A method for preparing a negative electrode sheet

Abstract

The present invention discloses a method for preparing a negative electrode sheet, comprising the following steps: using a coating machine to coat the negative electrode slurry on the front and back surfaces of a current collector to which a traction tension is applied, and then drying the current collector coated with the negative electrode slurry, sequentially undergoing a preheating drying stage, a constant speed drying stage, a speed reduction drying stage, and a balanced drying stage for drying, forming a negative electrode active layer with a raised stripe structure on the surface of the current collector after the drying, and rolling and cutting to obtain a negative electrode sheet with a double-sided raised stripe structure. The present invention controls the process parameters of the negative electrode sheet in the coating process and the drying process, in-situ coats the negative electrode sheet with stripes, reserves space for the expansion of the negative electrode sheet, reduces the expansion stress, and thereby improves the wrinkles of the electrode sheet and the expansion of the battery cell; at the same time, the stripe pattern on the surface of the electrode sheet increases the electrolyte flow channel and increases the electrolyte transmission interface area, which plays a role in improving the electrolyte infiltration.

Description

Technical Field

[0001] The invention relates to the technical field of batteries, and in particular to a method for preparing a negative electrode sheet. Background Art

[0002] Lithium-ion battery is a new type of green chemical power source. Compared with traditional nickel-cadmium battery and nickel-metal hydride battery, it has the advantages of high voltage, long life and high energy density. With the continuous updating and development of lithium battery technology, its advantages of light weight, high capacity and long life are gradually favored by consumers. However, in the process of lithium ion embedding, the active material of the negative electrode will undergo a large volume expansion (12% to 20%). During the cycle, the binder fatigues and the binding force weakens, which leads to poor contact between the negative electrode and the current collector. The volume expansion causes new active materials and new interfaces to be exposed, consuming active lithium to form a new SEI film, causing battery capacity decay.

[0003] In addition, in order to increase the energy density of the battery, the battery cell is now developing towards thick coating, high compaction density and large capacity, which is not conducive to the infiltration of the electrolyte into the electrode. The first injection volume cannot be increased, and the static time after injection becomes longer, which reduces production efficiency.

[0004] In order to improve the expansion of the battery cell and increase the electrolyte infiltration, the positive electrode plate currently adopts a dot embossing process to increase the thickness space before winding, leaving rebound space for the plate, so that the stress on the positive and negative electrode plates is relatively small, thereby improving the plate wrinkles and battery cell expansion; while due to the characteristics of materials such as graphite, the negative electrode plate will cause problems such as material falling and belt breakage when the embossing process is used. Therefore, the above method cannot be used to improve the expansion of the negative electrode plate, electrolyte infiltration and other problems. Summary of the invention

[0005] The present invention provides a method for preparing a negative electrode plate. By controlling the process parameters of the negative electrode plate in the coating process and the drying process, a striped negative electrode plate is coated in situ, and space is reserved for the expansion of the negative electrode plate, thereby reducing the expansion stress, thereby improving the plate wrinkles and battery cell expansion; at the same time, the striped pattern on the surface of the plate increases the electrolyte flow channel, thereby increasing the electrolyte transmission interface area, which plays a role in increasing the electrolyte infiltration.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0007] A first aspect of the present invention provides a method for preparing a negative electrode sheet, comprising:

[0008] An extrusion coater is used to coat the negative electrode slurry on the front and back surfaces of the current collector to which traction tension is applied, and then a drying treatment is carried out, so that the current collector coated with the negative electrode slurry is dried in sequence through a preheating drying stage, a constant speed drying stage, a speed reduction drying stage and a balanced drying stage. After the drying treatment, a negative electrode active layer with an alternate raised stripe structure is formed on the surface of the current collector, and a negative electrode sheet with a double-sided raised stripe structure is obtained by rolling and slitting.

[0009] Furthermore, the negative electrode slurry is obtained by uniformly mixing a negative electrode active material, a conductive agent, a binder, carboxymethyl cellulose and a solvent, wherein the mass ratio of the negative electrode active material to the conductive agent, the binder and the carboxymethyl cellulose is 92-96: 0.5-1.5: 1-2: 0.5-1.5.

