Electrode plate containing silicon negative electrode, battery and preparation method of electrode plate

Abstract

The invention discloses an electrode plate containing a silicon negative electrode, a battery and a preparation method of the electrode plate, and belongs to the field of lithium ion batteries. The electrode plate containing the silicon negative electrode comprises a current collector and further comprises a first coating arranged on the current collector and containing a silicon negative electrode and graphite negative electrode composite active material; the second coating layer is arranged on the first coating layer and only contains a graphite negative electrode single active material; the silicon negative electrode in the first coating is of a structure which is supported by a porous carbon skeleton and is embedded with nano silicon particles; the weight ratio of the silicon negative electrode to the graphite negative electrode in the first coating is 25%-100%, and the D50 particle size ratio of the silicon negative electrode to the graphite negative electrode is 50%-80%; according to the invention, the high doping amount of the silicon negative electrode can be ensured, and the influence of expansion of the silicon negative electrode after lithium intercalation on the stripping force and conductive connection of the pole piece is controlled; the compatibility of the two coatings is enhanced, the conductivity of the pure graphite negative electrode is better than that of a silicon-containing negative electrode, the fast charging capacity of the battery can be improved, and the deposition of lithium dendrites of a pole piece is avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and in particular to an electrode sheet containing a silicon negative electrode, a battery, and a method for preparing the electrode sheet. Background Art

[0002] In recent years, with the development of new energy vehicles and energy storage batteries, lithium-ion batteries have received widespread attention and experienced rapid growth. Increasingly stringent standards and requirements have led to higher demands on battery energy density and fast-charging performance. Silicon, with a capacity of up to 3579 mAh / g at room temperature, is considered the best alternative to existing commercial graphite anodes. However, due to the significant volume expansion (approximately 300%) of silicon after lithium insertion, its use as the sole anode active material can lead to significant internal stress variations in the electrode during charge and discharge. After multiple cycles, the electrode easily peels off from the current collector, increasing battery impedance and even causing battery inactivity.

[0003] There are two main approaches to solving the problem of silicon material expansion during lithiation: one is to improve the structural design of silicon materials, such as silicon oxide, silicon nanowires, silicon hollow nanospheres, silicon nanotubes, nanosilicon deposited in porous carbon (also known as new silicon carbon) and other structural forms; the other is to improve the structure of silicon-containing negative electrode sheets, including mixing silicon negative electrodes with graphite negative electrodes, optimizing the binder and conductive agent formula of silicon negative electrodes, and adopting double-layer or multi-layer coating electrode preparation technology.

[0004] Patent CN108550857A uses a gradient distribution of silicon content in the active material layer on the negative electrode plate. The middle layer uses active material with a high silicon content, and the outer layer uses active material with a low silicon content, forming a "sandwich" structure to alleviate the volume expansion of the battery cell during cycling.

[0005] Patent CN110148708A adopts a double-layer electrode design, with a bottom graphite coating close to the current collector and a silicon-containing coating away from the current collector. The silicon-containing coating contains 5wt.%-30wt.% silicon. The silicon material in the negative electrode accounts for 5% to 20% of the total active material weight of the negative electrode.

[0006] Patent CN112909262A prepares a double-layer silicon-containing negative electrode. By using the difference in the binder between the upper and lower layers, it not only ensures the adhesion between the electrode and the current collector, but also better suppresses the expansion of the silicon negative electrode, thereby improving the cycle performance of the battery.

[0007] Patent CN115000407A discloses a silicon negative electrode sheet. The binder system in the first coating layer is a CMC+PAA system that takes into account both flexibility and peel strength. The binder system in the second coating layer is a CMC+SBR system that takes into account both flexibility and inter-particle cohesion. This system provides better adhesion between active particles and effectively inhibits the expansion of silicon-based materials.

[0008] Patent CN119419217A provides a new "sandwich" negative electrode sheet structure, including a first graphite coating, a mixed coating and a second graphite coating. The average particle size of the polymer particles in the mixed coating is larger than the average particle size of the silicon; pure silicon and polymer particles are mixed between the first graphite coating and the second graphite coating, which can avoid direct contact between silicon and the negative electrode current collector, effectively inhibit the expansion and rebound of the silicon negative electrode, and improve the cycle stability while increasing the battery energy density.

