Positive electrode slurry, positive electrode plate, battery and electric equipment

Abstract

The invention provides positive electrode slurry, a positive electrode plate, a battery and electric equipment. The positive electrode slurry comprises an active material, a conductive agent, a binder, an expanding agent and a solvent, when a first preset temperature is reached, the volume of the expanding agent is expanded, the resistance of the expanding agent is gradually increased along with the rise of the temperature, and the first preset temperature is lower than the initial temperature of thermal runaway of a battery cell. Therefore, before thermal runaway of a battery cell of a positive pole piece prepared from the positive pole slurry and after the temperature of the battery cell reaches the first preset temperature, the expanding agent expands in volume and has a certain PTC effect, that is, the resistance of the expanding agent is gradually increased along with the temperature rise, so that the internal resistance of the battery cell is increased, and the self-produced heat of the battery cell is reduced; therefore, the temperature of the battery cell body is reduced, and the effect of effectively preventing the battery cell from thermal runaway is finally achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to positive electrode slurry, positive electrode sheets, batteries and electrical equipment. Background Art

[0002] In recent years, with the rapid growth of electrochemical energy storage devices, safety issues have become increasingly prominent. High-safety and high-stability lithium-ion energy storage systems are an inevitable choice for the development of the power industry. Based on the current single-cell safety protection measures (safety valves, thermal fuses, and BMS thermal management, etc.), it is no longer possible to prevent safety accidents. Therefore, the development of flame retardant materials and PTC materials (a positive temperature coefficient thermistor with the characteristic that the resistance value increases sharply with increasing temperature) has become a hot spot in the industry. Flame retardant materials include flame retardant electrolyte additives, ceramic diaphragms, flame retardant gas gels, etc. The single-cell current collector uses a new PTC material, which has a certain degree of overcharging, external short circuit, mechanical shock, etc., which causes the battery temperature to rise. The internal resistance of the single cell is increased through thermal effect, thereby reducing the self-heating of the cell.

[0003] However, both of the above methods have certain defects. For example, flame retardant materials are relatively ineffective in reducing the self-generated heat of battery cells; coating a PTC conductive layer on the current collector to improve the thermal safety performance of the battery cell only has a certain effect on overcharging and external short circuits, and has no obvious effect on thermal runaway caused by internal short circuits of the battery cell due to pure heating; most new PTC materials will produce NTC effect (negative temperature coefficient thermistor effect, which refers to the phenomenon that the resistivity of certain materials decreases with increasing temperature) at high temperatures (>120℃), and the response speed of the PTC material does not match the thermal runaway speed, and thermal runaway often occurs, but the PTC material has failed or is ineffective. Summary of the invention

[0004] The present invention aims to solve at least one of the technical problems in the related art to a certain extent. To this end, one purpose of the present invention is to provide a positive electrode slurry, wherein after the positive electrode sheet prepared by the positive electrode slurry is used in a battery, the expansion agent can expand in volume before the battery thermal runaway occurs, and has a PTC effect, which can significantly increase the internal resistance of the battery cell at a first predetermined temperature, thereby reducing the self-heating of the battery cell.

[0005] In one aspect of the present invention, the present invention provides a positive electrode slurry. According to an embodiment of the present invention, the positive electrode slurry includes: an active material, a conductive agent, a binder, an expansion agent and a solvent, wherein when the first predetermined temperature is reached, the expansion agent expands in volume, and the expansion agent gradually increases in resistance as the temperature increases, and the first predetermined temperature is less than the starting temperature of thermal runaway of the battery cell. Therefore, before the battery cell of the positive electrode sheet prepared using the positive electrode slurry undergoes thermal runaway, when the temperature of the battery cell reaches the first predetermined temperature, the expansion agent expands in volume and has a certain PTC effect, that is, the expansion agent gradually increases in resistance as the temperature increases, so that the internal resistance of the battery cell increases, the self-heating of the battery cell is reduced, and then the temperature of the battery cell body is reduced, and finally the effect of effectively preventing the battery cell from thermal runaway is achieved.

[0006] According to an embodiment of the present invention, the positive electrode slurry further includes a cracking agent, and when a second predetermined temperature is reached, the cracking agent begins to decompose and generate gas, and the second predetermined temperature is lower than a starting temperature of thermal runaway of the battery cell.

