Negative electrode slurry and preparation method thereof, negative electrode plate, battery cell and alkali metal ion secondary battery

Abstract

The invention provides negative electrode slurry and a preparation method thereof, a negative electrode plate, a battery cell and an alkali metal ion secondary battery, the negative electrode slurry comprises a negative electrode active material, a conductive agent, a binder, a film-forming additive and a solvent, the chemical formula of the film-forming additive is X-CyHzSO3N-R, X < + > is alkali metal ions, N < + > is an alkali metal ion, and R < + > is an alkali metal ion. R is selected from any one of halogen atoms and substituted or unsubstituted alkyl. The film-forming additive is added into the negative electrode slurry, so that the film-forming additive coats the surface of the negative electrode active material more uniformly and directly participates in the construction of the negative electrode structure, and the film can be formed on the surface of the negative electrode in situ in the pre-charging stage, so that the film-forming uniformity is ensured, and the problem that the negative electrode is not compact and thick due to insufficient wettability of an electrolyte is avoided. And the problem of non-uniform additive film formation is solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries and relates to a negative electrode slurry and a preparation method thereof, a negative electrode plate, a battery cell and an alkali metal ion secondary battery. Background Art

[0002] Lithium-ion batteries are widely used in the new energy sector due to their high energy density, high operating voltage, rechargeability, and mature commercial development prospects. As the energy density of lithium-ion batteries increases, transition metal cathode materials have obvious advantages. However, these materials often have relatively high operating voltages. Under high voltages, they are prone to particle breakage and interface damage during cycling, which can oxidize the electrolyte and reduce the battery's cycle life. Therefore, it is necessary to develop additives that can stabilize the positive and negative electrode interfaces under high voltages.

[0003] In the prior art, additives that stabilize the positive and negative electrode interfaces are typically added to the electrolyte. For example, CN120015942A discloses a flame-retardant electrolyte, a preparation method, and its application in graphite anodes. The electrolyte includes a lithium salt, an organic solvent, and a film-forming additive. The organic solvent is a mixed solvent comprising a fluorinated carboxylic acid ester and a hydrofluoroether. The concentration of the lithium salt in the organic solvent is 2 mol / L to 6 mol / L, and the film-forming additive is lithium difluorophosphate bis(oxalate). However, some functional additives (such as lithium difluorophosphate) have poor solubility and can only be used at low concentrations (typically <1%), limiting their performance-enhancing effects.

[0004] In addition, the compatibility requirements between solvents and additives in the electrolyte system are high. For example, although ether solvents can improve solubility, they cannot be used in practice due to their poor oxidative stability. Electrolyte additives must also take into account the performance of both positive and negative electrodes, but the demands of different electrodes for additives may conflict. For example, additives that optimize negative electrode film formation may have side effects on positive electrode materials.

[0005] Based on the above research, it is necessary to provide a negative electrode slurry that can solve the disadvantages of adding additives to the electrolyte, and can also avoid the problem of uneven additive film formation due to insufficient electrolyte wettability, large negative electrode compaction and thickness. Summary of the Invention

[0006] The object of the present invention is to provide a negative electrode slurry and a preparation method thereof, a negative electrode plate, a battery cell and an alkali metal ion secondary battery. By adding a film-forming additive to the negative electrode slurry, the film-forming additive is more evenly wrapped on the surface of the negative electrode active material and directly participates in the construction of the negative electrode structure. The film can be formed in situ on the negative electrode surface during the pre-charging stage, ensuring the uniformity of the film formation and avoiding the problem of uneven additive film formation due to insufficient electrolyte wettability, negative electrode compaction and large thickness.

[0007] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a negative electrode slurry, wherein the negative electrode slurry comprises a negative electrode active material, a conductive agent, a binder, a film-forming additive, and a solvent, wherein the film-forming additive has a structural formula as shown in Formula I):

[0009]

[0010] Among them, X + is an alkali metal ion, and R is selected from any one of a halogen atom and a substituted or unsubstituted alkyl group.

[0011] The present invention adds a specific film-forming additive to the negative electrode slurry. The film-forming additive can pre-form a film because the film-forming additive is uniformly dispersed on the surface of the negative electrode particles in advance, and can form a low-impedance inorganic alkali metal salt SEI film in situ during the pre-charging process, which not only ensures the uniformity of the film formation, but also improves the alkali metal ion mobility of the SEI; the film-forming additive can also enhance the dispersibility of the negative electrode slurry because the polar groups in the film-forming additive can attach to the surface of the conductive agent, reduce the van der Waals force between the particles, inhibit agglomeration, and thus enhance the dispersibility of the negative electrode slurry; the film-forming additive The additive can also optimize the bonding network, form hydrogen bond cross-linking with the binder, and improve the uniformity of the binder distribution and the stability of the electrode structure. Therefore, the film-forming additive of the present invention is more evenly wrapped on the surface of the active material, directly participates in the construction of the negative electrode structure, and can also form a pre-protective layer in the electrode preparation stage, thereby reducing the generation of electrolyte decomposition products during pre-charging. Moreover, in the pre-charging stage, the film-forming additive that has been dispersed in advance can form a film in situ on the negative electrode surface, ensuring the uniformity of the film formation and avoiding the problem of uneven additive film formation due to insufficient electrolyte wettability, negative electrode compaction and large thickness.

