Modified negative pole piece, battery and battery system

Abstract

The invention provides a modified negative pole piece, a battery and a battery system. The modified negative pole piece comprises a negative current collector; the modified active material layer is arranged on the surface of at least one side of the negative electrode current collector; the modified active material layer comprises an active material layer and a surface modification layer which are arranged in a laminated manner along the direction far away from the negative electrode current collector; the surface modification layer comprises at least two sub-modification layers, each sub-modification layer comprises a binder and a fast ion conductor electrolyte, and the content of the binder in the sub-modification layers is gradually reduced along the direction far away from the negative electrode current collector. On one hand, the infiltration state of the pole piece in the battery can be improved, the diffusion path of lithium ions can be shortened, the problem of stripping or falling of the active substance layer on the pole piece can be improved, and the structural stability of the battery can be improved, so that the rate capability and the cycle performance of the battery can be improved; the safety performance of the battery is improved and the overall cost of the battery is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials, and in particular relates to a modified negative electrode plate, a battery and a battery system. Background Art

[0002] Batteries are one of the core components of various new energy devices or equipment. In the battery manufacturing process, diaphragms with specific surface modification layers are often used to improve the performance of the battery. For example, diaphragms with inorganic coatings are used to improve the safety performance of the battery, diaphragms with functional coatings are used in combination with thermal composite processes to improve the interface contact state between the electrode and the diaphragm, thereby improving the electrical performance of the battery, and hybrid coating diaphragms with inorganic coatings and functional coatings are used in combination with thermal composite processes to improve the safety and electrical performance of the battery. For example, patent CN113644378A discloses a functional coating diaphragm and its preparation method and application, wherein the functional coating diaphragm is composed of the following components by weight: 10 parts of PVDF powder, 100 to 500 parts of alkaline solution, 1 to 10 parts of oxidant solution, 0.01 to 1 part of grafted modified monomer, 0.5 to 3 parts of polar polymer material particles, and 6 to 30 parts of dispersing solvent. CN111509173A discloses a functional coating separator for lithium-ion batteries and a preparation method thereof. The preparation steps are as follows: uniformly mixing ceramic powder and a coupling agent to obtain pretreated ceramic powder; adding a dispersant and a thickener to deionized water to dissolve the mixture, then adding the pretreated ceramic powder and a polymer emulsion and stirring to disperse the mixture uniformly; finally, adding a binder and a wetting agent and stirring to disperse the mixture uniformly to obtain a modified ceramic slurry; applying the modified ceramic slurry to one or both sides of a base film by coating, and drying to obtain a functional coating separator. However, separators with functional coatings also present some problems during use, such as the inorganic coating easily falling off after long-term storage, surface modification layers adhering to and peeling off, and high separator costs.

[0003] To this end, researchers have also explored providing a functional coating on the active material layer to improve the above situation. For example, CN114464770A provides an electrode sheet and a battery comprising the electrode sheet. The electrode sheet includes a current collector, a first active material layer, a second active material layer, and a functional coating. The first active material layer is provided on at least one side of the current collector, the second active material layer is provided on the surface of the first active material layer, and the functional coating is provided on the surface of the second active material layer; the electronic conductivity of the second active material layer is greater than that of the first active material layer. However, the above solution has limited effect on improving the safety performance of the battery, and the bonding strength between the coating and the active material layer is poor, the cost is quite high, and the effect on improving the cycle performance of the battery is limited.

[0004] Therefore, how to balance the improvement of battery cycle performance and safety performance is a technical problem that needs to be solved urgently. Summary of the Invention

[0005] In response to the shortcomings of the prior art, the present invention aims to provide a modified negative electrode plate, a battery, and a battery system. The present invention provides a surface modification layer containing a binder and a fast ion conductor electrolyte on the outer surface of the active material layer, and the binder content in each sub-modification layer decreases as it moves away from the negative electrode current collector. This design can, on the one hand, improve the wetting state of the battery plate, shorten the diffusion path of lithium ions, and alleviate the problem of peeling or falling of the active material layer on the plate, thereby improving the structural stability of the battery and thus improving the battery's rate performance and cycle performance. On the other hand, it can enhance the separator's resistance to thermal shrinkage, improve the battery's safety performance, and reduce the overall manufacturing cost of the battery, facilitating industrial production.

[0006] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a modified negative electrode plate, the modified negative electrode plate comprising:

[0008] Negative electrode current collector.

[0009] A modified active material layer is provided on at least one side surface of the negative electrode current collector.

[0010] The modified active material layer includes an active material layer and a surface modification layer stacked in a direction away from the negative electrode current collector; the surface modification layer includes at least two sub-modification layers, each sub-modification layer includes a binder and a fast ion conductor electrolyte, and the content of the binder in the sub-modification layer decreases in a direction away from the negative electrode current collector.

