Composite electrode active layer, electrode sheet and secondary battery

Abstract

Provided in the present application are a composite electrode active layer, an electrode sheet and a secondary battery. The composite electrode active layer comprises an active material layer and a composite insulating layer which are stacked in sequence, wherein the composite insulating layer comprises inorganic particles, a heat-resistant polymer and a thermosensitive polymer; the weight ratio of the inorganic particles to the heat-resistant polymer to the thermosensitive polymer is (50-100):(1-10):(5-50); the melting temperature of the heat-resistant polymer is 180-450ºC; and the softening temperature of the thermosensitive polymer is 80-120ºC.

Description

Composite electrode active layer, electrode sheet and secondary battery

[0001] This application claims priority to Chinese Patent Application No. 2024116920604, filed with the Chinese Patent Office on November 22, 2024, the entire contents of which are incorporated herein by reference.

[0002] Technical Field

[0003] This application relates to the field of secondary batteries, and more specifically, to a composite electrode active layer, an electrode sheet, and a secondary battery.

[0004] Background Technology

[0005] To meet the growing demand for batteries, high-capacity, high-energy-density rechargeable batteries are receiving increasing attention. Lithium-ion and sodium-ion batteries, as mainstream rechargeable battery products, are widely used in many fields such as new energy vehicles, wearable devices, and portable power supplies. The separator, as one of the commonly used components in current rechargeable batteries, mainly plays a role in ion transport and electron isolation. The pore-closure temperature and rupture temperature of the separator are key technical indicators characterizing the safety of the separator and even the safety of the battery cell. Currently, mass-produced separator substrates are all made of PE and PP materials. The pore-closure temperature of PE separators is ~130℃, and that of PP separators is ~150℃, which means that the separator cannot close its pores in time to prevent the transport of conductive ions when subjected to thermal abuse. At the same time, the rupture temperature of PE is ~145℃, and that of PP is ~170℃, further leading to separator rupture when the battery cell is subjected to thermal abuse, causing short circuits between the positive and negative electrodes, resulting in safety accidents such as smoke and explosions. Therefore, the separators in related technologies cannot truly be compatible with both low pore-closure temperatures and high rupture temperatures.

[0006] In the safety design of rechargeable batteries, the problem of internal short circuits in the electrodes is particularly important. Internal short circuits can cause a rapid increase in the battery's internal temperature, potentially leading to thermal runaway. Therefore, effectively preventing internal short circuits is one of the key issues that needs to be addressed in the design of rechargeable batteries.

[0007] Currently, methods to prevent internal short circuits in electrodes mainly fall into two categories: one is achieved by adding inorganic particles with thermal expansion and contraction properties to the active material layer. For example, Chinese patent CN103381436A discloses a composite electrode active material with thermal expansion and contraction properties. This active material uses a positive electrode active material as a base material, and adds inorganic particles with thermal expansion and contraction properties to the positive electrode active material. The amount of inorganic particles added is 1-10% of the positive electrode active material; the inorganic particles are inorganic powders with thermal expansion and contraction properties. In the above-mentioned patent technology, the amount of inorganic powder added is relatively small, and the inorganic powder and active material are not fully mixed. The inorganic powder is prone to forming voids in the electrode material, thereby increasing the capacity loss of the active material and negatively affecting the physical and electrochemical properties of the electrode material. The other method is achieved by setting insulating layers on both sides of the active material layer. For example, Chinese patent CN101937953A discloses a positive electrode layer for a lithium-ion battery. This positive electrode layer includes a positive electrode active material layer, an adhesive layer disposed on both sides of the positive electrode active material layer, and an insulating layer disposed on the side of the positive electrode active material layer away from the adhesive layer. The insulating layer has a coefficient of thermal expansion of less than 4 × 10⁻⁶. -5 An insulating layer with a low coefficient of thermal expansion at / ℃. In the aforementioned patented technology, to ensure that the coefficient of thermal expansion of the insulating layer is less than 4×10... -5 / ℃, its insulation layer is made of ceramic material, which is expensive and has a complex processing technology, resulting in high production costs.

[0008] Therefore, how to provide a composite electrode active layer that can have both a low pore-closing temperature and a high film-breaking temperature, so that it can improve the safety and stability of the corresponding secondary battery at high temperatures while playing the roles of ion transport and electron isolation, is one of the important technical problems that need to be solved in this field.

[0009] Technical issues

[0010] The secondary battery separators in related technologies are difficult to achieve both a low pore-closing temperature and a high membrane rupture temperature, which leads to poor safety and stability of the secondary battery at high temperatures.