[0012] X of the present invention + It is an alkali metal ion, for example, it can be a lithium ion, a sodium ion or a potassium ion, and R is selected from any one of a halogen atom, a substituted or unsubstituted alkyl group, such as any one of a halogen-substituted alkyl group, a methyl group, an ethyl group, a propyl group, a chloro group or a fluoro group.

[0013] Preferably, the chemical formula of the film-forming additive is XC y H z SO3N-R, X is an alkali metal, 3≤y≤6, for example, it can be 3, 4, 5 or 6, 2≤z≤8, for example, it can be 3, 4, 5, 6, 7 or 8, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0014] Preferably, based on 100 wt% of the non-solvent component in the negative electrode slurry, the content of the film-forming additive is 0.1 wt%-5 wt%, for example, it can be 0.1 wt%, 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt% or 5 wt%, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable, preferably 0.5 wt%-2 wt%.

[0015] In the negative electrode slurry of the present invention, the content of the film-forming additive in the components other than the solvent is preferably within a specific range, that is, preferably 0.5wt%-2wt%. If the content of the film-forming additive is too little, the film-forming effect thereof is reduced. If the content of the film-forming additive is too much, the interfacial impedance is too large, affecting the charging capacity.

[0016] Preferably, the negative electrode slurry further includes a regulator, and the regulator includes a carbonate compound.

[0017] Preferably, the carbonate compound includes ethylene carbonate and / or propylene carbonate.

[0018] The negative electrode slurry of the present invention further includes a carbonate compound as a regulator, which can improve coating and prevent the electrode from cracking.

[0019] Preferably, based on 100 wt% of the non-solvent component in the negative electrode slurry, the content of the regulator is 0 wt%-5 wt%, but excluding 0 wt%, for example, it can be 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt% or 5 wt%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0020] Preferably, based on the non-solvent component in the negative electrode slurry as 100wt%, the content of the negative electrode active material is 80wt%-96wt%, for example, it can be 80wt%, 82.5wt%, 85wt%, 87.5wt%, 90wt%, 92.5wt%, 95wt% or 96wt%, the content of the conductive agent is 0.5wt%-15wt%, for example, it can be 0.5wt%, 1wt%, 3wt%, 5wt%, 7wt%, 9wt%, 11wt%, 13wt% or 15wt%, and the content of the binder is 1wt%-10wt%, for example, it can be 1wt%, 3wt%, 5wt%, 7wt%, 9wt% or 10wt%, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0021] Preferably, the negative electrode active material includes any one or a combination of at least two of artificial graphite, natural graphite, silicon-based materials, hard carbon or lithium titanate, and the silicon-based materials include any one or a combination of at least two of silicon carbon, silicon oxide or pure silicon materials.

[0022] Preferably, the conductive agent includes any one of Ketjen black, conductive carbon black, carbon fiber, multi-walled carbon nanotube, single-walled carbon nanotube or graphene, or a combination of at least two thereof.

[0023] Preferably, the binder includes any one of styrene-butadiene rubber, nitrile-butadiene rubber, butadiene rubber, modified butadiene rubber, carboxyl-modified butadiene rubber, modified polyorganosiloxane polymer, sodium carboxymethyl cellulose or lithium carboxymethyl cellulose, or a combination of at least two thereof.

[0024] Preferably, the solvent comprises deionized water.

[0025] Preferably, the solid content of the negative electrode slurry is 40wt%-60wt%, for example, 40wt%, 45wt%, 50wt%, 55wt% or 60wt%, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0026] In a second aspect, the present invention provides a method for preparing the negative electrode slurry as described in the first aspect, the preparation method comprising the following steps:

[0027] The negative electrode active material, binder, conductive agent, film-forming additive and solvent are mixed, and then the pH and viscosity are adjusted, vacuum degassing and filtering are performed to obtain the negative electrode slurry.

[0028] Preferably, a regulator is also added during the mixing.

[0029] Preferably, the mixing of the negative electrode active material, the binder, the conductive agent, the film-forming additive and the solvent comprises the following steps:

[0030] (1) mixing a first binder and a solvent to obtain a premixed glue solution;

[0031] (2) Adding a conductive agent, a regulator and a film-forming additive to the premixed glue solution of step (1) for dispersion, then adding the negative electrode active material in batches for further dispersion, and finally adding a second binder for dispersion.