[0009] The above patents can improve the expansion problem of silicon-based negative electrodes to a certain extent, but each has its own shortcomings. Either there are too many types of materials and the preparation process is complicated, which is not conducive to large-scale production; or the silicon incorporation amount is low, which makes little contribution to improving the energy density of the battery. In view of this, the present invention is specially proposed. Summary of the Invention

[0010] The purpose of the present invention is to solve the problem that the expansion of the silicon negative electrode leads to poor conductive contact between the coated negative electrode and the current collector, or even peeling and falling off, while at the same time increasing the amount of silicon negative electrode incorporated as much as possible, improving the battery energy density, and improving the battery's fast charging capability, avoiding the deposition problem of lithium dendrites in the electrode sheet. A silicon-containing negative electrode electrode sheet, a battery, and a method for preparing the electrode sheet are proposed.

[0011] In order to achieve the above object, the present invention adopts the following technical solutions:

[0012] An electrode sheet containing a silicon negative electrode, comprising a current collector and:

[0013] A first coating layer provided on the current collector and containing a composite active material of a silicon negative electrode and a graphite negative electrode;

[0014] A second coating layer is provided on the first coating layer and contains only a single active material of the graphite negative electrode;

[0015] The silicon negative electrode in the first coating has a structure supported by a porous carbon skeleton and embedded with nano-silicon particles;

[0016] The weight ratio of the silicon negative electrode to the graphite negative electrode in the first coating layer is 25%-100%, and the D50 particle size ratio of the silicon negative electrode to the graphite negative electrode is 50%-80%;

[0017] The current collector is made of carbon-coated copper foil.

[0018] Preferably, the first coating layer further comprises a conductive agent containing carbon nanotubes and a binder containing PAA, and the total weight of the conductive agent and the binder does not exceed 5% of the total weight of the first coating layer.

[0019] Furthermore, it also includes a second coating layer provided on the first coating layer and containing only a single active substance of a graphite negative electrode; the graphite negative electrode in the second coating layer is the same as the graphite negative electrode in the first coating layer, the peeling force between the second coating layer and the first coating layer is greater than the peeling force between the first coating layer and the current collector, and the surface density of the second coating layer is 10%-30% of that of the first coating layer.

[0020] Preferably, the porosity of the first coating layer is not less than 30%, the weight of the graphite negative electrode of the second coating layer accounts for not less than 96% of the overall weight of the second coating layer, and the thickness of the second coating layer is not more than 30 μm.

[0021] Preferably, the average particle size of the nano-silicon particles is 1-10 nm, the silicon content of the nano-silicon particles accounts for 45%-50% by weight of the silicon negative electrode, and the shape of the nano-silicon particles is spherical; the carbon coating layer on the carbon-coated copper foil contains carbon nanotubes, and the thickness of the carbon coating layer does not exceed 2 μm.

[0022] Preferably, the conductive agent containing carbon nanotubes on the first coating layer has 1-10 tube wall layers and a tube length of 10-50 nm; the first coating layer also contains at least one of CMC and PVA binders.

[0023] A battery comprises a positive electrode, a negative electrode, an electrolyte and a shell, wherein the negative electrode is an electrode sheet containing silicon.

[0024] A method for preparing an electrode sheet containing a silicon negative electrode comprises the following steps:

[0025] S1, preparing the first coating: mixing the silicon negative electrode material and the graphite negative electrode material to form a negative electrode active material, uniformly mixing the negative electrode active material, the conductive agent, and the binder through a double planetary slurry mixing device, and adding a thickener during this process to form a first coating slurry;

[0026] S2, preparing the second coating: uniformly mixing the graphite negative electrode material, the conductive agent, and the binder through a double planetary slurry mixing device, and adding a thickener during this process to form a second coating slurry;

[0027] S3, using a dual-die coating head extrusion coating machine to place the first coating slurry and the second coating slurry on the lower die and the upper die respectively, and apply them to the current collector at the same time; after coating one side of the current collector, the other side of the current collector is coated in the same coating method; then it is baked in an oven, rolled, and slit to finally obtain an electrode sheet containing a silicon negative electrode.