[0010] Furthermore, the negative electrode active material can be selected from one or more of artificial graphite, natural graphite, silicon dioxide, and silicon carbon.

[0011] Furthermore, the conductive agent may be selected from one or more of conductive carbon black, carbon nanotubes, and graphene.

[0012] Furthermore, the binder may be selected from one or more of styrene-butadiene rubber and polyacrylic acid.

[0013] Furthermore, the solid content of the negative electrode slurry is preferably 45%-65%; the viscosity of the negative electrode slurry is preferably 2500-3500 Pa·s, and the fineness is <30 μm.

[0014] Furthermore, the current collector is copper foil, and the pulling tension is 40-90N; the pulling tension is controlled by an unwinding system to promote the formation of a regular raised structure of the negative electrode active layer while avoiding wrinkles on the current collector.

[0015] Furthermore, the negative electrode slurry coating speed is preferably 60-80 m / min.

[0016] Furthermore, the drying process is carried out in an oven, and the current collector coated with the negative electrode slurry is dried in sequence through a preheating drying stage, a constant speed drying stage, a speed reduction drying stage and a balanced drying stage by adjusting the oven temperature, the circulating fan frequency and the exhaust fan frequency;

[0017] The current collector coated with the negative electrode slurry in the oven is in a suspended state by regulating the traction tension, the circulation fan frequency, the exhaust fan frequency and the air inlet opening.

[0018] Furthermore, the temperature range of the oven is 70-90°C.

[0019] Furthermore, the frequency range of the circulating fan of the oven is 18-28 Hz.

[0020] Furthermore, the frequency range of the exhaust fan of the oven is 25-35 Hz.

[0021] Furthermore, the opening degree of the air inlet is 45% to 75%.

[0022] Furthermore, the drying process is carried out in a multi-section continuous oven; the multi-section continuous oven has three temperature zones distributed in sequence: low temperature section-high temperature section-low temperature section; the frequency of the circulating fan of the multi-section continuous oven first increases and then decreases with the arrangement order of the ovens.

[0023] Furthermore, the multi-section continuous oven is composed of 6 oven sections, including an upper and lower layer, and each layer is equipped with an exhaust fan; wherein, the temperature of the first and second oven sections is 70-80°C, the temperature of the third and fourth oven sections is 80-90°C, and the temperature of the fifth and sixth oven sections is 70-90°C; the frequencies of the circulating fans of each oven section are: 18-20Hz, 20-22Hz, 22-28Hz, 22-28Hz, 20-26Hz, 19-21Hz; the frequency of each exhaust fan is 25-35Hz.

[0024] The second aspect of the present invention provides a negative electrode sheet prepared by the preparation method described in the first aspect.

[0025] Furthermore, the height of the raised stripes on the surface of the negative electrode plate is 0.5-1.5 μm, and the interval between adjacent stripes is 2-3 cm.

[0026] A third aspect of the present invention provides a battery, comprising the negative electrode plate described in the second aspect.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1. The present invention sequentially subjects a current collector coated with a negative electrode slurry to a preheating drying stage, a constant speed drying stage, a speed reduction drying stage and a balanced drying stage for drying, so as to obtain a pole piece having a negative electrode active layer with an interval raised stripe structure on the surface; specifically, by regulating the traction tension of the current collector during coating, the temperature of the oven during the drying process of the pole piece, the frequency of the circulating fan, the frequency of the exhaust fan and the opening of the air inlet, the pole piece can be in a suspended state, and the pole piece fluctuates slightly under the blowing of the wind. At the same time, the pole piece sequentially undergoes preheating drying-constant speed drying-speed reduction drying and balanced drying stages, wherein the active material layer on the surface of the current collector shrinks laterally when the constant speed drying stage is transformed to the speed reduction drying stage, i.e., the rapid drying stage. At this stage, the active material layer of the pole piece completes the shaping from wet to dry, and a negative electrode active layer with a regular raised stripe structure is formed on the surface of the current collector, and a negative electrode pole piece with a double-sided raised stripe structure is obtained after rolling. The raised stripe structure formed on the surface of the negative electrode provides a reserved space for the expansion of the negative electrode, which can reduce the expansion stress and thus improve the electrode wrinkles and cell expansion; at the same time, the raised stripe structure on the electrode surface increases the flow channel of the electrolyte, thereby increasing the electrolyte transmission interface area, and thereby increasing the wetting effect of the electrolyte on the electrode.

