Composite current collector, preparation method thereof, electrode sheet, and lithium ion battery

Abstract

The present application relates to a kind of composite current collector and its preparation method, electrode sheet, lithium ion battery.The composite current collector includes composite support layer and conductive layer, composite support layer is dispersed in polymer matrix and inorganic heat-conducting fiber is arranged, inorganic heat-conducting fiber is selected from one or more of SiC fiber, Si3N4 Fiber, Mg3N2 Fiber, GaN fiber, AlN fiber and BN fiber.One aspect can improve the thermal conductivity of support layer, on the other hand, the toughening of support layer can be carried out.Moreover, the above fiber material is non-conductive fiber material, avoid to form conductive channel between the burr of conductive layer, dendrite, so that the breaking effect of composite current collector is better realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrochemical energy storage, in particular to a composite current collector, a preparation method thereof, an electrode sheet and a lithium ion battery. BACKGROUND

[0002] The conventional composite current collector is provided with a conductive layer on a polymer support layer, and the polymer support layer itself has poor thermal conductivity. During the charging and discharging process of the battery, the electrochemical reaction of the electrode generates heat. When the heat cannot be dissipated in time, local hot spots are easily formed inside the battery, thereby triggering a series of harmful side reactions, and even leading to thermal runaway, which seriously damages the electrochemical performance and safety performance of the battery. SUMMARY

[0003] Therefore, it is necessary to provide a composite current collector, a preparation method thereof, an electrode sheet and a lithium ion battery to improve the safety of the battery.

[0004] The first aspect of the present application provides a composite current collector, and the scheme is as follows:

[0005] The composite current collector comprises a composite support layer and a conductive layer, and the conductive layer is arranged on the composite support layer.

[0006] The composite support layer comprises a polymer matrix and inorganic thermally conductive fibers dispersed in the polymer matrix, and the inorganic thermally conductive fibers are selected from one or more of SiC fibers, Si3N4 fibers, Mg3N2 fibers, GaN fibers, AlN fibers and BN fibers.

[0007] In some embodiments, the surface of the inorganic thermally conductive fibers is modified with carboxyl groups.

[0008] In some embodiments, the composite current collector meets at least one of the following characteristics (1)~(5):

[0009] (1) The mass fraction of the inorganic thermally conductive fibers in the composite support layer is 1%~40%;

[0010] (2) The diameter of the inorganic thermally conductive fibers is 10nm~400nm;

[0011] (3) The length of the inorganic thermally conductive fibers is 0.1mm~6mm;

[0012] (4) The polymer matrix is selected from one or more of PET, PP and PI;

[0013] (5) The material of the conductive layer is selected from one or more of stainless steel, Cu, Ni, Al, Cu-Ni alloy and high-entropy alloy.

[0014] In some embodiments, the composite current collector further comprises an inorganic flame-retardant adhesive layer disposed between the composite support layer and the conductive layer, the material of the inorganic flame-retardant adhesive layer being selected from one or more of Al2O3, SiO2, TiO2, TiN, TaN, Si3N4, CrN, IZO.

[0015] The second aspect of the present application provides a method for preparing a composite current collector, the scheme being as follows:

[0016] A method for preparing a composite current collector, comprising the following steps:

[0017] Mixing a polymer matrix with inorganic heat-conductive fibers to obtain a composite support layer, the inorganic heat-conductive fibers being selected from one or more of SiC fibers, Si3N4 fibers, Mg3N2 fibers, GaN fibers, AlN fibers, and BN fibers;

[0018] Forming a conductive layer on the composite support layer.

[0019] In some embodiments, before the step of mixing the polymer matrix with the inorganic heat-conductive fibers, the method for preparing a composite current collector further comprises the following steps:

[0020] Mixing the inorganic heat-conductive fibers, a carboxylation reagent, and a solvent in a mass ratio of 10:(0.5-2):(80-100), and reacting at 80-120°C for 2-24h to modify carboxyl groups on the surface of the inorganic heat-conductive fibers, the carboxylation reagent being selected from one or more of chitosan, carboxymethyl cellulose, sodium carboxymethyl cellulose, oxalic acid, acetic acid, 3-(trimethoxysilyl)propyl acrylate, acrylic acid, acrylic anhydride, succinic anhydride, and maleic anhydride.

[0021] In some embodiments, after the step of mixing the polymer matrix with the inorganic heat-conductive fibers, and before the step of forming a conductive layer, the method for preparing a composite current collector further comprises the following steps:

[0022] Plasma surface pretreatment of the composite support layer to expose the inorganic heat-conductive fibers;

[0023] Forming an inorganic flame-retardant adhesive layer on the surface of the composite support layer exposing the inorganic heat-conductive fibers, the material of the inorganic flame-retardant adhesive layer being selected from one or more of Al2O3, SiO2, TiO2, TiN, TaN, Si3N4, CrN, IZO;

[0024] The conductive layer is formed on the side of the inorganic flame-retardant adhesive layer away from the composite support layer.

[0025] The third aspect of the present application provides an electrode tab, and the solution is as follows:

[0026] An electrode tab, comprising an electrode layer and the composite current collector described in any of the above embodiments or prepared by the preparation method of the composite current collector described in any of the above embodiments, wherein the electrode layer is arranged on the conductive layer of the composite current collector.