[0028] Furthermore, in the first coating layer, the ratio of the negative electrode active material components of silicon negative electrode material and graphite negative electrode material is 30%-70%; the ratio of each substance is negative electrode active material: 90-98%, conductive agent: 1-2%, binder: 1.5-3%, thickener: 0.1-1%;

[0029] In the second coating, the proportions of the various substances are: negative electrode active material: 90-98%, conductive agent: 1-2%, binder: 1.5-3%, thickener: 0.1-1%;

[0030] Furthermore, during the preparation of the first coating slurry, the solid content of the slurry is controlled between 50% and 65%, and the slurry temperature does not exceed 50°C.

[0031] Compared with the prior art, the present invention provides an electrode sheet containing a silicon negative electrode, a battery, and a method for preparing the electrode sheet, which have the following beneficial effects:

[0032] 1. In the electrode sheet containing a silicon negative electrode, in the first coating, the silicon negative electrode is selected to have a structure with a porous carbon skeleton supporting nano-silicon particles embedded therein, which has a smaller material intrinsic volume expansion after lithium insertion than pure silicon or silicon monoxide; the weight ratio of the silicon negative electrode to the graphite negative electrode is 25%-100%, and the D50 particle size ratio of the silicon negative electrode to the graphite negative electrode is 50%-80%; the first coating also contains a conductive agent of carbon nanotubes and a binder containing PAA, and the total weight of the conductive agent and the binder does not exceed 5% of the total weight of the first coating; this design can not only ensure a high incorporation amount of the silicon negative electrode, but also control the influence of the expansion of the silicon negative electrode after lithium insertion on the electrode sheet peeling force and conductive connection. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a schematic structural diagram of an electrode sheet containing a silicon negative electrode proposed in the present invention;

[0034] Figure 2 This is a schematic diagram of a cycle test of an electrode sheet containing a silicon negative electrode proposed in the present invention. DETAILED DESCRIPTION

[0035] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0036] Example 1:

[0037] Reference Figure 1-Figure 2, an electrode sheet containing a silicon negative electrode, comprising a current collector, a first coating containing a composite active material of a silicon negative electrode and a graphite negative electrode, and a second coating containing only a single active material of a graphite negative electrode; the first coating is located on the current collector, and the second coating is located on the first coating; the silicon negative electrode in the first coating is a structure supported by a porous carbon skeleton and embedded with nano-silicon particles; the weight ratio of the silicon negative electrode to the graphite negative electrode in the first coating is 25%-100%, and the D50 particle size ratio of the silicon negative electrode to the graphite negative electrode is 50%-80%.

[0038] Figure 1 This is the structural diagram of the electrode sheet in this application, in which the bottommost strip is the current collector, the top is the first coating, and the top is the second coating. Both the first coating and the second coating contain graphite negative electrode composite active material, and the first coating also contains silicon material.

[0039] The first coating layer also includes a conductive agent containing carbon nanotubes and a binder containing PAA, and the total weight of the conductive agent and the binder does not exceed 5% of the total weight of the first coating layer; specifically, the conductive agent containing carbon nanotubes preferably has 1-10 tube wall layers and a tube length of 10-50nm; in addition to the PAA binder, the binder in the first coating layer also includes at least one of CMC or PVA binders; this design can not only ensure a high incorporation amount of the silicon negative electrode, but also control the influence of the expansion of the silicon negative electrode after lithium insertion on the electrode peeling force and conductive connection.

[0040] The graphite negative electrode in the second coating is the same as the graphite negative electrode in the first coating, which enhances the compatibility of the two coatings. The conductivity of the pure graphite negative electrode is better than that of the silicon-containing negative electrode, which can improve the fast charging capability of the battery and avoid the deposition of lithium dendrites in the electrode sheet; the peeling force between the second coating and the first coating is greater than the peeling force between the first coating and the current collector, which can further restrain the stress generated by the expansion of the first coating. In order to reduce the negative impact on energy density, the surface density of the second coating is 10%-30% of the first coating.