[0029] 2. The present invention can prepare a negative electrode active layer with a regular raised stripe structure directly by controlling the process parameters during the electrode coating and drying process. No additional equipment is required, the operation is simple and the effect is excellent. It can effectively improve the wetting effect of the electrolyte on the electrode and alleviate the expansion stress of the electrode, which is beneficial to the improvement of battery production efficiency and cycle stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 A schematic diagram of the structure of a negative electrode sheet having a striped structure formed on the surface of the current collector after coating and drying;

[0031] Figure 2 A physical picture of the negative electrode sheet with a double-sided stripe structure prepared in Example 1;

[0032] Figure 3 This is a physical picture of the negative electrode sheet prepared in the comparative example;

[0033] Figure 4 This is a test diagram of the transverse thickness of the negative electrode sheet prepared in Example 1;

[0034] Figure 5 A comparison chart of the corresponding primary liquid injection volume of secondary lithium batteries manufactured using negative electrode sheets prepared in different embodiments and comparative examples; the control group in the figure corresponds to the sample comparative example, and examples 1 to 4 correspond to sample embodiments 1 to 4 respectively;

[0035] Figure 6The figures are comparison diagrams of the expansion rates of negative electrode sheets prepared in different embodiments and comparative examples after winding, formation and full charging; the control group in the figure corresponds to the sample comparative example, and Examples 1 to 4 correspond to Sample Embodiments 1 to 4, respectively. DETAILED DESCRIPTION

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art to which the present invention belongs. The terms used herein in the specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items. The term "includes" or "comprising" described in the present invention means that it may include or contain other components in addition to the components described. The term "includes" or "comprising" described in the present invention may also be replaced by the closed form "for" or "consisting of..."

[0037] As described in the background technology, in order to improve the expansion of the battery cell and increase the electrolyte infiltration effect, the positive electrode plate currently adopts a dot embossing process to increase the thickness space before winding, leaving rebound space for the plate to rebound, so that the stress on the positive and negative electrode plates is relatively small, thereby improving the plate wrinkles and battery cell expansion; however, due to the material properties of graphite and other materials, the use of an embossing process for the negative electrode plate will cause problems such as material falling off and tape breakage, so the above method cannot be used to effectively improve the problems existing in the expansion of the negative electrode plate and the electrolyte infiltration.

[0038] In order to solve the above technical problems, an embodiment of the present invention provides a method for preparing a negative electrode sheet, comprising:

[0039] An extrusion coater is used to coat the negative electrode slurry on the front and back surfaces of the current collector to which traction tension is applied, and then a drying treatment is carried out, so that the current collector coated with the negative electrode slurry is dried in sequence through a preheating drying stage, a constant speed drying stage, a speed reduction drying stage and a balanced drying stage. After the drying treatment, a negative electrode active layer with an alternate raised stripe structure is formed on the surface of the current collector, and a negative electrode sheet with a double-sided raised stripe structure is obtained by rolling and slitting.

[0040] In some preferred embodiments, the drying process is carried out in an oven, and the current collector coated with the negative electrode slurry is dried in sequence through a preheating drying stage, a constant speed drying stage, a speed reduction drying stage, and a balanced drying stage by regulating the oven temperature, the circulating fan frequency, and the exhaust fan frequency;

[0041] The current collector coated with the negative electrode slurry in the oven is in a suspended state by regulating the traction tension, the circulation fan frequency, the exhaust fan frequency and the air inlet opening.

