Thermosensitive conductive agent, gradient composite electrode, lithium ion battery and preparation method

Abstract

The invention discloses a thermosensitive conductive agent, a gradient composite electrode, a lithium ion battery and a preparation method, and belongs to the technical field of secondary batteries. The thermosensitive conductive agent comprises an inner core and a conductive shell arranged around the periphery of the inner core, the inner core comprises organic polymer porous microspheres and a liquid metal repair phase embedded in pores of the organic polymer porous microspheres, and the organic polymer porous microspheres comprise a thermal expansion material; after the thermal expansion material is heated to expand, the thermal expansion material extrudes the liquid metal repair phase, and the liquid metal repair phase releases the conductive material, so that the conductive material repairs cracks of the electrode coating; and the conductive shell provides a diffusion channel for active ions of the battery. The thermosensitive conductive agent is of a ternary structure, and can extrude a liquid metal repair phase in the expansion process, so that the liquid metal repair phase releases a conductive material to repair cracks, the electrical resistivity of an electrode is reduced, heat accumulation is reduced, and the thermal runaway risk of the secondary battery is reduced.

Description

Technical Field

[0001] This invention relates to the field of secondary battery technology, and in particular to a thermosensitive conductive agent, a gradient composite electrode, a lithium-ion battery, and a preparation method thereof. Background Technology

[0002] Research has found that one of the causes of thermal runaway in lithium-ion batteries is that during the charging and discharging process, the electrode materials continuously expand and contract, causing cracks in the conductive coating and deteriorating the interfacial contact. This leads to poor contact and reduced conductivity of the conductive coating, increasing the electrode resistivity and causing more electrical energy to be converted into heat, resulting in thermal runaway. Currently, there are no methods or materials available to repair cracks in the conductive coating of the electrodes under specific battery operating conditions. Summary of the Invention

[0003] In view of this, the present invention provides a thermosensitive conductive agent, a gradient composite electrode, a lithium-ion battery, and a preparation method thereof. The thermosensitive conductive agent has a ternary structure and can, under the battery working conditions, expand and squeeze the liquid metal repair phase, causing the liquid metal repair phase to release conductive material to repair cracks, reduce the resistivity of the electrode, reduce heat accumulation, and thus reduce the risk of thermal runaway of the secondary battery.

[0004] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0005] In a first aspect, the present invention provides a ternary thermosensitive conductive agent, comprising: a core and a conductive shell disposed around the periphery of the core.

[0006] The core comprises organic polymer porous microspheres and a liquid metal repair phase embedded in the pores of the organic polymer porous microspheres, wherein the organic polymer porous microspheres comprise a thermally expandable material;

[0007] After the thermal expansion material expands due to heat, it squeezes the liquid metal repair phase, and the liquid metal repair phase releases conductive material, which then repairs the cracks in the electrode coating.

[0008] The conductive casing provides a diffusion channel for the active ions in the battery.

[0009] Optionally, the core may further include a negative thermal expansion material.

[0010] Optionally, the negative thermal expansion material is ZrW2O8 with a mass fraction of 5wt% to 20wt%.

[0011] Optionally, the organic polymer porous microspheres include one or more combinations of poly-3-decylthiophene, poly-3-hexylthiophene, poly-3-octylthiophene, and polyaniline.

[0012] Optionally, the diameter of the organic polymer porous microspheres is 1 μm to 5 μm.

[0013] Optionally, the conductive shell comprises nitrogen-doped carbon nanotubes with a mass fraction of 1 wt% to 10 wt%.

[0014] Optionally, the longitudinal conductivity of the conductive shell is >10. 4 S / m.

[0015] In a second aspect, embodiments of the present invention provide a gradient composite electrode for use in lithium-ion batteries, comprising: a current collector and a multilayer conductive coating of a stacked structure disposed on the surface of the current collector;

[0016] Each layer of the conductive coating comprises: an electrode conductive material and a thermosensitive conductive agent provided in any of the above embodiments.

[0017] Optionally, the content of the thermosensitive conductive agent contained in the multiple conductive coatings decreases from the surface of the current collector toward the direction away from the current collector.

[0018] The stacked structure is a stacked double conductive coating, wherein the conductive coating closer to the current collector contains 10wt% to 30wt% of the thermosensitive conductive agent by mass, and the conductive coating farther from the current collector contains 2wt% to 8wt% of the thermosensitive conductive agent by mass.

[0019] Optionally, the conductive coating near the current collector may also include a positive electrode material and a thermosensitive binder.

