Electrode plate and preparation method thereof, battery and electric equipment

Abstract

The invention provides an electrode plate and a preparation method thereof, a battery and electric equipment, the electrode plate comprises an electrode current collector and an electrode active material layer located on at least one side surface of the electrode current collector, the electrode active material layer comprises an electrode active material and an auxiliary agent, and the auxiliary agent comprises an acrylic ester viscosity reducer and a polysiloxane surfactant. According to the invention, the stability and flexibility of the electrode active material layer and the binding force between the electrode active material layer and the electrode current collector can be improved, and the phenomena of cracking (such as cracking and layering) of the electrode active material layer, stripping of the electrode active material layer from the surface of the electrode current collector and the like are avoided; and particularly, the problems of cracking of an electrode active material layer of a high-surface-density thick electrode plate and the like can be avoided.

Description

Technical Field

[0001] The present invention relates to the field of batteries, and in particular to an electrode sheet and a preparation method thereof, a battery and an electrical device. Background Art

[0002] Batteries are common electrochemical energy storage devices with a wide range of applications. Electrode sheets are an important component of batteries and affect the energy density and cycle performance of batteries. However, in related technologies, due to factors such as the material composition and preparation process of electrode sheets, electrode sheets generally have problems such as easy cracking of the electrode active material layer, poor flexibility, and low bonding strength between the electrode active material layer and the electrode current collector. Especially for thick electrode sheets with high surface density, problems such as cracking of the electrode active material layer are more serious, affecting the safety and cycle performance of the battery. For example, in the preparation process of electrode sheets, after the electrode slurry used to form the electrode active material layer is coated on the electrode current collector, it needs to be dried. During the drying process, as the solvent evaporates, the coating is subjected to capillary stress, which compresses the particles such as the electrode active material in the coating, thereby cracking to release the drying stress, causing the electrode active material layer formed on the surface of the electrode current collector to crack (producing cracks and delamination, etc.). Summary of the Invention

[0003] The present invention provides an electrode sheet and a preparation method thereof, a battery and an electrical device, which at least solve the problems existing in the prior art such as easy cracking of the electrode active material layer, poor flexibility, and low bonding strength between the electrode active material layer and the electrode current collector.

[0004] In one aspect of the present invention, an electrode sheet is provided, comprising an electrode current collector and an electrode active material layer located on at least one side surface of the electrode current collector, wherein the electrode active material layer comprises an electrode active material and an auxiliary agent, wherein the auxiliary agent comprises an acrylate viscosity reducer and a polysiloxane surfactant.

[0005] According to one embodiment of the present invention, the acrylic ester viscosity reducer contains an amide group.

[0006] According to one embodiment of the present invention, the acrylate viscosity reducer includes an acrylate viscosity reducer having a structure shown in Formula I-1 and / or an acrylate viscosity reducer having a structure shown in Formula I-2:

[0007]

[0008] In formula I-1, n1 is an integer greater than 0; R1 is selected from H, halogen or *-RCONH2, R is selected from an alkyl group having 4 to 10 carbon atoms; R2 is selected from H or an alkyl group having 1 to 20 carbon atoms;

[0009]

[0010] In formula I-2, n1 is an integer greater than 0; R3 and R4 are each independently selected from an alkyl group having 8 to 20 carbon atoms.

[0011] 4. The electrode sheet according to claim 3, wherein the acrylic acid ester viscosity reducer having the structure shown in Formula I-1 comprises a polyacrylate having the structure shown in Formula I-11:

[0012]

[0013] According to one embodiment of the present invention, the polyacrylate having the structure shown in Formula I-11 includes one or more of the polyacrylates shown in Formula I-111, Formula I-112, and Formula I-113:

[0014]

[0015] According to one embodiment of the present invention, the polysiloxane surfactant includes a polysiloxane having a structure shown in Formula II:

[0016]

[0017] Wherein, m is an integer greater than 0, and R5 is selected from a polyether segment or an alkyl group with 4 to 8 carbon atoms.

[0018] According to one embodiment of the present invention, the polysiloxane having a structure represented by Formula II includes one or more polysiloxanes represented by Formula II-11, Formula II-12, and Formula II-13:

[0019]

[0020] According to one embodiment of the present invention, the weight average molecular weight of the polysiloxane surfactant is 600 to 10,000; and / or the weight average molecular weight of the acrylate viscosity reducer is 10,000 to 80,000.

[0021] According to one embodiment of the present invention, the mass ratio of the acrylate viscosity reducer to the electrode active material is 0.09% to 0.23%; and / or the mass ratio of the polysiloxane surfactant to the electrode active material is 0.15% to 0.35%.

[0022] According to one embodiment of the present invention, the particle size D50 of the electrode active material is 0.3 μm to 8 μm.

[0023] According to one embodiment of the present invention, the electrode active material layer further includes a conductive agent, wherein the conductive agent includes at least two of a zero-dimensional conductive agent, a one-dimensional conductive agent and a two-dimensional conductive agent; and / or the electrode active material layer further includes a binder.

[0024] According to one embodiment of the present invention, the electrode sheet is a positive electrode sheet.

[0025] According to one embodiment of the present invention, the electrode active material includes a positive electrode active material, and the positive electrode active material includes lithium iron phosphate and / or a ternary material.

[0026] According to one embodiment of the present invention, the surface density of the electrode active material layer of the electrode sheet is 500 g / m 2 ~630g / m 2 .

[0027] Another aspect of the present invention provides a method for preparing the above-mentioned electrode sheet, comprising the following steps: placing an electrode active material layer slurry on at least one side surface of the electrode current collector to form the electrode active material layer, thereby preparing the electrode sheet; wherein the electrode active material layer slurry comprises a liquid dispersion medium, the electrode active material and the auxiliary agent.

[0028] According to one embodiment of the present invention, the solid content of the electrode active material layer slurry is 60% to 65%.

[0029] Another aspect of the present invention provides a battery, comprising the electrode sheet or the electrode sheet prepared according to the method for preparing the electrode sheet.

[0030] Another aspect of the present invention provides an electrical device comprising the battery.

[0031] The electrode sheet and its preparation method, battery and electrical equipment provided by the present invention introduce an acrylate viscosity reducer and a polysiloxane surfactant into the electrode sheet, which can increase the surface density of the electrode sheet and can also improve the stability and flexibility of the electrode active material layer and the bonding strength between the electrode active material layer and the electrode current collector, thereby avoiding the occurrence of cracking of the electrode active material layer (such as cracks and delamination) and peeling of the electrode active material layer from the surface of the electrode current collector. In particular, it can avoid the problem of cracking of the electrode active material layer in thick electrode sheets with high surface density. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Schematic diagram of the coating and drying process;

[0033] Figure 2 Schematic diagram of the connection between the electrode sample and the steel plate when testing the 180° peeling force between the positive electrode active material layer and the positive electrode current collector of the positive electrode;

[0034] Figure 3 Schematic diagram of the connection relationship between the electrode sample, steel plate and the clamp of the tensile testing machine when testing the 180° peeling force between the positive electrode active material layer and the positive electrode current collector of the positive electrode. DETAILED DESCRIPTION

[0035] In order to enable those skilled in the art to better understand the scheme of the present invention, the present invention is further described in detail below. The specific embodiments listed below are only for describing the principles and features of the present invention. The examples are only used to explain the present invention and are not intended to limit the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts are within the scope of protection of the present invention.

[0036] In related technologies, due to factors such as the material composition and preparation process of electrode sheets, electrode sheets generally have problems such as easy cracking of the electrode active material layer, poor flexibility, and low bonding strength between the electrode active material layer and the electrode current collector, which affect the safety and cycle performance of the battery.

[0037] For example, electrode sheets are typically produced by a coating method (wet process), that is, an electrode slurry used to form an electrode active material layer is coated on an electrode current collector, and then dried and rolled to produce an electrode sheet. However, cracking of the coating layer is prone to occur during the coating and drying process, especially for the preparation of thick electrode sheets with high surface density. During the drying process, as the solvent in the electrode slurry evaporates, the coating layer is subjected to stress, resulting in cracks and delamination. This is not conducive to the preparation of thick electrode sheets with high surface density and limits high loading capacity.

