Composite negative electrode sheet, battery, and electric device

Abstract

The disclosure provides a composite negative electrode sheet, a battery and an electric device. The composite negative electrode sheet comprises: a current collector, the current collector has a plurality of active material accommodation holes which are open on the surface of the current collector and have bottoms in the current collector; a first active layer, the active material in the first active layer comprises a silicon active material, the silicon active material is in a nanosheet shape, the first active layer is arranged in contact with the surface of the current collector, and at least part of the silicon active material is located in the active material accommodation hole; and a second active layer, the second active layer comprises graphite, the second active layer is arranged on the side of the first active layer away from the current collector, and the second active layer covers the first active layer as a whole. The structural design is conducive to reducing the strain of the composite negative electrode sheet as a whole during charging and discharging, thereby significantly improving the problem of pulverization and falling off of the silicon active material, and making the composite negative electrode sheet have significantly higher cycle stability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a composite negative electrode sheet, a battery and an electric device. BACKGROUND

[0002] Due to the rapid development and wide application of portable electronic devices and electric vehicles, there is an urgent need for lithium ion batteries with high specific energy and long cycle life. Currently, commercially used lithium ion batteries mainly use graphite as the negative electrode material. However, the theoretical specific capacity of graphite is only 372 mAh / g, which limits the further improvement of the specific energy of lithium ion batteries.

[0003] Silicon has a very high lithium intercalation specific capacity (up to 4200 mAh / g) and a low lithium storage potential, and is an ideal new lithium storage material, which has attracted widespread attention from researchers. However, the volume expansion of silicon during lithium storage exceeds 300%, which easily causes pulverization and leads to the detachment of active materials from the current collector, resulting in a significant decrease in the cycle stability of the electrode. SUMMARY

[0004] Therefore, it is necessary to provide a composite negative electrode sheet capable of effectively inhibiting the pulverization and detachment of silicon active materials, which has a significantly higher cycle stability.

[0005] According to some embodiments of the present application, a composite negative electrode sheet is provided, which comprises:

[0006] a current collector having a plurality of active material accommodating holes which are open on the surface of the current collector and have bottoms in the current collector;

[0007] a first active layer, the active material in the first active layer comprising silicon active material, the silicon active material being in the form of nanosheets, the first active layer being arranged in contact with the surface of the current collector, and at least part of the silicon active material being located in the active material accommodating holes; and

[0008] a second active layer comprising graphite, the second active layer being arranged on the side of the first active layer away from the current collector, and the second active layer covering the first active layer as a whole.

[0009] In some embodiments of the present application, the ratio of the thickness of the first active layer to the thickness of the second active layer is 1: (0.2-1.5).

[0010] In some embodiments of the present application, the depth of the active material accommodating holes is 3-9 μm, and the overall thickness of the first active layer is 15-50 μm.

[0011] In some embodiments of the present disclosure, in the current collector, a pore size of the active material accommodation hole is 20 μm-100 μm; and / or,

[0012] The opening of all the active material accommodation holes on the surface of the current collector accounts for 30%-80% of the surface of the current collector.

[0013] In some embodiments of the present disclosure, in the first active layer, a thickness of the silicon active material is 5 nm-100 nm; and / or,

[0014] A radial dimension of the silicon active material is 100 nm-2000 nm.

[0015] In some embodiments of the present disclosure, the active material in the first active layer further comprises a carbon active material selected from one or more of graphite, hard carbon, soft carbon and graphene, and in the first active layer, a mass ratio of the silicon active material to the carbon active material is 1:(0.5-2); and / or,

[0016] A mass proportion of the active material in the first active layer in the first active layer is above 80%.

[0017] In some embodiments of the present disclosure, the first active layer further comprises at least one of a first conductive agent and a first binder; wherein,

[0018] The first conductive agent is selected from one or more of conductive carbon black, carbon nanotube, graphene, carbon nanofiber and carbon-coated tin nanowire.

[0019] In some embodiments of the present disclosure, a mass proportion of graphite in the second active layer is above 90%, and the second active layer further comprises at least one of a second conductive agent and a second binder.

