. Place the polymer-based film above the evaporation source, and place the aluminum chloride raw material in the evaporation source. After evacuating to 10 -3 -10 -5 Pa, raise the temperature of the evaporation source to 1000 - 1100 °C, and deposit the aluminum chloride layer on the upper and lower surfaces of the polymer-based film;

[0017] Step 2: After the deposition of the aluminum chloride layer in Step 1 is completed, evaporate and deposit a layer of metallic aluminum layer on the surface of the aluminum chloride layer. Place the aluminum wire in the evaporation source, evacuate to 10 -3 -10 -5 Pa, and raise the temperature of the evaporation source to 1350 - 1500 °C to obtain the current collector;

[0018] An electrode includes the above current collector, a polymer layer scraped on the surface of the current collector, and an active material coated on the surface of the polymer layer.

[0019] Furthermore, the specific preparation steps of the above electrode are as follows:

[0020] Step S1: Place the polymer-modified carbon nanotubes in a chloroform solution, ultrasonically disperse for 30 - 40 min, then add poly(3-dodecylthiophene) and stir until dissolved to obtain a polymer coating,

[0021] Step S2: Chemically etch the surface of the current collector, immerse it in the etching solution, take it out after etching for 1 - 2 minutes at 20 - 30°C, ultrasonically clean it with acetone, and then scrape and coat the polymer coating prepared in Step S2 to form a polymer film layer with a thickness of 200 - 300 nm on the surface of the current collector;

[0022] Step S3: Coat the active material on the surface of the polymer film layer prepared in Step S2 to obtain the electrode;

[0023] Among them, the dosage ratio of the polymer - modified carbon nanotubes and poly(3 - dodecylthiophene) in Step S1 is 0.05 mg : 0.1 - 0.3 mg / mL.

[0024] The polymer - modified carbon nanotubes are obtained by the following preparation steps:

[0025] Step s1: Place the carbon nanotubes in a mixed acid solution and ultrasonically disperse them for 2 h, then wash them with water until neutral, dry them, add deionized water and ultrasonically disperse for 30 - 40 min, add dopamine hydrochloride and stir for 1 - 2 h, then add Tris - HCl buffer solution and an alkali solution, adjust the pH of the system to 8.5, raise the temperature to 60°C, stir for 10 - 12 h, cool and separate the precipitate, vacuum - dry for 12 h, then take it out and heat it to 300 - 400°C for 2 - 3 h of heat preservation, and cool to obtain nitrogen - doped carbon nanotubes;

[0026] Step s2: Under a protective atmosphere, add the nitrogen - doped carbon nanotubes prepared in Step s1 and ferric chloride to an acetonitrile solvent and ultrasonically disperse for 30 - 40 min, dropwise add an acetonitrile solution of 3 - dodecylthiophene and react for 12 h, then pour it into methanol for sedimentation, wash it, add it to saturated hydrazine hydrate and stir overnight, separate and vacuum - dry to obtain polymer - modified carbon nanotubes;

[0027] Among them, the dosage ratio of carbon nanotubes and dopamine hydrochloride in Step s1 is 1:(1 - 2); the mixed acid solution is composed of nitric acid and sulfuric acid with a volume ratio of 1:3; the dosage ratio of nitrogen - doped carbon nanotubes and 3 - dodecylthiophene in Step s2 is 0.5 g : 0.1 mL.

[0028] Compared with the prior art, the beneficial effects of the present invention are:

[0029] 1. Add a layer of aluminum chloride between the polymer - based film and the metal aluminum layer, which effectively plays a safety protection role. When the battery undergoes thermal runaway and the temperature reaches 150°C, aluminum chloride begins to react with the metal aluminum layer, increasing the resistance of the current collector. When the temperature reaches 170°C, the reaction accelerates, and at this time, the current collector has been forced to lose its conductive function. When the temperature is greater than 200°C, aluminum chloride corrodes the metal aluminum layer, making it non - conductive, and preventing the explosion, spontaneous combustion and other hazards caused by the thermal runaway of the battery;