[0011] In the modified negative electrode plate provided by the present invention, a surface modification layer containing a binder and a fast ion conductor electrolyte is arranged on the outer surface of the active material layer, and includes at least two sub-modification layers, wherein the content of the binder in the sub-modification layer decreases in the direction away from the negative electrode current collector. This change trend can improve the wetting state of the plate in the battery. A good wetting state is conducive to enhancing ion conduction, enhancing ion conduction, optimizing the rate performance of the battery, and maintaining the structural stability of the active material layer on the plate, avoiding problems such as the coating falling or peeling, reducing the loss of active material, extending the service life of the battery, and optimizing the cycle performance of the battery. In addition, it helps to improve the heat shrinkage resistance of the diaphragm, avoid direct contact between the positive and negative electrodes due to the shrinkage of the diaphragm, thereby preventing internal short circuits in the battery, reducing the risk of thermal runaway, and improving the safety performance of the battery; at the same time, the synergistic combination of the binder and the fast ion conductor electrolyte in the surface modification layer is conducive to improving the dynamic performance of the battery while ensuring that the battery has a better mass energy density and a lower cost, which is conducive to industrial production.

[0012] In the present invention, there are at least two sub-modification layers, for example, two layers, three layers, or four layers.

[0013] It should be noted that the present invention does not limit the material of the negative electrode current collector. For example, it can be copper foil.

[0014] Preferably, the active material layer is a negative electrode active material layer.

[0015] It should be noted that the present invention does not limit the negative electrode active material in the negative electrode active material layer. For example, it can be graphite, hard carbon, silicon oxide or silicon carbon.

[0016] Preferably, the number of layers of the active material layer is at least one, for example, one layer, two layers or three layers.

[0017] Preferably, the binder comprises any one of carboxymethyl cellulose, styrene-butadiene rubber, polyvinylidene fluoride, polyvinyl alcohol, polyethylene oxide, polyimide, polyacrylic acid, or polyether, or a combination of at least two thereof. For example, the polyacrylic acid may be polyacrylic acid or sodium polyacrylate, and the polyether may be polyethersulfone or polyethylene oxide.

[0018] Preferably, the fast ion conductor electrolyte includes an oxide solid electrolyte and / or a sulfide solid electrolyte. For example, the oxide solid electrolyte may be LLZO (lithium lanthanum zirconium oxide) or LLTO (lithium lanthanum titanium oxide), and the sulfide solid electrolyte may be Li 10 GeP2S 12 Or Li6PS5Cl, etc.

[0019] Preferably, the content of the fast ion conductor electrolyte in the sub-modification layer decreases gradually in a direction away from the current collector.

[0020] In the present invention, the content of the fast ion conductor electrolyte in the sub-modification layer is limited to meet the above-mentioned variation trend, which is beneficial to improving the dynamic performance of the battery while ensuring that the battery has a better mass energy density and a lower cost.

[0021] Preferably, each of the sub-modification layers further comprises an inorganic material.

[0022] Preferably, the inorganic material includes any one or a combination of at least two of boehmite, aluminum oxide, silicon nitride, silicon carbide, silicon oxide, zirconium oxide, magnesium oxide, titanium oxide, cerium oxide, barium titanate, lithium titanium phosphate or lithium aluminate.

[0023] Preferably, in the surface modification layer, the content of the inorganic material in the sub-modification layer increases gradually in a direction away from the current collector.

[0024] In the present invention, the content change trend of the inorganic material in the sub-modification layer is limited. On the one hand, it is beneficial to allow the electrolyte to infiltrate the sub-modification layer close to the active material layer, improve the wetting state of the electrode, and improve the structural stability between the electrode and the diaphragm, reducing the loss of active materials caused by peeling or falling off of the active materials, thereby improving the overall performance of the battery. On the other hand, it is beneficial to allow inorganic materials with a higher mass fraction to be close to the diaphragm, thereby improving the diaphragm's resistance to heat shrinkage and improving the safety performance of the battery.

[0025] Preferably, the surface modification layer includes two sub-modification layers, which are sequentially denoted as a first sub-modification layer and a second sub-modification layer along a direction away from the current collector.

[0026] Preferably, the first sub-modified layer comprises the following components in terms of mass percentage:

[0027] Binder 0.4-100%, for example, it can be 0.4%, 1%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or 99.9%, fast ion conductor electrolyte 0.1-8%, for example, it can be 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7% or 8%, inorganic material 0.5-99.5%, for example, it can be 0.5%, 1%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or 99.5%, etc.

[0028] Preferably, the second sub-modified layer comprises the following components in terms of mass percentage:

[0029] Binder 0.4-100%, for example, it can be 0.4%, 1%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or 99.9%, fast ion conductor electrolyte 0.1-8%, for example, it can be 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7% or 8%, inorganic material 0.5-99.5%, for example, it can be 0.5%, 1%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or 99.5%, etc.

