Negative electrode sheet, battery cell, and battery

Abstract

The utility model discloses a kind of negative pole piece, battery cell and battery, negative pole piece includes negative pole current collector, negative pole active material layer and conductive electrolyte expansion layer.Negative pole active material layer is set on at least one side of the thickness direction of negative pole current collector;Conductive electrolyte expansion layer is set on the side of negative pole active material layer away from negative pole current collector, the side of conductive electrolyte expansion layer away from negative pole current collector is used to contact with lithium supplement layer, conductive electrolyte expansion layer can swell, and fill the gap between lithium supplement layer and negative pole active material layer.The negative pole piece of the utility model can improve the utilization rate of metal lithium in prelithiation reaction of lithium supplement layer.

Description

Technical Field

[0001] This utility model relates to the field of battery technology, and in particular to a negative electrode sheet, a battery cell, and a battery. Background Technology

[0002] Lithium-ion batteries often suffer from low initial efficiency of the negative electrode, especially silicon negative electrode materials. Due to the expansion of the material itself, the initial efficiency of silicon negative electrode materials is lower than that of graphite negative electrode materials. The low initial efficiency of the negative electrode will irreversibly consume the lithium in the positive electrode, resulting in a low overall battery capacity.

[0003] In related technologies, a thinning and composite lithium replenishment layer is applied to the negative electrode sheet using contact pre-lithiation methods such as rolling lithium replenishment and vapor deposition lithium replenishment. This achieves pre-lithiation of the negative electrode sheet, compensating for irreversible lithium loss and improving the battery's initial efficiency and capacity. However, during the pre-lithiation reaction, not all the lithium metal in the replenishment layer participates in the reaction. The utilization rate of the lithium metal in the replenishment layer is usually low. The unreacted lithium metal loses its electronic conductivity and forms dead lithium, which accumulates at the negative electrode interface, hindering lithium-ion diffusion and mass transfer. This leads to phenomena such as increased polarization and lithium plating in the battery. Utility Model Content

[0004] This invention aims to solve at least one of the technical problems existing in the prior art. To this end, this invention proposes a negative electrode sheet, a battery cell, and a battery that can improve the utilization rate of metallic lithium in the pre-lithiation reaction of the lithium replenishment layer.

[0005] This utility model embodiment provides a negative electrode sheet, the negative electrode sheet comprising:

[0006] Negative electrode current collector;

[0007] A negative electrode active material layer is disposed on at least one side in the thickness direction of the negative electrode current collector;

[0008] The conductive electrolyte expansion layer is disposed on the side of the negative electrode active material layer away from the negative electrode current collector. The side of the conductive electrolyte expansion layer away from the negative electrode current collector is used to contact the lithium replenishment layer. The conductive electrolyte expansion layer can expand and fill the gap between the lithium replenishment layer and the negative electrode active material layer.

[0009] The negative electrode sheet according to this utility model has at least the following beneficial effects:

[0010] By setting a conductive electrolyte expansion layer on the side of the negative electrode active material layer away from the negative electrode current collector for contact with the lithium replenishment layer, during the pre-lithiation reaction, even if the lithium replenishment layer is gradually consumed and the gap between the lithium replenishment layer and the negative electrode active material layer gradually increases, the conductive electrolyte expansion layer can fill the gap between the lithium replenishment layer and the negative electrode active material layer through its own expansion and maintain contact with the lithium replenishment layer. This ensures that the lithium replenishment layer and the negative electrode active material layer can always maintain an electrical connection. In this way, the metallic lithium in the lithium replenishment layer can basically enter the negative electrode active material layer, thereby improving the utilization rate of metallic lithium in the lithium replenishment layer during the pre-lithiation reaction, avoiding the phenomenon of dead lithium, and thus avoiding phenomena such as increased polarization and lithium plating in the battery, and improving the initial coulombic efficiency of the battery.

[0011] According to some embodiments of this utility model, negative electrode active material layers are respectively provided on opposite sides of the negative electrode current collector in the thickness direction, and a conductive electrolyte expansion layer is provided on the side of each negative electrode active material layer away from the negative electrode current collector.

[0012] According to some embodiments of the present invention, the product of the initial thickness of the conductive electrolyte expansion layer and the expansion rate of the conductive electrolyte expansion layer is greater than or equal to 0.9 times the initial thickness of the lithium replenishment layer, and less than or equal to 1.1 times the initial thickness of the lithium replenishment layer.

[0013] According to some embodiments of the present invention, the negative electrode active material layer includes a non-thinned portion and a thinned portion, the thinned portion being disposed on at least one side of the non-thinned portion along the width direction of the negative electrode current collector; the conductive electrolyte expansion layer includes a main region and an edge region, the edge region being disposed on at least one side of the main region along the width direction of the negative electrode current collector, the main region being located on the side of the non-thinned portion away from the negative electrode current collector, and the edge region being located on the side of the thinned portion away from the negative electrode current collector;

[0014] The initial thickness of the edge region is greater than the initial thickness of the main body region, and / or the expansion rate of the edge region is greater than the expansion rate of the main body region.

