CN112563463B

CN112563463B - Negative electrode additive, secondary battery, battery module, battery pack and device

Info

Publication number: CN112563463B
Application number: CN201910920084.3A
Authority: CN
Inventors: 陈宁
Original assignee: Contemporary Amperex Technology Co Ltd
Current assignee: Contemporary Amperex Technology Co Ltd
Priority date: 2019-09-26
Filing date: 2019-09-26
Publication date: 2022-06-07
Anticipated expiration: 2039-09-26
Also published as: CN112563463A; WO2021057305A1

Abstract

The application discloses a negative electrode additive, a secondary battery, a battery module, a battery pack and a device. The negative electrode additive includes: the core material and the composite protective layer coated on the outer surface of the core material; wherein the core material comprises metallic lithium or a lithium composite material; the composite protective layer includes a polymer and a silane compound. The cathode additive provided by the application can be added into a cathode diaphragm of a secondary battery as a lithium source and is used for compensating lithium consumption of the cathode of the secondary battery in the first charge and discharge process. The secondary battery provided by the application has high energy density and long cycle life.

Description

Negative electrode additive, secondary battery, battery module, battery pack and device

Technical Field

The present application relates to the field of battery technology, and in particular, to a negative electrode additive, a secondary battery, a battery module, a battery pack, and a device.

Background

With the exhaustion of non-renewable energy such as petroleum and the continuous development of new technologies, the application of secondary batteries in portable electronic devices, high-endurance, high-power electric vehicles has been increasingly demanded, and the development of batteries with high energy density has become a major point in the development of secondary batteries.

The current common problem is that the electrolyte of the secondary battery reacts with the cathode material at a solid-liquid interface in the first charging process to generate an SEI film. Since the reaction consumes a part of the active lithium ions, the initial discharge capacity of the secondary battery is lower than the charge capacity. Generally, the negative electrode material has about 10% capacity loss during the first charge and discharge process; meanwhile, many documents and patents report that the energy density of the lithium ion battery is improved by matching a high-nickel high-voltage anode material with a silicon-carbon anode, but the silicon-carbon anode has low first-effect and has capacity loss of about 40% during first charge and discharge. In addition, the SEI film decomposes, recombines, and thickens during normal use (circulation and storage) of the lithium ion battery, and also consumes a certain amount of active lithium, thereby causing the capacity attenuation of the battery cell and reducing the service life of the battery.

Aiming at the phenomena that the initial capacity of a lithium ion battery is reduced and the service life of the battery is reduced due to the consumption of active lithium by an SEI film of a negative electrode of the lithium ion battery, the existing solution comprises the following steps: (1) the negative electrode SEI film is preferentially formed before the battery is assembled through a special process, so that the consumption of active lithium during the negative electrode SEI film forming during the first charging is avoided, and the initial capacity of the battery is improved. The technical conditions of the scheme are severe, the process is complicated, great cost waste is caused, the negative electrode needs to be cleaned and dried for many times after being subjected to film forming, the bonding performance of the battery is greatly influenced, and the safety of the battery cannot be ensured. (2) Lithium-rich lithium of the pole piece provides an additional lithium source to compensate lithium ions consumed by SEI film formation during first charging, and lithium metal (lithium powder or lithium sheets) is mainly rolled onto the surface of the negative pole piece. Because the reaction activity of the metallic lithium is higher, the requirements on the environment and the operation of each procedure during production are very strict, the safety risk in the production process is higher, and the method is also unfavorable for the health of operators. (3) The first charging voltage is increased to increase the first lithium removal amount of the positive electrode, and the lithium ions removed more are used for supplementing SEI film formation consumption. The scheme is very simple to operate, but can influence the design of the battery cell, and because the gram capacity of the conventional positive active material is low, the positive electrode can meet the requirements of SEI (solid electrolyte interphase) film formation only by coating more active materials, and various performances of the battery cell can be adversely affected.

In addition, in order to improve the stability of lithium metal in air and ensure production safety, researchers mainly coat a polymer protective layer on the surface of lithium metal. The polymer protective layer has good flexibility, but the coating effect is poor, and the lithium metal still has a certain reaction with the surrounding environment.

In view of the above, it is necessary to provide a secondary battery capable of solving the above problems.

