WO2021057305A1 - Negative electrode additive, secondary battery, battery module, battery pack and device - Google Patents

Abstract

Disclosed are a negative electrode additive, a secondary battery, a battery module, a battery pack and a device. The negative electrode additive comprises a core material, and a composite protection layer coated on the outer surface of the core material, wherein the core material comprises metal lithium or a lithium composite material, and the composite protection layer comprises a polymer and a silane compound.

Description

Negative electrode additives, secondary batteries, battery modules, battery packs and devices

Cross-references to related applications

This application claims the priority of the Chinese patent application 201910920084.3 entitled "A negative electrode additive, secondary battery, battery module, battery pack and device" filed on September 26, 2019. The entire content of this application is incorporated by reference. Into this article.

Technical field

This application relates to the technical field of batteries, and in particular to a negative electrode additive, a secondary battery, a battery module, a battery pack and a device.

Background technique

With the depletion of non-renewable energy sources such as petroleum and the continuous development of new technologies, the application requirements for secondary batteries in portable electronic devices and high-endurance range and high-power performance electric vehicles are increasing, and the development of high-energy-density batteries has become a secondary concern. The focus of the development of secondary batteries.

The current common problem is that during the first charge of the secondary battery, the electrolyte will react with the negative electrode material at the solid-liquid interface and form a layer of SEI film. Since this reaction consumes part of the active lithium ions, the initial discharge capacity of the secondary battery will be lower than the charge capacity. Generally, the negative electrode material will have a capacity loss of about 10% during the first charge and discharge. At the same time, there have been many documents and patents reporting that the high nickel and high voltage positive electrode material is combined with the silicon carbon negative electrode to increase the energy density of the lithium ion battery. The first effect of the negative electrode is low, and the first charge and discharge will have a capacity loss of up to about 40%. In addition, the SEI film will decompose, recombine and thicken during the normal use of lithium-ion batteries (cycle and storage), and will consume a certain amount of active lithium, which will cause the cell capacity to decrease and reduce the battery life.

Summary of the invention

The first aspect of the present application provides a negative electrode additive, which includes: a core material, and a composite protective layer coated on the outer surface of the core material; wherein the core material includes one of metal lithium, lithium composite material, or Several; the composite protective layer includes a polymer and a silane compound.

In the negative electrode additive according to the first aspect described above, the lithium composite material includes a composite material of lithium and at least one selected from silicon, tin, aluminum, and carbon.

In any negative electrode additive according to the above first aspect, the polymer is soluble in carbonate-based solvents; optionally, the polymer is selected from polyalkylene carbonate, polyalkylene oxide, and polyalkylene oxide. One or more of polysiloxane, polyalkyl acrylate, and polyalkyl methacrylate.

In any negative electrode additive according to the above-mentioned first aspect, the silane compound is selected from one or more of epoxy silane, alkoxy silane, and silicate.

In any negative electrode additive according to the above first aspect, the epoxy silane is selected from the group consisting of γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, and γ-glycidoxypropyltriethoxysilane. One or more of glycidoxymethyldiethoxysilane and γ-glycidoxypropylmethyldimethoxysilane; the alkoxysilane is selected from methyltriethoxysilane, One or more of methyltrimethoxysilane and propyltrimethoxysilane; the silicate is selected from one or more of methyl orthosilicate, ethyl orthosilicate and propyl orthosilicate Kind.

In any negative electrode additive according to the above-mentioned first aspect, the average particle size D50 of the core material is 10 nm-30 μm, optionally 1 μm-20 μm.

The application also provides a method for preparing the negative electrode additive according to the first aspect of the application, comprising: dissolving the silane compound and the polymer in a carbonate solvent in a weight ratio of 1:1 to 1:20 Medium; add the inner core material after stirring uniformly, stir uniformly again and filter, and dry the filter residue in a vacuum oven at a temperature of 60° C.-100° C.

In the above method according to the present application, the boiling point of the carbonate-based solvent is 90° C.-130° C.; optionally, the carbonate-based solvent includes dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, One or more of methyl propyl carbonate.

The second aspect of the present application provides a negative pole piece, which includes a current collector and a negative electrode material coated on the current collector, and the negative electrode material includes a negative active material and the negative electrode according to the first aspect of the present application. additive.

