Secondary battery negative electrode inorganic binder, secondary battery negative electrode pole piece containing same and preparation method of secondary battery negative electrode inorganic binder

Abstract

The invention relates to a secondary battery negative electrode inorganic binder, a secondary battery negative electrode pole piece comprising the same and a preparation method, and provides a secondary battery negative electrode inorganic binder which comprises a metal belonging to a first main group and / or a second main group of a periodic table of elements and / or an alloy thereof and is used for binding a negative electrode material and / or a conductive agent. The invention also provides a secondary battery negative pole piece containing the inorganic binder, a preparation method of the negative pole piece, a secondary battery containing the negative pole piece, and an electric device containing the secondary battery. The metal (or alloy) used as the binder has high physical and chemical stability, and can continuously play the role of the binder in the state of a metal elementary substance (or alloy); the adhesive force is strong, the mechanical strength is high, the conductivity is high, and the reaction activity is low.

Description

Technical Field

[0001] The present disclosure relates to the field of secondary batteries, and in particular to an inorganic binder for a negative electrode of a secondary battery, a negative electrode sheet containing the same and a preparation method thereof, a secondary battery containing the negative electrode sheet, and an electrical device containing the secondary battery. Background Art

[0002] Electrode materials are a bottleneck limiting the improvement of secondary battery energy density. Taking lithium secondary batteries as an example, the low theoretical gram capacity of graphite anodes (372 mAh / g) limits the improvement of battery energy density. High-gram-capacity anode materials such as silicon, germanium, and tin are expected to further improve the energy density of lithium secondary batteries. However, these materials suffer from large volume expansion, intense side reactions, and low conductivity during electrochemical reactions, thereby reducing the structural stability and electrochemical performance of the anode during battery use. As an important inactive substance in batteries, binders play a key role in solving these problems. However, current mainstream binders, such as polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose, and styrene-butadiene rubber (SBR), suffer from low mechanical strength, weak adhesion, low conductivity, reductive decomposition, and the inability to suppress side reactions between the active material and the electrolyte. This has limited the application of new anode materials such as silicon, germanium, and tin. To address these issues, it is necessary to develop new binders that combine strong adhesion, high mechanical strength, high conductivity, and low reactivity.

[0003] A small number of existing technologies report the use of salts, oxides, and other substances as inorganic binders for secondary batteries. These substances, primarily composed of salts and metal oxides, have weak binding properties. These binders have low mechanical strength and are unable to withstand the volume expansion of high-capacity negative electrodes. They also require organic binders as auxiliary binders to improve adhesion. Furthermore, these binders exhibit low electronic and ionic conductivity, a narrow electrochemical window, and low reduction potential tolerance.

[0004] In lithium-ion battery lithium replenishment technology, there is a type of lithium replenishment method that uses metallic lithium (lithium foil or lithium particles) to cover the surface of the negative electrode coating. For example, in the Chinese patent application CN107093706A, a structure in which a layer of metallic sodium is covered on the surface of the graphite negative electrode is mentioned. In this type of combination of metal active material supplement (for example, lithium supplement) + negative electrode material, the main function of the metal is to supplement the active material for the battery (for example, lithium supplement), rather than a binder; the main implementation method is to set the metal on the surface of the negative electrode coating in the form of sheets / layers or particles. The main function of the introduced metal is to participate in the electrochemical reaction, gradually or quickly consumed during the battery cycle, and replenish the active material lost by the battery during the cycle, and the introduced metal is coated on the surface of the negative electrode coating and does not have the function of a binder for the negative electrode material.

[0005] Therefore, there is an urgent need in the art to develop a new inorganic binder for negative electrodes of secondary batteries that can overcome the above technical deficiencies. Summary of the Invention

[0006] The present disclosure provides a novel inorganic binder for secondary battery negative electrodes, thereby overcoming the above technical deficiencies.

[0007] In one aspect, the present disclosure provides an inorganic binder for a secondary battery negative electrode, wherein the inorganic binder comprises a metal and / or an alloy thereof belonging to the first main group and / or the second main group of the periodic table, and is used to bind a negative electrode material and / or a conductive agent.

[0008] In a preferred embodiment, the inorganic binder is distributed throughout the depth range of the negative electrode coating. The depth range described in this application refers to the size range of the negative electrode coating along its thickness direction.

[0009] In another preferred embodiment, the inorganic binder is at least partially in contact with the negative electrode material and / or the conductive agent.