[0032] Preferably, the first binder includes sodium carboxymethyl cellulose and / or lithium carboxymethyl cellulose, and the second binder includes styrene-butadiene rubber.

[0033] Preferably, in step (1), the revolution speed of the mixing of the first binder and the solvent is 0 rpm-50 rpm, for example, it can be 0 rpm, 10 rpm, 20 rpm, 30 rpm, 40 rpm or 50 rpm, the rotation speed is 500 rpm-3000 rpm, for example, it can be 500 rpm, 1000 rpm, 2000 rpm or 3000 rpm, and the time is 30 min-300 min, for example, it can be 30 min, 100 min, 200 min or 300 min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0034] Preferably, the revolution speed of the conductive agent, regulator and film-forming additive added for dispersion in step (2) is 0rpm-50rpm, for example, it can be 0rpm, 10rpm, 20rpm, 30rpm, 40rpm or 50rpm, the rotation speed is 500rpm-3000rpm, for example, it can be 500rpm, 1000rpm, 2000rpm or 3000rpm, and the time is 30min-300min, for example, it can be 30min, 100min, 200min or 300min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0035] Preferably, the revolution speed for adding the negative electrode active material in batches and continuing to disperse is 0 rpm-50 rpm, for example, it can be 0 rpm, 10 rpm, 20 rpm, 30 rpm, 40 rpm or 50 rpm, the rotation speed is 500 rpm-3000 rpm, for example, it can be 500 rpm, 1000 rpm, 2000 rpm or 3000 rpm, and the time is 30 min-300 min, for example, it can be 30 min, 100 min, 200 min or 300 min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0036] Preferably, when the negative electrode active material is added in batches in step (2), the interval between each batch is 10 min to 60 min, for example, it can be 10 min, 20 min, 30 min, 40 min, 50 min or 60 min, but it is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0037] Preferably, in step (2), the pH is adjusted to 8-9, for example, 8, 8.25, 8.5, 8.75 or 9, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0038] Preferably, in step (2), the viscosity is adjusted to 3000 cP-5000 cP, for example, 3000 cP, 3500 cP, 4000 cP, 4500 cP or 5000 cP, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0039] Preferably, the fineness of the negative electrode slurry is ≤35 μm, for example, it can be 35 μm, 30 μm, 25 μm, 20 μm or 15 μm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0040] In a third aspect, the present invention provides a negative electrode plate, comprising a current collector and a negative electrode active material layer located on at least one side of the current collector, wherein the negative electrode active material layer is obtained by coating the negative electrode slurry as described in the first aspect.

[0041] Preferably, the current collector comprises any one of copper foil, nickel foil, stainless steel foil, titanium foil, foam nickel, foam copper or polymer composite copper foil, or a combination of at least two thereof.

[0042] Preferably, in the negative electrode active material layer, the content of the film-forming additive is 0.1wt%-5wt% (for example, it can be 0.1wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt% or 5wt%), preferably 0.5wt%-2wt%, the content of the regulator is 0wt%-5wt% (for example, it can be 0.5wt%, 1wt%, 2wt%, 3wt%, 4wt% or 5wt%), and the content of the negative electrode active material is 80wt%- 96wt% (for example, it can be 80wt%, 82.5wt%, 85wt%, 87.5wt%, 90wt%, 92.5wt%, 95wt% or 96wt%), the content of the conductive agent is 0.5wt%-15wt% (for example, it can be 0.5wt%, 1wt%, 3wt%, 5wt%, 7wt%, 9wt%, 11wt%, 13wt% or 15wt%), and the content of the binder is 1wt%-10wt% (for example, it can be 1wt%, 3wt%, 5wt%, 7wt%, 9wt% or 10wt%).

[0043] Preferably, the method for preparing the negative electrode sheet comprises: coating the negative electrode slurry as described in the first aspect on at least one surface of a current collector, and then performing drying, roll pressing, die cutting, etc.

[0044] In a fourth aspect, the present invention provides a battery cell comprising a positive electrode sheet, a separator, an electrolyte, and a negative electrode sheet as described in the third aspect.

[0045] Preferably, the battery cell satisfies the following relationship: 0.01<(t×d×c) / p<4, for example, it can be 0.02, 0.05, 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 3.5 or 3.9, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0046] Where t is the content of film-forming additive in the negative electrode active material layer, in wt%; d is the surface density of the negative electrode sheet, in mg / cm 2 ; c is the electrolyte injection coefficient (electrolyte injection amount / battery cell capacity); p is the content of the negative electrode active material in the negative electrode active material layer, and the unit is wt%. The formula of the present invention is valid when the numerical value is valid under the above units.