[0038] Specifically, the cracking process of the coating formed during the drying process of the electrode slurry is as follows: Figure 1 As shown ( Figure 1 The arrows in the figure indicate the capillary stress on the particles in the electrode slurry): (a) During drying, the particles in the electrode slurry are suspended in the solvent; (b) As drying proceeds, the solvent in the electrode slurry evaporates, and the gas-liquid interface reaches the coating surface during the drying process. The curved liquid surface of the gas-liquid interface generates capillary bending force, compressing the particles; (c) As the drying process continues, the gas-liquid interface enters the interior of the coating, and the capillary bending force increases with the evaporation of the solvent, further compressing the particles; (d) Finally, the coating cracks at the end of drying (when the drying requirements are basically met) to release the drying stress.

[0039] Although the cracking problem of the electrode active material layer can be improved to a certain extent by reducing the coating speed, lowering the drying temperature and increasing the compaction density, the improvement effect is limited, especially for thick electrode sheets with high surface density, the cracking problem of the electrode active material layer cannot be effectively solved.

[0040] In view of this, an embodiment of the present invention provides an electrode sheet, comprising an electrode current collector and an electrode active material layer located on at least one side surface of the electrode current collector, the electrode active material layer comprising an electrode active material and an additive, the additive comprising an acrylate viscosity reducer and a polysiloxane surfactant.

[0041] According to the inventors' research, by introducing acrylic acid ester viscosity reducers and polysiloxane surfactants into the electrode active material layer, these additives can serve as anti-cracking additives, which can effectively increase the surface density of the electrode sheet and avoid cracking of the electrode active material layer. At the same time, they can also improve the flexibility of the electrode sheet and increase the bonding strength (peeling force) between the electrode active material layer and the electrode current collector, thereby avoiding problems such as peeling of the electrode active material layer from the electrode current collector.

[0042] In addition, by using additives such as acrylic acid ester viscosity reducers and polysiloxane surfactants, polysiloxane surfactants reduce the surface tension of the slurry system, thereby reducing the capillary force to compress the particles; acrylic acid ester viscosity reducers increase the solid content of the slurry, that is, reduce the solvent content of the electrode slurry, and are conducive to increasing the specific gravity of the active material content per unit volume of the system. The above can avoid the problem of coating cracking during the drying process of the electrode slurry, thereby facilitating the preparation of electrode sheets and improving the preparation efficiency and yield of electrode sheets. In particular, it can solve problems such as coating cracking during the preparation of thick electrode sheets and realize the preparation of thick electrode sheets with high loads. The reason for the analysis is that during the drying process, the key indicators that affect coating cracking basically conform to the relationship shown in Formula 1:

[0043]

[0044] Among them, h max is the electrode limit cracking thickness (or critical cracking thickness). The thicker the electrode active material layer is, the easier it is for the coating to crack during the drying process of the electrode slurry. max Equivalent to the maximum electrode thickness limited to avoid coating cracking, the surface density of the electrode at this time is the electrode's limit surface density), G represents the particle shear modulus, M represents the particle coordination number (equivalent to how many particles are wrapped / stacked around a particle), Φ rcp represents the volume fraction of random close-packed particles, R represents the particle radius, and γ represents the solvent-air surface tension. rcp It is positively correlated with the solid content of the electrode slurry. Wherein, the particles are mainly electrode active material particles.

[0045] From formula 1, we can see that the electrode sheet has a critical crack thickness h max , when the electrode thickness h<the electrode limit cracking thickness h maxWhen the electrode thickness h> the electrode limit cracking thickness h, the coating does not produce cracks. max Therefore, in order to solve the problem of coating cracking, h max Increase, that is, increase h max .

[0046] In the embodiment of the present invention, by adding an acrylic ester viscosity reducer and a polysiloxane surfactant to the electrode slurry, in such an electrode slurry system, on the one hand, the viscosity of the electrode slurry can be reduced based on the viscosity reducing effect of the acrylic ester viscosity reducer, thereby achieving the addition of more electrode active materials and other components to the electrode slurry, thereby increasing the solid content of the electrode slurry (equivalent to increasing the coordination number M and particle volume fraction Φ in formula 1). rcp ), on the other hand, based on the action of polysiloxane surfactants, the surface tension of the solvent (such as NMP) phase in the electrode slurry can be reduced, thereby reducing the surface tension of the entire electrode slurry system (i.e., reducing the surface tension γ in formula 1). Combining formula 1, it can be seen that the coordination number M and the particle volume fraction Φ rcp The increase of and the decrease of surface tension γ are both beneficial to increase the critical cracking thickness h of the electrode sheet. max , thereby avoiding the coating cracking problem, especially solving the coating cracking problem of thick electrode sheets with high surface density.

[0047] Therefore, in the embodiment of the present invention, based on the synergistic effect of the acrylate viscosity reducer and the polysiloxane surfactant introduced simultaneously into the electrode active material layer, a high loading amount of the electrode sheet can be achieved, and the surface density of the electrode sheet can be increased. Specifically, the limiting surface density of the electrode sheet can be increased, and the cracking of the electrode active material layer can be suppressed. At the same time, the flexibility of the electrode sheet can be improved, and the bonding strength (peeling force) between the electrode active material layer and the electrode current collector can be increased, thereby avoiding problems such as the electrode active material layer falling off and peeling off from the electrode current collector.

[0048] Specifically, the acrylate viscosity reducer can contain one or more of a carboxyl group (-COOH), an ester group (-COOR), an amide group (-RCONH2), a halogen group, and the like, wherein the halogen group can include fluorine (F) and / or chlorine (Cl). The carboxyl group and the amide group can serve as anchoring groups to further improve the wetting effect of the acrylate viscosity reducer, thereby increasing the surface density and flexibility of the electrode sheet, as well as the bonding strength between the electrode active material layer and the electrode current collector.

[0049] Further research has shown that when the acrylic acid ester viscosity reducer contains an amide group, that is, the acrylic acid ester viscosity reducer includes an acrylic acid ester viscosity reducer containing an amide group, the use of an acrylic acid ester viscosity reducer containing an amide group is conducive to further improving the flexibility of the electrode active material layer and the bonding strength between the electrode active material layer and the electrode current collector, avoiding the occurrence of cracking of the electrode active material layer, peeling of the electrode active material layer from the surface of the electrode current collector, and especially avoiding the cracking of the electrode active material layer of thick electrode sheets with high surface density. The reason for this is that structures such as the CN bond in the amide group can interact with particles of materials such as the electrode active material to form a physical anchor in space, physically isolate the particles, inhibit particle agglomeration, further reduce the viscosity of the electrode slurry, increase the surface density of the electrode sheet, and take into account the improvement of the flexibility of the electrode sheet and the bonding strength between the electrode active material layer and the electrode current collector, thereby inhibiting problems such as cracking and peeling of the coating.

[0050] In some embodiments, the amide group in the acrylate viscosity reducer may include -CONH2, which is beneficial to further improve the surface density, flexibility, and bonding strength between the electrode active material layer and the electrode current collector of the electrode sheet, thereby avoiding cracking of the electrode active material layer, peeling of the electrode active material layer from the surface of the electrode current collector, and other phenomena, especially avoiding cracking of the electrode active material layer of thick electrode sheets with high surface density.

[0051] In some embodiments, the acrylic viscosity reducer may include polyacrylate (such as Formula I-1). When it contains an amide group, the amide group may be on the side chain of the polyacrylate (for example, the amide group may be present on R1 or R2 of Formula I-1).

[0052] Specifically, the acrylate viscosity reducer has a polymer segment, which may include an acrylic polymer segment (such as Formula I-1) and / or a polyether segment (such as Formula I-2), which is conducive to adapting to components such as polysiloxane in the electrode active material layer, and further taking into account the surface density, flexibility, and bonding strength between the electrode active material layer and the electrode current collector of the electrode sheet.

[0053] Among them, when the acrylic ester viscosity reducer contains a polyether chain segment, the chain segment acts as a solvation chain segment, and the longer polyether chain segment stretches in the system, which can prevent the particles from approaching each other, thereby improving the dispersion of the particles and improving the surface density and flexibility of the electrode sheet.

[0054] In some specific embodiments, the acrylate viscosity reducer (polyacrylate) has a structure as shown in Formula I-1 (i.e., Formula I-1 is the main structural formula of polyacrylate) and / or an acrylate viscosity reducer having a structure as shown in Formula I-2, which is beneficial to further improve the surface density, flexibility, and bonding strength between the electrode active material layer and the electrode current collector of the electrode sheet, thereby avoiding cracking of the electrode active material layer, peeling of the electrode active material layer from the surface of the electrode current collector, and other phenomena, and in particular, can avoid problems such as cracking of the electrode active material layer of thick electrode sheets with high surface density.