A third aspect of the present application provides a secondary battery, including the negative pole piece according to the second aspect of the present application.

In some embodiments of the third aspect of the present application, the secondary battery can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

In some implementations of the third aspect of the present application, the above-mentioned battery modules can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

The fourth aspect of the present application provides a device including at least one of the secondary battery, battery module, or battery pack described in the third aspect of the present application, and the secondary battery, battery module, or battery pack can be used As the power source of the device, it can also be used as the energy storage unit of the device.

This application includes at least the following beneficial effects:

The negative electrode additive provided in this application can supplement the lithium ions consumed by the negative SEI film formation, effectively improve the first coulombic efficiency of the secondary battery, reduce the irreversible capacity loss of the secondary battery, and significantly improve the cycle life of the secondary battery.

Description of the drawings

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

Fig. 2 is an exploded view of Fig. 1.

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

Fig. 4 is a schematic diagram of an embodiment of a battery pack.

Fig. 5 is an exploded view of Fig. 4.

Fig. 6 is a schematic diagram of an embodiment of a device in which a secondary battery is used as a power source.

detailed description

In order to make the purpose of the invention, technical solutions, and beneficial technical effects of the present application clearer, the following describes the present application in detail with reference to specific embodiments. It should be understood that the embodiments described in this specification are only for explaining the application, not for limiting the application.

For simplicity, only some numerical ranges are explicitly disclosed herein. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, and any upper limit can be combined with any other upper limit to form an unspecified range. In addition, although not explicitly stated, every point or single value between the end points of the range is included in the range. Therefore, each point or single numerical value can be used as its own lower limit or upper limit, combined with any other point or single numerical value, or combined with other lower or upper limits to form an unspecified range.

In the description herein, it should be noted that, unless otherwise specified, "above" and "below" include the number, and "several" in "one or more" means two or more.

The above-mentioned summary of the invention in this application is not intended to describe each disclosed embodiment or every implementation in this application. The following description more specifically exemplifies exemplary embodiments. In many places throughout the application, guidance is provided through a series of examples, which can be used in various combinations. In each instance, the enumeration serves only as a representative group and should not be interpreted as an exhaustive list.

Aiming at the phenomenon that the negative electrode SEI film of lithium ion batteries consumes active lithium and causes the initial capacity and life of the battery to decrease, the existing solutions include: (1) Prioritize the formation of the negative electrode SEI film before battery assembly through a special process, thereby avoiding the first charge The negative SEI film formation consumes active lithium and increases the initial capacity of the battery. This kind of scheme has strict process conditions and cumbersome processes, resulting in large cost waste. After the negative electrode is formed into a film, it needs to be cleaned and dried many times, which has a great impact on the bonding performance of the battery and cannot guarantee the safety of the battery. (2) The pole piece is rich in lithium to provide an additional lithium source to compensate for the lithium ions consumed by the SEI film formation during the first charge, mainly by rolling the lithium metal (lithium powder or lithium piece) onto the surface of the negative pole piece. Due to the high reactivity of metal lithium, the environment and operation requirements of each process are very strict during production, and the safety risk during the production process is high, and it is also harmful to the health of the operators. (3) Increase the first charging voltage to increase the first delithiation amount of the positive electrode, and the extra lithium ions are used to supplement the SEI film formation consumption. The operation of this scheme is very simple, but it will affect the cell design. Due to the low gram capacity of the conventional positive electrode active material, the positive electrode needs to be coated with more active material to meet the requirements of SEI film formation, which will affect the performance of the cell. Negative Effects.

In addition, in order to improve the stability of lithium metal in the air and ensure production safety, researchers mainly do this by covering the surface of lithium metal with a polymer protective layer. The polymer protective layer is more flexible, but the coating effect is poor, and the lithium metal still has a certain reaction with the surrounding environment.

In view of this, it is indeed necessary to provide a secondary battery that can solve the above-mentioned problems.

Anode additives

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

According to some embodiments of the present application, the lithium composite material includes a composite material 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 connected to one or more silicon atoms in the silane compound.