[0015] According to some embodiments of the present invention, the product of the initial thickness of the edge region and the expansion rate of the edge region is greater than or equal to 1.05 times the product of the initial thickness of the main body region and the expansion rate of the main body region, and less than or equal to 3 times the product of the initial thickness of the main body region and the expansion rate of the main body region.

[0016] According to some embodiments of this utility model, the negative electrode sheet is the negative electrode sheet of a wound battery cell, and the negative electrode sheet is provided with a straight section and a bent section; the conductive electrolyte expansion layer includes a first section and a second section, the first section and the second section are arranged sequentially along the length direction of the negative electrode current collector, wherein the first section is located in the straight section and the second section is located in the bent section;

[0017] The initial thickness of the second segment is greater than the initial thickness of the first segment, and / or the expansion rate of the second segment is greater than the expansion rate of the first segment.

[0018] According to some embodiments of the present invention, the product of the initial thickness of the second segment and the expansion rate of the second segment is greater than or equal to 1.1 times the product of the initial thickness of the first segment and the expansion rate of the first segment, and less than or equal to 5 times the product of the initial thickness of the first segment and the expansion rate of the first segment.

[0019] According to some embodiments of the present invention, a second segment is provided on both the outer and inner sides of the bent segment, and the length of the second segment on the outer side is greater than the length of the second segment on the inner side.

[0020] This utility model embodiment also provides a battery cell, which includes a shell, an electrolyte, a positive electrode, a separator, and a negative electrode as described above. The electrolyte fills the interior of the shell, and the negative electrode, separator, and positive electrode are stacked in sequence and housed inside the shell.

[0021] This utility model embodiment also provides a battery, which includes the battery cell described above.

[0022] Additional aspects and advantages of this invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0023] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein:

[0024] Figure 1 This is a schematic diagram of the negative electrode sheet and the lithium replenishment layer in the first embodiment of this utility model;

[0025] Figure 2 This is a schematic diagram of the negative electrode sheet and the lithium replenishment layer in the second embodiment of this utility model;

[0026] Figure 3 This is a schematic diagram of the negative electrode sheet and the lithium replenishment layer in the third embodiment of the present invention. The negative electrode sheet is the negative electrode sheet of a wound battery cell. The figure shows the state of the negative electrode sheet after it is laid out.

[0027] Figure label:

[0028] Negative electrode plate 100; Straight section 101; Bending section 102;

[0029] Negative electrode current collector 10; Negative electrode active material layer 20; Non-thinned portion 21; Thinned portion 22; Conductive electrolyte expansion layer 30; Main body region 31; Edge region 32; First segment 33; Second segment 34;

[0030] Lithium replenishment layer 200. Detailed Implementation

[0031] The embodiments of this utility model are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this utility model, and should not be construed as limiting this utility model.

[0032] In the description of this utility model, it should be understood that the directional descriptions, such as up, down, front, back, left, right, etc., indicate the directional or positional relationship based on the directional or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this utility model.

[0033] In the description of this utility model, "several" means one or more, "multiple" means two or more, "greater than," "less than," and "exceeding" are understood to exclude the stated number, while "above," "below," and "within" are understood to include the stated number. The use of "first" and "second" in the description is merely for distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the order of the indicated technical features.

[0034] In the description of this utility model, unless otherwise explicitly defined, terms such as "setting," "installation," and "connection" should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this utility model in conjunction with the specific content of the technical solution.

[0035] In the description of this utility model, the terms "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this utility model. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0036] In related technologies, the lithium replenishment layer is located on the side of the negative electrode active material layer away from the negative electrode current collector. During the pre-lithiation reaction, the lithium replenishment layer is continuously consumed, and the gap between the lithium replenishment layer and the negative electrode active material layer gradually increases. This causes some of the metallic lithium in the lithium replenishment layer to be unable to participate in the pre-lithiation reaction. After losing its electronic conductivity, some of the metallic lithium forms dead lithium, which accumulates on the negative electrode interface, hindering the diffusion and mass transfer of lithium ions, resulting in phenomena such as increased polarization and lithium plating in the battery.

[0037] In view of this, such as Figure 1 As shown, Figure 1 This diagram illustrates the combination of the negative electrode sheet and the lithium replenishment layer in the first embodiment of the present invention. The present invention provides a negative electrode sheet 100 that can improve the utilization rate of metallic lithium in the lithium replenishment layer 200 during the pre-lithiation reaction.

[0038] The negative electrode 100 includes a negative current collector 10, a negative active material layer 20, and a conductive electrolyte expansion layer 30.

[0039] The negative electrode active material layer 20 is disposed on at least one side of the negative electrode current collector 10 in the thickness direction Z; the conductive electrolyte expansion layer 30 is disposed on the side of the negative electrode active material layer 20 away from the negative electrode current collector 10, and the side of the conductive electrolyte expansion layer 30 away from the negative electrode current collector 10 is used to contact the lithium replenishment layer 200. The conductive electrolyte expansion layer 30 can expand and fill the gap between the lithium replenishment layer 200 and the negative electrode active material layer 20.

