WO2024050810A1 - Binder composition and electrode sheet prepared from same - Google Patents

Abstract

A binder composition. The binder composition contains starch and polyvinyl alcohol, and the starch contains amylose and amylopectin. The present application further relates to a battery electrode sheet composition comprising the binder composition, a battery electrode sheet prepared from the battery electrode sheet composition, a secondary battery comprising the battery electrode sheet, a battery pack comprising the secondary battery, and an electric apparatus.

Description

A kind of binder composition and electrode pole piece prepared therefrom Technical field

The present application relates to a binder composition containing starch containing amylose and amylopectin and polyvinyl alcohol. The present application also relates to a battery pole piece composition comprising the binder composition, a battery pole piece prepared from the composition, a secondary battery comprising the battery pole piece, and a battery pack comprising the secondary battery. and electrical appliances.

Background technique

Secondary batteries have become the most popular energy storage system due to their low cost, long life, and good safety. They are now widely used in pure electric vehicles, hybrid electric vehicles, smart grids and other fields. Secondary batteries are mainly composed of positive electrode sheets, negative electrode sheets, isolation films and electrolytes. The preparation of battery electrode sheets (positive electrode sheets and negative electrode sheets) requires the use of binder materials to combine the active materials of the electrode sheets with conductive agents and other Additives bind together firmly. So far, most lithium-ion battery binders are mainly synthetic polymer materials such as PVDF, SBR, and CMC. However, the bonding capabilities of these materials still need to be improved, especially when the electrodes expand significantly during multiple cycles in the long battery life cycle or under high energy density and high active material loading, which can easily lead to embrittlement of the pole pieces. , or even cracking and demoulding.

Therefore, there is still a need to provide a new adhesive that can have sufficient adhesive force at a lower dosage and can suppress the tendency of the pole piece to crack and demold when the electrode expands.

Contents of the invention

This application was made in view of the above problems, and its purpose is to provide a binder to solve the technical problem that the electrode pole pieces of secondary batteries prepared therefrom are too brittle and prone to cracking and demolding.

In order to achieve the above object, the first aspect of the present application provides a binder composition, wherein the composition contains starch and polyvinyl alcohol, and the starch contains amylose and amylopectin.

The binder composition of the present application can greatly improve the brittleness of the pole piece by containing a mixture of starch and polyvinyl alcohol. The large number of hydroxyl groups on starch and polyvinyl alcohol can ensure that when the active material loading of the pole piece increases and the thickness of the pole piece increases significantly, the water loss rate in the thickness direction will not produce a large gradient, causing the pole piece to crack. At the same time, because the selected starch contains a large amount of amylopectin, stress is released during the heating and drying process, which can effectively improve the adhesion of the pole pieces and prevent cracking and demoulding.

In any embodiment, the number average molecular weight of the amylose is 500-160000g/mol, optionally 2000-50000g/mol, further optionally 5000-20000g/mol; and/or the branched chain The number average molecular weight of starch is 100000-1000000g/mol, optionally 150000-800000g/mol, further optionally 300000-600000g/mol. In any embodiment, the weight ratio of amylose and amylopectin in the starch is 1:1 to 1:10, optionally 1:3 to 1:8, further optionally 1:4 to 1:6. In any embodiment, the starch is present in an amount of from 10 to 95% by weight, optionally from 80 to 92% by weight, based on the dry weight of the binder composition. Amylose has a linear structure, which can increase the overall strength of the composition; amylopectin has a branched structure, which can improve the flexibility of the composition. By adjusting the ratio of amylose and amylopectin in starch and selecting appropriate molecular weight ranges, further improved adhesion and processing properties can be obtained.

In any embodiment, the weight ratio of starch and polyvinyl alcohol in the composition is 1.5:1 to 20:1, optionally 2:1 to 20:1, further optionally 5:1 to 10 :1. In any embodiment, the weight average molecular weight of the polyvinyl alcohol is 15000-250000g/mol, optionally 25000-120000g/mol, further optionally 30000-80000g/mol. In any embodiment, the polyvinyl alcohol is present in an amount of from 1 to 35% by weight, optionally from 7 to 20% by weight, based on the total weight of the binder composition. The hydroxyl groups contained in polyvinyl alcohol can form hydrogen bonds with the electrode active material, which not only improves the adhesion, but also makes this connection "self-healing" to a certain extent. By adjusting the molecular weight and content of polyvinyl alcohol, compositions with different bonding strengths can be obtained.

In any embodiment, the adhesive composition further includes at least one cross-linking agent selected from the group consisting of oxalic acid, polyvinylpyrrolidone, phosphorus oxychloride, sodium trimetaphosphate, adipic acid and one or more of hexametaphosphate, optionally oxalic acid. In any embodiment, the cross-linking agent is present in an amount of from 0.01 to 5% by weight, optionally from 0.2 to 1% by weight, based on the dry weight of the adhesive composition. The cross-linking agent can connect different parts of the starch or polyvinyl alcohol molecular chain by reacting with hydroxyl groups, for example, to play an "interlocking" role. By setting its content within a specific range, the cohesive force of the mixture of starch and polyvinyl alcohol can be further adjusted.

In any embodiment, the binder composition is an aqueous dispersion including water as solvent. In any embodiment, the binder composition has a solids content of 15-60 wt%, optionally 20-40 wt%. By adjusting the solid content of the binder composition by adding the amount of water, binders suitable for different battery systems can be prepared.

The present application also relates to a method for preparing an adhesive composition selected from the first aspect of the present application, comprising the following steps:

1) Add starch to deionized water and add polyvinyl alcohol. The weight ratio of starch to polyvinyl alcohol is 1.5:1 to 20:1. The starch contains amylose in a weight ratio of 1:1 to 1:10. and amylopectin, wherein the number average molecular weight of the amylose is 500-160000g/mol, and the number average molecular weight of the amylopectin is 100000-1000000g/mol;

2) Stir the mixture obtained in 1) at 50-99°C for 0.5-24 hours;

3) Optionally add at least one cross-linking agent to the above mixture, and continue stirring at 10-99°C for 0.5-24 hours.