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

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

among them

R ₁ , R ₂ and R ₃ are each independently selected from C ₁ -C ₆ alkoxy, C ₆ -C ₁₀ aryloxy, C ₁ -C ₆ alkanoyloxy, C ₆ -C ₁₀ aroyloxy The group consisting of R ₁ , R ₂ and R ₃ may be the same or different;

R _{4 is} selected from the _{group consisting of C 1} -C ₆ alkyl and C ₆ -C ₁₀ aryl, or selected from C ₁ -C ₆ alkoxy, C ₆ -C ₁₀ aryloxy, C ₁ -C ₆ alkane The group consisting of acyloxy and C ₆ -C _{10 aroyloxy;}

R ₅ and R ₆ are each independently selected from the _{group consisting of C 1} -C ₆ alkyl and C ₆ -C ₁₀ aryl; and

m is an integer from 0 to 4.

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

Suitable epoxy silanes include, for example, gamma-glycidoxypropyl trimethoxysilane (KH-560), gamma-glycidoxypropyl triethoxysilane (KH-561), gamma-glycidyl ether Oxymethyldiethoxysilane (KH-563) and γ-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 silicon Oxyanes; polyalkyl acrylates, such as polyethyl acrylate, polymethyl acrylate; polyalkyl methacrylates, such as polymethyl methacrylate, polyethyl methacrylate.

In the context of this application, polyalkylsiloxanes have the structure represented by Formula 2:

among them

R ₇ is an alkyl group; n is an integer from about 50 to about 1000, more optionally from about 1000 to about 5000; Z represents a terminal group that blocks the siloxane chain.

Optionally, the weight average molecular weight of the polymer is in the range of 10,000 to 500,000. In this case, it not only ensures that the polymer can withstand the high temperature of coating and baking during the preparation of the secondary battery, but also ensures that the polymer can be better dissolved in the carbonate solvent.

According to some embodiments of the present application, the average particle size D50 of the core material is 10 nm-30 μm, optionally 1 μm-20 μm.

According to some embodiments of the present application, the average thickness of the composite protective layer is 2nm-3μm, optionally 10nm-2μm, and further optionally 50nm-1μm.

In this application, the average particle size D50 is used to characterize the particle size of the core material, and its physical meaning is the particle size corresponding to 50% of the volume distribution of the core material particles, that is, the average particle size of the volume distribution. D50 can be measured by methods known in the art, for example, by laser diffraction. Specifically, a laser diffraction particle size distribution measuring instrument (such as 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, this application also provides a method for preparing the negative electrode additive, which includes the following steps: the silane compound and the polymer are adjusted in the order of 1:1 to 1:20, optionally 1:4 to 1:15, and further optional The weight ratio of ground 1:5 to 1:10 is dissolved in carbonate solvent, after stirring, add the core material, stir again and filter, and dry the filter residue in a vacuum oven at a temperature of 60℃-100℃ Thus, a negative electrode additive including a core material and a composite protective layer coated on the outer surface of the core material is formed.

According to some embodiments of the present application, the boiling point of the carbonate-based solvent is 90°C-130°C. Alternatively, the carbonate-based solvent may be selected from one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and methyl propyl carbonate.

The negative electrode additive provided in the present application has a composite protective layer, which can not only have a good coating effect, prevent the core lithium source from contacting air and react, but also can release the lithium source to participate in the negative electrode film-forming reaction after liquid injection. Without wishing to be limited by any theory, the inventor believes that the negative electrode additive provided according to this application includes a core material and a composite protective layer covering the outer surface of the core material. The composite protective layer is composed of a polymer and a silane compound. The mixture is formed, in which 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; due to the polymer contained in the composite protective layer It will continue to dissolve in the electrolyte containing carbonate solvents, and the exposed lithium source can easily participate in the electrochemical reaction. During charging, the lithium source in the additive can form an SEI film on the surface of the negative electrode, which reduces the irreversible lithium consumption of the positive electrode, so the initial discharge capacity can be improved. At the same time, the supplemented lithium source can also become active lithium. When the active lithium is insufficient during the cycle, the reserved active lithium can participate in the electrochemical reaction in time to reduce the capacity attenuation, thereby prolonging the battery life.

In some embodiments 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 epoxy silane, alkoxy One or more of silane and silicate; the polymer does not interact with N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, tetrahydrofuran, acetone or methanol Solvent reaction such as reaction.