Disclosure of Invention

In view of the problems in the background art, a first aspect of the present application provides an additive for a negative electrode, which can combine a high first coulombic efficiency with a good cycle performance when used for a negative electrode of a secondary battery.

A first aspect of the present application provides a negative electrode additive comprising: the core material and the composite protective layer coated on the outer surface of the core material; wherein the core material comprises one or more of metallic lithium and lithium composite material; the composite protective layer includes a polymer and a silane compound.

A second aspect of the present application provides a negative electrode sheet comprising a current collector and a negative electrode material coated on the current collector, the negative electrode material comprising a negative electrode active material and the negative electrode additive according to the first aspect of the embodiments of the present application.

A third aspect of the present application provides a secondary battery comprising a negative electrode tab according to the second aspect of the present application.

A fourth aspect of the present application provides a battery module including the secondary battery described in the third aspect of the present application.

A fifth aspect of the present application provides a battery pack including the battery module according to the fourth aspect of the present application.

A sixth aspect of the present application provides an apparatus comprising the secondary battery according to the third aspect of the present application, the secondary battery serving as a power source of the apparatus.

The application at least comprises the following beneficial effects:

the negative electrode additive provided by the application can supplement lithium ions consumed by negative electrode SEI film forming, effectively improves the first coulombic efficiency of the secondary battery, reduces the irreversible capacity loss of the secondary battery, and obviously improves the cycle life of the secondary battery.

Drawings

Fig. 1 is a schematic diagram of an embodiment of a secondary battery.

Fig. 2 is a schematic diagram of an embodiment of a battery module.

Fig. 3 is a schematic diagram of an embodiment of a battery pack.

Fig. 4 is an exploded view of fig. 3.

Fig. 5 is a schematic diagram of an embodiment of an apparatus in which a secondary battery is used as a power source.

Wherein the reference numerals are as follows:

1 Battery pack

2 upper box body

3 lower box body

4 cell module

5 Secondary Battery

Detailed Description

In order to make the purpose, technical solution and advantageous technical effects of the present invention clearer, the present invention is described in detail with reference to specific embodiments below. It should be understood that the embodiments described in this specification are only for the purpose of explaining the present application and are not intended to limit the present application.

For the sake of brevity, only some numerical ranges are explicitly disclosed herein. However, any lower limit may be combined with any upper limit to form ranges not explicitly recited; and any lower limit may be combined with any other lower limit to form a range not explicitly recited, and similarly any upper limit may be combined with any other upper limit to form a range not explicitly recited. Further, although not explicitly recited, every point or individual value between endpoints of a range is encompassed within the range. Thus, each point or individual value can form a range not explicitly recited as its own lower or upper limit in combination with any other point or individual value or in combination with other lower or upper limits.

In the description herein, it is to be noted that, unless otherwise specified, "above" and "below" are inclusive and "one or more" means "several" are two or more.

The above summary of the present application is not intended to describe each disclosed embodiment or every implementation of the present application. The following description more particularly exemplifies illustrative embodiments. At various points throughout this application, guidance is provided through a list of embodiments that can be used in various combinations. In each instance, the list is merely a representative group and should not be construed as exhaustive.

Negative electrode additive

A first aspect of the application provides a negative electrode additive, which comprises a core material and a composite protective layer coated on the outer surface of the core material; the core material comprises one or more of metallic lithium and lithium composite material; the composite protective layer includes a polymer and a silane compound.

According to certain embodiments of the present application, the lithium composite material comprises a composite of lithium and at least one of silicon, tin, aluminum, and carbon.

In the context according to the present application, "silane compound" refers to a silane compound having three or more condensable functional groups attached to one or more silicon atoms in the silane compound.

As suitable examples of the condensable functional group, alkoxy, aryloxy, alkanoyloxy, aroyloxy, preferably alkoxy, can be given.

