CN115832206A

CN115832206A - Negative electrode plate, secondary battery, battery module, battery pack, and electric device

Info

Publication number: CN115832206A
Application number: CN202111453650.8A
Authority: CN
Inventors: 杨成龙
Original assignee: Contemporary Amperex Technology Co Ltd
Current assignee: Contemporary Amperex Technology Co Ltd
Priority date: 2021-12-01
Filing date: 2021-12-01
Publication date: 2023-03-21

Abstract

The application provides a negative pole piece, including coating and current collector, the coating is located at least one surface of current collector, the coating includes first coating and second coating, first coating coat in the current collector surface, the second coating coat in the surface of first coating. Wherein the first coating layer comprises a silicon-based material and the second coating layer comprises one or more selected from Mg, ca, al as metal particles.

Description

Negative electrode plate, secondary battery, battery module, battery pack, and electric device

Technical Field

The application relates to the technical field of lithium batteries, in particular to a negative pole piece, a secondary battery, a battery module, a battery pack and an electric device.

Background

In recent years, with the wider application range of lithium ion secondary batteries, lithium ion secondary batteries are widely used in energy storage power systems such as hydraulic power, thermal power, wind power and solar power stations, and in a plurality of fields such as electric tools, electric bicycles, electric motorcycles, electric automobiles, military equipment and aerospace. As lithium ion secondary batteries have been greatly developed, higher requirements are also placed on energy density, cycle performance, safety performance, and the like. In addition, since the selection of the negative electrode active material is more limited, the silicon-based material active material is considered to be the best choice to meet the requirement of high energy density.

However, the silicon-based material has high surface activity and generates a volume expansion effect during charge and discharge cycles, so that the silicon-based material is pulverized. The improvement of the cycle performance of the material by means of coating or doping is currently a relatively effective means, but the conventional methods all cause different degrees of deterioration in the performance of the lithium ion secondary battery, for example, decrease in the gram capacity and deterioration in the cycle performance of the lithium ion secondary battery. Therefore, the existing modification technology of silicon-based materials still needs to be improved.

Disclosure of Invention

Technical problem to be solved by the invention

The present invention has been made in view of the above problems, and an object thereof is to provide a negative electrode tab that allows a secondary battery including the negative electrode tab to have both high energy density and excellent cycle performance.

Means for solving the problems

In order to achieve the above object, the present application provides a negative electrode sheet, a secondary battery, a battery module, a battery pack, and an electric device.

The first aspect of the application provides a negative pole piece, including coating and current collector, the coating is located at least one surface of current collector, the coating includes first coating and second coating, first coating coat in the current collector surface, the second coating coat in the surface of first coating. Wherein the first coating layer comprises a silicon-based material and the second coating layer comprises one or more selected from Mg, ca, al as metal particles.

Therefore, referring to fig. 1, the negative electrode plate of the present application is provided with a first coating layer and a second coating layer, and in the first coating layer, a silicon-based material is used as a negative electrode active material, so that the negative electrode plate has a high discharge capacity, and further, the energy density of the lithium ion secondary battery is ensured. The second coating contains metal particles of Ca, mg and Al, and the metal particles can form a stable Li-metal-Si phase with the silicon-based material and the embedded lithium ions in the circulation process of the negative pole piece, so that the surface activity of the silicon-based material is inhibited, the side reaction of the silicon-based material and the electrolyte is reduced, and the circulation performance of the lithium ion secondary battery containing the negative pole piece is greatly improved.

In any embodiment, the silicon-based material is SiO _x (x is more than or equal to 0 and less than 2), and one or more of Si and a mixture of Si and graphite, wherein in the mixture of Si and graphite, the weight proportion of Si is 40-70% and the weight proportion of graphite is 30-60% relative to the total weight of the mixture of Si and graphite. Therefore, the silicon-based material is selected as the negative electrode active material in order to improve the energy density of the lithium ion secondary battery.