[0030] 2. A polymer film layer is provided on the surface of the current collector, and poly (3-dodecylthiophene) mixed with carbon nanotubes is used; poly (3-dodecylthiophene) is a PTC material, which is a good conductor at room temperature, but when the temperature rises to the resistance switching temperature, the resistivity increases sharply. When it is coated on the surface of the current collector, when the battery temperature rises abnormally, it can effectively cut off the electron transmission between the current collector and the active material, interrupt the battery reaction, and provide a kind of overheating protection for the battery; the polymer modified carbon nanotubes added in the coating are obtained by depositing carbon nanotubes with dopamine and then pyrolyzing them to obtain nitrogen-doped carbon nanotubes, which improves the uniformity of the subsequent polymer coating, and is blended with poly (3-dodecylthiophene) to improve the dispersion of carbon nanotubes in the system and the uniformity of the polymer film layer; the polymer film layer and the aluminum chloride layer synergistically improve the safety protection of the current collector. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a schematic diagram of the structure of the electrode manufactured in Example 1. DETAILED DESCRIPTION

[0032] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] In the experiment, the etching solution was ANPE 80 / 5 / 5 / 10, from Microchemicals; poly(3-dodecylthiophene) with an average MW of 27,000 was purchased from Shanghai Aladdin; the carbon nanotubes had a diameter of 10-20 nm and were purchased from Xianfeng Nano.

[0034] The negative electrode sheet used in the assembled battery is a metal copper foil with a purity of >99%; the negative active materials include: 95% graphite: BFC series of BYD, 2% SP: Cabot Li-300, 1.5% CMC: FH6-A of Shandong Weifang Lite Composite Materials Co., Ltd., 1.5% SBR: Lanxess MP62;

[0035] The diaphragm is a 3+9+3 ceramic diaphragm purchased from Enjie;

[0036] The electrolyte was D90, purchased from Xinzhoubang;

[0037] The outer packaging is aluminum shell;

[0038] The positive electrode active materials include: 97% NCM: Defang Nano S90F, 1% SP: Cabot Li-300, 2% PVDF: Fluoroline 24937-79-9;

[0039] Example 1: A battery was prepared in this example, and the specific steps are as follows:

[0040] Step 1: Select a PET base film with a thickness of 6 μm. Using evaporation coating, place the PET base film above the evaporation source, and place the aluminum chloride raw material in the evaporation source. After evacuating to 10 -5 Pa, raise the temperature of the evaporation source to 1000 °C, and deposit a 1-μm aluminum chloride layer on the upper and lower surfaces of the PET base film;

[0041] Step 2: After the deposition of the aluminum chloride layer in Step 1 is completed, evaporate and deposit a 1-μm metal aluminum layer on the surface of the aluminum chloride layer. Place the aluminum wire in the evaporation source. After evacuating to 10 -5 Pa, raise the temperature of the evaporation source to 1500 °C to obtain the current collector;

[0042] Step 3: Coat the positive electrode active material on the surface of the current collector prepared in Step 2 to obtain a positive electrode plate, and assemble it with the negative electrode plate, separator, and electrolyte to obtain a battery.

[0043] Example 2: Referring to Example 1, adjust the thickness of the aluminum chloride layer to 2 μm, and the specific steps are as follows:

[0044] Step 1: Select a PET base film with a thickness of 6 μm. Using evaporation coating, place the PET base film above the evaporation source, and place the aluminum chloride raw material in the evaporation source. After evacuating to 10 -5 Pa, raise the temperature of the evaporation source to 1000 °C, and deposit a 2-μm aluminum chloride layer on the upper and lower surfaces of the PET base film;

[0045] Step 2: After the deposition of the aluminum chloride layer in Step 1 is completed, evaporate and deposit a 1-μm metal aluminum layer on the surface of the aluminum chloride layer. Place the aluminum wire in the evaporation source. After evacuating to 10 -5 Pa, raise the temperature of the evaporation source to 1500 °C to obtain the current collector;

[0046] Step 3: Coat the positive electrode active material on the surface of the current collector prepared in Step 2 to obtain a positive electrode plate, and assemble it with the negative electrode plate, separator, and electrolyte to obtain a battery.

