A quick-charging negative electrode sheet, a battery cell containing the same, and a battery

Abstract

The application belongs to the technical field of batteries, and particularly relates to a fast-charging negative electrode sheet, a battery cell containing the electrode sheet and a battery. The negative electrode sheet comprises a negative electrode current collector and an active material coating on one side or both sides of the negative electrode current collector. The active material coating comprises a conventional negative electrode material strip and a fast-charging negative electrode material strip arranged continuously along the length direction of the negative electrode current collector. In the width direction of the negative electrode current collector, the conventional negative electrode material strip and the fast-charging negative electrode material strip are alternately arranged with intervals. The electrode sheet can reduce the concentration polarization and the corresponding polarization voltage of the negative electrode, improve the rate capability of the battery cell as a whole, and can well balance the energy density and the power density of the battery.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of batteries, and particularly relates to a fast-charging negative electrode sheet, a battery cell containing the electrode sheet and a battery. BACKGROUND

[0002] With the continuous development of new energy vehicles, it also promotes the rapid progress of lithium ion battery technology. Through battery material and PACK structure optimization, the cruising range of new energy vehicles has been substantially improved. The cruising range of electric vehicles has increased from 150km in the early stage to 600-800km. These improvements have made the penetration rate of new energy electric vehicles reach about 30%. However, the biggest obstacle to further improve the penetration rate of new energy electric vehicles is the fast charging problem of new energy vehicles, that is, the fast charging performance of the battery cell. As we all know, the primary factor affecting the fast charging performance of the battery cell is the negative electrode of the battery cell, because the lithium intercalation potential of the commonly used graphite negative electrode is only 0.05V-0.2V. With the increase of the charging rate, the polarization of the battery cell increases, making the negative electrode potential lower. When the negative electrode potential is lower than 0V, lithium dendrites will be formed, which will pierce the separator and cause internal short circuit, affecting the safety performance of the battery.

[0003] CN114744149A discloses a negative electrode sheet, comprising: a negative electrode current collector, a first negative electrode active material layer and a second negative electrode active material layer, the first negative electrode active material layer is located between the second negative electrode active material layer and the negative electrode current collector in the thickness direction of the negative electrode sheet; the first negative electrode active material layer comprises a first negative electrode active material; the second negative electrode active material layer comprises a second negative electrode active material. Its main improvement of fast charging performance is through the layering arrangement of the current collector / first negative electrode active material layer / second active material layer in the thickness direction of the electrode sheet, wherein the large interlayer spacing of the second active material layer is beneficial to the fast charging and conduction of lithium ions, which can improve the fast charging performance of the battery. However, because the second negative electrode active material layer is usually a hard carbon type negative electrode, its compaction density and energy density are low, which will deteriorate the energy density of the negative electrode. Moreover, this combination has no improvement on the conduction path of lithium ions. It must be obtained through multiple coating, which increases the process difficulty and cost. SUMMARY

[0004] In view of the problems in the prior art, the application provides a fast-charging negative electrode sheet, a battery cell containing the electrode sheet and a battery.

[0005] To achieve the above-mentioned purpose, the technical scheme adopted by the application is as follows:

[0006] In a first aspect, the present application provides a negative electrode sheet, which comprises a negative electrode current collector and an active material coating layer on one side or both sides of the negative electrode current collector, the active material coating layer comprising a conventional negative electrode material strip and a fast-charging negative electrode material strip arranged continuously along the length direction of the negative electrode current collector, and the conventional negative electrode material strip and the fast-charging negative electrode material strip are alternately arranged in the width direction of the negative electrode current collector.

[0007] In the above-mentioned negative electrode sheet, as a preferred embodiment, the theoretical energy density of the active material of the conventional negative electrode material strip is greater than or equal to 140 mAh / g.

[0008] The conventional negative electrode material strip of the present application refers to a strip prepared by using a conventional negative electrode active material (one or more of natural graphite, artificial graphite, silicon-based material, tin-based material), a conductive agent, and a binder to prepare a slurry, and then coating and compacting the slurry on a current collector; as a preferred embodiment, the silicon-based material comprises one or more of elemental silicon, silicon oxide, silicon-carbon, and silicon alloy; the tin-based material comprises one or more of elemental tin and tin oxide; the interlayer spacing of the natural graphite is 0.335-0.3365 nm; preferably, the interlayer spacing of the artificial graphite is 0.335-0.3365 nm.