[0055]

[0056] In formula I-1, n1 is an integer greater than 0 (n1 represents the number of repeating units in the polyacrylate); R1 is selected from H, halogen or *-RCONH2, R is selected from an alkyl group with 4 to 10 carbon atoms, and R2 is selected from H or an alkyl group with 1 to 20 carbon atoms.

[0057] For example, when R2 is selected from an alkyl group having 1 to 20 carbon atoms, the acrylic acid ester viscosity reducer represented by Formula I-1 includes, for example, R2 being -C 18 H 37 of stearyl acrylate.

[0058] In some embodiments, in Formula I-1, R in -RCONH2 is an alkyl group with 4 to 10 carbon atoms, and the number of carbon atoms of the alkyl group is, for example, 4, 5, 6, 7 or 8, which is beneficial to further improve the surface density, flexibility and bonding strength of the electrode sheet between the electrode active material layer and the electrode current collector.

[0059]

[0060] In formula I-2, n1 is an integer greater than 0 (n1 represents the number of repeating units of the polyether segment in formula I-1, or the degree of polymerization of the polyether segment); R3 and R4 are each independently selected from an alkyl group having 8 to 20 carbon atoms, for example, an alkyl group having 8 to 18 carbon atoms.

[0061] In contrast, when Formula I-2 contains an acrylate block having 8 to 18 carbon atoms (i.e., R3 and R4 are each independently selected from an alkyl group having 8 to 18 carbon atoms), the fluidity of the electrode slurry can be improved, facilitating the preparation of the electrode sheet, and further enhancing the flexibility and other properties of the electrode sheet. For example, the alkyl group can be a stearyl group having 18 carbon atoms, but is not limited thereto.

[0062] For example, the acrylic ester adhesive having the structure represented by Formula I-1 may include a polyacrylate having the structure represented by Formula I-11 and / or a polyacrylate having the structure represented by Formula I-12.

[0063]

[0064] According to further research by the inventors, the use of polyacrylates represented by formula I-11 is more conducive to compatibility with polysiloxane surfactants. It can not only better exert the viscosity-reducing effect of the acrylic viscosity reducer on the electrode slurry and the effect of the polysiloxane surfactants on reducing the surface tension of the electrode slurry, thereby increasing the surface density of the electrode active material layer, but also improve the flexibility and other properties of the electrode active material layer containing these two types of additives. Therefore, when the acrylic viscosity reducer includes the polyacrylate represented by formula I-11, it is conducive to further taking into account the improvement of the surface density, flexibility and bonding strength of the electrode active material layer and the electrode current collector of the electrode sheet, thereby avoiding problems such as cracking of the electrode active material layer of thick electrode sheets with high surface density.

[0065] In some specific embodiments, the polyacrylate having the structure shown in Formula I-11 includes one or more of the polyacrylates shown in Formula I-111, Formula I-112, and Formula I-113:

[0066]

[0067]

[0068] Generally, the weight-average molecular weight of the acrylate viscosity reducer is not greater than 100,000. In some embodiments, the weight-average molecular weight of the acrylate viscosity reducer can be 10,000 to 80,000, for example, 10,000, 15,000, 18,000, 20,000, 21,000, 24,000, 26,000, 28,000, 30,000, 40,000, 50,000, 60,000, 70,000, 80,000 or a range consisting of any two of them. This is beneficial for better exerting the viscosity reduction effect of the acrylate viscosity reducer in the composition system of the electrode active material layer in which the acrylate viscosity reducer and the polysiloxane surfactant coexist, further taking into account the improvement of the surface density, flexibility and bonding strength of the electrode active material layer and the electrode current collector of the electrode sheet, and avoiding problems such as cracking of the electrode active material layer of a thick electrode sheet with high surface density.

[0069] In the embodiment of the present invention, an acrylic ester viscosity reducer (such as polyacrylate) having a preset structural formula (such as the above structural formula 1) and characteristics such as a weight-average molecular weight can be obtained by conventional methods in the art, for example, commercially available or homemade by conventional methods in the art. When making the acrylic ester viscosity reducer, its molecular weight and other characteristics can be regulated by conventional methods, and there is no particular limitation on this. For example, acrylic esters can be prepared by the preparation process of conventional homopolymer acrylic esters, using corresponding monomers to polymerize to form acrylic esters of a preset structure (after polymerization of the monomers, repeating units in the acrylic ester are formed), and the monomers are generally polymerized under the action of an initiator, and the initiator includes, for example, azobisisobutyronitrile, etc. In specific operations, the monomers can be pre-treated by removing alcohol and deoxygenating as needed, and then the initiator is added, and the temperature is regulated to the polymerization initiation temperature, so that the monomers undergo polymerization in the presence of the initiator. After the polymerization reaction is completed, the reaction can be terminated by adding a terminator to the reaction system, and the acrylic ester viscosity reducer is isolated.

[0070] In some embodiments, the mass ratio of the acrylate viscosity reducer to the electrode active material (main material) can be 0.09% to 0.23%, for example, 0.09%, 0.1%, 0.13%, 0.15%, 0.18%, 0.2%, 0.23% or a range consisting of any two of them. The mass ratio of the acrylate viscosity reducer to the electrode active material is not less than 0.09%, which can better play the role of the acrylate viscosity reducer in reducing the viscosity of the electrode slurry. At the same time, the mass ratio of the acrylate viscosity reducer to the electrode active material is not higher than 0.23%, which can maintain a smaller amount of high molecular components in the electrode slurry, improve the stability of the electrode slurry, and further take into account the improvement of the surface density, flexibility of the electrode sheet, and the bonding strength between the electrode active material layer and the electrode current collector.

[0071] In addition, the polysiloxane surfactant can be a polysiloxane having a structure shown in Formula 2 below (i.e., Formula 2 is the main structural formula of the polysiloxane surfactant), which is beneficial to further improve the surface density and flexibility of the electrode active material layer and the bonding force between the electrode active material layer and the electrode current collector, thereby avoiding the occurrence of cracking of the electrode active material layer, peeling of the electrode active material layer from the surface of the electrode current collector, and especially avoiding the problem of cracking of the electrode active material layer of thick electrode sheets with high surface density.

[0072]

[0073] Wherein, m is an integer greater than 0 (m represents the number of repeating units in the polysiloxane surfactant), R5 is selected from a polyether segment or an alkyl group with 4 to 8 carbon atoms, and the number of carbon atoms of the alkyl group is, for example, 4, 5, 6, 7 or 8.

[0074] Relatively speaking, when R5 in Formula II is selected from an alkyl group, especially an alkyl group with 4 to 8 carbon atoms, in the coexistence system of an acrylate viscosity reducer and the polysiloxane represented by Formula II, it is more conducive to the polysiloxane represented by Formula II to play the role of reducing the surface tension of the electrode slurry system, and further take into account the improvement of the surface density, flexibility and bonding strength of the electrode active material layer and the electrode current collector of the electrode sheet.

[0075] In the embodiment of the present invention, the alkyl group may be a straight-chain alkyl group.

[0076] In some embodiments, the polysiloxane represented by Formula II includes one or more of the polysiloxanes represented by Formula II-11, Formula II-12, and Formula II-13:

[0077]

[0078] In addition, when R5 is a polyether segment, the polysiloxane represented by Formula II is a polyether siloxane (or polyether silicone). The polyether segment may include an ethylene oxide unit (such as the ethylene oxide polymer segment in Formula II-1). ) and / or propylene oxide units (such as the propylene oxide polymer segment in formula II-1 In general, propylene oxide units are hydrophobic units and ethylene oxide units are hydrophilic units. Therefore, the degree of polymerization of propylene oxide units is greater than that of ethylene oxide (for example, x>y in Formula II-1), which is more conducive to the use of polyether silicones in oil phase systems, such as in positive electrode slurries (positive electrode slurries use organic solvents such as NMP and belong to oil phase systems).

[0079] For example, the polyether siloxane may have a structure as shown in the following formula II-2:

[0080]

[0081] In some embodiments, the weight average molecular weight of the polysiloxane surfactant can be 600 to 10,000, for example, 600, 1,000, 2,000, 2,500, 3,000, 3,500, 4,000, 4,500, 5,000, 6,000, 7,000, 8,000, 9,000, 10,000, or any two thereof.