[0030] Preferably, the first sub-modified layer comprises the following components in terms of mass percentage:

[0031] Binder 85-90%, for example, it can be 85%, 87.5%, 90%, 92.5%, 95%, 97.5%, 99% or 99.6%, etc., inorganic material 8-11%, for example, it can be 8%, 9%, 10% or 11%, etc., fast ion conductor electrolyte 2-4%, for example, it can be 2%, 2.5%, 3%, 3.5% or 4%, etc.

[0032] Preferably, the second sub-modified layer comprises the following components in terms of mass percentage:

[0033] Binder 0.3-8%, for example, it can be 0.3%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7% or 8%, etc., inorganic material 91-99.5%, for example, it can be 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99%, etc., fast ion conductor electrolyte 0.2-1%, for example, it can be 0.2%, 0.4%, 0.6%, 0.8% or 1%, etc.

[0034] Preferably, the first sub-modified layer and the second sub-modified layer are independently distributed in a continuous distribution or an intermittent distribution.

[0035] Preferably, the intermittent distribution includes any one of strip distribution, point-like distribution, polygonal distribution or irregular distribution, or a combination of at least two of them, preferably strip distribution.

[0036] It should be noted that the present invention does not limit the angle between the extension direction of the strip-shaped sub-modification layer and the length direction of the active material layer. For example, it can be equal to 90°, between 0-90°, or equal to 0.

[0037] Preferably, in the strip distribution, the width of the strip-shaped sub-decoration layer is 3-12 mm, for example, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, 11 mm or 12 mm.

[0038] In the present invention, the appropriate width is conducive to ensuring that the adhesive layer has a relatively appropriate coverage rate on the electrode, thereby improving the overall wetting state of the electrode, and then improving the overall performance of the battery, and reducing the path between the electrode-diaphragm-electrode sheet, improving the dynamic performance of the battery, and reducing the cost of the battery.

[0039] Preferably, in the strip distribution, the interval width between adjacent strip-shaped sub-decoration layers is 2-10 mm, for example, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm or 10 mm.

[0040] Preferably, the first sub-modification layer is distributed in an intermittent manner, and the second sub-modification layer is distributed in a continuous manner.

[0041] In the present invention, the first sub-modification layer adopts an intermittent distribution method, which helps to improve the wetting state of the electrolyte on the electrode and shorten the diffusion path of lithium ions, thereby improving the cycle performance and rate performance of the battery; the second sub-modification layer adopts a continuous distribution method, which helps to improve the heat shrinkage resistance of the diaphragm, thereby improving the safety of the battery.

[0042] Preferably, the coverage of the first sub-modification layer is 30-70%, for example, 30%, 40%, 50%, 60% or 70%.

[0043] It should be noted that the coverage refers to the area ratio of the first sub-modification layer covering the bottom active material layer.

[0044] In the present invention, an appropriate coverage rate is beneficial to the wetting state of the electrode in the battery. A good wetting state is beneficial to enhancing ion conduction, improving the dynamic performance of the battery, and maintaining the structural stability of the battery. At the same time, it can avoid excessive coverage of the active material layer by the binder, thereby affecting the dynamic performance of the battery, and at the same time can reduce the cost of the battery while ensuring the battery performance.

[0045] Preferably, the thickness of the first sub-modification layer is 0-10 μm, for example, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm, etc., preferably 0-5 μm.

[0046] Preferably, the thickness of the second sub-modification layer is 0-10 μm, for example, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm, etc., preferably 0-5 μm.

[0047] In the present invention, the appropriate thickness of the first sub-modification layer is beneficial to reducing the probability of the adhesive blocking the electrode or the diaphragm pores while ensuring the improvement of the electrode infiltration state, thereby improving the battery dynamics performance; the appropriate thickness of the second sub-modification layer is beneficial to ensuring that the diaphragm side has a higher porosity and reducing the overall cost of the battery while improving the diaphragm's resistance to thermal shrinkage, thereby improving the battery safety performance, which is beneficial to the industrialization of the battery.

[0048] Preferably, the modified negative electrode plate further includes a tab, and the tab is connected to the edge of the current collector.

[0049] In a second aspect, the present invention provides a battery comprising the modified negative electrode sheet as described in the first aspect.

[0050] For example, the battery may be a soft-pack battery, a square-shell battery, a special-shaped battery, or a cylindrical battery.

[0051] In a third aspect, the present invention provides a battery system, comprising the battery as described in the second aspect.

[0052] The numerical range described in the present invention includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0053] Compared with the prior art, the present invention has the following beneficial effects:

[0054] In the modified negative electrode plate provided by the present invention, a surface modification layer containing a binder and a fast ion conductor electrolyte is arranged on the outer surface of the active material layer, and includes at least two sub-modification layers, wherein the content of the binder in the sub-modification layer decreases in the direction away from the negative electrode current collector. This change trend can improve the wetting state of the plate in the battery. A good wetting state is conducive to enhancing ion conduction, enhancing ion conduction, optimizing the rate performance of the battery, and maintaining the structural stability of the active material layer on the plate, avoiding problems such as the coating falling or peeling, reducing the loss of active material, extending the service life of the battery, and optimizing the cycle performance of the battery. In addition, it helps to improve the heat shrinkage resistance of the diaphragm, avoid direct contact between the positive and negative electrodes due to the shrinkage of the diaphragm, thereby preventing internal short circuits in the battery, reducing the risk of thermal runaway, and improving the safety performance of the battery; at the same time, the synergistic combination of the binder and the fast ion conductor electrolyte in the surface modification layer is conducive to improving the dynamic performance of the battery while ensuring that the battery has a better mass energy density and a lower cost, which is conducive to industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 This is a schematic top view of the modified negative electrode sheet provided in Example 1 of the present invention.