[0007] According to an embodiment of the present invention, the positive electrode slurry further includes a dehumidifier.

[0008] According to an embodiment of the present invention, based on the total mass of the active slurry, the conductive agent, the binder and the expander, the positive electrode slurry includes, by mass percentage: 70% to 98% of the active material; 1% to 10% of the conductive agent; 1% to 10% of the binder; 0.01% to 5% of the expander; 0% to 5% of the cracking agent; and 0% to 5% of the dehydrating agent.

[0009] According to an embodiment of the present invention, the second predetermined temperature is greater than the first predetermined temperature.

[0010] According to an embodiment of the present invention, the expansion agent includes at least one of polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, polyacrylic acid, polymethyl methacrylate, polyvinyl alcohol, polyacrylamide, ABS resin and ABS modified resin.

[0011] According to an embodiment of the present invention, the cleavage agent includes at least one of ammonium salts, carbonates and bicarbonates. Preferably, the cleavage agent includes at least one of ammonium chloride, ammonium sulfate, ammonium bisulfate, ammonium nitrate, ammonium iodide, sodium bromide, ammonium bicarbonate, ammonium carbonate, sodium carbonate, sodium bicarbonate, silver carbonate, potassium carbonate and potassium bicarbonate.

[0012] According to an embodiment of the present invention, the dehydrating agent includes at least one of activated carbon, silica gel, activated alumina, molecular sieve and montmorillonite.

[0013] According to an embodiment of the present invention, the viscosity of the positive electrode slurry is 3000cp-4000cp.

[0014] In another aspect of the present invention, the present invention provides a positive electrode sheet. According to an embodiment of the present invention, the positive electrode sheet is prepared from the positive electrode slurry described above. Therefore, before the battery cell using the positive electrode sheet undergoes thermal runaway, when the temperature of the battery cell reaches the first predetermined temperature, the expansion agent expands in volume and has a certain PTC effect, that is, the expansion agent gradually increases in resistance as the temperature rises, thereby increasing the internal resistance of the battery cell, reducing the self-heating of the battery cell, and then reducing the temperature of the battery cell body, and finally achieving the effect of effectively preventing the battery cell from thermal runaway.

[0015] According to an embodiment of the present invention, at 25°C, the resistance of the positive electrode sheet is R0; at 120°C, the resistance of the positive electrode sheet is R1; at 200°C, the resistance of the positive electrode sheet is R2, wherein R0, R1 and R2 satisfy at least one of the following conditions: R1=3*R0~20*R0; R2=8*R0~60*R0.

[0016] In another aspect of the present invention, the present invention provides a battery. According to an embodiment of the present invention, the battery includes the positive electrode sheet described above. As a result, the battery is not prone to the adverse phenomenon of thermal runaway, thereby improving the safety and service life of the battery. It can be understood by those skilled in the art that the battery has all the features and advantages of the positive electrode slurry and the positive electrode sheet described above, and no further elaboration is given here.

[0017] According to an embodiment of the present invention, the battery is a lithium ion battery and / or a sodium ion battery.

[0018] In another aspect of the present invention, the present invention provides an electric device. According to an embodiment of the present invention, the electric device includes the battery described above. Thus, the electric device has good safety and a long service life. Those skilled in the art can understand that the battery has all the features and advantages of the battery described above, and no further elaboration is given here. DETAILED DESCRIPTION

[0019] The scheme of the present invention will be explained below in conjunction with the embodiments. It will be appreciated by those skilled in the art that the following embodiments are only used to illustrate the present invention and should not be considered as limiting the scope of the present invention. Where specific techniques or conditions are not indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. The reagents or instruments used are not indicated by the manufacturer and are all conventional products that can be obtained commercially.

[0020] The present invention is described below with reference to specific embodiments. It should be noted that these embodiments are merely illustrative and do not limit the present invention in any way.

[0021] In one aspect of the present invention, the present invention provides a positive electrode slurry. According to an embodiment of the present invention, the positive electrode slurry includes: an active material, a conductive agent, a binder, an expansion agent and a solvent, wherein when the first predetermined temperature is reached, the expansion agent expands in volume, and the expansion agent gradually increases in resistance as the temperature increases, and the first predetermined temperature is less than the starting temperature of thermal runaway of the battery cell. Therefore, before the battery cell of the positive electrode sheet prepared using the positive electrode slurry undergoes thermal runaway, when the temperature of the battery cell reaches the first predetermined temperature, the expansion agent expands in volume and has a certain PTC effect, that is, the expansion agent gradually increases in resistance as the temperature increases, so that the internal resistance of the battery cell increases, the self-heating of the battery cell is reduced, and then the temperature of the battery cell body is reduced, and finally the effect of effectively preventing the battery cell from thermal runaway is achieved.