[0041] The average particle size of the nano silicon particles is 1-10 nm, the silicon content of the nano silicon particles accounts for 45%-50% of the weight of the silicon negative electrode, and the shape of the nano silicon particles is spherical.

[0042] The porosity of the first coating is not less than 30%, the weight of the graphite negative electrode of the second coating accounts for not less than 96% of the overall weight of the second coating, and the thickness of the second coating is not more than 30 μm.

[0043] The current collector is made of any one of copper foil, composite copper foil or carbon-coated copper foil, and the current collector is preferably carbon-coated copper foil. The carbon coating layer on the carbon-coated copper foil contains at least carbon nanotubes, and the thickness of the carbon coating layer does not exceed 2 μm.

[0044] In the present invention, the design and preparation process of the electrode sheet containing silicon negative electrode is as follows:

[0045] The negative electrode active material in the first coating layer is a mixture of graphite and a silicon negative electrode with embedded nano-silicon particles supported by a porous carbon skeleton; wherein the silicon negative electrode is spherical, and the silicon content accounts for 49% by weight of the silicon negative electrode; the weight ratio of the silicon negative electrode to the graphite negative electrode is 65%, and the D50 particle size ratio of the silicon negative electrode to the graphite negative electrode is 60%; the conductive agent is a mixture of SP and carbon nanotubes CNT, wherein the carbon nanotubes are oligo-walled tubes with 3-7 wall layers and a tube length of about 40nm, and the addition amount of CNT accounts for 20% of the total weight of the conductive agent; the binder is a mixture of PAA, PVA, SBR and CMC, and the ratio of the four is 4:1:2:3; the specific gravity distribution of the active material, conductive agent and binder is 95.5:1.5:3;

[0046] The active material in the second coating contains only graphite, the same as the first coating, and the conductive agent and binder are the same as the first coating; the specific gravity distribution of the active material, conductive agent, and binder is 96:1.2:2.8;

[0047] The current collector is made of carbon-coated copper foil, the carbon coating layer contains the same carbon nanotubes as the first coating layer, the copper foil has a thickness of 6 μm, and the carbon coating layer has a thickness of 1±0.2 μm.

[0048] Subsequently, the above coating formula is evenly dispersed through the slurry and then evenly coated on the current collector through double-layer coating technology, where the surface density of the second coating is 20% of the first coating. After the coated electrode is subjected to the roller pressing process, the porosity of the electrode is about 35%.

[0049] The negative electrode sheet produced above, the positive electrode sheet containing high nickel ternary positive electrode with matching AP ratio, and the separator are wound and assembled into a cylindrical battery, and then the battery production is completed through baking, liquid injection, formation, capacity division and other processes.

[0050] The battery prepared in the present application comprises a positive electrode, a negative electrode, an electrolyte and a shell; the negative electrode adopts the above-mentioned silicon-containing negative electrode electrode sheet, and the positive electrode is preferably a ternary layered material with a high nickel content.

[0051] In this embodiment, a method for preparing an electrode sheet containing a silicon negative electrode is as follows:

[0052] Prepare the first coating, wherein the silicon negative electrode material and the graphite negative electrode material, the conductive agent, and the binder are uniformly mixed through a dual planetary slurry mixing device, and a thickener is added. The proportions of the substances are as follows: negative electrode active material: 95.3%, conductive agent: 1.6%, binder: 2.6%, thickener: 0.5%, and the final slurry viscosity is controlled at 4000-8000 mPa·s, the solid content is controlled at (50±1)%, and the fineness is controlled at ≤40 μm;

[0053] In the second coating, the graphite negative electrode material, conductive agent, and binder are uniformly mixed through a dual planetary slurry mixing device, and a thickener is added during this process. The proportions of each substance are negative electrode active material: 95.3%, conductive agent: 1.6%, binder: 2.6%, and thickener: 0.5%. The final slurry viscosity is controlled at 4000-8000mPa·s, the solid content is controlled at (50±1)%, and the fineness is controlled at ≤40μm.

