Secondary battery and electric device

Abstract

The application relates to a negative electrode sheet, a secondary battery and an electric device. The secondary battery comprises a negative electrode sheet, the negative electrode sheet comprises a negative electrode current collector and a conductive coating arranged on at least one surface of the negative electrode current collector, the conductive coating comprises a conductive agent and a binder, and the binder comprises a glyceride.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of secondary batteries, and particularly relates to a secondary battery and a power utilization device. BACKGROUND

[0002] The secondary battery is widely applied to various consumer electronic products and electric vehicles due to its light weight, no pollution and no memory effect.

[0003] In order to pursue high energy density, the metal battery in the secondary battery has attracted attention due to its high energy density. Taking a sodium metal battery as an example, the anode-free sodium metal battery in the sodium metal battery does not use an initial anode active material, which not only improves the energy density of the battery, but also reduces the production cost of the battery. However, without the protection of the anode active material on the negative electrode side, the sodium is continuously deposited unevenly on the negative electrode side during the cycle process, and sodium dendrites are formed, which leads to poor cycle stability of the anode-free metal sodium battery, and the cycle life of the anode-free metal sodium battery faces great challenges. SUMMARY

[0004] Therefore, it is necessary to provide a secondary battery and a power utilization device capable of improving cycle stability.

[0005] In a first aspect, the application provides a secondary battery, comprising a negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a conductive coating provided on at least one surface of the negative electrode current collector, the conductive coating comprising a conductive agent and a binder, and the binder comprising a glyceride.

[0006] Without wishing to be bound by any theory, in the above-mentioned secondary battery, the binder in the conductive coating of the negative electrode sheet comprises a glyceride. Such a binder not only has good adhesion, but also has fewer active protons compared to polyacrylic acid, reduces the side reaction between the conductive coating and the electrolyte, and thus improves the electrochemical performance of the battery. At the same time, compared to polyacrylate, the glyceride contains a glyceride group, which has better adhesion and mechanical properties. During the charging and discharging process of the secondary battery, when the metal repeatedly deposits or peels off on the surface of the conductive coating of the negative electrode sheet, the conductive coating can better act as a nucleation layer for the deposition of sodium, lithium and other metals, which can improve the uniformity of the metal layer deposited on the surface of the conductive coating, effectively inhibit the growth of metal dendrites, and improve the cycle performance of the anode-free secondary battery.

[0007] In addition, the conductive coating of the above-mentioned negative electrode sheet as a nucleation layer for the metal layer can effectively inhibit the growth of metal dendrites, improve the problem of short circuit in the battery caused by the metal dendrites piercing the separator and triggering thermal runaway, and improve the safety performance of the battery.

[0008] In any embodiment of the application, the negative electrode plate further comprises a metal layer, which is arranged on the surface of the conductive coating away from the negative current collector.

[0009] In any embodiment of the application, the metal layer is formed by at least one of sodium, lithium and potassium.

[0010] In any embodiment of the application, the glyceride is a water-soluble glyceride.

[0011] Optionally, the glyceride comprises at least one of glyceryl polyacrylate, glyceryl polymethacrylate, carboxymethylcellulose glyceride and glyceryl alginate.

[0012] In any embodiment of the application, the glyceride contains free carboxyl groups.

[0013] Optionally, the acid value of the glyceride is a, 0

[0014] In any embodiment of the application, the hydroxyl value of the glyceride is (10-20) mgKOH / g, optionally (10-15) mgKOH / g.

[0015] In any embodiment of the application, the mass content of the binder in the total mass of the binder and the conductive agent is 20%-99%, optionally 50%-70%.

[0016] In any embodiment of the application, the conductive agent comprises at least one of carbon nanotubes, graphene, conductive carbon black, conductive graphite, acetylene black, ketjen black and carbon fibers.

[0017] In any embodiment of the application, the thickness of the conductive coating is 0.2-5 μm, optionally 0.6-2 μm.

[0018] In any embodiment of the application, the area density of the conductive coating is (0.2-5) mg / 1540.25 mm 2 , optionally (0.5-3) mg / 1540.25 mm 2 .

[0019] In the second aspect of the application, a power-using device is provided, which comprises the secondary battery provided in the first aspect of the application. BRIEF DESCRIPTION OF DRAWINGS

[0020] In order to more clearly illustrate the technical solutions of the present application, the drawings used in the present application will be briefly introduced as follows. Obviously, the drawings described below are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort on the basis of the drawings.