[0082] In an embodiment of the present invention, a polysiloxane having a preset structural formula (such as the above structural formula 2) and a weight-average molecular weight can be obtained as a surfactant by conventional methods in the art, for example, commercially available or homemade by conventional methods in the art. When the polysiloxane is homemade, its molecular weight and other characteristics can be regulated by conventional methods, without particular limitation. For example, the polysiloxane can be prepared by a conventional silanol condensation method. During the specific operation, the silanol raw material and the solvent can be mixed to form a solution, and then a condensation reaction is carried out, wherein the condensation reaction can be in the presence of a catalyst, and the catalyst includes, for example, alkyl tin dilaurate, and the corresponding alkyl tin dilaurate can be selected according to different alkyl chain structures in combination with actual needs.

[0083] In some embodiments, the mass ratio of the polysiloxane surfactant to the electrode active material is 0.15% to 0.35%, for example, 0.15%, 0.18%, 0.2%, 0.23%, 0.25%, 0.28%, 0.3%, 0.33%, 0.35% or a range consisting of any two of them. In this way, the mass ratio of the polysiloxane surfactant to the electrode active material is not less than 0.15%, which can better play the role of the polysiloxane surfactant in reducing the surface tension of the solvent phase in the electrode slurry, thereby further reducing the surface tension of the entire electrode slurry system. At the same time, the mass ratio of the polysiloxane surfactant to the electrode active material is not higher than 0.35%, which can maintain a smaller amount of high molecular components in the electrode slurry, thereby further reducing the viscosity growth rate of the electrode slurry, improving the stability of the electrode slurry, being more conducive to the preparation of the electrode sheet, and further improving the performance of the electrode sheet.

[0084] In some embodiments, in the electrode active material layer, the mass ratio of the auxiliary agent to the electrode active material can be 0.18% to 0.45%, for example, 0.18%, 0.2%, 0.23%, 0.25%, 0.28%, 0.3%, 0.33%, 0.35%, 0.38%, 0.4%, 0.43%, 0.45% or a range consisting of any two of them.

[0085] In an embodiment of the present invention, the above-mentioned electrode sheet can be a positive electrode sheet, and accordingly, the above-mentioned electrode active material layer (electrode active material layer) is a positive electrode coating (positive electrode active material layer), wherein the electrode active material includes a positive electrode active material, and the electrode current collector is a positive electrode current collector.

[0086] The embodiment of the present invention may adopt a conventional positive electrode current collector in the art, for example, the positive electrode current collector includes aluminum foil.

[0087] In the related art, the positive electrode system generally has the problem of easy cracking of the coating. For example, in the preparation process of the positive electrode sheet, after the electrode slurry (positive electrode slurry) is applied to the surface of the positive electrode current collector, in the subsequent drying process, as the solvent (such as NMP) evaporates, the formed coating is prone to cracking and delamination. Especially for positive electrode sheets with high surface density, problems such as coating cracking are more likely to occur. In the implementation of the present invention, by introducing acrylate viscosity reducers and polysiloxane surfactants into the positive electrode coating, the cracking phenomenon of the positive electrode coating can be effectively avoided. At the same time, the flexibility of the electrode sheet can be improved, and the bonding strength (peeling strength) between the positive electrode coating and the positive electrode current collector can be improved, thereby avoiding problems such as peeling of the positive electrode coating from the positive electrode current collector. Therefore, the embodiment of the present invention can achieve a high load of the positive electrode sheet, increase the surface density of the positive electrode sheet, and at the same time take into account the improvement of the flexibility of the positive electrode sheet and the bonding strength between the positive electrode coating and the positive electrode current collector, and the suppression of cracking of the positive electrode coating.

[0088] In some embodiments, the positive electrode active material may include lithium iron phosphate (LFP) and / or a positive electrode ternary material, and the positive electrode ternary material may include, for example, a nickel-cobalt-manganese ternary material.

[0089] Generally, the particle size of the electrode active material is nanometer-scale. For example, when the electrode sheet is a positive electrode sheet, the electrode active material may include nano-lithium iron phosphate.

[0090] According to further research by the inventors, the particle size D50 of the electrode active material can be 0.3μm to 8μm, for example, 0.3μm, 0.6μm, 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm or a range consisting of any two of them, which is beneficial to further suppress problems such as cracking of the electrode active material layer. The reason for this is that by controlling the electrode activity within the above-mentioned range, it is beneficial to construct a strong shear modulus of the system, that is, to construct a system with sufficient cohesion to resist cracking stress. Thus, the shear modulus of the electrode slurry system used to form the electrode active material layer can be improved. At the same time, the above-mentioned acrylic acid viscosity reducer and polysiloxane surfactant are introduced to reduce the surface tension of the electrode slurry and increase the solid content of the electrode slurry, which can avoid the problem of coating cracking during the drying process after the electrode slurry is coated on the surface of the electrode current collector.

[0091] Generally, the electrode active material layer also includes a conductive agent. In some embodiments, the conductive agent may include at least two of a zero-dimensional conductive agent, a one-dimensional conductive agent, and a two-dimensional conductive agent, which is conducive to building a good conductive network in the electrode active material layer. At the same time, combined with components such as acrylic acid viscosity reducers and polysiloxane surfactants, the flexibility of the electrode sheet is improved to avoid cracking problems in the electrode active material layer.

[0092] In some embodiments, the particle size D50 of the zero-dimensional conductive agent can be 10 nm to 100 nm, for example, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, or a range consisting of any two thereof.

[0093] In some embodiments, the diameter of the one-dimensional conductive agent may be in the range of 1 nm to 50 nm, for example, 1 nm, 5 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, or any two thereof.

[0094] In some embodiments, the zero-dimensional conductive agent may include conductive carbon black.

[0095] In some embodiments, the one-dimensional conductive agent may include carbon nanotubes.

[0096] In some embodiments, the two-dimensional conductive agent may include graphene.

[0097] In some embodiments, the conductive agent in the electrode active material layer includes a zero-dimensional conductive agent (such as conductive carbon black) and a one-dimensional conductive agent (such as carbon nanotubes), and the mass ratio of the zero-dimensional conductive agent to the one-dimensional conductive agent is 1:(1.5~4), for example, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4 or a range consisting of any two of them.

[0098] In some embodiments, the mass ratio of the conductive agent to the electrode active material (i.e., the ratio of the total mass of the conductive agent in the electrode active material layer (the sum of the masses of all conductive agents) to the mass of the electrode active material) can be 0.9% to 1.7%, for example, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5% or a range composed of any two of them, which is beneficial to improve the conductivity of the electrode active material layer. At the same time, combined with components such as acrylic acid viscosity reducers and polysiloxane surfactants, the flexibility of the electrode sheet is improved to avoid cracking problems in the electrode active material layer.

[0099] In addition, the electrode active material layer may further include a binder, which can further improve the bonding between the components in the electrode active material layer and the bonding between the electrode active material layer and the electrode current collector.

[0100] In an embodiment of the present invention, the binder in the electrode sheet can be a conventional binder material in the art, for example, polyvinylidene fluoride (PVDF) and / or modified PVDF, wherein the modified PVDF includes, for example, a highly flexible PVDF material and / or a cationic surfactant-modified PVDF material. For example, a cationic surfactant-modified PVDF material is obtained by modifying PVDF with a cationic surfactant, which can impart properties such as low surface tension and high dispersion uniformity to PVDF. The modified PVDF material can specifically contain groups such as carbonyl (C=O) and amino (NH), which can impart properties such as higher toughness and lower elastic modulus to the PVDF bulk material.

[0101] In the positive electrode sheet, the conductive agent may include one or more of carbon black, carbon nanotubes (CNTs), acetylene black, graphene, Ketjen black, and carbon fiber; the binder may include one or more of polyvinylidene fluoride (PVDF), polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, etc.

[0102] The embodiment of the present invention may adopt a conventional positive electrode current collector in the art, for example, the positive electrode current collector includes aluminum foil.

[0103] In some embodiments, the mass ratio of the binder to the electrode active material can be 2.5% to 4.5%, for example, 3%, 3.3%, 3.5%, 3.8%, 4% or a range composed of any two of them, which is beneficial to improve the adhesion between the components in the electrode active material layer, and the bonding force between the electrode active material layer and the electrode current collector. At the same time, combined with components such as acrylate viscosity reducers and polysiloxane surfactants, the flexibility of the electrode sheet is improved, and the cracking problem of the electrode active material layer is avoided, especially the cracking problem of the coating of thick electrode sheets with high surface density can be avoided.