[0054] Then, a silicon negative electrode was prepared: a dual-die extrusion coating machine was used to place the first coating layer and the second coating layer on the lower die and upper die, respectively, and simultaneously coated on the current collector, which was a 6 μm carbon-coated copper foil; the coating double-sided density was 142 g / m 2 After coating one side of the current collector, the other side of the current collector is coated in the same coating method; then it is baked in an oven, the moisture content of the electrode is controlled at <800ppm, and then it is rolled by a roller press, the thickness of the electrode is controlled at 97.5um and the peel strength is ≥150N / m, and finally it is stripped to obtain a double-layer silicon-containing negative electrode sheet.

[0055] Then, a lithium-ion battery containing a silicon negative electrode sheet can be prepared. The process includes: winding the positive electrode sheet, the silicon negative electrode sheet, the separator and the electrolyte according to a conventional method, welding the connecting sheet, welding the cover plate, baking, injecting liquid and other steps to complete the battery production;

[0056] The preparation method of the positive electrode sheet is as follows: the mass ratio of the components of the positive electrode sheet slurry is NCM811: conductive agent: binder = 98:1.1:1, N-methylpyrrolidone is used as a solvent, NCM811, conductive agent and binder are added in sequence, and the mixture is evenly dispersed by a double planetary slurry mixer. The final slurry viscosity is controlled at 3000-7000mPa·s, the solid content is controlled at (75±1)%, and the fineness is controlled at ≤30μm. The mixed slurry is evenly coated on a 12μm thick current collector carbon-coated copper foil, and the coating double-sided density is 280g / m 2 The electrode is dried in an oven and rolled by a roller press. The thickness of the electrode is controlled at 91um and the peel strength is ≥200N / m. Finally, it is slit to obtain the positive electrode.

[0057] Example 2:

[0058] Compared with Example 1, the silicon content of Example 2 is reduced from 65% to 25%; the rest of the formula, structural design and manufacturing process are the same as Example 1.

[0059] In this embodiment, the steps of a method for preparing an electrode sheet containing a silicon negative electrode are as follows:

[0060] In the first coating, the silicon negative electrode material and the graphite negative electrode material, the conductive agent, and the binder are uniformly mixed through a dual planetary slurry mixing device, and a thickener is added. The silicon negative electrode material and the graphite negative electrode material are mixed to form a negative electrode active material. The proportions of each substance are negative electrode active material: 95.3%, conductive agent: 1.6%, binder: 2.6%, and thickener: 0.5%. The final slurry viscosity is controlled at 4000-8000mPa·s, the solid content is controlled at (50±1)%, and the fineness is controlled at ≤40μm;

[0061] The second coating layer is the same as that in Example 1, the method for preparing the silicon negative electrode sheet is the same as that in Example 1, and the method for preparing the lithium-ion battery containing the silicon negative electrode sheet is also the same as that in Example 1.

[0062] Example 3:

[0063] Compared with Example 1, the electrode of Example 3 uses a 6 μm thick copper foil as the current collector, and the rest of the formula, structural design and manufacturing process are the same as Example 1.

[0064] In this embodiment, the steps of a method for preparing an electrode sheet containing a silicon negative electrode are as follows:

[0065] In the first coating, the silicon negative electrode material and the graphite negative electrode material, the conductive agent and the binder are uniformly mixed through a dual planetary slurry mixing device, and a thickener is added. The silicon negative electrode material and the graphite negative electrode material are mixed to form a negative electrode active material; the proportions of each substance are negative electrode active material: 95.3%, conductive agent: 1.6%, binder: 2.6%, thickener: 0.5%, and the final slurry viscosity is controlled at 4000-8000mPa·s, the solid content is controlled at (50±1)%, and the fineness is controlled at ≤40μm.

[0066] The second coating layer is the same as that in Example 1, the method for preparing the silicon negative electrode sheet is the same as that in Example 1, and the method for preparing the lithium-ion battery containing the silicon negative electrode sheet is also the same as that in Example 1.

[0067] Example 4:

[0068] Compared with Example 1, the silicon negative electrode material parameters of Example 4 are different, wherein the silicon negative electrode is block-shaped, and the silicon content accounts for 45% by weight of the silicon negative electrode; the D50 particle size ratio of the silicon negative electrode to the graphite negative electrode is 70%; the rest of the formula, electrode design and battery manufacturing process are the same as Example 1.