[0009] In the above-mentioned negative electrode sheet, as a preferred embodiment, the width of each conventional negative electrode material strip is 20-300 mm; and / or, the width of each fast-charging negative electrode material strip is 1-50 mm, preferably 3-10 mm.

[0010] In the above-mentioned negative electrode sheet, as a preferred embodiment, the thickness of the active material coating layer is 50-240 μm.

[0011] In the above-mentioned negative electrode sheet, as a preferred embodiment, the number of fast-charging negative electrode material strips in the active material coating layer is 1-5, preferably 2-4; preferably, the number of conventional negative electrode material strips is 1-3.

[0012] The application sets the conventional negative electrode material strip and the fast-charging negative electrode material strip which are parallel to the long side of the current collector (i.e. continuously arranged along the length direction of the current collector) and alternately stacked along the width direction of the current collector, instead of the active material coating composed of only the conventional negative electrode material. Since the porosity of the fast-charging negative electrode material strip is higher than that of the conventional negative electrode material strip, more electrolyte can be accommodated. In addition, since the graphite negative electrode is formed by stacking multiple graphene materials, the lithium ion migration rate in the parallel graphene plane is faster, and after the conventional negative electrode material is compacted, the graphite material slips, so that the fast migration surface of most lithium ions is parallel to the current collector. At the same time, the fast-charging negative electrode material strip contains more electrolyte, and through the fast-charging negative electrode material strip, the lithium ions migrate quickly to the end of the conventional negative electrode material strip close to the current collector during fast charging, thereby reducing the concentration polarization of the negative electrode and the corresponding polarization voltage, and improving the overall rate capability of the battery cell. At the same time, the position of the fast-charging negative electrode material strip in the application is parallel to the long side (vertical direction) of the negative electrode current collector and is continuously spaced (alternately) arranged with the conventional negative electrode material strip, so that the amount of fast-charging negative electrode material with low energy density is reduced (compared to the structure of the conventional negative electrode material layer and the fast-charging negative electrode material layer stacked along the thickness direction of the pole piece in the prior art), but the arrangement of the fast-charging negative electrode strip is more conducive to the entry of lithium ions through the electrolyte of the fast-charging negative electrode strip into the conventional negative electrode material from the fast migration surface of the conventional negative electrode material, which can efficiently reduce the polarization of the negative electrode while maintaining high compaction density and energy density.

[0013] In the above negative pole piece, as a preferred embodiment, the porosity of the fast-charging negative electrode material strip is higher than that of the conventional negative electrode material strip; preferably, the difference between the porosities of the fast-charging negative electrode material strip and the conventional negative electrode material strip is greater than 3%; preferably, the porosity of the fast-charging negative electrode material strip is 25%-60%, and the porosity of the conventional negative electrode material strip is 20%-30%.

[0014] In the above negative pole piece, as a preferred embodiment, the raw material of the conventional negative electrode material strip includes negative electrode active material a, and the raw material of the fast-charging negative electrode material strip includes negative electrode active material b.

[0015] Preferably, the negative electrode active material a is one or more of natural graphite, artificial graphite, silicon-based material, and tin-based material; preferably, the silicon-based material includes one or more of elemental silicon, silicon oxide, silicon-carbon, and silicon alloy; preferably, the tin-based material includes one or more of elemental tin and tin oxide; preferably, the interlayer spacing of the natural graphite is 0.335-0.3365 nm; preferably, the interlayer spacing of the artificial graphite is 0.335-0.3365 nm.

[0016] Preferably, the negative active material b is one or more of fast-charging graphite, hard carbon, and soft carbon; preferably, the fast-charging graphite has an interlayer spacing greater than 0.3365 and less than or equal to 0.338 nm; preferably, the hard carbon has an interlayer spacing greater than 0.3365 and less than or equal to 0.420 nm; and preferably, the soft carbon has an interlayer spacing greater than 0.3365 and less than or equal to 0.420 nm.