[0010] In another preferred embodiment, the metal comprises at least one of the following: lithium, sodium, potassium, rubidium, cesium, magnesium, and calcium.

[0011] In another preferred embodiment, the inorganic binder is metallic sodium and / or a sodium alloy.

[0012] In another preferred embodiment, the proportion of the inorganic binder in the negative electrode coating is set to: 0.1 mass % to 90 mass %, preferably 5 mass % to 60 mass %, and preferably 5 mass % to 50 mass %.

[0013] In another aspect, the present disclosure provides a secondary battery negative electrode plate comprising the aforementioned inorganic binder, wherein the negative electrode material of the secondary battery negative electrode comprises a single substance or compound of silicon, germanium, tin, phosphorus, carbon, or a composite thereof. The single substance of carbon may be selected from graphite, graphene, hard carbon, soft carbon, mesocarbon microbeads, and the like.

[0014] In a preferred embodiment, the negative electrode material includes silicon element or compound, that is, a silicon-based negative electrode material is used.

[0015] In another preferred embodiment, the silicon-based negative electrode material includes one or more of nano-silicon, silicon oxide, silicon monoxide, carbon-composite silicon oxide or carbon-composite silicon monoxide.

[0016] In another preferred embodiment, the negative electrode plate may selectively include a current collector and / or a conductive agent.

[0017] In another aspect, the present disclosure provides a method for preparing the above-mentioned negative electrode sheet, the method comprising the following steps:

[0018] (i) mixing the metal and auxiliary components contained in the inorganic binder under an inert gas atmosphere, heating until melted, and uniformly mixing;

[0019] (ii) mixing the negative electrode material and the melted binder obtained in step (i) thoroughly under heating conditions, wherein a conductive agent may be optionally added; and

[0020] (iii) compounding the mixture of the inorganic binder and the negative electrode material obtained in step (ii) on the surface of the current collector.

[0021] On the other hand, the present disclosure provides a secondary battery comprising a positive electrode sheet, an electrolyte, and the above-mentioned negative electrode sheet.

[0022] The electrolyte is a solid electrolyte, a semi-solid electrolyte or a liquid electrolyte, preferably a liquid electrolyte; the electrolyte contains at least one fluorine-containing anion;

[0023] Preferably, it is at least one selected from bisfluorosulfonyl imide, hexafluorophosphate, bistrifluoromethanesulfonyl imide, difluorooxalatoborate, tetrafluoroborate, hexafluoroarsenate and difluorophosphate.

[0024] In another aspect, the present disclosure provides an electric device comprising the secondary battery.

[0025] Beneficial effects:

[0026] (1) The present disclosure uses alkali metals / alkaline earth metals (or alloys) as binders with high mechanical strength and high bonding force, which can withstand the repeated volume expansion of high-capacity negative electrodes and remain stable after the battery has undergone long cycles, continuously playing the role of a binder, which is beneficial to improving the stability of the electrode structure, thereby optimizing the capacity retention rate and kinetic characteristics of the battery.

[0027] (2) In the present disclosure, alkali metal / alkaline earth metal (or alloy) is used as a binder (e.g., metallic sodium), which has a high mutual solubility with the active material (e.g., lithium), can improve the storage capacity of lithium ions, and can inhibit the active material from being deposited in the form of dendrites (e.g., lithium dendrites).

[0028] (3) The alkali metal / alkaline earth metal (or alloy) used in the present disclosure as a binder has high ion conductivity and can block direct contact between the negative electrode material and the electrolyte, thereby promoting ion conduction while suppressing the side reaction between the active material and the electrolyte, thereby improving the service life of the battery.

[0029] (4) In the present disclosure, alkali metal / alkaline earth metal (or alloy) is used as a binder. The binder can participate in the formation of the solid electrolyte interface layer (SEI), or the binder itself plays the role of SEI, reducing the loss of active materials during the SEI formation / regeneration process.

[0030] (5) In the present disclosure, alkali metal / alkaline earth metal (or alloy) is used as a binder, which has high electronic conductivity. Therefore, the electrode using the binder of the present disclosure does not necessarily need to be supplemented with a conductive agent.

[0031] (6) The alkali metal / alkaline earth metal (or alloy) used in the present disclosure as a binder has high mechanical strength and workability. The mixture formed with the negative electrode material can form an electrode sheet in a self-supporting form. Therefore, the electrode in the present disclosure does not necessarily require a current collector.

