Semi-solid battery and preparation method thereof

Abstract

The invention provides a semi-solid battery and a preparation method thereof, and belongs to the technical field of secondary batteries, and a positive pole piece of the semi-solid battery comprises a positive pole piece and a negative pole piece. Wherein the positive pole piece comprises a positive active material layer, the positive active material layer comprises a first polymer, the first polymer comprises a repetitive unit derived from a first monomer, and the first monomer comprises at least one of three-functionality acrylic ester monomers and four-functionality acrylic ester monomers; the negative pole piece comprises a negative active material layer, the negative active material layer comprises a second polymer, the second polymer comprises a repetitive unit derived from a second monomer, and the second monomer comprises at least one of acrylic ester monomers with one functionality and acrylic ester monomers with two functionality. According to the invention, polymers formed by polymerization of monomers with different degrees of functionality are introduced into the positive pole piece and the negative pole piece, so as to realize directional control of the crosslinking degree of in-situ polymer films on the interfaces of the positive pole piece and the negative pole piece, so that good cycle performance of the battery can be maintained while the thermal safety performance of the battery is improved.

Description

Technical Field

[0001] This invention relates to the field of secondary battery technology, and in particular to a semi-solid-state battery and its preparation method. Background Technology

[0002] Semi-solid batteries, as a key transitional solution from liquid batteries to all-solid batteries, can significantly improve battery safety and energy density while maintaining good cycle performance by retaining a small amount of electrolyte in the battery.

[0003] In semi-solid-state batteries, the stability and kinetic performance of the interface between high-energy-density electrode active materials (such as high-nickel ternary cathode materials and silicon anode materials) and the electrolyte are poor, limiting their further application to higher energy densities. Currently, to optimize the electrode interface in semi-solid-state batteries, a single monomer and initiator are typically added to the electrolyte to simultaneously polymerize in situ on both the positive and negative electrode surfaces to form a polymer film. However, this in-situ polymerization technology does not differentiate between the optimization requirements of the positive and negative electrode interfaces. The polymer film formed simultaneously on both surfaces cannot simultaneously improve the thermal stability of the positive electrode interface and the kinetic performance of the negative electrode interface, resulting in an inability to simultaneously meet the battery's safety and cycle performance requirements.

[0004] Therefore, it is necessary to design a semi-solid-state battery and its preparation method to improve the above problems. Summary of the Invention

[0005] This invention provides a semi-solid-state battery and its preparation method, which addresses the technical problem that current interface optimization methods cannot simultaneously improve the thermal stability of the positive electrode interface and the dynamic performance of the negative electrode interface in semi-solid-state batteries.

[0006] In a first aspect, the present invention provides a semi-solid battery comprising a positive electrode, a separator, a negative electrode, and an electrolyte.

[0007] The positive electrode includes a positive current collector and a positive active material layer disposed on the positive current collector. The positive active material layer includes a first polymer, which includes repeating units derived from a first monomer. The first monomer includes at least one of a trifunctional acrylate monomer and a tetrafunctional acrylate monomer. The negative electrode includes a negative current collector and a negative active material layer disposed on the negative current collector. The negative active material layer includes a second polymer, which includes repeating units derived from a second monomer. The second monomer includes at least one of a monofunctional acrylate monomer and a difunctional acrylate monomer.

[0008] In one example of the present invention, the gel content of the positive electrode is greater than or equal to 80%, and the gel content of the negative electrode is less than or equal to 28%.

[0009] In one example of the present invention, the gel content of the positive electrode sheet is 80% to 88%.

[0010] In one example of the present invention, the gel content of the negative electrode sheet is 22% to 28%.

[0011] In one example of the present invention, the mass content of the first polymer in the positive electrode active material layer is 3% to 5%; and the mass content of the second polymer in the negative electrode active material layer is 1% to 3%.

[0012] In one example of the present invention, the functional acrylate monomer includes at least one of methyl acrylate, ethyl acrylate, butyl methacrylate, butyl acrylate, styrene, and vinyl acetate.

[0013] In one example of the present invention, the difunctional acrylate monomer includes at least one of diethylene glycol diacrylate, triethylene glycol diacrylate, 1,4-butanediol diacrylate, neopentyl glycol diacrylate, and hexanediol diacrylate.

[0014] In one example of the present invention, the trifunctional acrylate monomer includes at least one of trimethylolpropane trimethacrylate, glycerol triacrylate, and tri(2-hydroxyethyl)isocyanurate triacrylate.

[0015] In one example of the present invention, the tetrafunctional acrylate monomer includes at least one of bis(trimethylolpropane)tetraacrylate, pentaerythritol tetramethacrylate, ethoxylated pentaerythritol tetraacrylate, tetramethylolcyclohexylmethane tetraacrylate, and propoxylated pentaerythritol tetraacrylate.

[0016] In a second aspect, the present invention also provides a method for preparing a semi-solid-state battery, the method comprising:

[0017] The positive electrode active material, positive electrode conductive agent, positive electrode binder and first monomer are mixed in a first solvent according to a preset mass ratio to prepare a positive electrode slurry; the positive electrode slurry is coated on a positive electrode current collector and then dried by heating to obtain a positive electrode sheet;

[0018] The negative electrode active material, negative electrode conductive agent, negative electrode binder and second monomer are mixed in a second solvent according to a preset mass ratio to prepare a negative electrode slurry; the negative electrode slurry is coated on a negative electrode current collector and then dried by heating to obtain a negative electrode sheet;

[0019] The positive electrode, the negative electrode, and the separator are assembled into a battery cell, an electrolyte is injected into the battery cell, and the battery cell is subjected to thermal curing treatment to obtain a semi-solid battery; wherein, the electrolyte includes an initiator, which is used to initiate the polymerization of the first monomer and the second monomer.

[0020] In one example of the present invention, the thermal curing treatment of the battery cell includes: heating the battery cell at a temperature of 60°C to 80°C for 2 to 4 hours.