Negative pole piece

The second aspect of the present application provides a negative pole piece, which includes a current collector and a negative electrode material coated on the current collector, and the negative electrode material includes a negative active material and the negative electrode according to the first aspect of the present application. additive.

According to this application, the negative electrode active material is various inorganic or organic materials that can release lithium ions; optionally, the negative electrode active material is selected from lithium titanate, elemental silicon and its compounds, elemental tin and its compounds, and transition metals. And at least one of its compounds, lithiations, graphite, soft carbon, and hard carbon, such as natural graphite, artificial graphite, mesophase micro-carbon spheres (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite One or more of SiO, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO ₂ , spinel structure lithium titanate Li4Ti ₅ O ₁₂ and Li-Al alloy, for example, One or more of artificial graphite and hard carbon.

The specific structure and composition of the negative pole piece can refer to the conventional technology. The difference from the conventional technology is only that the current collector is coated with the negative electrode additive as described in the first aspect of the application. Therefore, according to some embodiments of the present application, the negative pole piece includes a current collector and a negative electrode material coated on the current collector, wherein the negative electrode material includes a negative active material, the negative electrode additive as described in the first aspect of the present application , Adhesives and conductive materials, etc.

Materials such as metal foil or porous metal plate can be used as the negative electrode current collector. Optionally, copper foil is used.

Regarding the binder and the conductive agent, the application does not specifically limit the binder and the conductive agent, and can be selected according to actual needs.

As an example, the above-mentioned binder may be styrene-butadiene rubber (SBR), water-based acrylic resin, carboxymethyl cellulose (CMC), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl butadiene rubber One or more of aldehyde (PVB), ethylene-vinyl acetate copolymer (EVA) and polyvinyl alcohol (PVA).

As an example, the aforementioned 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.

The negative pole piece may also include other optional additives, such as a thickener, such as carboxymethyl cellulose (CMC).

In the negative electrode piece 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, optionally 15:1 to 15:4, and further optionally 10:1 To 5:1.

The negative pole piece can be prepared according to the conventional method in the field, and the difference from the conventional method is only that the negative electrode additive as described in the first aspect of the present application is added. The conventional method is usually to disperse the negative electrode active material, conductive agent, binder and other optional additives in a solvent. The solvent can be deionized water or NMP to form a uniform negative electrode slurry. The negative electrode slurry is coated on the negative electrode collector. On the fluid, after drying, cold pressing and other processes, the negative pole piece is prepared.

In some embodiments according to the present application, the use of the negative electrode additive may include any of the following three methods, but is not limited thereto:

(1) The negative electrode additive is added to the negative electrode active material slurry and mixed and then coated on at least one surface of the current collector to form a negative electrode film layer;

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

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

Optionally, the addition of the negative electrode additive is carried out by adding the negative electrode additive to the negative electrode active material slurry and mixing it and coating it 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 stirring and coating the two separately, this has a certain relationship with the uniformity of the mixing of the materials. For uniform distribution, the lithium source in the negative electrode additive may be more easily diffused and transferred to the negative electrode material, thereby ensuring better cycle performance.

Secondary battery

A third aspect of the present application provides a secondary battery, which includes the negative pole piece according to the second aspect of the embodiments of the present application.

Since the secondary battery uses the negative pole piece according to the second aspect of the present application, the battery capacity decay speed is significantly reduced, and the life span is prolonged. This is because the negative electrode additive releases the lithium source on the one hand to participate in the SEI film formation, on the other hand, it can also become active lithium. When the active lithium is insufficient during the cycle, these reserved active lithium can participate in the electrochemical reaction in time to reduce the capacity The attenuation, thereby extending battery life.

Specifically, the secondary battery includes a positive pole piece, a negative pole piece, a separator, an electrolyte, and a casing. The structure and preparation method of the secondary battery can refer to conventional technology. The difference from the conventional technology is that the negative electrode piece is the negative electrode piece according to the second aspect of the present application.

The positive pole piece includes a positive active material that can extract and insert lithium ions. Specifically, the positive electrode active material can be selected from lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, the foregoing oxides and others. Compounds derived from transition metals or non-transition metals. Specifically, layered lithium-containing oxides, spinel-type lithium-containing oxides, olivine-type lithium-containing phosphate compounds, etc. 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 can also be used. These positive electrode active materials may be used alone or in combination of two or more. Optionally, the positive electrode active material is a nickel-cobalt-manganese ternary material.