[0056] Figure 2 This is a schematic cross-sectional view of the modified negative electrode sheet provided in Example 1 of the present invention.

[0057] Figure 3 This is a schematic top view of the modified negative electrode sheet provided in Example 4 of the present invention.

[0058] Figure 4 This is a schematic top view of the modified negative electrode sheet provided in Example 5 of the present invention.

[0059] Figure 5 This is a schematic top view of the modified negative electrode sheet provided in Example 6 of the present invention.

[0060] Among them, 1-negative electrode current collector; 2-negative electrode active material layer; 3-surface modification layer; 31-first sub-modification layer; 32-second sub-modification layer; 4-electrode tab. DETAILED DESCRIPTION

[0061] 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.

[0062] Example 1

[0063] This embodiment provides a modified negative electrode sheet, the top view and cross-sectional view of which are as follows: Figure 1 and Figure 2 As shown, the modified negative electrode plate includes:

[0064] Negative electrode current collector 1.

[0065] The modified active material layer is disposed on both side surfaces of the negative electrode current collector 1 .

[0066] The modified active material layer includes a negative electrode active material layer 2 and a surface modification layer 3 stacked in a direction away from the negative electrode current collector 1 .

[0067] The negative electrode current collector 1 is copper foil; the negative electrode active material layer 2 has one layer, and the materials of the negative electrode active material layer 2 include a negative electrode active material, a conductive agent and a binder. The negative electrode active material is graphite, the conductive agent is conductive carbon black, and the binder includes sodium carboxymethyl cellulose and styrene-butadiene rubber in a mass ratio of 1:1.

[0068] The materials in the surface modification layer 3 include a binder, a fast ion conductor electrolyte and an inorganic material. The binder is carboxymethyl cellulose, the inorganic material is aluminum oxide, and the fast ion conductor electrolyte is Li 10 GeP2S 12 .

[0069] The surface modification layer 3 includes a first sub-modification layer 31 and a second sub-modification layer 32 stacked in a direction away from the negative electrode current collector 1, wherein the first sub-modification layer 31 includes the following components in mass percentage: 88% binder, 9% inorganic material, and 3% fast ion conductor electrolyte; the second sub-modification layer 32 includes the following components in mass percentage: 4% binder, 95.4% inorganic material, and 0.6% fast ion conductor electrolyte.

[0070] The first sub-modification layer 31 and the second sub-modification layer 32 are distributed in the same intermittent distribution, which is a strip distribution. The angle between the extension direction of the strip sub-modification layer and the length direction of the negative electrode active material layer 2 is between 0-90°; the width of each strip sub-modification layer is 5 mm, and the interval width between adjacent strip sub-modification layers is 8 mm; the coverage of the first sub-modification layer 31 is 38.5%, the thickness of the first sub-modification layer 31 is 1.5 μm, and the thickness of the second sub-modification layer 32 is 3 μm.

[0071] The modified negative electrode plate further includes a tab 4 , which is connected to the edge of the negative electrode current collector 1 .

[0072] This embodiment also provides a method for preparing the modified negative electrode sheet, which comprises the following steps:

[0073] (1) Graphite, conductive carbon black, sodium carboxymethyl cellulose, and styrene-butadiene rubber are mixed in a mass fraction ratio of 95%:1.5%:1.5%:2% to prepare a negative electrode slurry, the negative electrode slurry is coated on both surfaces of a negative electrode current collector, and the negative electrode active material layer is formed after drying; wherein the edge side of the negative electrode current collector is connected to a tab.

[0074] (2) Carboxymethyl cellulose, aluminum oxide and fast ion conductor electrolyte were added to N-methyl pyrrolidone in a mass ratio of 88:9:3 and mixed evenly to obtain the preparation material of the first sub-modification layer; carboxymethyl cellulose, aluminum oxide and fast ion conductor electrolyte were added to N-methyl pyrrolidone in a mass ratio of 4:95.4:0.6 and mixed evenly to obtain the preparation material of the second sub-modification layer.

[0075] The slit coating method is used to intermittently coat the preparation material of the first sub-modification layer on the outer surface of the negative electrode active material layer, and after drying, a first sub-modification layer with a thickness of 1.5 μm is obtained; the slit coating method is used to intermittently coat the preparation material of the second sub-modification layer on the outer surface of the first sub-modification layer, and after drying, a second sub-modification layer with a thickness of 3 μm is obtained, and finally the modified negative electrode sheet is obtained.