In some embodiments, the silane compound has a structure represented by formula 1:

wherein

R₁、R₂And R₃Each independently selected from C₁-C₆Alkoxy radical, C₆-C₁₀Aryloxy group, C₁-C₆Alkanoyloxy group, C₆-C₁₀Group of aroyloxy radicals, in which R₁、R₂And R₃May be the same or different;

R₄selected from the group consisting of C₁-C₆Alkyl and C₆-C₁₀Aryl radicals or selected from the group consisting of C₁-C₆Alkoxy radical, C₆-C₁₀Aryloxy group, C₁-C₆Alkanoyloxy group, C₆-C₁₀A group consisting of aroyloxy groups;

R₅and R₆Each independently selected from C₁-C₆Alkyl and C₆-C₁₀Aryl groups; and is

m is an integer of 0 to 4.

Preferably, the silane compound is selected from one or more of epoxy silane, alkoxy silane and silicate ester.

Suitable epoxysilanes include, for example, gamma-glycidoxypropyltrimethoxysilane (KH-560), gamma-glycidoxypropyltriethoxysilane (KH-561), gamma-glycidoxymethyldiethoxysilane (KH-563), and gamma-glycidoxypropylmethyldimethoxysilane (KH-564); suitable alkoxysilanes include, for example, methyltriethoxysilane, methyltrimethoxysilane, and propyltrimethoxysilane; suitable silicates include, for example, methyl orthosilicate, ethyl orthosilicate, and propyl orthosilicate.

Examples of polymers include, but are not limited to, polyalkylene carbonates, such as polypropylene carbonate; polyalkylene oxides such as polyethylene oxide; polyalkylsiloxanes such as polyethyl siloxane; polyalkyl acrylates, such as polyethyl acrylate, polymethyl acrylate; polyalkyl methacrylates, such as polymethyl methacrylate, polyethyl methacrylate.

In the context of the present application, polyalkylsiloxanes have a structure represented by general formula 2:

wherein

R₇Is an alkyl group; n is an integer from about 50 to about 1000, more preferably from about 1000 to about 5000; z represents the terminal group of the blocked siloxane chain.

Preferably, the weight average molecular weight of the polymer is in the range of 10000-. In this case, it is ensured that the polymer can withstand the high temperature of coating baking in the production process of the secondary battery, and that the polymer can be well dissolved in a carbonate-based solvent.

According to certain embodiments of the present application, the average particle size D50 of the core material is between 10nm and 30 μm, preferably between 1 μm and 20 μm.

According to certain embodiments of the present application, the composite protective layer has an average thickness of 2nm to 3 μm, preferably 10nm to 2 μm, more preferably 50nm to 1 μm.

In the present application, the average particle diameter D50 is used to characterize the particle size of the core material, and its physical meaning is the particle diameter corresponding to 50% of the volume distribution of the particles of the core material, i.e., the volume distribution average particle diameter. D50 can be determined by methods known in the art, for example by laser diffraction. Specifically, a laser diffraction particle size distribution measuring instrument (e.g., Mastersizer 3000) can be used to measure the particle size distribution according to the particle size distribution laser diffraction method GB/T19077-2016, and then obtain the average particle size corresponding to the median value of the volume distribution.

In addition, the present application also provides a method of preparing the negative electrode additive, including the steps of: dissolving a silane compound and a polymer in a carbonate solvent according to a weight ratio of 1: 1-1: 20, preferably 1: 5-1: 10, uniformly stirring, adding a core material, uniformly stirring again, filtering, and drying filter residues in a vacuum oven at a temperature of 60-100 ℃, thereby forming the negative electrode additive comprising the core material and a composite protective layer coated on the outer surface of the core material.

According to certain embodiments of the present application, the carbonate-based solvent has a boiling point of 90 ℃ to 130 ℃. Preferably, the carbonate solvent may be one or more selected from dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate and propyl methyl carbonate.

The application provides the negative pole additive has composite protective layer, and it both can play better cladding effect, avoids kernel lithium source contact air to take place the reaction, can release the lithium source again and participate in negative pole film forming reaction after annotating the liquid. Without wishing to be bound by any theory, the inventors believe that the negative electrode additive provided according to the present application comprises a core material and a composite protective layer coated on the outer surface of the core material, the composite protective layer being formed from a mixture comprising a polymer and a silane compound, wherein the silane compound actually functions as a coupling agent, enhances the adhesion between the polymer and the core material, and effectively improves the coating ability of the polymer; since the polymer contained in the composite protective layer is continuously dissolved in an electrolyte containing a carbonate-based solvent, the exposed lithium source can relatively easily participate in electrochemical reactions. The lithium source in the additive can form an SEI film on the surface of the negative electrode during charging, so that the irreversible lithium consumption of the positive electrode is reduced, and the initial discharge capacity is improved. Meanwhile, the supplemented lithium source can also become active lithium, and when the active lithium is insufficient in the circulation process, the stored active lithium can participate in the electrochemical reaction in time, so that the capacity attenuation is reduced, and the service life of the battery is prolonged.