[0104] According to the inventors' research and analysis, by introducing acrylic ester viscosity reducers and polysiloxane surfactants into the electrode active material layer, the cracking problem of the electrode active material layer can be avoided, especially the cracking problem of the coating of thick electrode sheets with high surface density can be avoided, thereby achieving a high load of the electrode sheet. In addition, under such an electrode active material layer system, the content of the conductive agent and binder in the electrode active material layer is positively correlated with the critical cracking surface density of the electrode sheet. The following takes conductive carbon black and carbon nanotubes as examples, and prepares electrode sheets according to the coating method for exemplary explanation: For example, in the electrode active material layer, the mass ratio of the binder to the electrode active material is about 2.7% to 3.4%, and the mass ratio of the conductive agent to the electrode active material is about 0.9% to 1.2%. The critical cracking surface density of the electrode sheet can generally be 500g / m 2~530g / m 2 The mass ratio of the binder to the electrode active material is about 2.7% to 3.4%, the mass ratio of the conductive agent to the electrode active material is about 1.35% to 1.7%, and the critical cracking surface density of the electrode sheet can generally be 530g / m 2 ~540g / m 2 The mass ratio of the binder to the electrode active material is about 3.1% to 3.9%, the mass ratio of the conductive agent to the electrode active material is about 0.9% to 1.2%, and the critical cracking surface density of the electrode sheet can generally be 540g / m 2 ~570g / m 2 The mass ratio of the binder to the electrode active material is about 3.1% to 3.9%, the mass ratio of the conductive agent to the electrode active material is about 1.35% to 1.7%, and the critical cracking surface density of the electrode sheet can generally be 570g / m 2 ~590g / m 2 The mass ratio of the binder to the electrode active material is about 3.6% to 4.5%, the mass ratio of the conductive agent to the electrode active material is about 0.9% to 1.2%, and the critical cracking surface density of the electrode sheet can generally be 590g / m 2 ~610g / m 2 The mass ratio of the binder to the electrode active material is about 3.6% to 4.5%, the mass ratio of the conductive agent to the electrode active material is about 1.35% to 1.7%, and the critical cracking surface density of the electrode sheet can generally be 620g / m 2 ~630g / m 2 The positive correlation between the content of the conductive agent and binder in the electrode active material layer and the critical cracking surface density of the electrode sheet can be specifically expressed as:

[0105]

[0106] Wherein, ρ(x,y) represents the critical cracking surface density of the electrode sheet, A represents the amount (mass) of the electrode active material added to the electrode active material layer, x represents the factor of the amount of binder added to the electrode active material layer, 0≤x≤2, and x is, for example, 0, 1, or 2; y represents the factor of the amount of conductive agent added to the electrode active material layer, 0≤y≤1, and y is, for example, 0 or 1.

[0107] In the embodiment of the present invention, the surface density of the electrode active material layer of the electrode sheet can be 500g / m 2 ~630g / m 2 , for example 500g / m 2 , 530g / m 2 , 550g / m 2 , 580g / m 2 , 600g / m 2, 610g / m 2 , 620g / m 2 、630g / m 2 or any two thereof, especially up to 600g / m 2 ~620g / m 2 .

[0108] In the embodiment of the present invention, an electrode active material layer may be provided on one surface of the electrode current collector, or an electrode active material layer may be provided on two opposite surfaces (front and back) of the electrode current collector.

[0109] In an embodiment of the present invention, the electrode active material layer of the electrode sheet is formed by a slurry composition (or electrode active material layer slurry), which includes a liquid dispersion medium (or solvent), the electrode active material and the auxiliary agent.

[0110] Specifically, the slurry composition can be used as an electrode slurry, which is coated on the surface of the electrode current collector and then dried (baked) to form an electrode active material layer to prepare an electrode sheet. As mentioned above, by introducing an acrylate viscosity reducer and a polysiloxane surfactant into the electrode slurry, the problem of coating cracking during the drying process of the electrode slurry can be avoided. In particular, the problem of coating cracking during the preparation of thick electrode sheets can be solved, thereby realizing the preparation of thick electrode sheets with high loading capacity. For example, when preparing a surface density of up to 600 g / cm 2 ~620g / cm 2 When thick electrode sheets are used, coating cracking is not likely to occur.

[0111] In some embodiments, in the slurry composition, the liquid dispersion medium (solvent) may include an organic solvent, specifically N-methylpyrrolidone (NMP).

[0112] In some embodiments, the solid content of the slurry composition may be 60% to 65%, for example, 60%, 61%, 62%, 63%, 64%, 65%, or any two thereof.

[0113] The solid content of the slurry composition is substantially equal to the ratio of the sum of the masses of the other components in the slurry composition except the solvent to the total mass of the slurry composition.

[0114] Specifically, the slurry composition is a mixture of a solid component and a liquid component (i.e., a solvent). The solid component is other components other than the solvent, such as electrode active materials, acrylate viscosity reducers, polysiloxane surfactants, binders and conductive agents, etc., which are used to form an electrode active material layer. The solid content of the slurry composition is the ratio of the mass of the solid component to the total mass of the solid component and the liquid component (i.e., the mass of the slurry composition).

[0115] In a specific implementation, the preparation process of the slurry composition may include the following steps S1 to S4.

[0116] S1. Evenly mix the binder and the solvent to obtain a glue solution.

[0117] The solid content of the glue solution may be 5% to 10%, for example, 5%, 6%, 7%, 8%, 9%, 10% or any two thereof.

[0118] S2. Mix the glue solution and the conductive agent to obtain a mixed liquid.

[0119] The adhesive solution may be first defoamed and then evenly mixed with the conductive agent to obtain a mixed liquid. For example, the defoaming treatment may be performed by stirring at a low speed of 100 to 200 rpm for 1 to 2 hours. The dew point of the environment may be controlled to be ≤-14°C during the defoaming treatment.

[0120] S3. Adding electrode active materials into the mixed liquid.

[0121] The electrode active material can be added to the mixed liquid in batches, for example, in two or more batches, with the amount added each time being substantially the same. After the electrode active material is added to the mixed liquid, the mixed liquid is stirred evenly at a stirring speed of 700-800 rpm. During each addition of the electrode active material, the stirring time can be 1-1.5 hours, followed by the addition of the next batch of electrode active material, and so on.

[0122] S4. After all the electrode active materials are added to the mixed liquid, the above-mentioned auxiliary agents (acrylate viscosity reducer and polysiloxane surfactant) are added thereto to obtain a slurry composition.

[0123] During the process of adding the auxiliary agent, the stirring speed is maintained at 700 rpm to 800 rpm, and the stirring time can be 0.5 h to 1 h to obtain the slurry composition.

[0124] An embodiment of the present invention also provides a method for preparing the above-mentioned electrode sheet, comprising the following steps: placing an electrode active material layer slurry (electrode slurry) on at least one side surface of an electrode current collector to form an electrode active material layer to obtain an electrode sheet; wherein the electrode active material layer slurry comprises a liquid dispersion medium, the electrode active material and the auxiliary agent, that is, the electrode active material layer slurry is the above-mentioned slurry composition.

[0125] In the embodiment of the present invention, the electrode active material layer slurry can be coated on the surface of the electrode current collector by conventional methods in the art. Specifically, the slurry composition can be evenly coated on the surface of the electrode current collector using conventional coating equipment in the art, such as a rubber roller or a cloth roller. For example, a doctor blade can be used for coating, and the gap between the doctor blade and the coating interface is, for example, 250 to 400 μm (e.g., 250 μm, 300 μm, or 400 μm). In specific implementation, a doctor blade of appropriate size can be selected based on the preset surface density.

[0126] In the process of preparing the electrode sheet, after the electrode active material layer slurry is coated on the surface of the electrode current collector, it can be dried first and then subjected to processes such as roll pressing to obtain the electrode sheet.

[0127] Among them, rolling refers to applying pressure to the electrode active material layer to compact it to a preset thickness. The rolling process basically does not affect the surface density of the electrode active material layer of the electrode sheet (that is, the mass of the substance contained per unit area). That is, after the electrode active material layer slurry is coated on the surface of the electrode current collector and dried, the surface density of the coating formed is measured to be basically equal to the surface density of the electrode active material layer of the electrode sheet obtained after rolling.

