Negative pole piece, electrochemical device and electronic equipment

Abstract

The invention relates to a negative pole piece, an electrochemical device and electronic equipment, and belongs to the technical field of electrochemical energy storage. The negative pole piece comprises a conductive layer and a porous layer arranged on at least one side of the conductive layer, the porous layer comprises a porous material and metal inorganic salt loaded in the porous material, and the standard electrode potential of metal cations in the metal inorganic salt is higher than that of lithium ions. The negative pole piece provided by the invention can effectively inhibit the volume expansion of lithium metal and improve the interface stability, plays a dual role, and can synchronously inhibit the growth of lithium dendrites, improve the cycle performance of a lithium battery and prolong the cycle life of the battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrochemical energy storage, in particular to a negative electrode sheet, an electrochemical device and an electronic device. BACKGROUND

[0002] Lithium metal negative electrode has high specific capacity (3860 mAh / g) and low potential (-3.04V), so it is considered as one of the strong candidates to replace graphite, but the serious volume expansion of lithium metal makes it still face many challenges in practical application. Compared with graphite and other negative electrodes with accommodation properties such as silicon, lithium negative electrode is deposited in a flat plate during deposition, so the thickness inevitably increases, in addition, due to the serious dendrite problem during lithium deposition and serious side reaction with electrolyte, the deposition morphology of lithium metal negative electrode is loose and porous, which finally leads to unlimited volume expansion of lithium metal negative electrode.

[0003] However, the composite negative electrode scheme adopted in the prior art makes it difficult for lithium metal to be deposited entirely inside the material, which greatly reduces the space utilization of the material, resulting in that the inhibition of lithium expansion is far less than expected. SUMMARY

[0004] The purpose of the present application is to overcome the shortcomings of the prior art and provide a negative electrode sheet, an electrochemical device and an electronic device. The negative electrode sheet provided by the present application can simultaneously inhibit lithium dendrite growth and volume expansion, and improve the cycle life of the battery.

[0005] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows: The first aspect of the present application provides a negative electrode sheet, comprising a conductive layer and a porous layer arranged on at least one side of the conductive layer, the porous layer comprising a porous material and a metal inorganic salt loaded inside the porous material. The standard electrode potential of the metal cation in the metal inorganic salt is greater than the standard electrode potential of lithium ion.

[0006] As an embodiment of the present application, the porosity of the porous layer is φ, and φ≥75%.

[0007] As an embodiment of the present application, the conductive layer comprises one of lithium foil, lithium alloy foil, lithium-copper composite strip and copper foil.

[0008] As an embodiment of the present application, the porous material comprises at least one of foamed metal, porous carbon-based material, porous polymer-based material and porous ceramic material.

[0009] As an embodiment of the present application, the foamed metal comprises one of foamed copper and foamed nickel, the porous carbon-based material comprises carbon fiber film, the porous polymer-based material comprises polyimide porous film, and the porous ceramic material comprises porous alumina.

[0010] As an embodiment of the present application, the metal cation in the metal inorganic salt comprises at least one of gold ion, silver ion, tin ion, zinc ion, and magnesium ion.

[0011] As an embodiment of the present application, the anion in the metal inorganic salt comprises at least one of nitrate ion, phosphate ion, hexafluorophosphate ion, and tetrafluoroborate ion.

[0012] As an embodiment of the present application, the porous material comprises a foam metal, and the standard electrode potential of the foam metal is greater than or equal to the standard electrode potential of the metal cation in the metal inorganic salt.

[0013] As an embodiment of the present application, the porosity of the porous layer is φ, and 80 %≤φ≤96 %.

[0014] As an embodiment of the present application, the loading amount of the metal inorganic salt inside the porous material is L, and 0.1 mg / cm 2 ≤L≤0.99 mg / cm 2 .

[0015] As an embodiment of the present application, the thickness of the conductive layer is T1, and 10 μm≤T1≤40 μm.

[0016] As an embodiment of the present application, the thickness of the porous layer is T2, and 10 μm≤T2≤60 μm.

[0017] As an embodiment of the present application, the Dv50 particle size of the metal inorganic salt is D1, and 1 nm≤D1≤1 μm.