[0020] Optionally, the conductive coating away from the current collector further includes: a positive electrode material and an antioxidant with a mass fraction of 0.5 wt% to 3 wt%.

[0021] Thirdly, embodiments of the present invention provide a lithium-ion battery, comprising: the gradient composite electrode provided in the second aspect embodiments above.

[0022] Fourthly, embodiments of the present invention provide a method for preparing the thermosensitive conductive agent provided in the first aspect embodiment above, comprising:

[0023] Step 1: Ball milling and mixing the raw materials required to form organic polymer porous microspheres to obtain a mixture;

[0024] Step 2: Prepare organic polymer porous microspheres from the mixture by spray drying;

[0025] Step 3: Grow a conductive shell on the surface of the microspheres by chemical vapor deposition;

[0026] Step 4: Inject liquid metal microcapsules into the pores of the organic polymer porous microspheres using a vacuum impregnation method.

[0027] Fifthly, embodiments of the present invention provide a method for preparing a gradient composite electrode according to the second aspect embodiment described above, comprising:

[0028] The conductive slurry containing a heat-sensitive conductive agent is simultaneously and layered onto the surface of the current collector using a multi-die head of a coating machine and then cured.

[0029] The technical solution of the above invention has the following advantages or beneficial effects:

[0030] The ternary thermal conductive agent provided in this invention, through its core comprising organic polymer porous microspheres and a liquid metal repair phase embedded in the pores of the porous microspheres, works in conjunction with a conductive shell that provides diffusion channels for active ions in the battery. This not only ensures the transport and diffusion of active ions, but also, during battery operation, as the battery temperature rises, the thermally expanding material of the organic polymer porous microspheres expands and compresses the liquid metal repair phase embedded in the pores of the porous microspheres. After being compressed, the liquid metal repair phase releases conductive material that can repair cracks in the electrode coating, thereby reducing the resistivity of the electrode coating increased by cracks, restoring the conductivity of the conductive coating, reducing heat generation, reducing heat accumulation, and thus reducing the risk of battery thermal runaway.

[0031] Furthermore, once the battery temperature reaches a certain level, the thermistor can repair cracks in the electrode coating by releasing conductive materials, thereby increasing the temperature the battery can withstand and raising the battery's thermal runaway temperature.

[0032] In addition, after the liquid metal repair phase releases conductive materials, if the battery temperature continues to rise, the thermal expansion material continues to expand, completely enveloping the liquid metal repair phase, blocking the active ion transport or diffusion path, causing the battery to lose power, and further reducing the risk of battery thermal runaway. Attached Figure Description

[0033] Figure 1 This is a three-dimensional structural diagram of the core of a thermosensitive conductive agent provided according to an embodiment of the present invention;

[0034] Figure 2 This is a cross-sectional structural schematic diagram of the thermosensitive conductive agent according to an embodiment of the present invention;

[0035] Figure 3 This is a schematic cross-sectional view of the gradient composite electrode provided in an embodiment of the present invention;

[0036] Figure 4 This is a schematic diagram showing the relative positional relationship between the die head and the current collector according to an embodiment of the present invention.

[0037] Figure label:

[0038] 10-Core; 11-Organic polymer porous microspheres; 12-Liquid metal repair phase; 13-Negative thermal expansion material;

[0039] 20 - Conductive housing; 30 - Current collector; 40 - Conductive coating; 50 - Die head. Detailed Implementation

[0040] The thermosensitive conductive agents involved in this invention generally refer to those that respond to temperature changes and whose conductivity changes with temperature. At room temperature, thermosensitive conductive agents have high conductivity, but their conductivity decreases at high temperatures. Currently, the temperature response characteristics of thermosensitive conductive agents can effectively prevent and suppress thermal runaway, as they are one of the key technologies for improving the safety of secondary batteries (especially lithium-ion batteries). Specifically, before the battery temperature reaches the thermal runaway temperature, the resistance of the thermosensitive conductive agent increases sharply to cut off the diffusion or transport path of active ions such as lithium ions, thereby stopping or significantly slowing down the redox reactions of the battery electrodes (especially heat-generating side reactions), reducing heat generation. In addition, the thermosensitive conductive agent also undergoes volume expansion at high temperatures, further breaking the contact points of the conductive path and enhancing the insulation effect.