[0040] During the pre-lithiation reaction, the lithium replenishment layer 200 and the negative electrode active material layer 20 are electrically connected through the conductive electrolyte expansion layer 30. The lithium atoms in the lithium replenishment layer 200 undergo an oxidation reaction, losing electrons to generate lithium ions. Electrons and lithium ions are transferred to the surface or interior of the negative electrode active material layer 20 through the conductive electrolyte expansion layer 30. Electrons and lithium ions undergo a reduction reaction in the negative electrode active material layer 20 to form a lithium intercalation compound, thereby achieving the pre-lithiation of the negative electrode 100.

[0041] In the specific implementation process, the conductive electrolyte expansion layer 30 can be prepared by electrospinning, melt extrusion-stretching, phase separation, blown film and other methods. After the prepared conductive electrolyte expansion layer 30 is composited onto the side of the negative electrode active material layer 20 away from the negative electrode current collector 10, the lithium supplement layer 200 is thinned and composited onto the conductive electrolyte expansion layer 30 by lithium supplementation methods such as rolling lithium supplementation and vapor deposition lithium supplementation on the side of the conductive electrolyte expansion layer 30 away from the negative electrode current collector 10, thereby preparing the pre-lithiated negative electrode sheet 100.

[0042] In this embodiment of the invention, by providing a conductive electrolyte expansion layer 30 for contacting the lithium replenishment layer 200 on the side of the negative electrode active material layer 20 away from the negative electrode current collector 10, during the pre-lithiation reaction, even if the lithium replenishment layer 200 is gradually consumed, causing the gap between the lithium replenishment layer 200 and the negative electrode active material layer 20 to gradually increase, the conductive electrolyte expansion layer 30 can fill the gap between the lithium replenishment layer 200 and the negative electrode active material layer 20 through its own expansion, and maintain contact with the lithium replenishment layer 200, so that the lithium replenishment layer 200 and the negative electrode active material layer 20 can always maintain an electrical connection. In this way, the metallic lithium of the lithium replenishment layer 200 can basically enter the negative electrode active material layer 20, thereby improving the utilization rate of metallic lithium in the lithium replenishment layer 200 during the pre-lithiation reaction, avoiding the phenomenon of dead lithium, and thus avoiding phenomena such as increased polarization and lithium plating in the battery, and improving the initial coulombic efficiency of the battery.

[0043] Furthermore, even after the lithium replenishment layer 200 is depleted, the conductive electrolyte expansion layer 30 can still increase the liquid retention in its location, thereby improving battery cycle performance and other properties.

[0044] In some embodiments, the conductive electrolyte expansion layer 30 includes an expansion filler for providing an expansion effect to the conductive electrolyte expansion layer 30.

[0045] The expandable filler includes polystyrene and / or polystyrene derivatives, which can swell and foam under the action of organic solvents in the electrolyte.

[0046] In some embodiments, the conductive electrolyte expansion layer 30 further includes an elastomer, which is used to adjust the expansion ratio and buffering capacity of the conductive electrolyte expansion layer 30. The expansion ratio of the conductive electrolyte expansion layer 30 is related to the ratio of polystyrene to elastomer; the higher the proportion of elastomer, the lower the expansion ratio of the conductive electrolyte expansion layer 30.

[0047] The elastomer includes, but is not limited to, at least one of polybutadiene, polyisobutylene, ethylene-vinyl acetate copolymer, styrene-ethylene-butene-styrene copolymer, or polyurethane.

[0048] In some embodiments, the elastomer accounts for 1% to 30% of the mass of the conductive electrolyte expansion layer 30.

[0049] Preferably, the elastomer accounts for 5% to 17% of the mass of the conductive electrolyte expansion layer 30.

[0050] In this process, by utilizing the polymer in the expanding filler and elastomer to absorb the electrolyte and undergo swelling and foaming, the liquid retention function of the conductive electronic electrolyte expansion layer 30 can be achieved, thereby increasing the liquid retention of the negative electrode 100.

[0051] In some embodiments, the conductive electrolyte expansion layer 30 further includes a conductive filler, which is used to achieve electronic conduction between the lithium replenishment layer 200 and the negative electrode active material layer 20.

[0052] The conductive filler includes, but is not limited to, at least one of non-metallic fillers, polymer fillers, metallic fillers, and metal oxide fillers.

[0053] Among them, non-metallic fillers include, but are not limited to, at least one of carbon black, graphite, carbon fiber and carbon nanotubes; polymer fillers include, but are not limited to, conductive polymers; metallic fillers include, but are not limited to, at least one of copper and aluminum; and metal oxide fillers include, but are not limited to, at least one of copper oxide and zinc oxide.

[0054] In some embodiments, the percentage of the conductive filler in the conductive electrolyte expansion layer 30 by mass is 0.1% to 20%.

[0055] Preferably, the percentage of the conductive filler in the conductive electrolyte expansion layer 30 by mass is 0.5% to 13%.

[0056] In some embodiments, the resistance of the conductive electronic electrolyte expansion layer 30 is 0.01 to 100 mΩ.

[0057] Preferably, the resistance of the conductive electronic electrolyte expansion layer 30 is 0.01 to 30 mΩ.

