Negative electrode sheet, battery and electronic device

Abstract

The present application relates to a negative electrode plate, a battery, and an electronic device, which includes a current collector and an active material layer disposed on at least one surface of the current collector, wherein the active material layer includes a first composite active layer, a second composite active layer, and a third composite active layer stacked in sequence along the thickness direction of the current collector, and the first composite active layer is located between the current collector and the second composite active layer; wherein the gram capacity of the second composite active layer is greater than the gram capacity of the first composite active layer, and the gram capacity of the second composite active layer is greater than the gram capacity of the third composite active layer. The present application adopts a gram capacity differentiation design scheme, and the composite active layer with a larger gram capacity is located between the composite active layers with a smaller gram capacity, which can improve the stability of the contact interface between the active material layer, the current collector, and the electrolyte layer, maintain electrical connection and ion transport network, and improve battery cycle performance.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a negative electrode plate, a battery, and an electronic device. Background Art

[0002] In order to balance high energy density and high safety, solid-state batteries represented by lithium-ion batteries have emerged as a new generation of energy storage devices. Unlike traditional batteries using liquid electrolytes, in solid-state batteries, the electrochemical-mechanical effect is more significant due to the rigidity of solid / solid contact and the quite different mechanical properties between battery components. For example, the negative electrode active material has different chemical behaviors and elastic moduli from the solid electrolyte and foil, resulting in different volume changes during lithium insertion / delithiation in solid-state batteries, thereby generating interfacial gaps between the active material layer and the electrolyte layer / foil, and / or within the active material layer. This interfacial gap will cause the ion path to fail, resulting in the inability of the negative electrode active material to fully participate in the charge and discharge reaction, affecting the cycle life of the solid-state battery.

[0003] For the negative electrode active materials, it is necessary to solve the problem of large volume changes during the lithiation / delithiation process (for example, the formation of Li 3.75 Si (approximately 300% volume change when using Si), and the interfacial contact issues with the anode active material and ion transport material. Typically, the anode is a single layer of active material coated on a current collector. The active material layer comprises the anode active material, a solid electrolyte, a conductive agent, and a polymer binder. The solid electrolyte provides ionic conductivity, while the polymer binder maintains the connection between the solid components, thereby maintaining solid-solid interfacial contact.

[0004] However, the volume change of the negative electrode active material is still larger than that of the electrolyte layer / current collector layer, and the contact failure between the negative electrode active material layer and the electrolyte layer / foil is still easy to occur, affecting the stability of the electrode structure and the cycle performance. Summary of the Invention

[0005] The embodiments of the present application provide a negative electrode plate, a battery, and an electronic device to solve the problem in the related art that the volume change of the negative electrode active material is still large compared to the electrolyte layer / current collector layer, and the negative electrode active material layer and the electrolyte layer / foil are still prone to contact failure, which affects the stability of the electrode structure and the cycle performance.

[0006] In a first aspect, a negative electrode plate is provided, which is applied to a solid-state battery or an all-solid-state battery, and includes:

[0007] current collector;

[0008] and an active material layer disposed on at least one surface of the current collector, the active material layer comprising a first composite active layer, a second composite active layer, and a third composite active layer stacked sequentially along the thickness direction of the current collector, with the first composite active layer located between the current collector and the second composite active layer;

[0009] The gram capacity of the second composite active layer is greater than the gram capacity of the first composite active layer, and the gram capacity of the second composite active layer is greater than the gram capacity of the third composite active layer;

[0010] The average lithium insertion voltage of the second composite active layer is lower than the average lithium insertion voltage of the first composite active layer, and the average lithium insertion voltage of the second composite active layer is lower than the average lithium insertion voltage of the third composite active layer.

[0011] In some embodiments, the gram capacity of the first composite active layer is Cap1,600<Cap1<1200mAh / g;

[0012] The gram capacity of the second composite active layer is Cap2, 1200<Cap2<3600mAh / g;

[0013] The gram capacity of the third composite active layer is Cap3, 600<Cap3<1200mAh / g.

[0014] In some embodiments, the gram capacity of the first composite active layer is Cap1, and the gram capacity of the second composite active layer is Cap2;

[0015] Cap1: Cap2=1: (1.2~3).

[0016] In some embodiments, the gram capacity of the second composite active layer is Cap2, and the gram capacity of the third composite active layer is Cap3;

[0017] Cap3: Cap2=1: (1.2~3).