[0021] In one example of the present invention, the initiator has a mass content of 0.5% to 1.5% in the electrolyte.

[0022] In one example of the present invention, the initiator comprises azobisisobutyronitrile.

[0023] The semi-solid-state battery provided by this invention introduces a first polymer formed by in-situ polymerization of high-functionality acrylate monomers into the positive electrode to form a dense three-dimensional cross-linked film within the positive electrode. This three-dimensional cross-linked film can effectively prevent the release of active oxygen from the positive electrode active material at high temperatures, suppress the chain exothermic reaction between the positive and negative electrodes, and significantly improve the battery's thermal safety performance. Simultaneously, the semi-solid-state battery introduces a second polymer formed by in-situ polymerization of low-functionality acrylate monomers into the negative electrode to form a slightly cross-linked porous polymer film within the negative electrode. This porous polymer film can ensure rapid lithium-ion transport at the negative electrode interface and adapt to the volume expansion of lithium insertion / extraction at the negative electrode with good hardness and flexibility, thereby maintaining the stability of the negative electrode interface and preventing the deterioration of battery kinetic performance.

[0024] In summary, the semi-solid-state battery provided by this invention achieves directional control of the degree of crosslinking of the polymer film at the positive and negative electrode interfaces by introducing polymers formed by the polymerization of monomers with different functionalities into the positive and negative electrode sheets. This improves the thermal safety performance of the battery while maintaining good cycle performance. Detailed Implementation

[0025] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, unless otherwise specified, the following embodiments and features can be combined with each other. It should also be understood that the terminology used in the embodiments of the present invention is for describing specific implementation schemes and not for limiting the scope of protection of the present invention. Test methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions or according to the conditions recommended by the respective manufacturers.

[0026] It should be noted that the terms such as "upper", "lower", "left", "right", "middle" and "one" used in this specification are only for clarity of description and are not intended to limit the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered as part of the scope of the invention.

[0027] In this article, the self-heating initiation temperature T1 is the temperature at which the battery's self-heating rate exceeds the reference value without external heating, marking the precursor to thermal runaway.

[0028] The thermal runaway initiation temperature T2 is the temperature at which the battery temperature rise rate (dT / dt) reaches 1℃ / s, marking the official start of thermal runaway.

[0029] The highest thermal runaway temperature, T3, is the highest temperature reached by the battery during thermal runaway, reflecting the severity of the thermal runaway.

[0030] Currently, a single monomer and initiator are typically added to the electrolyte to simultaneously polymerize in situ on the positive and negative electrode surfaces, forming a polymer film to optimize the electrode interface in semi-solid-state batteries. However, this in-situ polymerization technology forms the same polymer film in both the positive and negative electrodes, making it difficult to simultaneously meet the optimization requirements of both interfaces. Introducing a low-crosslinking monomer into the electrolyte can improve the kinetic performance and structural stability of the negative electrode interface, but it cannot block oxygen release at the positive electrode interface, thus failing to improve the thermal safety performance of the semi-solid-state battery. Conversely, introducing a high-crosslinking monomer into the electrolyte can effectively block oxygen release from the positive electrode at high temperatures, but it increases the impedance of the negative electrode interface by 30% to 50%, affecting the kinetic performance of the negative electrode interface and leading to a severe degradation in battery cycle performance.

[0031] To address the aforementioned technical deficiencies, this application provides a semi-solid-state battery and its preparation method. By introducing acrylate monomers with different functionalities into the positive and negative electrode sheets, a highly cross-linked polymer film is formed in the positive electrode sheet and a low-cross-linked polymer film is formed in the negative electrode sheet after thermal curing. This simultaneously improves the thermal stability of the positive electrode interface and the kinetic performance of the negative electrode interface, thereby enhancing both the safety and cycle performance of the semi-solid-state battery.

[0032] In a first aspect, the present invention provides a semi-solid battery comprising a positive electrode, a separator, a negative electrode, and an electrolyte. The positive electrode, separator, and negative electrode are arranged sequentially along the thickness direction, and the electrolyte fills the space between the positive electrode and the negative electrode, and fully wets the positive electrode, separator, and negative electrode.

[0033] The positive electrode includes a positive current collector and a positive active material layer disposed on the positive current collector. The positive active material layer includes a positive active material, a positive conductive agent, a positive binder, and a first polymer. The negative electrode includes a negative current collector and a negative active material layer disposed on the negative current collector. The negative active material layer includes a negative active material, a negative conductive agent, a negative binder, a thickener, and a second polymer. In the battery, the positive and negative active materials can intercalate and deintercalate lithium ions to achieve energy storage and release. The electrolyte is the carrier for lithium ion transport between the positive and negative electrodes. The separator is permeable to lithium ions but non-conductive, thus separating the positive and negative electrodes to prevent short circuits.

[0034] In the positive electrode sheet, the first polymer includes repeating units derived from the first monomer, such as the first polymer being formed by polymerization of the first monomer. The first monomer includes at least one of trifunctional acrylate monomers and tetrafunctional acrylate monomers. The first polymer is formed in situ by polymerizing a higher-functionality acrylate monomer within the positive electrode active material layer. The formed first polymer is uniformly distributed within the positive electrode active material layer, and the cross-linked network constructed by the first polymer fills the spaces between the positive electrode active material particles and coats the outer surface of the particles. Furthermore, after the positive electrode sheet is immersed in the electrolyte, the first polymer enables the positive electrode sheet to achieve a high gel content.