In any embodiment, the Dv50=50 to 500nm of the metal particles in the second coating layer, and the weight proportion of the metal particles is 40 to 80% relative to the total weight of the second coating layer.

Therefore, the metal particles in the above Dv50 range are selected from the viewpoints of processing convenience and production cost. The metal powder with the smaller Dv50 is difficult to process, has higher cost, has smaller single particle mass, is easy to fly away, increases the storage cost and has larger safety risk. However, when the Dv50 of the metal particles is too large, the gaps between the metal particles are large and the layer of the metal particles having the same thickness is reduced, thereby resulting in that the metal particles cannot effectively cover the silicon-based material. Too large a metal particle Dv50 also tends to cause processing problems such as coating stringing.

In any embodiment, in the first coating layer, dv50=1.5 to 5 μm of the silicon-based material, and a weight proportion of the silicon-based material is 90 to 97% with respect to a total weight of the first coating layer.

Therefore, when the Dv50 of the silicon-based material is within the above range, the negative electrode plate has excellent processability, and when the Dv50 of the silicon-based material is within the above weight ratio range, the lithium ion secondary battery comprising the negative electrode plate has high energy density.

In any embodiment, the weight ratio of the metal particles to the silicon-based material is from 0.03 to 0.1.

Thus, the weight ratio of the silicon-based material to the metal particles is selected within the above range in the present application from the viewpoint of the silicon-based material that can be sufficiently covered with the metal particles. If the content of the metal particles is low, a complete coating layer cannot be formed on the surface of the silicon-based material, and the improvement effect of the cycle performance is poor; if the content of the metal particles is too high, the loading capacity of the negative active material in the negative pole piece is influenced, and further the energy density of the lithium ion secondary battery comprising the negative pole piece is influenced.

In any embodiment, the first coating has a coat weight CW =0.14 to 0.2g/1540.25mm ² . Therefore, the application selects the above coating weight range from the viewpoint of ensuring the energy density of the lithium ion secondary battery.

In any embodiment, the first coating has a thickness of 30 to 50 μm and the second coating has a thickness of 500 to 2000nm. Therefore, when the thickness of the second coating layer is too thin, the processing is difficult, the covering effect of the second coating layer is poor, and the cycle performance of the lithium ion secondary battery is not easily improved; when the thickness of the second coating is excessively thick, a large amount of active lithium ions are consumed by the Li-metal-Si phase formed during the first charge and discharge process, thereby deteriorating the energy density of the lithium ion secondary battery. When the thickness of the first coating is within the range, the negative pole piece has good processing performance, and winding and assembly of the battery cell are facilitated.

A second aspect of the present application provides a secondary battery comprising the negative electrode tab of the first aspect of the present application.

A third aspect of the present application provides a battery module including the secondary battery of the second aspect of the present application.

A fourth aspect of the present application provides a battery pack including the battery module of the third aspect of the present application.

A fifth aspect of the present application provides an electric device including at least one selected from the secondary battery of the second aspect of the present application, the battery module of the third aspect of the present application, or the battery pack of the fourth aspect of the present application.

Effects of the invention

The application provides a negative pole piece, secondary battery, battery module, battery package and electric device. The second coating of the negative pole piece contains metal particles of Ca, mg and Al, and the metal particles can form a stable Li-metal-Si phase with a silicon-based material and embedded lithium ions in the circulation process of the negative pole piece, so that the surface activity of the silicon-based material is inhibited, side reactions of the silicon-based material and electrolyte are reduced, and the circulation performance of the lithium ion secondary battery comprising the negative pole piece is greatly improved.

Drawings

Fig. 1 is a schematic view of a negative electrode tab of the present application.

Fig. 2 is a graph of cycle performance of the secondary batteries of example 1 and comparative example 1 of the present application.

Fig. 3 is a schematic view of a secondary battery according to an embodiment of the present application.

Fig. 4 is an exploded view of the secondary battery according to the embodiment of the present application shown in fig. 3.

Fig. 5 is a schematic view of a battery module according to an embodiment of the present application.