[0018] In some embodiments, the first composite active layer, the second composite active layer, and the third composite active layer all include a negative electrode active material, a binder, and a conductive agent.

[0019] In some embodiments, the negative electrode active material of the second composite active layer is a centrosymmetric active material.

[0020] In some embodiments, the center symmetry deviation of the negative electrode active material is ε, 0.1%≤ε≤20%.

[0021] In some embodiments, the mass ratio of the negative electrode active material, the conductive agent, and the binder is (30-120):1:(1-3).

[0022] In some embodiments, the first composite active layer, the second composite active layer, and the third composite active layer further include an electrolyte.

[0023] In some embodiments, the mass ratio of the negative electrode active material, the electrolyte, the conductive agent, and the binder is (20-75): (6-30): 1: (1-3).

[0024] In some embodiments, the negative electrode active material of the first composite active layer and / or the third composite active layer includes one or more of silicon-based materials, aluminum-based materials, tin-based materials, phosphorus-based materials, lithium titanate, soft carbon, and hard carbon.

[0025] In some embodiments, the silicon-based material includes one or more of silicon, silicon alloy, silicon oxide, and silicon-carbon composite;

[0026] And / or, the tin-based material includes one or more of tin, tin alloy, tin oxide, and tin-carbon composite;

[0027] And / or, the aluminum-based material includes one or more of aluminum, aluminum alloy, and aluminum-carbon composite;

[0028] And / or, the phosphorus-based material includes one or more of black phosphorus, phosphorus-carbon composites, and metal-phosphorus-carbon composites.

[0029] In some embodiments, the negative electrode active material of the second composite active layer includes a silicon-based material, or a silicon-based material mixed with one or more of conductive graphite, artificial graphite, natural graphite, mesophase carbon microbeads, and hard carbon.

[0030] In some embodiments, the electrolyte includes one or more of lithium nitride, a sulfide electrolyte, a hydride electrolyte, and a polymer electrolyte.

[0031] In some embodiments, the sulfide electrolyte includes (1-x)Li2S-xP2S5, Li6PS5Cl y , one or more of Li3PS4, wherein 0≤x<0.5, 0≤y<2;

[0032] and / or, the hydride comprises (1-z)LiBH4-zLiI, wherein 0≤z<1;

[0033] And / or, the polymer electrolyte includes a polymer resin and a lithium salt, the polymer resin includes one or more of polyethylene oxide, polypropylene oxide, polysiloxane, and polysilsesquioxane, and the lithium salt includes one or more of LiFSI, LiTFSI, LiCF3SO3, LiC4F9SO3, and LiC4F9SO3.

[0034] In some embodiments, the mass fraction of the electrolyte in the first composite active layer, the second composite active layer and / or the third composite active layer is w%, and 7%≤w%≤50%.

[0035] In some embodiments, the binder includes one or more of PAN, PEO, SEBS, TAP, PTFE, PIB, and PvDF.

[0036] In some embodiments, the conductive agent includes one or more of acetylene black, carbon black, carbon fiber, conductive graphite, graphene, and carbon nanotubes.

[0037] In some embodiments, the average lithium insertion voltage of the first composite active layer is U1, 0.01V<U1<1.6V;

[0038] The average lithium insertion voltage of the second composite active layer is U2, 0.01V<U2<0.9V;

[0039] The average lithium insertion voltage of the third composite active layer is U3, 0.01V<U3<1.6V.

[0040] In some embodiments, the thickness of the first composite active layer is H1, 1 μm

[0041] The thickness of the second composite active layer is H2, 10 μm<H2<100 μm;

[0042] The thickness of the third composite active layer is H3, 1 μm<H3<60 μm.

[0043] In a second aspect, a battery is provided, comprising any negative electrode plate as described above.

[0044] According to a third aspect, an electronic device is provided, characterized in that it comprises the battery as described above.