[0018] As a preferred embodiment of the present application, the Dv50 particle size of the metal inorganic salt is D1, and 1 nm≤D1≤0.5 μm.

[0019] As a preferred embodiment of the present application, the loading amount of the metal inorganic salt inside the porous material is L (mg / cm 2 ), the Dv50 particle size of the metal inorganic salt is D1 (μm), and 0.1≤L / D1≤0.98 is met.

[0020] As an embodiment of the present application, the preparation method of the negative electrode sheet comprises the following steps: The porous material is washed and dried, then the metal inorganic salt is deposited inside the porous material, and then the porous layer after the deposition treatment and the conductive layer are integrated and compacted to obtain the negative electrode sheet.

[0021] As an embodiment of the present application, the metal inorganic salt deposition method includes at least one of an immersion-precipitation method, an electrochemical deposition method, a hydrothermal-solvothermal method, and an ion exchange method.

[0022] The second aspect of the present application provides an electrochemical device including the negative electrode sheet as described above.

[0023] The third aspect of the present application provides an electronic device including the electrochemical device as described above.

[0024] Compared with the prior art, the present application has the following beneficial effects: (1) The negative electrode sheet provided by the present application forms a protective interface by depositing a metal inorganic salt on the inner surface of the porous material. During use, the metal cations are preferentially reduced to form lithiumophilic alloy sites, inducing lithium deposition inside the porous material and improving the space utilization of the absolute porous material. The phenomenon of "lithium growing from the top" that often occurs in porous materials is prevented. (2) The negative electrode sheet provided by the present application forms a protective interface by depositing a metal inorganic salt on the inner surface of the porous material. During use, the anions participate in reduction and form high-mechanical-strength SEI inorganic components in situ, which can effectively inhibit the growth of lithium dendrites and inhibit the expansion of the lithium negative electrode.

[0025] (3) The negative electrode sheet provided by the present application synchronously inhibits the growth of lithium dendrites and volume expansion through the synergistic effect of "induction-protection", thereby improving the cycle life of the battery. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 FIG. 1 is a structural schematic diagram of the negative electrode sheet of the present application. DETAILED DESCRIPTION

[0027] In order to better illustrate the purpose, technical scheme and advantages of the present application, the present application will be further described below in conjunction with specific examples. In the following examples, the test methods used are conventional methods unless otherwise specified. The materials, reagents, etc. used are commercially available unless otherwise specified.

[0028] In the present application, the open-ended technical features include both the closed technical solution consisting of the listed features and the open technical solution containing the listed features.

[0029] In this application, the numerical intervals are considered continuous, unless otherwise stated, and include the minimum and maximum values of the range, as well as every value between the minimum and maximum values. Further, when a range is provided, it is intended to include every integer within the range, unless otherwise indicated. Additionally, when a range is provided, it is intended to include the stated range and any sub-range thereof. In other words, unless otherwise stated, every range disclosed herein is intended to include any and all sub-ranges subsumed therein.

[0030] The components and materials used in the examples and comparative examples of the present application are commercially available unless otherwise specified, and the components and materials used in each parallel experiment are the same.

[0031] In the following description, all numbers disclosed herein are approximate unless otherwise indicated. And, unless otherwise indicated, each numerical range is intended to include every number and subset of numbers within the range. Also, unless otherwise indicated, every numerical range is intended to include every subrange within that range. At the very least, therefore, each number provided herein can be used as a minimum or maximum limit in a range, unless otherwise indicated. Every range disclosed herein is also intended to include any and all sub-ranges of the same numbers.

[0032] General Definitions The term "conductive layer" refers to a core functional layer that carries electrode active materials, provides electron transport channels, and maintains the stability of the electrode structure. Its core function is to ensure fast electron conduction, maintain electrode structure stability, and improve active material utilization and mass transfer efficiency.

[0033] The term "porous layer" refers to a functional layer that carries electrochemical reactions, ion transport, or electron conduction functions with specific pore structure as the core feature.

[0034] The term "porous material" refers to a support or carrier material with a three-dimensional interconnected or semi-interconnected porous structure, with a porosity typically ≥ 30%, and a pore size range covering nanometers to micrometers. In a battery, it mainly functions to carry active materials, buffer electrode volume expansion, construct electron / ion transport channels, and improve mass transfer efficiency.