[0011] Technical solutions

[0012] In a first aspect, embodiments of this application provide a composite electrode active layer, which includes an active material layer and a composite insulating layer stacked sequentially. The composite insulating layer includes a heat-resistant polymer, a thermosensitive polymer, and inorganic particles. The weight ratio of the inorganic particles, the heat-resistant polymer, and the thermosensitive polymer is (50~100):(1~10):(5~50). The melting temperature of the heat-resistant polymer is 180℃~450℃. The softening temperature of the thermosensitive polymer is 80℃~120℃.

[0013] Secondly, embodiments of this application provide an electrode sheet, including a current collector and an electrode active layer disposed on at least one side surface of the current collector. The electrode active layer is the aforementioned composite electrode active layer, and the active material layer in the composite electrode active layer is disposed in contact with the current collector. The electrode sheet is a negative electrode sheet and / or a positive electrode sheet.

[0014] Thirdly, embodiments of this application provide a secondary battery, including a positive electrode plate, a negative electrode plate, and an electrolyte, wherein the positive electrode plate is the aforementioned positive electrode plate; and / or, the negative electrode plate is the aforementioned negative electrode plate.

[0015] The beneficial effects of this application are:

[0016] 1. This application designs the composite electrode active layer to achieve a balance between low pore-closure temperature and high membrane breakage temperature, resulting in a composite electrode active layer with a porous structure and high-temperature resistance. Specifically, a porous composite insulating coating is formed on the surface of the active material layer. Compared to traditional separators, this coating effectively transports conductive ions while isolating direct contact between the positive and negative electrode materials. The composite insulating layer provided in this application utilizes a heat-resistant polymer as a high-melting-point binder, thereby achieving high-temperature resistance and solving the problem of membrane breakage thermal runaway caused by high temperatures in traditional separators. The addition of inorganic particles improves the mechanical strength and electrochemical stability of the composite insulating layer, further optimizing the overall performance of the battery. Furthermore, the composite insulating layer provided in this application also includes a thermosensitive polymer, whose melting temperature significantly optimizes the pore-closure temperature of the resulting composite insulating layer. That is, when applied to secondary batteries, the aforementioned thermosensitive polymer with a softening temperature of 80℃~120℃ can melt within this temperature range, blocking the porous structure in the coating and hindering the transfer of conductive ions at high temperatures, causing a rapid increase in its high-temperature internal resistance and preventing battery thermal runaway. In particular, in addition to the functional gains brought by each of the three components, the ratio of their dosages is indispensable. Based on this, this application strictly controls the ratio of the three components within the above range to allow for better coordination between the inorganic particles, the heat-resistant polymer, and the thermosensitive polymer, thereby significantly optimizing the porous structure of the resulting composite insulating layer, while ensuring that it has a low pore-closing temperature and a high film-breaking temperature, ultimately obtaining a high-temperature resistant composite electrode active layer.

[0017] 2. The negative electrode sheet and / or positive electrode sheet containing the above-mentioned composite electrode active layer obtained in this application have superior high temperature resistance characteristics, thereby exhibiting higher safety and stability at high temperatures.

[0018] 3. The composite electrode active layer obtained in this application, when combined with a current collector to obtain an electrode sheet and applied to a secondary battery, effectively solves the problem of thermal runaway caused by high temperature in traditional separators, and also prevents the occurrence of thermal runaway, significantly improving the high temperature safety of the corresponding secondary battery.

[0019] Implementation methods of this application

[0020] The first aspect of this application provides a composite electrode active layer, which includes an active material layer and a composite insulating layer stacked sequentially. The composite insulating layer includes a heat-resistant polymer, a thermosensitive polymer, and inorganic particles. The weight ratio of the inorganic particles, the heat-resistant polymer, and the thermosensitive polymer is (50~100):(1~10):(5~50). The melting temperature of the heat-resistant polymer is 180℃~450℃. The softening temperature of the thermosensitive polymer is 80℃~120℃.

[0021] In some embodiments of this application, the weight ratio of inorganic particles, heat-resistant polymer, and thermosensitive polymer is (65~85):(3~5):(10~30). Based on the above, this further optimized ratio not only improves the stability and mechanical strength of the composite insulation layer under normal operating conditions, but also enables a faster response when the battery overheats, effectively preventing the transport of conductive ions and further improving the safety and reliability of the battery.

[0022] For the heat-resistant polymers used in this application, they are preferably selected from one or more of polyacrylate polymers, polyimide polymers, and amide polymers, and more preferably from one or more of poly(m-phenylene isophthalamide), polyethylene terephthalate, and polybismaleimide. These heat-resistant polymers exhibit superior heat resistance and chemical stability, and can more effectively improve the thermal and electrochemical stability of the composite insulation layer.