[0032] (7) The alkali metal / alkaline earth metal (or alloy) used as the binder in the present disclosure has high physical and chemical stability and can continuously play the role of the binder in the state of a metal element (or alloy). DETAILED DESCRIPTION

[0033] " Scope " disclosed herein is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a scope with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for a particular parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0034] In this application, unless otherwise specified, all embodiments and preferred embodiments mentioned herein can be combined with each other to form a new technical solution. In this application, unless otherwise specified, all technical features and preferred features mentioned herein can be combined with each other to form a new technical solution.

[0035] In this application, unless otherwise specified, the terms "include" and "comprising" used herein may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0036] In the description herein, unless otherwise indicated, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0037] It should be understood that, in the description of this disclosure, the terms "first," "second," etc. are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of the technical features indicated. Thus, a feature defined as "first," "second," etc. may explicitly or implicitly include one or more of the features. In the description of this disclosure, unless otherwise specified, "plurality" means two or more.

[0038] It should be noted that, in the description of this disclosure, unless otherwise expressly specified or limited, the terms "disposed," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; and internal connections between two components. Those skilled in the art will understand the specific meanings of the above terms in this disclosure based on specific circumstances.

[0039] The mainstream binders in the prior art, such as PVDF, sodium carboxymethyl cellulose, SBR, etc., have problems such as low mechanical strength, weak bonding force, low electrical conductivity, reductive decomposition, and inability to suppress side reactions between active substances and electrolytes, thereby limiting the application of new negative electrode materials such as silicon, germanium, and tin. The inventors of this application have found through extensive and in-depth research that the single substance or alloy of alkali metals and alkaline earth metals (lithium, sodium, potassium, magnesium, and calcium) has high viscosity, low hardness, strong ion / electron conductivity, and does not have the problem of reductive decomposition, which meets the requirements of secondary battery negative electrode binders. Using alkali metals / alkaline earth metals (or alloys) as secondary battery negative electrode binders can solve and overcome the defects of the above-mentioned prior art. Based on the above findings, the present invention is completed.

[0040] In the first aspect of the present disclosure, an inorganic binder for the negative electrode of a secondary battery is provided. The inorganic binder is a metal and its low-hardness alloy material having a certain viscosity and low hardness at room temperature, having high viscosity, and containing metals and / or alloys thereof belonging to the first main group and / or the second main group of the periodic table, for example, lithium, sodium, potassium, rubidium, cesium, magnesium, and calcium. The inorganic binder of the present invention does not react with the negative electrode material and active substance of the secondary battery; the so-called active substance of the present invention is a substance that participates in the charge transfer and current carrying process of the secondary battery during the charge and discharge process, and is lithium for lithium-ion batteries. The negative electrode material reacts with the active substance during the charge and discharge process of the secondary battery. For example, for lithium-ion batteries, lithium ions are embedded in the negative electrode material during the charging process, and lithium ions are deintercalated from the negative electrode material during the discharging process.

[0041] Preferably, the inorganic binder is distributed throughout the depth of the negative electrode coating.

[0042] Preferably, the inorganic binder is in at least partial contact with the negative electrode material and / or the conductive agent.

[0043] Preferably, the inorganic binder is metallic sodium or a sodium alloy.

[0044] Preferably, the proportion of the inorganic binder in the negative electrode coating is set to: 0.1 mass % to 90 mass %, preferably 5 mass % to 60 mass %.

[0045] In a second aspect of the present disclosure, a secondary battery negative electrode plate is provided, which comprises the above-mentioned inorganic binder, wherein the negative electrode material of the secondary battery negative electrode plate may comprise a single substance of silicon, germanium, tin, phosphorus, carbon, or a compound thereof (such as silicon oxide, silicon monoxide), or a composite material thereof (such as a silicon-carbon composite).

[0046] Preferably, the negative electrode plate includes a silicon-based negative electrode material; the inorganic binder is heated and mixed with the silicon-based negative electrode material powder, and stirred evenly so that it is bonded to the silicon-based negative electrode material into one; or the inorganic binder is mixed with the negative electrode material powder by mechanical kneading, and the mixture is further bonded to the current collector.

[0047] In the present disclosure, the negative electrode sheet may selectively include a current collector and / or a conductive agent.

[0048] In the present disclosure, the current collector can be a metal foil or a composite current collector, for example, the metal foil can be a copper foil, silver foil, iron foil, or a foil composed of an alloy of the above metals; the composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer, and can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material base layer (such as a base layer made of materials such as polypropylene PP, polyethylene terephthalate PET, polybutylene terephthalate PBT, polystyrene PS, polyethylene PE and its copolymers).