In the secondary battery of the third aspect of the present application, the specific type of the separator is not specifically limited, and it can be any separator material used in existing batteries, such as polyethylene, polypropylene, polyvinylidene fluoride and their The multi-layer composite film, but not limited to these.

In the secondary battery of the third aspect of the present application, the positive pole piece further includes a binder and a conductive agent. The positive electrode slurry including the positive electrode active material, the binder and the conductive agent is coated on the positive electrode current collector, and the positive electrode pole piece is obtained after the positive electrode slurry is dried.

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

According to this application, the solvents suitable for the electrolyte are butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC) ) At least one of. In addition, in order to ensure the solubility of the solute and the negative electrode additive composite protective layer, an appropriate amount of ethylene carbonate (EC) or propylene carbonate (PC) can also be added to 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. This is because the polymer material contained in the composite protective layer is soluble in carbonate-based solvents. polymer. In this way, the core material of the negative electrode additive, that is, the lithium source, can be released, and can participate in the SEI film formation process of the negative electrode of the secondary battery in the subsequent charging process, which improves the first coulombic efficiency of the secondary battery.

The present application has no particular limitation on the shape of the secondary battery, which can be cylindrical, square or other arbitrary shapes. Fig. 1 shows a secondary battery 5 with a square structure as an example.

In some embodiments, the secondary battery may include an outer package. The outer packaging is used to encapsulate the positive pole piece, the negative pole piece and the electrolyte.

In some embodiments, referring to FIG. 2, the outer package may include a housing 51 and a cover 53. Wherein, the housing 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose to form an accommodating cavity. The housing 51 has an opening communicating with the containing cavity, and a cover plate 53 can cover the opening to close the containing cavity.

The positive pole piece, the negative pole piece and the separator may be formed into the electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is packaged in the receiving cavity. The electrolyte may be an electrolyte, and the electrolyte is infiltrated in the electrode assembly 52. The number of electrode assemblies 52 included in the secondary battery 5 can be one or several, which can be adjusted according to requirements.

In some embodiments, the outer packaging of the secondary battery may be a hard case, such as a hard plastic case, aluminum case, steel case, or the like. The outer packaging of the secondary battery may also be a soft bag, such as a pouch type soft bag. The material of the soft bag may be plastic, for example, it may include one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), and the like.

In some embodiments, the secondary battery can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

FIG. 3 is a battery module 4 as an example. Referring to FIG. 3, in the battery module 4, a plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4. Of course, it can also be arranged in any other manner. Furthermore, the plurality of secondary batteries 5 can be fixed by fasteners.

Optionally, the battery module 4 may further include a housing having an accommodating space, and a plurality of secondary batteries 5 are accommodated in the accommodating space.

In some embodiments, the above-mentioned battery modules can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

Figures 4 and 5 show the battery pack 1 as an example. 4 and 5, the battery pack 1 may include a battery box and a plurality of battery modules 4 provided in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can be covered on the lower box body 3 and forms a closed space for accommodating the battery module 4. A plurality of battery modules 4 can be arranged in the battery box in any manner.

Device

The fourth aspect of the present application provides a device comprising at least one of the secondary battery, battery module, or battery pack according to the third aspect of the present application, the secondary battery, battery module, or battery pack It can be used as the power source of the device, and can also be used as the energy storage unit of the device. The device can be, but is not limited to, mobile devices (such as mobile phones, laptop computers, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf Vehicles, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

The device can select a secondary battery, a battery module, or a battery pack according to its usage requirements.

Fig. 6 is a device as an example. The device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the requirements of the device for high power and high energy density of the secondary battery, a battery pack or a battery module can be used.

As another example, the device may be a mobile phone, a tablet computer, a notebook computer, and the like. The device is generally required to be thin and light, and a secondary battery can be used as a power source.

Example

The following examples more specifically describe the content disclosed in the present application, and these examples are only used for explanatory description, because various modifications and changes within the scope of the present disclosure are obvious to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on weight, and all reagents used in the examples are commercially available or synthesized according to conventional methods, and can be directly obtained. Used without further processing, the instruments used in the examples are all commercially available.