[0022] Among them, it should be noted that it is well known to those skilled in the art that thermal runaway of a battery cell refers to a series of exothermic reactions that occur during the charging and discharging process of the battery, which causes the battery temperature to rise sharply, and even causes fire or explosion in severe cases. After the battery cell reaches a certain temperature (i.e., the starting temperature T2 of thermal runaway), thermal decomposition and heat generation begin to occur inside the battery cell, causing the battery cell temperature to rise sharply and enter the thermal runaway stage. As thermal runaway occurs, the temperature inside the battery cell continues to rise, and when the temperature reaches T3, the battery cell fails. Among them, in some embodiments, the starting temperature T2 of thermal runaway of the battery cell is about 200°C, and T3 is approximately greater than 350°C.

[0023] According to some embodiments of the present invention, the expansion agent includes at least one of polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, polyacrylic acid, polymethyl methacrylate, polyvinyl alcohol, polyacrylamide, ABS resin and ABS modified resin. The expansion agent will undergo a dramatic volume expansion after reaching the first predetermined temperature, and has a certain PTC effect, that is, the expansion agent gradually increases with the increase of temperature, thereby significantly increasing the resistance of the battery cell, thereby achieving the effect of reducing the self-heating of the battery cell; at the same time, the expansion agent of the above material will not react adversely with the active material, conductive agent and binder in the positive electrode slurry. According to some embodiments of the present invention, when the temperature of the battery cell is greater than 120°C, the expansion agent of the above material begins to undergo a dramatic volume expansion, significantly increasing the internal resistance of the battery cell between 120°C and 300°C, thereby achieving the effect of reducing the self-heating of the battery cell, thereby avoiding thermal runaway of the battery cell. Moreover, further, after the expansion agent is added to the positive electrode slurry, it is also beneficial to improve the bonding force of the prepared positive electrode sheet, thereby helping to improve the long-term reliability of the positive electrode sheet.

[0024] According to some embodiments of the present invention, the positive electrode slurry further includes a cracking agent, and when the second predetermined temperature is reached, the cracking agent begins to decompose and generate gas, and the second predetermined temperature is less than the starting temperature of thermal runaway of the battery cell, that is, the starting temperature of the cracking agent decomposition is less than the starting temperature of thermal runaway of the battery cell. Before the battery cell thermal runaway occurs, when the temperature of the battery cell reaches the second predetermined temperature, the cracking agent begins to decompose and generate gas, and at the same time, the volume of the expansion agent expands, and the gas generated by the decomposition is distributed between the conductive agent and the active material, promoting the shedding or peeling between the conductive agent and the active material in the positive electrode plate, thereby causing a short circuit of the positive electrode plate, reducing the self-heating of the battery cell, and at the same time, it will cause the battery cell to open the valve in advance and release organic / inorganic gas carrying a large amount of heat, and the temperature of the battery cell body will be significantly reduced, thereby achieving self-blocking of the thermal runaway of the battery cell. Moreover, combined with the above-mentioned expansion of the expansion agent, the resistance gradually increases, so that the internal resistance of the battery cell increases, reducing the self-heating of the battery cell, and finally achieving dual protection of thermal runaway of the battery cell.

[0025] According to some embodiments of the present invention, the second predetermined temperature is greater than the first predetermined temperature. It can be seen that after the expansion agent begins to expand, the internal resistance of the battery cell begins to increase, reducing the self-heating of the battery cell, but when the temperature of the battery cell (or the temperature of the positive electrode) continues to rise to reach the second predetermined temperature, the cracking agent begins to decompose and produce gas, so when the temperature of the battery cell reaches a higher temperature, the decomposition of the cracking agent and the expansion of the expansion agent work together to better prevent the high-temperature battery cell from thermal runaway.