[0021] Figure 1 is a schematic diagram of a secondary battery according to an embodiment of the present application;

[0022] Figure 2 is a schematic diagram of a secondary battery according to an embodiment of the present application; Figure 1 is an exploded view of the secondary battery according to an embodiment of the present application shown in

[0023] Figure 3 is a schematic diagram of an electric device using the secondary battery according to an embodiment of the present application as a power source;

[0024] Explanation of Reference Numerals:

[0025] 1, secondary battery; 11, case; 12, electrode assembly; 13, cover plate; 2, electric device. DETAILED DESCRIPTION

[0026] Hereinafter, embodiments of the secondary battery and the electric device according to the present application will be described in detail with appropriate reference to the drawings. However, there will be cases where unnecessary detailed description is omitted. For example, there will be cases where detailed description of matters known well, repeated description of substantially identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the drawings and the following description are provided so that those skilled in the art can fully understand the present application, and are not intended to limit the subject matter recited in the claims.

[0027] The ranges disclosed herein are meant to be inclusive of the endpoints and include the end values in the range. Ranges can be combined, i.e., any of the lower and upper limits of the ranges can be combined to form a new range. For example, if a range is listed as 60-120 and 80-110, it is understood that the range can also be 60-110 and 80-120. Furthermore, if a minimum range value is listed as 1 and 2, and a maximum range value is listed as 3, 4, and 5, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, the use of "or" means "and / or" unless specifically stated otherwise, e.g., the phrase "A or B" means "A and / or B" or "A and B." In addition, the use of "comprising" (including the use of any of its derivatives and / or "including" and / or "containing" and / or "including" and / or "containing") is intended to mean "including, but not limited to." In addition, use of the term "example" is intended to indicate that an item so described is one of a possible plurality of items, is not a limitation on the scope of the item, and is not a limitation on the items that can be used in the present application. In addition, use of the term "for example" is intended to indicate that an item so described is one of a possible plurality of items, is not a limitation on the scope of the item, and is not a limitation on the items that can be used in the present application.

[0028] All embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, if not specifically stated otherwise.

[0029] All technical features and optional technical features of the present application can be combined with each other to form new technical solutions, if not specifically stated otherwise.

[0030] All steps of the present application can be performed in sequence or randomly, preferably in sequence, if not specifically stated otherwise. For example, the method comprises steps (a) and (b) means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, the method can further comprise step (c) means that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0031] The "includes" and "comprises" mentioned in the present application mean open-ended, if not specifically stated otherwise. For example, the "includes" and "comprises" can mean that other components not listed can also be included or contained, or only the listed components can be included or contained.

[0032] If not specifically stated, the term "or" in this application is inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, any of the following satisfy the condition "A or B": A is true (or present) and B is false (or not present); A is false (or not present) and B is true (or present); or both A and B are true (or present).

[0033] Unless otherwise defined, the terms used in this application have the meanings commonly understood by those skilled in the art. Unless otherwise defined, the values of each parameter mentioned in this application can be measured by various measurement methods commonly used in the art (for example, can be tested according to the methods given in the examples of this application).

[0034] Secondary battery

[0035] Secondary battery refers to a battery that can be activated by charging after discharging to continue to use the active material.

[0036] Generally, the secondary battery includes a positive electrode sheet, a negative electrode sheet, and an electrolyte.

[0037] Negative electrode sheet

[0038] An embodiment of the present application provides a negative electrode sheet, which includes a negative electrode current collector and a conductive coating layer provided on at least one surface of the negative electrode current collector. The conductive coating layer includes a conductive agent and a binder, and the binder includes a glyceride. The conductive coating layer does not contain a negative electrode active material.

[0039] It can be understood that the conductive coating layer does not contain a negative electrode active material, that is, the negative electrode sheet formed does not contain a negative electrode active material.

[0040] Without wishing to be bound by any theory, in the above-mentioned secondary battery, the binder in the conductive coating layer of the negative electrode sheet includes a glyceride. Such a binder not only has good adhesion, but also has fewer active protons compared to polyacrylic acid, reducing the side reaction between the conductive coating layer and the electrolyte, thereby improving the electrochemical performance of the battery. At the same time, compared to polyacrylate, glyceride contains glyceride groups, which have better adhesion and mechanical properties. During the charging and discharging process of the secondary battery, when the metal repeatedly deposits or peels off on the surface of the conductive coating layer of the negative electrode sheet, the conductive coating layer can better act as a nucleation layer for the deposition of metals such as sodium and lithium, can improve the uniformity of the metal layer deposited on the surface of the conductive coating layer, effectively inhibits the growth of metal dendrites, and improves the cycle performance of the secondary battery without a negative electrode.

[0041] In addition, the conductive coating layer of the above-mentioned negative electrode sheet as a nucleation layer for the metal layer can effectively inhibit the growth of metal dendrites, improve the problem of short circuit and heat runaway caused by metal dendrites piercing the separator in the battery, and improve the safety performance of the battery.