[0042] The present invention performs drying treatment by sequentially subjecting a current collector coated with a negative electrode slurry to a preheating drying stage, a constant speed drying stage, a speed reduction drying stage and a balanced drying stage, so as to obtain a pole piece having a negative electrode active layer with an interval raised stripe structure on the surface; specifically, the pole piece to be dried is sequentially subjected to the preheating drying stage, the constant speed drying stage, the speed reduction drying stage and the balanced drying stage by regulating the oven temperature, the circulation fan frequency and the exhaust fan frequency, and the pole piece is placed in a suspended state by reducing the traction tension of the pole piece, increasing the oven wind frequency and increasing the lower air inlet opening, and the pole piece fluctuates slightly under the blowing of the wind, and when the active material layer on the surface of the current collector is transformed from the constant speed drying stage to the speed reduction drying stage, that is, the rapid drying stage, the active material layer on the surface of the current collector will shrink laterally, and in this stage, the active material layer of the pole piece completes the shaping from wet to dry, thereby forming a negative electrode active layer with a regular raised stripe structure on the surface of the current collector, and after rolling, a negative electrode pole piece with a double-sided raised stripe structure is obtained. The raised stripe structure formed on the surface of the negative electrode provides a reserved space for the expansion of the negative electrode, which can reduce the expansion stress and thus improve the electrode wrinkles and cell expansion; at the same time, the raised stripe structure on the electrode surface increases the flow channel of the electrolyte, thereby increasing the electrolyte transmission interface area, and thus increasing the wetting effect of the electrolyte on the electrode.

[0043] In some preferred embodiments, the temperature range of the oven is preferably 70-90° C., the frequency range of the circulation fan of the oven is preferably 18-28 Hz, the frequency range of the exhaust fan of the oven is 30-35 Hz, and the opening of the air inlet is 45% to 75%.

[0044] In some preferred embodiments, the negative electrode slurry is obtained by uniformly mixing the negative electrode active material, the conductive agent, the binder, the carboxymethyl cellulose and the solvent; wherein the negative electrode active material can be selected from one or more of artificial graphite, natural graphite, silicon dioxide, silicon carbon, the conductive agent can be selected from one or more of conductive carbon black, carbon nanotubes, graphene, and the binder can be selected from one or more of styrene-butadiene rubber and polyacrylic acid; more preferably, the mass ratio of the negative electrode active material to the conductive agent, the binder and the carboxymethyl cellulose in the negative electrode slurry is preferably 92-96: 0.5-1.5: 1-2: 0.5-1.5. The present invention preferably adds a certain amount of carboxymethyl cellulose to the negative electrode slurry to prevent the sedimentation of the negative electrode material particles and ensure the stability of the viscosity, thereby ensuring the stability of the negative electrode slurry.

[0045] In some preferred embodiments, the solid content of the negative electrode slurry is preferably 45%-65%, for example, 45%, 50%, 55%, 60%, 65%, etc., including but not limited to the solid content values ​​listed above; the viscosity of the negative electrode slurry is preferably 2500-3500 Pa·s, more preferably 3000-3500 Pa·s, for example, 3000Pa·s, 3100Pa·s, 3200Pa·s, 3300Pa·s, 3400Pa·s, 3500Pa·s, etc., including but not limited to the viscosity values ​​listed above; the fineness of the negative electrode slurry is <30μm.

[0046] In some preferred embodiments, the current collector may be a copper foil, and the traction tension applied to the current collector is preferably 40-90 N. The wet slurry on the current collector will have a tendency to shrink in volume during the drying process, and reducing the tension to relax the copper foil a little is conducive to the formation of vertical stripes; but the tension should not be too small, otherwise the current collector will have wrinkles, so the present invention promotes the formation of the convex structure on the surface of the negative electrode active layer by appropriately reducing the traction tension of the current collector.

[0047] In some preferred embodiments, the coating speed of the negative electrode slurry is preferably 60-80 m / min, for example 60 m / min, 65 m / min, 70 m / min, 75 m / min, 80 m / min, etc., including but not limited to the coating speeds listed above.