[0027] The fourth aspect of the present application provides a lithium ion battery, and the solution is as follows:

[0028] A lithium ion battery, comprising a shell and a positive electrode tab, a negative electrode tab, a gel polymer electrolyte and a separator arranged in the shell, wherein the gel polymer electrolyte is arranged between the positive electrode tab and the negative electrode tab, and the separator is arranged in the gel polymer electrolyte; at least one of the positive electrode tab and the negative electrode tab is the electrode tab.

[0029] In some embodiments, the lithium ion battery meets at least one of the following characteristics (1)~(2):

[0030] (1) The gel polymer electrolyte is polymerized in situ from a precursor solution, wherein the precursor solution comprises 1,3-dioxolane, an initiator, a lithium salt and a PTC nano-ceramic material, and the mass fraction of the PTC nano-ceramic material in the gel polymer electrolyte is 5%~15%;

[0031] (2) The separator comprises a base film and a PTC effect layer arranged on the base film, and the material of the PTC effect layer comprises a PTC ceramic material.

[0032] Compared with the traditional solution, the composite current collector and its preparation method, the electrode tab and the lithium ion battery have the following beneficial effects:

[0033] The composite current collector and its preparation method set the composite support layer and the conductive layer, and the inorganic heat-conducting fiber is dispersed in the polymer matrix in the composite support layer, and the inorganic heat-conducting fiber is selected from one or more of SiC fiber, Si3N4 fiber, Mg3N2 fiber, GaN fiber, AlN fiber and BN fiber, which can improve the thermal conductivity of the composite support layer and improve the thermal safety performance of the battery, and on the other hand, it can improve the toughness of the composite support layer and improve the processing performance. Moreover, the above inorganic heat-conducting fiber is a non-conductive fiber material, which avoids the formation of conductive channels between the burrs and dendrites of the conductive layer, so as to better realize the breaking effect of the composite current collector.

[0034] The electrode tab has the composite current collector of any of the above embodiments or prepared by the preparation method of any of the above embodiments, thus has the corresponding technical features and can obtain the corresponding beneficial effects. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 Structure schematic diagram of the composite current collector of an embodiment.

[0036] REFERENCE SIGNS:

[0037] 100, composite current collector; 110, composite support layer; 120, conductive layer; 130, inorganic fire-retardant adhesive layer. DETAILED DESCRIPTION

[0038] In order to make the above objectives, features and advantages of the present application more apparent, specific embodiments of the present application will be described in detail below with reference to the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application. However, the present application can be practiced in a number of different ways beyond the specific embodiments described and it is therefore contemplated to cover all such modifications as fall within the scope of the application. It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting.

[0039] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description of the application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used in this description, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0040] In the description of the present application, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the purpose of facilitating the description of the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation of the present application.

[0041] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0042] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0043] like Figure 1 As shown, a composite current collector 100 in one embodiment includes a composite support layer 110 and a conductive layer 120. The conductive layer 120 is disposed on the composite support layer 110.

[0044] The composite support layer 110 includes a polymer matrix and inorganic thermally conductive fibers dispersed in the polymer matrix. The inorganic thermally conductive fibers are selected from one or more of silicon carbide (SiC) fibers, silicon nitride (Si3N4) fibers, magnesium nitride (Mg3N2) fibers, gallium nitride (GaN) fibers, aluminum nitride (AlN) fibers, and boron nitride (BN) fibers.

[0045] In some of these examples, the surface of the inorganic thermally conductive fibers is modified with carboxyl groups. By modifying the surface of the inorganic thermally conductive fibers with carboxyl groups, the surface activity of the fibers can be improved, promoting the bonding between the inorganic thermally conductive fibers and the polymer matrix, thereby enhancing the overall mechanical properties of the composite support layer 110.

[0046] The above-mentioned inorganic thermal conductive fibers with surface-modified carboxyl groups can be prepared by carboxylating the surface of the inorganic thermal conductive fibers.

[0047] In some of these examples, the carboxylation process includes the following steps:

[0048] The inorganic thermally conductive fiber, a carboxylating agent, and a solvent are mixed in a mass ratio of 10:(0.5-2):(80-100), and reacted at 80-120°C for 2-24h. The carboxylating agent may be, for example, but is not limited to, one or more of chitosan, carboxymethyl cellulose, sodium carboxymethyl cellulose, oxalic acid, acetic acid, 3-(trimethoxysilyl)propyl acrylate, acrylic acid, acrylic anhydride, succinic anhydride, and maleic anhydride.

[0049] In some examples, the mass fraction of the inorganic thermally conductive fiber in the composite support layer 110 is 1%-40%. Further, in some examples, the mass fraction of the inorganic thermally conductive fiber in the composite support layer 110 is 10%-15%. In some specific examples, the mass fraction of the inorganic thermally conductive fiber in the composite support layer 110 is 1%, 5%, 10%, 15%, 20%, 25%, 30%, 40%, etc.

[0050] In some examples, the diameter of the inorganic thermally conductive fiber is 10-400nm. Further, in some examples, the diameter of the inorganic thermally conductive fiber is 100-300nm. In some specific examples, the diameter of the inorganic thermally conductive fiber is 100nm, 130nm, 150nm, 180nm, 200nm, 230nm, 250nm, 300nm, 350nm, 400nm, etc., or a range between any two of the above values.

[0051] In some examples, the length of the inorganic thermally conductive fiber is 0.1-6mm. Further, in some examples, the length of the inorganic thermally conductive fiber is 1-5mm. In some specific examples, the length of the inorganic thermally conductive fiber is 0.1mm, 0.5mm, 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, etc., or a range between any two of the above values.