Fig. 6 is a schematic diagram of a battery pack according to an embodiment of the present application.

Fig. 7 is an exploded view of the battery pack according to the embodiment of the present application shown in fig. 6.

Fig. 8 is a schematic diagram of an electric device in which a secondary battery according to an embodiment of the present application is used as a power source.

Description of reference numerals:

1, a battery pack; 2, putting the box body on the box body; 3, discharging the box body; 4 a battery module; 5 a secondary battery; 51 a housing; 52 an electrode assembly; 53 Top cover Assembly

Detailed Description

Hereinafter, embodiments of the negative electrode sheet, the secondary battery, the battery module, the battery pack, and the electric device according to the present invention are specifically disclosed in detail with reference to the drawings as appropriate. But a detailed description thereof will be omitted. For example, detailed descriptions of already known matters and repetitive descriptions of actually the same configurations may be omitted. This is to avoid unnecessarily obscuring the following description, and to facilitate understanding by those skilled in the art. The drawings and the following description are provided for those skilled in the art to fully understand the present application, and are not intended to limit the subject matter recited in the claims.

The "ranges" disclosed herein are defined in terms of lower limits and upper limits, with a given range being defined by a selection of one lower limit and one upper limit that define the boundaries of the particular range. Ranges defined in this manner may or may not include the stated limits and may be arbitrarily combined, i.e., any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, it is understood that ranges of 60-110 and 80-120 are also contemplated. Furthermore, if the

minimum range values

1 and 2 are listed, and if the

maximum range values

3,4, and 5 are listed, the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise stated, the numerical range "a-b" represents a shorthand representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, a numerical range of "0 to 5" indicates that all real numbers between "0 to 5" have been listed herein, and "0 to 5" is simply an abbreviated representation of the combination of these numbers. In addition, when a parameter is an integer of 2 or more, it is equivalent to disclose that the parameter is, for example, an integer of 2, 3,4, 5, 6, 7, 8, 9, 10, 11, 12, or the like.

All embodiments and alternative embodiments of the present application may be combined with each other to form new solutions, if not specifically stated.

All technical and optional features of the present application may be combined with each other to form new solutions, if not otherwise specified.

All steps of the present application may be performed sequentially or randomly, preferably sequentially, if not specifically stated. For example, the method comprises steps (a) and (b), meaning that the method may comprise steps (a) and (b) performed sequentially, and may also comprise steps (b) and (a) performed sequentially. For example, reference to the process further comprising step (c) means that step (c) may be added to the process in any order, for example, the process may comprise steps (a), (b) and (c), may also comprise steps (a), (c) and (b), may also comprise steps (c), (a) and (b), etc.

The terms "comprises" and "comprising" as used herein mean either open or closed unless otherwise specified. For example, the terms "comprising" and "comprises" may mean that additional components not listed may also be included or included, or that only listed components may be included or included.

In this application, the term "or" is inclusive, if not otherwise specified. For example, the phrase "a or B" means "a, B, or both a and B. More specifically, either of the following conditions satisfies the condition "a or B": a is true (or present) and B is false (or not present); a is false (or not present) and B is true (or present); or both a and B are true (or present).

Negative pole piece

In an embodiment of the present application, the present application provides a negative electrode plate, which is characterized in that, including coating and current collector, the coating is located at least one surface of current collector, the coating includes first coating and second coating, first coating coat in the current collector surface, the second coating coat in the surface of first coating. Wherein the first coating layer comprises a silicon-based material and the second coating layer comprises one or more of Mg, ca, al as metal particles.