[0017] In the negative electrode tab described above, as a preferred embodiment, the raw material of the conventional negative electrode material strip includes the negative active material a, the conductive agent, and the binder; preferably, the raw material of the conventional negative electrode material strip includes 90-98 wt% of the negative active material a, 0.5-5 wt% of the conductive agent, and 0.5-5 wt% of the binder.

[0018] In the negative electrode tab described above, as a preferred embodiment, the raw material of the fast-charging negative electrode material strip includes the negative active material b, the conductive agent, and the binder; preferably, the raw material of the fast-charging negative electrode material strip includes 90-98 wt% of the negative active material b, 0.5-5 wt% of the conductive agent, and 0.5-5 wt% of the binder.

[0019] In the negative electrode tab described above, as a preferred embodiment, the binder is a lithium ion battery binder; preferably, the binder includes one or more of SBR, CMC, PAA, PAA-Li, PAA-Na, PVA, and PVDF.

[0020] In the negative electrode tab described above, as a preferred embodiment, the conductive agent includes one or more of conductive carbon black, acetylene black, ketjen black, conductive graphite, conductive carbon fiber, carbon nanotube, graphene, metal powder, or carbon fiber.

[0021] In a second aspect, the present application provides a battery cell, which includes the negative electrode tab of the first aspect described above.

[0022] In a third aspect, the present application provides a battery, which includes the battery cell of the second aspect described above.

[0023] Compared with the prior art, the present application has at least the following beneficial effects:

[0024] 1. By providing the fast-charging negative electrode material strip, since it has a higher porosity, it can accommodate more electrolyte, so that when fast-charging, lithium ions migrate through the electrolyte accommodated by the fast-charging negative electrode material strip to the graphite of the conventional negative electrode material strip close to the current collector, reducing the concentration polarization of the negative electrode and the corresponding polarization voltage; improving the rate capability of the battery as a whole.

[0025] 2、The coating method of the application can significantly improve the electrochemical performance of the negative electrode sheet by using only a small amount of fast-charging negative electrode material, and the design is more flexible, so that the energy density of the negative electrode as a whole is higher.

[0026] 3、In addition, due to the design of the fast-charging negative electrode material strip and the high porosity of the fast-charging negative electrode material strip, the electrolyte can be infiltrated, the electrolyte infiltration time can be reduced, and the production efficiency can be improved.

[0027] 4、Compared with the traditional structure of the multilayer electrode sheet alternately stacked in the thickness direction, the negative electrode sheet provided by the application only needs to be coated once, so that the production cost can be reduced and the production efficiency can be improved. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 is a cross-sectional view of the negative electrode sheet of the application along the width direction of the electrode sheet.

[0029] Figure 2 is a top view of the negative electrode sheet of the application.

[0030] BRIEF DESCRIPTION OF DRAWINGS: 1, negative electrode current collector; 2, active material coating; 2-1, fast-charging negative electrode material strip; 2-2, conventional negative electrode material strip. DETAILED DESCRIPTION

[0031] The application is aimed at the problem of lithium precipitation in the negative electrode of a fast-charging battery, and a fast-charging negative electrode material strip is arranged in the negative electrode sheet (which can quickly migrate lithium ions released from the positive electrode during fast charging to the graphite structure inside the battery), so as to reduce concentration polarization and avoid the growth of lithium dendrites during fast charging.

[0032] In order to make the purpose, technical scheme and advantages of the application clearer, the technical scheme in the embodiments of the application will be described clearly and completely below in combination with the embodiments of the application. Those skilled in the art should understand that the embodiments are only used to help understand the application, and should not be regarded as a specific limitation on the application. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the application.

[0033] In the description of the present application, the terms "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom" and the like indicate the orientation or positional relationship shown in the drawings, which are only for the convenience of describing the present application and are not required to be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. The terms "connected", "connected", "provided" used in the present application should be understood broadly, for example, it can be fixed connection or detachable connection; it can be directly connected or indirectly connected through intermediate components; it can be wired electrical connection, wireless electrical connection or wireless communication signal connection, and the specific meaning of the above terms can be understood by those skilled in the art according to the specific circumstances.