[0052] Optionally, the polymer matrix may be, but is not limited to, one or more of PET, PP, and PI.

[0053] Optionally, the material of the conductive layer 120 may be, but is not limited to, stainless steel, Cu, Ni, Al, Cu-Ni alloy, high-entropy alloy, etc.

[0054] As shown in FIG. 1, the composite support layer 110 includes a polymer matrix 111 and an inorganic thermally conductive fiber 112. Figure 1As shown, in some examples, the composite current collector 100 further comprises an inorganic flame-retardant adhesive layer 130 disposed between the composite support layer 110 and the conductive layer 120. The material of the inorganic flame-retardant adhesive layer 130 is selected from one or more of Al2O3, SiO2, TiO2, TiN, TaN, Si3N4, CrN, IZO. By disposing the inorganic flame-retardant adhesive layer 130 of the above-mentioned material between the composite support layer 110 and the conductive layer 120, on the one hand, it can play a role in fire prevention and improve safety performance, and on the other hand, it can also play a role in improving the bonding force between the composite support layer 110 and the conductive layer 120.

[0055] In some examples, the thickness of the composite support layer 110 is 4-10 µm. Further, in some examples, the thickness of the composite support layer 110 is 6-8 µm. In some specific examples, the thickness of the composite support layer 110 is 4 µm, 5 µm, 6 µm, 7 µm, 8 µm, 9 µm, 10 µm, etc.

[0056] In some examples, the thickness of the conductive layer 120 is 1-2 µm. Further, in some examples, the thickness of the conductive layer 120 is 1.2-1.8 µm. In some specific examples, the thickness of the conductive layer 120 is 1 µm, 1.2 µm, 1.4 µm, 1.6 µm, 1.8 µm, 2 µm, etc.

[0057] In some examples, the thickness of the inorganic flame-retardant adhesive layer 130 is 10-100 nm. Further, in some examples, the thickness of the inorganic flame-retardant adhesive layer 130 is 30-70 nm. In some specific examples, the thickness of the inorganic flame-retardant adhesive layer 130 is 10 nm, 20 nm, 40 nm, 60 nm, 80 nm, 100 nm, etc.

[0058] The composite current collector 100 described above is provided with a composite support layer 110 and a conductive layer 120, and the composite support layer 110 is provided with inorganic heat-conductive fibers in a polymer matrix, the inorganic heat-conductive fibers being selected from one or more of SiC fibers, Si3N4 fibers, Mg3N2 fibers, GaN fibers, AlN fibers, and BN fibers, which on the one hand can improve the thermal conductivity of the composite support layer 110 and improve the thermal safety performance of the battery, and on the other hand can improve the toughness of the composite support layer 110 and improve the processing performance. Moreover, the inorganic heat-conductive fibers described above are non-conductive fiber materials, which can avoid the formation of conductive channels between burrs and dendrites of the conductive layer 120, thereby better achieving the breaking effect of the composite current collector 100.

[0059] Further, the present application also provides a preparation method of the composite current collector 100 of any of the above examples.

[0060] The method for preparing the composite current collector 100 of an embodiment includes the following steps:

[0061] In step S110, the polymer matrix is mixed with the inorganic thermally conductive fiber to obtain a composite support layer 110. The inorganic thermally conductive fiber is selected from one or more of SiC fiber, Si3N4 fiber, Mg3N2 fiber, GaN fiber, AlN fiber, and BN fiber.

[0062] In step S120, an electrically conductive layer 120 is formed on the composite support layer 110.

[0063] In some examples, in step S110, the polymer matrix and the inorganic thermally conductive fiber are heated to 160-450°C, the polymer matrix is melted, mixed with the inorganic thermally conductive fiber, the mixing time is 0.5-6h, and then the composite support layer 110 is formed by molding. The molding method can be, but is not limited to, one of mold molding, autoclave molding, and calender molding.

[0064] In some examples, before the step of mixing the polymer matrix with the inorganic thermally conductive fiber, the method for preparing the composite current collector 100 further includes the following steps:

[0065] The inorganic thermally conductive fiber, the carboxylation reagent, and the solvent are mixed in a mass ratio of 10:(0.5-2):(80-100), and reacted at 80-120°C for 2-24h to modify the carboxyl group on the surface of the inorganic thermally conductive fiber.

[0066] The carboxylation reagent is, for example, but not limited to, one or more of chitosan, carboxymethyl cellulose, sodium carboxymethyl cellulose, oxalic acid, acetic acid, 3-(trimethoxysilyl) propyl acrylate, acrylic acid, acrylic anhydride, succinic anhydride, and maleic anhydride. The solvent is, for example, but not limited to, water, DMF, etc.

[0067] In some examples, before step S120, the method for preparing the composite current collector 100 further includes the following steps:

[0068] The inorganic flame-retardant adhesive layer 130 is formed on the composite support layer 110, i.e., the inorganic flame-retardant adhesive layer 130 is arranged between the composite support layer 110 and the electrically conductive layer 120. The material of the inorganic flame-retardant adhesive layer 130 is selected from one or more of Al2O3, SiO2, TiO2, TiN, TaN, Si3N4, CrN, and IZO.

[0069] In some examples, the inorganic flame-retardant adhesive layer 130 is prepared by a magnetron sputtering process. When a radio frequency mode is used for film plating, the deposition cavity is vacuumed to 1x10 -5 Pa-8x10 -5Pa, inert gas (such as argon) with a flow rate of 20sccm~100sccm is introduced, the working pressure is controlled to be 0.1Pa~2Pa, and the working power is 60W~100W.