[0047] The amount of the film-forming additive used in the present invention is affected by the surface density of the negative electrode plate, the proportion of the negative electrode active material and the electrolyte injection coefficient. Therefore, when t, d, c and p satisfy the above relationship, the comprehensive performance of the battery cell is optimal.

[0048] Preferably, 0.1 wt%≤t≤5 wt%, for example, it can be 0.1 wt%, 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt% or 5 wt%, 4 mg / cm 2 ≤d≤16mg / cm 2 , for example, it can be 4 mg / cm 2 , 6mg / cm 2 , 8mg / cm 2 、10mg / cm 2 , 12mg / cm 2 , 14mg / cm 2 or 16 mg / cm 2 , 2≤c≤4, for example, it can be 2, 2.5, 3, 3.5 or 4, 80wt%≤p≤96wt%, for example, it can be 80wt%, 82.5wt%, 85wt%, 87.5wt%, 90wt%, 92.5wt%, 95wt% or 96wt%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0049] The amount t of the film-forming additive described in the present invention needs to take into account the negative electrode protection effect of the battery cell and the interface film-forming impedance, so there are upper and lower limits to the added amount; for the surface density d, the negative electrode surface density d is obtained according to the battery cell design requirements. When the surface density is high, the battery cell charging capacity requirement is not high, and too much film-forming additive is not needed. When the surface density is small, the negative electrode protection performance requirements are high, and more film-forming additives need to be added. Therefore, the added amount t and the surface density d are negatively correlated.

[0050] The electrolyte filling coefficient is determined according to the battery cell design. Although the film-forming additive is in the negative electrode slurry, it is related to the electrolyte filling coefficient. It plays a role similar to that of an electrolyte additive. Therefore, similar to an electrolyte additive, there are upper and lower limits to meet the requirements of improving the battery cell performance and balancing electrical properties such as impedance. The proportion of negative electrode active material p is directly proportional to the amount of film-forming additive. When the proportion of negative electrode active material is large, more additives are also required. In summary, the most appropriate amount of film-forming additive is affected by the surface density of the negative electrode design, the proportion of negative electrode active material and the electrolyte filling coefficient.

[0051] Preferably, 0.018<(t×d×c) / p<1.1, for example, it can be 0.02, 0.05, 0.075, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1.0, 1.05 or 1.09, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0052] Preferably, 0.1 wt%≤t≤2 wt%, for example, 0.1 wt%, 0.5 wt%, 1 wt%, 1.5 wt% or 2 wt%, 7 mg / cm 2 ≤d≤12mg / cm 2 , for example, it can be 7mg / cm 2 , 8mg / cm 2 , 9mg / cm 2 、10mg / cm 2 、11mg / cm 2 or 12 mg / cm 2 , 2.5≤c≤4, for example, it can be 2.5, 3, 3.5 or 4, 90wt%≤p≤96wt%, for example, it can be 90wt%, 91wt%, 92wt%, 93wt%, 94wt%, 95wt% or 96wt%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0053] Preferably, the positive electrode plate includes any one or a combination of at least two of lithium iron phosphate, lithium iron manganese phosphate, NCM, NCA, lithium cobalt oxide, lithium manganese oxide, lithium nickel manganese oxide, layered oxides, polyanion compounds or Prussian blue.

[0054] Preferably, the diaphragm includes any one of a glass fiber membrane, a polyolefin membrane (such as PE, PP, modified polyolefin), polyimide, polyetheretherketone or an aramid fiber membrane, or a combination of at least two thereof.

[0055] In a fifth aspect, the present invention provides an alkali metal ion secondary battery, wherein the alkali metal ion secondary battery comprises the negative electrode sheet as described in the third aspect, or the battery cell as described in the fourth aspect.

[0056] Compared with the prior art, the present invention has the following beneficial effects:

[0057] The present invention adds a specific film-forming additive to the negative electrode slurry. The film-forming additive can pre-form a film because the film-forming additive is uniformly dispersed on the surface of the negative electrode particles in advance, and can form a low-impedance inorganic alkali metal salt SEI film in situ during the pre-charging process, which not only ensures the uniformity of the film formation, but also improves the alkali metal ion mobility of the SEI; the film-forming additive can also enhance the dispersibility of the negative electrode slurry because the polar groups in the film-forming additive can attach to the surface of the conductive agent, reduce the van der Waals force between the particles, inhibit agglomeration, and thus enhance the dispersibility of the negative electrode slurry; the film-forming additive The additive can also optimize the bonding network, form hydrogen bond cross-linking with the binder, and improve the uniformity of the binder distribution and the stability of the electrode structure. Therefore, the film-forming additive of the present invention is more evenly wrapped on the surface of the active material, directly participates in the construction of the negative electrode structure, and can also form a pre-protective layer in the electrode preparation stage, thereby reducing the generation of electrolyte decomposition products during pre-charging. Moreover, in the pre-charging stage, the film-forming additive that has been dispersed in advance can form a film in situ on the negative electrode surface, ensuring the uniformity of the film formation and avoiding the problem of uneven additive film formation due to insufficient electrolyte wettability, negative electrode compaction and large thickness. DETAILED DESCRIPTION