In any embodiment, the temperature in step 2) is 70-95°C, and/or the stirring time is 8-15 hours. In any embodiment, the temperature in step 3) is 70-95°C, and/or the stirring time is 8-15 hours.

A second aspect of the application provides a composition for preparing a battery pole piece, which includes a positive or negative active material, a conductive agent and a binder composition according to the first aspect of the application, and optionally water and Dispersant.

A third aspect of the present application provides an electrode pole piece prepared by using a binder composition selected from the first aspect of the present application.

A fourth aspect of the present application provides a secondary battery including an electrode pole piece selected from the third aspect of the present application. The electrode pole piece may be a positive electrode pole piece and/or a negative electrode pole piece.

A fifth aspect of the present application provides a battery pack including the secondary battery selected from the fourth aspect of the present application.

A sixth aspect of the present application provides an electrical device, which includes a secondary battery selected from the fourth aspect of the present application or a battery pack of the fifth aspect of the present application.

Description of the drawings

In order to explain the technical solution of the present application more clearly, the drawings required to be used in the embodiments of the present application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on the drawings without exerting creative efforts.

Figure 1 is a schematic diagram of a lithium ion secondary battery in one embodiment of the present application.

FIG. 2 is an exploded view of the lithium ion secondary battery in one embodiment of the present application shown in FIG. 1 .

Figure 3 is a schematic diagram of a battery pack in an embodiment of the present application.

FIG. 4 is an exploded view of the battery pack in one embodiment of the present application shown in FIG. 3 .

Figure 5 is a schematic diagram of a device in which a battery pack is used as a power source in an embodiment of the present application.

Figure 6 is a schematic diagram of the bonding between starch molecules and cross-linking agent molecules and active materials.

Explanation of reference signs

1 battery pack

2 upper box

3 lower cabinets

4 battery modules

5Lithium-ion secondary battery

51 shell

52 electrode assembly

53 cover

Detailed ways

For the sake of simplicity, this application specifically discloses certain numerical ranges. However, any lower limit can be combined with any upper limit to form an unexpressed range; and any lower limit can be combined with other lower limits to form an unexpressed range, and likewise any upper limit can be combined with any other upper limit to form an unexpressed range. Furthermore, each individually disclosed point or single value may itself serve as a lower or upper limit in combination with any other point or single value or with other lower or upper limits to form a range not expressly recited.

With the rapid popularity of electric vehicles and other electric vehicles, the market demand for high-energy-density lithium-ion batteries is becoming increasingly urgent. Reducing the content of auxiliary materials such as adhesion or adding silicon to the anode material is currently an important means to increase energy density. Reducing the amount of adhesive requires increasing the adhesive force per unit mass. The current main methods include grafting, copolymerization, blending, etc. of existing binding polymers; in order to improve the binding of high-expansion silicon materials, additives with hydroxyl or carboxyl groups are generally added to coat the surface of the silicon material. . Another way to increase energy density is to increase the active material load per unit area of the pole piece. However, during the pole piece coating process, an increase in load means an increase in pole piece thickness. The pole pieces are more likely to become brittle and crack during the drying process, affecting the appearance and performance of the pole pieces. If softener is added to the pole piece, there will be additive residue problems and the weight of the battery will also increase.

The selection of binder needs to consider the connection between active particles and active particles, active particles and conductive agent, active particles and current collector, and also consider whether it can adapt to the coating and drying process during the pole piece processing to ensure that the pole piece can Remove the solvent normally and keep the pole piece intact. Since the existing battery pole pieces, especially the anode, will undergo large volume changes during the process of deintercalating lithium, the binder needs to be able to maintain the bonding effect without failure amidst the continuous volume changes of the pole pieces.

Existing commonly used anode binders, such as the combination of SBR and CMC, can maintain the initial effective bonding effect, but cannot adapt to the long-term anode volume expansion, especially as more and more silicon-containing anodes will bring about comparison. Greater expansion of graphite anodes. Since both SBR and CMC are rigid polymer chains, they cannot heal after breaking. Generally, in the later stages of the battery life cycle, due to the substantial increase in the thickness of the binder pole piece, the expansion force soars, seriously affecting the safety of the battery core. On the other hand, in order to increase the energy density of the battery core, the active material loading of the pole piece has also been greatly increased. During the coating and drying process, the difference in drying speed caused by the increase in thickness can easily cause the pole piece to crack, making it difficult to manufacture.

Therefore, there is a need in the art to provide a new binder composition that can be used to prepare electrode pole pieces with improved brittleness and adhesive force, so that secondary batteries are not prone to cracking after multiple cycles of a long life cycle. mold, even in the presence of significant electrode expansion.

Specifically, the first aspect of the present application provides a binder composition, wherein the composition contains starch and polyvinyl alcohol, and the starch contains amylose and amylopectin.

The inventor found that the binder composition of the present application can greatly improve the brittleness of the pole piece by including a mixture of starch and polyvinyl alcohol. Without being limited to any theory, the inventor believes that the large number of hydroxyl groups on starch and polyvinyl alcohol can ensure that when the active material loading of the pole piece is increased and the thickness of the pole piece is greatly increased, the water loss rate in the thickness direction will not be significantly increased. Large gradients lead to pole piece cracking. At the same time, because the selected starch contains a large amount of amylopectin, stress is released during the heating and drying process, which can effectively improve the adhesion of the pole pieces and prevent cracking and demoulding. In addition, starch and polyvinyl alcohol are connected to each other through a large number of hydrogen bonds and can tightly bind active materials, especially silicon or silicone materials. Even under conditions of large stress changes, hydrogen bonds have a stronger binding force on active substances than other van der Waals forces. Compared with rigid chains connected by chemical bonds, they can automatically repair themselves after the hydrogen bonds are destroyed, which has a certain " Self-healing" ability. The molecular chain includes both rigid chains composed of starch straight chains and flexible chains composed of branched chains. The branched chains connected by polyvinyl alcohol at different positions are interconnected to enhance the overall bonding force.