[0070] In some examples, the conductive layer 120 is prepared by a magnetron sputtering process. When using a direct current mode for film deposition, after cleaning the chamber, inert gas (such as argon) with a flow rate of 20sccm~100sccm is introduced, the working pressure is controlled to be 0.5Pa~10Pa, and the working power is 100W~300W.

[0071] In some examples, after step S110 and before step S120, the method for preparing the composite current collector further comprises the following steps:

[0072] The composite support layer 110 is subjected to plasma surface pretreatment to expose the inorganic heat-conductive fibers;

[0073] An inorganic flame-retardant adhesive layer 130 is formed on the surface of the composite support layer 110 exposed to the inorganic heat-conductive fibers, and the material of the inorganic flame-retardant adhesive layer is selected from one or more of Al2O3, SiO2, TiO2, TiN, TaN, Si3N4, CrN, and IZO.

[0074] In some examples, the plasma surface pretreatment comprises the following steps:

[0075] The composite support layer 110 is transferred to a magnetron sputtering chamber, vacuumed to 5×10 -5 Pa~8×10 -5 Pa, Ar is introduced at a flow rate of 10sccm~100sccm, and plasma is generated to bombard the surface of the composite support layer 110 at a power of 40W~100W. The time of the plasma surface pretreatment is, for example, 2min~8min.

[0076] In the above examples, by subjecting the composite support layer 110 to plasma surface pretreatment, the inorganic heat-conductive fibers are exposed, which can improve the polarity and roughness of the surface of the composite support layer 110. In addition, the high aspect ratio and high surface roughness of the inorganic heat-conductive fibers can provide a physical anchoring effect, and form a three-dimensional interlocking structure with the inorganic flame-retardant adhesive layer 130 deposited on the surface, thereby improving the bonding force between the composite support layer 110 and the inorganic flame-retardant adhesive layer 130. In addition, the O atoms in the carboxyl groups on the surface of the inorganic heat-conductive fibers can also form coordination bonds with Si, Al, Ti, Zn, Ta, Cr, In, etc. in the inorganic flame-retardant adhesive layer 130, thereby improving the interlayer bonding force.

[0077] Further, the application also provides an electrode tab.

[0078] The electrode tab of one embodiment includes an electrode layer and the composite current collector 100 of any of the above examples or the composite current collector 100 prepared by the preparation method of any of the above examples. The electrode layer is disposed on the conductive layer 120 of the composite current collector 100.

[0079] The electrode tab has the composite current collector 100 of any of the above examples or the composite current collector 100 prepared by the preparation method of any of the above examples, and thus has the corresponding technical features and can obtain the corresponding beneficial effects.

[0080] Optionally, the electrode tab can be a positive electrode tab or a negative electrode tab.

[0081] In some examples, the electrode tab is a positive electrode tab. Correspondingly, the electrode layer is a positive electrode layer.

[0082] The positive electrode layer contains a positive electrode material. Exemplarily, the positive electrode material includes one or more of LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.1 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.9 Co 0.05 Mn 0.05 O2.

[0083] It can be understood that the positive electrode layer can further contain a positive electrode binder, a positive electrode conductive agent, etc.

[0084] Exemplarily, the positive electrode binder includes one or more of polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, polyvinyl fluoride, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, butadiene styrene rubber, epoxy resin, and nylon.

[0085] Exemplarily, the positive electrode conductive agent includes one or more of carbon black, acetylene black, and ketjen black.

[0086] In some examples, the positive electrode layer contains 80-90 parts by weight of the positive electrode material, 5-10 parts by weight of the positive electrode binder, and 5-10 parts by weight of the positive electrode conductive agent, with the total parts by weight being 100. In one specific example, the positive electrode layer contains 84 parts by weight of the positive electrode material, 8 parts by weight of the positive electrode binder, and 8 parts by weight of the positive electrode conductive agent. Among them, the positive electrode material is preferably LiNi0.6 Co 0.1 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.9 Co 0.05 Mn 0.05 at least one of O2, LiNi

[0087] In some examples, the electrode tab is a negative electrode tab. Accordingly, the electrode layer is a negative electrode layer.

[0088] The negative electrode layer contains a negative electrode material. Illustratively, the negative electrode material includes one or more of natural graphite, artificial graphite, micro-silicon material, soft carbon, hard carbon, lithium metal, lithium metal alloy, and transition metal oxide, for example.

[0089] It can be appreciated that the negative electrode layer can further include a negative electrode binder, a negative electrode conductive agent, and the like.

[0090] Illustratively, the negative electrode binder includes one or more of polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, polyvinyl fluoride, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, butadiene styrene rubber, epoxy resin, and nylon, for example.

[0091] Illustratively, the negative electrode conductive agent includes one or more of carbon black, acetylene black, and ketjen black, for example.

[0092] In some examples, the negative electrode layer includes 70-90 parts by weight of the negative electrode material, 5-15 parts by weight of the negative electrode binder, and 5-15 parts by weight of the negative electrode conductive agent, with the total parts by weight being 100 parts. In one specific example, the negative electrode layer includes 80 parts by weight of the negative electrode material, 10 parts by weight of the negative electrode binder, and 10 parts by weight of the negative electrode conductive agent.

[0093] Further, the present application also provides a lithium ion battery.