[0045] The beneficial effects of the technical solution provided by this application include:

[0046] ​Generally speaking, the greater the gram capacity of the negative electrode active material, the greater the volume expansion rate with charge and discharge. On the one hand, the gram capacity of the first composite active layer in contact with the current collector and the third composite active layer in contact with the electrolyte layer are both low, and the volume expansion rate with charge and discharge is smaller, and the deformation is smaller, thereby maintaining interlayer contact. The first composite active layer and the third composite active layer are in contact with the second composite active layer, and they expand simultaneously with charge and discharge. Although the second composite active layer has a greater volume expansion rate with charge and discharge, because it is flanked by the first composite active layer and the third composite active layer, it also expands synchronously with charge and discharge, and the relative volume expansion rate between the layers is reduced, thereby maintaining interlayer contact. At the same time, because the second composite active layer is an active layer with similar properties to the first composite active layer and the third composite active layer, the contact between the three active layers is more stable than the contact with the current collector or the electrolyte layer.

[0047] Therefore, this application adopts a differentiated design scheme of gram capacity, and places the composite active layer with larger gram capacity between the composite active layers with smaller gram capacity, which can improve the stability of the contact interface between the active material layer and the current collector and electrolyte layer, maintain electrical connection and ion transport network, and improve battery cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0049] Figure 1 Schematic diagram of the negative electrode structure provided in this application;

[0050] Figure 2 This is a cycle performance diagram of Example 3 and Comparative Example 1 of the present application.

[0051] In the figure: 1. first composite active layer; 2. second composite active layer; 3. third composite active layer; 4. current collector; 5. electrolyte layer. DETAILED DESCRIPTION

[0052] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0053] Currently, to improve the electrode structure stability and cycle performance of solid-state batteries, it is necessary to add a binder and electrolyte with elastic properties to the electrode. These are used to mitigate the volume change of the negative electrode active material during the charge and discharge process, enhance the interfacial contact between the components within the all-solid-state composite negative electrode plate, and provide a lithium ion transmission path. However, during the research process, the inventors found that flexible binders have limited improvement on the volume change of the negative electrode active material. The macroscopic interface between the negative electrode composite active layer and the current collector / electrolyte layer is prone to detachment. At the same time, the negative electrode active material particles have irregular morphology and anisotropic volume change, which can easily lead to large local deformation, resulting in gaps between the electrolyte and the negative electrode, resulting in loss of lithium ion pathways, and thus battery cycle degradation.

[0054] In order to solve the above problems, the inventors have designed a negative electrode plate that can alleviate the negative electrode volume change gradient. Figure 1 As shown, an embodiment of the present application provides a negative electrode sheet, which includes a current collector 4 and an active material layer arranged on at least one surface of the current collector 4, wherein the active material layer includes a first composite active layer 1, a second composite active layer 2 and a third composite active layer 3 stacked in sequence along the thickness direction of the current collector, and the first composite active layer 1 is located between the current collector 4 and the second composite active layer 2; wherein the gram capacity of the second composite active layer 2 is greater than the gram capacity of the first composite active layer 1, and the gram capacity of the second composite active layer 2 is greater than the gram capacity of the third composite active layer 3.

[0055] The negative electrode plate provided in the present application includes a current collector and an active material layer. According to the present application, the active material layer includes a first composite active layer, a second composite active layer and a third composite active layer. The second composite active layer with a higher gram capacity is arranged between the first composite active layer with a lower gram capacity and the third composite active layer.

[0056] It can be understood that the gram capacity of the composite active layer is mainly affected by the negative electrode active material it contains. The larger the gram capacity of the negative electrode active material, the larger the gram capacity of the corresponding composite active layer. Therefore, in this application, the gram capacity of the composite active layer refers to the gram capacity of the negative electrode active material of the composite active layer.

[0057] Generally speaking, the greater the gram capacity of the negative electrode active material, the greater the volume expansion rate with charge and discharge. On the one hand, the gram capacity of the first composite active layer in contact with the current collector 4 and the third composite active layer in contact with the electrolyte layer 5 are both lower, and the volume expansion rate with charge and discharge is smaller, and the deformation is smaller, thereby maintaining interlayer contact.

[0058] On the other hand, the first and third composite active layers are in contact with the second composite active layer, expanding simultaneously during charging and discharging. Although the second composite active layer has a greater volume expansion rate with charging and discharging, because it is flanked by the first and third composite active layers, it also expands synchronously with charging and discharging, reducing the relative volume expansion rate between the layers and thus maintaining interlayer contact. Furthermore, because the second composite active layer, the first and third composite active layers are all active layers with similar properties, contact between the three active layers is more stable than contact with the current collector 4 or electrolyte layer 5.