[0023] To obtain a composite insulating layer with stronger mechanical properties while maintaining a high melting temperature, a preferred heat-resistant polymer is poly(m-phenylene isophthalamide) and polyethylene terephthalate (PET), with a weight ratio of 1:(0.8~1.2). Extensive experiments have shown that this combination can more fully utilize the complementary properties of the two heat-resistant polymers, thereby providing the resulting composite insulating layer with higher heat resistance and mechanical strength, and thus significantly optimizing the high-temperature safety of the corresponding secondary battery.

[0024] For the thermosensitive polymer in this application, it is preferably selected from one or more of polyol polymers and polyvinyl alcohol polymers, and more preferably from polyethylene glycol and / or polyacrylic acid. Compared with other polymers in the art with softening temperatures in the same temperature range of 80°C to 120°C, the above-mentioned thermosensitive polymer has better thermosensitive properties, can respond more quickly when the battery it is in overheats, prevent the transport of conductive ions, play a more effective self-protection role, and ultimately significantly reduce the possibility of short circuits inside the battery.

[0025] Furthermore, through extensive experiments, the inventors selected polyethylene glycol and polyvinyl alcohol as the optimal thermosensitive polymers, with a weight ratio of 1:(1.8~2.0) for polyethylene glycol to polyvinyl alcohol. This is to provide the resulting composite insulating layer with superior thermosensitive properties while further balancing and improving its chemical stability, ultimately resulting in better high-temperature safety for the corresponding secondary battery.

[0026] Furthermore, in order to more significantly optimize the porous structure of the obtained composite insulating layer and thus obtain electrode sheets with higher mechanical strength and greater stability, it is preferred that the D50 of the inorganic particles is 0.1μm~6.0μm and the (D90-D10) / D50 is 0.5~3.0.

[0027] In some embodiments of this application, the inorganic particles are selected from one or more of boehmite (with the molecular formula Al(OH)3), Al2O3, BaTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, SiO2, Y2O3, SiC, and TiO2. These inorganic particles not only improve the mechanical strength and electrochemical stability of the composite insulating layer, but also enhance the thermal stability of the resulting composite insulating layer and the corresponding secondary battery. Through extensive experimentation, the inventors have further optimized the inorganic particles to be BaTiO3 and TiO2, with a weight ratio of BaTiO3 to TiO2 of (0.1~10):1, more preferably (0.4~0.5):1. The combination of BaTiO3 and TiO2 in the above ratio provides excellent electrochemical performance and thermal stability, and more effectively absorbs heat when the secondary battery is overheated, further improving battery safety. In addition, BaTiO3 has a positive temperature coefficient effect, and its resistance increases with increasing temperature, which can further increase the internal resistance of the battery at high temperatures and prevent thermal runaway. It also has good chemical stability and is not easy to decompose and collapse at high temperatures, ensuring the structural stability of the insulation layer. The combination of the two can achieve a synergistic effect.

[0028] Furthermore, to better leverage the enhancing effect of the composite insulating layer on the heat resistance of the composite electrode active layer and obtain an electrode sheet with better high-temperature stability, the thickness of the composite insulating layer is preferably 4μm~20μm. A preferred thickness ratio of the composite insulating layer to the active material layer is (0.01~0.5):1, which better balances thermal stability and electrochemical performance, allowing the electrode sheet to maintain good thermal stability while possessing higher energy density.

[0029] Preferably, the active material layer is a positive electrode active layer and / or a negative electrode active material layer; more preferably, the positive electrode material is selected from one or more of iron phosphate, manganese iron phosphate, and nickel-cobalt-manganese ternary materials; specifically, when the secondary battery is a lithium-ion battery, the positive electrode material can be LFP, LMFP, and NCM. And / or, the negative electrode material is selected from one or more of graphite, silicon, and silicon-carbon composite materials.

[0030] In some embodiments of this application, the inorganic particles are BaTiO3 and TiO2, and the weight ratio of BaTiO3 to TiO2 is (0.4~0.5):1; and / or, the heat-resistant polymer is poly(m-phenylene isophthalamide) and polyethylene terephthalate, and the weight ratio of poly(m-phenylene isophthalamide) to polyethylene terephthalate is 1:(0.8~1.2); and / or, the thermosensitive polymer is polyethylene glycol and polyvinyl alcohol, and the weight ratio of polyethylene glycol to polyvinyl alcohol is 1:(1.8~2.0). The inventors optimized the component amounts of the composite insulating layer through extensive experiments, obtaining the aforementioned specific solution. When the composite insulating layer formed by this solution, together with the active material layer, forms a composite electrode active layer and is applied in a secondary battery, the resulting secondary battery exhibits higher high-temperature safety.