[0034] The embodiments of the present application are implemented on the premise of the technical scheme of the present application, and detailed implementation modes and processes are given, but the protection scope of the present application is not limited to the following embodiments, and the process parameters not specified in the following embodiments are generally according to the conventional conditions.

[0035] The endpoints of the ranges and any values disclosed in the present application are not limited to the precise values stated. These ranges and values should be construed as approximately the values. For numerical ranges, the endpoints of the ranges are combined with the individual points to form new ranges, which are to be considered as specifically disclosed.

[0036] In the present application, unless otherwise specified and / or described, all the numerical values related to the amount of components are "parts by weight". The process parameters not specified in the following examples are generally according to the conventional conditions.

[0037] The specific embodiment of the present application provides a negative electrode sheet, the structural schematic diagram of which is shown in Figure 1 and Figure 2 , wherein Figure 1 is the cross-sectional view of the negative electrode sheet along the width direction of the sheet, Figure 2 is the top view of the negative electrode sheet, which comprises a negative electrode current collector 1 and an active material coating layer 2 on one side or both sides of the negative electrode current collector 1, the active material coating layer 2 is composed of a plurality of conventional negative electrode material strips 2-2 and fast-charging negative electrode material strips 2-1, wherein the conventional negative electrode material strips 2-2 and the fast-charging negative electrode material strips 2-1 are parallel to the long side (longitudinal direction) of the negative electrode current collector 1, and in the width direction of the negative electrode current collector 1, the arrangement mode of the conventional negative electrode material strips 2-2 and the fast-charging negative electrode material strips 2-1 is alternate arrangement with intervals.

[0038] Further, the width of the conventional negative material strip 2-2 is 20-300mm;

[0039] Further, the width of the fast-charging negative material strip 2-1 is 1-50mm, preferably 3-10mm;

[0040] Further, the thickness of the active material coating 2 is 50-240μm (the thickness of the active material coating 2 is also the thickness of the fast-charging negative material strip 2-1 and the conventional negative material strip 2-2);

[0041] Further, in the active material coating 2, the number of the fast-charging negative material strip 2-1 is 1-5, preferably 2-4;

[0042] Further, in the active material coating 2, the number of the conventional negative material strip 2-2 is 1-3;

[0043] Further, the porosity of the fast-charging negative material strip 2-1 is higher than that of the conventional negative material strip 2-2; preferably, the porosity of the fast-charging negative material strip 2-1 is 25%-60%, and the porosity of the conventional negative material strip 2-2 is 20%-30%.

[0044] Further, the raw material of the conventional negative material strip 2-2 includes a negative active material a, and the raw material of the fast-charging negative material strip 2-1 includes a negative active material b;

[0045] Further, the negative active material a is one or more of natural graphite, artificial graphite, silicon-based material, tin-based material; preferably, the silicon-based material includes one or more of elemental silicon, silicon oxide, silicon-carbon, silicon alloy; preferably, the tin-based material includes one or more of elemental tin, tin oxide; preferably, the interlayer spacing of the natural graphite is 0.335-0.3365nm; preferably, the interlayer spacing of the artificial graphite is 0.335-0.3365nm;

[0046] Further, the negative active material b is one or more of fast-charging graphite, hard carbon, soft carbon; preferably, the interlayer spacing of the fast-charging graphite is greater than 0.3365 and less than or equal to 0.338nm; preferably, the interlayer spacing of the hard carbon is greater than 0.3365 and less than or equal to 0.420nm; preferably, the interlayer spacing of the soft carbon is greater than 0.3365 and less than or equal to 0.420nm.

[0047] Further, the raw material of the conventional negative material strip 2-2 includes a negative active material a, a conductive agent and a binder; preferably, the raw material of the conventional negative material strip 2-2 includes 90-98wt% of the negative active material a, 0.5-5wt% of the conductive agent and 0.5-5wt% of the binder.