[0069] In this embodiment, the steps of a method for preparing an electrode sheet containing a silicon negative electrode are as follows:

[0070] In the first coating, the silicon negative electrode material and the graphite negative electrode material, the conductive agent and the binder are uniformly mixed through a dual planetary slurry mixing device, and a thickener is added. The silicon negative electrode material and the graphite negative electrode material are mixed to form a negative electrode active material; the proportions of each substance are negative electrode active material: 95.3%, conductive agent: 1.6%, binder: 2.6%, thickener: 0.5%, and the final slurry viscosity is controlled at 4000-8000mPa·s, the solid content is controlled at (50±1)%, and the fineness is controlled at ≤40μm.

[0071] The second coating is the same as that in Example 1. The method for preparing the silicon negative electrode sheet is the same as that in Example 1. The method for preparing the lithium ion battery containing the silicon negative electrode sheet is also the same as that in Example 1.

[0072] Example 5:

[0073] A control group electrode 1 was prepared. Compared with Example 1, this electrode only included the first coating layer and did not have the second coating layer. The rest was the same as Example 1.

[0074] Example 6:

[0075] A control group electrode 2 was prepared. Compared with Example 1, this electrode only contained the second coating layer but not the first coating layer. The rest was the same as Example 1.

[0076] Control group 1:

[0077] A pole piece of control group 1 is set; the pole piece of the control group is a single-layer pole piece, and its preparation steps are as follows: preparation of active material layer: the silicon negative electrode material and the graphite negative electrode material, the conductive agent and the binder are uniformly mixed through a double planetary slurry mixing device, and a thickener is added. The silicon negative electrode material and the graphite negative electrode material are mixed to form a negative electrode active material, wherein the silicon negative electrode material: the graphite negative electrode material is 30%; the D50 particle size ratio of the silicon negative electrode material to the graphite negative electrode material is 50%; the proportion of each substance is negative electrode active material: 95.3%, conductive agent: 1.6%, binder: 2.6%, thickener: 0.5%, the final slurry viscosity is controlled at 4000-8000mPa·s, the solid content is controlled at (50±1)%, and the fineness is controlled at ≤40μm.

[0078] The active material is placed on the lower die of a dual-die extrusion coater and coated on the current collector, which is a 6um carbon-coated copper foil. The coating double-sided density is 142g / m 2 After coating one side of the current collector, the other side of the current collector is coated in the same coating manner; then, the electrode is baked in an oven, and the moisture content of the electrode is controlled to be less than 800 ppm. Then, the electrode is rolled by a roller press, and the thickness of the electrode is controlled to be 97.5 μm and the peel strength is ≥150 N / m. Finally, the electrode is stripped to obtain a double-layer silicon-containing negative electrode sheet; the lithium-ion battery preparation method of the negative electrode sheet is the same as that in Example 1.

[0079] Control group 2:

[0080] A pole piece of control group 2 is set; the pole piece of control group 2 is a single-layer pole piece, and its preparation steps are as follows: the silicon negative electrode material and the graphite negative electrode material, the conductive agent, and the binder are uniformly mixed through a double planetary slurry mixing device, and a thickener is added, and the silicon negative electrode material and the graphite negative electrode material are mixed to form a negative electrode active material, wherein the silicon negative electrode material: the graphite negative electrode material is 30%; the D50 particle size ratio of the silicon negative electrode material to the graphite negative electrode material is 80%; the proportion of each substance is negative electrode active material: 95.3%, conductive agent: 1.6%, binder: 2.6%, thickener: 0.5%, the final slurry viscosity is controlled at 4000-8000mPa·s, the solid content is controlled at (50±1)%, and the fineness is controlled at ≤40μm; the remaining steps are the same as in control group 1.

[0081] In combination with the above-mentioned Examples 1 to 6, the performance characterization conclusions are as follows:

[0082] The negative electrode sheet prepared in the embodiment was tested for peel strength, expansion rate after formation and full charge disassembly (the growth rate of thickness after full charge relative to thickness after rolling), and energy density. The results are shown in the table below.