In an embodiment according to the present application, the lithium composite material includes a composite material of lithium and at least one selected from silicon, tin, aluminum, and carbon; the silane compound is selected from one or more of epoxy silane, alkoxy silane and silicate ester; the polymer does not react with solvents such as N, N-dimethylformamide, N-dimethylacetamide, N-methylpyrrolidone, tetrahydrofuran, acetone, or methanol.

Negative pole piece

A second aspect of embodiments of the present application provides a negative electrode tab comprising a current collector and a negative electrode material coated on the current collector, the negative electrode material comprising a negative electrode active material and the negative electrode additive according to the first aspect of embodiments of the present application.

According to the present application, the negative electrode active material is various inorganic or organic materials capable of deintercalating lithium ions; preferably, the negative electrode active material is selected from at least one of lithium titanate, elemental silicon and compounds thereof, elemental tin and compounds thereof, transition metals and compounds thereof, lithiates, graphite, soft carbon, and hard carbon, such as natural graphite, artificial graphite, mesophase microcarbospheres (abbreviated as MCMB), hard carbon, soft carbon, silicon-carbon composite, SiO, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO ₂Lithium titanate Li4Ti with spinel structure₅O₁₂And Li-Al alloy, preferably artificial graphite and hard carbon.

The specific structure and composition of the negative electrode sheet can be referred to conventional techniques, and the only difference from the conventional techniques is that the current collector is coated with the negative electrode additive as described in the first aspect of the present application. Thus, according to certain embodiments of the present application, a negative electrode tab comprises a current collector and a negative electrode material coated on the current collector, wherein the negative electrode material comprises a negative electrode active material, a negative electrode additive as described in the first aspect of the present application, a binder, a conductive material, and the like.

As the negative electrode current collector, a material such as a metal foil or a porous metal plate may be used. Preferably, a copper foil is used.

As for the binder and the conductive agent, the binder and the conductive agent are not particularly limited and may be selected according to actual needs.

As an example, the binder may be one or more of Styrene Butadiene Rubber (SBR), aqueous acrylic resin, carboxymethyl cellulose (CMC), polyvinylidene fluoride (PVDF), Polytetrafluoroethylene (PTFE), polyvinyl butyral (PVB), ethylene-vinyl acetate copolymer (EVA), and polyvinyl alcohol (PVA).

As an example, the conductive agent may be one or more of graphite, superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

Other optional additives, such as thickeners, for example, carboxymethylcellulose (CMC), may also be included in the negative electrode sheet.

In the negative electrode tab according to the present application, the weight ratio of the negative electrode active material to the negative electrode additive is 20:1 to 3:1, preferably 15:1 to 15:4, more preferably 10:1 to 5: 1.

The negative electrode sheet may be prepared according to conventional methods in the art, differing from conventional methods only in that the negative electrode additive as described in the first aspect of the present application is added. In a conventional method, a negative electrode active material, a conductive agent, a binder and other optional additives are dispersed in a solvent, wherein the solvent can be deionized water or NMP, so as to form uniform negative electrode slurry, the negative electrode slurry is coated on a negative electrode current collector, and the negative electrode pole piece is prepared after the working procedures of drying, cold pressing and the like.

In an embodiment according to the present application, the manner of using the negative electrode additive may include any one of the following three manners, but is not limited thereto:

(1) adding the negative electrode additive into the negative electrode active material slurry, mixing, and coating on at least one surface of the current collector to form a negative electrode film layer;

(2) preparing the negative electrode additive into slurry, coating the slurry on at least one surface of the current collector, and then coating negative electrode active material slurry on the coating containing the negative electrode additive;

(3) And coating the slurry of the negative active material on at least one surface of the current collector to form a negative film layer, and then coating the slurry prepared by the negative additive on the surface of the negative film layer.