[0042] It is worth mentioning that in the secondary battery of the present application, the negative electrode tab does not contain negative active material in the preparation stage of the battery, and the active ions such as sodium ions and lithium ions are repeatedly deposited or peeled off on the conductive coating in the continuous charging and discharging process. It can be understood that these active ions are derived from the positive active material.

[0043] The negative current collector can adopt a conventional metal foil or a composite current collector. Among them, the composite current collector can be formed by arranging a metal material on a polymer substrate. As an example, the negative current collector can adopt a copper foil, an aluminum foil, etc.

[0044] In some embodiments, the glycerol ester is a water-soluble glycerol ester. When preparing the conductive coating, water can be used as a solvent to prepare a conductive slurry, which is low in cost and environmentally friendly.

[0045] Further, the glycerol ester includes at least one of polyacrylic glycerol ester, polymethacrylic glycerol ester, carboxymethyl cellulose glycerol ester, and alginic acid glycerol ester. These glycerol esters are formed by low-temperature esterification reaction of polyacrylic acid, polymethacrylic acid, carboxymethyl cellulose, or alginic acid with glycerol to form a three-dimensional network cross-linked reinforced binder, which has good mechanical properties.

[0046] In some embodiments, the glycerol ester contains free carboxyl groups. The glycerol ester can anchor the conductive agent on the surface of the negative current collector through the free carboxyl groups, thereby enhancing the adhesion of the conductive agent on the negative current collector, improving the stability of the negative electrode tab, improving the stability of nucleation, and being beneficial to prolonging the cycle life of the battery.

[0047] Further, the acid value of the glycerol ester is a, and 0

[0048] In some embodiments, the glycerol ester has a hydroxyl value of (10-20) mgKOH / g. If the hydroxyl value is less than 10 mgKOH / g, it indicates that the esterification cross-linking density of the glycerol ester is insufficient, which will reduce the adhesion of the conductive agent on the current collector; if the hydroxyl value is greater than 20 mgKOH / g, the esterification cross-linking degree of the glycerol ester is relatively large, which will also lead to the reduction of the mechanical toughness of the binder and increase the brittleness of the conductive coating.

[0049] In this paper, the hydroxyl value is measured according to the method ASTM E222-17, and the acid value is measured according to ISO3682-1996.

[0050] Further, the carboxymethyl cellulose glycerin ester can have a molecular weight of 120-650 thousand and a degree of substitution of 0.5-0.9. If the degree of substitution is too high, the hygroscopicity and hydrophilicity are stronger, which can result in too high water content of the negative electrode sheet and cause serious battery side reactions and affect the battery performance. If the degree of substitution is too low, the carboxymethyl cellulose has strong lipophilicity, which affects the dispersibility of the water-soluble binder and the conductive agent and affects the adhesion between the conductive coating and the negative current collector. The molecular weight of the carboxymethyl cellulose glycerin ester also affects the viscosity of the slurry and the dispersibility of the conductive agent. If the molecular weight of the carboxymethyl cellulose glycerin ester is too small, the adhesion strength of the conductive agent is reduced; if the molecular weight of the carboxymethyl cellulose glycerin ester is too large, the viscosity of the system is too high, the dispersibility of the conductive agent is poor, and the conductive agent is prone to agglomeration.

[0051] For example, the carboxymethyl cellulose glycerin ester can have a molecular weight of 350 thousand and a degree of substitution of 0.7.

[0052] In some embodiments, the adhesion between the negative current collector and the conductive coating is 1.5-5 N.

[0053] In some embodiments, the content of the binder in the total mass of the binder and the conductive agent is 20%-99%, or 50%-70%. For example, the content of the binder in the total mass of the binder and the conductive agent is 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, or 99%, or a range defined by any two of the above values.

[0054] In some embodiments, the conductive agent includes at least one of carbon nanotubes, graphene, conductive carbon black, conductive graphite, acetylene black, ketjen black, and carbon fibers.

[0055] In some embodiments, the thickness of the conductive coating is 0.2-5 μm, for example, 0.2 μm, 0.4 μm, 0.6 μm, 1 μm, 2 μm, 3 μm, 4 μm, or 5 μm, or 0.6-2 μm, or a range defined by any two of the above values. If the thickness of the conductive coating is too small, the conductive coating cannot function as a good nucleation layer; if the thickness of the conductive coating is too large, the ion migration is hindered, which reduces the uniformity of sodium deposition and reduces the energy density of the battery.

[0056] In some embodiments, the areal density of the conductive coating is (0.2-5) mg / 1540.25 mm 2 , or (0.5-3) mg / 1540.25 mm 2 .