Although the mechanism is not clear, the applicant has surprisingly found through a large number of experiments: according to the lithium ion secondary battery, the first coating and the second coating are arranged on the negative electrode plate, and the silicon-based material is used as a negative electrode active material in the first coating, so that the gram capacity is higher, and the energy density of the lithium ion secondary battery is further ensured. The second coating contains metal particles Ca, mg and Al, and the metal particles can form a stable Li-metal-Si phase with the silicon-based material and the embedded lithium ions, so that the surface activity of the silicon-based material is inhibited, the side reaction of the silicon-based material and the electrolyte is reduced, and the cycle performance of the lithium ion secondary battery comprising the negative pole piece is greatly improved. For example, referring to fig. 2, fig. 2 is a graph of the cycle performance of example 1 and comparative example 1 of the present application, during the charge and discharge cycles of the negative electrode tab.

In some embodiments, the silicon-based material is SiO _x (x is more than or equal to 0 and less than 2), and one or more of Si and a mixture of Si and graphite, wherein in the mixture of Si and graphite, the weight proportion of Si is 40-70% and the weight proportion of graphite is 30-60% relative to the total weight of the mixture of Si and graphite. Therefore, the silicon-based material is selected as the negative electrode active material in order to improve the energy density of the lithium ion secondary battery.

In some embodiments, the Dv50=50 to 500nm of the metal particles in the second coating layer, and the weight proportion of the metal particles is 40 to 80% relative to the total weight of the second coating layer.

Therefore, the metal particles in the above Dv50 range are selected from the viewpoints of processing convenience and production cost. The metal powder with the smaller Dv50 is difficult to process, has higher cost, has smaller single particle mass, is easy to fly away, increases the storage cost and has larger safety risk. However, when the Dv50 of the metal particles is too large, the gaps between the metal particles are large and the layer of the metal particles at the same thickness is reduced, thereby causing the metal particles not to effectively cover the silicon-based material. Too large a metal particle Dv50 also tends to cause processing problems such as coating stringing.

In some embodiments, in the first coating layer, dv50=1.5 to 5 μm of the silicon-based material, and a weight proportion of the silicon-based material is 90 to 97% with respect to a total weight of the first coating layer.

In some embodiments, the weight ratio of the metal particles to the silicon-based material is from 0.03 to 0.1. Thus, the weight ratio of the silicon-based material to the metal particles is selected within the above range in the present application from the viewpoint of the silicon-based material that can be sufficiently covered with the metal particles. If the content of the metal particles is low, a complete coating layer cannot be formed on the surface of the silicon-based material, and the improvement effect of the cycle performance is poor; if the content of the metal particles is too high, the loading capacity of the negative active material in the negative pole piece is influenced, and further the energy density of the lithium ion secondary battery comprising the negative pole piece is influenced.

In some embodiments, the first coating has a coat weight CW =0.14 to 0.2g/1540.25mm ² . Therefore, the coating weight is selected in the present application from the viewpoint of ensuring the energy density of the lithium ion secondary battery.

In some embodiments, the first coating has a thickness of 30 to 50 μm and the second coating has a thickness of 500 to 2000nm. Therefore, when the thickness of the second coating layer is too thin, the processing is difficult and the coverage effect of the second coating layer is poor, which is not enough to improve the cycle performance of the lithium ion secondary battery; when the thickness of the second coating is excessively thick, a Li-metal-Si phase formed during the first charge and discharge consumes a part of lithium ions, resulting in a large energy density loss of the lithium ion secondary battery. When the thickness of the first coating is within the range, the negative pole piece has good processing performance, and winding and assembly of the battery cell are facilitated.

The average volume distribution particle diameter Dv50 is a particle diameter corresponding to 50% of the cumulative volume distribution percentage of the silicon-based material and the metal particles. In the present application, the volume average particle diameter Dv50 of the negative electrode active material may be determined by a laser diffraction particle size analysis method. For example, with reference to the standard GB/T19077-2016, using a laser particle Size analyzer (e.g., malvern Master Size 3000).

The secondary battery, the battery module, the battery pack, and the electric device according to the present invention will be described below with reference to the drawings as appropriate.

In one embodiment of the present application, a secondary battery is provided.