[0128] In the embodiments of the present invention, unless otherwise specified, the drying, rolling, and other processes involved in the preparation of the electrode sheet are conventional operations in the art and are not particularly limited. For example, after the electrode active material layer slurry is coated on the surface of the electrode current collector, it can be dried (baked) in a drying device such as an oven or a forced air drying oven, and the drying temperature can be 80°C to 90°C.

[0129] In a specific implementation, after drying is completed, the surface morphology of the formed electrode active material layer (e.g., whether cracking of the coating occurs) can be observed using a microscope (e.g., an optical microscope); after rolling is completed, the surface morphology of the electrode active material layer (e.g., whether cracking of the coating occurs) can be further observed using a microscope (e.g., an optical microscope). In the embodiments of the present invention, by using an acrylate viscosity reducer and a polysiloxane surfactant, the flexibility of the prepared electrode sheet and the bonding strength between the electrode sheet and the electrode current collector can be improved, effectively solving the problem of coating cracking.

[0130] An embodiment of the present invention further provides a battery, comprising the above-mentioned electrode sheet or an electrode sheet manufactured according to the above-mentioned method for manufacturing the electrode sheet. The battery has corresponding advantages to the above-mentioned electrode sheet, which will not be described in detail.

[0131] Generally speaking, a battery includes an electrolyte, a battery cell, and a shell that encapsulates the battery cell. The electrolyte is injected into the battery cell in the shell. The battery cell includes a positive electrode sheet, a negative electrode sheet, and a separator located between the positive electrode sheet and the negative electrode sheet.

[0132] Specifically, the electrode sheet (the electrode active material layer contains an acrylate viscosity reducer and a polysiloxane surfactant) may be a positive electrode sheet.

[0133] In some embodiments, the negative electrode sheet may include a negative electrode current collector and a negative electrode coating located on at least one side surface of the negative electrode current collector. Specifically, the negative electrode coating may be provided on one side surface of the negative electrode current collector, or the negative electrode coating may be provided on both sides of the negative electrode current collector in the thickness direction.

[0134] Specifically, the negative electrode coating (negative electrode active material layer) may include a negative electrode active material, a conductive agent and a binder, all of which may be conventional materials in the art. For example, the negative electrode active material may include graphite, the conductive agent may include one or more of conductive carbon black, carbon nanotubes (CNTs), acetylene black, graphene, Ketjen black, and carbon fibers; the binder may include one or more of sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate.

[0135] The embodiment of the present invention may use a conventional negative electrode current collector in the art, for example, the negative electrode current collector includes copper foil.

[0136] In an embodiment of the present invention, the negative electrode sheet can be prepared by conventional methods in the art, for example, by a coating method. Specifically, the components used to form the negative electrode coating, such as the negative electrode active material, the conductive agent, and the binder, can be dispersed in a solvent, such as water, to prepare a negative electrode slurry, which is then coated on the surface of the negative electrode current collector. After drying, rolling, and other processes, the negative electrode sheet is obtained.

[0137] The electrolyte of the embodiment of the present invention can be a conventional electrolyte in the field. For example, the electrolyte is a non-aqueous electrolyte, which may specifically include an organic solvent, an additive and an electrolyte salt. The organic solvent includes, for example, one or more of ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), vinylene carbonate (VC) and propylene carbonate (PC). The electrolyte salt may include a lithium salt, and the lithium salt includes, for example, lithium hexafluorophosphate (LiPF6), etc., but is not limited thereto.

[0138] In the embodiment of the present invention, the separator is used to separate the positive electrode sheet and the negative electrode sheet to prevent the positive electrode sheet and the negative electrode sheet from short-circuiting. The embodiment of the present invention can adopt conventional separators in the art without special limitation.

[0139] In the embodiment of the present invention, conventional shell materials in the art may be used to encapsulate the battery cell. The shell may include, for example, a soft packaging material such as an aluminum-plastic film, but is not limited thereto.

[0140] In the embodiment of the present invention, components such as positive electrode sheets, separators and negative electrode sheets can be assembled into a battery by conventional methods in the field. For example, the positive electrode sheets, separators and negative electrode sheets can be stacked in an alternating manner to produce a laminated battery cell, or the positive electrode sheets, separators and negative electrode sheets can be stacked in sequence and then wound to form a wound battery cell; the battery cell is then placed in a shell (outer packaging), and after conventional processes such as liquid injection (i.e., injecting electrolyte) and packaging, a battery is produced.

[0141] Generally, the above-mentioned battery can be used as a single cell; alternatively, the above-mentioned battery can also be a battery pack formed by connecting multiple single cells, each of which is independently a single cell assembled from components such as a positive electrode sheet, a separator and a negative electrode sheet, wherein these single cells can be electrically connected by conventional methods in the art, such as series connection, parallel connection, or a mixture of these connection methods, etc., without any special restrictions.

[0142] An embodiment of the present invention further provides an electrical device, comprising the above-mentioned battery or the above-mentioned battery pack. The electrical device has advantages corresponding to those of the above-mentioned electrode sheet, which will not be described in detail.

[0143] The electrical equipment in the embodiments of the present invention can be conventional electrical equipment in this field, such as power equipment (such as electric vehicles, electric cars), electronic equipment (such as mobile phones, tablets, laptops, digital cameras, etc.), wearable devices (such as watches, bracelets, VR glasses, etc.), energy storage power stations, etc., without special restrictions.

[0144] In an embodiment of the present invention, materials such as acrylate viscosity reducers and polysiloxane surfactants and their contents in the electrode active material layer can be detected by Fourier transform infrared spectroscopy (infrared analysis), nuclear magnetic resonance analysis, thermogravimetric analysis, and organic element analysis. For example, in the electrode active material layer, organic materials such as acrylate viscosity reducers, polysiloxane surfactants, and binders have different decomposition temperatures, and their contents can be detected by thermogravimetric analysis. At the same time, these organic materials contain different groups, which can be qualitatively characterized by infrared analysis (for example, detecting characteristic peaks of each group, such as detecting whether amide groups are contained in acrylate viscosity reducers), and combined with nuclear magnetic resonance analysis to determine the chemical shifts of elements such as hydrogen, the structure and other characteristics of each organic material can be determined.

[0145] In specific implementation, after obtaining the electrode sheet, the electrode active material layer can be scraped off from the electrode current collector (specifically, the front, middle and rear three regions in the length direction of the electrode sheet can be selected, and the electrode active material layer materials of these three regions can be scraped off respectively), and the scraped electrode active material layer materials are evenly dispersed in a solvent, and the solvent used is, for example, NMP. The solvent is then removed by centrifugal separation or the like, and dried (for example, dried at 100°C±5°C) to remove the solvent to obtain a solid powder; then the electrode active material and other particulate components in the solid powder are removed by solvent washing or the like to obtain an organic material (the organic material mainly includes acrylate viscosity reducers, polysiloxane surfactants and binders), and then the above-mentioned thermogravimetric analysis, infrared analysis and nuclear magnetic resonance analysis and other tests are performed to measure the structure and other characteristics of materials such as acrylate viscosity reducers and polysiloxane surfactants.

[0146] In the embodiment of the present invention, the weight average molecular weight of materials such as acrylate viscosity reducer, polysiloxane surfactant can be measured by conventional methods in this area, for example, the above-mentioned materials involved are tested by gel permeation chromatography equipment (i.e. GPC), according to different sample systems, different GPC solvent systems and test conditions can be selected, for example, for acrylate viscosity reducer, DMF (N, N-dimethylformamide) is used as GPC solvent system, and for polyether silicone surfactant, DMSO (dimethyl sulfoxide) is used as solvent phase. For sample demand, 5-10ml of liquid sample is selected. Before GPC sample delivery, it is necessary to confirm the solubility of the sample in the above-mentioned mobile phase. The general sample dissolution time is 4-6h. For insoluble samples, 12-24h is required. During the dissolution process, violent oscillation cannot be performed to avoid the interruption of polymer chains. The sample after dissolution ensures that the filter head is not blocked. Secondly, after the sample is dissolved, the above-mentioned organic phase sample needs to pass through a 0.45μm filter membrane. The sample concentration is generally controlled at 2-5mg / mL. The higher the sample molecular weight, the lower the concentration. Conversely, the lower the sample molecular weight, the higher the concentration.