[0035] Since the first polymer is formed by polymerizing acrylate monomers with high functionality, it can construct a dense three-dimensional polymer film in the positive electrode active material layer. This three-dimensional polymer film can effectively block the decomposition and oxygen release of the positive electrode active material at high temperatures, suppress the chain exothermic reaction between the negative electrode active material and active oxygen at high temperatures, reduce the probability of thermal runaway of the battery, and thus effectively improve the thermal safety performance of the battery. After the interface modification of the first polymer, the self-heating initiation temperature T1 of the semi-solid-state battery is increased by at least 20°C (increased to 100°C and above), the thermal runaway initiation temperature T2 is increased by at least 40°C (increased to 180°C and above), and the maximum thermal runaway temperature T3 of the battery is reduced by 400°C (reduced to 450°C and below).

[0036] In the negative electrode, the second polymer comprises repeating units derived from a second monomer, such that the second polymer is formed by polymerization of the second monomer. The second monomer includes at least one of a monofunctional acrylate monomer and a difunctional acrylate monomer. Specifically, the second polymer is formed by in-situ polymerization of a lower-functionality acrylate monomer within the negative electrode active material layer. The slightly cross-linked porous membrane formed by the low-functionality acrylate monomer polymer is uniformly distributed within the negative electrode active material layer and fills the spaces between the positive electrode active material particles. This porous membrane constructed from the second polymer achieves a low gel content after the negative electrode is wetted by the electrolyte.

[0037] The porous membrane constructed from the second polymer can ensure rapid lithium-ion transport within the negative electrode active material layer and significantly reduce the transport impedance of lithium-ions at the interface of the negative electrode active material. Simultaneously, the porous membrane constructed from the second polymer can adapt to the volume expansion caused by lithium insertion / extraction at the negative electrode with good hardness and flexibility, maintaining the long-term stability of the negative electrode interface and preventing the degradation of the battery's kinetic performance during long cycles, thereby significantly improving the battery's cycle performance.

[0038] By introducing acrylate monomers with different functionalities, this application allows for the simultaneous formation of polymer films with varying degrees of crosslinking within both the positive and negative electrode sheets. This results in a higher gel content in the positive electrode sheet after immersion in the electrolyte, and a lower gel content in the negative electrode sheet. In some embodiments, the gel content of the positive electrode sheet is greater than or equal to 80% to ensure the first polymer's barrier effect against oxygen release from the positive electrode; the gel content of the negative electrode sheet is less than or equal to 28% to ensure the second polymer's kinetic improvement effect on the negative electrode interface.

[0039] Optionally, in some embodiments, the gel content of the positive electrode sheet is any value within the range of 80% to 88%, for example, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, or 88%. In some embodiments, the gel content of the negative electrode sheet is any value within the range of 22% to 28%, for example, 22%, 23%, 24%, 25%, 26%, 27%, or 28%.

[0040] In some embodiments, the mass content of the first polymer in the positive electrode active material layer is any value within the range of 3% to 5%, for example, the mass content of the first polymer can be 3%, 3.5%, 4%, 4.5%, or 5%. When the mass content of the first polymer in the positive electrode active material layer is within the above range, the gel content of the positive electrode sheet can be maintained above 80%, ensuring that the first polymer in the positive electrode sheet has a sufficient barrier effect on the high-temperature oxygen release of the positive electrode active material; at the same time, it also avoids introducing too much highly cross-linked first polymer to excessively increase the positive electrode interface impedance, thereby causing the battery cycle performance to degrade.

[0041] In some embodiments, the mass content of the second polymer in the negative electrode active material layer is any value within the range of 1% to 3%, for example, the mass content of the second polymer can be 1%, 1.5%, 2%, 2.5%, or 3%. When the mass content of the second polymer in the negative electrode active material layer is within the above range, the gel content of the negative electrode sheet can be prevented from increasing to 30% or more, thereby preventing an increase in the ion transport impedance at the negative electrode interface, which would cause a decline in battery cycle performance.

[0042] Introducing both trifunctional and tetrafunctional acrylate monomers into the first monomer can improve the hardness and crosslinking density of the first polymer, thereby enhancing its barrier effect against oxygen release from the positive electrode. Simultaneously, the introduction of trifunctional acrylate monomers can also improve the solvent resistance of the first polymer, enhance the internal structural stability of the positive electrode sheet, and further reduce the probability of direct contact between the positive electrode active material and the electrolyte, thus reducing the occurrence of side reactions between the positive electrode active material and the electrolyte, and ultimately improving the battery's cycle stability.

[0043] In some embodiments, the trifunctional acrylate monomers include at least one of trimethylolpropane trimethacrylate (TMPTMA), glycerol triacrylate (GTA), and tri(2-hydroxyethyl)isocyanurate triacrylate (THEICTA).

[0044] In some embodiments, the tetrafunctional acrylate monomers include at least one of bis(trimethylolpropane)tetraacrylate (Di-TMPTA), pentaerythritol tetramethacrylate (PETMA), ethoxylated pentaerythritol tetraacrylate (EO-PETTA), tetramethylolcyclohexylmethane tetraacrylate (TMCHA-TA), and propoxylated pentaerythritol tetraacrylate (PO-PETTA).

[0045] Introducing a monofunctional acrylate monomer into the second monomer can adjust the flexibility of the second polymer and enhance its ability to adapt to volume changes during the negative electrode cycle, thereby improving the structural stability of the negative electrode interface. Introducing a difunctional acrylate monomer can appropriately increase the crosslinking degree of the second polymer, so that the second polymer has sufficient hardness and crosslinking degree to maintain the long-term coverage effect of the second polymer on the surface of the negative electrode active material particles.

[0046] In some embodiments, a functional acrylate monomer includes at least one of methyl acrylate (MA), ethyl acrylate (EA), butyl methacrylate (BMA), butyl acrylate (BA), styrene (St), and vinyl acetate (VAc).

[0047] In some embodiments, the difunctional acrylate monomers include at least one of diethylene glycol diacrylate (DEGDA), triethylene glycol diacrylate (TEGDA), 1,4-butanediol diacrylate (BDDA), neopentyl glycol diacrylate (NPGDA), and hexanediol diacrylate (HDDA).