[0076] Example 2

[0077] This embodiment provides a modified negative electrode plate, the modified negative electrode plate comprising:

[0078] Negative electrode current collector.

[0079] A modified active material layer is provided on both side surfaces of the negative electrode current collector.

[0080] The modified active material layer includes a negative electrode active material layer and a surface modification layer stacked in a direction away from the negative electrode current collector.

[0081] The negative electrode current collector is copper foil, the number of layers of the negative electrode active material layer is one, and the materials of the negative electrode active material layer include a negative electrode active material, a conductive agent and a binder. The negative electrode active material is graphite, the conductive agent is conductive carbon, and the binder includes sodium carboxymethyl cellulose and styrene-butadiene rubber in a mass ratio of 1:1.

[0082] The materials in the surface modification layer include a binder, a fast ion conductor electrolyte and an inorganic material, wherein the binder is carboxymethyl cellulose, the inorganic material is silicon nitride, and the fast ion conductor electrolyte is Li 10 GeP2S 12 .

[0083] The surface modification layer includes a first sub-modification layer and a second sub-modification layer stacked in a direction away from the negative electrode current collector, wherein the first sub-modification layer includes the following components in mass percentage: 85% binder, 11% inorganic material, and 4% fast ion conductor electrolyte; the second sub-modification layer includes the following components in mass percentage: 0.3% binder, 99.5% inorganic material, and 0.2% fast ion conductor electrolyte.

[0084] The distribution mode of the first sub-modification layer and the second sub-modification layer are the same intermittent distribution, and the intermittent distribution is a strip distribution. The angle between the extension direction of the strip sub-modification layer and the length direction of the negative electrode active material layer is between 0-90°; the width of each strip sub-modification layer is 3mm, and the interval width between adjacent strip sub-modification layers is 2mm; the coverage of the first sub-modification layer is 60%, the thickness of the first sub-modification layer is 1μm, and the thickness of the second sub-modification layer is 2μm.

[0085] The modified negative electrode plate further includes a tab connected to an edge of the negative electrode current collector.

[0086] This embodiment also provides a method for preparing the modified negative electrode sheet, which comprises the following steps:

[0087] (1) Graphite, conductive carbon black, sodium carboxymethyl cellulose, and styrene-butadiene rubber are mixed in a mass fraction ratio of 95%:1.5%:1.5%:2% to prepare a negative electrode slurry, the negative electrode slurry is coated on both surfaces of a negative electrode current collector, and the negative electrode active material layer is formed after drying; wherein the edge side of the negative electrode current collector is connected to a tab.

[0088] (2) Carboxymethyl cellulose, silicon nitride and fast ion conductor electrolyte were added to N-methyl pyrrolidone in a mass ratio of 85:11:4 and mixed evenly to obtain the preparation material of the first sub-modification layer; carboxymethyl cellulose, silicon nitride and fast ion conductor electrolyte were added to N-methyl pyrrolidone in a mass ratio of 0.3:99.5:0.2 and mixed evenly to obtain the preparation material of the second sub-modification layer.

[0089] The slit coating method is used to intermittently coat the preparation material of the first sub-modification layer on the outer surface of the negative electrode active material layer, and after drying, a first sub-modification layer with a thickness of 1 μm is obtained; the slit coating method is used to intermittently coat the preparation material of the second sub-modification layer on the outer surface of the first sub-modification layer, and after drying, a second sub-modification layer with a thickness of 2 μm is obtained, and finally the modified negative electrode sheet is obtained.

[0090] Example 3

[0091] This embodiment provides a modified negative electrode plate, the modified negative electrode plate comprising:

[0092] Negative electrode current collector.

[0093] A modified active material layer is provided on both side surfaces of the negative electrode current collector.

[0094] The modified active material layer includes a negative electrode active material layer and a surface modification layer stacked in a direction away from the negative electrode current collector.

[0095] The negative electrode current collector is copper foil, the number of layers of the negative electrode active material layer is one, and the materials of the negative electrode active material layer include a negative electrode active material, a conductive agent and a binder. The negative electrode active material is graphite, the conductive agent is conductive carbon, and the binder includes sodium carboxymethyl cellulose and styrene-butadiene rubber in a mass ratio of 1:1.

[0096] The materials in the surface modification layer include a binder, a fast ion conductor electrolyte and an inorganic material, wherein the binder is carboxymethyl cellulose, the inorganic material is titanium oxide, and the fast ion conductor electrolyte is Li 10 GeP2S 12 .

[0097] The surface modification layer includes a first sub-modification layer and a second sub-modification layer stacked in a direction away from the negative electrode current collector, wherein the first sub-modification layer includes the following components in mass percentage: 90% binder, 8% inorganic material, and 2% fast ion conductor electrolyte; the second sub-modification layer includes the following components in mass percentage: 8% binder, 91% inorganic material, and 1% fast ion conductor electrolyte.