[0031] A second aspect of this application provides an electrode sheet comprising a current collector and an electrode active layer disposed on at least one surface of the current collector, the electrode active layer being the aforementioned composite electrode active layer, wherein the active material layer in the composite electrode active layer is in contact with the current collector; preferably, a composite insulating layer is disposed on the surface of the active material layer away from the current collector by a coating process, and the coating surface density of the composite insulating layer during coating is 15 g / m². 2 ~45g / m 2 The electrode sheet is a negative electrode sheet and / or a positive electrode sheet. The negative electrode sheet and / or positive electrode sheet obtained in this application, containing the above-mentioned composite electrode active layer, possesses superior high-temperature resistance, thus exhibiting higher safety and stability at high temperatures. In particular, during the preparation of the electrode sheet, the composite insulating layer is coated with a surface density of 15 g / m². 2 ~45g / m 2The coating method allows for a tighter bond between the electrode and the active material layer, thereby significantly improving the high-temperature thermal stability and structural stability of the resulting negative electrode sheet and / or positive electrode sheet.

[0032] Regarding the formation of the positive electrode material active layer and / or negative electrode material active layer, in order to better integrate them with the subsequently coated composite insulating layer during the preparation process, and to form an electrode sheet with higher electrochemical performance, high temperature resistance, and structural stability, in some embodiments of this application: the electrode sheet is a positive electrode sheet, the current collector is a positive current collector, the active material layer is a positive electrode material active layer, the positive electrode material active layer is applied to the positive current collector by a coating process, and the coating surface density of the positive electrode material active layer during coating is 100 g / m². 2 ~400g / m 2 ; and / or, the electrode sheet is a negative electrode sheet, the current collector is a negative current collector, the active material layer is a negative electrode active layer, the negative electrode active layer is applied to the negative current collector by a coating process, and the coating surface density of the negative electrode active layer during coating is 40 g / m². 2 ~200g / m 2 .

[0033] Specifically, in actual production applications, the coating process can be selected from gravure coating, transfer coating, extrusion coating, and doctor blade coating. Meanwhile, in the coating process, one or more of the following can be used as dispersants for the mixed slurry used in the coating: DI water (deionized water), N-methyl-2-pyrrolidone (NMP), and dimethylformamide (DMF).

[0034] A third aspect of this application provides a secondary battery, including a positive electrode sheet, a negative electrode sheet, and an electrolyte, wherein the positive electrode sheet is the aforementioned positive electrode sheet; and / or, the negative electrode sheet is the aforementioned negative electrode sheet. The composite electrode active layer obtained in this application, when combined with a current collector to form an electrode sheet and applied to a secondary battery, effectively solves the problem of thermal runaway caused by high temperatures in traditional separators, while also preventing thermal runaway and significantly improving the high-temperature safety of the corresponding secondary battery. Example

[0035] A method for preparing a composite electrode active layer:

[0036] (1) Boehmite was selected as the inorganic particles, poly(m-phenylene isophthalamide) was selected as the heat-resistant polymer, and polyethylene glycol (PEG) was selected as the heat-sensitive polymer. The materials were mixed according to the weight ratio of inorganic particles: heat-resistant polymer: heat-sensitive polymer of 65:5:30, and NMP was used as the dispersant to obtain the composite insulation layer mixed slurry.

[0037] Among them, boehmite has a D50 of 0.1 μm and (D90-D10) / D50 of 3; the heat-resistant polymer poly(m-phenylene isophthalamide) has a melting temperature of 270℃; and the heat-sensitive polymer PEG has a softening temperature of 85℃.

[0038] (2) Using LFP as the positive electrode active material, PVDF as the binder, conductive carbon black and carbon nanotubes (CNT) as conductive agents, the positive electrode active material: conductive carbon black: CNT: PVDF is prepared according to a weight ratio of 95:0.5:0.5:2.0, and NMP is used as the dispersant to obtain the positive electrode mixed slurry.

[0039] (3) Using graphite as the negative electrode active material, SBR as the binder, CMC as the thickener, and conductive carbon black as the conductive agent, the negative electrode active material: conductive carbon black: SBR: CMC are mixed in a weight ratio of 96:1:2:1, and deionized water is used as the dispersant to obtain the negative electrode mixed slurry.

[0040] (4) Using aluminum foil as the positive current collector, according to 100g / m 2 The obtained positive electrode slurry was coated onto both sides of the positive electrode current collector using a coating density of 40 g / m². After rolling, a positive electrode material active layer with a thickness of 55 μm was formed on both sides. Copper foil was used as the negative electrode current collector, and the coating density was adjusted to achieve a coating density of 40 g / m². 2 The obtained negative electrode mixed slurry was coated on both sides of the negative electrode current collector by coating the surface density of the coating, and after rolling, a negative electrode material active layer with a thickness of 30μm was formed on both sides.