[0048] In some preferred embodiments, the drying process is carried out in a multi-section continuous oven. During the drying process, the multi-section continuous oven has three temperature zones, namely, a low temperature section, a high temperature section, and a low temperature section, and the frequency of the circulating fan of the multi-section continuous oven first increases and then decreases with the arrangement order of the ovens.

[0049] Specifically, the multi-section continuous oven is composed of 6 oven sections, including an upper and lower layer, and each layer is equipped with an exhaust fan; wherein, the temperature of the first and second oven sections is 70-80°C, the temperature of the third and fourth oven sections is 80-90°C, and the temperature of the fifth and sixth oven sections is 70-90°C; the frequencies of the circulating fans of each oven section are: 18-20Hz, 20-22Hz, 22-28Hz, 22-28Hz, 20-26Hz, 19-21Hz; the frequency of each exhaust fan is 25-35Hz respectively.

[0050] In some preferred embodiments, the opening of the air inlet is 45% to 60%. The dried electrode is kept in a suspended state by adjusting the wind frequency and the opening of the air inlet, and the slurry layer does not rub against the oven air inlet.

[0051] The embodiment of the present invention also provides a negative electrode plate prepared by the above preparation method, which has a double-sided raised stripe structure.

[0052] In some preferred embodiments, the height of the raised stripes on the surface of the negative electrode plate is 0.5-1.5 μm, and the interval between adjacent stripes is 2-3 cm.

[0053] In addition, an embodiment of the present invention provides a battery comprising the above-mentioned negative electrode plate.

[0054] In some preferred embodiments of the present invention, the above-mentioned secondary battery comprises a positive electrode plate, a negative electrode plate, a separator and an electrolyte; wherein the positive electrode active material in the positive electrode plate may be one or more of lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese oxide, lithium iron phosphate, lithium cobalt oxide, and lithium manganese oxide; the isolation membrane may be a polymer organic separator of at least one of polyethylene, polypropylene, polyacrylonitrile, polyvinyl alcohol, and polyvinylidene fluoride.

[0055] The present invention is further described below in conjunction with specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0056] Example 1

[0057] This embodiment relates to the preparation of a negative electrode sheet, comprising the following steps:

[0058] (1) 96 parts of artificial graphite, a negative electrode active material, 1 part of conductive carbon black, 2 parts of styrene-butadiene rubber, and 1 part of carboxymethyl cellulose were placed in a stirrer and stirred with water to prepare a negative electrode slurry having a solid content of 55%, a viscosity of 3500 Pa.s, and a fineness of 25 μm;

[0059] (2) The negative electrode slurry prepared in step (1) is coated onto the front and back surfaces of the current collector with traction tension by an extrusion coater, and then dried in an oven, and rolled and cut to obtain negative electrode sheets.

[0060] During the coating process of this embodiment: the coating speed is 70m / min, and the pulling tension is 55N;

[0061] In this embodiment, the coated electrode is dried through 6 continuous ovens (including 6 circulating fans, 1 in each oven; the continuous oven includes upper and lower layers, each layer is provided with 1 exhaust fan). The temperature of each oven, the frequency of the circulating fan and the frequency of the exhaust fan are shown in the following table:

[0062]

[0063]

[0064] The actual picture of the negative electrode sheet prepared in this embodiment is as follows Figure 2The lateral thickness of the negative electrode sheet after rolling in this embodiment was tested by scanning from left to right using a laser thickness gauge, and 50 locations were selected in sequence to measure the thickness. The test results are shown in FIG. Figure 4 As shown, the thickness of the pole piece fluctuates regularly along the lateral direction, which is consistent with the raised stripe structure formed on the surface of the pole piece. It can be seen that a regular channel structure can be formed on the surface of the pole piece by the above preparation method.

[0065] Example 2

[0066] This embodiment relates to the preparation of a negative electrode sheet, and the only difference from Embodiment 1 is that the viscosity of the negative electrode slurry is different. The viscosity of the negative electrode slurry prepared in this embodiment is 2500 Pa·s. The other operations are the same, and a negative electrode sheet with a double-sided raised stripe structure is prepared.