[0057] The areal density is calculated according to the following formula: areal density = mass of the conductive coating / area of the conductive coating. Wherein, the mass of the conductive coating = total mass of the electrode sheet containing the conductive coating - mass of the negative current collector, which can be tested by using conventional mass testing methods such as a balance, etc., and the area can be measured by using an electrode sheet size detection system.

[0058] The above negative electrode sheet can be prepared by the following preparation method. The preparation method comprises the following steps S10-S20:

[0059] S10, mixing the conductive agent, the binder and the solvent to obtain a conductive coating.

[0060] Further, the solvent used in S10 comprises water.

[0061] S20, coating the conductive coating obtained in step S10 on at least one surface of the negative current collector to form a conductive coating.

[0062] The secondary battery using the above negative electrode sheet is a metal battery.

[0063] In some embodiments, the negative electrode sheet in the secondary battery further comprises a metal layer, which is disposed on the surface of the conductive coating away from the negative current collector. The metal layer can be formed by deposition of active ions in the positive active material during the charging and discharging process of the secondary battery.

[0064] Optionally, the metal layer is a metal layer formed by at least one element of sodium, lithium and potassium.

[0065] Positive electrode sheet

[0066] In the secondary battery, the positive electrode sheet generally comprises a positive current collector and a positive film layer disposed on the positive current collector. Wherein, the positive film layer comprises a positive active material.

[0067] The positive current collector can use a conventional metal foil or a composite current collector, which can be formed by disposing a metal material on a polymer substrate. As an example, the positive current collector can use an aluminum foil.

[0068] The specific type of positive active material can use the active material known in the art that can be used in the positive electrode sheet of the secondary battery, which can be selected by a person skilled in the art according to actual needs.

[0069] As an example, the positive active material can include a sodium-ion active material, which can employ positive active materials for sodium-ion batteries known in the art. As an example, the sodium-ion active material can include at least one of the following materials: Prussian blue (PBA) type, chemical formula (NaxMA[MB(CN)6]·zH2O, where MAand MBare transition metal ions, which are compounds composed of sodium, transition metal and cyanide, such as Na4Fe2(CN)6, Na4Fe(CN)6, Na 1.72 MnFe2(CN)6, NaMnMn(CN)6, NaNiFe(CN)6, etc.; oxide type, chemical formula NaxMO2, 0 < x < 1, M is a transition metal element, which is composed of transition metal oxides, and the variable valence transition metals involved are mainly vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni) and copper (Cu), among which the use of manganese and iron, which are relatively abundant resources, is the most common, such as NaCrO2, NaMnO2, NaMnO2, Na 0.61 Ti 0.48 Mn 0.52 O2, Na[Fe 0.5 Co 0.5 ]O2, NaMnO2, Na[Ni 0.25 Fe 0.5 Mn 0.25 ]O2, etc.; and polyanion compound type, chemical formula Na x M y [(XO m ) n- ] z , M is a metal ion with variable valence, X is an element such as P, S and V, which is composed of sodium, transition metal and anion, among which the transition metal mainly includes iron, vanadium, cobalt, etc., and the anion mainly includes phosphate, pyrophosphate, fluorophosphate and sulfate, such as NaMnFe2(PO4)6, Na2MnP2O7, Na3V2(PO4)3, Na2Fe2(SO4)3, NaFePO4, Na3V2(PO4)2F3, Na4Co3(PO4)2(P2O7).

[0070] As an example, the positive active material can include a lithium-ion active material, which includes but is not limited to one or more of lithium transition metal oxides, lithium-containing phosphates of olivine structure, and modified compounds of each of them. Examples of lithium transition metal oxides can include but are not limited to one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and modified compounds of each of them. Examples of lithium-containing phosphates of olivine structure can include but are not limited to one or more of lithium iron phosphate, a composite of lithium iron phosphate and carbon, lithium manganese phosphate, a composite of lithium manganese phosphate and carbon, lithium manganese iron phosphate, a composite of lithium manganese iron phosphate and carbon, and modified compounds of each of them. These materials can all be obtained through commercial channels.

[0071] In some embodiments, the modified compounds of each of the above materials can be a doping modification and / or a surface coating modification to the material.

[0072] Further, the positive film layer can also optionally include a binder, a conductive agent, and other optional additives.

[0073] As an example, the conductive agent can be one or more of super P carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, Super P (SP), graphene, and carbon nanofibers.

[0074] As an example, the binder can be one or more of styrene butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyacrylic acid (PAA), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), and polyvinyl butyral (PVB).