[0058] In some embodiments, negative electrode active material layers 20 are respectively provided on opposite sides of the negative electrode current collector 10 in the thickness direction Z, and each negative electrode active material layer 20 is provided with a conductive electrolyte expansion layer 30 on the side opposite to the negative electrode current collector 10. In this way, pre-lithiation can be performed on both sides of the negative electrode sheet 100 along the thickness direction Z of the current collector, so as to achieve effective lithium replenishment on both sides of the negative electrode sheet 100, which can further improve the first coulombic efficiency of the battery and the battery cycle performance.

[0059] In some embodiments, the product of the initial thickness of the conductive electrolyte expansion layer 30 and the expansion rate of the conductive electrolyte expansion layer 30 is greater than or equal to 0.9 times the initial thickness of the lithium replenishment layer 200, and less than or equal to 1.1 times the initial thickness of the lithium replenishment layer 200.

[0060] The initial thickness of the lithium replenishment layer 200 is the thickness of the lithium replenishment layer 200 before expansion, the initial thickness of the conductive electrolyte expansion layer 30 is the thickness of the conductive electrolyte expansion layer 30 before expansion, and the product of the initial thickness of the conductive electrolyte expansion layer 30 and the expansion rate of the conductive electrolyte expansion layer 30 is equal to the thickness of the conductive electrolyte expansion layer 30 after expansion.

[0061] In this embodiment, by limiting the thickness of the expanded conductive electrolyte layer 30, it is possible to ensure mutual contact between the expanded conductive electrolyte layer 30 and the lithium replenishment layer 200, so that electronic conductivity always exists between the lithium replenishment layer 200 and the negative electrode active material layer. At the same time, it is possible to avoid the expansion of the expanded conductive electrolyte layer 30 leading to an increase in the gap between the negative electrode sheet 100 and the separator, thus avoiding affecting the performance and energy density of the battery.

[0062] If the thickness of the expanded electronic electrolyte layer 30 is greater than 1.1 times the initial thickness of the lithium replenishment layer 200, it will affect the energy density of the battery; if the thickness of the expanded electronic electrolyte layer 30 is less than 0.9 times the initial thickness of the lithium replenishment layer 200, it will affect the lithium replenishment efficiency, causing the lithium replenishment layer 200 to not be fully utilized, which in turn leads to low long-cycle stability of the battery.

[0063] In some embodiments, the initial thickness of the lithium replenishment layer 200 is 0.1 μm to 5 μm.

[0064] Preferably, the initial thickness of the lithium replenishment layer 200 is 0.4 μm to 2.5 μm.

[0065] In some embodiments, the initial thickness of the conductive electrolyte expansion layer 30 is 0.1 to 2 μm; or, the expansion rate of the conductive electrolyte expansion layer 30 is 200% to 400%; or, the initial thickness of the conductive electrolyte expansion layer 30 is 0.1 to 2 μm, and the expansion rate of the conductive electrolyte expansion layer 30 is 200% to 400%.

[0066] Preferably, the initial thickness of the conductive electronic electrolyte expansion layer 30 is 0.3 μm to 1 μm.

[0067] Preferably, the expansion rate of the conductive electronic electrolyte expansion layer 30 is 200% to 400%.

[0068] In this embodiment, by further limiting the initial thickness of the conductive electrolyte expansion layer 30 and / or the expansion rate of the conductive electrolyte expansion layer 30, the mutual contact between the conductive electrolyte expansion layer 30 and the lithium replenishment layer 200 can be further guaranteed, so that there is always electronic conductivity between the lithium replenishment layer 200 and the negative electrode active material layer. This further avoids the increase in the gap between the negative electrode sheet 100 and the separator after the conductive electrolyte expansion layer 30 expands, and further avoids affecting the performance and energy density of the battery.

[0069] During the production of electrodes, it is usually necessary to thin the edge of the active material layer along the width direction of the current collector to form a thinned portion. In the negative electrode 100, the thinned portion is located at the edge of the negative electrode active material layer 20 along the width direction Y of the negative electrode current collector 10. Because a gap is generated between the thinned portion and the lithium replenishment layer 200 after the thinned portion is thinned, the participation rate of metallic lithium in the lithium replenishment layer 200 corresponding to the thinned portion is relatively low in the subsequent pre-lithiation reaction.

[0070] In view of this, such as Figure 2 As shown, Figure 2 This diagram illustrates the interaction between the negative electrode sheet and the lithium replenishment layer in a second embodiment of the present invention. In some embodiments, the negative electrode active material layer 20 includes a non-thinned portion 21 and a thinned portion 22, with the thinned portion 22 disposed on at least one side of the non-thinned portion 21 along the width direction Y of the negative electrode current collector 10. The conductive electrolyte expansion layer 30 includes a main region 31 and an edge region 32, with the edge region 32 disposed on at least one side of the main region 31 along the width direction Y of the negative electrode current collector 10. The main region 31 is located on the side of the non-thinned portion 21 facing away from the negative electrode current collector 10, and the edge region 32 is located on the side of the thinned portion 22 facing away from the negative electrode current collector 10. The initial thickness of the edge region 32 is greater than the initial thickness of the main region 31; or, the expansion rate of the edge region 32 is greater than the expansion rate of the main region 31; or, the initial thickness of the edge region 32 is greater than the initial thickness of the main region 31, and the expansion rate of the edge region 32 is greater than the expansion rate of the main region 31.