[0035] The term "metallic inorganic salt" refers to an inorganic compound formed by the combination of metal cations and inorganic anions through ionic bonds, without organic functional groups such as carbon-hydrogen bonds.

[0036] The term "standard electrode potential" refers to the cell electromotive force measured when an electrode made of the metal and a standard hydrogen electrode (SHE, whose electrode potential is artificially defined as 0 V) form a primary cell under standard conditions (25℃, 101325 Pa normal pressure, ion concentration participating in the reaction is 1 mol / L, and the metal surface is in a pure and smooth state); the lower (more negative) the standard electrode potential, the stronger the reducing property of the metal, the easier it is to lose electrons and be oxidized into ions, and the weaker the oxidizing property of the ion, the more difficult it is to be reduced into metal; on the contrary, the higher (more positive), the weaker the reducing property of the metal, the more difficult it is to be oxidized, and the stronger the oxidizing property of the ion, the easier it is to be reduced into metal.

[0037] The term "Dv50 particle size": as used herein and in the claims, is defined as "volume median particle size", which is a core characteristic parameter of the particle size distribution of a particle system, and refers to the particle size value corresponding to the cumulative volume of 50% of the total particle volume in the cumulative volume distribution curve of the particles.

[0038] I. Negative electrode tab To solve the serious dendrite problem and volume expansion problem in the existing lithium deposition process of the negative electrode, the present application provides a negative electrode tab: The negative electrode tab provided by the present application comprises a conductive layer and a porous layer arranged on at least one side of the conductive layer, wherein the porous layer comprises a porous material and a metal inorganic salt loaded in the interior of the porous material. The standard electrode potential of the metal cation in the metal inorganic salt is greater than the standard electrode potential of lithium ion.

[0039] In some embodiments, the porosity of the porous layer is φ, and φ≥75%.

[0040] In some embodiments, the conductive layer comprises one of lithium foil, lithium alloy foil, lithium-copper composite tape, and copper foil.

[0041] In some embodiments, the porous material comprises at least one of foamed metal, porous carbon-based material, porous polymer-based material, and porous ceramic material.

[0042] In some embodiments, the foamed metal comprises one of foamed copper and foamed nickel, the porous carbon-based material comprises carbon fiber film, the porous polymer-based material comprises polyimide porous film, and the porous ceramic material comprises porous alumina.

[0043] In some embodiments, the metal cation in the metal inorganic salt comprises at least one of gold ion, silver ion, tin ion, zinc ion, and magnesium ion. In some embodiments, the anion in the metal inorganic salt comprises at least one of nitrate ion, phosphate ion, hexafluorophosphate ion, and tetrafluoroborate ion.

[0044] The application provides a negative electrode with the functions of providing expansion space and in-situ induction-protection. The negative electrode is composed of a porous layer and a conductive layer. The component in the porous layer that plays the in-situ induction-protection role on the surface of the porous material is a metal inorganic salt.

[0045] The application uses a metal cation inorganic salt with a standard electrode potential greater than that of lithium ions, which is loaded in the pores of the porous material to form a protective interface. During the first charging process of the battery, the metal inorganic salt is dissociated in the electrolyte, and its cations can be preferentially electrochemically reduced and deposited on the inner surface of the porous material, and then alloyed with the subsequently deposited lithium to form an alloy with lithium metal, which has good lithium affinity, thereby forming uniformly distributed lithium-affine sites inside the porous layer. Further, the anion in the metal inorganic salt is preferably a SEI inorganic component that can be reduced in-situ to form a high-mechanical-strength inorganic-rich solid-state electrolyte interface film. The SEI component formed by the above-mentioned anion includes but is not limited to lithium fluoride, lithium nitride, lithium oxynitride, lithium phosphide, lithium phosphide, lithium boron oxide, etc. The SEI elastic modulus of the battery negative electrode cycled for 50 weeks is higher than 10 GPa by atomic force microscope test, which has good mechanical properties.