[0058] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0059] Example 1

[0060] This embodiment provides a negative electrode slurry, wherein the non-solvent composition of the negative electrode slurry includes 94 wt% of artificial graphite, 1 wt% of SP, 0.5 wt% of sodium carboxymethyl cellulose, 0.5 wt% of styrene-butadiene rubber, 2 wt% of a film-forming additive, and 2 wt% of a regulator, wherein the regulator is ethylene carbonate, and the film-forming additive is:

[0061] (This substance was provided by Anhui Jinhe);

[0062] The solvent of the negative electrode slurry is deionized water, and the solid content is 40wt%;

[0063] The method for preparing the negative electrode slurry comprises the following steps:

[0064] (1) Sodium carboxymethyl cellulose and deionized water were mixed and stirred until a transparent colloid was obtained to obtain a premixed colloid solution, wherein the mixing speed was 50 rpm, the rotation speed was 1000 rpm, and the mixing time was 300 min;

[0065] (2) Add SP, regulator and film-forming additive to the premixed glue solution and disperse at high speed. The revolution speed of the dispersion is 10 rpm, the rotation speed is 1000 rpm, and the time is 300 min. Then, add artificial graphite in multiple batches, with an interval of 60 min between each batch, and continue to disperse until there is no particle agglomeration. The revolution speed of the dispersion is 50 rpm and the rotation speed is 3000 rpm.

[0066] (3) Adding styrene-butadiene rubber emulsion to the system of step (2), adjusting the slurry pH to 8, adjusting the slurry viscosity to 3000 cP, and filtering to a fineness of 25 μm after vacuum degassing to obtain the negative electrode slurry.

[0067] This embodiment further provides a battery cell, comprising an NCM613 positive electrode sheet, a PE separator, a commercial medium-nickel high-voltage electrolyte, and a negative electrode sheet. The negative electrode sheet is obtained by coating the negative electrode slurry described in this embodiment on both sides of a copper foil, followed by drying, rolling, and die-cutting.

[0068] The battery cell satisfies the following relationship: (t×d×c) / p=0.45;

[0069] Wherein, t is the content of the film-forming additive in the negative electrode active material layer, specifically 2 wt%; d is the surface density of the negative electrode sheet, specifically 7.5 mg / cm 2 ; c is the electrolyte injection coefficient, specifically 2.8; p is the content of the negative electrode active material in the negative electrode active material layer, specifically 94wt%.

[0070] Example 2

[0071] This embodiment provides a negative electrode slurry, wherein the non-solvent composition of the negative electrode slurry includes 94wt% artificial graphite, 1wt% SP, 0.5wt% sodium carboxymethyl cellulose, 0.5wt% styrene-butadiene rubber, 2wt% film-forming additive and 2wt% regulator, wherein the regulator is ethylene carbonate, and the film-forming additive is

[0072] Lithium fluoroacetylsulfonate, the specific structural formula is (This substance was provided by Anhui Jinhe);

[0073] The solvent of the negative electrode slurry is deionized water, and the solid content is 60wt%;

[0074] The method for preparing the negative electrode slurry comprises the following steps:

[0075] (1) Sodium carboxymethyl cellulose and deionized water were mixed and stirred until a transparent colloid was obtained to obtain a premixed colloid solution, wherein the mixing speed was 10 rpm, the rotation speed was 3000 rpm, and the mixing time was 100 min;

[0076] (2) Add SP, regulator and film-forming additive to the premixed glue solution and disperse at high speed. The revolution speed of the dispersion is 50 rpm, the rotation speed is 3000 rpm, and the time is 300 min. Then, add artificial graphite in multiple batches, with an interval of 10 min between each batch, and continue to disperse until there is no particle agglomeration. The revolution speed of the dispersion is 10 rpm and the rotation speed is 1000 rpm.

[0077] (3) Adding styrene-butadiene rubber emulsion to the system of step (2), adjusting the slurry pH to 9, adjusting the slurry viscosity to 5000 cP, and filtering to a fineness of 35 μm after vacuum degassing to obtain the negative electrode slurry.

[0078] This embodiment further provides a battery cell, comprising an NCM613 positive electrode sheet, a PE separator, a commercial medium-nickel high-voltage electrolyte, and a negative electrode sheet. The negative electrode sheet is obtained by coating the negative electrode slurry described in this embodiment on both sides of a copper foil, followed by drying, rolling, and die-cutting.