[0047] Example 3: Referring to Example 1, adjust the thickness of the aluminum chloride layer to 3 μm, and the specific steps are as follows:

[0048] Step 1: Select a PET base film with a thickness of 6 μm. Using evaporation coating, place the PET base film above the evaporation source, and place the aluminum chloride raw material in the evaporation source. After evacuating to 10 -5 Pa, raise the temperature of the evaporation source to 1000 °C, and deposit a 3-μm aluminum chloride layer on the upper and lower surfaces of the PET base film;

[0049] Step 2: After the deposition of the aluminum chloride layer in Step 1 is completed, evaporate and deposit a 1-μm metal aluminum layer on the surface of the aluminum chloride layer. Place the aluminum wire in the evaporation source, evacuate to 10 -5 Pa, and then raise the temperature of the evaporation source to 1500 °C to obtain the current collector;

[0050] Step 3: Coat the positive electrode active material on the surface of the current collector prepared in Step 2 to obtain a positive electrode plate, and assemble it with a negative electrode plate, a separator, and an electrolyte to obtain a battery.

[0051] Example 4: Referring to Example 1, coat a polymer film layer on the surface of the current collector. The specific steps are as follows:

[0052] Step 1: Select a PET base film with a thickness of 6 μm. Using evaporation coating, place the PET base film above the evaporation source and the aluminum chloride raw material in the evaporation source. Evacuate to 10 -5 Pa, then raise the temperature of the evaporation source to 1000 °C to deposit a 1-μm aluminum chloride layer on the upper and lower surfaces of the PET base film;

[0053] Step 2: After the deposition of the aluminum chloride layer in Step 1 is completed, evaporate and deposit a 1-μm metal aluminum layer on the surface of the aluminum chloride layer. Place the aluminum wire in the evaporation source, evacuate to 10 -5 Pa, and then raise the temperature of the evaporation source to 1500 °C to obtain the current collector;

[0054] Step 3: Chemically etch the current collector, immerse it in the etching solution, take it out after etching for 2 min at 25 °C, ultrasonically clean it with acetone, then scrape and coat the polymer coating, and volatilize the solvent at room temperature to form a polymer film layer with a thickness of 200 nm on the surface of the current collector;

[0055] Step 4: Coat the positive electrode active material on the polymer film layer surface of the current collector to obtain a positive electrode plate, and assemble it with a negative electrode plate, a separator, and an electrolyte to obtain a battery;

[0056] Among them, the preparation steps of the polymer coating are as follows:

[0057] Step S1: Place 0.5 g of carbon nanotubes in a 20-mL mixed solution of nitric acid and sulfuric acid with a volume ratio of 1:3, ultrasonically disperse for 2 h, wash with deionized water until the filtrate is neutral, dry, add 20 mL of deionized water, ultrasonically disperse for 30 min, add 1 g of hydrochloric acid dopamine, stir for 1 h, then add Tris-HCl buffer solution and alkali solution, adjust the pH of the system to 8.5, raise the temperature to 60 °C, stir for 10 h, cool, separate the precipitate, vacuum dry for 12 h, then take it out and heat to 300 °C and keep it warm for 2 h. After natural cooling, obtain nitrogen-doped carbon nanotubes;

[0058] Step S2: Under an argon atmosphere, add the nitrogen-doped carbon nanotubes prepared in Step S1 and 0.2 g of ferric chloride to 100 mL of acetonitrile solvent and ultrasonically disperse for 30 min. Gradually add 50 mL of an acetonitrile solution mixed with 0.1 mL of 3-dodecylthiophene dropwise to the above reaction solution. After waiting for the reaction for 12 h, slowly pour it into methanol for sedimentation. Separate the solid, wash it until the filtrate is colorless, then add it to saturated hydrazine hydrate and stir overnight. Separate the product for Soxhlet extraction. Place it in a Soxhlet extractor and repeatedly extract with methanol at 65 °C for 24 h to remove impurities. After vacuum drying, polymer-modified carbon nanotubes are obtained;

[0059] Step S3: Take 0.05 mg of the polymer-modified carbon nanotubes prepared in Step S2, place them in 10 mL of chloroform solution, ultrasonically disperse for 30 min, and then add 3 mg of poly(3-dodecylthiophene) and stir until dissolved to obtain a polymer coating.