[0046] The negative electrode provided by the application realizes the induction-protection mechanism by designing a specific porous layer: cation electrochemical reduction→alloying with lithium, anion reduction to form SEI: During the charging process of the battery, the metal cations inside the porous material preferentially form lithium-affine alloy sites through electrochemical reduction, inducing the uniform deposition of lithium metal inside the porous material; its anion synchronously participates in reduction to construct a high-mechanical-strength SEI protective layer in-situ. Through the synergistic effect of “induction-protection”, the growth of lithium dendrites and volume expansion can be simultaneously inhibited during the use of the battery, and the cycle life of the battery is improved.

[0047] In some embodiments, the metal cation in the metal inorganic salt includes at least one of silver ion, zinc ion, and magnesium ion. In some embodiments, the anion in the metal inorganic salt includes at least one of nitrate ion and phosphate ion.

[0048] In some embodiments, the porous material includes a foam metal, and the standard electrode potential of the foam metal is greater than or equal to the standard electrode potential of the metal cation in the metal inorganic salt.

[0049] The combination of the metal inorganic salt and the porous material in the porous layer needs to meet the condition that no displacement reaction occurs, to ensure that the metal cations therein can be reduced by electrons through the external circuit during the first charging of the battery, so as to realize the in-situ formation of the lithiumophilic sites. Therefore, the combination of the porous material and the metal inorganic salt in the present application does not include: the combination of foamed nickel and tin salt, silver salt or gold salt, the combination of foamed copper and silver salt or gold salt, and the like, which do not meet the specific requirements.

[0050] In some embodiments, the porosity of the porous layer is φ, and 80 %≤φ≤96 %, for example, can be 80 %, 81 %, 82 %, 83 %, 84 %, 85 %, 86 %, 87 %, 88 %, 89 %, 90 %, 91 %, 92 %, 93 %, 94 %, 95 %, 96 %, or a range formed by any two of them.

[0051] It is preferred to use a porous material with high porosity, and to improve the porosity of the porous layer to a certain level, so as to provide more space for the expansion of lithium metal.

[0052] In some embodiments, the loading amount of the metal inorganic salt inside the porous material is L, and 0.01 mg / cm 2 ≤L≤0.99 g / cm 2 , for example, can be 0.01 mg / cm 2 , 0.022 mg / cm 2 , 0.049 mg / cm 2 , 0.05 mg / cm 2 , 0.1 mg / cm 2 , 0.15 mg / cm 2 , 0.2 mg / cm 2 , 0.25 mg / cm 2 , 0.3 mg / cm 2 , 0.35 mg / cm 2 , 0.4 mg / cm 2 , 0.45 mg / cm 2 , 0.5 mg / cm 2 , 0.55 mg / cm 2 , 0.6 mg / cm 2 , 0.65 mg / cm 2 , 0.7 mg / cm 2 , 0.75 mg / cm 2 , 0.8 mg / cm 2 , 0.85 mg / cm 2 , 0.9 mg / cm 2 , 0.978 mg / cm 20.99 mg / cm 2 or a range between any two of the listed values.

[0053] In some embodiments, the conductive layer has a thickness T1, and 10 μm≤ T1≤ 40 μm, for example, 10 μm, 12 μm, 14 μm, 16 μm, 18 μm, 20 μm, 22 μm, 24 μm, 26 μm, 28 μm, 30 μm, 32 μm, 34 μm, 36 μm, 38 μm, 40 μm, or a range between any two of the listed values.

[0054] In some embodiments, the porous layer has a thickness T2, and 10 μm≤ T2≤ 60 μm, for example, 10 μm, 12 μm, 14 μm, 16 μm, 18 μm, 20 μm, 22 μm, 24 μm, 26 μm, 28 μm, 30 μm, 32 μm, 34 μm, 36 μm, 38 μm, 40 μm, 42 μm, 44 μm, 46 μm, 48 μm, 50 μm, 52 μm, 54 μm, 56 μm, 58 μm, 60 μm, or a range between any two of the listed values. In some embodiments, the metal inorganic salt has a Dv50 particle size D1, and 1 nm≤ D1≤ 1 μm, for example, 1 nm, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 0.10 μm, 0.15 μm, 0.20 μm, 0.25 μm, 0.30 μm, 0.35 μm, 0.40 μm, 0.45 μm, 0.50 μm, 0.55 μm, 0.60 μm, 0.65 μm, 0.70 μm, 0.75 μm, 0.80 μm, 0.85 μm, 0.90 μm, 0.95 μm, 1.00 μm, or a range between any two of the listed values.