[0059] For easier understanding, let's assume, for example, that the expansion rates of the first and third composite active layers are 60%, and the expansion rate of the second composite active layer is 100%. When only the second composite active layer is present, the interface expansion rate differences between the second composite active layer and the current collector 4, and between the second composite active layer and the electrolyte, are both close to 100%. When all three layers are present, the expansion rate differences between the second composite active layer and the first composite active layer are 40%, the expansion rate differences between the second composite active layer and the third composite active layer are 40%, and the expansion rate differences between the first and third composite active layers and the current collector 4 / electrolyte layer 5 interfaces are 60%. These differences are all smaller than when only one layer is present. This demonstrates that the above approach reduces the volume change gradient.

[0060] Therefore, the present application adopts a differentiated design scheme of gram capacity, and places the composite active layer with larger gram capacity between the composite active layers with smaller gram capacity, which can improve the stability of the contact interface between the active material layer and the current collector 4 and the electrolyte layer 5, improve the stability of the solid-state battery electrode structure, maintain electrical connection and ion transport network, and improve battery cycle performance.

[0061] As mentioned above, for a given negative electrode active material, the gram capacity is positively correlated with the volume expansion rate of the material. Setting the gram capacity of the first composite active layer and the third composite active layer on both sides within an appropriate range can prevent the composite active layer from expanding too much and can reduce the volume change gradient between the active material layer and the current collector and electrolyte layer. Reducing this volume change gradient can reduce the shedding of the active material layer and the current collector / electrolyte layer, maintain electrical connection and ion transport network, and thus improve the cycle performance of the solid-state battery.

[0062] The gram capacity of the first composite active layer 1 is Cap1, 600<Cap1<1200mAh / g; for example, as an example, Cap1 is 700mAh / g, 800mAh / g, 900mAh / g, 1000mAh / g, 1100mAh / g, 1150mAh / g or within the range of any of the above values.

[0063] The gram capacity of the second composite active layer 2 is Cap2, 1200<Cap2<3600mAh / g; for example, as an example, Cap2 is 1300mAh / g, 1500mAh / g, 1800mAh / g, 2000mAh / g, 2500mAh / g, 2800mAh / g, 3000mAh / g, 3300mAh / g, 3500mAh / g or within the range of any of the above values.

[0064] The gram capacity of the third composite active layer 3 is Cap3, 600<Cap3<1200mAh / g. For example, as an example, Cap3 is 700mAh / g, 800mAh / g, 900mAh / g, 1000mAh / g, 1100mAh / g, 1150mAh / g or within the range of any of the above values.

[0065] Preferably, 800<Cap1<1100mAh / g, 1500<Cap2<2600mAh / g, 800<Cap3<1100mAh / g.

[0066] Furthermore, the gram capacity of the negative electrode active material of the first composite active layer 1 is Cap1, and the gram capacity of the negative electrode active material of the second composite active layer 2 is Cap2, with Cap1:Cap2 = 1:(1.2-3). For example, Cap1:Cap2 = 1:1.2, 1:1.3, 1:1.4, 1:1.6, 1:1.8, 1:2.0, 1:2.2, 1:2.4, 1:2.5, 1:2.6, 1:2.8, 1:3, or any range consisting of the above values. Preferably, Cap1:Cap2 = 1:(1.5-2). Generally speaking, the greater the gram capacity of the negative electrode active material, the greater the volume expansion rate with charge and discharge. If the Cap1:Cap2 ratio is too high, the expansion rate of the first composite active layer 1 and the second composite active layer 2 are too close, resulting in a large difference in expansion rate between the first composite active layer 1 and the current collector 4, which can easily cause interface detachment between the first composite active layer 1 and the current collector 4. If the Cap1:Cap2 ratio is too low, the expansion rate of the first composite active layer 1 and the expansion rate of the second composite active layer 2 will differ too much, and interface peeling between the first composite active layer and the second composite active layer 2 may easily occur.