Example 1

Preparation of negative electrode additives

Add methyl orthosilicate and polyethyl methacrylate to diethyl carbonate in a weight ratio of 1:3, control the temperature at 45°C, stir well to dissolve it completely, and form methyl orthosilicate with a mass concentration of 2%, polyethyl methacrylate with a mass concentration of 6% solution. After the solution is cooled to room temperature, metallic lithium particles with an average particle size of 3μm are added to the solution, fully stirred to uniformly disperse the lithium particles, filtered, and the filter residue is dried in a vacuum box at 80°C to obtain the negative electrode additive .

Preparation of negative pole piece

The negative electrode active material graphite, the above-mentioned negative electrode additive, the conductive carbon Super P, and the binder PVDF are dissolved in N-methylpyrrolidone (NMP) at a weight ratio of 82:13:2:3, and a uniform negative electrode slurry is obtained by stirring. The negative electrode slurry is evenly coated on the copper foil, dried in an oven at 120 DEG C, and then cold pressed and slit to obtain negative electrode pieces.

Preparation of positive pole piece

The positive electrode active material (LiNi _0.5 Co _0.2 Mn _0.3 O ₂ ), the binder polyvinylidene fluoride, and the conductive agent acetylene black are mixed in a weight ratio of 98:1:1, and N-methylpyrrolidone (NMP) is added. Stir under the action of a stirrer until the system becomes uniform and transparent to obtain the positive electrode slurry; coat the positive electrode slurry evenly on the aluminum foil; dry the aluminum foil at room temperature and transfer it to an oven at 120°C for 1 hour, then cold press and slit to obtain Positive pole piece.

Isolation film

A polypropylene film is used as the isolation membrane.

Preparation of electrolyte

Mix ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of EC:EMC:DEC=1:1:1 to obtain an organic solvent. The lithium salt LiPF _{6 is} dissolved in an organic solvent and mixed uniformly to obtain an electrolyte, wherein _{the concentration of LiPF 6} is 1 mol/L.

Preparation of secondary battery

The positive pole piece, the separator, and the negative pole piece are stacked in order, and the battery is obtained after winding, and the battery is packed in an outer package, and the electrolyte is added and sealed to obtain a secondary battery.

The preparation methods of Examples 2-16 and Comparative Examples 1-3 are similar to those of Example 1, and the difference lies in the adjustment of process parameters. See Table 1 for details.

Table 1

Test part

First coulomb efficiency

Charge the secondary battery at a constant current of 0.1C to a voltage of 4.25V at a constant temperature of 25°C, then charge it at a constant voltage of 4.25V until the current is less than or equal to 0.05mA, and then let it stand for 2min. The charging capacity at this time It is the first charge capacity, denoted as c ₀ , and then discharged at a constant current rate of 0.1C to a voltage of 2.8V. The discharge capacity at this time is the first discharge capacity, denoted as d ₀ .

The first coulombic efficiency is equal to the first discharge capacity divided by the first charge capacity, that is, ice ₀ =d ₀ /c ₀ ×100%. The experimental results are shown in Table 2.

Cycle performance test

The battery obtained above was subjected to a cycle test at 25°C, and the charging and discharging conditions were as follows: charging with a current of 1C to 4.2V, continuing to charge with a constant voltage to 0.05C, and then discharging with a current of 1C to 2.8V. The charging and discharging cycle is repeated until the last discharge capacity decays to 80% of the first discharge capacity. The test results are shown in Table 2.

Table 2

It can be seen from Examples 1-16 and Comparative Example 1 that when the additive of the first aspect of the application is added to the negative pole piece, the first-time coulombic efficiency and cycle performance of the battery are greatly improved.

The additive coating layer of Comparative Example 2 only contains a polymer, and the additive coating layer of Comparative Example 3 only contains a silane compound, neither of which has a significant improvement effect on the battery.

The above are only specific implementations of this application, but the protection scope of this application is not limited to this. Anyone familiar with the technical field can easily think of various equivalents within the technical scope disclosed in this application. Modifications or replacements, these modifications or replacements shall be covered within the scope of protection of this application. Therefore, the protection scope of this application should be subject to the protection scope of the claims.