[0055] In some embodiments, the metal inorganic salt has a Dv50 particle size D1, and 1 nm≤ D1≤ 0.5 μm.

[0056] In some embodiments, the metal inorganic salt has a Dv50 particle size D1, and D1= 0.1-0.2 μm.

[0057] In some embodiments, the metal inorganic salt has a loading L (mg / cm2) inside the porous material, and 0.1 mg / cm2≤ L ≤ 0.5 mg / cm2. 2), the Dv50 particle size of the metal inorganic salt is D1 (pm), and satisfies 0.1≤L / D1≤0.98, for example, can be 0.1, 0.19, 0.198, 0.22, 0.245, 0.25, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 0.978, 0.98, or a range formed by any two of the above values.

[0058] In some embodiments, the loading amount of the metal inorganic salt inside the porous material is L (mg / cm 2 ), the Dv50 particle size of the metal inorganic salt is D1 (pm), and satisfies 0.19≤L / D1≤0.25.

[0059] II. Preparation method of negative electrode sheet The application provides a preparation method of the negative electrode sheet, comprising the following steps: The porous material is washed and dried, then the metal inorganic salt is deposited inside the porous material, and then the porous layer after the deposition treatment is integrated with the conductive layer to obtain the negative electrode sheet.

[0060] In some embodiments, the deposition method of the metal inorganic salt comprises at least one of the following: immersion-deposition method, electrochemical deposition method, hydrothermal-solvothermal method, ion exchange method.

[0061] The metal inorganic salt is adsorbed or deposited inside the porous material by using the above preparation method, and the displacement reaction between the metal ion and the porous material is controlled, so that the metal inorganic salt can form lithium metal induced sites and lithium metal interface protection layer in situ through electrochemical reduction reaction in the use of the battery, realizing the dual-function design of induction-protection.

[0062] III. Electrochemical device The application provides an electrochemical device comprising the negative electrode sheet as described above. In some embodiments, the electrochemical device further comprises a positive electrode, a separator, and an electrolyte.

[0063] The electrochemical device of the application includes any device that undergoes electrochemical reactions, and specific examples thereof include primary batteries, secondary batteries, fuel cells, solar cells, or capacitors of all kinds. In particular, the electrochemical device is a lithium secondary battery, including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

[0064] positive electrode The electrochemical device of the application includes a positive electrode, wherein the positive electrode comprises a positive electrode current collector and a positive electrode active layer disposed on at least one surface of the positive electrode current collector.

[0065] In some embodiments, the kind of the positive electrode current collector is not particularly limited, and it can be a material known to be suitable for use as a positive electrode current collector.

[0066] In some embodiments, the positive electrode current collector includes a metal material such as aluminum, stainless steel, a nickel plating layer, titanium, tantalum, and the like, and a carbon material such as carbon cloth, carbon paper, and the like.

[0067] The form of the positive electrode current collector is not particularly limited. When the positive electrode current collector is a metal material, the form of the positive electrode current collector can be a metal foil, a metal cylinder, a metal roll, a metal sheet, a metal foil, a metal sheet mesh, a punched metal, a foamed metal, and the like. When the positive electrode current collector is a carbon material, the form of the positive electrode current collector can include, but is not limited to, a carbon sheet, a carbon film, a carbon cylinder, and the like.

[0068] In some embodiments, the positive electrode active layer includes a positive electrode active material, a positive electrode binder, and a positive electrode conductive agent.

[0069] In some embodiments, the kind of the positive electrode active material is not particularly limited, and it can include LiCoO2, LiFePO4, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.5 Co 0.2 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 0.95 Co 0.025 Mn 0.025 O2, xLi2MnO3·(1-x)LiMO2(M=Ni, Co, Mn, and the like).