[0041] As described in the background art, further research into the causes of battery thermal runaway reveals that, for thermal runaway caused by cracks in the conductive coating of the electrodes, repairing these cracks can prevent the runaway. Therefore, providing materials and methods that can promptly repair cracks during battery operation can help improve battery performance. In addition, existing thermistors have some unresolved issues: thermal response hysteresis. Existing thermistors generally have low temperature sensitivity, requiring higher temperatures (e.g., carbon black / polymers require temperatures exceeding 80°C) to trigger a resistance jump. However, a large amount of heat accumulates in the early stages of thermal runaway (60°C–80°C), and this accumulated heat, if not properly dissipated, accelerates battery thermal runaway. Existing thermistors, after repeated expansion, can cause the conductive network to break and become irreversible. Expansion of the thermistor can permanently increase electrode resistance by over 50%, accelerating battery capacity decay. Existing thermistors also suffer from poor interfacial compatibility, leading to poor active ion conduction, increased interfacial side reactions, accelerated electrolyte decomposition, and shortened battery life.

[0042] To address the aforementioned problems in the prior art, embodiments of the present invention provide a ternary thermosensitive conductive agent, a gradient composite electrode based on the ternary thermosensitive conductive agent, a lithium-ion battery, and a preparation method thereof.

[0043] The following description, in conjunction with the accompanying drawings, illustrates exemplary embodiments of the present invention, including various details to aid understanding. These details should be considered merely exemplary. Therefore, those skilled in the art will recognize that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of the invention. Similarly, for clarity and brevity, descriptions of well-known functions and structures are omitted in the following description.

[0044] It should be noted that, unless otherwise specified, the embodiments of the present invention and the technical features thereof can be combined with each other.

[0045] in, Figure 1 This diagram illustrates a three-dimensional structure of the core of the thermosensitive conductive agent provided in an embodiment of the present invention. Figure 2 This diagram shows a cross-sectional structure of the thermosensitive conductive agent provided in an embodiment of the present invention. Figure 3 A cross-sectional schematic diagram of the gradient composite electrode provided in an embodiment of the present invention is shown.

[0046] Specifically, such as Figure 1 and Figure 2 As shown, the ternary thermal conductive agent provided in this embodiment of the invention may include: a core 10 and a conductive shell 20 disposed around the outer periphery of the core.

[0047] The core 10 includes organic polymer porous microspheres 11 and a liquid metal repair phase 12 embedded in the pores of the organic polymer porous microspheres 11. The organic polymer porous microspheres 11 include thermally expandable materials.

[0048] After the thermal expansion material expands due to heat, it squeezes the liquid metal repair phase 12, and the liquid metal repair phase releases the conductive material, which then repairs the cracks in the electrode coating.

[0049] The conductive casing 20 provides a diffusion channel for the active ions of the battery.

[0050] In this invention, the thermal expansion material generally refers to an organic polymer material whose volume increases with increasing temperature.

[0051] The porous microspheres 11 involved in the embodiments of the present invention generally refer to spherical structures with a diameter of micrometers or nanometers and having pores.

[0052] The liquid metal repair phase 12 involved in the embodiments of the present invention generally exists in the form of a capsule. When squeezed, the capsule ruptures and releases the conductive material inside. Therefore, the conductive material released by the liquid metal repair phase 12 is generally liquid metal. This liquid metal exhibits a flow state, electrical conductivity and thermal conductivity at a specific temperature or under specific conditions. In addition to repairing cracks in the electrode coating, it can also conduct accumulated heat to dissipate heat for the battery.

[0053] Since a distinct interface is formed between the organic polymer porous microspheres 11 of the core 10 and the electrolyte, which is not conducive to the diffusion of active ions, in order to avoid the accumulation of active ions at the interface formed between the organic polymer porous microspheres 11 and the electrolyte and the interface side reactions, the present invention designs a conductive shell 20 of the thermosensitive conductive agent, which can provide a diffusion channel for the active ions (such as lithium ions) of the battery, so that the active ions can diffuse rapidly and reduce the interface side reactions.

[0054] The ternary thermal conductive agent provided in this invention, through its core comprising organic polymer porous microspheres and a liquid metal repair phase embedded in the pores of the porous microspheres, works in conjunction with a conductive shell that provides diffusion channels for active ions in the battery. This not only ensures the transport and diffusion of active ions, but also, during battery operation, as the battery temperature rises, the thermally expanding material of the organic polymer porous microspheres expands and compresses the liquid metal repair phase embedded in the pores of the porous microspheres. After being compressed, the liquid metal repair phase releases conductive material that can repair cracks in the electrode coating, thereby reducing the resistivity of the electrode coating increased by cracks, restoring the conductivity of the conductive coating, reducing heat generation, reducing heat accumulation, and thus reducing the risk of battery thermal runaway.