[0060] Example 5: Refer to Example 4 and adjust the thickness of the polymer film layer to 300 nm. The specific steps are as follows:

[0061] Step 1: Select a PET base film with a thickness of 6 μm. Using evaporation coating, place the PET base film above the evaporation source and place the aluminum chloride raw material in the evaporation source. After evacuating to 10 -5 Pa, raise the temperature of the evaporation source to 1000 °C and deposit a 1-μm aluminum chloride layer on the upper and lower surfaces of the PET base film;

[0062] Step 2: After the deposition of the aluminum chloride layer in Step 1 is completed, evaporate a 1-μm metal aluminum layer on the surface of the aluminum chloride layer. Place the aluminum wire in the evaporation source. After evacuating to 10 -5 Pa, raise the temperature of the evaporation source to 1500 °C to obtain the current collector;

[0063] Step 3: Chemically etch the current collector, immerse it in the etching solution, take it out after etching at 25 °C for 2 min, ultrasonically clean it with acetone, and then scrape and coat the polymer coating. Volatilize the solvent at room temperature to form a polymer film layer with a thickness of 300 nm on the surface of the current collector;

[0064] Step 4: Coat the positive electrode active material on the polymer film layer surface of the current collector to obtain a positive electrode plate, and assemble it with the negative electrode plate, separator, and electrolyte to obtain a battery;

[0065] Among them, the preparation steps of the polymer coating are as follows:

[0066] Step S1: Place 0.5 g of carbon nanotubes in 20 mL of a nitric acid and sulfuric acid mixture with a volume ratio of 1:3, ultrasonically disperse for 2 h, wash with deionized water until the filtrate is neutral, dry, add 20 mL of deionized water, ultrasonically disperse for 30 min, add 1 g of dopamine hydrochloride, stir for 1 h, then add Tris-HCl buffer solution and an alkali solution, adjust the pH of the system to 8.5, raise the temperature to 60 °C, stir for 10 h, separate the precipitate after cooling, vacuum dry for 12 h, then take out and heat to 300 °C and keep warm for 2 h. After natural cooling, nitrogen-doped carbon nanotubes are obtained;

[0067] Step S2: Under an argon atmosphere, add the nitrogen-doped carbon nanotubes prepared in Step S1 and 0.2 g of ferric chloride to 100 mL of acetonitrile solvent, ultrasonically disperse for 30 min, dropwise add 50 mL of an acetonitrile solution mixed with 0.1 mL of 3-dodecylthiophene to the above reaction solution, wait for the reaction for 12 h, then slowly pour it into methanol for sedimentation, separate the solid, wash until the filtrate is colorless, then add it to saturated hydrazine hydrate and stir overnight, separate the product for Soxhlet extraction, place it in a Soxhlet extractor, and repeatedly extract with methanol at 65 °C for 24 h to remove impurities. After vacuum drying, polymer-modified carbon nanotubes are obtained;

[0068] Step S3: Take 0.05 mg of the polymer-modified carbon nanotubes prepared in Step S2, place them in 10 mL of chloroform solution, ultrasonically disperse for 30 min, then add 3 mg of poly(3-dodecylthiophene) and stir until dissolved to obtain a polymer coating.

[0069] Comparative Example 1: Select a traditional current collector: a metal foil with a thickness of 13 μm, grade 1100, purchased from Nano;

[0070] Coat the surface of the traditional current collector with a positive electrode active material to obtain a positive electrode plate, and assemble it with a negative electrode plate, a separator, and an electrolyte to obtain a battery.

[0071] Comparative Example 2: Select a composite current collector: the middle is made of PET material with a thickness of 6 μm, and both sides are plated with aluminum layers with a thickness of 1 μm, purchased from Nali;

[0072] Coat the surface of the composite current collector with a positive electrode active material to obtain a positive electrode plate, and assemble it with a negative electrode plate, a separator, and an electrolyte to obtain a battery.