[0020] Further, the present disclosure also provides a battery comprising a negative electrode sheet, a positive electrode sheet and an electrolyte; the positive electrode sheet and the negative electrode sheet are oppositely arranged, and the negative electrode sheet is the composite negative electrode sheet according to any of the above embodiments.

[0021] Further, the present disclosure also provides an electrical equipment comprising an electrical main body and the battery according to any of the above embodiments.

[0022] The composite negative electrode tab of the present disclosure comprises a current collector, a first active layer and a second active layer. The active material accommodating holes are arranged in the current collector, and the silicon active material in the form of nanosheets is contained in the first active layer. The active material accommodating holes can accommodate the silicon active material in the form of nanosheets and form good electrical contact with the silicon active material to provide better electron conduction capability. More importantly, the silicon active material in the form of nanosheets is sparsely distributed in the active material accommodating holes. Therefore, there are more vacancies in the active material accommodating holes and abundant space can be reserved for the volume change of the silicon active material, and at the same time, the graphite material in the second active layer can inhibit the upward expansion of the silicon active material. The above two factors work together to reduce the strain of the composite negative electrode tab as a whole during the charging and discharging process, thereby significantly improving the problem of powdering and falling off of the silicon active material. Experiments have proved that, compared with other tabs without the above structure, the composite negative electrode tab has significantly higher cycle stability. DETAILED DESCRIPTION

[0023] The embodiments of the technical solutions of the present application will be described in detail below. The following embodiments are only used to more clearly illustrate the technical solutions of the present application, and therefore only serve as examples, and cannot limit the protection scope of the present application.

[0024] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the present application; the terms "include" and "have" and any variations thereof in the specification and claims of the present application are intended to cover non-exclusive inclusion.

[0025] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "a plurality of" is two or more, unless otherwise explicitly and specifically limited.

[0026] In this document, the reference to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily all refer to the same embodiment, nor is it necessarily mutually exclusive of other embodiments. It is explicitly and implicitly understood that the embodiments described herein can be combined with other embodiments.

[0027] In the description of the embodiments of the present application, the term "and / or" is only to describe the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B, which can represent the existence of A alone, the existence of A and B at the same time, and the existence of B alone. In addition, the character " / " in this paper generally represents that the front and rear associated objects are in an "or" relationship.

[0028] In the description of the embodiments of the present application, the term "a plurality of" refers to two or more (including two), and similarly, "a plurality of groups" refers to two or more groups (including two groups), and "a plurality of pieces" refers to two or more pieces (including two pieces).

[0029] In the description of the embodiments of the present application, unless otherwise explicitly specified and limited, the technical terms "mounting", "connection", "connection", "fixing" and the like should be understood in a broad sense, for example, it can be fixedly connected, or it can be detachably connected, or it can be integrated; it can be mechanical connection, or it can be electrical connection; it can be directly connected, or it can be indirectly connected through an intermediate medium; it can be the internal communication of two elements or the interaction relationship between two elements. For those skilled in the art, the specific meaning of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0030] The present disclosure provides a composite negative electrode tab, which comprises: a current collector, the current collector has a plurality of active material accommodation holes which are open on the surface of the current collector and the bottom of which is located in the current collector. A first active layer, the active material in the first active layer comprises a silicon active material, the silicon active material is in the form of nanosheet, the first active layer is arranged on the surface of the current collector, and at least part of the silicon active material is located in the active material accommodation hole. And a second active layer, the second active layer comprises graphite, the second active layer is arranged on the side of the first active layer away from the current collector, and the second active layer covers the first active layer as a whole.

[0031] The composite negative electrode tab of the present disclosure is based on the following technical concept: when filled in the hole of the current collector, the distribution of the silicon active material in the form of nanosheet in the hole is relatively sparse, which means that there are more vacancies in the hole of the current collector and a rich space can be reserved for the volume change of the silicon active material. On this basis, the graphite in the second active layer arranged above is in the form of sheet layer structure, which can block the volume expansion of the silicon active material towards the upper side. Therefore, during the charging and discharging process, the silicon active material mainly expands towards the inside of the hole of the current collector, and the strain of the first active layer and the second active layer above the current collector as a whole is also relatively small, so that the problem of powdering and falling off of the silicon active material is obviously improved. Experiments have proved that, compared with other tabs without the above structure, the composite negative electrode tab has significantly higher cycle stability.