[0026] According to an embodiment of the present invention, the cracking agent includes at least one of ammonium salts, carbonates and bicarbonates. In some specific embodiments, the cracking agent includes at least one of ammonium chloride, ammonium sulfate, ammonium bisulfate, ammonium nitrate, ammonium iodide, sodium bromide, ammonium bicarbonate, ammonium carbonate, sodium carbonate, sodium bicarbonate, silver carbonate, potassium carbonate and potassium bicarbonate. The cracking agent of the above materials can decompose between 150°C and 500°C to produce CO 2 ,CO,N 2 and / or NH 3 The above-mentioned gases can not only promote the shedding or peeling between the conductive agent and the active material in the positive electrode sheet, thereby causing a short circuit in the positive electrode sheet and reducing the self-heating of the battery cell, but also cause the battery cell to open the valve in advance and release organic / inorganic gases carrying a large amount of heat, significantly reducing the temperature of the battery cell body, thereby achieving self-blocking of thermal runaway of the battery cell; at the same time, CO 2 ,CO,N 2 and / or NH 3 Such gases will not have adverse effects on the isolation membrane, electrolyte, negative electrode plate and other structures in the battery cell.

[0027] According to some embodiments of the present invention, the positive electrode slurry further includes a dehydrating agent. Thus, by adding the dehydrating agent, the water content in the positive electrode plate and the electrolyte can be greatly reduced, which helps to inhibit the decomposition of the electrolyte, improve the stability of the electrolyte, and thus improve the overall safety of the battery cell; and before the battery cell undergoes thermal runaway, the dehydrating agent absorbs the water and free acid (water system) in the electrolyte, which can help reduce the decomposition of the negative electrode separator (SEI film), prolong the time of thermal runaway of the battery cell, and further ensure the safety of the battery cell.

[0028] According to some embodiments of the present invention, the dewatering agent includes at least one of activated carbon, silica gel (such as silicon oxide, etc.), activated alumina, molecular sieve and montmorillonite. Thus, the dewatering agent of the above materials has a good dewatering effect, and will not cause adverse effects on components such as active materials, conductive agents, and binders, that is, the above dewatering agent will not have side reactions with components such as active materials, conductive agents, and binders. Further, when activated carbon is used as a dewatering agent, since activated carbon has a certain conductivity, the dewatering agent activated carbon can also serve as a part of the conductive agent.

[0029] According to some embodiments of the present invention, based on the total mass of the active slurry, the conductive agent, the binder and the expander, the positive electrode slurry includes, by mass percentage: 70% to 98% (e.g., 70%, 72%, 75%, 78%, 80%, 82%, 85%, 88%, 90%, 92%, 95%, 98%, etc.) of active material; 1% to 10% (e.g., 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, etc.) of conductive agent; 1% to 10% (e.g., 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, etc.) of conductive agent; , 5%, 6%, 7%, 8%, 9%, 10%, etc.) of binder; 0.01% to 5% (such as 0.01%, 0.05%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, etc.) of expander; 0% to 5% (such as 0.01%, 0.05%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, etc.) of cracking agent; 0% to 5% (such as 0.01%, 0.05%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, etc.) of dehydrating agent. Therefore, the positive electrode slurry with the above ratio can effectively avoid thermal runaway of the battery cell, and at the same time, the proportion of cracking agent, expander and dehydrating agent is small, which will not cause a large negative impact on the capacity of the battery, that is, to ensure the better specific capacity of the battery. Among them, the amount of solvent can be flexibly adjusted according to the viscosity requirement of the positive electrode slurry. In some embodiments, the viscosity of the positive electrode slurry is 3000cp~4000cp, for example, the viscosity of the positive electrode slurry is 3000cp, 3100cp, 3200cp, 3300cp, 3400cp, 3500cp, 3600cp, 3700cp, 3800cp, 3900cp, 4000cp, etc. Therefore, the content of the solvent can be adjusted according to the above requirements for the viscosity of the positive electrode slurry to meet the viscosity requirements of the positive electrode slurry. It is further explained that the addition of the expansion agent, the cracking agent and the dehydrating agent can still adjust the viscosity of the positive electrode slurry to 3000cp~4000cp to meet the battery's requirements for the viscosity of the positive electrode slurry.