[0041] (5) According to 15g / m 2 The obtained composite insulating layer mixture slurry was coated onto two positive electrode material active layers and two negative electrode material active layers to form composite electrode active layers, with the thickness of the composite insulating layer being 4 μm.

[0042] The thickness ratio of the composite insulating layer to the active layer of the negative electrode material is 0.133:1, and the thickness ratio of the composite insulating layer to the active layer of the positive electrode material is 0.08:1. Example

[0043] A method for preparing a composite electrode active layer:

[0044] (1) Select Al2O3 as inorganic particles, polyethylene terephthalate as heat-resistant polymer, and polyvinyl alcohol as heat-sensitive polymer. Mix the materials according to the weight ratio of inorganic particles: heat-resistant polymer: heat-sensitive polymer of 85:5:10, and use DI water as dispersant to obtain composite insulation layer mixed slurry.

[0045] Among them, the D50 of Al2O3 is 6μm, and the (D90-D10) / D50 is 0.5; the melting temperature of the heat-resistant polymer polyethylene terephthalate is 260℃; and the softening temperature of the heat-sensitive polymer polyvinyl alcohol is 96℃.

[0046] (2) A positive electrode mixed slurry was obtained by referring to the conditions in Example 1.

[0047] (3) A negative electrode mixed slurry was obtained by referring to the conditions in Example 1.

[0048] (4) Using aluminum foil as the positive current collector, according to 400g / m 2 The obtained positive electrode slurry was coated onto both sides of the positive electrode current collector using a coating density of 210 μm, and after rolling, a positive electrode material active layer with a thickness of 210 μm was formed on both sides. Copper foil was used as the negative electrode current collector, with a coating density of 200 g / m 2 The obtained negative electrode mixed slurry was coated on both sides of the negative electrode current collector with a coating surface density of 130 μm, and after rolling, a negative electrode material active layer with a thickness of 130 μm was formed on both sides.

[0049] (5) According to 45g / m 2 The obtained composite insulating layer mixture slurry was coated onto two positive electrode material active layers and two negative electrode material active layers to form composite electrode active layers, with the thickness of the composite insulating layer being 20 μm.

[0050] The thickness ratio of the composite insulating layer to the active layer of the negative electrode material is 0.15:1, and the thickness ratio of the composite insulating layer to the active layer of the positive electrode material is 0.10:1. Example

[0051] A method for preparing a composite electrode active layer:

[0052] (1) BaTiO3 and TiO2 (BaTiO3:TiO2=0.5:1, weight ratio) were selected as inorganic particles, a mixture of poly(m-phenylene isophthalamide) and polyethylene terephthalate was selected as heat-resistant polymer (poly(m-phenylene isophthalamide): polyethylene terephthalate=1:1, weight ratio), and a mixture of polyvinyl alcohol and PEG was selected as heat-sensitive polymer (PEG: polyvinyl alcohol=1:2, weight ratio). The inorganic particles: heat-resistant polymer: heat-sensitive polymer were mixed according to a weight ratio of 75:3:22, and DMF was used as a dispersant to obtain a composite insulation layer mixed slurry.

[0053] Among them, BaTiO3 has a D50 of 3 μm and (D90-D10) / D50 of 1.5; TiO2 has a D50 of 1.2 μm and (D90-D10) / D50 of 2.7; the melting temperature of the mixture formed by poly(m-phenylene isophthalamide) and polyethylene terephthalate is 264℃; and the softening temperature of the mixture formed by polyvinyl alcohol and PEG is 89℃.

[0054] (2) A positive electrode mixed slurry was obtained by referring to the conditions in Example 1.

[0055] (3) A negative electrode mixed slurry was obtained by referring to the conditions in Example 1.

[0056] (4) Using aluminum foil as the positive current collector, according to 250g / m 2 The obtained positive electrode slurry was coated onto both sides of the positive electrode current collector, and after rolling, a positive electrode material active layer with a thickness of 132 μm was formed on both sides; copper foil was used as the negative electrode current collector, with a coating density of 120 g / m 2 The obtained negative electrode mixed slurry was coated on both sides of the negative electrode current collector with a coating surface density of 78 μm. After rolling, a negative electrode material active layer with a thickness of 78 μm was formed on both sides of the negative electrode current collector.

[0057] (5) According to 30g / m 2 The obtained composite insulating layer mixture slurry was coated onto two positive electrode material active layers and two negative electrode material active layers to form composite electrode active layers, with the thickness of the composite insulating layer being 12 μm.