[0032] In this embodiment, the composite negative electrode sheet comprises a current collector, a first active layer and a second active layer. The current collector has a plurality of active material accommodating holes which are open on the surface of the current collector and have bottoms in the current collector. The active material in the first active layer comprises silicon active material, the silicon active material is in the form of nanosheets, the first active layer is arranged on the surface of the current collector, and at least part of the silicon active material is located in the active material accommodating holes. The second active layer comprises graphite, the second active layer is arranged on the side of the first active layer away from the current collector, and the second active layer covers the first active layer as a whole.

[0033] As an example of this embodiment, the material of the current collector is an electrically conductive material. Further, the material of the current collector is metal, for example, the material of the current collector can comprise one or more of copper, aluminum, iron and silver.

[0034] As an example of this embodiment, the ratio of the thickness of the first active layer to the thickness of the second active layer is 1: (0.2-1.5). The second active layer designed with this ratio has a strong blocking and inhibiting effect on the first active layer, which can further improve the cycle capacity retention rate of the negative electrode sheet.

[0035] As a further example of this embodiment, the ratio of the thickness of the first active layer to the thickness of the second active layer can be 1:0.2, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, or the ratio of the thickness of the first active layer to the thickness of the second active layer can also be between any two of the above values.

[0036] As an example of this embodiment, part of the first active layer can be arranged in the active material accommodating holes, and another part of the first active layer can be arranged above the current collector, that is, the bottom end of the first active layer can be located in the active material accommodating holes, and the top end of the first active layer can be higher than the opening of the active material accommodating holes. The active material accommodating holes can provide a certain expansion space during the volume expansion of the silicon active material.

[0037] As an example of this embodiment, the depth of the active material accommodating hole is 3-9 μm, and the overall thickness of the first active layer is 15-50 μm. The volume expansion of the first active layer with this thickness is relatively limited during charging and discharging, and the design of the depth of the active material accommodating hole can provide sufficient accommodation space for the silicon active material in the first active layer. It can be understood that the overall thickness of the first active layer refers to the height difference between the top end of the first active layer and the bottom end of the first active layer.

[0038] As a further example of this embodiment, the depth of the active material accommodation hole can be 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or the depth of the active material accommodation hole can also be between any two of the above.

[0039] As an example of this embodiment, the ratio of the depth of the active material accommodation hole to the thickness of the current collector is (1~3):4.

[0040] As a further example of this embodiment, the overall thickness of the first active layer can be 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, or the overall thickness of the first active layer can also be between any two of the above.

[0041] As an example of this embodiment, the aperture of the active material accommodation hole is 20 μm~100 μm. The active material accommodation hole in this aperture range can provide sufficient space for the expansion of the silicon active material.

[0042] As a further example of this embodiment, the aperture of the active material accommodation hole can be 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 50 μm, 60 μm, 80 μm, 100 μm, or the aperture of the active material accommodation hole can also be between any two of the above.

[0043] As an example of this embodiment, the cross-sectional shape of the active material accommodation hole can be a regular polygon or an irregular polygon. Among them, the regular polygon can be a triangle, a square, a rectangle, a circle, an ellipse, a diamond, or a regular pentagon.

[0044] As an example of this embodiment, the opening of all active material accommodation holes on the current collector surface accounts for 30%~80% of the current collector surface.

[0045] As a further example of this embodiment, the opening of all active material accommodation holes on the current collector surface accounts for 30%, 40%, 50%, 60%, 70%, 80% of the current collector surface, or it can also be between any two of the above.

[0046] As an example of this embodiment, in the first active layer, the thickness of the silicon active material is 5 nm~100 nm. Further, the thickness of the silicon active material is 5 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 80 nm, 100 nm, or the thickness of the silicon active material can also be between any two of the above.

[0047] As an example of this embodiment, the radial dimension of the silicon active material in the first active layer is 100 nm to 2000 nm. Further, the radial dimension of the silicon active material is 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 700 nm, 1000 nm, 1500 nm, 2000 nm, or the radial dimension of the silicon active material can be between any two of the above dimensions.

[0048] As an example of this embodiment, the silicon active material is selected from one or more of silicon, silicon monoxide, and silicon alloy. Further, the silicon active material can include one or more of silicon nanoplate, silicon monoxide nanoplate, and silicon alloy nanoplate.