[0147] In an embodiment of the present invention, the particle size D50 of the material (such as the particle size D50 of the electrode active material) refers to the particle size corresponding to when the volume of the material is 50% of the total volume measured from the small particle size on the particle size distribution curve of the material, that is, the particle size D50 of the material refers to the particle size corresponding to when the volume is accumulated to 50% from the small particle size in the particle size distribution of the material.

[0148] In an embodiment of the present invention, after obtaining the electrode sheet, when testing the particle size of the electrode active material, the coating can be scraped off the electrode sheet, and then a solid particle product (mainly the electrode active material) can be obtained by solvent washing or the like, and then the particle size D50 of the electrode active material can be measured using a conventional particle size testing instrument in the field such as a laser particle size analyzer.

[0149] In an embodiment of the present invention, the testing process of the electrode active material layer density (double-sided surface density) of the electrode sheet may include: taking an electrode sheet sample, testing the mass m1 of the electrode sheet sample (specifically, the electrode sheet sample can be placed on an analytical balance to measure its mass m1), and using conventional instruments or tools to test the single-sided surface area S of the electrode sheet sample in the thickness direction (or calculating the surface area S of the electrode sheet sample based on the dimensional characteristics such as the diameter of the electrode sheet sample); then removing the electrode active material layer on the positive electrode sheet sample (for example, scraping or washing off the electrode active material layer with a solvent), and testing the obtained mass m2 of the electrode current collector, then the electrode active material layer density of the electrode sheet = (m1-m2) / S.

[0150] The present invention is further described below through specific examples.

[0151] In the following examples, the positive electrode sheets prepared in each example and comparative example were subjected to a 180° peel strength test (i.e., the 180° peel strength of the positive electrode coating and the positive electrode current collector (aluminum foil) of the positive electrode sheet was measured) and a flexibility test according to the following process:

[0152] (1) 180° peel strength test

[0153] 1. Based on the beam bending theory of elastic substrates, the peeling force is decomposed into the splitting stress σ and shear stress λ at the peeling separation position. When λ < σ, a simplified expression for the peel strength can be obtained. According to the formula, a peeling angle of 180° is substituted to obtain the peel strength value. The equipment used is a universal material testing machine, and the specific operation is as follows:

[0154] 1. Cut the electrode, take the positive electrode, and use a customized knife die to cut the positive electrode into electrode samples with a length of 400mm and a width of 10-50mm;

[0155] 2. Paste and fix the electrode: Take a flat thin steel plate (about 200-300mm in length and 40-60mm in width); first stick a double-sided tape in the center of the steel plate. The length should be greater than the test length of the electrode sample and the same width as the electrode sample. The specific diagram is as follows Figure 2 As shown; smooth it with force to ensure that the double-sided tape is tightly attached to the center of the steel plate; bend the electrode sample into two parts, namely the first part and the second part; attach the second part of the electrode sample to the surface of the double-sided tape facing away from the steel plate, and untie the double-sided tape at the end (so that a gap is formed between the end of the electrode sample (the end where the first part and the second part are connected) and the double-sided tape), attach the second part of the electrode sample to the double-sided tape, and ensure that the electrode and the double-sided tape are matched and attached;

[0156] 3. If Figure 3As shown, there are two clamps (upper clamp and lower clamp) on the tensile testing machine. Insert the steel plate with the fixed electrode sample into the lower clamp and fix it vertically; insert the unadhesive electrode (first part) into the upper clamp and fix it so that the electrode (second part) attached to the double-sided tape is 180° from the electrode (first part) fixed by the upper clamp; after fixing the sample, set the relevant tensile speed to 10m / min and start the tensile test to measure the 180° peeling force of the positive electrode coating of the positive electrode sheet and the positive electrode current collector (aluminum foil).

[0157] (2) Flexibility test

[0158] The flexibility of the positive electrode was tested by referring to the method for testing the flexibility of the lithium-ion battery electrode in the patent document of application number 201510967513.4 (see the patent document of application number 201510967513.4). Figure 1 、 Figure 2 a and Figure 2 b), the test process is briefly described as follows:

[0159] A test strip of a certain area is cut from the lithium-ion battery electrode (positive electrode) to be tested; the metal foil (aluminum foil) side of the test strip is affixed to a section of test tape (a positive electrode coating is formed on both sides of the aluminum foil, and the positive electrode coating on one side is scraped off to expose the aluminum foil surface, which is then affixed to the test tape); the tape is bonded end to end to form a tape loop, with the side with the test strip affixed facing outward; the tape loop is wrapped around a driving shaft and a test shaft, and the driving shaft is rotated to perform a rotation test; and the drop of the positive electrode coating of the positive electrode sheet at different rotation speeds is detected to determine the flexibility level of the test strip (the flexibility level is represented by a combination of the corresponding driving shaft rotation number when the coating drops and the corresponding coating drop rate).

[0160] Among them, referring to the record in the patent document with application number 201510967513.4, the flexibility level of the electrode is ranked as follows: D1>D2>D3>D4>D5>C1>C2>C3>C4>C5>B1>B2>B3>B4>B5>A1>A2>A3>A4>A5, that is, in the above order, the flexibility of the battery electrode becomes worse.

[0161] Example 1

[0162] 1. Preparation of positive electrode slurry (slurry composition)

[0163] S1. Evenly mix the binder and the solvent (NMP) to obtain a glue solution; wherein the solid content of the glue solution is 6.5%.

[0164] S2. Defoaming the glue solution and then mixing it with the conductive agent to obtain a mixed liquid; wherein, during the defoaming process, the dew point environment is controlled to be ≤-14°C, the stirring speed is 150 rpm, and the stirring time (i.e., the defoaming time) is 1.5 h;

[0165] S3. Divide the LFP into two equal parts and add them into the mixed liquid twice; wherein, the stirring speed of the mixed liquid is maintained at 750 rpm, and the stirring time after each addition of LFP is 75 minutes.

[0166] S4. After all the LFP is added to the mixed liquid, the stirring speed is maintained at 750 rpm, and an acrylic viscosity reducer and a polysiloxane surfactant are added thereto. The stirring time is 45 minutes to obtain a slurry composition.

[0167] In the slurry composition, the mass ratio of the acrylic ester viscosity reducer to the LFP is 0.15%, and the mass ratio of the polysiloxane surfactant to the LFP is 0.25%.

[0168] In the slurry composition, the conductive agent is conductive carbon black and carbon nanotubes, the mass ratio of the conductive carbon black to the carbon nanotubes is 1:2; and the ratio of the total mass of the conductive agent to the mass of the LFP is 1.3%.

[0169] In the slurry composition, the binder is PVDF, and the mass ratio of the binder to LFP is 3.5%.

[0170] The solid content of the slurry composition was 62%.

[0171] 2. Preparation of positive electrode

[0172] The slurry composition was applied to both the front and back surfaces of an aluminum foil and dried in an oven at 85°C. The surface morphology of the formed coating (whether there were cracks) was observed using an optical microscope, and an area density test was performed (the test results were substantially equal to the area density of the positive electrode coating of the prepared positive electrode sheet, see Table 1); and then, after roller pressing, an electrode sheet was prepared (the electrode sheet (i.e., the positive electrode sheet) included an aluminum foil and a positive electrode coating (i.e., an electrode active material layer) located on both the front and back surfaces of the aluminum foil).

[0173] After the electrode sheet is prepared, the surface morphology of the electrode active material layer (whether cracks or the like are present) is observed again using an optical microscope.

[0174] In addition, the 180° peeling force between the electrode active material layer and the electrode current collector in the electrode sheet and the flexibility of the electrode sheet were measured and are shown in Table 2.

[0175] Examples 2 to 19, Comparative Examples 1 to 3: The difference from Example 1 is that the structure of the viscosity reducer, the weight average molecular weight of the viscosity reducer, the mass ratio of the viscosity reducer to LFP, the structure of the surfactant, the weight average molecular weight of the surfactant, the mass ratio of the surfactant to LFP, the particle size D50 of the LFP and other conditions are different. See Table 1 for details. Except for the differences shown in Table 1, the other conditions are the same as in Example 1.