[0055] Furthermore, once the battery temperature reaches a certain level, the thermistor can repair cracks in the electrode coating by releasing conductive materials, thereby increasing the temperature the battery can withstand and raising the battery's thermal runaway temperature.

[0056] In addition, after the liquid metal repair phase releases conductive materials, if the battery temperature continues to rise, the thermal expansion material continues to expand, completely enveloping the liquid metal repair phase, blocking the active ion transport or diffusion path, causing the battery to lose power, and further reducing the risk of battery thermal runaway.

[0057] It is worth noting that at lower temperatures, during the process of thermal expansion material expanding and compressing the liquid metal repair phase embedded in the pores of porous microspheres, the expansion of thermal expansion material partially blocks the diffusion path of active ions, which increases the resistance. After the crack is repaired and the battery temperature decreases, the thermal expansion material contracts, the resistance decreases, and the battery returns to normal operation.

[0058] The principle of the ternary structure thermosensitive conductive agent for regulating thermal runaway provided in this invention embodiment is as follows: After the battery temperature reaches a certain temperature (far below the lower limit of the battery's thermal runaway temperature), the thermal expansion material of the organically polymerized porous microspheres 11 expands due to heat and squeezes the liquid metal repair phase embedded in the pores, causing the liquid metal repair phase to release conductive material. This conductive material repairs the cracks in the electrode coating, thereby improving the conductivity of the electrode coating and preventing heat accumulation caused by cracks. Although the expansion of the thermal expansion material during crack repair may block some diffusion paths of active ions, causing an increase in resistance, after crack repair and battery temperature reduction, the thermal expansion material contracts, the resistance decreases, and the battery returns to normal operation. If the thermal runaway is not caused by cracks, the battery temperature will continue to rise, and the thermal expansion material of the organically polymerized porous microspheres 11 will continue to expand. After expanding to a certain extent, the thermal expansion material can completely block the transport or diffusion paths of active ions, thereby blocking the redox reaction of the electrode, causing the battery to stop working, and reducing the risk of battery thermal runaway. Therefore, how to select thermally expanding materials, how to better control the relationship between the expansion temperature of thermally expanding materials and the lower limit of the battery's thermal runaway, how to ensure that the liquid metal repair phase can release conductive materials relatively completely, and how to block the diffusion path of active ions in a timely manner when the battery experiences thermal runaway are the core issues that need to be addressed in the thermally sensitive conductive agent designed in the embodiments of this invention.

[0059] Research has found that before thermal runaway, batteries accumulate a significant amount of heat at temperatures reaching 60°C to 80°C. Furthermore, repairing cracks in the electrode coating can alleviate battery temperature fluctuations at this temperature. Therefore, it is necessary to select organic porous materials capable of thermal expansion within the 60°C to 80°C temperature range. For example, organic polymeric porous microspheres may include one or more combinations of poly-3-decylthiophene, poly-3-hexylthiophene, poly-3-octylthiophene, and polyaniline. These organic polymeric porous microspheres, formed from one or more of these polymers, can expand and compress the liquid metal repair phase at battery temperatures reaching 60°C to 80°C, and the released conductive material effectively repairs cracks in the conductive coating.

[0060] Furthermore, in order to better compress the liquid metal repair phase, the thermosensitive conductive agent provided in the embodiments of the present invention includes, for example... Figure 2As shown, a negative thermal expansion material 13 is also introduced within the core 10. This negative thermal expansion material 13 expands within a lower temperature range, and it can cooperate with the thermal expansion material to compress the liquid metal repair phase, releasing conductive material and thus improving the release of conductive material. Furthermore, as the battery temperature increases further, the negative thermal expansion material 13 contracts, unaffecting the expansion of the thermal expansion material. This allows the thermal expansion material to block the transport path of active ions. In other words, within a certain temperature range, the negative thermal expansion material 13 can cooperate with the thermal expansion material to compress the liquid metal repair phase, releasing more conductive material and better repairing cracks. As the battery temperature further increases, the negative thermal expansion material 13 contracts, preventing further expansion of the thermal expansion material from being affected by the negative thermal expansion material 13, thus achieving the purpose of blocking the transport or diffusion path of active ions.