Preferably, the negative electrode additive is added by adding the negative electrode additive into the negative electrode active material slurry, mixing and coating the mixture on at least one surface of the current collector to form a negative electrode film layer. Because the effect of mixing, stirring and coating the negative electrode active material and the negative electrode additive is better than the effect of respectively stirring and coating the negative electrode active material and the negative electrode additive, and the effect has a certain relation with the mixing uniformity of the materials, the mixing, stirring and coating are more uniformly distributed corresponding to the raw materials, and the lithium source in the negative electrode additive is likely to be more easily diffused and transferred to the negative electrode material, thereby ensuring better cycle performance.

Secondary battery

A third aspect of the embodiments of the present application provides a secondary battery including the negative electrode tab according to the second aspect of the embodiments of the present application.

Because the secondary battery adopts the negative pole piece according to the second aspect of the embodiment of the application, the capacity attenuation speed of the battery is obviously reduced, and the service life is prolonged. The reason is that the negative electrode additive releases lithium source which can participate in SEI film formation on one hand and can also become active lithium on the other hand, and when the active lithium is insufficient in the circulation process, the stored active lithium can participate in the electrochemical reaction in time, so that the capacity attenuation is reduced, and the service life of the battery is prolonged.

Specifically, the secondary battery comprises a positive pole piece, a negative pole piece, a separation film, electrolyte and a shell. The structure and the preparation method of the secondary battery can refer to the conventional technology, and the difference from the conventional technology is that the negative pole piece is the negative pole piece according to the second aspect of the embodiment of the application.

The positive pole piece comprises a positive active substance capable of extracting and inserting lithium ions. Specifically, the positive active material may be selected from lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt aluminum oxide, and compounds obtained by adding other transition metals or non-transition metals to the aforementioned oxides. Specifically, a layered lithium-containing oxide, a spinel-type lithium-containing oxide, an olivine-type lithium-containing phosphate compound, or the like can be used. However, the present application is not limited to these materials, and other conventionally known materials that can be used as a positive electrode active material of a secondary battery may be used. These positive electrode active materials may be used alone or in combination of two or more. Preferably, the positive electrode active material is a nickel-cobalt-manganese ternary material.

In the secondary battery of the third aspect of the embodiment of the present application, the specific kind of the separator is not particularly limited, and may be any separator material used in existing batteries, such as, but not limited to, polyethylene, polypropylene, polyvinylidene fluoride, and multilayer composite films thereof.

In the secondary battery of the third aspect of the embodiment of the present application, the positive electrode sheet further includes a binder and a conductive agent. And coating the positive electrode slurry comprising the positive electrode active substance, the binder and the conductive agent on a positive electrode current collector, and drying the positive electrode slurry to obtain the positive electrode piece.

According to the present application, the electrolyte includes a solute lithium salt and a solvent. Suitable solute lithium salts include, but are not limited to, lithium hexafluorophosphate (LiPF)₆) Lithium tetrafluoroborate (LiBF)₄) Lithium perchlorate (LiClO)₄) Lithium bis (fluorosulfonyl) imide (LiN (SO)₂F)₂) Lithium bis (trifluoromethylsulfonyl) imide (LiN (CF)₃SO₂)₂) Lithium bis (oxalato) borate (LiBOB), lithium difluoro (oxalato) borate (LiDFOB). The molar concentration of solute lithium salt as electrolyte in the electrolyte is 0.5-2 mol/L.

According to the present application, a solvent suitable for the electrolyte is at least one of Butylene Carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), Ethyl Methyl Carbonate (EMC), and propyl methyl carbonate (MPC). In addition, in order to ensure the solubility of the solute and the composite protective layer of the negative electrode additive, a proper amount of Ethylene Carbonate (EC) or Propylene Carbonate (PC) can also be added into the electrolyte solvent.

The solvent of the electrolyte can ensure that the composite protective layer of the negative electrode additive can be dissolved after the secondary battery is injected, because the polymer material contained in the composite protective layer is a polymer soluble in a carbonate-based solvent. Therefore, the core material of the negative electrode additive, namely the lithium source, can be released, and can participate in the SEI film forming process of the negative electrode of the secondary battery in the subsequent charging process, so that the first coulombic efficiency of the secondary battery is improved.