Starch is a cheap, abundant, and biodegradable natural polymer that is a mixture of amylose and amylopectin. Amylose is composed of linear linear polysaccharides, and amylopectin is a highly branched polysaccharide. Currently, amylose and amylopectin can be separated from starch mixtures through technical means. The main means include compounding agent separation, salt separation, polymer controlled crystallization, cellulose adsorption, and chromatographic separation. In some embodiments of the present application, the starch consists of amylose and amylose. There are a large number of hydroxyl groups in starch molecules, which can slow down the rapid evaporation of water molecules during processing, ensure that the pole piece has a certain degree of flexibility, and at the same time, it can promote the bonding with the hydroxyl groups on the surface of the silicon nanoparticles during use of the pole piece. Intermolecular hydrogen bonds can be formed between starch molecules and silicon nanoparticles, and their strength is better than the poor van der Waals force connection between silicon and conventional PVDF, SBR and other adhesives.

In some embodiments, the number average molecular weight of the amylose is 500-160000g/mol, optionally 2000-50000g/mol, optionally 5000-20000g/mol; and/or the amylopectin The number average molecular weight is 100000-1000000g/mol, optionally 150000-800000g/mol, optionally 300000-600000g/mol. The number average molecular weight is measured according to GB/T 36214-2018 standard. The inventors found that by selecting amylose and the number average molecular weight of amylose within a specific range, pole pieces with higher adhesion and cohesion can be obtained. In addition, the starch may also contain amylose and/or amylopectin with a number average molecular weight outside the above range, and its content does not exceed 10% by weight, optionally does not exceed 5% by weight, or does not exceed 1% by weight. , or 0% by weight, based on the total weight of the starch.

In some embodiments, in any embodiment, the weight ratio of amylose and amylopectin in the starch is 1:1 to 1:10, optionally 1:3 to 1:8, may The chosen area is 1:4 to 1:6. The ratio of amylose to amylopectin in starch can be used to adjust the strength and toughness of the binder composition. In some embodiments, the starch is present in an amount of 10-95% by weight, optionally 80-92% by weight, based on the dry weight of the binder composition. The inventors found that by selecting amylose and amylopectin within a specific weight ratio range, pole pieces with fewer surface cracks and higher cohesion can be obtained. When the starch in the composition only contains amylose, or only amylose, the pole piece prepared therefrom does not even meet the requirements for pole pieces in this field, such as a large number of obvious cracks and powder loss.

In some embodiments, the weight ratio of starch and polyvinyl alcohol in the composition is 1.5:1-20:1, optionally 2:1 to 20:1, optionally 5:1 to 10: 1. In some embodiments, the polyvinyl alcohol has a weight average molecular weight of 15,000-250,000 g/mol, optionally 25,000-120,000 g/mol. Further optionally, it is 30000-80000g/mol. In some embodiments, the polyvinyl alcohol is present in an amount of 1-35% by weight, optionally 7-20% by weight, based on the dry weight of the binder composition.

In some embodiments, the adhesive composition further includes at least one cross-linking agent selected from the group consisting of oxalic acid, polyvinylpyrrolidone, phosphorus oxychloride, sodium trimetaphosphate, adipic acid , one or more of hexametaphosphate, optionally oxalic acid. Adding some cross-linking agents to the mixture of starch and polyvinyl alcohol can further enhance the "interlocking" effect of the binder. As shown in Figure 6, the cross-linking agent, specifically for example oxalic acid, can form ester bonds with two hydroxyl groups at different positions in amylose and/or amylopectin, "locking" these different positions. together, thereby increasing the bonding ability of the binder molecular chain. The polyvinyl alcohol molecules are not shown in Figure 6 . In fact, polyvinyl alcohol molecular chains also contain hydroxyl groups, which can also react with the cross-linking agent to further enhance the "interlocking" effect of the binder. In some embodiments, the cross-linking agent is present in an amount of 0.01-5% by weight, optionally 0.2-1% by weight, based on the dry weight of the adhesive composition. Of course, the addition of cross-linking agent is not necessary. In some embodiments, the adhesive composition does not include any cross-linking agent.

In some embodiments, the adhesive composition may also include other additives. The additives may be, for example, film-forming aids, rheology modifiers, tackifiers, flame retardants or defoamers. The further additives may be present in an amount of 0 to 10% by weight, optionally 1 to 5% by weight, based on the dry weight of the binder composition.

In some embodiments, the binder composition is an aqueous dispersion including water as a solvent. The binder combination can be formed by dispersing a starch mixture containing specific proportions of amylose and amylopectin in deionized water with stirring at an elevated temperature, and then adding a specific proportion of polyvinyl alcohol while heating and stirring. aqueous dispersion of the substance. In addition, the adhesive composition may also contain a small amount of other solvents, such as commonly used organic solvents, such as ethanol, toluene, dimethyl sulfoxide, N,N-dimethylformamide, and the like. In some embodiments, the binder composition has a solids content of 15-60 wt%, optionally 20-40 wt%. The content of organic solvent in the adhesive composition is less than 5% by weight, optionally less than 1% by weight, and further optionally 0% by weight. Of course, the solid content of the binder composition can be adjusted as needed by changing the amount of water added, and is not limited to the above range.