[0094] The lithium ion battery of one embodiment includes a housing and a positive electrode tab, a negative electrode tab, a gel polymer electrolyte, and a separator disposed in the housing. The gel polymer electrolyte is disposed between the positive electrode tab and the negative electrode tab. The separator is disposed in the gel polymer electrolyte. At least one of the positive electrode tab and the negative electrode tab is the electrode tab described above.

[0095] To improve safety performance, lithium ion batteries use gel polymer electrolyte. The gel polymer electrolyte is formed by in-situ polymerization of a precursor solution. More specifically, the separator absorbs the precursor solution during the liquid injection process, and the precursor solution is polymerized in-situ in the cell to obtain the gel polymer electrolyte.

[0096] To improve the safety performance of lithium ion batteries, in some examples, the precursor solution includes 1,3-dioxolane (DOL), an initiator, a lithium salt, and a PTC nano-ceramic material.

[0097] The PTC (Positive Temperature Coefficient) effect refers to a large increase in the electrical resistance of a material when the temperature exceeds a certain critical value. Adding the PTC nano-ceramic material to the gel polymer electrolyte, at room temperature, the PTC nano-ceramic material can improve the degree of dissociation of the lithium salt due to its high dielectric constant, and improve the ion conductivity of the electrolyte. The excellent polarization performance of the PTC nano-ceramic material can form a uniform internal electric field, guiding the uniform and rapid migration of lithium ions. When the battery is short-circuited and the temperature rises, the resistance of the PTC nano-ceramic material rapidly increases, limiting the loop current and slowing down the abnormal heating of the cell, and the gel polymer electrolyte improves the safety performance.

[0098] In some examples, the mass fraction of the PTC nano-ceramic material in the gel polymer electrolyte is 5% to 15%.

[0099] The PTC nano-ceramic material may, for example, but not limited to, be one or more selected from (PbFe 0.67 W 0.33 O3) 0.2 (PbZr 0.53 Ti 0.47 O3) 0.8 , (PbLu 0.5 Nb 0.5 O3) 0.78 (PbTiO3) 0.22 , BaTiO3, BaZr 0.1 Ti 0.9 O3, BaZr 0.15 Ti 0.85 O3, BaZr 0.18 Ti 0.82 O3, and (BaZr 0.2 Ti 0.8 O3) 0.5 (Ba 0.7 Ca 0.3 TiO3) 0.5 The Curie temperature of the above-mentioned PTC nano-ceramic materials is shown in Table 1.

[0100] Table 1 Curie temperature of PTC nanoceramic material

[0101]

[0102] The PTC transition temperature of the PTC nanoceramic material is generally 20-60℃ lower than the Curie temperature. When the temperature inside the battery reaches about 100℃, the resistance of the PTC nanoceramic material rapidly increases, thereby limiting the loop current and slowing down the abnormal heating of the battery cell.

[0103] The role of the initiator is to initiate the ring-opening polymerization of 1,3-dioxolane. The initiator may be, but is not limited to, at least one of AlF3, SnF2, AlCl3, AlI3, Sn(OTf)2.

[0104] To improve the electrochemical performance, in some examples, the lithium salt includes LiTFSI and LiNO3 in a molar ratio of (5-7.5):1. The double salt system of LiTFSI and LiNO3 helps to generate an SEI film rich in beneficial inorganic components such as fluorides and nitrides through synergistic effect, improves the interface stability, and inhibits the interface side reactions and dendrite growth.

[0105] LITFSI has a high degree of dissociation in DOL, and as the main salt, it can ensure a high ionic conductivity. However, it is found that the addition of LiNO3 will significantly affect the ring-opening polymerization of 1,3-dioxolane. Therefore, a polymerization promoter may be further added to the precursor solution to promote the rate of polymerization reaction. The polymerization promoter may be, but is not limited to, at least one of 1,1,1-trifluoro-2,3-epoxypropane (TFEP), propylene oxide (PO), and butylene oxide (BO).

[0106] In some examples, the precursor solution further contains an additive. The additive may be, but is not limited to, at least one of LiPF6, LiDFOB, and LiBF4. The above lithium salt additive also has the effect of initiating the polymerization reaction.

[0107] In some examples, the method for preparing the gel polymer electrolyte includes the following steps:

[0108] The 1,3-dioxolane (DOL), the initiator, the lithium salt, and the PTC nanoceramic material are mixed to obtain a precursor solution. The precursor solution is introduced into the battery cell through a liquid injection process, and then in-situ polymerization is carried out at 25-60℃ for 2-14 days to obtain the gel polymer electrolyte.

[0109] To improve the safety performance of the lithium ion battery, in some examples, the separator includes a base film and a PTC effect layer disposed on the base film. The material of the PTC effect layer includes a PTC ceramic material.

[0110] By incorporating PTC ceramic materials with the PTC effect onto the separator, not only can the mechanical properties and high-temperature resistance of the separator be improved, but the ion flow through the separator can also be homogenized. When an internal short circuit occurs in the battery cell and the internal temperature rises rapidly, the PTC effect of the PTC ceramic material can be triggered, causing a sharp increase in interface resistance, which suppresses the short-circuit current and further enhances the safety performance of the battery cell.

[0111] Optionally, the PTC effect layer can be disposed on one side of the base film or on both sides of the base film.