[0058] The thickness ratio of the composite insulating layer to the active layer of the negative electrode material is 0.15:1, and the thickness ratio of the composite insulating layer to the active layer of the positive electrode material is 0.09:1. Example

[0059] A method for preparing a composite electrode active layer:

[0060] The only difference between this embodiment and Embodiment 1 is that the weight ratio of inorganic particles: heat-resistant polymer: thermosensitive polymer in step (1) is changed to 50:1:50. Example

[0061] A method for preparing a composite electrode active layer:

[0062] The only difference between this embodiment and Embodiment 1 is that the weight ratio of inorganic particles: heat-resistant polymer: thermosensitive polymer in step (1) is changed to 100:10:5. Example

[0063] A method for preparing a composite electrode active layer:

[0064] The only difference between this embodiment and Embodiment 1 is that the particle size distribution of the boehmite used is changed so that its D50 is 0.05 μm and (D90-D10) / D50 is 4.0. Example

[0065] A method for preparing a composite electrode active layer:

[0066] The only difference between this embodiment and Embodiment 2 is that the particle size distribution of the Al2O3 used is changed so that its D50 is 8.0 μm and (D90-D10) / D50 is 0.3. Example

[0067] A method for preparing a composite electrode active layer:

[0068] The only difference between this embodiment and embodiment 3 is that the ratio of BaTiO3 to TiO2 used is changed to BaTiO3:TiO2 = 0.1. Example

[0069] A method for preparing a composite electrode active layer:

[0070] The only difference between this embodiment and embodiment 3 is that the ratio of BaTiO3 to TiO2 used is changed to BaTiO3:TiO2=10. Example

[0071] A method for preparing a composite electrode active layer:

[0072] The only difference between this embodiment and Embodiment 3 is that the weight ratio of the heat-resistant polymer poly(m-phenylene isophthalamide) to polyethylene terephthalate is changed to 1:0.5. Example

[0073] A method for preparing a composite electrode active layer:

[0074] The only difference between this embodiment and Embodiment 3 is that the weight ratio of the heat-resistant polymer poly(m-phenylene isophthalamide) to polyethylene terephthalate is changed to 1:2. Example

[0075] A method for preparing a composite electrode active layer:

[0076] The only difference between this embodiment and Embodiment 3 is that the weight ratio of the thermosensitive polymer PEG to polyvinyl alcohol is changed to 1:1. Example

[0077] A method for preparing a composite electrode active layer:

[0078] The only difference between this embodiment and Embodiment 3 is that the weight ratio of the thermosensitive polymer PEG to polyvinyl alcohol is changed to 1:3. Example

[0079] A method for preparing a composite electrode active layer:

[0080] The difference between this embodiment and embodiment 3 lies only in steps (4) and (5), specifically:

[0081] (4) Using aluminum foil as the positive current collector, according to 80g / m 2 The obtained positive electrode slurry was coated onto both sides of the positive electrode current collector, and a positive electrode material active layer with a thickness of 350 μm was formed on both sides. Copper foil was used as the negative electrode current collector, and the coating density was adjusted according to 30 g / m². 2 The obtained negative electrode mixed slurry was coated on both sides of the negative electrode current collector with a coating surface density of 50 μm, and a negative electrode material active layer with a thickness of 50 μm was formed on both sides.

[0082] (5) According to 10g / m 2 The obtained composite insulating layer mixture slurry was coated onto two positive electrode material active layers and two negative electrode material active layers to form composite electrode active layers, with the thickness of the composite insulating layer being 30 μm.

[0083] The thickness ratio of the composite insulating layer to the active layer of the negative electrode material is 0.6:1, and the thickness ratio of the composite insulating layer to the active layer of the positive electrode material is 0.009:1. Example

[0084] A method for preparing a composite electrode active layer:

[0085] The difference between this embodiment and embodiment 3 lies only in steps (4) and (5), specifically:

[0086] (4) Using aluminum foil as the positive current collector, according to 500g / m 2The obtained positive electrode slurry was coated onto both sides of the positive electrode current collector, and a positive electrode material active layer with a thickness of 350 μm was formed on both sides. Copper foil was used as the negative electrode current collector, and the coating density was adjusted according to 300 g / m². 2 The obtained negative electrode mixed slurry was coated on both sides of the negative electrode current collector with a coating surface density of 5 μm, and a negative electrode material active layer with a thickness of 5 μm was formed on both sides.

[0087] (5) According to 60g / m 2 The obtained composite insulating layer mixture slurry was coated onto two positive electrode material active layers and two negative electrode material active layers to form composite electrode active layers, with the thickness of the composite insulating layer being 3 μm.

[0088] The thickness ratio of the composite insulating layer to the active layer of the negative electrode material is 0.6:1, and the thickness ratio of the composite insulating layer to the active layer of the positive electrode material is 0.009:1.

[0089] Comparative Example 1

[0090] The only difference between this comparative example and Example 1 is that no composite insulating layer was prepared. Furthermore, in preparing the cell sample in this comparative example, EJ's 9+2+2 type separator was used.