[0048] In addition, it should be noted that the positive current collector in the positive electrode sheet of this application can be made of foil with good conductivity and mechanical strength, such as aluminum, nickel, titanium, gold, silver, chromium, molybdenum, copper, stainless steel or carbon, etc.; in addition to foil, the positive current collector can also be any one or more of the following forms: film, mesh, porous, foam or non-woven fabric.

[0049] The positive electrode active material is selected from one or more of lithium iron phosphate (LFP), lithium manganese iron phosphate (LMFP), lithium cobalt oxide (LCO), lithium nickel oxide (LNO), lithium manganese oxide (LMO), lithium nickel manganese oxide (LNMO), lithium nickel cobalt manganese oxide (NCM), lithium nickel cobalt aluminum oxide (NCA), and lithium-rich manganese oxide (LRMO). The positive electrode conductive agent can be selected from at least one of conductive materials such as carbon black (Super P), acetylene black, carbon nanotubes (CNT), graphene, and carbon nanofibers (VGCF); the positive electrode binder can be selected from at least one of polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE), for example, PVDF can be used as the positive electrode binder.

[0050] In this application, the negative electrode current collector can be made of foil with good conductivity and mechanical strength, such as aluminum, nickel, titanium, gold, silver, chromium, molybdenum, copper, stainless steel or carbon. In addition to foil, the negative electrode current collector can also be any one or more of the following forms: film, mesh, porous, foam or non-woven fabric.

[0051] The negative electrode active material is selected from one or more of the following: tin, artificial graphite (single-crystal graphite, polycrystalline graphite, pyrolytic graphite, graphite fiber, etc.), natural graphite (bulk graphite, flake graphite, earthy graphite, etc.), soft carbon, hard carbon, pure silicon (crystalline silicon, amorphous silicon, or organosilicon), silicon oxide compounds, silicon carbide compounds, and nano-metal oxides (Fe2O3, CuO, SnO2, Mn3O4 nanoparticles). In some embodiments, the negative electrode active material may be a Gr-doped silicon negative electrode material, such as Gr-doped pure silicon, silicon oxide compounds, or silicon carbide compounds.

[0052] The negative electrode conductive agent can be selected from at least one conductive material such as carbon black (Super P), acetylene black, carbon nanotubes (CNT), graphene, and carbon nanofibers (VGCF). The negative electrode binder is selected from at least one binder such as polyvinylidene fluoride (PVDF), vinyl fluoride-hexafluoropropylene (PVDF-HFP), polyethylene oxide (PEO), polymethyl methacrylate (PMMA), nitrile rubber (NBR), hydrogenated nitrile rubber (HNBR), and styrene-butadiene rubber (SBR). The thickener is selected from carboxymethyl cellulose, which can be sodium carboxymethyl cellulose (CMC-Na) or lithium carboxymethyl cellulose (CMC-Li).

[0053] In this application, the diaphragm is selected from conventional porous polymer membranes in the art. For example, the diaphragm material may be selected from one or more combinations of polyvinylidene fluoride, polystyrene, polyarylether sulfone, polyvinyl chloride, polypropylene, polyethylene, polyamide, polyimide, polyacrylic acid, polyacetal, polycarbonate, polyester, polyetherimide, polyimide, polyketone, polyphenylene ether, polyphenylene sulfide, polymethylpentene, polysulfone nonwoven glass, glass fiber materials, ceramics, metal oxides, and composites of organic and inorganic substances. For example, in one instance, the diaphragm is a porous polyethylene (PE) or polypropylene (PP) membrane, optionally a PP / PE / PP porous membrane, with a thickness of 9 μm to 18 μm, such as 9 μm, 12 μm, 16 μm or 18 μm; an air permeability of 180 s / 100 mL to 380 s / 100 mL, such as 180 s / 100 mL, 280 s / 100 mL or 380 s / 100 mL; and a porosity of 30% to 50%, such as 30%, 40% or 50%.

[0054] In this application, the electrolyte can be any conventional type of electrolyte in the art. For example, the electrolyte can be prepared by mixing a small molecule plasticizer and a lithium salt in a mass ratio of (8-9):(1-2). The small molecule plasticizer is selected from one or more combinations of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, fluorinated ethylene carbonate, dipropyl carbonate, dimethyl sulfoxide dimethoxyethane, N-methyl-2-pyrrolidone, γ-butyrolactone, and polyethylene glycol dimethyl ether; the lithium salt is selected from one or more combinations of LiBF4, LiBF6, LiAsF6, LiPF6, LiClO4, LiFSI, LiTFSI, LiB(C6H5)4, LiAlCl4, LiBr, LiCF3SO3, LiN(CF3SO2)2, and LiC(CF3SOSO2)3.

[0055] In a second aspect, the present invention also provides a method for preparing a semi-solid-state battery, the method comprising the following steps:

[0056] S1. The positive electrode active material, positive electrode conductive agent, positive electrode binder and first monomer are mixed in a first solvent according to a preset mass ratio to prepare a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector and then dried by heating to obtain a positive electrode sheet;

[0057] S2. The negative electrode active material, negative electrode conductive agent, negative electrode binder and second monomer are mixed in a second solvent according to a preset mass ratio to prepare a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector and dried by heating to obtain a negative electrode sheet;

[0058] S3. Assemble the positive electrode, the negative electrode, and the separator into a battery cell, inject electrolyte into the battery cell, and perform thermal curing treatment on the battery cell to obtain a semi-solid battery.

[0059] In some embodiments, in step S1, the positive electrode active material, positive electrode conductive agent, positive electrode binder, and first monomer are mixed in a first solvent (such as N-methylpyrrolidone) at a mass ratio of (90-95):(1-2):(1-2):(3-5) to adjust and form a positive electrode slurry with a viscosity of 3000-5000 mPa·s. The positive electrode slurry is coated onto a positive electrode current collector and dried under vacuum to form a positive electrode sheet.