[0112] In some of these examples, the PTC ceramic material is selected from (PbFe) 0.67 W 0.33 O3) 0.2 (PbZr 0.53 Ti 0.47 O3) 0.8 、(PbLu 0.5 Nb 0.5 O3) 0.78 (PbTiO3) 0.22 BaTiO3, BaZr 0.1 Ti 0.9 O3, BaZr 0.15 Ti 0.85 O3, BaZr 0.18 Ti 0.82 O3 and (BaZr) 0.2 Ti 0.8 O3) 0.5 (Ba 0.7 Ca 0.3 TiO3) 0.5 One or more of them.

[0113] PTC effect layers can be prepared using physical vapor deposition processes, such as magnetron sputtering and evaporation.

[0114] In some of these examples, the PTC effect layer was fabricated using a magnetron sputtering process. When using RF mode deposition, the deposition chamber was evacuated to 1 × 10⁻⁶. -5 Pa ~8×10 -5 Pa, with an inert gas (such as argon) flow rate of 20 sccm to 100 sccm, and a working pressure of 0.1 Pa to 1 Pa, and a working power of 20 W to 80 W.

[0115] In some examples, the PTC effect layer has a thickness of 100 nm to 300 nm. Further, in some examples, the PTC effect layer has a thickness of 150 nm to 250 nm. In some specific examples, the PTC effect layer has a thickness of 100 nm, 130 nm, 150 nm, 180 nm, 200 nm, 230 nm, 250 nm, 300 nm, etc.

[0116] Optionally, the material of the base film can be, but is not limited to, one or more of PP, PE, and PI.

[0117] In some examples, the base film has a thickness of 12 µm to 25 µm. Further, in some examples, the base film has a thickness of 15 µm to 20 µm. In some specific examples, the base film has a thickness of 12 µm, 14 µm, 16 µm, 18 µm, 20 µm, 22 µm, 24 µm, 25 µm, etc.

[0118] The following specific examples are provided to further illustrate the present application. The present application provides the following specific examples for better further understanding of the present application, and is not limited to the specific examples, and does not constitute a limitation on the protection scope of the present application.

[0119] Example 1

[0120] The present example provides a lithium ion battery, comprising a shell and a positive electrode sheet, a negative electrode sheet, a gel polymer electrolyte, and a separator disposed in the shell.

[0121] The preparation method of the positive electrode composite current collector of the present example comprises the following steps:

[0122] Step 1, take AlN fibers, chitosan, and deionized water, mix according to the mass ratio of 10:1:100, react at 100°C for 12h, to obtain carboxylated AlN fibers.

[0123] Step 2, mix the PET substrate and the carboxylated AlN fibers, and heat to 300°C for 2h to melt the PET substrate. Among them, the mass fraction of AIN fibers is 15%, the diameter of AIN fibers is about 50 nm, and the length is about 0.4 mm. After uniform melting and mixing, a 6 µm thick composite support layer is obtained by mold forming.

[0124] Step 3, transfer the composite support layer to a magnetron sputtering cavity, vacuumize to 8×10 -5 Pa, introduce Ar at 50sccm, generate plasma to bombard the surface of the composite support layer at a power of 70W, and the treatment time is 5min.

[0125] Step 4, then adjust the Ar flow to 20 sccm, control the working pressure to be 0.2 Pa, and the power to be 60 W, deposit Al2O3 on the surface of the composite support layer to form an inorganic flame-retardant adhesive layer with a thickness of 50 nm.

[0126] Step 5, after cleaning the cavity, adjust the working pressure to 1 Pa, set the power to 200 W, deposit metal Al on the surface of the inorganic flame-retardant adhesive layer to form a 1 µm thick conductive layer, and obtain the positive composite current collector.

[0127] The preparation method of the negative composite current collector of the embodiment includes the following steps:

[0128] Step 1, mix AlN fibers, chitosan and deionized water according to a mass ratio of 10:1:100, and react at 100°C for 12 h to obtain carboxylated AlN fibers.

[0129] Step 2, mix the PP substrate and the carboxylated AlN fibers, and heat to 220°C for 2 h to melt the PP substrate. Among them, the mass fraction of the AlN fibers is 12%, the diameter of the AlN fibers is about 50 nm, and the length is about 0.4 mm. After uniform melting and mixing, a 4.5 µm thick composite support layer is obtained by mold forming.

[0130] Step 3, transfer the composite support layer into a magnetron sputtering cavity, vacuumize to 8×10 -5 Pa, introduce Ar at 50 sccm, generate plasma to bombard the surface of the composite support layer at a power of 70 W, and the treatment time is 5 min.

[0131] Step 4, then adjust the Ar flow to 20 sccm, control the working pressure to be 0.2 Pa, and the power to be 60 W, deposit Al2O3 on the surface of the composite support layer to form an inorganic flame-retardant adhesive layer with a thickness of 50 nm.

[0132] Step 5, after cleaning the cavity, adjust the working pressure to 1 Pa, set the power to 200 W, deposit metal Al on the surface of the inorganic flame-retardant adhesive layer to form a 1 µm thick conductive layer, and obtain the positive composite current collector.

[0133] The preparation method of the negative composite current collector of the embodiment includes the following steps:

[0134] Transfer a PE-based film with a thickness of 16 µm into a magnetron sputtering cavity, vacuumize the cavity to an air pressure of 8×10 - 5 Pa, introduce Ar at a flow rate of 20 sccm, control the working pressure to be 0.5 Pa, and the power to be 80 W, and deposit PTC ceramic material (PbFe 0.67 W 0.33 O3) on the surface of the PE-based film by radio frequency (RF) magnetron sputtering to form a 40 nm thick inorganic flame-retardant adhesive layer.0.2 (PbZr 0.53 Ti 0.47 O3) 0.8 A PTC effect layer with a thickness of 200 nm is formed on the surface of the PE base film close to the negative electrode side by sputtering.