[0049] In the present disclosure, examples of the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0050] In the present disclosure, the inorganic binder is fully mixed with the silicon-based negative electrode material, which can prevent silicon from contacting with the electrolyte, avoid side reactions between silicon and the electrolyte, and improve the coulombic efficiency and service life of the battery.

[0051] In the present disclosure, the silicon-based negative electrode material includes one or more of nano-silicon, silicon oxide, silicon monoxide, carbon-composite silicon oxide or carbon-composite silicon monoxide.

[0052] In a third aspect of the present disclosure, a method for preparing the above-mentioned negative electrode sheet is provided, the method comprising the following steps:

[0053] (i) mixing the metal and auxiliary components contained in the inorganic binder under an inert gas atmosphere, heating until melted, and uniformly mixing;

[0054] (ii) mixing the negative electrode material (e.g., silicon) and the melted binder obtained in step (i) thoroughly and uniformly under heating conditions, wherein a conductive agent may be optionally added; and

[0055] (iii) compounding the mixture of the inorganic binder and the negative electrode material obtained in step (ii) on the surface of the current collector.

[0056] In a fourth aspect of the present disclosure, a secondary battery is provided, which includes a positive electrode plate, an electrolyte, and the above-mentioned negative electrode plate.

[0057] The secondary battery of this application includes a positive electrode (pole), a negative electrode (pole), and an electrolyte. During the battery's charge and discharge process, active ions are embedded and released back and forth between the positive and negative electrodes. The electrolyte acts as a conductor of ions between the positive and negative electrodes.

[0058] [Positive electrode]

[0059] In the secondary battery of the present application, the positive electrode plate includes a positive electrode current collector and a positive electrode film layer (or positive electrode active material layer) provided on at least one surface of the positive electrode current collector and including a positive electrode material. For example, the positive electrode current collector has two surfaces opposite to each other in the thickness direction of the positive electrode current collector, and the positive electrode film layer is provided on any one or both of the two opposite surfaces of the positive electrode current collector. In the secondary battery of the present application, the positive electrode current collector may be a metal foil or a composite current collector. For example, the metal foil may be an aluminum foil, and the composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene PP, polyethylene terephthalate PET, polybutylene terephthalate PBT, polystyrene PS, polyethylene PE and its copolymers, etc.).

[0060] In the secondary battery of the present application, the positive electrode material (substance) can be a positive electrode material for a secondary battery known in the art. For example, the positive electrode material may include one or more of the following: olivine-structured phosphates, transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other conventional materials that can be used as positive electrode materials for secondary batteries may also be used, including but not limited to layered oxides of active ions, polyanionic materials, or Prussian blue-based materials.

[0061] In some embodiments, the positive electrode film layer may also optionally include a binder. Non-limiting examples of binders that can be used for the positive electrode film layer may include one or more of the following: polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin. In an embodiment of the present application, each of the first positive active material layer and / or the second positive active material layer independently contains a binder selected from polyvinylidene fluoride, polyacrylic acid, polytetrafluoroethylene, polyimide and a combination thereof.

[0062] In some embodiments, the positive electrode film layer may further optionally include a conductive agent. Examples of conductive agents for the positive electrode film layer may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In an embodiment of the present application, the first positive electrode active material layer and / or the second positive electrode active material layer each independently contain a conductive agent selected from graphite, carbon black, acetylene black, graphene, carbon nanotubes, and combinations thereof.

[0063] In one embodiment of the present application, the positive electrode can be prepared in the following manner: the components for preparing the positive electrode, such as the positive electrode material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as N-methylpyrrolidone) to form a uniform positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0064] [Electrolytes]

[0065] The electrolyte conducts ions between the positive and negative electrodes. The electrolyte can be selected from at least one of a solid electrolyte, a semi-solid electrolyte, and a liquid electrolyte. The electrolyte contains at least one fluorine-containing anion; preferably, at least one of bis(fluorosulfonyl)imide, hexafluorophosphate, bis(trifluoromethanesulfonyl)imide, difluorooxalatoborate, tetrafluoroborate, hexafluoroarsenate, and difluorophosphate. A metal binder is used in conjunction with the above-mentioned fluorine-containing electrolyte to achieve its desired effect.

[0066] In one embodiment of the present application, the electrolyte may optionally contain additives. For example, the additives may include one or more of the following: negative electrode film-forming additives, positive electrode film-forming additives, and additives capable of improving certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature performance.