[0049] As an example of this embodiment, the active material in the first active layer further includes a carbon active material selected from one or more of graphite, hard carbon, soft carbon, and graphene. It can be appreciated that the silicon active material and the carbon active material can exist in the first active layer in a mixed manner.

[0050] As a further example of this embodiment, in the first active layer, the mass ratio of the silicon active material to the carbon active material is 1: (0.5 to 2). For example, the mass ratio of the silicon active material to the carbon active material can be 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:1, 1:1.2, 1:1.4, 1:1.6, 1:1.8, 1:2, or the mass ratio of the silicon active material to the carbon active material can be between any two of the above mass ratios.

[0051] As an example of this embodiment, the mass proportion of the active material in the first active layer is 80% or more. For example, the mass proportion of the active material in the first active layer can be 80%, 82%, 85%, 88%, 90%, 92%, 95%, 98%, or the mass proportion of the active material in the first active layer can be between any two of the above mass proportions. It can be appreciated that in this embodiment, the active material includes the silicon active material, and the active material can further include the carbon active material.

[0052] As an example of this embodiment, the first active layer further includes at least one of a first conductive agent and a first binder.

[0053] As a further example of this embodiment, the first conductive agent is selected from one or more of conductive carbon black, carbon nanotube, graphene, carbon nanofiber, and carbon-coated tin nanowire. In this embodiment, the first conductive agent includes carbon nanotube and carbon-coated tin nanowire.

[0054] As a further example of this embodiment, the first binder can be selected from one or more of polyvinylpyrrolidone, polyvinylidene fluoride, polyethylene oxide, polytetrafluoroethylene, carboxymethyl cellulose, and a copolymer of styrene and butadiene.

[0055] As a further example of this embodiment, the first active layer further comprises a first dispersant. The first dispersant can be selected from sodium carboxymethyl cellulose.

[0056] As an example of this embodiment, the mass percentage of graphite in the second active layer is above 90%. It can be understood that the graphite in the second active layer not only can be used to inhibit the expansion of the silicon active material upward, but also can be used as an active material participating in the charging and discharging process.

[0057] As an example of this embodiment, the graphite can be selected from flake graphite.

[0058] As a further example of this embodiment, the mass percentage of graphite in the second active layer can be 90%, 92%, 95%, 98%, or the mass percentage of graphite in the second active layer can be between any two of the above mass percentages.

[0059] As a further example of this embodiment, the second active layer further comprises at least one of a second conductive agent and a second binder.

[0060] As a further example of this embodiment, the second conductive agent can be selected from one or more of conductive carbon black, carbon nanotubes, graphene, and carbon nanofibers.

[0061] As a further example of this embodiment, the second binder can be selected from one or more of polyvinylpyrrolidone, polyvinylidene fluoride, polyethylene oxide, polytetrafluoroethylene, carboxymethyl cellulose, and a copolymer of styrene and butadiene.

[0062] As a further example of this embodiment, the second active layer further comprises a second dispersant. The second dispersant can be selected from sodium carboxymethyl cellulose.

[0063] The present disclosure also provides a preparation method of the composite negative electrode sheet described above, comprising the following steps.

[0064] Step S1, a first slurry containing a silicon active material is coated on a current collector.

[0065] In this embodiment, the current collector has a plurality of active material accommodation holes which are open on the surface of the current collector and have bottoms in the current collector.

[0066] In this embodiment, the silicon active material is in the form of nanosheets. It can be appreciated that, during the coating process, the silicon active material in the form of nanosheets is difficult to be fully filled into the active material accommodation holes of the current collector, due to the limitation of the flow ability of the slurry and the structural characteristics of the nanosheets themselves, so that there is space in the active material accommodation holes to accommodate the volume expansion of silicon.

[0067] As an example of this embodiment, the active material in the first slurry further includes a carbon active material selected from one or more of graphite, hard carbon, soft carbon and graphene.