[0060] In some embodiments, in step S2, the negative electrode active material, negative electrode conductive agent, negative electrode binder, thickener, and second monomer are mixed in a second solvent (such as deionized water) at a mass ratio of (92-94):(0.2-1.5):(1-3):(1-2):(1-3) to adjust and form a negative electrode slurry with a viscosity of 4000-6000 mPa·s. The negative electrode slurry is coated onto a negative electrode current collector and dried under vacuum to form a negative electrode sheet.

[0061] In some embodiments, step S3 includes the following steps;

[0062] S31. The positive electrode, separator and negative electrode are stacked in sequence and placed in an aluminum-plastic film to obtain an electrode assembly; the electrode assembly is placed in a housing and fully baked to reduce its water content to below 450ppm in order to make a battery cell.

[0063] S32. Inject electrolyte into the battery cell and allow it to stand for a preset time to allow the electrolyte to fully wet the positive electrode, negative electrode, and separator. The electrolyte includes an initiator that can initiate the polymerization of the first monomer in the positive electrode and the second monomer in the negative electrode at a preset thermosetting temperature. The injected electrolyte has a mass content of 10%–15% in the battery cell, and the standing time after injection can be 30 minutes to 2 hours.

[0064] S33. The battery cell is placed at a preset thermal curing temperature for heating and curing treatment, so that the first monomer in the positive electrode sheet is polymerized in situ to form the first polymer, and the second monomer in the negative electrode sheet is polymerized in situ to form the second polymer, thereby making a semi-solid battery.

[0065] In some embodiments, in step S32, the mass content of the initiator in the provided electrolyte is any value within the range of 0.5% to 1.5%, for example, it can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, or 1.5%. When the mass content of the initiator in the electrolyte is within the above-mentioned suitable range, it can promote the full cross-linking of acrylate monomers in the positive and negative electrode sheets, and avoid introducing too much initiator into the electrolyte, which would lead to initiator decomposition and gas generation, thereby affecting the battery cycle life.

[0066] In addition, it should be noted that in step S32, the initiator introduced into the electrolyte can be any initiator material capable of initiating the polymerization of acrylate monomers. For example, in some embodiments, the initiator includes azobisisobutyronitrile (AIBN).

[0067] In some embodiments, in step S33, the battery cell is heated at a temperature of 60°C to 80°C for 2 to 4 hours to induce the first monomer in the positive electrode to fully polymerize in situ to form a first polymer, and the second monomer in the negative electrode to fully polymerize in situ to form a second polymer. Simultaneously, heating and curing at the above temperature ensures that the acrylate monomers in the positive and negative electrode sheets are completely polymerized without compromising the structural stability of the electrolyte.

[0068] The technical solution of the present invention will be described in detail below through several specific embodiments and comparative examples. Unless otherwise stated, the raw materials and reagents used in the following embodiments are commercially available products or can be prepared by conventional methods in the art.

[0069] Example 1

[0070] This embodiment provides a semi-solid-state battery, the composition and preparation process of which are described below:

[0071] (1) Preparation of positive electrode sheet: The positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1 O2, acetylene black (positive electrode conductive agent), PVDF (positive electrode binder), and TMPTA (first monomer) were mixed in a mass ratio of 93:2:2:3. After mixing, N-methylpyrrolidone (NMP) was added to adjust the viscosity to 4000 Pa·s to prepare the positive electrode slurry. The positive electrode slurry was coated onto a 12 μm thick aluminum foil for the positive electrode current collector. The coated current collector was then dried under vacuum at 120°C for 12 hours, and finally rolled to a compaction density of 3.5 g / cm³. 3 It is then cut into positive electrode sheets with a length and width of 100mm × 100mm.

[0072] (2) Preparation of the negative electrode sheet: Silicon negative electrode active material (obtained by mixing silicon-carbon material and graphite, with a mass ratio of silicon-carbon material to graphite of 3:7), negative electrode conductive agent SuperP, negative electrode binder SBR, thickener, and second monomer EGDA were mixed in a mass ratio of 92.5:1.5:2:2:2. After mixing, deionized water was added to adjust the viscosity to 5000 Pa·s to prepare the negative electrode slurry. The negative electrode slurry was coated onto an 8 μm thick copper foil for the negative electrode current collector. The coated negative electrode current collector was then dried in a vacuum environment at 110°C for 10 hours, and finally rolled to a compaction density of 1.5 g / cm³. 3 It is then cut into negative electrode sheets with a length and width of 102mm × 102mm.

[0073] (3) Electrolyte preparation: In an argon-protected glove box (water and oxygen content both less than or equal to 0.1 ppm), battery-grade ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed in a mass ratio of 3:5:2 to form a solvent. A predetermined mass ratio of lithium salt LiPF6 was dissolved in the solvent to adjust the lithium salt concentration in the electrolyte to 1 mol / L. Finally, the initiator AIBN was added to the solvent and stirred for 2 hours to ensure complete dissolution, thus obtaining the electrolyte. The initiator content in the electrolyte was 1% by mass.

[0074] (4) A PE film with a thickness of 12μm was used as the separator. The positive electrode, separator and negative electrode were alternately stacked and packaged in an aluminum-plastic film shell under a vacuum of -0.095MPa to form a bare cell. Then, electrolyte was injected into the cell and left to stand for 30 minutes to allow the electrolyte to fully wet the electrodes and separator. The injected battery was then placed in a constant temperature oven and heated at 70℃ for 3 hours. Finally, after heating and curing, the battery was charged to 4.25V at a constant current and constant voltage rate of 0.1C. After standing for 10 minutes, the battery was discharged to 2.5V at a constant current rate of 0.1C to complete the battery activation.

[0075] Example 2

[0076] This embodiment provides a semi-solid battery with the same system as that in Embodiment 1. The difference between this embodiment and Embodiment 1 is that in step (1), the positive electrode active material, positive electrode conductive agent, positive electrode binder and the first monomer are mixed in a mass ratio of 92:2:2:4.