[0061] The negative thermal expansion material 13 selected in this embodiment of the invention can be a ceramic oxide, a metal alloy, a metal framework structure compound, such as one or more combinations of ZrW2O8, HfMo2O8, Sc2(WO4)3, LiAlSiO4, ZIF-4, or ZIF-8. Preferably, the negative thermal expansion material 13 selected in this embodiment of the invention is ZrW2O8, which is a conventional material in current batteries, has a low cost, and can form a good combination with the organic polymer porous microspheres 11. More preferably, the mass fraction of ZrW2O8 in the thermosensitive conductive agent is generally 5wt% to 20wt%. For example, the mass fraction of ZrW2O8 in the thermosensitive conductive agent can be 5wt%, 8wt%, 10wt%, 13wt%, 15wt%, 18wt%, or 20wt%, etc. By controlling the mass fraction of ZrW2O8 in the thermosensitive conductive agent, a better combination can be formed between ZrW2O8 and the thermal expansion material, ensuring that the conductive material is fully released before the battery thermal runaway, and enabling the thermosensitive conductive agent to block the diffusion path of active ions when the battery thermal runaway occurs.

[0062] Furthermore, the diameter of the organic polymer porous microspheres provided in the embodiments of the present invention is generally 1 μm to 5 μm. For example, the diameter of the organic polymer porous microspheres can be 1 μm, 2 μm, 3 μm, 4 μm, or 5 μm, etc., so that the effect of the expansion of the organic polymer porous microspheres matches the battery temperature.

[0063] Furthermore, the liquid metal repair phase provided in this embodiment of the invention is generally an alloy microcapsule. This alloy microcapsule typically includes a coating layer and a liquid alloy filled within the coating layer (this liquid alloy is the conductive material released from the aforementioned alloy microcapsule). The liquid alloy can be a Ga-In-Sn alloy, Ga-In alloy, Bi-Sn alloy, etc. The coating layer can be selected from commonly used coating layers in existing alloy capsules; the material used for the coating layer is not limited here. Preferably, the diameter of the alloy microcapsule is generally 100nm to 300nm. For example, the diameter of the alloy microcapsule can be 100nm, 150nm, 200nm, or 300nm, etc. By controlling the diameter of the alloy microcapsule, it can be embedded within the pores of the organic polymer porous microspheres 11, and the thermally expanding material can effectively compress the alloy microcapsule during the expansion process.

[0064] Furthermore, the thermosensitive conductive agent provided in this embodiment of the invention includes a conductive shell 20 comprising nitrogen-doped carbon nanotubes with a mass fraction of 1 wt% to 10 wt%. Exemplarily, the mass fraction of the nitrogen-doped carbon nanotubes is 1 wt%, 3 wt%, 5 wt%, 8 wt%, or 10 wt%. By controlling the mass fraction of the nitrogen-doped carbon nanotubes, the conductivity of the conductive shell 20 can be effectively guaranteed, and the diffusion ability of active ions can be improved. It is worth noting that the mass fraction of the nitrogen-doped carbon nanotubes generally refers to the mass fraction of nitrogen-doped carbon nanotubes in the thermosensitive conductive agent.

[0065] In this embodiment of the invention, the longitudinal conductivity of the conductive housing 20 can also be controlled to be >10. 4 The conductivity (S / m) is used to ensure the conductivity of the conductive shell 20 and the diffusion ability of active ions. The longitudinal conductivity of the conductive shell 20 is generally the conductivity of the conductive shell in the radial direction of the microspheres.

[0066] In addition, in this embodiment of the invention, the nitrogen-doped carbon nanotubes of the conductive shell 20 are generally perpendicular to the organic polymer porous microspheres 11, that is, the extension line of the axis of the nitrogen-doped carbon nanotubes passes through or is close to the center of the organic polymer porous microspheres 11, so as to ensure that active ions can diffuse rapidly from the conductive shell 20 to the organic polymer porous microspheres 11 and ensure the performance of the battery.

[0067] Furthermore, embodiments of the present invention also provide a gradient composite electrode for use in lithium-ion batteries. For example... Figure 3As shown, the gradient composite electrode may include a current collector 30 and a multilayer conductive coating 40 with a stacked structure disposed on the surface of the current collector 30. Each conductive coating 40 may include an electrode conductive material and a thermosensitive conductive agent provided in any of the above embodiments. The electrode conductive material is generally one or more of the positive electrode materials of the battery, such as ternary materials (NCM), lithium iron phosphate, lithium cobalt oxide, lithium nickel cobalt aluminum oxide, and lithium manganese oxide. In addition to the positive electrode material and the thermosensitive conductive agent, the conductive coating 40 may also include a binder such as poly(N-isopropylacrylamide) and an antioxidant such as β-carotene.