Battery module

A fourth aspect of the embodiment of the present application provides a battery module including the secondary battery described in the third aspect of the present application. The number of secondary batteries in the battery module may be adjusted according to the application, capacity design, etc. of the battery module.

Battery pack

A fifth aspect of the embodiments of the present application provides a battery pack including the battery module according to the fourth aspect of the present application.

Device

A sixth aspect of the embodiments of the present application provides an apparatus comprising the secondary battery described in the third aspect of the present application, which is used as a power source of the apparatus. Preferably, the apparatus comprises a mobile device, an electric vehicle, an electric train, a satellite, a ship and an energy storage system.

Examples

The present disclosure is more particularly described in the following examples that are intended as illustrative only, since various modifications and changes within the scope of the present disclosure will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are on a weight basis, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used as is without further treatment, and the equipment used in the examples is commercially available.

Example 1

Preparation of negative electrode additive

Adding methyl orthosilicate and polyethylmethacrylate into diethyl carbonate according to the weight ratio of 1:3, controlling the temperature at 45 ℃, fully stirring to completely dissolve the methyl orthosilicate and the polyethylmethacrylate to form a solution with the mass concentration of 2% and 6% of the polyethyl methacrylate. And after the solution is cooled to room temperature, adding the metallic lithium particles with the average particle size of 3 mu m into the solution, fully stirring to uniformly disperse the lithium particles, filtering, and drying filter residues in a vacuum box at 80 ℃ to obtain the negative electrode additive.

Preparation of negative pole piece

Dissolving the negative electrode active material graphite, the negative electrode additive, the conductive carbon Super P and the binder PVDF in a weight ratio of 82:13:2:3 in N-methylpyrrolidone (NMP), and stirring to obtain uniform negative electrode slurry. And uniformly coating the negative electrode slurry on a copper foil, drying by using a 120 ℃ oven, and then performing cold pressing and slitting to obtain a negative electrode plate.

Preparation of positive pole piece

Mixing the positive electrode active material (LiNi)_0.5Co_0.2Mn_0.3O₂) Mixing polyvinylidene fluoride serving as a binder and acetylene black serving as a conductive agent according to a weight ratio of 98:1:1, adding N-methyl pyrrolidone (NMP), and stirring under the action of a vacuum stirrer until the system becomes uniform and transparent to obtain anode slurry; uniformly coating the anode slurry on an aluminum foil; and (3) airing the aluminum foil at room temperature, transferring the aluminum foil to a 120 ℃ oven for drying for 1h, and then performing cold pressing and slitting to obtain the positive pole piece.

Isolation film

A polypropylene film was used as the separator.

Preparation of the electrolyte

Mixing Ethylene Carbonate (EC), Ethyl Methyl Carbonate (EMC) and diethyl carbonate (DEC) according to the volume ratio of EC: EMC: DEC ═ 1:1:1 to obtain an organic solvent, and fully drying lithium salt LiPF₆Dissolving in organic solvent, mixing to obtain electrolyte, wherein LiPF₆The concentration of (2) is 1 mol/L.

Manufacture of secondary batteryPrepare for

And (3) stacking the positive pole piece, the isolating membrane and the negative pole piece in sequence, winding to obtain a battery core, putting the battery core into an outer package, adding the electrolyte and sealing to obtain the secondary battery.

The preparation methods of examples 2-16 and comparative examples 1-3 are similar to example 1, except for the control of process parameters, which are detailed in table 1.

TABLE 1

Test section

First coulombic efficiency

Charging the secondary battery at constant temperature of 25 deg.C with constant current of 0.1C to voltage of 4.25V, charging at constant voltage of 4.25V to current of 0.05mA or less, standing for 2min to obtain initial charge capacity, and recording as C₀Then, constant current discharge is carried out at a rate of 0.1C until the voltage is 2.8V, and the discharge capacity at the time is the first discharge capacity and is marked as d₀。

The first coulombic efficiency is equal to the first discharge capacity divided by the first charge capacity, i.e., ice ₀＝d₀/c₀X 100%. The results are shown in Table 2.