[0176] The viscosity reducer used in Example 17 has a structure as shown in Formula I-100:

[0177]

[0178] For each embodiment and comparative example, positive electrode sheets with different surface densities were prepared according to the above-mentioned preparation process of the positive electrode sheet, and the coating layer after drying and the electrode active material layer in the prepared electrode sheet were observed to see whether cracks appeared. The maximum surface density of the electrode active material layer (positive electrode coating) corresponding to the absence of cracks in the coating layer after drying and the electrode active material layer in the prepared electrode sheet was recorded as the limiting surface density (see Table 2). That is, when the surface density of the electrode active material layer of the positive electrode sheet exceeds the limiting surface density, cracks appear in the electrode active material layer of the positive electrode sheet. It is understandable that the limiting surface density exists between 5g / m 2 For example, the surface density of the positive electrode coating of Comparative Example 1 is 480 g / m 2 , which means that according to the scheme of comparative example 1, the surface density of the positive electrode coating exceeds 475-485 g / m 2 Cracks will appear.

[0179] Table 1

[0180]

[0181] Table 2

[0182] Example Cathode coating limit density 180° peeling force Flexibility of the positive electrode Example 1 535 0.35 D3 Example 2 520 0.30 D3 Example 3 540 0.30 D3 Example 4 520 0.20 D4 Example 5 540 0.20 D4 Example 6 510 0.28 D3 Example 7 530 0.30 D3 Example 8 540 0.30 D3 Example 9 540 0.30 D3 Example 10 510 0.24 D3 Example 11 520 0.25 D3 Example 12 530 0.27 D3 Example 13 560 0.27 D3 Example 14 550 0.30 D3 Example 15 530 0.3 D3 Example 16 540 0.28 D3 Example 17 510 0.3 D3 Example 18 530 0.3 D3 Example 19 533 0.32 D3 Comparative Example 1 480 0.22 D4 Comparative Example 2 420 0.25 D3 Comparative Example 3 420 0.25 D3

[0183] As can be seen from Table 1, compared with Comparative Examples 1 to 3, Examples 1 to 19 can significantly improve the limiting surface density of the positive electrode sheet by introducing an acrylate viscosity reducer and a polysiloxane surfactant into the positive electrode coating based on the synergistic effect of the two, effectively solving the problem of cracking of the positive electrode coating, especially solving the coating cracking problem of the positive electrode sheet with high surface density. At the same time, Examples 1 and 19 can also take into account the improvement of the higher peeling force between the positive electrode coating and the positive electrode current collector and the flexibility of the positive electrode sheet, thereby avoiding the problem of the positive electrode coating peeling off from the positive electrode current collector.

[0184] It can be further seen that, compared with Examples 4 and 5, Examples 1 to 3 can further improve the surface density, flexibility, and bonding strength between the positive electrode coating and the positive electrode current collector of the positive electrode sheet by further controlling the mass ratio of the acrylic acid ester viscosity reducer to the positive electrode active material within the range of 0.09% to 0.23%.

[0185] It can be further seen that, relative to Example 6, Examples 1, 7 and 8 can further improve the ultimate surface density of the positive electrode sheet and the peeling force between the positive electrode coating and the positive electrode current collector, while improving the flexibility of the positive electrode sheet, by further controlling the mass ratio of the polysiloxane surfactant to the positive electrode active material within the range of 0.15% to 0.35%.

[0186] It can be further seen that, relative to Example 9, Example 1, Example 7 and Example 8 further control the mass ratio of the polysiloxane surfactant to the positive electrode active material within the range of 0.15% to 0.35%. While taking into account the improvement of the surface density, flexibility and bonding strength between the positive electrode coating and the positive electrode current collector of the positive electrode sheet, the use of relatively less polysiloxane surfactant is also beneficial to maintaining less polymer components in the positive electrode slurry, thereby further reducing the viscosity growth rate of the positive electrode slurry, improving the stability of the positive electrode slurry, and further improving the preparation efficiency of the positive electrode sheet and the performance of the prepared positive electrode sheet.

[0187] It can be further seen that, relative to Example 10, Example 1 and Examples 11 to 14 further control the particle size D50 of the positive electrode active material (LFP) within the range of 0.3 μm to 8 μm, which is beneficial to further improve the limiting surface density of the positive electrode sheet and the peeling force between the positive electrode coating and the positive electrode current collector, while maintaining good flexibility of the positive electrode sheet.

[0188] It can be further seen that, compared with Example 17, Example 1, Example 15 and Example 16 can further improve the performance of the positive electrode sheet, such as the limiting surface density, by adopting an acrylate viscosity reducer containing an amide group.

[0189] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An electrode sheet, characterized in that: The invention comprises an electrode current collector and an electrode active material layer located on at least one side surface of the electrode current collector. The electrode active material layer comprises an electrode active material and an auxiliary agent. The auxiliary agent comprises an acrylate viscosity reducer and a polysiloxane surfactant.

2. The electrode sheet according to claim 1, characterized in that The acrylic ester viscosity reducer contains an amide group.

3. The electrode sheet according to claim 1, characterized in that The acrylate viscosity reducer includes an acrylate viscosity reducer having a structure shown in Formula I-1 and / or an acrylate viscosity reducer having a structure shown in Formula I-2: In formula I-1, n1 is an integer greater than 0; R1 is selected from H, halogen or *-RCONH2, R is selected from an alkyl group having 4 to 10 carbon atoms; R2 is selected from H or an alkyl group having 1 to 20 carbon atoms; In formula I-2, n1 is an integer greater than 0; R3 and R4 are each independently selected from an alkyl group having 8 to 20 carbon atoms.

4. The electrode sheet according to claim 3, characterized in that The acrylic acid ester viscosity reducer having the structure shown in Formula I-1 includes a polyacrylate having the structure shown in Formula I-11:

5. The electrode sheet according to claim 4, characterized in that The polyacrylate having the structure shown in formula I-11 includes one or more of the polyacrylates shown in formula I-111, formula I-112, and formula I-113:

6. The electrode sheet according to any one of claims 1 to 5, characterized in that: The polysiloxane surfactant includes a polysiloxane having a structure shown in Formula II: Wherein, m is an integer greater than 0, and R5 is selected from a polyether segment or an alkyl group with 4 to 8 carbon atoms.

7. The electrode sheet according to claim 6, characterized in that The polysiloxane having the structure shown in Formula II includes one or more polysiloxanes shown in Formula II-11, Formula II-12, and Formula II-13:

8. The electrode sheet according to any one of claims 1 to 7, characterized in that: The weight average molecular weight of the polysiloxane surfactant is 600 to 10,000; And / or, the weight average molecular weight of the acrylic ester viscosity reducer is 10,000 to 80,000.

9. The electrode sheet according to any one of claims 1 to 8, characterized in that: The mass ratio of the acrylic acid ester viscosity reducer to the electrode active material is 0.09% to 0.23%; And / or, the mass ratio of the polysiloxane surfactant to the electrode active material is 0.15% to 0.35%.

10. The electrode sheet according to any one of claims 1 to 9, characterized in that: The particle size D50 of the electrode active material is 0.3 μm to 8 μm.

11. The electrode sheet according to any one of claims 1 to 10, characterized in that: The electrode active material layer further includes a conductive agent, wherein the conductive agent includes at least two of a zero-dimensional conductive agent, a one-dimensional conductive agent, and a two-dimensional conductive agent; And / or, the electrode active material layer further includes a binder.

12. The electrode sheet according to any one of claims 1 to 11, characterized in that: The electrode sheet is a positive electrode sheet.

13. The electrode sheet according to claim 12, characterized in that: The electrode active material includes a positive electrode active material, and the positive electrode active material includes lithium iron phosphate and / or a ternary material.

14. The electrode sheet according to any one of claims 1 to 13, characterized in that: The surface density of the electrode active material layer of the electrode sheet is 500 g / m 2 ~630g / m 2 .

15. A method for preparing an electrode sheet according to any one of claims 1 to 14, characterized in that: The following steps are involved: The electrode active material layer slurry is disposed on at least one side surface of the electrode current collector to form the electrode active material layer, thereby producing the electrode sheet; wherein the electrode active material layer slurry includes a liquid dispersion medium, the electrode active material and the auxiliary agent. 16 . The method for preparing an electrode sheet according to claim 15 , wherein the solid content of the electrode active material layer slurry is 60% to 65%.

17. A battery, characterized in that: The electrode sheet comprises the electrode sheet according to any one of claims 1 to 14 or the electrode sheet prepared according to the method for preparing the electrode sheet according to claim 15 or 16.

18. An electrical device, characterized in that: Including the battery according to claim 17.

Images