[0068] By introducing a multilayer conductive coating 40 with a stacked structure into the gradient composite electrode and adding the thermosensitive conductive agent provided in any of the above embodiments into the conductive coating 40, the thermosensitive conductive agent releases conductive material to fill the cracks in the conductive coating 40 during the battery heating process, thereby repairing the conductive coating 40 and improving the conductivity and thermal conductivity of the conductive coating 40, so as to effectively reduce the risk of battery thermal runaway.

[0069] In this embodiment of the invention, in order to effectively repair the cracks in the conductive coating 40 and simultaneously block the diffusion path of active ions after the battery reaches the thermal runaway temperature, thereby reducing the risk of battery thermal runaway, the diffusion path is adjusted from the surface of the current collector 30 towards the direction away from the current collector 30 (e.g., ...). Figure 3 As shown in direction D), the content of the thermosensitive conductive agent contained in the multilayer conductive coating 40 decreases progressively. That is, the inner conductive coating 40 contains a higher content of thermosensitive conductive agent, mainly used to repair cracks, while the outer conductive coating 40 contains a lower content of thermosensitive conductive agent, mainly serving to block the diffusion path of active ions.

[0070] More preferably, the stacked structure is a stacked double-layer conductive coating 40, wherein the conductive coating 40 near the current collector 30 contains a thermosensitive conductive agent with a mass fraction of 10wt% to 30wt%, and the conductive coating 40 away from the current collector 30 contains a mass fraction of 2wt% to 8wt%. For example, the mass fraction of the thermosensitive conductive agent in the conductive coating 40 near the current collector 30 can be 10wt%, 15wt%, 20wt%, 25wt%, or 30wt%, etc., and the mass fraction of the thermosensitive conductive agent in the conductive coating 40 away from the current collector 30 can be 2wt%, 3wt%, 5wt%, 6wt%, or 8wt%, etc. By matching the mass fraction of the thermosensitive conductive agent in the inner conductive coating 40 with that in the outer conductive coating 40, it is ensured that while repairing cracks in the conductive coating 40, the diffusion path of active ions can be effectively blocked.

[0071] More preferably, the conductive coating 40 near the current collector 30 also includes a positive electrode material and a thermosensitive binder. The thermosensitive binder can better improve the adhesion between the inner conductive coating 40 and the current collector 30, reducing the risk of the conductive coating 40 falling off. Furthermore, the combination of the thermosensitive binder and the thermosensitive conductive agent can enable a rapid response at a lower temperature after the battery reaches the thermal runaway temperature, blocking the diffusion path of active ions.

[0072] Furthermore, the conductive coating 40 located away from the current collector 30 also includes a positive electrode material and an antioxidant with a mass fraction of 0.5 wt% to 3 wt%. For example, the antioxidant can be β-carotene. By adding an antioxidant to the outer conductive coating 40, reactive oxygen species can be captured, reducing side reactions at the electrode interface by more than 60%, ensuring the effectiveness of the conductive coating 40, reducing the risk of failure, and improving its reliability. Preferably, the mass fraction of the antioxidant contained in the conductive coating 40 located away from the current collector 30 can be 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, or 3 wt%, etc. By controlling the mass fraction of the antioxidant, the response temperature of the outer conductive coating 40 can be increased.

[0073] Preferably, for the conductive coatings 40 in the multilayer structure, the response temperature of each conductive coating 40 is generally controlled to increase from the inside to the outside. For example, the response temperature of the inner conductive coating 40 is 60°C, and the response temperature of the outer conductive coating 40 is 180°C. By controlling the response temperature of each conductive coating 40 to increase from the inside to the outside, cracks can be quickly filled by the inner conductive coating 40 at a lower temperature, while the diffusion path of active ions can be quickly cut off by the outer conductive coating 40 after the temperature rises.

[0074] Furthermore, embodiments of the present invention also provide a lithium-ion battery. The lithium-ion battery casing includes: the gradient composite electrode provided in any of the above embodiments.

[0075] Furthermore, embodiments of the present invention also provide a method for preparing the thermosensitive conductive agent provided in any of the above embodiments. Specifically, the method for preparing the thermosensitive conductive agent may include the following steps A1 to A4:

[0076] Step A1: Ball milling and mixing the raw materials required to form organic polymer porous microspheres to obtain a mixture.

[0077] For example, the raw material may include poly-3-decylthiophene and ZrW2O8. The ball milling parameters used for this ball milling mixture can be adjusted according to actual needs.

[0078] Step A2: Prepare organic polymer porous microspheres from the mixture by spray drying.