[0075] In some embodiments, the positive electrode sheet can be prepared by dispersing the above components for preparing the positive electrode sheet, such as the positive active material, the conductive agent, the binder, and any other components, in a solvent to form a positive electrode slurry; coating the positive electrode slurry on a positive electrode current collector, and after processes such as drying, cold pressing, etc., obtaining the positive electrode sheet. As an example, the solvent includes N-methyl pyrrolidone.

[0076] Electrolyte

[0077] The electrolyte functions to conduct ions between the positive electrode sheet and the negative electrode sheet. The type of electrolyte can be selected as needed. For example, the electrolyte can be liquid, gel, or all-solid.

[0078] In some of the embodiments, the electrolyte uses an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0079] In some embodiments, the electrolyte salt includes at least one of an electrolyte sodium salt and an electrolyte lithium salt.

[0080] Optionally, the electrolyte sodium salt is selected from at least one of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium perchlorate, sodium hexafluoroarsenate, sodium bisfluorosulfonylimide, sodium bis-trifluoromethanesulfonylimide, sodium trifluoromethylsulfonate, sodium difluorophosphate, sodium difluoroboric oxalate, sodium bisoxalate borate, sodium bis(trifluoromethylsulfonyl)imide, sodium difluorodioxalate phosphate, and sodium tetrafluorodioxalate phosphate.

[0081] Optionally, the electrolyte lithium salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonylimide, lithium bis-trifluoromethanesulfonylimide, lithium trifluoromethylsulfonate, lithium difluorophosphate, lithium difluoroboric oxalate, lithium bisoxalate borate, lithium bis(trifluoromethylsulfonyl)imide, lithium difluorodioxalate phosphate, and lithium tetrafluorodioxalate phosphate.

[0082] Further, in the electrolyte, the concentration of the electrolyte salt is 0.5 mol / L to 8 mol / L, and optionally 1 mol / L to 4 mol / L.

[0083] In some embodiments, the solvent in the electrolyte includes at least one of an ether solvent, an ester solvent, and a sulfone solvent.

[0084] Optionally, the solvent in the electrolyte includes an ether solvent. The ether solvent molecules in the electrolyte can construct a stable electrode / electrolyte interface on the metal surface of the negative electrode tab of the secondary battery, form a stable solid electrolyte interface (SEI), and reduce electrochemical polarization.

[0085] As an example, the ether solvent can include at least one of ethylene glycol dimethyl ether (DME), diethylene glycol dimethyl ether (DEGDME), triethylene glycol dimethyl ether (TRGDME), tetraethylene glycol dimethyl ether (TEGDME), 1,3-dioxolane (DOL), tetrahydrofuran, methyl tetrahydrofuran, diphenyl ether, and crown ether.

[0086] As an example, the ester solvent can include at least one of vinyl carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), propenylene carbonate, fluoroethylene carbonate (FEC), methyl ethyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), γ-butyrolactone (BL), 1,3-propane sultone (1,3-PS), methyl propionate (MP), methyl butyrate (MB), ethyl acetate (EA), ethyl propionate (EP), propyl propionate (PP), and ethyl butyrate (EB).

[0087] As an example, sulfone solvents include sulfolane, dimethylsulfoxide, methyl ethylsulfoxide, and dimethyl sulfoxide (DMSO).

[0088] In some embodiments, the electrolyte solution can also optionally include an additive. For example, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and can also include an additive that can improve certain properties of the battery, such as an additive that improves overcharge performance of the battery, an additive that improves high or low temperature performance of the battery, etc.

[0089] Separator film

[0090] In some embodiments, the secondary battery also includes a separator film. The separator film is disposed between the positive electrode sheet and the negative electrode sheet, and functions to separate the two. The type of separator film used in the present application can be any known porous structure separator film that has good chemical stability and mechanical stability.

[0091] In some embodiments, the material of the separator film can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator film can be a single layer film or a multi-layer composite film. When the separator film is a multi-layer composite film, the materials of the layers can be the same or different.

[0092] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator film can be used to make an electrode assembly through a winding process or a stacking process.

[0093] In some embodiments, the secondary battery can include an outer package. The outer package can be used to encapsulate the electrode assembly and the electrolyte solution described above.

[0094] In some embodiments, the outer package of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the secondary battery can also be a soft package, such as a pouch-type soft package. The material of the soft package can be plastic, and as plastic, polypropylene, polybutylene terephthalate, and polybutylene succinate, etc. can be listed.

[0095] The shape of the secondary battery according to the embodiments of the present application can be cylindrical, square, or any other shape. For example, Figure 1 is a square structure secondary battery 1 as an example.