The present application also relates to a method for preparing an adhesive composition selected from the first aspect of the present application, comprising the following steps:

1) Add starch to deionized water and add polyvinyl alcohol. The weight ratio of starch to polyvinyl alcohol is 1.5:1 to 20:1. The starch contains amylose in a weight ratio of 1:1 to 1:10. and amylopectin, wherein the number average molecular weight of the amylose is 500-160000g/mol, and the number average molecular weight of the amylopectin is 100000-1000000g/mol;

2) Stir the mixture obtained in 1) at 50-99°C for 0.5-24 hours;

3) Optionally add at least one cross-linking agent to the above mixture, and continue stirring at 10-99°C for 0.5-24 hours;

4) Optionally cool the mixture.

The starch can be subjected to the process of removing impurities in advance and then dried in an oven. The drying temperature can be, for example, 60-100°C, and the drying time can be 2-24 hours. The mixing of each component can be achieved by stirring in the container, for example, by stirring with a mixer at a rotation speed of 2000 rpm until there is no visible precipitation at the bottom of the container.

In some embodiments, the temperature in step 2) is 70-95°C, and/or the stirring time is 8-15 hours. In some embodiments, the temperature in step 3) is 70-95°C, and/or the stirring time is 8-15 hours. The temperature and stirring time in steps 2) and 3) can be adjusted accordingly according to the actual situation and are not limited to the above range. The resulting mixture is left to cool, for example to room temperature, and the solids content of the mixture can then be measured. The solid content of the mixture can be adjusted by changing the amount of deionized water added to adapt to the requirements of different battery systems. In some embodiments, the mixture has a solids content of 15-60 wt%, optionally 20-40 wt%. In some embodiments, the mixture can be heated such that the mixture is in the form of a paste.

A second aspect of the application provides a composition for preparing a battery pole piece, which includes an electrode active material, a conductive agent and a binder composition according to the first aspect of the application, and optionally water and a dispersant . The battery pole piece is specifically a positive pole piece and/or a negative pole piece. The electrode active material may be a positive active material or a negative active material. The electrode active material and conductive agent can be conventionally selected as needed, which will be described in detail below.

A third aspect of the present application provides an electrode pole piece prepared by using a binder composition selected from the first aspect of the present application.

A fourth aspect of the present application provides a secondary battery including an electrode pole piece selected from the third aspect of the present application. The electrode pole piece may be a positive electrode pole piece and/or a negative electrode pole piece.

A fifth aspect of the present application provides a battery pack including the secondary battery selected from the fourth aspect of the present application.

A sixth aspect of the present application provides an electrical device, which includes a secondary battery selected from the fourth aspect of the present application or a battery pack of the fifth aspect of the present application.

The materials for the various components of the cells mentioned in this application can be selected from a wide range. In some embodiments, the battery is specifically a lithium-ion secondary battery. The battery cells of the lithium ion secondary battery will be described in detail below.

Typically, a lithium-ion secondary battery includes a positive electrode plate, a negative electrode plate, a separator and an electrolyte. During the charging and discharging process of the battery, active ions are inserted and detached back and forth between the positive and negative electrodes. The isolation film is arranged between the positive electrode piece and the negative electrode piece to play the role of isolation. The electrolyte plays a role in conducting ions between the positive and negative electrodes.

[Electrolyte]

The electrolyte plays a role in conducting ions between the positive and negative electrodes. The electrolyte includes electrolyte salts and solvents.

In this application, the electrolyte salt can be a commonly used electrolyte salt in lithium ion secondary batteries, such as lithium salt, including the above-mentioned lithium salt as a high thermal stability salt, a lithium salt as a low resistance additive, or lithium that inhibits aluminum foil corrosion. Salt. As an example, the electrolyte salt may be selected from lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium hexafluoroarsenate (LiAsF ₆ ), lithium bisfluorosulfonyl imide (LiFSI), bistrifluoromethanesulfonyl Lithium imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluoromethanesulfonate borate (LiDFOB), lithium difluorophosphate (LiPO ₂ F ₂ ), lithium difluorodioxalate phosphate (LiDFOP), fluorosulfonic acid Lithium (LiSO ₃ F), difluorodioxalate (NDFOP), Li ₂ F(SO ₂ N) ₂ SO ₂ F, KFSI, CsFSI, Ba(FSI) ₂ and LiFSO ₂ NSO ₂ CH ₂ CH ₂ CF ₃ More than one of them.

The type of solvent is not particularly limited and can be selected according to actual needs. In some embodiments, the solvent is a non-aqueous solvent. Alternatively, the solvent may include one or more of chain carbonate, cyclic carbonate, and carboxylic acid ester. In some embodiments, the solvent may be selected from ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), Dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate Ester (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB) , one of ethyl butyrate (EB), 1,4-butyrolactone (GBL), tetrahydrofuran, sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS) and diethyl sulfone (ESE) above.

In some embodiments, other additives are optionally included in the electrolyte. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain properties of the battery, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and battery low-temperature performance. additives, etc. As an example, the additive is selected from the group consisting of unsaturated bond-containing cyclic carbonate compounds, halogen-substituted cyclic carbonate compounds, sulfate compounds, sulfite compounds, sultone compounds, disulfonic acid compounds, nitrile compounds, aromatic compounds At least one of a compound, an isocyanate compound, a phosphazene compound, a cyclic acid anhydride compound, a phosphite compound, a phosphate compound, a borate compound, and a carboxylate compound.

[Positive pole piece]

The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector. The positive electrode active material layer includes a positive electrode active material and a conductive agent.