[0071] The initial thickness of the main body region 31 is the same as the thickness of the edge region 32 before expansion. The product of the initial thickness of the main body region 31 and the expansion rate of the main body region 31 is equal to the thickness of the main body region 31 after expansion. The product of the initial thickness of the edge region 32 and the expansion rate of the edge region 32 is equal to the thickness of the edge region 32 after expansion.

[0072] In this embodiment, by making the initial thickness of the edge region 32 greater than the initial thickness of the main body region 31, and / or making the expansion rate of the edge region 32 greater than the expansion rate of the main body region 31, the edge region 32 can fill the gap between the thinned portion 22 and the lithium replenishment layer 200, so that the lithium replenishment layer 200 can always maintain an electrical connection with the thinned portion 22 through the edge region 32, ensuring that the metallic lithium in the lithium replenishment layer 200 can basically participate in the pre-lithiation reaction process, improving the utilization rate of metallic lithium in the lithium replenishment layer 200 in the pre-lithiation reaction, reducing the risk of lithium deposition at the edge of the negative electrode 100, and reducing the risk of internal short circuit caused by the edge burrs of the negative electrode 100 piercing the separator in the battery, thereby improving the safety of the battery.

[0073] In some embodiments, thinning portions 22 are provided on both sides of the non-thinned portion 21 along the width direction Y of the negative electrode current collector 10, and edge regions 32 are provided on both sides of the main body region 31 along the width direction Y of the negative electrode current collector 10. Each edge region 32 is provided on the side of each thinned portion 22 away from the negative electrode current collector 10 and fills the space between the lithium replenishment layers 200 of the thinned portion 22.

[0074] In some embodiments, the product of the initial thickness of the edge region 32 and the expansion rate of the edge region 32 is greater than or equal to 1.05 times the product of the initial thickness of the body region 31 and the expansion rate of the body region 31, and less than or equal to 3 times the product of the initial thickness of the body region 31 and the expansion rate of the body region 31.

[0075] In this embodiment, by limiting the thickness of the expanded main region 31 and the expanded edge region 32, it is possible to ensure that the main region 31 and the edge region 32 are in contact with the lithium replenishment layer 200, so that there is always electronic conductivity between the lithium replenishment layer 200 and the negative electrode active material layer. At the same time, it is possible to avoid the expansion of the main region 31 and the edge region 32, which would increase the gap between the negative electrode sheet 100 and the separator, thus avoiding affecting the performance and energy density of the battery.

[0076] In some embodiments, the initial thickness of the lithium replenishment layer 200 is 0.1 μm to 5 μm.

[0077] Preferably, the initial thickness of the lithium replenishment layer 200 is 0.4 μm to 2.5 μm.

[0078] In some embodiments, the initial thickness of the main body region 31 is 0.1 to 2 μm; or, the expansion rate of the main body region 31 is 200% to 400%; or, the initial thickness of the main body region 31 is 0.1 to 2 μm, and the expansion rate of the main body region 31 is 200% to 400%.

[0079] Preferably, the initial thickness of the main body region 31 is 0.3 μm to 1 μm.

[0080] Preferably, the expansion rate of the main body region 31 is 200% to 400%.

[0081] In some embodiments, the initial thickness of the edge region 32 is 0.1 to 2 μm; or, the expansion rate of the edge region 32 is 200% to 400%; or, the initial thickness of the edge region 32 is 0.1 to 2 μm, and the expansion rate of the edge region 32 is 200% to 400%.

[0082] Preferably, the initial thickness of the edge region 32 is 0.3 μm to 1 μm.

[0083] Preferably, the expansion rate of the edge region 32 is 200% to 400%.

[0084] It is understood that the negative electrode 100 provided in this embodiment of the present invention can be applied to wound cells or stacked cells.

[0085] Specifically, in a wound cell, the negative electrode 100 is wound into a roll. The wound negative electrode 100 has a straight section 101 and a bent section 102. The bent section 102 connects two adjacent straight sections 101. Since the bent section 102 forms a corner between two adjacent straight sections 101, the structure of the bent section 102 is not as compact as that of the straight section 101. As a result, a certain gap will be generated between the negative electrode active material layer 20 and the lithium replenishment layer 200 at the bent section 102, which leads to a lower participation rate of metallic lithium in the lithium replenishment layer 200 at the bent section 102 in the subsequent pre-lithiation reaction.

[0086] In view of this, such as Figure 3 As shown, Figure 3 This diagram illustrates the cooperation between the negative electrode sheet and the lithium replenishment layer in a third embodiment of the present invention. The negative electrode sheet is a negative electrode sheet of a wound battery cell. The diagram shows the state of the negative electrode sheet after it has been unwound. In some embodiments, the negative electrode sheet 100 is a negative electrode sheet 100 of a wound battery cell, and the negative electrode sheet 100 has a straight section 101 and a bent section 102. The conductive electrolyte expansion layer 30 includes a first section 33 and a second section 34, which are sequentially arranged along the length direction X of the negative electrode current collector 10. The first section 33 is located in the straight section 101, and the second section 34 is located in the bent section 102.