[0091] Comparative Example 2

[0092] The only difference between this comparative example and Example 2 is that no composite insulating layer was prepared. Furthermore, in preparing the cell sample in this comparative example, EJ's 7+3+3 type separator was used.

[0093] Comparative Example 3

[0094] The only difference between this comparative example and Example 3 is that no composite insulating layer was prepared. Furthermore, in preparing the cell sample, this comparative example used EJ's 12+2 type separator.

[0095] Comparative Example 4

[0096] A method for preparing a composite electrode active layer:

[0097] The only difference between this comparative example and Example 3 is that the composite insulating layer does not contain a heat-sensitive polymer, and the weight ratio of inorganic particles to heat-resistant polymer is changed to 75:25.

[0098] Comparative Example 5

[0099] A method for preparing a composite electrode active layer:

[0100] The only difference between this comparative example and Example 3 is that the composite insulation layer does not contain heat-resistant polymers, and the weight ratio of inorganic particles to heat-sensitive polymers is changed to 75:25.

[0101] Test methods

[0102] Battery sample preparation: The positive and negative electrode sheets obtained in each embodiment and comparative example were stacked sequentially, and then a core was obtained by stacking. The core was placed in a soft-pack outer packaging shell, dried, and then injected with D73 electrolyte at a rate of 4.0 g / Ah. After vacuum sealing, standing, formation, and capacity testing, a lithium-ion battery sample with a capacity of 1.5Ah was obtained. For the comparative example without a composite insulating layer, the obtained negative electrode sheet, separator, and positive electrode sheet were stacked to prepare a core, and then a battery sample with the same capacity was obtained by the same method as above.

[0103] Performance testing of battery samples:

[0104] (1) Discharge capacity retention rate (60℃, 7d): Under constant temperature environment of 25℃, the obtained secondary battery sample was left to stand for 24 hours after formation, charged to 3.65V with constant current and constant voltage at 0.33C, and cut off current at 0.05C; then discharged to 2.5V with constant current at 0.33C, and the discharge capacity C1 was recorded; then charged to 3.65V with constant current and constant voltage at 0.33C, and cut off current at 0.05C, left to stand at 60℃ for 7d, and then discharged to 2.5V with constant current at 0.33C, and the discharge capacity C2 was recorded. The discharge capacity retention rate R = C2 / C1 × 100%.

[0105] (2) Impedance: Internal resistance. After the battery samples obtained above were formed and tested, they were left to stand at 25°C for 24 hours. Then, IMP1, i.e., internal resistance at room temperature, was tested using a HIOKI voltage internal resistance meter. At the same time, the battery samples were placed in a 120°C constant temperature oven for 30 minutes, and then left to stand at 25°C for 30 minutes. IMP2, i.e., internal resistance after high temperature storage, was tested using a HIOKI voltage internal resistance meter.

[0106] (3) Safety test: The safety performance of the battery is verified by a hot box test. In this test, a thermocouple is attached to the surface of the battery and the battery is placed in a hot box. The battery is heated from an initial temperature (25℃) to 180℃ at a heating rate of 5±1℃ / min and stored for 30min. The temperature of the hot box is required to be 180℃. Then, the temperature is kept constant and the changes in battery temperature and voltage over time are recorded. The time t and temperature T from when the battery is kept at a constant temperature of 180℃ in the hot box until a voltage drop occurs are determined.

[0107] The results of the above tests are shown in Table 1.

[0108] Table 1

[0109]

[0110] As can be seen from the above description, the embodiments of this application have achieved the preparation of a composite electrode active layer that is resistant to high temperature and has excellent electrical performance, thus solving the problem of thermal runaway caused by high temperature in traditional separators in the field of secondary batteries.

[0111] Specifically, compared with Comparative Examples 1-3, Examples 1-3 showed a significant increase in IMP internal resistance after thermal storage, indicating that ion conduction in the liquid phase was hindered, resulting in a good thermosensitive effect and preventing the cell from rapidly continuing to discharge under thermal runaway conditions at 120°C, thus exhibiting good safety performance. Furthermore, in the 180°C thermal shock test, no voltage drop occurred, indicating that no short circuit occurred inside the cell, demonstrating high safety performance. Compared with Comparative Example 4, Examples 1-3 showed that without the thermosensitive polymer, the cell would continue to discharge even under thermal runaway conditions at 120°C without a change in internal resistance, while the introduction of the thermosensitive polymer could mitigate this risk. Compared with Comparative Example 5, Examples 1-3 showed that without the heat-resistant polymer as a binder, the thermosensitive polymer melted, and a short circuit between the positive and negative electrode plates still existed.