[0067] [Isolation film]

[0068] In one embodiment of the present application, the secondary battery further comprises a separator, which separates the anode side of the secondary battery from the cathode side, and provides selective permeation or blocking for substances of different types, sizes and charges in the system. For example, the separator can insulate electrons, physically isolate the positive and negative electrodes of the secondary battery, prevent internal short circuits and form an electric field in a certain direction, and at the same time allow ions in the battery to pass through the separator and move between the positive and negative electrodes. In one embodiment of the present application, the material used to prepare the separator may include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer can be the same or different. In an embodiment of the present application, the separator is selected from polyolefin separators, polyester separators, polyimide separators, polyamide separators and cellulose separators.

[0069] In one embodiment of the present application, the positive electrode sheet, negative electrode sheet and separator can be made into an electrode assembly / bare cell through a winding process or a lamination process.

[0070] In one embodiment of the present application, the secondary battery may include an outer packaging that can be used to encapsulate the above-mentioned electrode assembly and electrolyte. In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. In other embodiments, the outer packaging of the secondary battery can be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc.

[0071] The shape of the secondary battery of the present application may be cylindrical, square or any other shape. The outer packaging may include a shell and a cover plate, and the shell may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell has an opening connected to the receiving cavity, and the cover plate can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can be formed into an electrode assembly through a winding process or a lamination process, and the electrode assembly is encapsulated in the receiving cavity, and the electrolyte is impregnated in the electrode assembly. The number of electrode assemblies contained in the secondary battery may be one or more.

[0072] In one embodiment of the present application, several secondary batteries may be assembled together to form a battery module. The battery module includes two or more secondary batteries, and the specific number depends on the application of the battery module and the parameters of a single battery module.

[0073] In a battery module, multiple secondary batteries may be arranged sequentially along the length of the battery module. Of course, they may also be arranged in any other manner. Furthermore, the multiple secondary batteries may be secured using fasteners. Optionally, the battery module may further include a housing having a storage space, wherein the multiple secondary batteries are housed in the storage space.

[0074] In one embodiment of the present application, two or more of the aforementioned battery modules can be assembled into a battery pack. The number of battery modules contained in the battery pack depends on the application of the battery pack and the parameters of the individual battery modules. The battery pack can include a battery box and multiple battery modules disposed within the battery box. The battery box includes an upper box body and a lower box body. The upper box body can cover the lower box body and fit well therewith to form an enclosed space for accommodating the battery modules. The two or more battery modules can be arranged in the battery box in any desired manner.

[0075] In one embodiment of the present application, an exemplary battery pack may include a battery case and a plurality of battery modules disposed within the battery case. The battery case includes an upper case and a lower case, with the upper case covering the lower case and forming an enclosed space for accommodating the battery modules. The plurality of battery modules may be arranged in any manner within the battery case.

[0076] In a fifth aspect of the present disclosure, an electric device is provided, which includes the above-mentioned secondary battery.

[0077] In one embodiment of the present application, an electrical device of the present application includes at least one of the secondary battery, battery module, or battery pack of the present application, and the secondary battery, battery module, or battery pack can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device includes, but is not limited to, mobile digital devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc.

[0078] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0079] In the following, based on specific examples, the effect of the negative electrode sheet prepared using the inorganic binder of the present invention on the performance of the secondary battery is characterized. However, it should be pointed out in particular that the scope of protection of this application is defined by the claims and is not limited to the above specific embodiments.

[0080] Example

[0081] Unless otherwise specified, all raw materials used in the present invention were of analytical grade and all water used was deionized water.

[0082] Examples 1-6

[0083] The technical solution for preparing negative electrode sheets using inorganic binders is as follows:

[0084] (1) Prepare the raw materials. Under an Ar atmosphere, weigh silicon dioxide (average particle size 20 nm) and sodium or potassium metal powder and place them in a mortar (see the table below). Grind until the mixture is uniform to obtain a negative electrode material containing an inorganic binder.

[0085] (2) Coating. In an Ar atmosphere, the above negative electrode material was coated at a temperature of 20 mg / cm 2 The negative electrode sheet is obtained by hot pressing the negative electrode material onto the copper foil at a surface density of 100 nm. This step is to evenly coat the negative electrode material on the copper foil so that it can form a stable electrode structure.

[0086] Comparative Example 1

[0087] Commercially available styrene-butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC) were used as binders in a mass ratio of 60:40.