Cycle performance test

The battery obtained above was subjected to a cycle test at 25 ℃ under the following charge-discharge conditions: charging to 4.2V with 1C current, then continuing to charge to 0.05C with constant voltage, and then discharging to 2.8V with 1C current. The discharge capacity was cycled until the last discharge capacity was attenuated to 80% of the first discharge capacity, and the test results are shown in table 2.

TABLE 2

From examples 1 to 16 and comparative example 1, it can be seen that when the additive of the first aspect of the present application is added to the negative electrode tab, the first coulombic efficiency and the cycle performance of the battery are both greatly improved.

The additive coating layer of comparative example 2, which contained only a polymer, and the additive coating layer of comparative example 3, which contained only a silane compound, did not exhibit any significant improvement effect on the battery.

While the invention has been described with reference to specific embodiments, the scope of the invention is not limited thereto, and those skilled in the art can easily conceive various equivalent modifications or substitutions within the technical scope of the invention. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims

1. The utility model provides a secondary battery, includes positive pole piece, negative pole piece, barrier film and electrolyte, the negative pole piece includes that the negative pole mass flow body and setting just contain the negative pole rete of negative pole active material on the at least one surface of the mass flow body of negative pole, its characterized in that, the negative pole rete still includes the negative pole additive, and it includes: the core material and the composite protective layer coated on the outer surface of the core material; the core material comprises one or more of metallic lithium and lithium composite material; the composite protective layer includes a polymer and a silane compound.

2. The secondary battery of claim 1, wherein the lithium composite comprises a composite of lithium and at least one selected from the group consisting of silicon, tin, aluminum, and carbon.

3. The secondary battery according to claim 1, wherein the polymer is soluble in a carbonate-based solvent.

4. The secondary battery according to claim 1, wherein the polymer is one or more selected from the group consisting of polyalkylene carbonate, polyalkylene oxide, polyalkylsiloxane, polyalkylacrylate, and polyalkylmethacrylate.

5. The secondary battery according to claim 1, wherein the silane compound is one or more selected from the group consisting of epoxysilane, alkoxysilane, and silicate.

6. The secondary battery according to claim 5, wherein the epoxysilane is selected from one or more of gamma-glycidoxypropyltrimethoxysilane, gamma-glycidoxypropyltriethoxysilane, gamma-glycidoxymethyldiethoxysilane and gamma-glycidoxypropylmethyldimethoxysilane; the alkoxy silane is selected from one or more of methyl triethoxysilane, methyl trimethoxysilane and propyl trimethoxysilane; the silicate is selected from one or more of methyl orthosilicate, ethyl orthosilicate and propyl orthosilicate.

7. The secondary battery according to claim 1, wherein the average particle diameter D50 of the core material is 10nm to 30 μm.

8. The secondary battery according to claim 1, wherein the average particle diameter D50 of the core material is 1 μm to 20 μm.

9. The secondary battery according to any one of claims 1 to 8, wherein a weight ratio of the negative electrode active material to the additive for a negative electrode is 20:1 to 3: 1.

10. The secondary battery according to any one of claims 1 to 8, wherein a weight ratio of the negative electrode active material to the additive for a negative electrode is 15:1 to 15: 4.

11. The secondary battery according to any one of claims 1 to 8, wherein a weight ratio of the negative electrode active material to the additive for a negative electrode is 10:1 to 5: 1.

12. A method of preparing a negative electrode additive as defined in any one of claims 1 to 11:

dissolving the silane compound and the polymer in a weight ratio of 1:1 to 1:20 in a carbonate solvent; and adding the core material after uniformly stirring, filtering after uniformly stirring again, and drying filter residues in a vacuum oven at the temperature of 60-100 ℃.

13. The method according to claim 12, wherein the carbonate-based solvent has a boiling point of 90 ℃ to 130 ℃.

14. The method according to claim 12, wherein the carbonate solvent comprises one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and propyl methyl carbonate.

15. A battery module characterized by comprising the secondary battery according to any one of claims 1 to 11.

16. A battery pack characterized by comprising the battery module according to claim 15.

17. A device characterized by comprising the secondary battery according to any one of claims 1 to 11 as a power source for the device.

18. The apparatus of claim 17, wherein the apparatus comprises a mobile device, an electric vehicle, an electric train, a satellite, a marine vessel, and an energy storage system.