[0098] The distribution mode of the first sub-modification layer and the second sub-modification layer are both the same intermittent distribution, and the intermittent distribution is a strip distribution. The angle between the extension direction of the strip sub-modification layer and the length direction of the negative electrode active material layer is between 0-90°; the width of each strip sub-modification layer is 12 mm, and the interval width between adjacent strip sub-modification layers is 10 mm; the coverage of the first sub-modification layer is 54.5%, the thickness of the first sub-modification layer is 2 μm, and the thickness of the second sub-modification layer is 1 μm.

[0099] The modified negative electrode plate further includes a tab connected to an edge of the negative electrode current collector.

[0100] This embodiment also provides a method for preparing the modified negative electrode sheet, which comprises the following steps:

[0101] (1) Graphite, conductive carbon black, sodium carboxymethyl cellulose, and styrene-butadiene rubber are mixed in a mass fraction ratio of 95%:1.5%:1.5%:2% to prepare a negative electrode slurry, the negative electrode slurry is coated on both surfaces of a negative electrode current collector, and the negative electrode active material layer is formed after drying; wherein the edge side of the negative electrode current collector is connected to a tab.

[0102] (2) Carboxymethyl cellulose, titanium oxide and fast ion conductor electrolyte are added to N-methyl pyrrolidone in a mass ratio of 90:8:2 and mixed evenly to obtain a preparation material for the first sub-modification layer; carboxymethyl cellulose, titanium oxide and fast ion conductor electrolyte are added to N-methyl pyrrolidone in a mass ratio of 8:91:1 and mixed evenly to obtain a preparation material for the second sub-modification layer.

[0103] The slit coating method is used to intermittently coat the preparation material of the first sub-modification layer on the outer surface of the negative electrode active material layer, and after drying, a first sub-modification layer with a thickness of 2 μm is obtained; the slit coating method is used to intermittently coat the preparation material of the second sub-modification layer on the outer surface of the first sub-modification layer, and after drying, a second sub-modification layer with a thickness of 1 μm is obtained, and finally the modified negative electrode sheet is obtained.

[0104] Example 4

[0105] The difference between this embodiment and embodiment 1 is that the angle between the extension direction of the strip-shaped sub-modification layer and the length direction of the negative electrode active material layer is equal to 90°.

[0106] The rest of the preparation methods and parameters remained the same as in Example 1.

[0107] Figure 3 A schematic top view of the modified negative electrode sheet provided in this embodiment is shown.

[0108] Example 5

[0109] The difference between this embodiment and embodiment 1 is that the angle between the extension direction of the strip-shaped sub-modified layer and the length direction of the negative electrode active material layer is equal to 0, and the interval width between adjacent strip-shaped sub-modified layers is 10 mm.

[0110] The rest of the preparation methods and parameters remained the same as in Example 1.

[0111] Figure 4 A schematic top view of the modified negative electrode sheet provided in this embodiment is shown.

[0112] Example 6

[0113] The difference between this embodiment and embodiment 5 is that the intermittent distribution of the second sub-modification layer is a point-like distribution.

[0114] The rest of the preparation methods and parameters remained the same as in Example 5.

[0115] Figure 5 A schematic top view of the modified negative electrode sheet provided in this embodiment is shown.

[0116] Example 7

[0117] The difference between this embodiment and embodiment 1 is that the distribution mode of the second sub-modification layer is continuous distribution, that is, the coating method of the preparation material of the second sub-modification layer in step (2) is the doctor blade coating method.

[0118] The rest of the preparation methods and parameters remained the same as in Example 1.

[0119] Example 8

[0120] The difference between this embodiment and embodiment 1 is that the width of each strip-shaped sub-decoration layer is 1 mm.

[0121] The rest of the preparation methods and parameters remained the same as in Example 1.

[0122] Example 9

[0123] The difference between this embodiment and embodiment 1 is that the width of each strip-shaped sub-decoration layer is 20 mm.

[0124] The rest of the preparation methods and parameters remained the same as in Example 1.

[0125] Example 10

[0126] The difference between this embodiment and embodiment 1 is that the coverage of the first sub-modification layer is 15%.

[0127] The rest of the preparation methods and parameters remained the same as in Example 1.

[0128] Example 11

[0129] The difference between this embodiment and embodiment 1 is that the coverage of the first sub-modification layer is 90%.

[0130] The rest of the preparation methods and parameters remained the same as in Example 1.

[0131] Example 12

[0132] The difference between this embodiment and embodiment 1 is that the first sub-modification layer includes the following components in mass percentage: 90% binder, 9.4% inorganic material, and 0.6% fast ion conductor electrolyte; the second sub-modification layer includes the following components in mass percentage: 3% binder, 95% inorganic material, and 2% fast ion conductor electrolyte.

[0133] The rest of the preparation methods and parameters remained the same as in Example 1.