As an example, the positive electrode current collector has two surfaces facing each other in its own thickness direction, and the positive electrode active material layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

In the lithium ion secondary battery of the present application, the positive electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil can be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming metal materials (such as aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver and silver alloys, etc.) on polymer material substrates (such as polypropylene (PP), polyterephthalene). Formed on substrates such as ethylene formate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

The positive active material layer disposed on the surface of the positive current collector includes a positive active material. The positive active material used in the present application may have any conventional positive active material used in secondary batteries. In some embodiments, the cathode active material may include one or more selected from the group consisting of lithium transition metal oxides, lithium-containing phosphates with an olivine structure, and their respective modified compounds. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide One or more of lithium nickel cobalt aluminum oxide and its modified compounds. Examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, lithium iron phosphate, composites of lithium iron phosphate and carbon, lithium manganese phosphate, composites of lithium manganese phosphate and carbon, lithium iron manganese phosphate, lithium iron manganese phosphate One or more of the composite materials with carbon and its modified compounds. These materials are commercially available. The positive active material may be coated with carbon on its surface.

The positive active material layer optionally includes a conductive agent. However, there is no specific restriction on the type of conductive agent, and those skilled in the art can select according to actual needs. As an example, the conductive agent used for the cathode material may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

The positive active material layer also includes a binder. The binder is the binder composition described above. In addition to the adhesive compositions described above, the adhesive may also include other adhesives. As examples, other binders may be styrene-butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyacrylic acid One or more of (PAA), carboxymethylcellulose (CMC), polyvinyl alcohol (PVA) and polyvinyl butyral (PVB).

In this application, the positive electrode piece can be prepared according to methods known in the art. As an example, the carbon-coated cathode active material, conductive agent and aqueous binder can be dispersed in a solvent (such as water) to form a uniform cathode slurry; the cathode slurry is coated on the cathode current collector and dried After drying, cold pressing and other processes, the positive electrode piece is obtained.

[Negative pole piece]

The negative electrode sheet includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector, where the negative electrode material layer includes a negative electrode active material.

As an example, the negative electrode current collector has two surfaces opposite in its own thickness direction, and the negative electrode material layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

In the lithium ion secondary battery of the present application, the negative electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, copper foil can be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base material. The composite current collector can be formed by forming metal materials (such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as polypropylene (PP), polyterephthalene). Formed on substrates such as ethylene formate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

In the lithium ion secondary battery of the present application, the negative electrode material layer usually contains a negative electrode active material and an optional binder, an optional conductive agent and other optional auxiliaries, and is usually formed by coating and drying the negative electrode slurry. . Negative electrode slurry coating is usually formed by dispersing the negative electrode active material and optional conductive agent and binder in a solvent and stirring evenly. The solvent can be N-methylpyrrolidone (NMP) or deionized water.

The specific type of negative electrode active material is not limited. Active materials known in the art that can be used in the negative electrode of lithium ion secondary batteries can be used, and those skilled in the art can select according to actual needs. As an example, the negative active material may be selected from one or more of graphite, soft carbon, hard carbon, mesocarbon microspheres, carbon fiber, carbon nanotubes, elemental silicon, silicon oxide compounds, silicon carbon composites, and lithium titanate. kind.

As an example, the conductive agent may be selected from one or more types of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

The negative active material layer also includes a binder. The binder is the binder composition described above. In addition to the adhesive compositions described above, the adhesive may also include other adhesives. As examples, other binders may be selected from styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA) , one or more of polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).

Other optional auxiliaries are, for example, thickeners (such as sodium carboxymethyl cellulose (CMC-Na)).

[Isolation film]

Lithium-ion secondary batteries using an electrolyte also include a separator. The isolation film is arranged between the positive electrode piece and the negative electrode piece to play the role of isolation. There is no particular restriction on the type of isolation membrane in this application. Any well-known porous structure isolation membrane with good chemical stability and mechanical stability can be used. In some embodiments, the material of the isolation membrane can be selected from at least one type selected from the group consisting of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation film can be a single-layer film or a multi-layer composite film, with no special restrictions. When the isolation film is a multi-layer composite film, the materials of each layer can be the same or different, and there is no particular limitation.

In some embodiments, the positive electrode piece, the negative electrode piece and the separator film can be made into an electrode assembly through a winding process or a lamination process.

In some embodiments, the secondary battery may include an outer packaging. The outer packaging can be used to package the above-mentioned electrode assembly and electrolyte.

In some embodiments, the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery may also be a soft bag, such as a bag-type soft bag. The material of the soft bag may be plastic. Examples of plastics include polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

This application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square or any other shape. For example, FIG. 1 shows a square-structured lithium ion secondary battery 5 as an example.

In some embodiments, referring to FIG. 2 , the outer package may include a housing 51 and a cover 53 . The housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity. The housing 51 has an opening communicating with the accommodation cavity, and the cover plate 53 can cover the opening to close the accommodation cavity. The positive electrode piece, the negative electrode piece and the isolation film can be formed into the electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is packaged in the containing cavity. The electrolyte soaks into the electrode assembly 52 . The number of electrode assemblies 52 contained in the lithium ion secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

In some embodiments, lithium-ion secondary batteries can be assembled into the battery module 4. The number of lithium-ion secondary batteries contained in the battery module 4 can be one or more. Those skilled in the art can determine the specific number according to the application of the battery module 4. and capacity to choose. In the battery module 4, a plurality of lithium ion secondary batteries 5 may be arranged in sequence along the length direction of the battery module. Of course, it can also be arranged in any other way. Furthermore, the plurality of lithium ion secondary batteries 5 can be fixed by fasteners. Optionally, the battery module 4 may further include a housing having an accommodation space in which a plurality of lithium ion secondary batteries 5 are accommodated.

In some embodiments, the above-mentioned lithium ion secondary batteries 5 or battery modules 4 can be assembled into a battery pack 1 . The number of lithium ion secondary batteries 5 or battery modules 4 contained in the battery pack 1 can be determined by those skilled in the art according to the battery pack 1 Choose your application and capacity.