Claims

1. A composite electrode active layer, the composite electrode active layer comprising an active material layer and a composite insulating layer stacked sequentially, the composite insulating layer comprising inorganic particles, a heat-resistant polymer, and a heat-sensitive polymer; The weight ratio of the inorganic particles, the heat-resistant polymer, and the thermosensitive polymer is (50~100):(1~10):(5~50). The melting temperature of the heat-resistant polymer is 180℃~450℃; The softening temperature of the thermosensitive polymer is 80℃~120℃.

2. The composite electrode active layer according to claim 1, wherein, The weight ratio of the inorganic particles, the heat-resistant polymer, and the thermosensitive polymer is (65~85):(3~5):(10~30).

3. The composite electrode active layer according to claim 1 or 2, wherein, The heat-resistant polymer is selected from one or more of polyacrylate polymers, polyimide polymers, and amide polymers.

4. The composite electrode active layer according to claim 3, wherein, The heat-resistant polymer is selected from one or more of poly(m-phenylene isophthalamide), polyethylene terephthalate, and polybismaleimide.

5. The composite electrode active layer according to any one of claims 1 to 4, wherein, The thermosensitive polymer is selected from one or more of polyol polymers and polyvinyl alcohol polymers.

6. The composite electrode active layer according to claim 5, wherein, The thermosensitive polymer is polyethylene glycol and / or polyvinyl alcohol.

7. The composite electrode active layer according to any one of claims 1 to 6, wherein, The inorganic particles have a D50 of 0.1 μm to 6.0 μm and a (D90-D10) / D50 of 0.5 to 3.

0.

8. The composite electrode active layer according to claim 7, wherein, The inorganic particles are selected from one or more of boehmite, Al2O3, BaTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, SiO2, Y2O3, SiC, and TiO2.

9. The composite electrode active layer according to claim 7 or 8, wherein, The inorganic particles are BaTiO3 and TiO2, and the weight ratio of BaTiO3 to TiO2 is (0.1~10):

1.

10. The composite electrode active layer according to any one of claims 1 to 9, wherein, The thickness of the composite insulating layer is 4μm to 20μm.

11. The composite electrode active layer according to claim 10, wherein, The thickness ratio of the composite insulating layer to the active material layer is (0.01~0.5):

1.

12. The composite electrode active layer according to claim 10 or 11, wherein, The active material layer is a positive electrode active layer and / or a negative electrode active material layer.

13. The composite electrode active layer according to claim 12, wherein, The positive electrode material is selected from one or more of iron phosphate, manganese iron phosphate, and nickel-cobalt-manganese ternary materials; and / or, the negative electrode material is selected from one or more of graphite, silicon, and silicon-carbon composite materials.

14. The composite electrode active layer according to any one of claims 1 to 13, wherein, The inorganic particles are BaTiO3 and TiO2, and the weight ratio of BaTiO3 to TiO2 is (0.4~0.5):1; and / or, The heat-resistant polymer is poly(m-phenylene isophthalamide) and polyethylene terephthalate, and the weight ratio of poly(m-phenylene isophthalamide) to polyethylene terephthalate is 1:(0.8~1.2); and / or, The thermosensitive polymer is polyethylene glycol and polyvinyl alcohol, and the weight ratio of polyethylene glycol to polyvinyl alcohol is 1:(1.8~2.0).

15. An electrode sheet comprising a current collector and an electrode active layer disposed on at least one surface of the current collector, wherein, The electrode active layer is a composite electrode active layer according to any one of claims 1 to 14, and the active material layer in the composite electrode active layer is in contact with the current collector. The electrode sheet is a negative electrode sheet and / or a positive electrode sheet.

16. The electrode sheet according to claim 15, wherein, The composite insulating layer is applied to the surface of the active material layer away from the current collector via a coating process, and the surface density of the composite insulating layer during coating is 15 g / m². 2 ~45g / m 2 .

17. The electrode sheet according to claim 15 or 16, wherein, The electrode sheet is the positive electrode sheet, the current collector is the positive current collector, and the active material layer is the positive electrode material active layer. The positive electrode material active layer is deposited on the positive current collector by a coating process, and the coating surface density of the positive electrode material active layer during coating is 100 g / m². 2 ~400g / m 2 ; and / or, The electrode sheet is the negative electrode sheet, the current collector is the negative current collector, and the active material layer is the negative electrode material active layer. The negative electrode material active layer is deposited on the negative electrode current collector by a coating process, and the coating surface density of the negative electrode material active layer during coating is 40 g / m². 2 ~200g / m 2 .

18. A secondary battery, comprising a positive electrode plate, a negative electrode plate, and an electrolyte, wherein, The positive electrode sheet is the electrode sheet according to any one of claims 15 to 17; and / or, the negative electrode sheet is the electrode sheet according to any one of claims 15 to 17.

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