[0030] In some embodiments of the present invention, if the positive electrode slurry is used to prepare a positive electrode sheet of a lithium-ion battery, the active material in the positive electrode slurry may be a positive electrode active material for lithium-ion batteries known in the art. As an example, the positive electrode active material may include at least one of the following materials: a lithium-containing phosphate with an olivine structure, a lithium transition metal oxide. The above-mentioned positive electrode active materials may be used alone or in combination of two or more. Among them, the lithium transition metal oxide includes but is not limited to lithium cobalt oxide (such as LiCoO 2 ), lithium nickel oxide (such as LiNiO 2 ), lithium manganese oxide (such as LiMnO 2 、LiMn 2 O 4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide and modified compounds thereof; examples of lithium phosphates containing olivine structures include but are not limited to lithium iron phosphate (such as LiFePO 4 (also referred to as LFP), composite materials of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO 4 ), at least one of a composite material of lithium manganese phosphate and carbon, a composite material of lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0031] In some embodiments of the present invention, if the positive electrode slurry is used to prepare a positive electrode sheet of a sodium ion battery, the active material in the positive electrode slurry includes an interlayer transition metal oxide Na e MO 2 , Prussian blue compounds Na f M1[M2(CN) 6 ] and polyanionic compounds Na d M g (X a O b ) c Z h At least one of, wherein M, M1 and M2 are respectively one or more transition metal atoms, X is one or more of Si, S, P, As, B, Mo, W, Ge elements, and Z is one or more of F and OH, wherein M, M1 and M2 can be the same element or different elements.

[0032] In some embodiments of the present invention, the conductive agent may be at least one of graphite, graphene, conductive carbon, CNTs, and the like.

[0033] In some embodiments of the present invention, the binder may be one or more polymer resins, wherein the polymer resin includes but is not limited to polymer resin materials such as acrylic resin, modified acrylic resin, and amide resin.

[0034] In some embodiments of the present invention, the solvent may be an oil-based solvent, such as one or more mixed solvents of NMP, chloroform, acetone, ethyl acetate, dimethylamide, and the like.

[0035] In another aspect of the present invention, the present invention provides a positive electrode sheet. According to an embodiment of the present invention, the positive electrode sheet is prepared from the positive electrode slurry described above. Therefore, before the battery cell using the positive electrode sheet undergoes thermal runaway, when the temperature of the battery cell reaches the first predetermined temperature, the expansion agent expands in volume and has a certain PTC effect, that is, the expansion agent gradually increases in resistance as the temperature rises, thereby increasing the internal resistance of the battery cell, reducing the self-heating of the battery cell, and then reducing the temperature of the battery cell body, and finally achieving the effect of effectively preventing the battery cell from thermal runaway.

[0036] According to some embodiments of the present invention, at 25°C, the resistance of the positive electrode sheet is R0; at 120°C, the resistance of the positive electrode sheet is R1, then R1 = 3*R0~20*R0, it can be seen that at 120°C, the expansion agent has undergone volume expansion, thereby increasing the resistance of the positive electrode sheet, and compared with the resistance value of the positive electrode sheet at 25°C, the resistance of the positive electrode sheet at 120°C increases several times, thereby effectively and quickly increasing the overall internal resistance of the battery cell, thereby effectively preventing it from thermal runaway. According to some other embodiments of the present invention, at 200°C, the resistance of the positive electrode sheet is R2, then R2 = 8*R0~60*R0. It can be seen that as the temperature increases, the resistance value of the positive electrode sheet increases further significantly, so when the temperature of the battery cell further increases, the internal resistance of the battery cell will also increase further, thereby effectively preventing the thermal runaway of the battery cell.

[0037] In some embodiments of the present invention, there are no special requirements for the specific method of preparing positive electrode sheets from positive electrode slurry, and those skilled in the art can flexibly choose according to actual needs and commonly used technical means. In some embodiments, the method of preparing positive electrode sheets from positive electrode slurry includes: ① weighing active materials, conductive agents, binders, expanders, cracking agents, dehydrating agents and other raw materials according to a predetermined mass ratio; ② mixing the above various raw materials evenly with a stirrer; ③ adjusting the viscosity by solvent to obtain a positive electrode slurry with a suitable viscosity; ④ forming a positive electrode sheet on the surface of aluminum foil by coating, spin coating or spraying; ⑤ drying in a tunnel furnace to remove the solvent to form a positive electrode sheet.

[0038] In another aspect of the present invention, the present invention provides a battery. According to an embodiment of the present invention, the battery includes the positive electrode sheet described above. As a result, the battery is not prone to the adverse phenomenon of thermal runaway, thereby improving the safety and service life of the battery. It can be understood by those skilled in the art that the battery has all the features and advantages of the positive electrode slurry and the positive electrode sheet described above, and no further elaboration is given here.