[0048] Further, the raw material of the fast-charging negative material strip 2-1 comprises the negative active material b, the conductive agent, and the binder; preferably, the raw material of the fast-charging negative material strip 2-1 comprises 90-98 wt% of the negative active material b, 0.5-5 wt% of the conductive agent, and 0.5-5 wt% of the binder.

[0049] Further, the binder is a lithium ion battery binder; preferably, the binder comprises one or more of SBR, CMC, PAA, PAA-Li, PAA-Na, PVA, and PVDF.

[0050] Further, the conductive agent comprises one or more of conductive carbon black, acetylene black, ketjen black, conductive graphite, conductive carbon fiber, carbon nanotube, graphene, metal powder, or carbon fiber.

[0051] The product parameters used in the embodiments of the present application are as follows:

[0052] The interlayer spacing of the natural graphite is 0.335-0.3365 nm;

[0053] The interlayer spacing of the artificial graphite is 0.335-0.3365 nm;

[0054] The interlayer spacing of the fast-charging graphite is greater than 0.3365 nm and less than or equal to 0.338 nm;

[0055] The interlayer spacing of the hard carbon is greater than 0.3365 nm and less than or equal to 0.420 nm;

[0056] The interlayer spacing of the soft carbon is greater than 0.3365 nm and less than or equal to 0.420 nm;

[0057] The calculation method of the porosity in the present application is: the porosity of the negative material on the pole piece = 1-(the cold-pressed density of the negative material on the pole piece / the average real density of the negative material) x 100%.

[0058] The technical solutions of the present application are further described in detail through the description of specific embodiments.

[0059] Embodiment 1

[0060] Preparation of the positive pole piece

[0061] The positive active material LiNi 0.8 Co 0.1 Mn 0.1O2, conductive carbon black Super-P, binder PVDF in a weight ratio of 97.6:1.3:1.1 in an N-methyl pyrrolidone (NMP) solvent system, and the positive electrode slurry is obtained by stirring with a vacuum stirrer; the positive electrode slurry is coated on both surfaces of an Al foil substrate with a thickness of 12 μm, and the coating weight is 7.5 mAh / cm 2 The positive electrode material strip is obtained by drying, cold pressing, slitting, and cutting in sequence, and the thickness of the positive electrode material strip after cold pressing is 115 μm, and the active mass density is 3.55 g / cc (the active mass density refers to the compacted density = coating weight / volume of the material).

[0062] Preparation of a negative electrode material strip

[0063] In this embodiment, the negative electrode active material a is artificial graphite.

[0064] In this embodiment, the negative electrode active material b is hard carbon.

[0065] A slurry for preparing a conventional negative electrode material strip is configured: the negative electrode active material a, conductive carbon black (conductive agent), butadiene-styrene rubber (binder), and sodium carboxymethyl cellulose (binder) are dissolved in deionized water in a weight ratio of 96.5:1:1.2:1.3, and the conventional negative electrode material strip slurry is obtained after sufficient stirring and mixing;

[0066] A slurry for preparing a fast-charging negative electrode material strip is configured: the negative electrode active material b, conductive carbon black (conductive agent), butadiene-styrene rubber (binder), and sodium carboxymethyl cellulose (binder) are dissolved in deionized water in a weight ratio of 94:3:1.6:1.4, and the fast-charging negative electrode material strip slurry is obtained after sufficient stirring and mixing;

[0067] The conventional negative electrode material strip slurry and the fast-charging negative electrode material strip slurry prepared in this embodiment are coated on one surface of a negative electrode current collector (a Cu foil with a thickness of 6 μm) by a multi-mode extrusion coater, and the negative electrode material strip with an active material layer (a conventional negative electrode material strip and a fast-charging negative electrode material strip arranged in parallel and spaced apart from each other) is obtained after drying, cold pressing, and cutting in sequence, the active material layer is composed of 2 conventional negative electrode material strips with a width of 26 mm and 3 fast-charging negative electrode material strips with a width of 3 mm, and the thickness of the negative electrode material strip after cold pressing is 160 μm, and the active mass density of the negative electrode material strip is 1.55 g / cc.