[0067] Example 3

[0068] This embodiment relates to the preparation of a negative electrode sheet, and the only difference from the embodiment 1 is that the oven temperature is set differently, as shown in the following table:

[0069]

[0070] The remaining operations are the same, and a negative electrode sheet with a double-sided raised stripe structure is prepared.

[0071] Example 4

[0072] This embodiment relates to the preparation of a negative electrode sheet, and the only difference from Embodiment 1 is that the frequency setting of the oven circulation fan is different, as shown in the following table:

[0073]

[0074] Comparative Example

[0075] This comparative example relates to the preparation of a negative electrode sheet, which differs from Example 1 in the following aspects:

[0076] Traction tension during coating: The traction tension during coating of this comparative example is 70N;

[0077] The temperature of the oven, the frequency of the circulation fan and the frequency of the exhaust fan during the drying process are shown in the following table:

[0078]

[0079] Compared with Examples 1 to 4, in this comparative example, the frequency of the circulating fan is reduced in the first three sections of the oven, and a smaller air inlet opening is used in the last section of the oven. The electrode to be dried falls on the roller during the drying process and is not in a suspended state. Due to the contact friction between the roller and the electrode, the lateral shrinkage of the active material layer during the drying process is reduced, thereby preparing the following Figure 3 The electrode sheet shown has a flat surface and no protruding structure. The transverse thickness of the negative electrode sheet after rolling in this comparative example was tested by scanning from left to right using a laser thickness gauge, and 50 locations were selected in sequence to measure the thickness. The test results are shown in Figure 1. Figure 4 As shown, the thickness of the pole piece is relatively consistent, without regular fluctuations.

[0080] Performance Testing

[0081] The negative electrode sheets prepared in the above embodiments and comparative examples were used to construct lithium-ion secondary batteries, and the amount of liquid injected once when different negative electrode sheets were used to construct lithium-ion secondary batteries was tested, as well as the expansion rate of the negative electrode sheets after winding, formation or full charging.

[0082] The preparation process of lithium-ion secondary batteries is as follows:

[0083] (1) Preparation of positive electrode sheet: positive electrode active material (lithium iron phosphate), conductive agent (conductive carbon black), binder (polyvinylidene fluoride) and NMP are mixed in a mass ratio of (97:1:2) to prepare positive electrode slurry, which is then coated on positive electrode current collector aluminum foil and dried, rolled, cut into pieces, and slit into strips to prepare positive electrode sheets;

[0084] (2) The positive electrode sheet, separator (using 14 μm polypropylene separator) and negative electrode sheet are wound into a bare cell, the bare cell is placed in a battery case, dried to remove moisture, and the electrolyte is injected into the battery case. The amount of electrolyte injected when the battery is filled for the first time is recorded, as shown in Table 1 below:

[0085] Table 1

[0086] Sample One injection volume Increase percentage Example 1 1060 6.0％ Example 2 1010 1.0％ Example 3 1031 3.1％ Example 4 1043 4.3％ Comparative Example 1000 0％

[0087] The percentage increase in the table is the ratio of the difference between the one-time injection amount of the embodiment and the comparative example to the one-time injection amount of the comparative example.

[0088] After the electrolyte is injected, the lithium-ion secondary battery is packaged and the expansion rate of the negative electrode sheet of the lithium-ion secondary battery constructed with the above different negative electrode sheets is tested after formation and the first full charge.

[0089] Formation conditions: (0.1C constant current charging for 7 minutes; standing for 3 minutes; 0.16C constant current charging for 120 minutes)

[0090] Full charge conditions: (0.33C constant current and constant voltage charging to 3.65V, cut-off current 0.05C; stand for 5 minutes;).