[0067] The gram capacity of the negative electrode active material of the second composite active layer 2 is Cap2, and the gram capacity of the negative electrode active material of the third composite active layer 3 is Cap3, with Cap3:Cap2 = 1:(1.2-3). For example, Cap3:Cap2 = 1:1.2, 1:1.3, 1:1.4, 1:1.6, 1:1.8, 1:2.0, 1:2.2, 1:2.4, 1:2.5, 1:2.6, 1:2.8, 1:3, or any range consisting of these values. Preferably, Cap3:Cap2 = 1:(1.5-2). If the Cap3:Cap2 ratio is too high, the expansion rate of the third composite active layer 3 is too close to that of the second composite active layer 2, resulting in a significant difference in expansion rate between the third composite active layer 3 and the electrolyte layer 5, which can easily cause interface detachment between the third composite active layer 3 and the electrolyte layer 5. If the Cap3:Cap2 ratio is too low, the expansion rate of the third composite active layer 3 differs too much from the expansion rate of the second composite active layer 2 , and interface peeling between the third composite active layer 3 and the second composite active layer 2 is likely to occur.

[0068] The lithium insertion voltage of the composite active layer is set within an appropriate range, so that the first composite active layer 1 and the third composite active layer 3 can be inserted with lithium first, and the second composite active layer 2 can be inserted with lithium later. This can prevent a large volume change gradient from occurring between the composite active layers, enhance the stability of the electrode structure, and thereby improve the cycle performance of the solid-state battery.

[0069] Specifically, the average lithium insertion voltage of the second composite active layer 2 is lower than that of the first composite active layer 1 , and the average lithium insertion voltage of the second composite active layer 2 is lower than that of the third composite active layer 3 .

[0070] Generally speaking, the higher the average lithium insertion voltage of the first composite active layer 1, the easier it is to preferentially insert lithium, thereby avoiding the high volume change caused by preferential lithium insertion in the second composite active layer 2. However, if the average lithium insertion voltage of the first composite active layer 1 is too high, there is a risk that the battery cell will be prematurely terminated due to a rapid rise in the negative electrode potential under high discharge rate conditions. If the average lithium insertion voltage of the first composite active layer 1 is too low, it is not conducive to achieving a high average lithium insertion voltage difference between the first composite active layer 1 and the second composite active layer 2, and preferential lithium insertion in the first composite active layer 1 cannot be achieved. Based on this, in some preferred embodiments, the average lithium insertion voltage of the first composite active layer 1 is U1, 0.01V<U1<1.6V; for example, as an example, U1=0.02V, 0.03V, 0.05V, 0.1V, 0.2V, 0.3V, 0.4V, 0.5V, 0.6V, 0.7V, 0.8V, 0.9V, 1.0V, 1.1V, 1.2V, 1.3V, 1.4V, 1.5V, 1.6V or within the range composed of any of the above values.

[0071] If the average lithium insertion voltage of the second composite active layer 2 is too high, the average discharge voltage of the battery cell will be too low, affecting the energy density of the battery cell. If the average lithium insertion voltage of the second composite active layer 2 is too low, lithium deposition may easily occur during charging, thereby posing a safety risk. Based on this, in some preferred embodiments, the average lithium insertion voltage of the second composite active layer 2 is U2, 0.01V<U2<0.9V; for example, U2=0.02V, 0.03V, 0.05V, 0.1V, 0.2V, 0.3V, 0.4V, 0.5V, 0.6V, 0.7V, 0.8V, 0.9V or any of the above values.

[0072] Similar to the first composite active layer 1, the higher the average lithium insertion voltage of the third composite active layer 3, the easier it is to preferentially insert lithium, thereby avoiding the high volume change caused by the preferential lithium insertion of the second composite active layer 2. However, if the average lithium insertion voltage of the third composite active layer 3 is too high, under high discharge rate conditions, the battery cell is at risk of premature discharge termination due to the rapid rise in the negative electrode potential. If the average lithium insertion voltage of the third composite active layer 3 is too low, it is not conducive to achieving a high average lithium insertion voltage difference between the third composite active layer 3 and the second composite active layer 2, and the preferential lithium insertion of the third composite active layer 3 cannot be achieved. Based on this, in some preferred embodiments, the average lithium insertion voltage of the third composite active layer 3 is U3, 0.01V<U3<1.6V. For example, as an example, U3 = 0.02V, 0.03V, 0.05V, 0.1V, 0.2V, 0.3V, 0.4V, 0.5V, 0.6V, 0.7V, 0.8V, 0.9V, 1.0V, 1.1V, 1.2V, 1.3V, 1.4V, 1.5V, 1.6V or any range consisting of the above values.

[0073] Preferably, 0.08V<U1<1.5V; 0.01V<U2<0.6V; 0.08V<U 13 <1.5V.