[0087] The initial thickness of the second segment 34 is greater than the initial thickness of the first segment 33; or, the expansion rate of the second segment 34 is greater than the expansion rate of the first segment 33; or, the initial thickness of the second segment 34 is greater than the initial thickness of the first segment 33, and the expansion rate of the second segment 34 is greater than the expansion rate of the first segment 33.

[0088] The initial thickness of the first segment 33 is the thickness of the first segment 33 before expansion, the initial thickness of the second segment 34 is the thickness of the second segment 34 before expansion, the product of the initial thickness of the first segment 33 and the expansion rate of the first segment 33 is equal to the thickness of the first segment 33 after expansion, and the product of the initial thickness of the second segment 34 and the expansion rate of the second segment 34 is equal to the thickness of the second segment 34 after expansion.

[0089] In this embodiment, by making the initial thickness of the second segment 34 greater than the initial thickness of the first segment 33, and / or making the expansion rate of the second segment 34 greater than the expansion rate of the first segment 33, the second segment 34 can fill the gap between the negative electrode active material layer 20 and the lithium replenishment layer 200 at the bending segment 102. This allows the lithium replenishment layer 200 to maintain an electrical connection with the negative electrode active material layer 20 at the bending segment 102 through the second segment 34, ensuring that the metallic lithium in the lithium replenishment layer 200 can basically participate in the pre-lithiation reaction process, improving the utilization rate of metallic lithium in the lithium replenishment layer 200 during the pre-lithiation reaction. Furthermore, it can prevent the electrolyte at the bending segment 102 from being squeezed out due to the expansion of the negative electrode sheet 100, increasing the electrolyte retention at the bending segment 102 and preventing lithium plating at the bending segment 102.

[0090] In some embodiments, the product of the initial thickness of the second segment 34 and the expansion rate of the second segment 34 is greater than or equal to 1.1 times the product of the initial thickness of the first segment 33 and the expansion rate of the first segment 33, and less than or equal to 5 times the product of the initial thickness of the first segment 33 and the expansion rate of the first segment 33.

[0091] In this embodiment, by limiting the thickness of the first segment 33 after expansion and the thickness of the second segment 34 after expansion, it is possible to ensure that the first segment 33 and the second segment 34 are in contact with the lithium replenishment layer 200, so that there is always electronic conductivity between the lithium replenishment layer 200 and the negative electrode active material layer. At the same time, it is possible to avoid the increase in the gap between the negative electrode sheet 100 and the separator after the first segment 33 and the second segment 34 expand, so as to avoid affecting the performance and energy density of the battery.

[0092] In some embodiments, the initial thickness of the lithium replenishment layer 200 is 0.1 μm to 5 μm.

[0093] Preferably, the initial thickness of the lithium replenishment layer 200 is 0.4 μm to 2.5 μm.

[0094] In some embodiments, the initial thickness of the first segment 33 is 0.1 to 2 μm; or, the expansion rate of the first segment 33 is 200% to 400%; or, the initial thickness of the first segment 33 is 0.1 to 2 μm, and the expansion rate of the first segment 33 is 200% to 400%.

[0095] Preferably, the initial thickness of the first segment 33 is 0.3 μm to 1 μm.

[0096] Preferably, the expansion rate of the first segment 33 is 200% to 400%.

[0097] In some embodiments, the initial thickness of the second segment 34 is 0.1 to 2 μm; or, the expansion rate of the second segment 34 is 200% to 400%; or, the initial thickness of the second segment 34 is 0.1 to 2 μm, and the expansion rate of the second segment 34 is 200% to 400%.

[0098] Preferably, the initial thickness of the second segment 34 is 0.3 μm to 1 μm.

[0099] Preferably, the expansion rate of the second segment 34 is 200% to 400%.

[0100] After the negative electrode sheet 100 is wound into a coil to form a bent section 102, because the negative electrode sheet 100 has a certain thickness, the arc length of the negative electrode active material layer 20 on the outer side of the bent section 102 will be greater than the arc length of the negative electrode active material layer 20 on the inner side.

[0101] Therefore, in some embodiments, a second segment 34 is provided on both the outer and inner sides of the bent section 102. The length of the second segment 34 on the outer side is greater than the length of the second segment 34 on the inner side. In this way, after the negative electrode sheet 100 is wound into a roll, the arc length of the second segment 34 on the outer side can match the arc length of the outer negative electrode active material layer 20, ensuring that the second segment 34 on the outer side can effectively fill the gap between the outer negative electrode active material layer 20 and the lithium replenishment layer 200. The arc length of the second segment 34 on the inner side can match the arc length of the inner negative electrode active material layer 20, ensuring that the second segment 34 on the inner side can effectively fill the gap between the inner negative electrode active material layer 20 and the lithium replenishment layer 200.

[0102] The outer side of the bent section 102 refers to the side of the bent section 102 that is away from the center of the wound negative electrode sheet 100; the inner side of the bent section 102 refers to the other side of the bent section 102 that is close to the center of the wound negative electrode sheet 100.