[0134] Comparative Example 1

[0135] The difference between this comparative example and Example 1 is that the first sub-modification layer includes the following components in mass percentage: 90% binder and 10% inorganic material; the second sub-modification layer includes the following components in mass percentage: 90% binder and 10% inorganic material.

[0136] The rest of the preparation methods and parameters remained the same as in Example 1.

[0137] Comparative Example 2

[0138] The difference between this comparative example and Example 1 is that the first sub-modification layer includes the following components in mass percentage: 3.7% binder and 96.3% inorganic material; the second sub-modification layer includes the following components in mass percentage: 96.5% binder and 3.5% inorganic material.

[0139] Comparative Example 3

[0140] The difference between this comparative example and Example 1 is that the first sub-modified layer and the second sub-modified layer do not contain a fast ion conductor electrolyte.

[0141] The rest of the preparation methods and parameters remained the same as in Example 1.

[0142] Performance Testing

[0143] A battery is made based on the modified negative electrode sheets provided in the above embodiments and comparative examples, and the specific steps include:

[0144] To prepare the positive electrode sheet, lithium nickel cobalt manganese oxide, conductive carbon black, and polyvinylidene fluoride are mixed in a mass fraction of 96%:2%:2% through slurry mixing, coating, rolling, die cutting and other processes to prepare the positive electrode sheet; the obtained modified negative electrode sheet, the positive electrode sheet and the separator are stacked, packaged, baked, and liquid-filled to prepare a 30Ah soft-pack battery for performance testing and comparative analysis.

[0145] The above batteries were tested for cycle performance, rate performance and safety performance.

[0146] Test conditions for cycle performance: Place the prepared soft-pack battery in a high-temperature box, connect the test equipment, fully charge the battery using the constant current and constant voltage method, and fully discharge the battery using the constant current method, and continue to cycle for 600 cycles to compare the capacity retention rate of the soft-pack battery.

[0147] Test conditions for rate performance: Place the prepared soft-pack battery in a room temperature box, connect the test equipment, fully charge the battery using the constant current and constant voltage method, and discharge the battery at 1C and 10C to the cut-off voltage respectively, and calculate the battery's 10C discharge capacity retention rate.

[0148] Safety performance testing method: Place the prepared soft-pack batteries in a room temperature chamber, connect them to the test equipment, and fully charge them using the constant current and constant voltage method. Then, place the batteries in a needle penetrator and perform a needle penetration test to evaluate the needle penetration pass rate. Each group tests 10 soft-pack batteries.

[0149] The test results are shown in Table 1.

[0150] Table 1

[0151]

[0152] analyze:

[0153] As shown in Table 1, the modified negative electrode provided by the present invention can increase the battery's liquid retention, improve the battery's electrode wetting state, extend the battery's service life, and optimize the battery's cycle performance. Furthermore, it helps shorten the lithium ion transmission distance, improving the battery's rate capability; it can also enhance the thermal shrinkage resistance of the battery's separator, improving battery safety.

[0154] From the comparison between Example 1 and Example 7, it can be seen that the first sub-modification layer adopts an intermittent distribution method, which helps to improve the wetting state of the electrolyte on the electrode and shorten the diffusion path of lithium ions, thereby improving the rate performance of the battery; the second sub-modification layer adopts a continuous distribution method, which helps to improve the heat shrinkage resistance of the diaphragm, thereby improving the safety of the battery.

[0155] It can be seen from Example 1 and Examples 8-9 that if the width of each strip-shaped sub-modification layer is too small, but the intervals between the sub-modification layers are relatively large, it is not conducive to improving the rate performance, cycle performance and safety performance of the battery. This is mainly because the excessively small width of the sub-modification layer cannot effectively increase the liquid retention at the interface between the electrode and the diaphragm, improve the wetting state of the electrode, shorten the diffusion path of lithium ions, and improve the heat shrinkage resistance of the diaphragm, thereby affecting the rate performance, cycle performance and safety performance of the battery; if the width of each strip-shaped sub-modification layer is too large, although it is beneficial to improving the rate performance, cycle performance and safety performance of the battery, it will increase the amount of materials such as binders, inorganic materials and electrolytes, which is not conducive to reducing the cost of the battery.

[0156] From Example 1 and Examples 10-11, if the coverage of the sub-modification layer is too small, it will not be conducive to improving the rate performance, cycle performance and safety performance of the battery. The main reason is that the too small coverage of the sub-modification layer has limited effects on improving the electrolyte retention, improving the electrode wetting state, shortening the lithium ion diffusion path, and improving the thermal shrinkage resistance of the diaphragm; if the coverage of the sub-modification layer is too large, it will be beneficial to improving the cycle performance and safety performance of the battery, but it will not be conducive to improving the rate performance of the battery, and will significantly increase the cost of the battery.

[0157] From the comparison between Example 1 and Example 12, it can be seen that the content of the fast ion conductor electrolyte in the sub-modified layer increases in the direction away from the current collector, which is also beneficial to improving the kinetic performance and cycle performance of the battery, but the improvement is small, and the degree of improvement is not ideal compared to the increase in battery cost.