[0074] The first composite active layer 1, the second composite active layer 2 and the third composite active layer 3 all include negative electrode active materials, a binder and a conductive agent. The negative electrode material can transport ions through its intrinsic ion diffusion capacity and also act as a lithium ion transport channel. For example, the lithium ion conductivity of graphite is 10 -6 -10 -5 S / cm, the lithium ion conductivity of silicon is 10 -4 -10 -3 .

[0075] The negative electrode active material, the binder and the conductive agent are mixed to form a slurry, so that the binder and the conductive agent are filled between the particles of the negative electrode active material, and then the slurry is used for coating.

[0076] As an example, the mass ratio of the negative electrode active material, the conductive agent, and the binder is (30-120):1:(1-3).

[0077] Furthermore, according to actual preparation requirements, an electrolyte may be added to the above slurry to improve the negative electrode lithium ion transmission capacity and battery rate performance.

[0078] As an example, the mass ratio of the negative electrode active material, the electrolyte, the conductive agent and the binder is (20-75): (6-30): 1: (1-3).

[0079] Generally speaking, the negative electrode active material particles are irregular particles and have anisotropic expansion, which can easily lead to large deformation of local areas in the electrode sheet, thereby causing contact failure in the active material layer, affecting the stability of the electrode structure and the cycle performance. In order to solve this problem, the negative electrode active material of the second composite active layer 2 in this application adopts a centrally symmetrical active material.

[0080] The negative electrode active material particles in the second composite active layer 2 exhibit centrosymmetry. This higher symmetry reduces uneven deformation and prevents excessive local deformation. Therefore, during charge and discharge, the deformation between the negative electrode active material and the electrolyte, binder, and conductive agent is relatively uniform. This makes it easier to maintain a stable contact interface under the action of external forces, and less likely to form gaps between the negative electrode active material and the negative electrode active material after delithiation. This allows for an electrode structure that adapts to the expansion of the negative electrode active material, maintains the stability of the contact interface, and improves the stability of the solid-state battery's electrolytic structure, cycling performance, and charge and discharge capabilities.

[0081] The centrosymmetry of the negative electrode active material of the second composite active layer 2 is controlled within an appropriate range, and the volume changes of the negative electrode active material particles in all directions are similar, which prevents excessive local volume changes in the composite active layer, reduces the gaps generated in the composite active layer during charge and discharge, and maintains the stability of the electrode structure in the composite active layer, thereby improving the cycle performance. In this application, the centrosymmetric deviation of the negative electrode active material is ε, 0.1%≤ε≤20%, and the centrosymmetric deviation ε>20%. The material particles are long strips, or have sharp edges or holes, and the expansion has large anisotropy, which can easily lead to local stress concentration in the composite active layer, causing cracking of the negative electrode, or causing local cracks. The centrosymmetric deviation ε<0.1% does not improve the isotropic expansion of the material much, requires the material to be nearly spherical, has a low material synthesis yield, and is costly. For example, as an example, ε=0.2%, 0.5%, 1%, 2%, 3%, 4%, 5%, 8%, 10%, 12%, 14%, 16%, 18%, 19% or any range consisting of the above values, preferably, 0.3%≤ε≤10%.

[0082] The negative electrode active material of the first composite active layer 1 and / or the third composite active layer 3 includes one or more of silicon-based materials, aluminum-based materials, tin-based materials, phosphorus-based materials, lithium titanate, soft carbon and hard carbon.

[0083] Optionally, the silicon-based material includes silicon alone, silicon alloy, silicon monoxide, silicon-carbon composite or a combination thereof.

[0084] Optionally, the tin-based material includes tin alone, a tin alloy, tin oxide, a tin-carbon composite, or a combination thereof.

[0085] Optionally, the aluminum-based material includes aluminum alone, aluminum alloy, aluminum-carbon composite or a combination thereof.

[0086] Optionally, the phosphorus-based material includes black phosphorus, a phosphorus-carbon composite, a metal-phosphorus-carbon composite material, or a combination thereof.

[0087] The average particle size of the negative electrode active material of the first composite active layer 1 is 0.05-30 μm, and can be selected from 0.08-15 μm. Different particle sizes of negative electrode active materials are used in combination, and small particle size materials can fill the gaps in the accumulation of large particle size materials to achieve similar initial porosity of the negative electrode sheet.