3 and 4 illustrate a battery pack 1 as an example. Referring to FIGS. 3 and 4 , the battery pack 1 may include a battery box and a plurality of battery cells arranged in the battery box. The battery box includes an upper box 2 and a lower box 3. The upper box 2 can be covered with the lower box 3 and form a closed space for accommodating battery cells.

In addition, this application also provides a device, which includes the battery pack provided by this application. The battery pack can be used as a power source for the device or as an energy storage unit for the device. The device may be, but is not limited to, a mobile device (such as a mobile phone, a laptop, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, or an electric golf ball). vehicles, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc. As the device, a battery pack can be selected according to its usage requirements.

Figure 5 is an example device. The device is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, etc. In order to meet the device's requirements for high power and high energy density of lithium-ion secondary batteries, battery packs or battery modules can be used.

Example

Hereinafter, examples of the present application will be described. The embodiments described below are illustrative and are only used to explain the present application and are not to be construed as limitations of the present application. If specific techniques or conditions are not specified in the examples, the techniques or conditions described in literature in the field or product instructions will be followed. If the manufacturer of the reagents or instruments used is not indicated, they are all conventional products that can be purchased commercially. Unless otherwise indicated, all content ratios are weight ratios, and all experiments are conducted at normal temperature (25°C) and normal pressure.

The following raw materials were used:

Amylose A1: number average molecular weight is 15000g/mol, density is 1.5g/cm ³ , purchased from Sigma-Aldrich;

Amylose A2: number average molecular weight is 5000g/mol, density is 1.5g/cm ³ , purchased from Sigma-Aldrich;

Amylose A3: number average molecular weight is 2000g/mol, density is 1.5g/cm ³ , purchased from Sigma-Aldrich;

Amylose A4: number average molecular weight is 150000g/mol, density is 1.5g/cm ³ , purchased from Sigma-Aldrich;

Amylopectin B1: number average molecular weight is 350000g/mol, density is 1.6g/cm ³ , purchased from Sigma-Aldrich;

Amylopectin B2: number average molecular weight is 600000g/mol, density is 1.6g/cm ³ , purchased from Sigma-Aldrich;

Amylopectin B3: number average molecular weight is 150000g/mol, density is 1.6g/cm ³ , purchased from Sigma-Aldrich;

Amylopectin B4: number average molecular weight is 800000g/mol, density is 1.6g/cm ³ , purchased from Sigma-Aldrich;

Polyvinyl alcohol V1: weight average molecular weight is 47000g/mol, purchased from Aladdin Reagent (Shanghai) Co., Ltd.;

Polyvinyl alcohol V2: weight average molecular weight is 31000g/mol, purchased from Aladdin Reagent (Shanghai) Co., Ltd.;

Polyvinyl alcohol V3: weight average molecular weight is 107000g/mol, purchased from Aladdin Reagent (Shanghai) Co., Ltd.;

Polyvinyl alcohol V4: weight average molecular weight is 205000g/mol, purchased from Aladdin Reagent (Shanghai) Co., Ltd.

Example 1:

Take a certain amount of amylose A1 and amylopectin B1 and dry them in an oven at 80°C for 12 hours. Take out 2 parts of amylose A1 and 8 parts of amylopectin B1, add all 10 parts of starch to 30 parts of deionized water, and stir at room temperature for 30 minutes. Add 2 parts of polyvinyl alcohol V1 to the mixture, and stir at 80°C for 12 hours. Then add 0.05 part of oxalic acid, raise the temperature to 90°C and continue stirring for 2 hours. Then wait for the temperature to cool to room temperature and then test the solid content for later use.

Preparation of the negative electrode sheet: Take 94 parts of the negative active material artificial graphite, 1 part of the conductive agent carbon black, take 5 parts of the binder prepared above (5 parts refers to the actual solid amount), dissolve it in the solvent deionized water, and mix evenly Finally, the negative electrode slurry is prepared. The negative electrode slurry is evenly coated on the negative electrode current collector copper foil in multiple batches, and then dried, cold pressed, and cut to obtain negative electrode sheets. The loading capacity and compaction density of the negative electrode piece: the coating weight is 10mg/mm ² and the compaction density is 1.6g/cm ³ .

Preparation of lithium-ion batteries:

Dissolve the positive active material LiNi _0.8 Co _0.1 Mn _0.1 O ₂ (NCM811), the conductive agent acetylene black, and the binder polyvinylidene fluoride (PVDF) in the solvent N-methylpyrrolidone (at a weight ratio of 90:5:5). NMP), stir thoroughly and mix evenly to obtain the positive electrode slurry; then apply the positive electrode slurry evenly on the positive electrode current collector, and then dry, cold press, and cut to obtain a single-sided positive electrode sheet film layer weight of 350 mg /1540.25mm ² positive electrode pieces.

In an argon atmosphere glove box (H ₂ O <0.1ppm, O ₂ <0.1ppm), mix the organic solvent EC/EMC evenly according to the volume ratio of 3/7, add 12.5% LiPF ₆ lithium salt and dissolve it in the organic solvent. Stir evenly to obtain the corresponding electrolyte.

An 8μm PE porous film is used as the base, and a 2μm ceramic coating is coated on both sides as an isolation membrane.

Stack the positive electrode sheet, isolation film and negative electrode sheet prepared as above in order so that the isolation film is between the positive and negative electrode sheets to play an isolation role, then wind up to obtain a bare battery core, and weld the bare battery core The tabs are removed, and the bare battery core is put into an aluminum case, baked at 80°C to remove water, and then electrolyte is injected and sealed to obtain an uncharged battery. The uncharged battery is then sequentially subjected to processes such as standing, hot and cold pressing, formation, shaping, and capacity testing to obtain the lithium ion secondary battery product of Example 1.