[0103] This utility model embodiment also provides a battery cell, which includes an electrolyte, a shell, a positive electrode, a separator, and a negative electrode 100 provided in any of the above embodiments. The electrolyte is filled inside the shell, and the negative electrode 100, the separator, and the positive electrode are stacked in sequence and housed inside the shell.

[0104] The electrolyte includes at least one of ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl formate, methyl butyrate, methyl acetate, ethyl propionate, and polycarbonate.

[0105] The outer shell can be made of aluminum-plastic film or steel, etc.

[0106] The battery cells from the above embodiments were used to test the electrolyte retention, energy density, initial coulombic efficiency, and cycle capacity retention. The experimental results are shown in Table 1 below.

[0107] Table 1

[0108]

[0109]

[0110] Among them, the battery cells of Examples 1 to 8 in Table 1 adopt the negative electrode structure of the first embodiment of this utility model, that is, they adopt... Figure 1 The negative electrode structure is shown.

[0111] The resistance of the electrolyte expansion layer, electrolyte retention, energy density, initial coulombic efficiency, and cycle capacity retention of the battery cell, as shown in Table 1 above, can be obtained using the following corresponding methods:

[0112] Method for testing the resistance of the conductive electrolyte expansion layer: The resistance of the conductive electrolyte expansion layer is tested using the four-probe method. Specifically, four probes are arranged at equal intervals and contact the surface of the conductive electrolyte expansion layer. A constant current is passed through the two outer probes, and the voltage drop is measured on the two inner probes. The resistance of the electrolyte expansion layer can then be calculated by dividing the voltage drop by the current.

[0113] The method for calculating the liquid retention capacity of a battery cell is as follows: Weigh the battery cell after the second sealing process and before liquid injection. Subtract the weight of the gas bag from the weight of the cell after the second sealing process, and subtract the weight of the cell before liquid injection, to calculate the liquid retention capacity of the battery cell. The gas bag is the bag used to store the gas generated during the battery cell formation process; it is removed during the second sealing process.

[0114] The method for calculating the energy density of a battery cell: Energy density refers to volumetric energy density. The volumetric energy density of a battery cell can be calculated by multiplying its discharge capacity by its operating voltage and then dividing by its volume.

[0115] The initial coulombic efficiency of a battery cell is calculated by dividing the initial discharge capacity by the initial charge capacity. The initial discharge capacity refers to the discharge capacity during the cell's capacity grading process, while the initial charge capacity refers to the charge capacity during both the cell formation and capacity grading processes.

[0116] The method for testing the cycle capacity retention rate of a battery cell is as follows: Under 25°C conditions, the battery cell is charged and discharged for the first time. It is charged at a constant current of 2C to the cutoff voltage of 4.53V, and then charged at a constant voltage of 4.53V until the current is less than 0.025C. After resting for 5 minutes, it is discharged at a constant current of 0.5C to the cutoff voltage of 3.0V. The discharge capacity of the battery cell is measured as A. Then, in an environment of 25°C, the above steps are performed for N (e.g., 600) charge and discharge cycles. The discharge capacity of the secondary battery in the Nth (e.g., 600th) cycle is measured as B. The cycle capacity retention rate is calculated as B / A.

[0117] As can be seen from Table 1, the battery cell provided in this embodiment of the present invention, by providing a conductive electrolyte expansion layer 30 for contacting the lithium replenishment layer 200 on the side of the negative electrode active material layer 20 away from the negative electrode current collector 10, allows the conductive electrolyte expansion layer 30 to fill the gap between the lithium replenishment layer 200 and the negative electrode active material layer 20 through its own expansion during the pre-lithiation reaction, even if the lithium replenishment layer 200 is gradually consumed and the gap between the lithium replenishment layer 200 and the negative electrode active material layer 20 gradually increases, and maintains contact with the lithium replenishment layer 200. This ensures that the lithium replenishment layer 200 and the negative electrode active material layer 20 can always maintain an electrical connection. In this way, the metallic lithium of the lithium replenishment layer 200 can basically enter the negative electrode active material layer 20, thereby improving the utilization rate of metallic lithium in the lithium replenishment layer 200 during the pre-lithiation reaction, and thus improving the battery cell's liquid retention, energy density, initial coulombic efficiency, and cycle capacity retention rate.

[0118] The product of the initial thickness of the conductive electrolyte expansion layer 30 and the expansion rate of the conductive electrolyte expansion layer 30 is greater than or equal to 0.9 times the initial thickness of the lithium replenishment layer 200, and less than or equal to 1.1 times the initial thickness of the lithium replenishment layer 200.