[0079] The battery cell satisfies the following relationship: (t×d×c) / p=0.45;

[0080] Wherein, t is the content of the film-forming additive in the negative electrode active material layer, specifically 2 wt%; d is the surface density of the negative electrode sheet, specifically 7.5 mg / cm 2 ; c is the electrolyte injection coefficient, specifically 2.8; p is the content of the negative electrode active material in the negative electrode active material layer, specifically 94wt%.

[0081] Example 3

[0082] This embodiment provides a negative electrode slurry, which is the same as that in Example 1;

[0083] The preparation method of the negative electrode slurry is the same as that of Example 1

[0084] This embodiment further provides a battery cell, comprising an NCM613 positive electrode sheet, a PE separator, a commercial medium-nickel high-voltage electrolyte, and a negative electrode sheet. The negative electrode sheet is obtained by coating the negative electrode slurry described in this embodiment on both sides of a copper foil, followed by drying, rolling, and die-cutting.

[0085] The battery cell satisfies the following relationship: (t×d×c) / p=1.02;

[0086] Wherein, t is the content of the film-forming additive in the negative electrode active material layer, specifically 2 wt%; d is the surface density of the negative electrode sheet, specifically 12 mg / cm 2 ; c is the electrolyte injection coefficient, specifically 4; p is the content of the negative electrode active material in the negative electrode active material layer, specifically 94wt%.

[0087] Example 4

[0088] This embodiment provides a negative electrode slurry, wherein the non-solvent composition of the negative electrode slurry includes 96 wt% of artificial graphite, 1 wt% of SP, 0.5 wt% of sodium carboxymethyl cellulose, 0.5 wt% of styrene-butadiene rubber, 0.1 wt% of a film-forming additive, and 1.9 wt% of a regulator, wherein the regulator is ethylene carbonate, and the film-forming additive is:

[0089] (This substance was provided by Anhui Jinhe);

[0090] The solvent of the negative electrode slurry is deionized water, and the solid content is 40wt%;

[0091] The preparation method of the negative electrode slurry is the same as that of Example 1 except that the formula amount is changed.

[0092] This embodiment further provides a battery cell, comprising an NCM613 positive electrode sheet, a PE separator, a commercial medium-nickel high-voltage electrolyte, and a negative electrode sheet. The negative electrode sheet is obtained by coating the negative electrode slurry described in this embodiment on both sides of a copper foil, followed by drying, rolling, and die-cutting.

[0093] The battery cell satisfies the following relationship: (t×d×c) / p=0.022;

[0094] Wherein, t is the content of the film-forming additive in the negative electrode active material layer, specifically 0.1 wt%; d is the surface density of the negative electrode sheet, specifically 7.5 mg / cm 2 ; c is the electrolyte injection coefficient, specifically 2.8; p is the content of the negative electrode active material in the negative electrode active material layer, specifically 96wt%.

[0095] Example 5

[0096] This embodiment provides a negative electrode slurry, wherein the non-solvent composition of the negative electrode slurry includes 96 wt% of artificial graphite, 1 wt% of SP, 0.5 wt% of carboxymethyl cellulose, 0.5 wt% of styrene-butadiene rubber, 0.5 wt% of a film-forming additive, and 1.5 wt% of a regulator, wherein the regulator is ethylene carbonate, and the film-forming additive is:

[0097] (This substance was provided by Anhui Jinhe);

[0098] The solvent of the negative electrode slurry is deionized water, and the solid content is 40wt%;

[0099] The preparation method of the negative electrode slurry is the same as that of Example 1 except that the formula amount is changed.

[0100] This embodiment further provides a battery cell, comprising an NCM613 positive electrode sheet, a PE separator, a commercial medium-nickel high-voltage electrolyte, and a negative electrode sheet. The negative electrode sheet is obtained by coating the negative electrode slurry described in this embodiment on both sides of a copper foil, followed by drying, rolling, and die-cutting.

[0101] The battery cell satisfies the following relationship: (t×d×c) / p=0.11;

[0102] Wherein, t is the content of the film-forming additive in the negative electrode active material layer, specifically 0.5 wt%; d is the surface density of the negative electrode sheet, specifically 7.5 mg / cm 2 ; c is the electrolyte injection coefficient, specifically 2.8; p is the content of the negative electrode active material in the negative electrode active material layer, specifically 96wt%.

[0103] Example 6

[0104] This embodiment provides a negative electrode slurry, wherein the non-solvent composition of the negative electrode slurry includes 91 wt% of artificial graphite, 1 wt% of SP, 0.5 wt% of carboxymethyl cellulose, 0.5 wt% of styrene-butadiene rubber, 5 wt% of a film-forming additive, and 2 wt% of a regulator, wherein the regulator is ethylene carbonate, and the film-forming additive is:

[0105] (This substance was provided by Anhui Jinhe);

[0106] The solvent of the negative electrode slurry is deionized water, and the solid content is 40wt%;

[0107] The preparation method of the negative electrode slurry is the same as that of Example 1 except that the formula amount is changed.