[0091] The test results are shown in Table 2 below:

[0092] Table 2

[0093]

[0094]

[0095] It can be seen from Tables 1 and 2 that the negative electrode plates with double-sided raised stripe structures prepared in Examples 1-4 have higher liquid injection volumes and lower expansion rates after formation and full charging. It is speculated that this is because the raised stripe structure formed on the surface of the plate increases the flow channel of the electrolyte and increases the electrolyte transmission interface area, thereby increasing the wetting effect of the electrolyte on the plate; at the same time, the raised stripe structure on the surface provides a reserved space for the expansion of the negative electrode plate, thereby reducing the expansion rate of the negative electrode plate after formation and full charging.

[0096] The above-described embodiments are only preferred embodiments for fully illustrating the present invention, and the protection scope of the present invention is not limited thereto. Equivalent substitutions or changes made by those skilled in the art based on the present invention are within the protection scope of the present invention. The protection scope of the present invention shall be subject to the claims.

Claims

1. A method for preparing a negative electrode sheet, characterized in that: include: A coating machine is used to coat the negative electrode slurry on the front and back surfaces of the current collector to which a traction tension is applied, and then a drying treatment is performed, so that the current collector coated with the negative electrode slurry is dried in sequence through a preheating drying stage, a constant speed drying stage, a speed reduction drying stage, and a balanced drying stage, and after the drying treatment, a negative electrode active layer having an alternate convex stripe structure is formed on the surface of the current collector, and a negative electrode sheet having a double-sided convex stripe structure is obtained by rolling and slitting; The drying process is carried out in an oven, and the current collector coated with the negative electrode slurry is dried in sequence through a preheating drying stage, a constant speed drying stage, a speed reduction drying stage and a balanced drying stage by adjusting the oven temperature, the circulating fan frequency and the exhaust fan frequency; The current collector coated with the negative electrode slurry in the oven is in a suspended state by regulating the traction tension, the circulation fan frequency, the exhaust fan frequency and the air inlet opening.

2. The preparation method according to claim 1, characterized in that: The negative electrode slurry is obtained by uniformly mixing a negative electrode active material, a conductive agent, a binder, carboxymethyl cellulose and a solvent, wherein the mass ratio of the negative electrode active material to the conductive agent, the binder and the carboxymethyl cellulose is 92-96: 0.5-1.5: 1-2: 0.5-1.5; The negative electrode slurry has a solid content of 45%-65%, a viscosity of 2500-3500 Pa·s, and a fineness of < 30 μm.

3. The preparation method according to claim 1, characterized in that: The current collector is copper foil, and the pulling tension is 40-90 N; The negative electrode slurry coating speed is 60-80 m / min.

4. The preparation method according to claim 1, characterized in that: The temperature range of the oven is 70-90°C; The frequency range of the circulating fan of the oven is 18-28 Hz; The frequency range of the exhaust fan of the oven is 25-35 Hz; The opening of the air inlet is 45% to 75%.

5. The preparation method according to claim 1, characterized in that: The drying process is carried out in a multi-section continuous oven; The multi-section continuous oven has three temperature zones, which are low temperature zone, high temperature zone and low temperature zone, distributed in sequence; the frequency of the circulating fan of the multi-section continuous oven increases first and then decreases with the arrangement order of the ovens.

6. The preparation method according to claim 5, characterized in that: The multi-section continuous oven is composed of 6 sections of ovens, including upper and lower layers, each layer is equipped with an exhaust fan; Among them, the temperature of the first and second ovens is 70-80 ℃, the temperature of the third and fourth ovens is 80-90 ℃, and the temperature of the fifth and sixth ovens is 70-90 ℃; The frequencies of the circulation fans of each oven section are: 18-20 Hz, 20-22 Hz, 22-28 Hz, 22-28 Hz, 20-26Hz, 19-21 Hz; The frequency of each exhaust fan is 25-35 Hz.

7. A negative electrode plate, characterized in that: The negative electrode plate is prepared by the preparation method according to any one of claims 1 to 6.

8. The negative electrode sheet according to claim 7, characterized in that: The height of the raised stripes on the surface of the negative electrode plate is 0.5-1.5 μm, and the interval between adjacent stripes is 2-3 cm.

9. A battery, characterized in that: Contains the negative electrode sheet as described in claim 7 or 8.

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