[0068] Preparation of an electrolyte

[0069] Vinyl carbonate (EC), methyl ethyl carbonate (EMC), and dimethyl carbonate (DMC) are mixed in a volume ratio of 3:3:4 to obtain an organic solvent, and then LiPF6 that is sufficiently dried is dissolved in the organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0070] Preparation of the separator film

[0071] The separator film substrate is 9 μm thick polyethylene (PE), and 3 μm aluminum oxide ceramic layers are coated on both sides of the separator film substrate, and dried.

[0072] Preparation of the lithium ion secondary battery

[0073] The positive electrode sheet, the separator film, and the negative electrode sheet prepared in this embodiment are stacked in order, with the separator film between the positive electrode sheet and the negative electrode sheet to play a separating role, and then wound to obtain a bare cell; the qualified bare cell is placed in an aluminum plastic film, dried, and then injected with electrolyte, and subjected to processes such as vacuum packaging, standing, formation, and shaping to obtain a lithium ion secondary battery, which has a capacity of about 5000 mAh.

[0074] Example 2

[0075] In this embodiment, a lithium ion secondary battery is prepared, wherein the preparation of the positive electrode sheet, the preparation of the electrolyte, the preparation of the separator film, and the preparation steps of the lithium ion secondary battery are the same as in Example 1, and the only difference is the preparation of the negative electrode sheet.

[0076] Preparation of the negative electrode sheet

[0077] In this embodiment, the negative electrode active material a is composed of 95 wt% artificial graphite and 5 wt% silicon-carbon.

[0078] In this embodiment, the negative electrode active material b is hard carbon.

[0079] A slurry for preparing a conventional negative electrode material strip is configured: the negative electrode active material a, conductive carbon black (conductive agent), butadiene rubber (binder), and sodium carboxymethyl cellulose (binder) are dissolved in deionized water in a weight ratio of 96.5:1:1.2:1.3, and the slurry is obtained after the mixture is fully stirred and mixed uniformly;

[0080] A slurry for preparing a fast-charging negative electrode material strip is configured: the negative electrode active material b, conductive carbon black (conductive agent), butadiene rubber (binder), and sodium carboxymethyl cellulose (binder) are dissolved in deionized water in a weight ratio of 94:3:1.6:1.4, and the slurry is obtained after the mixture is fully stirred and mixed uniformly;

[0081] The conventional negative electrode material strip slurry and the fast-charging negative electrode material strip slurry prepared in this example were coated on one surface of a negative electrode current collector (a Cu foil with a thickness of 6 μm) by a multi-mode extrusion coater, and the negative electrode current collector was sequentially subjected to drying, cold pressing, and cutting to obtain a negative electrode tab coated with an active material layer (the conventional negative electrode material strips and the fast-charging negative electrode material strips were arranged in parallel to the long side of the current collector and were spaced apart), the active material layer was composed of 2 conventional negative electrode material strips with a width of 26 mm and 3 fast-charging negative electrode material strips with a width of 3 mm, the thickness of the negative electrode tab after cold pressing was 140 μm, and the active mass density of the negative electrode tab was 1.55 g / cc.

[0082] In Examples 1-7, the preparation of the positive electrode tab, the preparation of the electrolyte, the preparation of the separator, and the preparation of the lithium ion secondary battery were the same, and in Examples 1-7, the active mass density of the prepared negative electrode tab was 1.55 g / cc.

[0083] The slurry formulation, porosity, number of strips, and width of the conventional negative electrode material strips and the fast-charging negative electrode material strips shown in Examples 3-7 are shown in Table 1 below.

[0084] Table 1

[0085]

[0086]

[0087] Comparative Example 1

[0088] In this comparative example, a lithium ion secondary battery was prepared, wherein the preparation of the positive electrode tab, the preparation of the electrolyte, the preparation of the separator, and the preparation steps of the lithium ion secondary battery were the same as in Example 1, and the only difference was the preparation of the negative electrode tab.