[0079] The temperatures, such as inlet temperature, outlet temperature, and pressure, designed for the spray drying process can all be based on existing conventional parameters.

[0080] Step A3: Grow a conductive shell on the surface of the microspheres by chemical vapor deposition.

[0081] This chemical vapor deposition can be plasma-enhanced chemical vapor deposition, low-temperature chemical vapor deposition, low-pressure chemical vapor deposition, etc. Through this step, materials containing nitrogen-doped carbon nanotubes are formed on the outer periphery of organic polymer porous microspheres to form a conductive shell.

[0082] Step A4: Inject liquid metal microcapsules into the pores of organic polymer porous microspheres using a vacuum impregnation method.

[0083] Furthermore, embodiments of the present invention provide a method for preparing a gradient composite electrode according to any of the above embodiments. The method for preparing the gradient composite electrode includes: simultaneously and layering a conductive slurry containing a thermosensitive conductive agent onto the surface of the current collector 30 using a multi-die head of a coating machine, followed by curing.

[0084] Specifically, the relative positional relationship between the multiple mold heads 50 (exemplarily two mold heads 50) and the collector 30 is as follows: Figure 4 As shown, two parallel die heads 50 synchronously extrude and spray a conductive slurry containing a thermosensitive conductive agent and move along the S direction, thereby forming a double layer of conductive slurry on the surface of the current collector 30 and curing it. By synchronously extruding and spraying and then curing, there can be no obvious interface between the sprayed multilayer conductive slurry, thereby reducing the interface resistance between the formed conductive coating 40 and the gradient composite electrode.

[0085] Furthermore, performance tests were conducted on existing electrodes (without the thermosensitive conductive agent provided in this embodiment) and gradient composite electrodes prepared using the method provided in this embodiment. The test results are shown in Table 1 below. It is worth noting that the thermosensitive conductive agent preparation process introduced in the gradient composite electrode tested in this embodiment involves: doping 10 wt% ZrW2O8 into poly-3-decylthiophene microspheres via ball milling; depositing nitrogen-doped carbon nanotubes on the outer periphery of the microspheres via chemical vapor deposition to form a conductive shell; then embedding 200 nm diameter Ga-In-Sn alloy microcapsules into the pores of the poly-3-decylthiophene microspheres via vacuum impregnation; subsequently, two layers of slurry were simultaneously extruded and sprayed using a dual-die head and cured. The resulting gradient composite electrode comprises two stacked conductive coatings, wherein the inner conductive coating contains 20 wt% thermosensitive conductive agent, and the outer conductive coating contains 5 wt% thermosensitive conductive agent and 1 wt% antioxidant β-carotene. The test revealed that the response temperature of the inner conductive coating is 60°C, and the response temperature of the outer conductive coating is 180°C. In addition, the positive electrode material used in both the existing electrode and the gradient composite electrode provided in the embodiments of the present invention is LiCoO2.

[0086] Table 1

[0087] Test Project Existing electrodes Gradient composite electrode Resistance jump factor <![CDATA[10 3 times @100℃]]> <![CDATA[10 5 double @60℃]]> Thermal runaway trigger temperature 126.3℃ 203.6℃ Overcharge test Fire (100%) No fire (100%)

[0088] The test results in Table 1 above show that, compared to existing electrodes (with a battery temperature of 100℃, the resistance increases by 10). 3 The gradient composite electrode provided in this embodiment of the invention exhibits a 10-fold increase in resistance at 60°C. 5 The increase in resistance by 100 times indicates that the gradient composite electrode provided in this embodiment of the invention can respond to battery thermal runaway at relatively low temperatures. The resistance jump at 60°C is mainly due to the expansion of the poly-3-decylthiophene microspheres, a thermosensitive conductive agent in the inner conductive coating, which blocks the diffusion path of active ions. Regarding the temperature rise caused by cracks in the conductive coating, the liquid alloy released during the expansion of the poly-3-decylthiophene microspheres repairs the cracks, thereby lowering the battery temperature. The poly-3-decylthiophene microspheres then shrink, restoring the battery to its normal operating state. Furthermore, compared to batteries with existing electrodes, the battery using the gradient composite electrode provided in this embodiment of the invention exhibits a significantly higher thermal runaway trigger temperature, delayed by 77.3°C. This means that the battery using the gradient composite electrode provided in this embodiment of the invention only experiences thermal runaway at higher temperatures, demonstrating that the thermosensitive conductive agent provided in this embodiment of the invention can improve the battery's thermal runaway trigger temperature and enhance battery safety by repairing cracks in the conductive coating.