[0068] As an example of this embodiment, the first slurry further contains at least one of a first conductive agent and a first binder. The first conductive agent is selected from one or more of conductive carbon black, carbon nanotube, graphene, carbon nanofiber and carbon-coated tin nanowire. In this embodiment, the first conductive agent includes carbon nanotube and carbon-coated tin nanowire. The first binder can be selected from one or more of polyvinylpyrrolidone, polyvinylidene fluoride, polyethylene oxide, polytetrafluoroethylene, carboxymethyl cellulose and a copolymer of styrene and butadiene.

[0069] As an example of this embodiment, the first slurry further includes a first dispersant. The first dispersant can be selected from sodium carboxymethyl cellulose.

[0070] As an example of this embodiment, the solid content in the first slurry is 40% to 49%. For example, the solid content in the first slurry can be 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, or the solid content in the first slurry can also be between any two of the above proportions.

[0071] As an example of this embodiment, the viscosity of the first slurry can be 2000 mPa·s to 6000 mPa·s.

[0072] Step S2, coating the second slurry containing graphite on the current collector.

[0073] As an example of this embodiment, the second slurry further contains at least one of a second conductive agent and a second binder. The second conductive agent is selected from one or more of conductive carbon black, carbon nanotube, graphene and carbon nanofiber. The second binder can be selected from one or more of polyvinylpyrrolidone, polyvinylidene fluoride, polyethylene oxide, polytetrafluoroethylene, carboxymethyl cellulose and a copolymer of styrene and butadiene.

[0074] As an example of this embodiment, the second slurry further includes a second dispersant. The second dispersant can be selected from sodium carboxymethyl cellulose.

[0075] As an example of this embodiment, the solid content in the second slurry is 40% to 49%. For example, the solid content in the second slurry can be 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, or the solid content in the second slurry can also be between any two of the above ratios.

[0076] As an example of this embodiment, the viscosity of the second slurry can be 2000 mPa s to 6000 mPa s.

[0077] As an example of this embodiment, after the first slurry and the second slurry are applied to the first active layer, further comprising: drying the current collector on which the first slurry and the second slurry are applied to remove the solvents in the first slurry and the second slurry, and respectively forming the first active layer and the second active layer.

[0078] It can be understood that the thicknesses of the first active layer and the second active layer can be controlled by respectively controlling the amounts of the first slurry and the second slurry applied.

[0079] Through the above steps S1 to S2, the composite negative electrode sheet as in the above embodiments can be prepared.

[0080] On the other hand, the present disclosure also provides a battery, which comprises a positive electrode sheet and a negative electrode sheet, the positive electrode sheet and the negative electrode sheet being oppositely arranged, and the negative electrode sheet comprising the negative electrode sheet as in any one of the above embodiments.

[0081] As an example of this embodiment, the positive electrode sheet comprises a positive electrode current collector and a positive electrode active layer.

[0082] As an example of this embodiment, the positive electrode active layer comprises a positive electrode active material. The positive electrode active material is selected from one or more of lithium cobaltate, lithium nickelate, lithium manganate, a layered ternary positive electrode material, spinel lithium nickel-manganese acid, lithium iron phosphate, lithium iron-manganese phosphate, lithium manganese phosphate, and lithium cobalt phosphate.

[0083] In this embodiment, the battery can be a lithium ion battery.

[0084] Further, the present disclosure also provides a power-consuming device, which comprises a functional body and a battery as in any one of the above embodiments, the battery being used to supply power to the functional body.

[0085] As some examples of this embodiment, the power-consuming device can be a mobile phone, a notebook computer, a smart watch, or an electric vehicle.

[0086] The present application is further described in detail below with reference to several specific embodiments, which should not be construed as limiting the scope of the present application.

[0087] Unless otherwise defined, all terms used in the description herein are to be interpreted in accordance with their ordinary meaning in the art. The professional terms used herein are merely used to describe specific embodiments and are not intended to limit the scope of the present application.

[0088] Some specific examples are listed below. It should be noted that the examples described below are exemplary and are only used to explain the present application and cannot be understood as limiting the present application. If the specific technology or condition is not specified in the examples, it is carried out according to the technology or condition described in the literature in the art or according to the product manual. If the reagent or instrument used is not specified by the manufacturer, it is a conventional product that can be obtained by purchase.

[0089] Example 1

[0090] A porous copper foil with a thickness of 12 μm is used as the current collector, wherein the hole depth is about 6 μm and the hole diameter is about 35 μm.