[0073] Comparative Example 3: As a comparative experiment for Example 5, do not perform a nitrogen-doped layer on the polymer-modified carbon nanotubes. The specific steps are as follows:

[0074] Step 1: Select a PET base film with a thickness of 6 μm, use evaporation coating, place the PET base film above the evaporation source, place the aluminum chloride raw material in the evaporation source, evacuate to 10 -5After reaching 10 Pa, raise the temperature of the evaporation source to 1000 °C, and deposit a 1-μm aluminum chloride layer on the upper and lower surfaces of the PET base film;

[0075] Step 2: After the deposition of the aluminum chloride layer in Step 1 is completed, evaporate a 1-μm aluminum metal layer on the surface of the aluminum chloride layer. Place the aluminum wire in the evaporation source, evacuate to 10 -5 Pa, and then raise the temperature of the evaporation source to 1500 °C to obtain the current collector;

[0076] Step 3: Chemically etch the current collector, immerse it in the etching solution, take it out after etching for 2 minutes at 25 °C, ultrasonically clean it with acetone, then scrape and coat the polymer coating, and volatilize the solvent at room temperature to form a polymer film layer with a thickness of 300 nm on the surface of the current collector;

[0077] Step 4: Coat the positive electrode active material on the polymer film layer of the current collector to obtain a positive electrode plate, and assemble it with a negative electrode plate, a separator, and an electrolyte to obtain a battery;

[0078] Among them, the preparation steps of the polymer coating are as follows:

[0079] Step S1: Place 0.5 g of carbon nanotubes in a 20-mL mixed solution of nitric acid and sulfuric acid with a volume ratio of 1:3, ultrasonically disperse for 2 hours, wash with deionized water until the filtrate is neutral, dry, and under an argon atmosphere, add 0.2 g of ferric chloride to 100 mL of acetonitrile solvent and ultrasonically disperse for 30 minutes. Gradually add 50 mL of an acetonitrile solution mixed with 0.1 mL of 3-dodecylthiophene dropwise to the above reaction solution. After waiting for the reaction for 12 hours, slowly pour it into methanol for sedimentation, separate the solid, wash until the filtrate is colorless, then add it to saturated hydrazine hydrate and stir overnight. Separate the product for Soxhlet extraction, place it in a Soxhlet extractor, and repeatedly extract with methanol at 65 °C for 24 hours to remove impurities. After vacuum drying, obtain polymer-modified carbon nanotubes;

[0080] Step S3: Take 0.05 mg of the polymer-modified carbon nanotubes prepared in Step S2, place them in 10 mL of chloroform solution, ultrasonically disperse for 30 minutes, and then add 3 mg of poly(3-dodecylthiophene) and stir until dissolved to obtain the polymer coating.

[0081] Comparative Example 4: As a comparative experiment of Example 1, adjust the thickness of the aluminum chloride layer to 100 nm, and the specific steps are as follows:

[0082] Step 1: Select a PET base film with a thickness of 6 μm, and use evaporation coating. Place the PET base film above the evaporation source, and place the aluminum chloride raw material in the evaporation source. Evacuate to 10 -5 Pa, then raise the temperature of the evaporation source to 1000 °C, and deposit a 100-nm aluminum chloride layer on the upper and lower surfaces of the PET base film;

[0083] Step 2: After the deposition of the aluminum chloride layer in Step 1 is completed, a 1-μm metal aluminum layer is evaporated on the surface of the aluminum chloride layer. Place the aluminum wire in the evaporation source, evacuate to 10 -5 Pa, and then raise the temperature of the evaporation source to 1500 °C to obtain the current collector;

[0084] Step 3: Coating the positive electrode active material on the surface of the current collector prepared in Step 2 to obtain a positive electrode plate, and assembling it with a negative electrode plate, a separator, and an electrolyte to obtain a battery.

[0085] Detection test

[0086] According to GB / T 31485, the overcharge, over-discharge, needle puncture, and extrusion methods are used to test the safety protection performance of the batteries prepared in Examples 1-5 and Comparative Examples 1-4:

[0087] 1. Overcharge test:

[0088] Select the batteries prepared in Examples 1-5 and Comparative Examples 1-4 to ensure that their initial state is fully charged or nearly fully charged; charge the battery with a constant current. The charging current is usually set higher than the standard charging current of the battery, and here it is set to 1C (C is the rated capacity of the battery, and 1C means charging with the current of the battery's rated capacity). Continue charging until the battery voltage reaches 4.2V or obvious abnormal phenomena occur, such as battery heating, sharp voltage rise, etc. During the charging process, use a data acquisition system to record the voltage, current, temperature and other parameters of the battery in real time.