[0158] From the comparison between Example 1 and Comparative Examples 1-2, it can be seen that if the mass percentage of the binder component in the second sub-modification layer is equal to or too high as the mass percentage of the binder component in the first sub-modification layer, the heat shrinkage resistance of the diaphragm will be significantly deteriorated, and the higher liquid retention capacity will further lead to the deterioration of the battery safety performance.

[0159] From the comparison between Example 1 and Comparative Example 3, it can be seen that if the first sub-modified layer and the second sub-modified layer do not contain a fast ion conductor electrolyte, it is not conducive to improving the performance of the battery.

[0160] It should be noted that while the present invention illustrates the process method through the above-described embodiments, the present invention is not limited to the above-described process steps, and does not necessarily rely on the above-described process steps for implementation. Those skilled in the art will appreciate that any improvements to the present invention, equivalent replacements for the raw materials used, additions of auxiliary components, and selection of specific methods, etc., fall within the scope of protection and disclosure of the present invention.

Claims

1. A modified negative electrode plate, characterized in that: The modified negative electrode plate comprises: negative electrode current collector; a modified active material layer, the modified active material layer being disposed on at least one side surface of the negative electrode current collector; The modified active material layer includes an active material layer and a surface modification layer stacked in a direction away from the negative electrode current collector; the surface modification layer includes at least two sub-modification layers, each sub-modification layer includes a binder and a fast ion conductor electrolyte, and the content of the binder in the sub-modification layer decreases in a direction away from the current collector.

2. The modified negative electrode sheet according to claim 1, characterized in that: The binder comprises any one or a combination of at least two of carboxymethyl cellulose, styrene-butadiene rubber, polyvinylidene fluoride, polyvinyl alcohol, polyethylene oxide, polyimide, polyacrylic acid or polyether; Preferably, the content of the fast ion conductor electrolyte in the sub-modification layer decreases gradually in a direction away from the current collector.

3. The modified negative electrode sheet according to claim 1 or 2, characterized in that: Each of the sub-modification layers also includes an inorganic material; Preferably, the inorganic material comprises any one or a combination of at least two of boehmite, aluminum oxide, silicon nitride, silicon carbide, silicon oxide, zirconium oxide, magnesium oxide, titanium oxide, cerium oxide, barium titanate, lithium titanium phosphate or lithium aluminate; Preferably, the content of the inorganic material in the sub-modification layer increases gradually in a direction away from the current collector.

4. The modified negative electrode sheet according to any one of claims 1 to 3, characterized in that: The surface modification layer includes two sub-modification layers, which are sequentially denoted as a first sub-modification layer and a second sub-modification layer along a direction away from the current collector; Preferably, the first sub-modified layer comprises the following components in terms of mass percentage: Binder 0.4-100%, fast ion conductor electrolyte 0.1-8%, inorganic material 0.5-99.5%; Preferably, the second sub-modified layer comprises the following components in terms of mass percentage: Binder 0.4-100%, fast ion conductor electrolyte 0.1-8%, inorganic material 0.5-99.5%.

5. The modified negative electrode sheet according to claim 4, characterized in that: The first sub-modified layer comprises the following components in terms of mass percentage: Binder 85-90%, inorganic material 8-11%, fast ion conductor electrolyte 2-4%; Preferably, the second sub-modified layer comprises the following components in terms of mass percentage: Binder 0.3-8%, inorganic material 91-99.5%, fast ion conductor electrolyte 0.2-1%.

6. The modified negative electrode sheet according to claim 4 or 5, characterized in that: The distribution modes of the first sub-modified layer and the second sub-modified layer are independently continuous distribution or intermittent distribution; Preferably, the intermittent distribution includes any one of strip distribution, point-like distribution, polygonal distribution or irregular distribution, or a combination of at least two thereof, preferably strip distribution; Preferably, in the strip distribution, the width of the strip-shaped sub-decoration layer is 3-12 mm; Preferably, in the strip distribution, the interval width between adjacent strip-shaped sub-decoration layers is 2-10 mm; Preferably, the first sub-modification layer is distributed in an intermittent manner, and the second sub-modification layer is distributed in a continuous manner; Preferably, the coverage of the first sub-modification layer is 30-70%.

7. The modified negative electrode sheet according to any one of claims 4 to 6, characterized in that: The thickness of the first sub-modification layer is 0-10 μm, preferably 0-5 μm; Preferably, the thickness of the second sub-modification layer is 0-10 μm, preferably 0-5 μm.

8. The modified negative electrode sheet according to any one of claims 1 to 7, characterized in that: The modified negative electrode plate further includes a tab connected to an edge of the current collector.

9. A battery, characterized in that: The battery comprises the modified negative electrode sheet according to any one of claims 1 to 8.

10. A battery system, characterized in that: The battery system includes the battery according to claim 9.

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