[0091] Silicon nanosheets, carbon-coated tin nanowires, conductive carbon black, single-walled carbon nanotubes, butadiene-styrene rubber (binder) and sodium carboxymethyl cellulose (dispersant) are mixed according to a mass ratio of 90:5:0.5:0.5:2:2, and an appropriate amount of deionized water is added. A first slurry is prepared under the action of a vacuum stirrer according to a suitable homogenization process, wherein the solid content is about 45% and the viscosity is 4000 mPa·s.

[0092] Graphite, conductive carbon black, butadiene-styrene rubber and sodium carboxymethyl cellulose are mixed according to a mass ratio of 97.5:0.5:1.5:0.5, and an appropriate amount of deionized water is added. A second slurry is prepared under the action of a vacuum stirrer according to a suitable homogenization process, wherein the solid content is about 45% and the viscosity is 4000 mPa·s.

[0093] The first slurry and the second slurry described above are sequentially coated on the surface of the porous copper foil by using a double-layer coating machine, and dried to form a first active layer and a second active layer, respectively. The thickness of the first active layer is 30 μm, and the thickness of the second active layer is 10 μm.

[0094] Example 2

[0095] The main difference between Example 2 and Example 1 is the first slurry, and the raw material ratio is as follows: silicon suboxide nanosheets, conductive agent (90% conductive carbon black and 10% single-walled carbon nanotubes), butadiene-styrene rubber and sodium carboxymethyl cellulose are mixed according to a mass ratio of 97.5:0.5:2:0.5.

[0096] Example 3

[0097] The main difference between Example 3 and Example 1 is the first slurry, the raw material ratio of which is as follows: first mix graphite and silicon nanosheet in a 1:1 ratio as active material, then mix the active material, conductive agent (90% conductive carbon black and 10% single-walled carbon nanotube), butadiene rubber and sodium carboxymethyl cellulose in a mass ratio of 97.5:0.5:2:0.5.

[0098] Example 4

[0099] The main difference between Example 4 and Example 1 is the first slurry, the raw material ratio of which is as follows: first mix graphite and silicon nanosheet in a 1:1 ratio as active material, then mix the active material, conductive carbon black, single-walled carbon nanotube, butadiene rubber and sodium carboxymethyl cellulose in a mass ratio of 95:0.2:0.8:2:2.

[0100] Comparative Example 1

[0101] The main difference between Comparative Example 1 and Example 1 is that Comparative Example 1 mixes the first slurry and the second slurry in a 3:1 ratio before coating, and the active layer formed by coating has a thickness of 40 μm.

[0102] Comparative Example 2

[0103] The main difference between Comparative Example 2 and Example 1 is that Comparative Example 2 uses a flat copper foil with a thickness of 12 μm as the current collector instead of a porous copper foil.

[0104] Comparative Example 3

[0105] The main difference between Comparative Example 3 and Example 1 is that Comparative Example 3 uses silicon nanoparticles instead of silicon nanosheet in Example 1.

[0106] Test: The negative electrode sheets prepared in each of the above examples and comparative examples are used to form lithium ion batteries in the following manner. An electrolyte is prepared by dissolving 1 mol / L lithium hexafluorophosphate in a mixed solvent of EC and DMC in a volume ratio of 1:1. A half battery is prepared by pairing the negative electrode sheet with a lithium sheet, using a three-layer film of PP / PE / PP as a separator to separate the negative electrode sheet and the lithium sheet, and injecting the electrolyte to form a coin-type half battery. The cutoff voltage is set to 0.01 V-1.0 V, and the rate is set to 0.2 C. The batteries of each of the above examples and comparative examples are subjected to 100 cycles of charge and discharge, and the first cycle reversible capacity, the 100th cycle reversible capacity, the cycle capacity retention rate and the volume expansion rate of the electrode sheet are tested, and the results are shown in Table 1.

[0107] Table 1

[0108]

[0109] Referring to Table 1, the battery prepared in Example 1 has a significantly higher cycle capacity retention rate and a lower volume expansion rate, indicating that the strain of the composite negative electrode sheet as a whole during the charging and discharging process is relatively low, and the composite negative electrode sheet has a significantly higher cycle stability. Examples 2-4 have similar structures to Example 1, the main difference being only the active material used, which results in a difference in the first-week reversible capacity, but Examples 2-4 also have a significantly higher cycle capacity retention rate and a lower volume expansion rate.