In general, a secondary battery includes a positive electrode tab, a negative electrode tab, an electrolyte, and a separator. In the process of charging and discharging the battery, active ions are embedded and separated back and forth between the positive pole piece and the negative pole piece. The electrolyte plays a role in conducting ions between the positive pole piece and the negative pole piece. The isolating membrane is arranged between the positive pole piece and the negative pole piece, mainly plays a role in preventing the short circuit of the positive pole and the negative pole, and can enable ions to pass through.

[ Positive electrode sheet ]

The positive pole piece comprises a positive current collector and a positive pole film layer arranged on at least one surface of the positive current collector, wherein the positive pole film layer comprises a positive active material.

As an example, the positive electrode current collector has two surfaces opposite in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two surfaces opposite to the positive electrode current collector.

In some embodiments, the positive electrode current collector may employ a metal foil or a composite current collector. For example, as the metal foil, aluminum foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel alloy, titanium alloy, silver alloy, etc.) on a base material of a polymer material (e.g., a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

In some embodiments, the positive active material may employ a positive active material for a battery, which is well known in the art. As an example, the positive electrode active material may include at least one of the following materials: olivine structured lithium-containing phosphates, lithium transition metal oxides and their respective modified compounds. However, the present application is not limited to these materials, and other conventional materials that can be used as a positive electrode active material of a battery may be used. These positive electrode active materials may be used alone only one,two or more kinds may be used in combination. Among them, examples of the lithium transition metal oxide may include, but are not limited to, lithium cobalt oxide (e.g., liCoO) ₂ ) Lithium nickel oxide (e.g., liNiO) ₂ ) Lithium manganese oxides (e.g., liMnO) ₂ 、LiMn ₂ O ₄ ) Lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (e.g., liNi) _1/3 Co _1/3 Mn _1/3 O ₂ (may also be abbreviated as NCM) ₃₃₃ )、LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (may also be abbreviated as NCM) ₅₂₃ )、LiNi _0.5 Co _0.25 Mn _0.25 O ₂ (may also be abbreviated as NCM) ₂₁₁ )、LiNi _0.6 Co _0.2 Mn _0.2 O ₂ (may also be abbreviated as NCM) ₆₂₂ )、LiNi _0.8 Co _0.1 Mn _0.1 O ₂ (may also be abbreviated as NCM) ₈₁₁ ) Lithium nickel cobalt aluminum oxides (e.g., liNi) _0.85 Co _0.15 Al _0.05 O ₂ ) And modified compounds thereof, and the like. Examples of olivine structured lithium-containing phosphates may include, but are not limited to, lithium iron phosphate (e.g., liFePO) ₄ (also referred to as LFP for short)), a composite material of lithium iron phosphate and carbon, and lithium manganese phosphate (e.g., liMnPO) ₄ ) At least one of a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

In some embodiments, the positive electrode film layer further optionally includes a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluoroacrylate resin.

In some embodiments, the positive electrode film layer further optionally includes a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

In some embodiments, the positive electrode sheet may be prepared by: dispersing the above components for preparing the positive electrode sheet, such as the positive active material, the conductive agent, the binder and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; and coating the positive electrode slurry on a positive electrode current collector, and drying, cold pressing and the like to obtain the positive electrode piece.

[ electrolyte ]

The electrolyte plays a role in conducting ions between the positive pole piece and the negative pole piece. The electrolyte is not particularly limited and may be selected as desired. For example, the electrolyte may be liquid, gel, or all solid.

In some embodiments, the electrolyte is an electrolytic solution. The electrolyte includes an electrolyte salt and a solvent.

In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis-fluorosulfonylimide, lithium bis-trifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalato borate, lithium dioxaoxalato borate, lithium difluorodioxaoxalato phosphate, and lithium tetrafluorooxalato phosphate.

In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1, 4-butyrolactone, sulfolane, dimethylsulfone, methylethylsulfone, and diethylsulfone.

In some embodiments, the electrolyte further optionally includes an additive. For example, the additives may include a negative electrode film-forming additive, a positive electrode film-forming additive, and may further include additives capable of improving certain properties of the battery, such as an additive for improving overcharge properties of the battery, an additive for improving high-temperature or low-temperature properties of the battery, and the like.