[0108] This embodiment further provides a battery cell, comprising an NCM613 positive electrode sheet, a PE separator, a commercial medium-nickel high-voltage electrolyte, and a negative electrode sheet. The negative electrode sheet is obtained by coating the negative electrode slurry described in this embodiment on both sides of a copper foil, followed by drying, rolling, and die-cutting.

[0109] The battery cell satisfies the following relationship: (t×d×c) / p=1.15;

[0110] Wherein, t is the content of the film-forming additive in the negative electrode active material layer, specifically 5 wt%; d is the surface density of the negative electrode sheet, specifically 7.5 mg / cm 2 ; c is the electrolyte injection coefficient, specifically 2.8; p is the content of the negative electrode active material in the negative electrode active material layer, specifically 91wt%.

[0111] Example 7

[0112] This embodiment provides a negative electrode slurry, wherein the non-solvent composition of the negative electrode slurry includes 96 wt% of artificial graphite, 1 wt% of SP, 0.5 wt% of carboxymethyl cellulose, 0.5 wt% of styrene-butadiene rubber, 0.05 wt% of a film-forming additive, and 1.95 wt% of a regulator, wherein the regulator is ethylene carbonate, and the film-forming additive is:

[0113] (This substance was provided by Anhui Jinhe);

[0114] The solvent of the negative electrode slurry is deionized water, and the solid content is 40wt%;

[0115] The preparation method of the negative electrode slurry is the same as that of Example 1 except that the formula amount is changed.

[0116] This embodiment further provides a battery cell, comprising an NCM613 positive electrode sheet, a PE separator, a commercial medium-nickel high-voltage electrolyte, and a negative electrode sheet. The negative electrode sheet is obtained by coating the negative electrode slurry described in this embodiment on both sides of a copper foil, followed by drying, rolling, and die-cutting.

[0117] The battery cell satisfies the following relationship: (t×d×c) / p=0.011;

[0118] Wherein, t is the content of the film-forming additive in the negative electrode active material layer, specifically 0.05 wt%; d is the surface density of the negative electrode sheet, specifically 7.5 mg / cm 2 ; c is the electrolyte injection coefficient, specifically 2.8; p is the content of the negative electrode active material in the negative electrode active material layer, specifically 96wt%.

[0119] Example 8

[0120] This embodiment provides a negative electrode slurry, which is the same as that of Example 1 except that the regulator is not included, the content of SP is 2 wt %, the content of carboxymethyl cellulose is 1 wt %, and the content of styrene-butadiene rubber is 1 wt %.

[0121] This embodiment further provides a battery cell, which is the same as that of embodiment 1 except that the negative electrode slurry of this embodiment is used to prepare the negative electrode sheet to change the adaptability of the battery cell.

[0122] Comparative Example 1

[0123] This comparative example provides a negative electrode slurry, which is the same as Example 1 except that it does not include film-forming additives and regulators, the content of artificial graphite is 96wt%, the content of SP is 2wt%, the content of carboxymethyl cellulose is 1wt%, and the content of styrene-butadiene rubber is 1wt%.

[0124] This comparative example also provides a battery cell, which is the same as Example 1 except that the negative electrode slurry described in this comparative example is used to prepare the negative electrode sheet to change the adaptability of the battery cell.

[0125] Comparative Example 2

[0126] This comparative example provides a negative electrode slurry, which is the same as that of comparative example 1;

[0127] This comparative example also provides a battery cell, which is the same as Example 1 except that the negative electrode slurry described in this comparative example is used to prepare the negative electrode plate, and the electrolyte includes 2wt% of the film-forming additive described in Example 1, 12.5wt% of LiPF6, 0.5wt% of VC, 1wt% of DTD, EC and EMC, EC / EMC = 3:7 (volume ratio), so that the adaptability of the battery cell changes.

[0128] The values ​​of t and (t×d×c) / p in the above embodiments and comparative examples are shown in Table 1. The battery cells obtained in the above embodiments and comparative examples were tested for line impedance DCIR at 25°C and 50% SOC, and for capacity retention after 500 cycles at 25°C, 1C charge and 1C discharge, and 0-100% DOD. The capacity recovery rate was tested after 60 days of storage at 55°C at 100% SOC. The test results are shown in Table 1.