[0088] Comparative Example 2

[0089] Commercially available acrylamide and hydroxyethyl acrylamide were used as monomers, and the mass ratio of acrylamide to hydroxyethyl acrylamide was 50:10.

[0090] Comparative Example 3

[0091] Commercially available hydroxyethyl acrylamide and methacryloyloxyethyl trimethyl ammonium chloride are used as monomers, and the mass ratio of hydroxyethyl acrylamide to methacryloyloxyethyl trimethyl ammonium chloride is 10:30.

[0092] Test Method

[0093] Cyclic performance test

[0094] The negative electrode sheets from Examples 1-7 and Comparative Examples 1-3 were assembled into cylindrical 18650 batteries, where the positive electrode active material was lithium iron phosphate. The batteries were subjected to room temperature cycling testing. The room temperature cycling test method involves charging the battery at a constant current of 1C to 4.0V, then at a constant voltage of 4.0V to a cutoff current of 0.01C, and then discharging at a constant current of 1C to 2.5V. Capacity retention after 500 cycles is measured. The results are shown in the table below.

[0095]

[0096] As can be seen from the above table, the present invention uses a certain component of sodium, potassium metal or alloy material as a binder for the negative electrode material, such as an inorganic binder for a silicon-based negative electrode material, which can greatly improve the cycle performance of the negative electrode material, which is significantly better than the cycle performance of batteries using other binders, and also significantly improves the first coulombic efficiency of the secondary battery.

[0097] In general, the key to preparing anode materials, especially silicon-based anode materials, lies in the role of the binder. By mixing a certain proportion of metallic sodium or sodium alloy materials into the silicon-based anode material, the various components of the silicon-based anode material can be bonded together, forming a stable electrode structure.

Claims

1. An inorganic binder for a secondary battery negative electrode, characterized in that: The inorganic binder comprises a metal belonging to the first main group and / or the second main group of the periodic table and / or an alloy thereof, and is used to bind the negative electrode material and / or the conductive agent in the negative electrode coating.

2. The inorganic binder according to claim 1, characterized in that The inorganic binder is distributed throughout the depth of the negative electrode coating.

3. The inorganic binder according to claim 1, characterized in that The inorganic binder is in at least partial contact with the negative electrode material and / or the conductive agent.

4. The inorganic binder according to claim 1, characterized in that The metal comprises at least one of lithium, sodium, potassium, rubidium, cesium, magnesium and calcium.

5. The inorganic binder according to claim 1, characterized in that The inorganic binder is metallic sodium and / or sodium alloy.

6. The inorganic binder according to claim 1, characterized in that The ratio of the inorganic binder in the negative electrode coating is set to 0.1 mass % to 90 mass %, preferably 5 mass % to 60 mass %.

7. A negative electrode plate for a secondary battery, characterized in that: It comprises the inorganic binder according to any one of claims 1 to 6, wherein the negative electrode material of the secondary battery comprises a single substance or compound of silicon, germanium, tin, phosphorus, carbon, or a composite material thereof.

8. The negative electrode sheet according to claim 7, characterized in that: The silicon element or compound includes one or more of nano silicon, silicon oxide, silicon monoxide, carbon composite silicon oxide or carbon composite silicon monoxide.

9. The negative electrode sheet according to claim 7, characterized in that: The negative electrode plate includes a current collector and / or a conductive agent.

10. A method for preparing the negative electrode sheet according to claim 7, characterized in that: The method comprises the following steps: (i) mixing the metal and auxiliary components contained in the inorganic binder under an inert gas atmosphere, heating until melted, and uniformly mixing; (ii) mixing the negative electrode material and the melted inorganic binder obtained in step (i) thoroughly under heating conditions, wherein a conductive agent may be optionally added; and (iii) compounding the mixture of the inorganic binder and the negative electrode material obtained in step (ii) on the surface of the current collector to form a negative electrode coating.

11. A secondary battery, characterized in that: The invention comprises a positive electrode sheet, an electrolyte and a negative electrode sheet according to any one of claims 7 to 9.

12. The secondary battery according to claim 11, wherein The electrolyte comprises at least one fluoride-containing anion; Preferably, it is at least one selected from bisfluorosulfonyl imide, hexafluorophosphate, bistrifluoromethanesulfonyl imide, difluorooxalatoborate, tetrafluoroborate, hexafluoroarsenate and difluorophosphate.

13. An electrical device, characterized in that: It includes the secondary battery according to claim 11.

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