[0083] Table 1:

[0084]

[0085] Reference Figure 1-Figure 2 Comparing Example 5 and Example 1 of the comparative group, it can be seen that the double-layer electrode piece with silicon negative electrode and graphite negative electrode as the first layer and graphite as the second layer has greater peeling strength than the single-layer electrode piece of silicon negative electrode and graphite, and has a lower full-charge expansion rate, indicating that the electrode piece design scheme of the present invention is more conducive to improving the peeling strength of the electrode piece and limiting the expansion of the silicon material during the charging and discharging process of the lithium battery.

[0086] By comparing Example 1 and Example 6, it can be seen that the electrode designed by this patent is comparable to the graphite control group in peel strength and full-charge expansion rate, but the energy density of the corresponding battery is increased by 131Wh / Kg.

[0087] By comparing Example 1 and Example 3, it can be seen that the electrode peeling force corresponding to the carbon-coated copper foil group is greater than that of the copper foil group, and the full-charge expansion rate is smaller than that of the copper foil group. This means that the presence of the carbon coating layer increases the force between the current collector and the active material layer, thereby improving the overall peeling strength of the electrode.

[0088] By comparing Example 1 and Example 4, it can be seen that the present invention can increase the negative electrode capacity by designing different D50 particle size ratios of the silicon negative electrode and the graphite negative electrode and different electrode porosities, thereby improving the energy density of the battery.

[0089] Then, the lithium batteries prepared in the embodiment and the comparative example were subjected to cycle performance tests at 45°C in a 1C / 1C manner. Figure 2 ; Comparing Example 1, Example 2, Example 3, Example 4 and Example 5, it can be seen that the lithium battery containing a double-layer electrode sheet with a silicon negative electrode and a graphite negative electrode as the first layer and graphite as the second layer has better cycle performance than the lithium battery with a silicon negative electrode and a single-layer graphite electrode sheet. The double-layer design can significantly improve the cycle stability of the battery. Comparing Example 1, Example 2 and Example 6, it can be seen that even if the silicon content in the system increases, the cycle performance of the battery is not seriously deteriorated, which is similar to the graphite system battery in Example 6. Comparing Example 1 and Example 4, it can be found that as the porosity of the electrode sheet increases, the battery cycle is better, because the large porosity can absorb more electrolyte.

[0090] In summary, the present invention can effectively optimize the insufficient peeling force of the silicon-carbon negative electrode sheet and the peeling of the active material from the current collector due to volume expansion, which ultimately leads to low irreversible capacity and poor cycle performance of the silicon negative electrode, through designs such as multi-layer coating structure, optimization of silicon negative electrode morphology, content, adjustment of particle size and porosity, and change of current collector type.

[0091] The negative electrode sheets prepared in Examples 1 to 6 and Control Groups 1 and 2 were subjected to a peel strength test (the thickness after full charge relative to the thickness growth rate after rolling). The results are shown in the following table:

[0092] Table 2:

[0093]

[0094] By comparing the control group 1 and the example 1, it can be seen that the double-layer electrode sheet with silicon negative electrode material and graphite negative electrode material as the first layer and the single active material of the graphite negative electrode as the second layer has a greater peeling strength than the single-layer electrode sheet of silicon negative electrode and graphite; this shows that the electrode sheet design of the present invention is more conducive to improving the peeling strength of the electrode sheet. At the same time, the present application can also limit the expansion of the silicon material during the charging and discharging process of the lithium battery.

[0095] By comparing Examples 1 to 3 and Control Group 1, it can be seen that as the weight ratio of silicon negative electrode to graphite gradually increases, it is not conducive to the peeling of the electrode and the expansion of the corresponding battery. However, compared with the single-layer electrode structure, the double-layer electrode design proposed in this patent can improve this situation, which means that it is beneficial to increase the silicon content in the system and thus increase the battery capacity.

[0096] By comparing Example 1, Example 4, Control Group 1 and Control Group 2, it can be seen that the larger the D50 particle size ratio of the silicon negative electrode material to the graphite negative electrode material, the more unfavorable it is for the peeling of the electrode sheet and the expansion of the corresponding battery, but compared with the single-layer electrode sheet structure, the double-layer electrode sheet design is better.