[0119] If the thickness of the expanded conductive electrolyte layer 30 is greater than 1.1 times the initial thickness of the lithium replenishment layer 200, it will affect the energy density of the battery. For example, in Example 2 of Table 1, the product of the initial thickness of the conductive electrolyte layer 30 and the expansion rate of the conductive electrolyte layer 30 (0.48μm*240%=1.152μm) is greater than 1.1 times the initial thickness of the lithium replenishment layer 200 (1.1*1μm=1.1μm), which will cause the cell energy density of Example 2 to be lower than that of Examples 1, 3 to 8. If the thickness of the expanded conductive electrolyte layer 30 is greater than 1.1 times the initial thickness of the lithium replenishment layer 200 (1.1*1μm=1.1μm), it will affect the energy density of the battery. If the initial thickness of the lithium replenishment layer 200 is less than 0.9 times, it will affect the lithium replenishment efficiency, causing the lithium replenishment layer 200 to not be fully utilized, which in turn leads to low long-cycle stability of the battery cell. For example, in Example 6 of Table 1, the product of the initial thickness of the conductive electrolyte expansion layer 30 and the expansion rate of the conductive electrolyte expansion layer 30 (0.45μm*240%=1.08μm) is less than 0.9 times the initial thickness of the lithium replenishment layer 200 (0.9*1.5μm=1.35μm), which will cause the battery cell cycle capacity retention rate of Example 6 to be lower than that of Examples 1 to 5, Example 7 and Example 8.

[0120] This utility model embodiment also provides a battery, which includes the battery cell described above.

[0121] The battery of this utility model embodiment has the beneficial effects of a battery cell, which will not be elaborated here.

[0122] It should be noted that the battery provided in this embodiment only shows the part related to the technical problem to be solved by this embodiment. It is understood that the battery provided in this embodiment also includes other structures for realizing the function of the battery, including but not limited to tabs for connecting to external circuits for charging / discharging.

[0123] Within the scope of knowledge possessed by those skilled in the art, various modifications can be made without departing from the spirit of this utility model. Furthermore, embodiments of this utility model and features thereof can be combined with each other, unless otherwise specified.

Claims

1. A negative electrode sheet, characterized in that, include: Negative electrode current collector; A negative electrode active material layer is disposed on at least one side in the thickness direction of the negative electrode current collector; A conductive electrolyte expansion layer is disposed on the side of the negative electrode active material layer away from the negative electrode current collector. The side of the conductive electrolyte expansion layer away from the negative electrode current collector is used to contact the lithium replenishment layer. The conductive electrolyte expansion layer can expand and fill the gap between the lithium replenishment layer and the negative electrode active material layer.

2. The negative electrode sheet according to claim 1, characterized in that, The negative electrode current collector has negative electrode active material layers on opposite sides in the thickness direction, and each negative electrode active material layer has a conductive electrolyte expansion layer on the side opposite to the negative electrode current collector.

3. The negative electrode sheet according to claim 1, characterized in that, The product of the initial thickness of the conductive electrolyte expansion layer and the expansion rate of the conductive electrolyte expansion layer is greater than or equal to 0.9 times the initial thickness of the lithium replenishment layer, and less than or equal to 1.1 times the initial thickness of the lithium replenishment layer.

4. The negative electrode sheet according to claim 1, characterized in that, The negative electrode active material layer includes a non-thinned portion and a thinned portion, the thinned portion being disposed on at least one side of the non-thinned portion along the width direction of the negative electrode current collector; the conductive electrolyte expansion layer includes a main region and an edge region, the edge region being disposed on at least one side of the main region along the width direction of the negative electrode current collector, the main region being located on the side of the non-thinned portion opposite to the negative electrode current collector, and the edge region being located on the side of the thinned portion opposite to the negative electrode current collector; The initial thickness of the edge region is greater than the initial thickness of the main body region, and / or the expansion rate of the edge region is greater than the expansion rate of the main body region.

5. The negative electrode sheet according to claim 4, characterized in that, The product of the initial thickness of the edge region and the expansion rate of the edge region is greater than or equal to 1.05 times the product of the initial thickness of the main body region and the expansion rate of the main body region, and less than or equal to 3 times the product of the initial thickness of the main body region and the expansion rate of the main body region.

6. The negative electrode sheet according to claim 1, characterized in that, The negative electrode sheet is the negative electrode sheet of a wound battery cell, and the negative electrode sheet is provided with a straight section and a bent section; the conductive electrolyte expansion layer includes a first section and a second section, the first section and the second section are arranged sequentially along the length direction of the negative electrode current collector, wherein the first section is located in the straight section and the second section is located in the bent section; The initial thickness of the second segment is greater than the initial thickness of the first segment, and / or the expansion rate of the second segment is greater than the expansion rate of the first segment.

7. The negative electrode sheet according to claim 6, characterized in that, The product of the initial thickness of the second segment and the expansion rate of the second segment is greater than or equal to 1.1 times the product of the initial thickness of the first segment and the expansion rate of the first segment, and less than or equal to 5 times the product of the initial thickness of the first segment and the expansion rate of the first segment.

8. The negative electrode sheet according to claim 6, characterized in that, The second segment is provided on both the outer and inner sides of the bent section, and the length of the second segment on the outer side is greater than the length of the second segment on the inner side.

9. A battery cell, characterized in that, The device includes a housing, an electrolyte, a positive electrode, a separator, and a negative electrode as described in any one of claims 1 to 8, wherein the electrolyte fills the interior of the housing, and the negative electrode, the separator, and the positive electrode are stacked sequentially and housed within the housing.

10. A battery, characterized in that, Includes the battery cell described in claim 9.

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