[0089] 2. Over-discharge test:

[0090] Constant current discharge to over-discharge: Select the batteries prepared in Examples 1-5 and Comparative Examples 1-4 to ensure that their initial state is fully charged or nearly fully charged. Connect an electronic load and set it to the constant current discharge mode. The discharge current is generally selected as the rated discharge current of the battery or appropriately increased according to the test requirements. Here it is set to 0.5C. After starting the discharge, closely monitor the voltage change of the battery. When the battery voltage drops to near the over-discharge protection voltage of 2.5V, slow down the data recording interval to more finely observe the changes in battery voltage, current and other parameters. Until the battery voltage reaches the over-discharge protection voltage or the battery cannot continue to discharge.

[0091] 3. Needle puncture test method

[0092] Select the batteries prepared in Examples 1-5 and Comparative Examples 1-4 to ensure that their appearance has no obvious damage, deformation and other defects, and all performance indicators meet the normal production specifications. Charge the battery to be tested according to the standard charging process to ensure that the battery is in a fully charged state (SOC = 100%). Place the fully charged battery on the test bench and fix it. Set the needle puncture speed to 25 mm / s, and the diameter is Adjust the high-temperature resistant steel needle to a direction perpendicular to the battery plate and align it with the geometric center position of the punctured surface. Start the needle puncturing equipment to make the steel needle penetrate the battery at a set speed and direction, and the steel needle stays in the battery. After the steel needle penetrates the battery, observe and record the battery's status within 1 hour, including whether it catches fire, explodes, or smokes. At the same time, use a data acquisition system to record the changes in parameters such as the battery's voltage, current, and temperature in real-time. After 1 hour, take out the punctured battery. Check the battery's appearance to see if there are any phenomena such as liquid leakage, bulging, or deformation, and further analyze the damage to the battery's internal structure.

[0093] 4. Extrusion test method

[0094] Select the batteries prepared in Examples 1-5 and Comparative Examples 1-4, ensure that their appearances have no obvious defects such as damage or deformation, and all performance indicators meet the normal production specifications. Charge them fully according to the standard charging process. Fix the battery between two parallel planes of the extrusion testing machine, adjust the extrusion plate so that the square battery needs to rotate 90° around its longitudinal axis to make both sides withstand the extrusion force; set the parameters: the extrusion plate is a semi-cylinder with a radius of 75 mm, the extrusion speed is 5 mm / s, and the extrusion force is controlled at 13.5 kN. Start the equipment and apply pressure in a direction perpendicular to the battery plate. Stop the extrusion when the voltage reaches 0 V or the deformation amount reaches 30% or the extrusion force reaches the specified value, and maintain for 10 minutes. Within the 10 minutes of maintaining the pressure and within 1 hour afterwards, observe and record whether the battery has phenomena such as expansion, liquid leakage, smoking, catching fire, or explosion, and record the changes in parameters such as the battery's voltage, current, and temperature at the same time.

[0095] The above test data are recorded in Table 1:

[0096] Table 1

[0097]

[0098] Conclusion: The batteries prepared in Examples 1-5 passed the overcharge, over-discharge, needle puncture, and extrusion safety tests, showing a good safety passing rate; comparing the data of Example 1 and Comparative Examples 1-2, it can be seen that inserting an aluminum chloride layer between the polymer layer and the aluminum metal layer effectively improves the battery's safety; comparing the data of Example 1 and Examples 4 and 5, it can be seen that the added polymer film layer improves the safety performance on the basis of the protection of aluminum chloride, having a good safety protection mechanism; comparing the data of Example 5 and Comparative Example 3, it can be seen that nitrogen doping is beneficial to improving the uniformity of the coating, thereby enhancing the protection effect of the polymer film layer. Comparing the data of Example 1 and Comparative Example 4, it can be seen that too low a thickness of the aluminum chloride layer is difficult to play a good safety protection role.

[0099] It is obvious to those skilled in the art that the present invention is not limited to the details of the above-described exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention. Therefore, in any regard, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Accordingly, all changes that fall within the meaning and scope of the equivalent elements of the claims are intended to be embraced within the present invention. Any reference signs in the claims should not be construed as limiting the claims concerned.

Claims

1. A current collector with a safety protection mechanism, characterized in that, It includes a polymer base film, an aluminum chloride layer, and a metallic aluminum layer; the aluminum chloride layer is disposed between the polymer base film and the metallic aluminum layer.