[0089] Preparation of the negative electrode tab

[0090] The negative electrode tab of this comparative example was coated only with one kind of negative electrode slurry, and the negative electrode slurry of this comparative example was the same as the conventional negative electrode material strip slurry in Example 1, and the configuration method was as follows: artificial graphite (negative electrode active material a), conductive carbon black (conductive agent), butadiene rubber (binder), and sodium carboxymethyl cellulose (binder) were dissolved in deionized water in a weight ratio of 96.5:1:1.2:1.3, and after being fully stirred and mixed uniformly, the conventional negative electrode material strip slurry was obtained.

[0091] The conventional negative electrode material strip slurry was coated on one surface of a negative electrode current collector (a Cu foil with a thickness of 6 μm), and the negative electrode current collector was sequentially subjected to drying, cold pressing, and cutting to obtain a negative electrode tab, and after cold pressing, the thickness of the negative electrode tab after cold pressing was 160 μm, and the active mass density of the negative electrode tab was 1.55 g / cc.

[0092] Comparative Example 2

[0093] In the present comparative example, a lithium ion secondary battery was prepared, wherein the preparation of the positive electrode sheet, the preparation of the electrolyte, the preparation of the separator, and the preparation steps of the lithium ion secondary battery were the same as in Example 1, with the exception that the preparation of the negative electrode sheet was different.

[0094] Preparation of the negative electrode sheet

[0095] The negative electrode sheet of the present comparative example was coated only with a negative electrode slurry, which was the same as the conventional negative electrode material strip slurry in Example 2, and the configuration method was as follows:

[0096] The negative electrode active material was composed of 95wt% artificial graphite and 5wt% silicon-carbon.

[0097] Preparation of the negative electrode slurry: the negative electrode active material (graphite 95wt% + silicon-carbon negative electrode 5wt%), conductive carbon black (conductive agent), butadiene rubber (binder), and sodium carboxymethyl cellulose (binder) were dissolved in deionized water in a weight ratio of 96.5:1:1.2:1.3, and after being thoroughly stirred and mixed uniformly, a negative electrode slurry was obtained;

[0098] The negative electrode slurry was coated on one surface of the negative electrode current collector (Cu foil with a thickness of 6μm), and after drying, cold pressing, and cutting, a negative electrode sheet was obtained. After cold pressing, the thickness of the negative electrode sheet was 140μm, and the active mass density of the negative electrode sheet was 1.55g / cc.

[0099] Comparative Example 3

[0100] In the present comparative example, a lithium ion secondary battery was prepared, wherein the preparation of the positive electrode sheet, the preparation of the electrolyte, the preparation of the separator, and the preparation steps of the lithium ion secondary battery were the same as in Example 1, with the exception that the preparation of the negative electrode sheet was different.

[0101] Preparation of the negative electrode sheet

[0102] In the present comparative example, the composition and ratio of the slurry for preparing the conventional negative electrode material strip and the slurry for preparing the fast-charging negative electrode material strip were exactly the same as in Example 2.

[0103] First, the conventional negative electrode slurry was coated on the negative electrode current collector (a Cu foil with a thickness of 6 μm) by an extrusion coater, and then the fast-charging negative electrode slurry was coated on the surface of the conventional negative electrode slurry (i.e., the conventional negative electrode material strip and the fast-charging negative electrode material strip were stacked in the thickness direction of the negative electrode sheet, and the coating weight ratio of the two slurries was the same as that of Example 2) by an extrusion coater after drying, and then the double-layer coated negative electrode sheet was obtained after drying, cold pressing, and cutting in sequence. The thickness of the negative electrode sheet after cold pressing was 145 μm. The active mass density of the negative electrode sheet was 1.55 g / cc.

[0104] Detection Example

[0105] The batteries prepared in Examples 1-7 and Comparative Examples 1-3 above were subjected to rate performance detection, and the energy density of the battery cell was calculated. The detection method of the rate performance was as follows:

[0106] 1C capacity: Under the condition of 25℃, the battery was discharged at 1C to 2.75V, rested for 1 hour, charged at 1C to 4.2V, rested for 1 hour, and finally discharged at 1C to 2.75V and the 1C discharge capacity was detected.