[0070] separator The separator separates the negative electrode and the positive electrode and provides a path for lithium ion migration. The use of the separator is not particularly limited as long as it is a separator commonly used in lithium secondary batteries. In particular, a separator having a small resistance to movement of electrolyte ions and excellent electrolyte impregnability is preferred. Specifically, a porous polymer film, such as a porous polymer film formed of a polyolefin-based polymer (e.g., an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, an ethylene / methacrylate copolymer, or the like) or a laminate structure having two or more layers, can be used. In addition, a non-woven fabric formed of a conventional porous non-woven fabric (e.g., a glass fiber having a high melting point, a polyethylene terephthalate fiber, or the like) can be used. In addition, a coated separator containing a ceramic component or a polymer material to ensure heat resistance or mechanical strength can be used, and can be optionally used as a single layer or a multi-layer structure.

[0071] Generally, the separator includes a base material and a coating layer coated on the surface of the base film.

[0072] electrolyte The liquid electrolyte (electrolyte solution) can include an electrolyte salt and an organic solvent, where the specific kinds and compositions of the electrolyte salt and the organic solvent are not particularly limited, including a positive electrode film-forming additive, a negative electrode film-forming additive, and a cycle and low-temperature improving additive, etc.

[0073] Four, Electronic Device The present application provides an electronic device including the electrochemical device as described above.

[0074] The electronic device of the present application is not particularly limited, which can be any electronic device known in the prior art.

[0075] The use of the electrochemical device of the present application is not particularly limited, which can be used in any electronic device known in the prior art. According to some embodiments of the present application, the electronic device includes, but is not limited to, a mobile phone, a mobile phone, a smart phone, a notebook computer, a tablet computer, a wearable device, a smart watch, a smart bracelet, smart glasses, a mobile power supply, a television, a game console, a gamepad, a digital camera, a smart speaker, earphones, a keyboard, a mouse, a display, a drone, a sound system, a household appliance, a toy, a power tool, a car, a motorcycle, an electric bicycle, a bicycle, a robot, a robotic dog, an industrial robot, a humanoid robot, etc.

[0076] The preparation of the full battery is described below by way of example and in conjunction with specific embodiments, and those skilled in the art will understand that the preparation methods described in the present application are only examples, and any other suitable preparation method is within the scope of the present application.

[0077] In the following examples and comparative examples, the disassembly and pretreatment method of the battery is as follows: the battery is frozen at -20℃ for 12 hours, then disassembled at room temperature, and the electrode sheet is placed in a vacuum drying oven for drying for 12 hours to remove residual electrolyte. In the following examples and comparative examples, the test method for the porosity of the porous layer is as follows: the peeled porous layer is tested by mercury injection method to obtain the porosity of the porous layer. In the following examples and comparative examples, the test method for the particle size Dv50 of the metal inorganic salt is as follows: the particle size distribution of the particles is obtained by testing the particle size by a laser particle size analyzer, a particle size distribution curve is generated, and the volume median diameter Dv50 is obtained. In the following examples and comparative examples, the test method for the loading amount of the metal inorganic salt in the porous material is as follows: the mass difference before and after loading is divided by the surface area of the porous material to obtain the loading amount, and the surface area of the porous material is obtained by BET method. In the following examples and comparative examples, the test method for the thickness of the conductive layer and the thickness of the porous layer is as follows: the thickness is obtained by reading the test data by an electrode thickness instrument.

[0078] Example 1 The application discloses a preparation method of a full battery, which comprises the following steps: (1) Preparation of a negative electrode: A foam nickel with a thickness of 60 μm and a porosity of 98% is cut into a required size, subjected to acid washing and drying treatment, immersed in a hexane suspension solution of zinc nitrate with a concentration of 1 M, taken out after standing for 4 h, and dried to obtain a porous layer. The obtained porous layer and a lithium foil with a thickness of 20 μm are integrated by a flat plate hot press with a pressure of 400 MPa and a temperature of 80℃ to obtain a negative electrode sheet.

[0079] (2) Preparation of a positive electrode: active material LiCoO2, conductive agent acetylene black, conductive carbon nanotube and binder polyvinylidene fluoride (PVDF) are uniformly dispersed in an N-methyl pyrrolidone solvent system according to a weight ratio of 98.2:0.5:0.3:1.0, coated on a 9 μm aluminum current collector, then cold-pressed and divided to obtain a positive electrode sheet, and cut into a required size.

[0080] (3) Isolation film: PE is used as an isolation film with a thickness of 16 μm.