Example 2-5:

Repeat Example 1, except that the weight ratio of starch to polyvinyl alcohol is as shown in Table 1 below (by adjusting the amount of polyvinyl alcohol added). In each embodiment, as described above, the corresponding negative electrode plate and the corresponding lithium ion secondary battery product are produced.

The negative electrode sheets and lithium ion secondary batteries of Examples 1-5 were tested, and the results are shown in Table 1 below.

Table 1

​	Starch to polyvinyl alcohol weight ratio	Coated appearance	Adhesion	cohesion	Expansion after 1000 cycles
Example 1	5:1	No cracks	21N/m	1.14Mpa	27%
Example 2	10:1	No cracks	23N/m	1.28Mpa	27%
Example 3	1.5:1	Intermittent small amount of cracks	5N/m	0.52Mpa	35%
Example 4	2:1	Intermittent small amount of cracks	8N/m	0.56Mpa	35%
Example 5	20:1	Intermittent small amount of cracks	13N/m	0.77Mpa	34%

Coating appearance inspection methods and standards:

Observe the appearance of the pole pieces at the end of the coating machine oven and at the winding point of the pole pieces. If the pole piece has less than 3 cracks with a length of less than 3 mm on any continuous 100-meter inner surface, it is defined as no cracks; if there are less than 5 cracks with a length of less than 5 mm and is not crack-free, it is defined as a small amount of intermittent cracks; if the length and number of cracks If it is greater than the above standards, it is defined as a large number of continuous cracks.

Pole piece adhesion test method:

Step 1: Select a steel plate with a smooth appearance, dust-free paper and alcohol, wipe the surface of the steel plate, and stick the special double-sided tape on the steel plate. The width of the tape is 20mm x length 90-150mm. The tape is parallel to the edge of the steel plate, and the tape reaches both edges of the steel plate. The distance is equal. (Note: Do not touch the adhesive side of the double-sided tape with your hands.)

Step 2: Take the pole piece to be tested, use a blade to cut out a sample with a width of 30 mm x a length of 100-160 mm, and stick the cut pole piece sample on the double-sided tape. Align the edge of the pole piece with the edge of the steel plate to ensure that the pole piece is in line with the edge of the steel plate. Double-sided tape fits smoothly.

Step 3: When the length of the steel plate is longer than the length of the pole piece, use paper tape to insert it above or below the pole, and fix it with wrinkle glue. With the test side facing up, use a 2kg pressure roller to roll it back and forth 3-4 times.

Step 4: Fold the paper tape upwards and fix the end of the steel plate that is not attached to the pole piece with the lower clamp. The upper clamp holds the paper tape parallel to the steel plate.

Step 5: Operate the tensile machine, set and read the bonding force value.

Pole piece cohesion test method:

Step 1: Apply the special double-sided tape to the steel plate. The width of the tape is 20mm x the length is 90-150mm.

Step 2: Paste the pole piece sample intercepted in step 1 on the double-sided tape with the test side facing up.

Step 3: Stick the low-viscosity green tape with a width of 20mm and a length greater than the sample length of 80-200mm flatly on the surface of the test surface, and roll it three times in the same direction with a pressure roller.

Step 4: Turn on the power of the high-speed rail tensile machine, the indicator light will be on, and adjust the limit block to the appropriate position.

Step 5: Fix the end of the steel plate that is not attached to the pole piece with the lower clamp. Fold the green glue with the hard paper upward and fix it with the upper clamp.

Step 6: Set the parameters of the tensile machine, where the tensile speed is 10mm/min and the length is >15mm.

Step 7: Read the cohesion value, repeat three times, and take the average

Method for measuring expansion after 1000 cycles:

Take the battery core after 1000 cycles of 0.33C charge and discharge test, use a spiral micrometer to measure the thickness h ₁ of the pole piece, and compare it with the thickness h ₀ of the battery core pole piece in the initial state.

The performance data of subsequent examples are the same as the above test methods.

Examples 6-12 and Comparative Examples 1-2:

Repeat Example 1, except that the weight ratio of amylose to amylopectin in the starch is as shown in Table 2 below (the total weight of starch remains unchanged). In each embodiment, as described above, the corresponding negative electrode plate and the corresponding lithium ion secondary battery product are produced.

The negative electrode plates and lithium ion secondary batteries of Examples 6-12 and Comparative Examples 1-2 were tested, and the results are summarized with the results of Example 1, as shown in Table 2 below.

Table 2

*: The pole piece has obvious cracking and powder loss.

Examples 13-15:

Repeat Example 1, except that the types of amylose in the starch are as shown in Table 3 below. In each embodiment, as described above, the corresponding negative electrode plate and the corresponding lithium ion secondary battery product are produced.

The negative electrode plates and lithium ion secondary batteries of Examples 13-15 were tested, and the results are summarized with the results of Example 1, as shown in Table 3 below.

table 3

​	Amylose type	Coated appearance	Adhesion force	cohesion	Expansion after 1000 cycles
Example 1	A1	No cracks	21N/m	1.14Mpa	27%
Example 13	A2	No cracks	15N/m	0.88Mpa	29%
Example 14	A3	Intermittent small amount of cracks	7N/m	0.55Mpa	31%
Example 15	A4	Intermittent small amount of cracks	6N/m	0.31Mpa	32%

Examples 16-18:

Repeat Example 1, except that the types of amylopectin in the starch are as shown in Table 4 below. Each embodiment is as described above, and the corresponding negative electrode plate and the corresponding lithium ion secondary battery product are produced.

The negative electrode plates and lithium ion secondary batteries of Examples 16-18 were tested, and the results are summarized with the results of Example 1, as shown in Table 4 below.