[0077] Example 3

[0078] This embodiment provides a semi-solid battery with the same system as that in Embodiment 1. The difference between this embodiment and Embodiment 1 is that in step (1), the positive electrode active material, positive electrode conductive agent, positive electrode binder and the first monomer are mixed in a mass ratio of 91:2:2:5.

[0079] Example 4

[0080] This embodiment provides a semi-solid battery with the same system as in Embodiment 1. The difference between this embodiment and Embodiment 1 is that in step (1), the positive electrode active material, positive electrode conductive agent, positive electrode binder and the first monomer are mixed in a mass ratio of 93.5:2:2:2.5.

[0081] Example 5

[0082] This embodiment provides a semi-solid battery with the same system as that in Embodiment 1. The difference between this embodiment and Embodiment 1 is that in step (1), the positive electrode active material, positive electrode conductive agent, positive electrode binder and the first monomer are mixed in a mass ratio of 90.5:2:2:5.5.

[0083] Example 6

[0084] This embodiment provides a semi-solid battery with the same system as in Embodiment 1. The difference between this embodiment and Embodiment 1 is that in step (2), the negative electrode active material, negative electrode conductive agent, negative electrode binder, thickener and second monomer are mixed in a mass ratio of 91.5:1.5:2:2:3.

[0085] Example 7

[0086] This embodiment provides a semi-solid battery with the same system as in Embodiment 1. The difference between this embodiment and Embodiment 1 is that in step (2), the negative electrode active material, negative electrode conductive agent, negative electrode binder, thickener and second monomer are mixed in a mass ratio of 93.5:1.5:2:2:1.

[0087] Example 8

[0088] This embodiment provides a semi-solid battery with the same system as in Embodiment 1. The difference between this embodiment and Embodiment 1 is that in step (2), the negative electrode active material, negative electrode conductive agent, negative electrode binder, thickener and second monomer are mixed in a mass ratio of 94:1.5:2:2:0.5.

[0089] Example 9

[0090] This embodiment provides a semi-solid battery with the same system as in Embodiment 1. The difference between this embodiment and Embodiment 1 is that in step (2), the negative electrode active material, negative electrode conductive agent, negative electrode binder, thickener and second monomer are mixed in a mass ratio of 92:1.5:2:2:3.5.

[0091] Example 10

[0092] This embodiment provides a semi-solid-state battery with the same system as that in Embodiment 1. The difference between this embodiment and Embodiment 1 is that the first cell is PETTA.

[0093] Example 11

[0094] This embodiment provides a semi-solid-state battery with the same system as that in Embodiment 1. The difference between this embodiment and Embodiment 1 is that the second cell is MMA.

[0095] Example 12

[0096] This embodiment provides a semi-solid battery with the same system as that in Embodiment 1. The difference between this embodiment and Embodiment 1 is that the mass content of the initiator in the electrolyte in step (3) is 0.5%.

[0097] Example 13

[0098] This embodiment provides a semi-solid battery with the same system as that in Embodiment 1. The difference between this embodiment and Embodiment 1 is that the mass content of the initiator in the electrolyte in step (3) is 1.5%.

[0099] Example 14

[0100] This embodiment provides a semi-solid battery with the same system as that in Embodiment 1. The difference between this embodiment and Embodiment 1 is that the mass content of the initiator in the electrolyte in step (3) is 0.3%.

[0101] Example 15

[0102] This embodiment provides a semi-solid battery with the same system as in Embodiment 1. The difference between this embodiment and Embodiment 1 is that the mass content of the initiator in the electrolyte in step (3) is 1.8%.

[0103] Example 16

[0104] This embodiment provides a semi-solid battery with the same system as that in Embodiment 1. The difference between this embodiment and Embodiment 1 is that the heating and curing temperature for the liquid-filled battery in step (4) is 80°C and the heating and curing time is 2 hours.

[0105] Example 17

[0106] This embodiment provides a semi-solid battery with the same system as that in Embodiment 1. The difference between this embodiment and Embodiment 1 is that the heating and curing temperature for the liquid-filled battery in step (4) is 60°C and the heating and curing time is 4 hours.

[0107] Example 18

[0108] This embodiment provides a semi-solid battery with the same system as that in Embodiment 1. The difference between this embodiment and Embodiment 1 is that the heating and curing temperature of the liquid-filled battery in step (4) is 85°C.

[0109] Example 19

[0110] This embodiment provides a semi-solid battery with the same system as that in Embodiment 1. The difference between this embodiment and Embodiment 1 is that the heating and curing temperature of the liquid-filled battery in step (4) is 55°C.

[0111] Example 20

[0112] This embodiment provides a semi-solid battery with the same system as that in Embodiment 1. The difference between this embodiment and Embodiment 1 is that the heating and curing time for the liquid-filled battery in step (4) is 5 hours.

[0113] Example 21

[0114] This embodiment provides a semi-solid battery with the same system as that in Embodiment 1. The difference between this embodiment and Embodiment 1 is that the heating and curing time for the liquid-filled battery in step (4) is 1 hour.

[0115] Comparative Example 1

[0116] This comparative example provides a semi-solid-state battery with the same system as Example 1. The difference between this comparative example and Example 1 is that the first cell is not introduced into the positive electrode in step (1), and the second cell is not introduced into the negative electrode in step (2).

[0117] Comparative Example 2

[0118] This comparative example provides a semi-solid-state battery with the same system as Example 1. The difference between this comparative example and Example 1 is that the first cell in step (1) is changed to EGDA.

[0119] Comparative Example 3

[0120] This comparative example provides a semi-solid-state battery with the same system as Example 1. The difference between this comparative example and Example 1 is that the second cell in step (2) is changed to PETTA.