2. The current collector with a safety protection mechanism according to claim 1, characterized in that, The thickness of the aluminum chloride layer is 1 - 3 μm; the polymer base film is any one of a polypropylene film and a polyester film, with a thickness of 1 - 10 μm; the aluminum content of the metallic aluminum layer is > 99%, and the thickness is 0.5 - 3 μm.

3. A method for preparing a current collector having a safety protection mechanism as described in claim 1, characterized in that, It includes the following preparation steps: Step 1: Select a polymer-based film. Using evaporation coating, place the polymer-based film above the evaporation source, and place the aluminum chloride raw material in the evaporation source. After evacuating to 10 -3 -10 -5 Pa, raise the temperature of the evaporation source to 1000 - 1100 °C, and deposit aluminum chloride layers on the upper and lower surfaces of the polymer-based film; Step 2: After the deposition of the aluminum chloride layer in Step 1 is completed, a layer of metallic aluminum is vapor-deposited on the surface of the aluminum chloride layer. Place the aluminum wire in the evaporation source, evacuate to 10 -3 -10 -5 Pa, and then raise the temperature of the evaporation source to 1350 - 1500 °C to obtain the current collector.

4. A pole piece, characterized in that, It includes the current collector described in any one of claims 1 - 2. A polymer layer is scrape-coated on the surface of the current collector, and an active material is coated on the surface of the polymer layer.

5. A method for preparing a pole piece as described in claim 4, characterized in that, It includes the following preparation steps: Step S1: Place the polymer-modified carbon nanotubes in a chloroform solution, ultrasonically disperse for 30 - 40 min, then add poly(3-dodecylthiophene) and stir until dissolved to obtain a polymer coating. Step S2: Chemically etch the surface of the current collector, immerse it in the etching solution, take it out after etching at 20 - 30 °C for 1 - 2 min, ultrasonically clean with acetone, and then scrape-coat the polymer coating prepared in step S2 to form a polymer film layer with a thickness of 200 - 300 nm on the surface of the current collector. Step S3: Coat the active material on the surface of the polymer film layer prepared in step S2 to obtain the electrode sheet.

6. The preparation method of a pole piece according to claim 5, characterized in that, In step S1, the dosage ratio of the polymer-modified carbon nanotubes to poly(3-dodecylthiophene) is 0.05 mg : 0.1 - 0.3 mg / mL; in step S3, the active material includes: 97% ternary cathode material, 1% conductive carbon black, and 2% polyvinylidene fluoride.

7. The preparation method of a pole piece according to claim 5, characterized in that, The preparation steps of the polymer-modified carbon nanotubes in step S1 are as follows: Step s1: Place the carbon nanotubes in a mixed acid solution, ultrasonically disperse for 2 h, wash with water until neutral, dry, add deionized water and ultrasonically disperse for 30 - 40 min, add hydrochloric acid dopamine and stir for 1 - 2 h, then add Tris-HCl buffer solution and an alkali solution, adjust the pH of the system to 8.5, raise the temperature to 60 °C, stir for 10 - 12 h, cool and separate the precipitate, vacuum dry for 12 h, then take it out and heat to 300 - 400 °C and keep warm for 2 - 3 h, and cool to obtain nitrogen-doped carbon nanotubes. Step s2: Under a protective atmosphere, add the nitrogen-doped carbon nanotubes prepared in step s1 and ferric chloride to an acetonitrile solvent, ultrasonically disperse for 30 - 40 min, dropwise add an acetonitrile solution of 3-dodecylthiophene and react for 12 h, then pour it into methanol for sedimentation, wash, add it to saturated hydrazine hydrate and stir overnight, separate and vacuum dry to obtain the polymer-modified carbon nanotubes.

8. The method for preparing an electrode sheet according to claim 7, wherein In step s1, the dosage ratio of the carbon nanotubes to hydrochloric acid dopamine is 1 : (1 - 2); the mixed acid solution is composed of nitric acid and sulfuric acid with a volume ratio of 1:3; in step s2, the dosage ratio of the nitrogen-doped carbon nanotubes to 3-dodecylthiophene is 0.5 g : 0.1 mL.

9. A lithium battery, characterized in that, It includes the electrode sheet prepared by the preparation method described in claim 5.

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