In addition, in those cases where conventions similar to "at least one of A, B and C, etc." are used, such structures usually have the meaning of conventions that those skilled in the art would understand (for example, "have A, B and "System with at least one of C" shall include but not limited to systems with A alone, B alone, C alone, A and B, A and C, B and C, and/or A, B and C, etc. ). In those cases where conventions similar to "at least one of A, B or C, etc." are used, such structures have the meaning of conventions that will be understood by those skilled in the art (for example, "having at least one of A, B or C" "One system" shall include, but is not limited to, A alone, B alone, C alone, A and B, A and C, B and C, and/or A, B and C, etc.). Those skilled in the art will further understand that, in fact, whether in the specification, claims or drawings, any abstract words and/or phrases that present two or more alternative terms should be understood as considering including these terms One, the possibility of one or both of these terms. For example, the phrase "A or B" will be understood to include the possibilities of "A" or "B" or "A and B."

In addition, where features or aspects of the present disclosure are described in terms of the Markush group, those skilled in the art will recognize that the application is therefore also described in terms of any single member or a subset of members of the Markush group.

Claims (13)

1. A negative electrode additive comprising: a core material and a composite protective layer covering the outer surface of the core material; wherein the core material includes one or more of metal lithium and lithium composite materials; the composite The protective layer includes a polymer and a silane compound.
2. The negative electrode additive according to claim 1, wherein the lithium composite material includes a composite material of lithium and at least one selected from silicon, tin, aluminum, and carbon.
3. The negative electrode additive according to any one of claims 1-2, wherein the polymer is soluble in carbonate solvents; optionally, the polymer is selected from polyalkylene carbonate, polyalkylene One or more of base oxide, polyalkylsiloxane, polyalkyl acrylate, and polyalkyl methacrylate.
4. The negative electrode additive according to any one of claims 1 to 3, wherein the silane compound is selected from one or more of epoxy silane, alkoxy silane, and silicate.
5. The negative electrode additive according to claim 4, wherein the epoxy silane is selected from the group consisting of γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, and γ-glycidoxypropyltriethoxysilane. One or more of glycidoxymethyldiethoxysilane and γ-glycidoxypropylmethyldimethoxysilane; the alkoxysilane is selected from methyltriethoxysilane, One or more of methyltrimethoxysilane and propyltrimethoxysilane; the silicate is selected from one or more of methyl orthosilicate, ethyl orthosilicate and propyl orthosilicate Kind.
6. The negative electrode additive according to any one of claims 1 to 5, wherein the average particle size D50 of the core material is 10nm-30μm, optionally 1μm-20μm.
7. A method for preparing the negative electrode additive according to any one of claims 1-6:

   Dissolve the silane compound and the polymer in a carbonate solvent in a weight ratio of 1:1 to 1:20; stir evenly and add the core material, the core material includes metal lithium, lithium composite material One or more; stir again and then filter, and dry the filter residue in a vacuum oven at a temperature of 60° C.-100° C. to obtain the negative electrode additive;

   Wherein, the negative electrode additive includes: a core material, and a composite protective layer coated on the outer surface of the core material; the core material includes one or more of metal lithium and lithium composite materials; the composite protective layer Including polymers and silane compounds.
8. The preparation method according to claim 7, wherein the boiling point of the carbonate-based solvent is 90° C.-130° C.; optionally, the carbonate-based solvent includes dimethyl carbonate, diethyl carbonate, and methyl carbonate. One or more of ethyl and methyl propyl carbonate.
9. A secondary battery includes a negative electrode piece, the negative electrode piece comprising a negative electrode current collector and a negative electrode film layer arranged on at least one surface of the negative electrode current collector and containing a negative electrode active material, wherein the negative electrode film layer further includes The negative electrode additive according to any one of claims 1-6 or the negative electrode additive prepared by the method according to any one of claims 7-8.
10. The secondary battery according to claim 9, wherein the weight ratio of the negative electrode active material to the negative electrode additive is 20:1 to 3:1, optionally 15:1 to 15:4, and further optionally 10:1～5:1.
11. A battery module comprising the secondary battery according to any one of claims 9-10.
12. A battery pack comprising the battery module according to claim 11.
13. A device comprising at least one of the secondary battery according to any one of claims 9-10, the battery module according to claim 11, or the battery pack according to claim 12.

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