[0121] The gel content of the positive and negative electrode sheets in the semi-solid batteries provided in Examples 1 to 21 and Comparative Examples 1 to 3 was measured, and the thermal safety performance and cycle performance of the semi-solid batteries prepared in Examples 1 to 21 and Comparative Examples 1 to 3 were tested to verify the improvement effect of the proposed solution on battery performance. The test results are shown in Table 1.

[0122] Gel content test of positive and negative electrode sheets: After the battery is thermosetting, take 1g of each of the positive and negative electrode sheets (accurate to 0.001g), cut them into small pieces, and put them into a Soxhlet extractor. Extract with dimethyl carbonate (DMC) solvent under reflux for 24 hours. Dry the residue after extraction under vacuum at 80℃ to constant weight, and then weigh the dried residue (accurate to 0.001g). Finally, calculate the gel content according to the formula "(mass after drying / initial mass)×100%".

[0123] Semi-solid-state battery cycle performance testing: Using a charge-discharge testing system, the battery was charged at a constant current rate of 1C to 4.25V under a constant temperature environment of 25℃, and then charged at a constant voltage of 4.25V to a constant current rate of 0.05C. After resting for 5 minutes, the battery was discharged at a constant current rate of 1C to 2.5V, and the initial cycle discharge capacity was tested. The battery was subjected to 500 charge-discharge cycles under the above conditions, and the discharge capacity in the 500th cycle was recorded to obtain the capacity retention rate after 500 cycles. The capacity retention rate after 500 cycles was calculated using the following formula: Capacity retention rate (%) = (Discharge capacity after 500 cycles / Initial cycle discharge capacity) × 100%. The charge-discharge accuracy was calibrated every 50 cycles during the test.

[0124] Thermal safety performance testing of semi-solid-state batteries: An accelerated calorimeter (ARC) was used. The battery was placed in a sealed reactor, and after purging the air, the temperature was increased from room temperature at a rate of 5°C / min. After each temperature increase, the temperature was held for 15 minutes before heating was stopped to allow the cell temperature to reach ambient temperature. During the heating process, the cell temperature and pressure changes were monitored in real time: when the temperature increase rate increased from ≤0.1°C / min to >0.1°C / min, the temperature was recorded as T1 (self-exothermic initiation temperature); when the temperature increase rate suddenly increased to >2°C / min, the temperature was recorded as T2 (thermal runaway trigger temperature); when the temperature reached its peak and then began to decrease, the peak temperature was recorded as T3 (thermal runaway peak temperature). An inert atmosphere was maintained inside the reactor during the test to avoid external interference.

[0125] Table 1: Performance test results of batteries prepared in Examples 1 to 21 and Comparative Examples 1 to 3

[0126]

[0127]

[0128] Comparing the test results of Examples 1 to 21 and Comparative Example 1, it can be seen that the embodiments of this disclosure, by introducing a highly cross-linked first polymer into the positive electrode sheet, can effectively block the release of active oxygen from the positive electrode active material into the battery when the internal temperature of the battery rises, and suppress the chain exothermic reaction between the negative electrode active material and active oxygen, thus significantly improving the thermal safety performance of the battery. At the same time, the embodiments of this disclosure also introduce a low-cross-linked second polymer into the negative electrode sheet to reduce the transport impedance of lithium ions at the negative electrode interface and adapt to the huge volume deformation of the negative electrode active material during charging and discharging, maintaining the long-term stability of the negative electrode interface, thereby greatly improving the cycle performance of the battery. Compared to Comparative Example 1, in this embodiment, after introducing polymers with monomers of different functionalities into the electrode sheet, the self-heating onset temperature T1 of the semi-solid battery is increased to above 95°C, the thermal runaway onset temperature T2 is increased to above 170°C, and the maximum thermal runaway temperature T3 of the battery is reduced to below 500°C. At the same time, the 500cls cycle capacity retention rate of the semi-solid battery is increased by at least 10% (the 500cls cycle capacity retention rate is increased to above 85%), which can meet the long-term use requirements of the semi-solid system.

[0129] Comparing the test results of Example 1 and Comparative Example 2, it can be seen that, although the cycle performance of the semi-solid-state battery in Comparative Example 2, which only introduces low-functionality acrylate monomers in both the positive and negative electrodes, is significantly improved compared to before modification, the low-crosslinking polymer in the positive electrode cannot effectively block oxygen release, resulting in a less than ideal improvement in the thermal safety performance of the semi-solid-state battery. In contrast to Comparative Example 2, this application's embodiment introduces low-functionality acrylate monomers in the negative electrode and high-functionality acrylate monomers in the positive electrode. This allows the battery to form a low-crosslinking second polymer in the negative electrode and a high-crosslinking first polymer in the positive electrode after thermosetting. This enables the negative electrode to improve interfacial kinetics by introducing the second polymer, while the positive electrode can effectively block oxygen release from the high-temperature decomposition of the positive electrode active material using the first polymer. This achieves a significant improvement in thermal safety performance while ensuring good cycle performance.

[0130] Comparing the test results of Example 1 and Comparative Example 3, it can be seen that if only high-functionality acrylate monomers are introduced into both the positive and negative electrodes of the semi-solid-state battery in Comparative Example 3, the thermal safety performance of the semi-solid-state battery is significantly improved compared to before modification. However, the highly cross-linked polymer in the negative electrode will block the lithium-ion transport channels and reduce the flexibility of the polymer, thereby seriously affecting the kinetic performance of the negative electrode interface and causing the cycle performance of the semi-solid-state battery to degrade. Compared with Comparative Example 3, the embodiments of this application introduce high-functionality acrylate monomers into the positive electrode and low-functionality acrylate monomers into the negative electrode. This allows the battery to form a low-crosslinked second polymer in the negative electrode and a highly cross-linked first polymer in the positive electrode after thermosetting. This allows the positive electrode to effectively improve the thermal stability using the first polymer, while also improving the interfacial kinetic performance and stability by introducing the second polymer into the negative electrode, thus improving both the thermal safety performance and cycle performance of the battery.