[0096] In some embodiments, with reference to Figure 2The outer package can include a housing 11 and a cover plate 13. The housing 11 can 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 housing 11 has an opening communicating with the receiving cavity, and the cover plate 13 can be arranged on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the separator can form the electrode assembly 12 through a winding process or a stacking process. The electrode assembly 12 is packaged in the receiving cavity. The above-mentioned gel electrolyte is impregnated in the electrode assembly 12. The number of electrode assemblies 12 contained in the secondary battery 1 can be one or more, and a person skilled in the art can select according to the specific actual needs.

[0097] In addition, the application also provides a power utilization device, which includes at least one of the secondary battery, the battery module or the battery pack provided by the application. The secondary battery, the battery module or the battery pack can be used as a power supply of the power utilization device, or can be used as an energy storage unit of the power utilization device. The power utilization device can include a mobile device, an electric vehicle, an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto. Among them, the mobile device can be a mobile phone, a notebook computer, etc.; the electric vehicle can be a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc., but is not limited thereto.

[0098] As the power utilization device, the secondary battery, the battery module or the battery pack can be selected according to the use requirements thereof.

[0099] Figure 3 The power utilization device 2 is an example. The power utilization device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc.

[0100] The device as another example can be a mobile phone, a tablet computer, a notebook computer, etc.

[0101] The above raw materials, which are not particularly specified, can be obtained by purchase on the market.

[0102] In order to make the purpose, technical scheme and advantages of the application more concise and clear, the application is described by the following specific examples, but the application is not limited to these examples only. The examples described below are only better examples of the application, which can be used to describe the application, and cannot be understood as limiting the scope of the application. It should be pointed out that any modification, equivalent replacement and improvement made within the spirit and principle of the application should be included in the protection scope of the application.

[0103] In order to better illustrate the application, the content of the application is further described below in combination with examples. The following are specific examples.

[0104] Example 1

[0105] 1) Preparation of the negative electrode sheet

[0106] The binder and the conductive agent were added to water and stirred to form a uniform conductive slurry. The conductive slurry was coated on the surface of the copper foil, and then transferred to a vacuum drying oven to completely dry to form a conductive coating. The conductive coating was then punched to obtain the negative electrode sheet. The parameters of the binder, the conductive agent, and the conductive coating are shown in Table 1. Among them, the content of the binder refers to the mass content of the binder in the total mass of the binder and the conductive agent; the areal density of the conductive coating is 2 mg / 1540.25 mm 2 .

[0107] 2) Preparation of the positive electrode sheet

[0108] A 10 wt% polyvinylidene fluoride binder was fully dissolved in N-methyl pyrrolidone, and a 10 wt% carbon black conductive agent and a 80 wt% positive active material Na4Fe3(PO4)2P2O7 were added to form a uniformly dispersed slurry. The slurry was uniformly coated on the surface of the aluminum foil, and then transferred to a vacuum drying oven for complete drying. The obtained electrode sheet was rolled and then punched to obtain the positive electrode sheet.

[0109] 3) Preparation of the electrolyte

[0110] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), a sodium salt sodium hexafluorophosphate was dissolved in an organic solvent ethylene glycol dimethyl ether, and stirred uniformly to obtain an electrolyte with a concentration of 1.0 mol / L of the sodium salt sodium hexafluorophosphate.

[0111] 4) Isolation film

[0112] A polypropylene film with a thickness of 10 μm was used as the isolation film.

[0113] 5) Preparation of the sodium battery

[0114] The above-mentioned positive electrode sheet, isolation film, and negative current collector were stacked in order, with the isolation film between the positive electrode and the negative current collector to play a role of isolation, and the above-mentioned electrolyte was added to assemble a stacked battery.

[0115] Other embodiments

[0116] It is basically the same as Example 1, except that some parameters are different as shown in Table 1.

[0117] Specifically, compared with Example 1, the difference between Examples 2-4 is only that the specific type of the binder is different.

[0118] Compared with Example 1, the difference between Examples 5-6 is only that the type of the conductive agent is different.

[0119] The difference between Examples 7-8 and Example 1 is only that the acid value of the polyglyceryl triacrylate is different.

[0120] The difference between Examples 7-8 and Example 1 is only that the acid value of the polyglyceryl triacrylate is different.

[0121] The difference between Examples 11-13 and Example 1 is only that the mass content of the binder is different.

[0122] The difference between Examples 14-15 and Example 1 is only that the thickness of the conductive coating is different.

[0123] Comparative Example 1

[0124] The difference between Example 1 and Comparative Example 1 is that the conductive coating is omitted and only the copper foil in Example 1 is used as the negative electrode tab.

[0125] Comparative Examples 2-4

[0126] The difference between Example 1 and Comparative Examples 2-4 is that the type of binder is different. The specific types are shown in Table 1.