[ isolation film ]

In some embodiments, a separator is further included in the secondary battery. The type of the separator is not particularly limited, and any known separator having a porous structure and good chemical and mechanical stability may be used.

In some embodiments, the material of the isolation film may be at least one selected from glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The separator may be a single-layer film or a multilayer composite film, and is not particularly limited. When the separator is a multilayer composite film, the materials of the respective layers may be the same or different, and are not particularly limited.

In some embodiments, the positive electrode tab, the negative electrode tab, and the separator may be manufactured into an electrode assembly through a winding process or a lamination process.

In some embodiments, the secondary battery may include an exterior package. The exterior package may be used to enclose the electrode assembly and electrolyte.

In some embodiments, the outer package of the secondary battery may be a hard case, such as a hard plastic case, an aluminum case, a steel case, or the like. The outer package of the secondary battery may also be a pouch, such as a pouch-type pouch. The material of the soft bag may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, polybutylene succinate, and the like.

The shape of the secondary battery is not particularly limited, and may be a cylindrical shape, a square shape, or any other arbitrary shape. For example, fig. 3 is a secondary battery 5 of a square structure as an example.

In some embodiments, referring to fig. 4, the overwrap may include a housing 51 and a cover plate 53. The housing 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose to form an accommodating cavity. The housing 51 has an opening communicating with the accommodating chamber, and a cover plate 53 can be provided to cover the opening to close the accommodating chamber. The positive electrode tab, the negative electrode tab, and the separator may be formed into the electrode assembly 52 through a winding process or a lamination process. An electrode assembly 52 is enclosed within the receiving cavity. The electrolyte is impregnated into the electrode assembly 52. The number of electrode assemblies 52 contained in the secondary battery 5 may be one or more, and those skilled in the art can select them according to the actual needs.

In some embodiments, the secondary batteries may be assembled into a battery module, and the number of the secondary batteries contained in the battery module may be one or more, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery module.

Fig. 5 is a battery module 4 as an example. Referring to fig. 5, in the battery module 4, a plurality of secondary batteries 5 may be arranged in series along the longitudinal direction of the battery module 4. Of course, the arrangement may be in any other manner. The plurality of secondary batteries 5 may be further fixed by a fastener.

Alternatively, the battery module 4 may further include a case having an accommodation space in which the plurality of secondary batteries 5 are accommodated.

In some embodiments, the battery modules may be assembled into a battery pack, and the number of the battery modules contained in the battery pack may be one or more, and the specific number may be selected by one skilled in the art according to the application and the capacity of the battery pack.

Fig. 6 and 7 are a battery pack 1 as an example. Referring to fig. 6 and 7, a battery pack 1 may include a battery case and a plurality of battery modules 4 disposed in the battery case. The battery box comprises an upper box body 2 and a lower box body 3, wherein the upper box body 2 can be covered on the lower box body 3 and forms a closed space for accommodating the battery module 4. A plurality of battery modules 4 may be arranged in any manner in the battery box.

In addition, this application still provides a power consumption device, power consumption device includes at least one in secondary battery, battery module or the battery package that this application provided. The secondary battery, the battery module, or the battery pack may be used as a power source of the electric device, and may also be used as an energy storage unit of the electric device. The powered device may include a mobile device (e.g., a mobile phone, a laptop computer, etc.), an electric vehicle (e.g., a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship, a satellite, an energy storage system, etc., but is not limited thereto.

As the electricity-using device, a secondary battery, a battery module, or a battery pack may be selected according to the use requirement thereof.

Fig. 8 is an electric device as an example. The electric device is a pure electric vehicle, a hybrid electric vehicle or a plug-in hybrid electric vehicle and the like. In order to meet the demand of the electric device for high power and high energy density of the secondary battery, a battery pack or a battery module may be used.