[0131] Comparing the test results of Examples 1 to 3 and Examples 4 to 5, it can be seen that when the mass content of the first polymer in the positive electrode active material layer is 3% to 5%, the gel content of the positive electrode sheet reaches over 80%, and the improvement effect on the thermal safety performance and cycle performance of the semi-solid-state battery is optimal. If the mass content of the first polymer is too low, the gel content of the positive electrode sheet decreases significantly, and the first polymer in the positive electrode sheet cannot effectively block the decomposition and oxygen release of the positive electrode active material, resulting in poor thermal safety performance of the semi-solid-state battery. If the mass content of the first polymer is too high, too much first polymer is introduced into the positive electrode sheet, leading to an increase in the interfacial impedance of the positive electrode sheet and causing a decline in battery cycle performance.

[0132] Comparing the test results of Examples 1, 6, 7 and Examples 8 to 9, it can be seen that when the mass content of the second polymer in the negative electrode active material layer is 1% to 3%, the gel content of the negative electrode sheet is limited to below 28%, achieving the optimal improvement effect on the thermal safety performance and cycle performance of the semi-solid-state battery. If the mass content of the second polymer is too high, the gel content of the negative electrode sheet increases to over 30%, leading to an increase in the impedance of ion transport at the negative electrode interface and a decrease in battery cycle performance.

[0133] Comparing the test results of Examples 1, 12, 13 and Examples 14, 15, it can be seen that when the mass content of the initiator in the electrolyte is within the suitable range of 0.5% to 1.5%, it can promote the full cross-linking of acrylate monomers introduced into the positive and negative electrode sheets, and avoid introducing too much initiator, which would damage the electrochemical stability of the electrolyte and thus cause the battery cycle life to decrease. If the mass content of the initiator in the electrolyte is too low, it is difficult to promote the complete polymerization of acrylate monomers during the thermosetting process, resulting in poor improvement effect of the introduced monomers on the battery cycle performance and thermal safety performance; if the mass content of the initiator in the electrolyte is too high, too much initiator remaining in the electrolyte after thermosetting is prone to decomposition and gas generation, which deteriorates the battery kinetic performance and causes the battery cycle life to decrease.

[0134] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A semi-solid-state battery, characterized in that, Includes positive electrode, separator, negative electrode, and electrolyte; The positive electrode sheet includes a positive current collector and a positive active material layer disposed on the positive current collector. The positive active material layer includes a first polymer, which includes repeating units derived from a first monomer. The first monomer includes at least one of a trifunctional acrylate monomer and a tetrafunctional acrylate monomer. The negative electrode sheet includes a negative current collector and a negative active material layer disposed on the negative current collector. The negative active material layer includes a second polymer, which includes repeating units derived from a second monomer. The second monomer includes at least one of a monofunctional acrylate monomer and a difunctional acrylate monomer.

2. The semi-solid-state battery according to claim 1, characterized in that, The positive electrode has a gel content greater than or equal to 80%, and the negative electrode has a gel content less than or equal to 28%.

3. The semi-solid-state battery according to claim 2, characterized in that, The positive electrode has a gel content of 80% to 88%; and / or, the negative electrode has a gel content of 22% to 28%.

4. The semi-solid-state battery according to claim 1, characterized in that, The first polymer has a mass content of 3% to 5% in the positive electrode active material layer; the second polymer has a mass content of 1% to 3% in the negative electrode active material layer.

5. The semi-solid-state battery according to claim 1, characterized in that, The monofunctional acrylate monomers include at least one of methyl acrylate, ethyl acrylate, butyl methacrylate, butyl acrylate, styrene, and vinyl acetate; the difunctional acrylate monomers include at least one of diethylene glycol diacrylate, triethylene glycol diacrylate, 1,4-butanediol diacrylate, neopentyl glycol diacrylate, and hexanediol diacrylate.

6. The semi-solid-state battery according to claim 1, characterized in that, The trifunctional acrylate monomers include at least one of trimethylolpropane trimethacrylate, glycerol triacrylate, and tri(2-hydroxyethyl)isocyanurate triacrylate; the tetrafunctional acrylate monomers include at least one of bis(trimethylolpropane tetraacrylate), pentaerythritol tetramethacrylate, ethoxylated pentaerythritol tetraacrylate, tetramethylolcyclohexylmethane tetraacrylate, and propoxylated pentaerythritol tetraacrylate.

7. A method for preparing a semi-solid-state battery according to any one of claims 1 to 6, characterized in that, include: The positive electrode active material, positive electrode conductive agent, positive electrode binder and first monomer are mixed in a first solvent according to a preset mass ratio to prepare a positive electrode slurry; the positive electrode slurry is coated on a positive electrode current collector and then dried by heating to obtain a positive electrode sheet; The negative electrode active material, negative electrode conductive agent, negative electrode binder and second monomer are mixed in a second solvent according to a preset mass ratio to prepare a negative electrode slurry; the negative electrode slurry is coated on a negative electrode current collector and then dried by heating to obtain a negative electrode sheet; The positive electrode, the negative electrode, and the separator are assembled into a battery cell, an electrolyte is injected into the battery cell, and the battery cell is subjected to thermal curing treatment to obtain a semi-solid battery; wherein, the electrolyte includes an initiator, which is used to initiate the polymerization of the first monomer and the second monomer.

8. The preparation method according to claim 7, characterized in that, The thermal curing treatment of the battery cell includes: The battery cell is heated at a temperature of 60°C to 80°C for 2 to 4 hours.

9. The preparation method according to claim 7, characterized in that, The initiator has a mass content of 0.5% to 1.5% in the electrolyte.

10. The preparation method according to claim 7, characterized in that, The initiator includes azobisisobutyronitrile.

Images