[0129] Table 1

[0130]

[0131]

[0132] From Table 1 above, we can see that:

[0133] It can be seen from Examples 1-3 and Comparative Example 1 that the present invention can form a low-impedance inorganic lithium salt SEI film in situ during the pre-charging process by adding a film-forming additive to the negative electrode slurry, which not only ensures the uniformity of the film formation, but also improves the alkali metal ion mobility of the SEI, thereby reducing the battery cell impedance and improving the battery cell cycle performance and high-temperature storage performance; It can be seen from Examples 1-3 and Comparative Example 2 that even if the film-forming additive of the present invention is added to the electrolyte, since the electrolyte needs to enter the negative electrode plate to form a film, it will lead to uneven film formation, and the obtained battery cell impedance, cycle performance and high-temperature storage performance are all inferior to Examples 1-3; It can be seen from Examples 1 and 4-7 that the present invention preferably adds the film-forming additive within a specific content range, and at the same time, it is preferred that (t×d×c) / p satisfies a specific range, thereby further reducing the battery cell impedance and improving the battery cell cycle performance and high-temperature storage performance; It can be seen from Examples 1 and 8 that the present invention preferably also adds a regulator to the negative electrode slurry, which cooperates with the film-forming additive to further improve the performance of the battery cell.

[0134] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and disclosure scope of the present invention.

Claims

1. A negative electrode slurry, characterized in that: The negative electrode slurry includes a negative electrode active material, a conductive agent, a binder, a film-forming additive and a solvent. The structural formula of the film-forming additive is shown in Formula I): Among them, X + is an alkali metal ion, and R is selected from any one of a halogen atom and a substituted or unsubstituted alkyl group.

2. The negative electrode slurry according to claim 1, characterized in that Based on 100 wt% of the non-solvent component in the negative electrode slurry, the content of the film-forming additive is 0.1 wt%-5 wt%, preferably 0.5 wt%-2 wt%; Preferably, the negative electrode slurry further includes a regulator, and the regulator includes a carbonate compound; Preferably, the carbonate compound includes ethylene carbonate and / or propylene carbonate; Preferably, based on 100 wt % of the non-solvent component in the negative electrode slurry, the content of the regulator is 0 wt % to 5 wt %, but excluding 0 wt %.

3. The negative electrode slurry according to claim 1 or 2, characterized in that: Based on 100 wt% of the non-solvent component in the negative electrode slurry, the content of the negative electrode active material is 80 wt%-96 wt%, the content of the conductive agent is 0.5 wt%-15 wt%, and the content of the binder is 1 wt%-10 wt%; Preferably, the solvent comprises deionized water; Preferably, the solid content of the negative electrode slurry is 40 wt%-60 wt%.

4. A method for preparing the negative electrode slurry according to any one of claims 1 to 3, characterized in that: The preparation method comprises the following steps: The negative electrode active material, binder, conductive agent, film-forming additive and solvent are mixed, and then the pH and viscosity are adjusted, vacuum degassing and filtering are performed to obtain the negative electrode slurry.

5. The preparation method according to claim 4, characterized in that A conditioning agent is also added during the mixing; Preferably, the mixing of the negative electrode active material, the binder, the conductive agent, the film-forming additive and the solvent comprises the following steps: (1) mixing a first binder and a solvent to obtain a premixed adhesive; (2) adding a conductive agent, a regulator, and a film-forming additive to the premixed glue solution of step (1) for dispersion, then adding the negative electrode active material in batches for further dispersion, and finally adding a second binder for dispersion; Preferably, when the negative electrode active material is added in batches in step (2), the interval between each batch is 10 min to 60 min; Preferably, in step (2), the pH is adjusted to 8-9; Preferably, in step (2), the viscosity is adjusted to 3000 cP-5000 cP; Preferably, the fineness of the negative electrode slurry is ≤35 μm.

6. A negative electrode plate, characterized in that: The negative electrode plate includes a current collector and a negative electrode active material layer located on at least one side surface of the current collector, and the negative electrode active material layer is obtained by coating the negative electrode slurry according to any one of claims 1 to 3.

7. A battery cell, characterized in that: The battery cell comprises a positive electrode sheet, a separator, an electrolyte and the negative electrode sheet as claimed in claim 6.

8. The battery cell according to claim 7, characterized in that The battery cell satisfies the following relationship: 0.01<(t×d×c) / p<4; Where t is the content of film-forming additive in the negative electrode active material layer, in wt%; d is the surface density of the negative electrode sheet, in mg / cm 2 ; c is the electrolyte injection coefficient; p is the content of the negative electrode active material in the negative electrode active material layer, in wt%; Preferably, 0.1 wt% ≤ t ≤ 5 wt%, 4 mg / cm 2 ≤d≤16mg / cm 2 , 2≤c≤4, 80wt%≤p≤96wt%.

9. The battery cell according to claim 8, characterized in that: 0.018<(t×d×c) / p<1.1; Preferably, 0.1 wt% ≤ t ≤ 2 wt%, 7 mg / cm 2 ≤d≤12mg / cm 2 , 2.5≤c≤4, 90wt%≤p≤96wt%.

10. An alkali metal ion secondary battery, characterized in that: The alkali metal ion secondary battery comprises the negative electrode sheet according to claim 6, or the battery cell according to any one of claims 7 to 9.

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