As another example, the device may be a cell phone, tablet, laptop, etc. The device is generally required to be thin and light, and a secondary battery may be used as a power source.

Examples

Hereinafter, examples of the present application will be described. The following embodiments are described as illustrative only and are not to be construed as limiting the present application. The examples, where specific techniques or conditions are not indicated, are to be construed according to the techniques or conditions described in the literature in the art or according to the product specifications. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products commercially available.

Example 1

A first coating layer: mixing Si, a conductive agent carbon nanotube CNT, a binder lithium polyacrylate Li-PAA and a dispersant carboxymethyl cellulose lithium Li-CMC in a mass ratio of 90 ² And coating the coating on a copper foil current collector, and drying and cold pressing to obtain a first coating.

And (3) second coating: and (2) mixing the metal particles Mg, the conductive agent Super P and the binder PVDF according to a mass ratio of 5.

Wherein Dv50=2.5 μm for Si, dv50=200nm for Mg of the metal particles, metal particles: silica-based material = 0.05.

Example 2

The conditions were the same as in example 1 except that the silicon-based material was changed to SiO with Dv50=3 μm.

Example 3

The same conditions as in example 1 were used except that the silicon-based material was changed to a mixture of Si and graphite, wherein the mass ratio of Si was 40% and the weight ratio of graphite was 60% with respect to the total weight of the mixture of Si and graphite.

Example 4

The conditions were the same as in example 1 except that the metal particles were changed to Al, and Dv50=300nm of the metal particles Al.

Example 5

The same conditions as in example 1 were used except that the metal particle: silicon-based material =0.03 (wt: wt).

Example 6

The same conditions as in example 1 were used except that the metal particle: silicon-based material =0.1 (wt: wt).

Comparative example 1

Mixing Si, a conductive agent carbon nanotube CNT, a binder lithium polyacrylate Li-PAA and a dispersant carboxymethyl cellulose lithium Li-CMC in a mass ratio of 90 ² Coating on a copper foil current collector, drying and cold pressing to obtain the coating.

Comparative example 2

The conditions were the same as in example 1 except that the metal particles Mg were changed to metal particles Zn.

Comparative example 3

The conditions were the same as in example 1 except that the metal particles Mg were changed to metal particles Cr.

Comparative example 4

The conditions were the same as in example 1 except that the metal particles Mg were replaced with the metal particles Ti.

The parameters of the negative electrode sheets of examples 1 to 6 and comparative examples 1 to 4 are shown in table 1 below.

Table 1: parameter results of examples 1 to 6 and comparative examples 1 to 4

In addition, the negative electrode sheets obtained in examples 1 to 6 and comparative examples 1 to 4 were prepared into button cells as follows, respectively, and subjected to performance tests. The test results are shown in table 2 below.

(1) Preparation of button cell

Adopting the negative pole pieces in the above embodiments and comparative examples, and taking a metal lithium piece as a counter electrode; a Polyethylene (PE) film is used as a separation film; mixing Ethylene Carbonate (EC), ethyl Methyl Carbonate (EMC), diethyl carbonate (DEC) in a volume ratio of 1 ₆ The concentration of (A) is 1mol/L; the above parts were assembled into CR2430 button cells in an argon-protected glove box.

(3) Initial gram capacity and cycle performance test of button cell

Each button cell prepared above is circulated under 0.005-3V, and firstly, the discharge is carried out to 0.005V according to 0.1C, and the capacity at this time is the lithium intercalation capacity which is marked as C0; and standing for 5 minutes, charging to 3V according to 0.1C, wherein the capacity at the moment is the initial lithium removal capacity which is marked as D0, and the first effect is D0/C0 x 100%. Dividing the tested delithiation capacity value (namely C0) by the mass of the negative active material in the button cell to obtain the initial gram capacity of the negative active material, calculating the delithiation capacity after the circulation by using the same method to obtain the gram capacity after the circulation of 250 circles, and obtaining the capacity retention rate after the circulation (the gram capacity after the circulation/the initial gram capacity is 100%).