[0135] The preparation method of the positive electrode tab of the embodiment includes the following steps:

[0136] The positive electrode active material NCM811, the binder PVDF, and the conductive agent SP are mixed in a mass ratio of 84:8:8, and then added to a solvent NMP for homogenization to obtain a positive electrode slurry. The positive electrode slurry is coated on the surface of the positive electrode composite current collector, and a positive electrode tab is obtained after drying.

[0137] The preparation method of the negative electrode tab of the embodiment includes the following steps:

[0138] The negative electrode active material graphite, the binder CMC, SBR, and the conductive agent SP are mixed in a mass ratio of 80:4:6:10, and then added to deionized water for homogenization to obtain a negative electrode slurry. The negative electrode slurry is coated on the surface of the negative electrode composite current collector, and a negative electrode tab is obtained after drying.

[0139] The preparation method of the gel polymer electrolyte of the embodiment includes the following steps:

[0140] 1M LiTFSI, 0.2M LiNO3 are dissolved in 1,3-dioxolane, then a polymerization promoter propylene oxide is added, and then an initiator AlF3 and an additive LiPF6 are added to obtain a precursor solution. The concentration of LiTFSI is 1 mol / L, the concentration of LiNO3 is 0.2 mol / L, the addition amount of the polymerization promoter is 5%, the addition amount of the initiator is 0.5%, and the addition amount of the additive is 2.5%.

[0141] After assembling the above positive electrode tab, negative electrode tab, and separator in the shell, the precursor electrolyte is injected into the shell, and the gel polymer electrolyte is formed by in-situ polymerization at 50°C for 2 days.

[0142] Example 2

[0143] The steps of the embodiment are basically the same as those of Example 1, except that the fibers in the positive electrode composite current collector and the negative electrode composite current collector are GaN fibers, and the material of the inorganic flame-retardant adhesive layer in the negative electrode composite current collector is Si3N4.

[0144] Example 3

[0145] The steps of the embodiment are basically the same as those of Example 1, except that the fibers in the positive electrode composite current collector and the negative electrode composite current collector are Mg3N2 fibers.

[0146] Example 4

[0147] The steps of this example are basically the same as those of Example 3, except that the PTC ceramic material in the separator is PLN 0.78 PT 0.22 .

[0148] Example 5

[0149] The steps of this example are basically the same as those of Example 3, except that the PTC ceramic material in the separator is BZT 0.5 BCT 0.5 .

[0150] Example 6

[0151] The steps of this example are basically the same as those of Example 1, except that the PTC ceramic material in the separator is PFW 0.2 PZT 0.8 ; the gel polymer electrolyte is further added with PTC nanoceramic material PFW 0.2 PZT 0.8 , and the addition amount is 5%.

[0152] Example 7

[0153] The steps of this example are basically the same as those of Example 6, except that the separator does not contain PTC ceramic material.

[0154] Comparative Example 1

[0155] The preparation method of the positive electrode composite current collector of this comparative example comprises the following steps:

[0156] A 6-µm-thick PET polymer layer is cleaned by anhydrous ethanol and dried, and then transferred to a multi-target magnetron sputtering cavity, the cavity is vacuumed to an air pressure of 4×10 -5 Pa, Ar with a flow rate of 20 sccm is introduced, the working air pressure is controlled to be 1 Pa, and the power is 200 W, metal Al is deposited on the surface of the PET polymer layer to form a 1-µm-thick conductive layer, and the positive electrode composite current collector is obtained.

[0157] The preparation method of the negative electrode composite current collector of this comparative example comprises the following steps:

[0158] A 4.5-µm-thick PP polymer layer is cleaned by anhydrous ethanol and dried, and then transferred to a multi-target magnetron sputtering cavity, the cavity is vacuumed to an air pressure of 4×10 -5 Pa, Ar with a flow rate of 20 sccm is introduced, the working air pressure is controlled to be 1 Pa, and the power is 220 W, metal Cu is deposited on the surface of the PET polymer layer to form a 1-µm-thick conductive layer, and the negative electrode composite current collector is obtained.

[0159] The preparation method of the positive electrode sheet of this comparative example comprises the following steps:

[0160] The positive active material NCM811, the binder PVDF and the conductive agent SP were mixed in a mass ratio of 84:8:8, and then added to a solvent NMP to obtain a positive electrode slurry. The positive electrode slurry was coated on the surface of the above-mentioned positive electrode composite current collector, and a positive electrode sheet was obtained after drying.

[0161] The preparation method of the negative electrode sheet of the present comparative example comprises the following steps:

[0162] The negative active material graphite, the binder CMC, SBR and the conductive agent SP were mixed in a mass ratio of 80:4:6:10, and then added to deionized water to obtain a negative electrode slurry. The negative electrode slurry was coated on the surface of the above-mentioned negative electrode composite current collector, and a negative electrode sheet was obtained after drying.

[0163] The lithium ion battery of the present comparative example was assembled using the above-mentioned positive electrode sheet, the above-mentioned negative electrode sheet and a PE separator with a thickness of 16 µm, and was injected with a precursor solution, which was 1M LiTFSI dissolved in 1,3-dioxolane, and then 0.5% initiator AlF3 was added, followed by in-situ polymerization at 50°C for 2 days to form a gel polymer electrolyte.