[0127] The following is a performance test of the negative electrode tab

[0128] Specifically, it is a test of the adhesion between the negative electrode current collector and the conductive coating in the negative electrode tab of each example and comparative example, and the test method is as follows:

[0129] 1. Cutting the tab

[0130] Take the negative electrode tab and cut the tab with a custom knife mold, length 400 mm * width 50 mm.

[0131] 2. Paste the fixed tab

[0132] Take a flat thin steel plate, about 200-300 mm long and 50 mm wide; first paste a double-sided tape in the center of the steel plate (the length should be longer than the sample test length, and the width should be the same as the tab), and smooth it out to ensure that the double-sided tape is tightly attached to the center of the steel plate. Peel off the double-sided tape and attach the negative electrode tab to the tape. Make sure the negative electrode tab and the tape are properly matched and attached, otherwise the test will not be accurate and the peel curve will have jumps or waves.

[0133] 3. Install the test

[0134] The two clamps on the tensile testing machine are used to fix the negative electrode sheet. One end of the negative electrode sheet is fixed on the fixed clamp of the tensile testing machine, and the other end is fixed on the other clamp of the tensile testing machine. After fixing the test sample, first calibrate and zero set, set the test width, the electrode sheet peeling length is 100 mm, the peeling speed is 800 mm / min, then start the test, and the adhesion between the negative electrode current collector and the conductive coating in the negative electrode sheet can be obtained.

[0135] The following is the battery performance test.

[0136] 1) Coulomb efficiency

[0137] Take Example 1 as an example. The prepared sodium battery is charged at a constant current of 1 / 3C to 3.7V at 25℃, and then charged at 3.7V constant voltage until the current drops to 0.05C, to obtain the first charge capacity (Cc1); then discharged at a constant current of 1 / 3C to 2.5V, to obtain the first discharge capacity (Cd1), and the sodium battery coulomb efficiency is calculated according to the following formula.

[0138] Sodium battery coulomb efficiency = first discharge capacity (Cd1) / first charge capacity (Cc1)

[0139] The test process of other examples and comparative examples is the same as above.

[0140] 2) Capacity retention rate

[0141] Take Example 1 as an example. The sodium battery is charged at a constant current of 1C to 3.7V at 25℃, and then charged at 3.7V constant voltage until the current drops to 0.05C, and then discharged at a constant current of 1C to 2.5V, to obtain the first discharge capacity (Cd1); so repeat the charge and discharge to the nth cycle, get the discharge capacity of the sodium battery after n cycles, recorded as Cdn, and the sodium battery capacity retention rate is calculated according to the following formula:

[0142] Capacity retention rate = discharge capacity after n cycles (Cdn) / first discharge capacity (Cd1).

[0143] The test process of other examples and comparative examples is the same as above.

[0144] 3) Sodium dendrite grade

[0145] The above sodium battery after 100 cycles is disassembled in an argon atmosphere glove box (H2O <0.1 ppm, O2 <0.1 ppm), and a metal layer, i.e. a sodium metal layer, can be seen on the surface of the negative electrode sheet. According to the morphology of the sodium metal layer on the surface of the negative electrode sheet, the visual method is used to determine the grade of sodium dendrite precipitation of the sodium metal layer. The evaluation standard is as follows:

[0146] Grade 0: The sodium metal layer on the surface of the entire negative electrode plate is flat and uniformly deposited (dense), and there is no visible uneven area.

[0147] Grade 1: The maximum area of a single sodium uneven deposition area in the sodium metal layer on the surface of the entire negative electrode plate is ≤2*2mm 2 , and the number of sodium uneven deposition areas on the surface of the entire negative electrode plate is ≤5.

[0148] Grade 2: The maximum area of a single sodium uneven deposition area on the surface of the entire negative electrode plate is ≤5*5mm 2 , and the number of sodium uneven deposition areas on the surface of the entire negative electrode plate is ≤5. 2 , and the number of sodium uneven deposition areas on the surface of the entire negative electrode plate is ≤5.

[0149] Grade 3: There is sodium deposition that does not meet the above-mentioned 0-2 grade determination conditions.

[0150] Table 1

[0151]

[0152] From Table 1, it can be seen that Comparative Example 1 does not set the conductive coating, and the coulombic efficiency and cycle capacity retention rate are not high, and there is a more serious sodium deposition problem; Comparative Examples 1-2 use polyacrylic acid or carboxymethyl cellulose as the binder, and compared with Comparative Example 1, the coulombic efficiency and cycle capacity retention rate are improved, but the sodium deposition problem has not been improved; Comparative Example 4 uses polybutyl acrylate as the binder, and the performance of the battery is comparable to that of Comparative Example 1. Comparative Examples 2-4 only enhance the adhesion of the conductive agent on the current collector, and the adhesion is still slightly lower than that of the present application. In addition, the present application not only enhances the adhesion of the conductive coating on the current collector, but also improves the mechanical properties of the conductive coating. The two work together to improve the overall stability of the negative electrode plate, thereby improving the problem of uneven sodium deposition.