[0081] (4) Electrolyte: lithium bisfluorosulfonylimide (LiFSI), ethylene glycol dimethyl ether (DME) and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) are mixed according to a molar ratio of 1:1.2:1.2 to prepare an electrolyte.

[0082] (5) Full battery preparation: the above positive electrode sheet, separator, negative electrode sheet and electrolyte are assembled into a single-layer soft package battery.

[0083] Example 2-11 Example 2-11 differs from Example 1 only in that the prepared negative electrode is different: Example 2-3 uses a nickel foam porous material with different porosities, resulting in different porosities of the porous layer of the negative electrode; Example 4-7 uses different types of porous materials, resulting in different porous layers and porosities of the negative electrode; Examples 8-11 use different types of metal inorganic salt suspensions with the same concentration for soaking, and Examples 9 and 11 also use different porous materials to form different metal inorganic salt loadings; The comparison of the negative electrodes in Examples 1-11 is as follows in Table 1.

[0084] Table 1 Examples 12-19 Examples 12-19 differ from Example 1 only in that the prepared negative electrode is different: Examples 12-15 adjust the parameters of the nickel foam porous material soaking treatment in the zinc nitrate hexane suspension, resulting in different metal inorganic salt particle sizes D1 and different loadings L; Examples 16-17 use different thicknesses of the conductive layer; Examples 18-20 use different thicknesses of the porous layer; The comparison of the negative electrodes in Examples 1 and 12-20 is as follows in Table 2.

[0085] Table 2 Comparative Examples 1-8 Comparative Examples 1-8 differ from Example 1 only in that the prepared negative electrode is different: Comparative Examples 1-5 refer to the preparation method of Example 1, using different porous materials, but without soaking treatment of the metal inorganic salt suspension, so that the porous material of the negative electrode has no metal inorganic salt inside; Comparative Example 6 uses a single lithium foil as the negative electrode without a porous layer; In Comparative Example 7, the metal inorganic salt suspension used for soaking treatment is replaced by an aqueous silver nitrate solution, so that the nickel foam and the silver ions in the solution undergo a displacement reaction, forming nano-silver in situ inside the porous material. After washing, it is also integrated with the conductive layer to form the corresponding negative electrode; The metal inorganic salt suspension used in the soaking treatment in Comparative Example 8 was replaced by an organic salt, zinc citrate, to obtain a corresponding negative electrode.

[0086] The comparison of the negative electrodes in Example 1 and Comparative Examples 1-8 is shown in Table 3 below.

[0087] Table 3 Effect Example To explore the performance of the negative electrode provided in the present application and its use in full batteries, the full batteries in the examples and comparative examples were tested as follows: (1) Negative electrode expansion rate test: the above battery was subjected to 0.1C charging to the cut-off voltage and 0.5C discharging for 20 cycles, and the thickness of the negative electrode at 100% SOC in the first week and the thickness of the negative electrode at 100% SOC after 20 cycles were tested, respectively. The expansion rate of each negative electrode was calculated by the negative electrode expansion rate formula: Negative electrode expansion rate = [(100% SOC negative electrode thickness after 20 weeks - 100% SOC negative electrode thickness in the first week) / 100% SOC negative electrode thickness in the first week] x 100%; (2) Cell cycle expansion rate: the above battery was subjected to 0.1C charging to the cut-off voltage and 0.5C discharging for 20 cycles, and the thickness of the cell at 100% SOC in the first week and the thickness of the cell at 100% SOC after 20 cycles were tested, respectively. The cell expansion rate was calculated by the cell expansion rate formula: Cell expansion rate = [(100% SOC cell thickness after 20 weeks - 100% SOC cell thickness in the first week) / 100% SOC cell thickness in the first week] x 100%; (3) Cell cycle attenuation rate: the above battery was subjected to 0.5C charging to the cut-off voltage, and the percentage of the remaining capacity after 100 cycles to the initial capacity was calculated. The results of the above tests are shown in Table 4.