[0039] According to an embodiment of the present invention, the battery is a lithium ion battery and / or a sodium ion battery. It can be seen that the above scheme of the present invention can be used for both lithium ion batteries and sodium ion batteries, which expands the application field of the above positive electrode slurry.

[0040] In some embodiments of the present invention, the above-mentioned battery, in addition to the above-mentioned positive electrode plate, also includes an isolation membrane, an electrolyte and a negative electrode plate, wherein there are no special requirements for the material selection and parameter setting of the isolation membrane, electrolyte and negative electrode plate, and technical personnel in this field can make flexible choices based on actual needs, and no restrictions are imposed here.

[0041] In another aspect of the present invention, the present invention provides an electric device. According to an embodiment of the present invention, the electric device includes the battery described above. Thus, the electric device has good safety and a long service life. Those skilled in the art can understand that the battery has all the features and advantages of the battery described above, and no further elaboration is given here.

[0042] According to the embodiments of the present invention, there are no special requirements for the specific type of the electrical equipment, and those skilled in the art can flexibly select according to actual needs. For example, the electrical equipment can be a mobile device such as a mobile phone, a laptop computer, or an electric vehicle such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc., but is not limited thereto.

[0043] Example

[0044] Example 1

[0045] The composition and weight percentage of the positive electrode slurry are as follows: lithium iron phosphate 90%; binder (PVDF) 7%; conductive agent (C) 2%; expansion agent polyacrylic acid 1%; solvent is NMP.

[0046] Making positive electrode slurry and positive electrode sheet:

[0047] ① Weigh the active material, conductive agent, binder, expander and other raw materials according to the predetermined mass ratio;

[0048] ②Use a stirrer to mix the above raw materials evenly;

[0049] ③ Adjust the viscosity through the solvent to obtain a positive electrode slurry with suitable viscosity;

[0050] ④ Forming a positive electrode sheet on the surface of the aluminum foil by coating, spin coating or spraying;

[0051] ⑤ Dry in a tunnel furnace to remove the solvent and make the positive electrode sheet.

[0052] Assemble lithium-ion batteries: use graphite negative electrode: graphite: carbon black: SBR: CMC = 95:2:1.5:1.5; prepare the negative electrode sheet in the same steps as the positive electrode; use 14umPP separator, and prepare dry batteries by multi-layer lamination or winding of the negative electrode, separator, and positive electrode. After baking to remove moisture from the electrode sheet, add carbonate electrolyte.

[0053] Example 2

[0054] The difference from Example 1 is that the components and weight percentages of the positive electrode slurry are as follows: lithium iron phosphate 90%; binder (PVDF) 5%; conductive agent (C) 2%; expansion agent polyacrylic acid 3%; and the solvent is NMP.

[0055] Example 3

[0056] The difference from Example 1 is that the components and weight percentages of the positive electrode slurry are as follows: lithium iron phosphate 90%; binder (PVDF) 3%; conductive agent (C) 2%; expansion agent polyacrylic acid 5%; and the solvent is NMP.

[0057] Example 4

[0058] The difference from Example 1 is that the components and weight percentages of the positive electrode slurry are as follows: lithium iron phosphate 90%; binder (PVDF) 3%; conductive agent (C) 2%; expansion agent polyacrylic acid 3%; cracking agent sodium carbonate 2%; and the solvent is NMP.

[0059] Example 5

[0060] The difference from Example 1 is that the components and weight percentages of the positive electrode slurry are as follows: lithium iron phosphate 90%; binder (PVDF) 1%; conductive agent (C) 2%; expansion agent polyacrylic acid 2%; cracking agent sodium carbonate 5%; and the solvent is NMP.

[0061] Example 6

[0062] The difference from Example 1 is that the components and weight percentages of the positive electrode slurry are as follows: lithium iron phosphate 90%; binder (PVDF) 2%; conductive agent (C) 2%; expansion agent polyacrylic acid 2%; cracking agent sodium carbonate 2%; dehydrating agent activated alumina 2%; and the solvent is NMP.