[0153] Compared with each comparative example, the glyceride is used as the binder in each embodiment of the present application, which not only improves the coulombic efficiency and cycle capacity retention rate, but also greatly improves the degree of sodium deposition.

[0154] Specifically, compared with Example 1, the difference between Examples 2-4 is only that the specific type of the binder is different, and the results show that: Examples 1-4 all achieve good coulombic efficiency, cycle capacity retention rate, and no obvious sodium deposition problem; Further, compared with Example 4, the coulombic efficiency, cycle capacity retention rate of the battery of Examples 1-3 is better, and the sodium deposition level is lower.

[0155] Compared with Example 1, the difference of Examples 5-6 is only in the type of conductive agent, and the results show that: each example achieves good coulomb efficiency, cycle capacity retention rate, and no obvious sodium precipitation problem; further, compared with Examples 5-6, the coulomb efficiency, cycle capacity retention rate of the battery of Example 1 is better, and the sodium precipitation level is lower.

[0156] Each technical feature of the above-described embodiments can be combined arbitrarily, and for the sake of brevity, each technical feature in the above-described embodiments is not described in all possible combinations, however, as long as the combination of technical features does not exist contradictory, it should be considered as the scope of the present disclosure.

[0157] The above-described embodiments only express several embodiments of the present application, which are described in detail and in detail, but should not be construed as limiting the scope of the patent. It should be noted that for ordinary skilled in the art, without departing from the concept of the present application, a number of variations and improvements can be made, which are within the scope of the present application. Therefore, the scope of protection of the present application should be subject to the appended claims, and the description and drawings can be used to explain the content of the claims.

Claims

1. A secondary battery, characterized in that, The secondary battery is a metal battery, and the secondary battery includes a negative electrode sheet, the negative electrode sheet includes a negative current collector and a conductive coating disposed on at least one surface of the negative current collector, the conductive coating includes a conductive agent and a binder, the binder includes glyceryl ester, the glyceryl ester includes at least one of polyglyceryl acrylate, polyglyceryl methacrylate and glyceryl alginate; in the total mass of the binder and the conductive agent, the mass content of the binder is 20% to 99%; the negative electrode sheet also includes a metal layer, the metal layer is disposed on the surface of the conductive coating away from the negative current collector.

2. The secondary battery as described in claim 1, characterized in that, The metal layer is formed from at least one element selected from sodium, lithium, and potassium.

3. The secondary battery as described in claim 1, characterized in that, The glyceride contains a free carboxyl group.

4. The secondary battery as described in claim 3, characterized in that, The acid value of the glyceride is a, where 0 < a ≤ 0.5 mg KOH / g.

5. The secondary battery as described in claim 4, characterized in that, 0.2mgKOH / g≤a≤0.4mgKOH / g.

6. The secondary battery according to any one of claims 1 to 5, characterized in that, The hydroxyl value of the glyceride is (10~20) mgKOH / g.

7. The secondary battery as described in claim 6, characterized in that, The hydroxyl value of the glyceride is (10~15) mgKOH / g.

8. The secondary battery according to any one of claims 1 to 5, characterized in that, In the total mass of the adhesive and the conductive agent, the mass content of the adhesive is 50% to 70%.

9. The secondary battery according to any one of claims 1 to 5, characterized in that, The conductive agent includes at least one of carbon nanotubes, graphene, conductive carbon black, conductive graphite, and carbon fiber.

10. The secondary battery according to any one of claims 1 to 5, characterized in that, The conductive agent includes at least one of acetylene black and Ketjen black.

11. The secondary battery according to any one of claims 1 to 5, characterized in that, The thickness of the conductive coating is 0.2μm to 5μm.

12. The secondary battery as described in claim 11, characterized in that, The thickness of the conductive coating is 0.6μm to 2μm.

13. The secondary battery according to any one of claims 1 to 5, characterized in that, The areal density of the conductive coating is 0.2 mg / 1540.25 mm. 2 ~5mg / 1540.25mm 2 .

14. The secondary battery as described in claim 13, characterized in that, The areal density of the conductive coating is 0.5 mg / 1540.25 mm. 2 ~3mg / 1540.25mm 2 .

15. An electrical appliance, characterized in that, The electrical device includes a secondary battery as described in any one of claims 1 to 14.

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