Table 2: results of Performance test of examples 1 to 6 and comparative examples 1 to 4

From the above results, it can be seen that the negative electrode plates in examples 1 to 6 all have the second coating layer containing Mg metal particles, and the Si-based material in the negative electrode plates, the metal particles and the intercalated lithium ions form a Li-metal-Si phase in the process of circulation, and the phase can stably exist on the surface of the Si-based material particles, can inhibit the reactivity of the surface of the Si-based material particles, and reduce the side reactions with the electrolyte, thereby obtaining a good effect in improving the circulation performance of the Si-based material. Also, the pulverization of the silicon-based material is suppressed.

On the other hand, comparative examples 1 to 4 were not effectively improved in cycle performance. The negative pole piece in the comparative example 1 is not provided with the second coating containing the metal particles, the surface of the silicon-based material particles still has high reactivity, and the silicon-based material particles generate side reaction with electrolyte to generate an unstable SEI film, so that the cycle performance of the silicon-based material is influenced. The metal particles Zn in the comparative example 2, the metal particles Cr in the comparative example 3, and the metal particles Ti in the comparative example 4 not only cannot form a stable Li-metal-Si phase on the surface of the particles of the Si-based material, thereby avoiding a side reaction between the Si-based material and the electrolyte, but also consume a large amount of active lithium ions during the charging and discharging processes, and thus, the cycle performance and the first coulomb efficiency of the Si-based material cannot be effectively improved.

The present application is not limited to the above embodiments. The above embodiments are merely examples, and embodiments having substantially the same configuration as the technical idea and exhibiting the same operation and effect within the technical scope of the present application are all included in the technical scope of the present application. In addition, various modifications that can be conceived by those skilled in the art are applied to the embodiments and other embodiments are also included in the scope of the present application, in which some of the constituent elements in the embodiments are combined and constructed, without departing from the scope of the present application.

Claims

1. A negative pole piece is characterized by comprising a coating layer and a current collector, wherein the coating layer is positioned on at least one surface of the current collector and comprises a first coating and a second coating, the first coating is coated on the surface of the current collector, the second coating is coated on the surface of the first coating,

wherein the first coating layer comprises a silicon-based material and the second coating layer comprises one or more selected from Mg, ca, al as metal particles.

2. The negative electrode plate of claim 1, wherein the silicon-based material is SiO _x (x is more than or equal to 0 and less than 2), si, one or more of mixtures of Si and graphite,

optionally, in the mixture of Si and graphite, a weight ratio of the Si is 40 to 70% and a weight ratio of the graphite is 30 to 60% with respect to a total weight of the mixture of Si and graphite.

3. The negative electrode sheet according to claim 1 or 2, wherein in the second coating layer, dv50= 50-500 nm of the metal particles, and

the weight proportion of the metal particles is 40-80% relative to the total weight of the second coating.

4. The negative electrode plate as claimed in any one of claims 1 to 3, wherein the Dv50= 1.5-5 μm of the silicon-based material in the first coating layer, and

the weight proportion of the silicon-based material is 90-97% relative to the total weight of the first coating.

5. The negative electrode plate as claimed in any one of claims 1 to 4, wherein the weight ratio of the metal particles to the silicon-based material is 0.03 to 0.1.

6. The negative electrode sheet of any one of claims 1 to 5, wherein the first coating has a coat weight CW = 0.14-0.2 g/1540.25mm ² 。

7. The negative electrode plate as claimed in any one of claims 1 to 6, wherein the thickness of the first coating layer is 30 to 50 μm, and the thickness of the second coating layer is 500 to 2000nm.

8. A secondary battery comprising the negative electrode sheet according to any one of claims 1 to 7.

9. A battery module characterized by comprising the secondary battery according to claim 8.

10. A battery pack comprising the battery module according to claim 9.

11. An electric device comprising at least one selected from the secondary battery according to claim 8, the battery module according to claim 9, and the battery pack according to claim 10.