[0107] 2C capacity: Under the condition of 25℃, the battery was discharged at 1C to 2.75V, rested for 1 hour, charged at 2C to 4.2V, rested for 1 hour, and finally discharged at 2C to 2.75V and the 2C discharge capacity was detected.

[0108] 3C capacity: Under the condition of 25℃, the battery was discharged at 1C to 2.75V, rested for 1 hour, charged at 3C to 4.2V, rested for 1 hour, and finally discharged at 3C to 2.75V and the 3C discharge capacity was detected.

[0109] Table 2

[0110]

[0111] Finally, it should be noted that the above is only a preferred embodiment of the present application and is not intended to limit the present application. Although the present application has been described in detail with reference to the embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent replacements to some technical features, but any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A negative electrode sheet, characterized in that, The negative electrode sheet includes a negative current collector and an active material coating located on one or both sides of the negative current collector. The active material coating includes conventional negative electrode material strips and fast-charging negative electrode material strips continuously arranged along the length direction of the negative current collector. In the width direction of the negative current collector, the conventional negative electrode material strips and fast-charging negative electrode material strips are alternately arranged. The porosity of the fast-charging negative electrode material strip is higher than that of the conventional negative electrode material strip; The porosity of the fast-charging negative electrode material strip is 25%-60%; The porosity of the conventional negative electrode material strip is 20%-30%; The raw materials of the conventional negative electrode material strip include negative electrode active material a, and the raw materials of the fast-charging negative electrode material strip include negative electrode active material b; The negative electrode active material a is one or more of natural graphite and artificial graphite; The negative electrode active material b is one or more of fast-charging graphite, hard carbon, and soft carbon; The interlayer spacing of the natural graphite is 0.335-0.3365 nm; The interlayer spacing of the artificial graphite is 0.335-0.3365 nm; The interlayer spacing of the fast-charging graphite is greater than 0.3365 nm and less than or equal to 0.338 nm. The interlayer spacing of the hard carbon is greater than 0.3365 nm and less than or equal to 0.420 nm; The interlayer spacing of the soft carbon is greater than 0.3365 nm and less than or equal to 0.420 nm.

2. The negative electrode sheet as described in claim 1, characterized in that, The theoretical energy density of the active material in the conventional negative electrode strip reaches over 330 mAh / g.

3. The negative electrode sheet as described in claim 1 or 2, characterized in that, The width of each of the conventional negative electrode material strips is 20-300 mm; And / or, the width of each of the fast-charging negative electrode material strips is 1-50mm; And / or, the thickness of the active material coating is 50-240 μm; And / or, the number of fast-charging negative electrode material strips is 1-5; And / or, the number of strips in a conventional negative electrode material is 1-3; And / or, the difference in porosity between the fast-charging negative electrode material strip and the conventional negative electrode material strip is greater than 3%.

4. The negative electrode sheet as described in claim 3, characterized in that, The width of each of the fast-charging negative electrode material strips is 3-10mm; And / or, the number of fast-charging negative electrode material strips is 2-4.

5. The negative electrode sheet as described in claim 1, characterized in that, The raw materials for the conventional negative electrode material strip include negative electrode active material a, conductive agent and binder; And / or, the raw materials of the fast-charging negative electrode material strip include negative electrode active material b, conductive agent, and binder.

6. The negative electrode sheet as described in claim 5, characterized in that, The raw materials for the conventional negative electrode material strip include 90-98 wt% negative electrode active material a, 0.5-5 wt% conductive agent and 0.5-5 wt% binder; And / or, the raw materials of the fast-charging negative electrode material strip include 90-98 wt% of negative electrode active material b, 0.5-5 wt% of conductive agent and 0.5-5 wt% of binder; And / or, the adhesive is an adhesive for lithium-ion batteries; And / or, the adhesive comprises one or more of SBR, CMC, PAA, PAA-Li, PAA-Na, PVA, and PVDF; And / or, the conductive agent includes one or more of conductive carbon black, acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, carbon nanotubes, graphene, metal powder or carbon fiber.

7. A battery cell, characterized in that, The battery cell includes the negative electrode sheet as described in any one of claims 1-6.

8. A battery, characterized in that, The battery includes the cell as described in claim 7.

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