[0088] Table 4 From Table 4, it can be seen that: From the data of the examples and comparative examples, it can be seen that, compared with the comparative examples, the negative electrode provided in the present application has a significant inhibitory effect on lithium expansion and cell expansion, and can improve the cycle performance of the battery. In the comparative examples, no metal inorganic salt is loaded, no porous layer is integrated, inorganic salt is introduced to generate metal elements in situ by displacement reaction, or organic acid metal salt is used for compounding, which will cause the negative electrode expansion rate and the cell cycle expansion to increase significantly, and will affect the cycle performance.

[0089] The kinds of porous materials and inorganic metal salts provided by the application in Examples 1-11 have relatively small effects on battery cycle and expansion, and the cycle performance of the battery and the cell expansion are both within the ideal range. As can be seen from Comparative Examples 1 and 12-15, the particle size and loading amount of the metal inorganic salt and the relationship between the two have a greater impact on the battery performance, and there is an optimal interval, and larger or smaller will cause fluctuations in the cycle and expansion of the battery. As can be seen from Example 1 and Examples 16-20, the thickness of the conductive layer and the thickness of the porous layer also have a certain impact on the battery performance, wherein the thickness of the conductive layer mainly affects the cycle performance of the battery, and the thickness of the porous layer affects the expansion performance of the battery.

[0090] In summary, the application provides a negative electrode sheet, by loading metal inorganic salts inside the porous material, controlling specific metal inorganic salt cation-anion combinations, and adjusting appropriate coverage and metal inorganic salt particle size and other parameters, so that the metal cation can preferentially form a lithiumophilic alloy site through electrochemical reduction when the negative electrode is used, induce lithium deposition inside the porous material, and improve the space utilization of the absolute porous material; the anion participates in reduction at the same time, in-situ forms a high-mechanical-strength SEI inorganic component, which can effectively inhibit the growth of lithium dendrites and suppress the expansion of the lithium negative electrode; and the synergistic effect of "induction-protection" is comprehensively realized, the growth of lithium dendrites and volume expansion are simultaneously inhibited, and the cycle life of the battery is improved.

[0091] Finally, it should be explained that the above examples are only used to illustrate the technical solutions of the application and not to limit the protection scope of the application, although the application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the application can be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the application.

Claims

1. A negative electrode sheet, characterized in that, It includes a conductive layer and a porous layer disposed on at least one side of the conductive layer, wherein the porous layer includes a porous material and a metal inorganic salt loaded inside the porous material; The standard electrode potential of the metal cation in the metal inorganic salt is greater than that of the lithium ion.

2. The negative electrode sheet as described in claim 1, characterized in that, The conductive layer includes one of lithium foil, lithium alloy foil, lithium copper composite strip, and copper foil.

3. The negative electrode sheet as described in claim 1, characterized in that, The porous material includes at least one of foamed metal, porous carbon-based material, porous polymer-based material, and porous ceramic material.

4. The negative electrode sheet as described in claim 1, characterized in that, The metal cations in the inorganic metal salt include at least one of gold ions, silver ions, tin ions, zinc ions, and magnesium ions. And / or, the anions in the metal inorganic salt include at least one of nitrate ions, phosphate ions, hexafluorophosphate ions, and tetrafluoroborate ions.

5. The negative electrode sheet as described in claim 3 or 4, characterized in that, The porous material includes foamed metal, wherein the standard electrode potential of the foamed metal is greater than or equal to the standard electrode potential of the metal cation in the metal inorganic salt.

6. The negative electrode sheet as described in claim 1, characterized in that, The porosity of the porous layer is φ, and 80%≤φ≤96%.

7. The negative electrode sheet as described in claim 1, characterized in that, The loading of the metal inorganic salt inside the porous material is L, and 0.01 mg / cm³. 2 ≤L≤0.99mg / cm 2 .

8. The negative electrode sheet as described in claim 1, characterized in that, The thickness of the conductive layer is T1, and 10μm≤T1≤40μm; And / or, the thickness of the porous layer is T2, and 10μm≤T2≤60μm.

9. The negative electrode sheet as described in claim 1, characterized in that, The Dv50 particle size of the metal inorganic salt is D1, and 1nm≤D1≤1μm.

10. An electrochemical device, characterized in that, Includes the negative electrode sheet as described in any one of claims 1-9.

11. An electronic device, characterized in that, Includes the electrochemical device as described in claim 10.

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