[0063] Example 7

[0064] The difference from Example 1 is that the components and weight percentages of the positive electrode slurry are as follows: lithium iron phosphate 90%; binder (PVDF) 1%; conductive agent (C) 2%; expansion agent polyacrylic acid 1%; cracking agent sodium carbonate 1%; dehydrating agent activated alumina 5%; and the solvent is NMP.

[0065] Example 8

[0066] The difference from Example 2 is that the expansion agent is polyethylene.

[0067] Example 9

[0068] The difference from Example 2 is that the swelling agent is polyacrylamide.

[0069] Example 10

[0070] The difference from Example 2 is that the expansion agent is polyvinyl chloride.

[0071] Embodiment 11

[0072] The difference from Example 2 is that the expansion agent is ABS resin.

[0073] Example 12

[0074] The difference from Example 5 is that the cleavage agent is potassium carbonate.

[0075] Embodiment 13

[0076] The difference from Example 5 is that the lysing agent is sodium bicarbonate.

[0077] Embodiment 14

[0078] The difference from Example 5 is that the cleavage agent is potassium bicarbonate.

[0079] Embodiment 15

[0080] The difference from Example 5 is that the cleavage agent is ammonium bicarbonate.

[0081] Example 16

[0082] The difference from Example 6 is that the water removal agent is activated carbon.

[0083] Embodiment 17

[0084] The difference from Example 6 is that the water removing agent is silica gel.

[0085] Embodiment 18

[0086] The difference from Example 6 is that the water removing agent is montmorillonite.

[0087] Comparative Example 1

[0088] The difference from Example 1 is that the composition and weight percentage of the positive electrode slurry are as follows: lithium iron phosphate 90%; binder (PVDF) 5%; conductive agent (C) 5%; solvent is NMP.

[0089] The performance test is as follows:

[0090] First, viscosity test: the method in the national standard GB / T17473 was used to test the viscosity of the positive electrode slurries in the above-mentioned Examples 1 to 18 and Comparative Example 1, respectively. The test results are shown in Table 1. It can be seen from the data in Table 1 that compared with Comparative Example 1, the viscosity of the positive electrode slurries in Examples 1 to 18 increased slightly, but all met the product requirement of 3000cp to 4000cp, and did not affect the actual production of the positive electrode sheets and batteries.

[0091] Table 1

[0092]

[0093]

[0094] Second, the peeling force test: the method in the national standard GB / T4815 was used to test the peeling force of the positive electrode sheets in the above-mentioned Examples 1 to 18 and Comparative Example 1. The test results are shown in Table 2. It can be seen from the peeling data in Table 2 that the addition of the expander is beneficial to the improvement of the binder force of the positive electrode sheet, thereby helping to improve the long-term reliability of the positive electrode sheet. Moreover, when a certain proportion of the expander is added, the cracking agent and the dehydrating agent are added, and the peeling force is improved compared with Comparative Example 1. It can also be further seen that within the dosage range of the present invention, as the amount of the expander increases, the peeling force gradually increases.

[0095] Table 2

[0096]

[0097]

[0098] Third, thermal runaway test: The method in the national standard GBT-36276-2023 was used to conduct thermal runaway tests on the batteries in the above-mentioned Examples 1 to 18 and Comparative Example 1, respectively. The test results are shown in Table 3. It can be seen from the data in Table 3 that by adding an expander, a cracking agent and a dehydrating agent to the positive electrode slurry, the maximum temperature of the battery is significantly reduced, the maximum voltage is also significantly optimized, and the thermal runaway time is significantly prolonged, which greatly reduces the thermal runaway risk of the battery and gives the battery a longer reaction time. Among them, it can be seen from Examples 1 to 3 that with the increase of the expander content, the maximum temperature and the maximum voltage of the battery gradually decrease, and the thermal runaway time gradually increases; compared with Examples 1 to 3, in Examples 4 and 5, after further adding a cracking agent, the maximum temperature and the maximum voltage of the battery are further reduced, and the thermal runaway time is further prolonged; in Examples 6 and 7, it can be seen that the addition of a dehydrating agent can further prolong the thermal runaway of the battery.