Table 4

​	Amylopectin Type	Coated appearance	Adhesion force	cohesion	Expansion after 1000 cycles
Example 1	B1	No cracks	21N/m	1.14Mpa	27%
Example 16	B2	No cracks	15N/m	0.77Mpa	30%
Example 17	B3	Persistence of numerous cracks	8N/m	0.55Mpa	38%
Example 18	B4	A small amount intermittently	5N/m	0.37Mpa	37%

Examples 19-21:

Repeat Example 1, except that the types of polyvinyl alcohol are as shown in Table 5 below. In each embodiment, as described above, the corresponding negative electrode plate and the corresponding lithium ion secondary battery product are produced.

The negative electrode plates and lithium ion secondary batteries of Examples 19-21 were tested, and the results are summarized with the results of Example 1, as shown in Table 5 below.

table 5

​	PVA type	Coated appearance	Adhesion force	cohesion	Expansion after 1000 cycles
Example 1	V1	No cracks	21N/m	1.14Mpa	27%
Example 19	V2	No cracks	17N/m	0.77Mpa	30%
Example 20	V3	Intermittent small amount of cracks	8N/m	0.55Mpa	33%
Example 21	V4	Persistence of numerous cracks	3N/m	0.12Mpa	40%

Example 22-23:

Repeat Example 1, except that the types of cross-linking agents are as shown in Table 6 below. In each embodiment, as described above, the corresponding negative electrode plate and the corresponding lithium ion secondary battery product are produced.

The negative electrode plates and lithium ion secondary batteries of Examples 22-23 were tested, and the results are summarized with the results of Example 1, as shown in Table 6 below.

Table 6

​	Cross-linking agent type	Coated appearance	Adhesion force	cohesion	Expansion after 1000 cycles
Example 1	Oxalic acid	No cracks	21N/m	1.14Mpa	27%
Example 22	Adipic acid	No cracks	10N/m	0.87Mpa	31%
Example 23	Polyvinylpyrrolidone	No cracks	8N/m	0.67Mpa	31%

Although the present application has been described with reference to the embodiments, various modifications may be made and equivalents may be substituted for components thereof without departing from the scope of the application. In particular, as long as there is no structural conflict, the technical features mentioned in the various embodiments can be combined in any way. The application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims (19)

1. A binder composition, wherein the composition contains starch and polyvinyl alcohol, and the starch contains amylose and amylopectin.
2. The binder composition according to claim 1, wherein the number average molecular weight of the amylose is 500-160000g/mol, optionally 2000-50000g/mol, optionally 5000-20000g/mol; And/or the number average molecular weight of the amylopectin is 100000-1000000g/mol, optionally 150000-800000g/mol, optionally 300000-600000g/mol.
3. The adhesive composition according to any one of claims 1 to 2, wherein the weight ratio of starch and polyvinyl alcohol in the composition is 1.5:1-20:1, optionally 2:1 to 20:1, optionally 5:1 to 10:1.
4. The binder composition according to any one of claims 1 to 3, wherein the weight ratio of amylose and amylopectin in the starch is 1:1 to 1:10, optionally 1:3 to 1:8, optionally 1:4 to 1:6.
5. The binder composition according to any one of claims 1 to 4, wherein the content of starch is 10-95% by weight, optionally 80-92% by weight, based on the binder composition of dry weight.
6. The adhesive composition according to any one of claims 1 to 5, wherein the polyvinyl alcohol has a weight average molecular weight of 15000-250000g/mol, optionally 25000-120000g/mol. Further optionally, it is 30000-80000g/mol.
7. The adhesive composition according to any one of claims 1 to 6, wherein the content of polyvinyl alcohol is 1-35% by weight, optionally 7-20% by weight, based on the adhesive Dry weight of the composition.
8. The adhesive composition according to any one of claims 1 to 7, further comprising at least one cross-linking agent selected from the group consisting of oxalic acid, polyvinylpyrrolidone, phosphorus oxychloride, trichloride and One or more of sodium metaphosphate, adipic acid, and hexametaphosphate, optionally oxalic acid.
9. The adhesive composition according to claim 8, wherein the content of the cross-linking agent is 0.01-5% by weight, optionally 0.2-1% by weight, based on the dry weight of the adhesive composition .
10. The adhesive composition according to any one of claims 1 to 9, which is an aqueous dispersion containing water as a solvent.
11. A method for preparing the adhesive composition according to any one of claims 1 to 10, comprising the following steps:

    1) Add starch to deionized water and add polyvinyl alcohol. The weight ratio of starch to polyvinyl alcohol is 1.5:1 to 20:1. The starch contains amylose in a weight ratio of 1:1 to 1:10. and amylopectin, wherein the number average molecular weight of the amylose is 500-160000g/mol, and the number average molecular weight of the amylopectin is 100000-1000000g/mol;

    2) Stir the mixture obtained in 1) at 50-99°C for 0.5-24 hours;

    3) Optionally add at least one cross-linking agent to the above mixture, and continue stirring at 10-99°C for 0.5-24 hours.
12. The method according to claim 11, wherein the temperature in step 2) is 70-95°C, and/or the stirring time is 8-15 hours.
13. The method according to claim 11 or 12, wherein the temperature in step 3) is 70-95°C, and/or the stirring time is 8-15 hours.
14. A composition for preparing battery pole sheets, which includes an electrode active material, a conductive agent and a binder composition according to any one of claims 1 to 10, and optionally water and a dispersant.
15. A battery pole piece prepared by using the binder composition according to any one of claims 1 to 10 or the composition according to claim 14.
16. The battery pole piece according to claim 15, which is a positive pole piece and/or a negative pole piece.
17. A secondary battery including the battery pole piece according to claim 15 or 16.
18. A battery pack containing the secondary battery according to claim 17.
19. An electric device including the secondary battery according to claim 17 or the battery pack according to claim 18.

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