[0164] Comparative Example 2

[0165] The present comparative example differs from Example 1 only in that no LiNO3 and no polymerization promoter propylene oxide were added when preparing the gel polymer electrolyte.

[0166] Comparative Example 3

[0167] The present comparative example differs from Example 1 only in that no AlN fibers were added in the support layers of the positive electrode composite current collector and the negative electrode composite current collector.

[0168] Comparative Example 4

[0169] The present comparative example differs from Example 1 only in that no inorganic flame-retardant adhesive layer was prepared in the positive electrode composite current collector and the negative electrode composite current collector.

[0170] Comparative Example 5

[0171] The present comparative example differs from Example 1 only in that no PTC effect layer was formed on the PE base film when preparing the separator.

[0172] The tensile strength of the composite current collector prepared in the above examples and comparative examples, the peeling strength of the conductive layer were tested. The lithium ion batteries prepared in the above examples and comparative examples were fully charged, and the internal resistance values at 25°C and 80°C were tested, and the internal resistance ratio was calculated. The lithium ion batteries were subjected to room temperature cycle test under 1C / 1C charge and discharge conditions, and the cycle number when the battery capacity decayed to 80% was recorded. The test results are shown in Table 2.

[0173] Table 2

[0174]

[0175] Each technical feature of the above-described embodiments can be combined with any other technical feature, and for the sake of brevity, not all possible combinations are described, but it is understood that the scope of the present disclosure includes all such possible combinations.

[0176] The above-described embodiments are merely representative of several embodiments of the present disclosure, and the description is relatively specific and detailed, but should not be construed as limiting the scope of the patent. It should be noted that, for those skilled in the art, without departing from the concept of the present disclosure, a number of modifications and improvements can be made, which are all within the scope of the present disclosure. Therefore, the scope of the patent of the present disclosure should be subject to the appended claims.

Claims

1. A method for preparing a composite current collector, characterized in that, Includes the following steps: A polymer matrix is ​​mixed with inorganic thermally conductive fibers to obtain a composite support layer. The inorganic thermally conductive fibers are selected from one or more of SiC fibers, Si3N4 fibers, Mg3N2 fibers, GaN fibers, AlN fibers, and BN fibers. A conductive layer is formed on the composite support layer; Prior to the step of mixing the polymer matrix with the inorganic thermally conductive fiber, the preparation method further includes the following steps: The inorganic thermally conductive fiber, carboxylating agent, and solvent are mixed in a mass ratio of 10:(0.5~2):(80~100) and reacted at 80℃~120℃ for 2h~24h to modify the surface of the inorganic thermally conductive fiber with carboxyl groups. The carboxylating agent is selected from one or more of chitosan, carboxymethyl cellulose, sodium carboxymethyl cellulose, oxalic acid, acetic acid, 3-(trimethoxysilyl)propylacrylic acid, acrylic acid, acrylic anhydride, succinic anhydride, and maleic anhydride. After the step of mixing the polymer matrix with the inorganic thermally conductive fiber, and before the step of forming the conductive layer, the method for preparing the composite current collector further includes the following steps: The composite support layer is subjected to plasma surface pretreatment to expose the inorganic thermally conductive fibers; An inorganic flame-retardant adhesive layer is deposited on the surface of the composite support layer exposing the inorganic thermally conductive fibers. The material of the inorganic flame-retardant adhesive layer is selected from one or more of Al2O3, SiO2, TiO2, TiN, TaN, Si3N4, CrN, and IZO. The conductive layer is formed on the side of the inorganic flame-retardant adhesive layer away from the composite support layer.

2. The method for preparing the composite current collector as described in claim 1, characterized in that, The inorganic thermally conductive fiber has a mass fraction of 1% to 40% in the composite support layer.

3. The method for preparing the composite current collector as described in claim 1, characterized in that, The diameter of the inorganic thermally conductive fiber is 10nm~400nm.

4. The method for preparing the composite current collector as described in claim 1, characterized in that, The length of the inorganic thermally conductive fiber is 0.1 mm to 6 mm.

5. The method for preparing the composite current collector as described in claim 1, characterized in that, The polymer matrix is ​​selected from one or more of PET, PP and PI.

6. The method for preparing the composite current collector as described in claim 1, characterized in that, The material of the conductive layer is selected from one or more of stainless steel, Cu, Ni, Al, Cu-Ni alloy, and high-entropy alloy.

7. An electrode sheet, characterized in that, The present invention includes an electrode layer and a composite current collector prepared by the method of any one of claims 1 to 6, wherein the electrode layer is disposed on the conductive layer of the composite current collector.

8. A lithium-ion battery, characterized in that, The device includes a housing and a positive electrode, a negative electrode, a gel polymer electrolyte, and a separator disposed within the housing. The gel polymer electrolyte is disposed between the positive electrode and the negative electrode, and the separator is disposed within the gel polymer electrolyte. At least one of the positive electrode and the negative electrode is the electrode as described in claim 7.

9. The lithium-ion battery as described in claim 8, characterized in that, The lithium-ion battery meets at least one of the following characteristics (1) to (2): (1) The gel polymer electrolyte is formed by in-situ polymerization of a precursor solution, wherein the precursor solution contains 1,3-dioxolane, an initiator, a lithium salt, and a PTC nano-ceramic material, and the mass fraction of the PTC nano-ceramic material in the gel polymer electrolyte is 5%~15%; (2) The diaphragm includes a base membrane and a PTC effect layer disposed on the base membrane, wherein the material of the PTC effect layer includes PTC ceramic material.

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