[0099] Table 3

[0100]

[0101]

[0102] Fourth, the resistivity test of the positive electrode sheet: a four-probe film resistor was used to measure the positive electrode sheet with a diameter of 14 mm. The test was performed at 25°C and 120°C under a pressure of 19 MPa. The test results are shown in Table 4. From the data in Table 4, it can be seen that the resistivity of the positive electrode sheet in Comparative Example 1 does not change much with temperature. When the temperature rises to 120°C in Example 1, the resistivity of the positive electrode sheet increases by about 3 times. When the temperature rises to 120°C in Example 2, the resistivity of the positive electrode sheet increases by about 13 times. In other embodiments, the resistivity increases several times compared to Comparative Example 1. It can be confirmed that the positive electrode sheet of the present invention can achieve a significant PTC effect at 120°C, increase the internal resistance of the battery cell, and effectively prevent thermal runaway of the battery cell.

[0103] Table 4

[0104]

[0105] Fifth, battery moisture test - Karl Fischer coulometric method: The Karl Fischer heating furnace method was used to test the moisture content of the positive electrode slurry in the above-mentioned embodiments and comparative example 1, the electrolyte taken out from the battery cell standing at room temperature for 5 days, and the electrolyte taken out from the battery cell standing at 80°C for 1 day. The test results are shown in Table 5. It can be seen from Table 5 that the water content in the positive electrode slurry and the electrolyte with the addition of the dehydrating agent is greatly reduced compared with the embodiments and comparative examples without the addition of the dehydrating agent.

[0106] Table 5

[0107]

[0108]

[0109] The terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0110] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, unless they are contradictory.

[0111] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A positive electrode slurry, characterized in that: include: Active material, conductive agent, binder, expansion agent and solvent, wherein the expansion agent expands in volume when a first predetermined temperature is reached, and the resistance of the expansion agent gradually increases with the increase of temperature, and the first predetermined temperature is lower than the starting temperature of thermal runaway of the battery cell.

2. The positive electrode slurry according to claim 1, characterized in that It further includes a cracking agent, which starts to decompose and generate gas when a second predetermined temperature is reached, and the second predetermined temperature is lower than a starting temperature of thermal runaway of the battery cell.

3. The positive electrode slurry according to claim 2, characterized in that Further comprising a water removal agent.

4. The positive electrode slurry according to claim 3, characterized in that: Based on the total mass of the active slurry, the conductive agent, the binder and the expander, the positive electrode slurry includes, by mass percentage: 70% to 98% of the active material; 1% to 10% of the conductive agent; 1% to 10% of the binder; 0.01% to 5% of the swelling agent; 0% to 5% of the lysing agent; 0% to 5% of the dehydrating agent.

5. The positive electrode slurry according to claim 2, characterized in that: The second predetermined temperature is greater than the first predetermined temperature.

6. The positive electrode slurry according to any one of claims 1 to 5, characterized in that The expansion agent includes at least one of polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, polyacrylic acid, polymethyl methacrylate, polyvinyl alcohol, polyacrylamide, ABS resin and ABS modified resin.

7. The positive electrode slurry according to any one of claims 2 to 5, characterized in that The lysing agent comprises at least one of an ammonium salt, a carbonate and a bicarbonate, Preferably, the lysing agent includes at least one of ammonium chloride, ammonium sulfate, ammonium bisulfate, ammonium nitrate, ammonium iodide, sodium bromide, ammonium bicarbonate, ammonium carbonate, sodium carbonate, sodium bicarbonate, silver carbonate, potassium carbonate and potassium bicarbonate.

8. The positive electrode slurry according to claim 3 or 4, characterized in that: The dehydrating agent includes at least one of activated carbon, silica gel, activated alumina, molecular sieve and montmorillonite.

9. The positive electrode slurry according to any one of claims 1 to 5, characterized in that: The viscosity of the positive electrode slurry is 3000cp-4000cp.

10. A positive electrode sheet, characterized in that: The positive electrode slurry is prepared from any one of claims 1 to 9.

11. The positive electrode sheet according to claim 10, characterized in that: At 25°C, the resistance of the positive electrode sheet is R0; at 120°C, the resistance of the positive electrode sheet is R1; at 200°C, the resistance of the positive electrode sheet is R2, wherein R0, R1 and R2 satisfy at least one of the following conditions: R1=3*R0~20*R0; R2=8*R0~60*R0.

12. A battery, characterized in that: Including the positive electrode sheet as described in claim 10 or 11.

13. The battery according to claim 12, characterized in that The battery is a lithium ion battery and / or a sodium ion battery.

14. An electrical device, characterized in that: A battery comprising the battery of claim 12 or 13.

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