[0097] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. An electrode sheet containing a silicon negative electrode, comprising a current collector, characterized in that: Also includes: A first coating layer provided on the current collector and containing a composite active material of a silicon negative electrode and a graphite negative electrode; The silicon negative electrode in the first coating has a structure supported by a porous carbon skeleton and embedded with nano-silicon particles; The weight ratio of the silicon negative electrode to the graphite negative electrode in the first coating layer is 25%-100%, and the D50 particle size ratio of the silicon negative electrode to the graphite negative electrode is 50%-80%; The current collector is made of carbon-coated copper foil.

2. The electrode sheet containing silicon negative electrode according to claim 1, characterized in that: The first coating layer further includes a conductive agent containing carbon nanotubes and a binder containing PAA, and the total weight of the conductive agent and the binder does not exceed 5% of the total weight of the first coating layer.

3. The electrode sheet containing silicon negative electrode according to claim 2, characterized in that: Also included is a second coating layer disposed on the first coating layer and containing only a single active material of the graphite negative electrode; The graphite negative electrode in the second coating is the same as the graphite negative electrode in the first coating, the peeling force between the second coating and the first coating is greater than the peeling force between the first coating and the current collector, and the surface density of the second coating is 10%-30% of that of the first coating.

4. The electrode sheet containing silicon negative electrode according to claim 3, characterized in that: The porosity of the first coating layer is not less than 30%, the weight of the graphite negative electrode of the second coating layer accounts for not less than 96% of the overall weight of the second coating layer, and the thickness of the second coating layer is not more than 30 μm.

5. The electrode sheet containing silicon negative electrode according to claim 1, characterized in that: The average particle size of the nano-silicon particles is 1-10 nm, the silicon content of the nano-silicon particles accounts for 45%-50% of the weight of the silicon negative electrode, and the shape of the nano-silicon particles is spherical; The carbon coating layer on the carbon-coated copper foil contains carbon nanotubes, and the thickness of the carbon coating layer does not exceed 2 μm.

6. The electrode sheet containing silicon negative electrode according to claim 2, characterized in that: The first coating layer contains a conductive agent containing carbon nanotubes, wherein the number of tube wall layers is 1-10 and the tube length is 10-50 nm. The first coating layer also contains at least one of CMC and PVA adhesives.

7. A battery, characterized in that: The invention comprises a positive electrode, a negative electrode, an electrolyte and a shell. The negative electrode is an electrode sheet containing silicon as claimed in any one of claims 1 to 6.

8. A method for preparing an electrode sheet containing a silicon negative electrode, for preparing an electrode sheet containing a silicon negative electrode as claimed in claim 3 or 4, characterized in that: The following steps are involved: S1, preparing the first coating: mixing the silicon negative electrode material and the graphite negative electrode material to form a negative electrode active material, uniformly mixing the negative electrode active material, the conductive agent, and the binder through a double planetary slurry mixing device, and adding a thickener during this process to form a first coating slurry; S2, preparing the second coating: uniformly mixing the graphite negative electrode material, the conductive agent, and the binder through a double planetary slurry mixing device, and adding a thickener during this process to form a second coating slurry; S3, using a dual-die coating head extrusion coating machine to place the first coating slurry and the second coating slurry on the lower die and the upper die respectively, and apply them to the current collector at the same time; after coating one side of the current collector, the other side of the current collector is coated in the same coating method; then it is baked in an oven, rolled, and slit to finally obtain an electrode sheet containing a silicon negative electrode.

9. The method for preparing a silicon-containing negative electrode sheet according to claim 8, characterized in that: In the first coating, the ratio of the negative electrode active material components in the silicon negative electrode material and the graphite negative electrode material is 30%-70%; the ratio of each substance is negative electrode active material: 90-98%, conductive agent: 1-2%, binder: 1.5-3%, thickener: 0.1-1%; In the second coating layer, the proportions of the various substances are: negative electrode active material: 90-98%, conductive agent: 1-2%, binder: 1.5-3%, thickener: 0.1-1%.

10. The method for preparing a silicon-containing negative electrode sheet according to claim 9, characterized in that ,During the preparation of the first coating layer, the solid content of the ,first coating slurry is controlled between 50% and 65%, and the slurry temperature does not exceed 50°C.

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