[0089] Furthermore, overcharge tests were conducted on batteries with existing electrodes and batteries using the gradient composite electrode provided in the embodiments of the present invention, respectively. The test results show that the gradient composite electrode provided in the embodiments of the present invention can further improve battery safety.

[0090] In addition, the battery using the gradient composite electrode provided in the embodiments of the present invention was tested for cycle stability and rate performance. The test results show that the gradient composite electrode provided in the embodiments of the present invention can only increase its resistance by 8% after the battery has undergone 500 cycles, which further illustrates that the gradient composite electrode provided in the embodiments of the present invention can effectively repair cracks, reduce resistance, and improve battery cycle stability.

[0091] In addition, by selecting Ga-In-Sn alloy, the Ga-In-Sn alloy can be separated and extracted by acid treatment in the gradient composite electrode of waste batteries, so that the recovery rate of Ga-In-Sn alloy can reach more than 95%, reducing costs and making the material recyclable.

[0092] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can occur depending on design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A heat-sensitive conductive agent of a ternary structure, characterized by Comprising: a core (10) and a conductive shell (20) arranged around the periphery of the core, the core (10) comprises organic polymeric porous microspheres (11) and a liquid metal healing phase (12) embedded in the pores of the organic polymeric porous microspheres (11), the organic polymeric porous microspheres (11) comprise a thermal expansion material; after the thermal expansion material is heated and expanded, the thermal expansion material extrudes the liquid metal healing phase, the liquid metal healing phase releases conductive material, and the conductive material heals the cracks of the electrode coating; the conductive shell (20) provides a diffusion channel for active ions of the battery.

2. The thermosensitive conductive agent according to claim 1, wherein the core (10) further comprises a negative thermal expansion material (13); preferably, the negative thermal expansion material is ZrW2O8 with a mass fraction of 5wt%-20wt%; and / or the liquid metal healing phase is an alloy microcapsule.

3. The thermosensitive conductive agent according to claim 1 or 2, wherein the organic polymeric porous microspheres comprise one or more combinations of poly-3-decylthiophene, poly-3-hexylthiophene, poly-3-octylthiophene, and polyaniline; and / or the diameter of the organic polymeric porous microspheres is 1μm-5μm; and / or the conductive shell (20) comprises nitrogen-doped carbon nanotubes with a mass fraction of 1wt%-10wt%; and / or The longitudinal electrical conductivity of the electrically conductive shell (20) is > 10 4 S / m.

4. A gradient composite electrode applied to a lithium ion battery, characterized by, Comprising: a current collector (30) and a multilayer conductive coating (40) of a layered structure arranged on the surface of the current collector (30); each layer of the conductive coating (40) comprises an electrode conductive material and the thermosensitive conductive agent of any one of claims 1-3.

5. The gradient composite electrode according to claim 4, wherein from the surface of the current collector (30) to the direction away from the current collector (30), the content of the thermosensitive conductive agent contained in the multilayer conductive coating (40) decreases.

6. The gradient composite electrode according to claim 5, wherein the layered structure is a layered double-layer conductive coating (40), wherein the conductive coating (40) close to the current collector (30) contains the thermosensitive conductive agent with a mass fraction of 10wt%-30wt%, and the conductive coating (40) away from the current collector (30) contains the thermosensitive conductive agent with a mass fraction of 2wt%-8wt%.

7. The gradient composite electrode according to claim 6, wherein the conductive coating (40) close to the current collector (30) further comprises a positive electrode material and a thermosensitive binder; and / or the conductive coating (40) away from the current collector (30) further comprises a positive electrode material and an antioxidant with a mass fraction of 0.5wt%-3wt%.

8. A lithium-ion battery, characterized by Comprising: the gradient composite electrode of any one of claims 4-7.

9. A method for producing the heat-sensitive electrically conductive agent according to any one of claims 1 to 3, characterized by, Comprising: Step 1, ball-milling the raw materials required for forming the organic polymeric porous microspheres to obtain a mixture; Step 2, preparing the organic polymeric porous microspheres by spray drying the mixture; Step 3, growing a conductive shell on the surface of the microspheres by chemical vapor deposition; Step 4, injecting the liquid metal microcapsule into the pores of the organic polymeric porous microspheres by a vacuum impregnation method.

10. A method of manufacturing the gradient composite electrode according to any one of claims 4 to 7, characterized by, Comprise: A conductive paste containing a thermosensitive conductive agent is extrusion sprayed on the surface of the current collector (30) using a multi-mode head of a coater, and is cured.

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