[0110] Compared with Example 1, Comparative Example 1 mixes and coats the first slurry and the second slurry. Among them, the cycle capacity retention rate of Comparative Example 1 is only 81.73%, which is significantly lower than that of Example 1, and the volume expansion rate of the electrode sheet of Comparative Example 1 is also significantly higher than that of Example 1. This shows that the second active layer needs to be set on the basis of the first active layer in order to more effectively inhibit the volume expansion of the first active layer. Comparative Example 2 uses a flat copper foil, and the cycle capacity retention rate is only 87.69%, and the volume expansion rate of the electrode sheet of Comparative Example 2 is also significantly higher than that of Example 1. This shows that the use of a porous copper foil with active material accommodation holes can more effectively inhibit the volume expansion of the first active layer. Comparative Example 3 uses silicon nanoparticles instead of silicon nanosheets, and the cycle capacity retention rate is only 73.54%, and the volume expansion rate is even higher. This is mainly because the silicon nanoparticles can fill the active material accommodation holes, at this time the active material accommodation holes basically do not have space for volume change, and at this time the second active layer alone is also difficult to inhibit the expansion, pulverization and falling off of the first active layer.

[0111] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and embodiments having the same technical idea and playing the same role and effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, within the scope of the main idea of the present application, various modifications that can be thought of by those skilled in the art, other ways constructed by combining part of the components of the embodiments are also included in the scope of the present application.

Claims

1. A composite negative electrode sheet, characterized by comprising: The application relates to a composite negative electrode sheet, which comprises: a current collector having a plurality of active material accommodating holes which are open on the surface of the current collector and have bottoms in the current collector; a first active layer, wherein the active material in the first active layer comprises silicon active material in the form of nanosheets, the first active layer is arranged on the surface of the current collector, and at least part of the silicon active material is located in the active material accommodating holes; and a second active layer comprising graphite, which is arranged on the side of the first active layer away from the current collector and covers the first active layer as a whole. The depth of the active material accommodating holes is 3-9 mu m. In the current collector, the diameter of the active material accommodating holes is 20-100 mu m. In the first active layer, the thickness of the silicon active material is 5-100 nm, and the radial dimension of the silicon active material is 100-2000 nm.

2. The composite negative electrode sheet according to claim 1, characterized by, The ratio of the thickness of the first active layer to the thickness of the second active layer is 1: (0.2-1.5).

3. The composite negative electrode sheet according to claim 1, characterized by, The overall thickness of the first active layer is 15-50 mu m.

4. The composite negative electrode sheet according to claim 3, characterized by The openings of all the active material accommodating holes on the surface of the current collector account for 30-80% of the surface of the current collector.

5. The composite negative electrode sheet according to any one of claims 1 to 4, characterized by The active material in the first active layer further comprises carbon active material selected from one or more of graphite, hard carbon, soft carbon and graphene, and in the first active layer, the mass ratio of the silicon active material to the carbon active material is 1: (0.5-2).

6. The composite negative electrode sheet according to any one of claims 1 to 4, characterized by The mass proportion of the active material in the first active layer in the first active layer is above 80%.

7. The composite negative electrode sheet according to any one of claims 1 to 4, characterized by The first active layer further comprises at least one of a first conductive agent and a first binder; wherein The first conductive agent is selected from one or more of conductive carbon black, carbon nanotubes, graphene, carbon nanofibers and carbon-coated tin nanowires.

8. The composite negative electrode sheet according to any one of claims 1 to 4, characterized by The mass proportion of graphite in the second active layer is above 90%, and the second active layer further comprises at least one of a second conductive agent and a second binder.

9. A battery, characterized by The application further relates to a battery, which comprises a negative electrode sheet, a positive electrode sheet and an electrolyte; the positive electrode sheet and the negative electrode sheet are oppositely arranged, and the negative electrode sheet is the composite negative electrode sheet.

10. An electric device, characterized by The application further relates to an electric device, which comprises a battery for supplying power to the electric device.

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