[0088] The negative electrode active material of the second composite active layer 2 includes a silicon-based material, or a silicon-based material blended with one or more of conductive graphite, artificial graphite, natural graphite, mesocarbon microbeads, and hard carbon. The silicon-based material includes elemental silicon, a silicon alloy, a silicon-oxygen material, a silicon-carbon composite, or a combination thereof.

[0089] By selecting appropriate negative electrode active materials and their combinations, and adjusting the average lithium insertion voltage of different composite active layers, it is possible to achieve lithium insertion in the first and third composite active layers first, while the second composite active layer expands first and then inserts lithium. This allows the first and third composite active layers to expand first, reducing the volume change gradient at the interface, minimizing crack formation, and maintaining stable contact in the lithium-ion battery.

[0090] The electrolyte is made of a material having lithium ion transfer capability, including one or more of lithium nitride, sulfide electrolyte, hydride electrolyte and polymer electrolyte.

[0091] Optionally, the sulfide electrolyte includes (1-x)Li2S-xP2S5, Li6PS5Cl y , Li3PS4 or a combination thereof, wherein 0≤x<0.5, 0≤y<2.

[0092] Optionally, the hydride comprises (1-z)LiBH4-zLiI, wherein 0≤z<1.

[0093] Optionally, the polymer electrolyte is a polymer resin and a lithium salt, the polymer resin includes polyethylene oxide, polypropylene oxide, polysiloxane, polysilsesquioxane or a combination thereof, and the lithium salt includes LiFSI, LiTFSI, LiCF3SO3, LiC4F9SO3, LiC4F9SO3 or a combination thereof.

[0094] Selecting a suitable electrolyte can allow lithium ions to be transported mainly through the electrolyte of the composite active layer, thereby improving the uniformity of lithium insertion in each composite active layer and improving the stability of the electrode structure.

[0095] The mass fraction of the electrolyte in the first composite active layer 1 is w%, and 7%≤w%≤50%.

[0096] The mass fraction of the electrolyte in the second composite active layer 2 is w%, and 7%≤w%≤50%.

[0097] The mass fraction of the electrolyte in the third composite active layer 3 is w%, and 7%≤w%≤50%.

[0098] The mass fraction of the electrolyte in the composite active layer is set within a suitable range, which is conducive to forming an efficient lithium ion transmission network, reducing particle failure due to local contact, and improving the cycle performance of the solid-state battery.

[0099] The binder includes one or more of PAN, PEO, SEBS, TAP, PTFE, PIB and PvDF.

[0100] The conductive agent includes one or more of acetylene black, carbon black, carbon fiber, conductive graphite, graphene and carbon nanotubes.

[0101] The thickness of each composite active layer is within an appropriate range, which is conducive to alleviating the expansion difference between the active material layer and the current collector / electrolyte layer, improving the cycle performance of the solid-state battery, and not reducing the overall gram capacity of the active material layer, which is conducive to maintaining the high energy density of the battery.

[0102] The first composite active layer 1 is located between the current collector 4 and the second composite active layer 2, and serves to reduce the volume change gradient. If the first composite active layer is too thin, processing will be a major challenge, the uniformity of the composite layer cannot be guaranteed, and the buffering effect on the interface volume change will be poor. At the same time, the first composite active layer 1 near the current collector 4 and the second composite active layer 2 will experience different expansion, resulting in different stresses, and a certain thickness is required for stress release. If the first composite active layer 1 is too thick, the volume change buffering will not be further improved, and due to the low specific capacity of the negative electrode contained, the energy density of the battery cell will be affected. Based on this, in some preferred embodiments, the thickness of the first composite active layer 1 is H1, 1μm

[0103] The second composite active layer is the main lithium storage location of the negative electrode active layer. If the thickness is too low, the energy density of the battery cell will be reduced. If the thickness is too high, it will easily affect the rate performance of the battery cell. Based on this, in some preferred embodiments, the thickness of the second composite active layer 2 is H2, 10μm<H2<100μm; for example, as an example, H2=11μm, 20μm, 30μm, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm or within the range of any of the above values.

[0104] The third composite active layer 3 is located between the electrolyte layer and the second composite active layer 2, and serves to reduce the volume change gradient. If the third composite active layer 3 is too thin, processing will be a major challenge, the uniformity of the composite layer cannot be guaranteed, and the buffering effect on the interface volume change will be poor. At the same time, the third composite active layer 3 near the electrolyte layer and the second composite active layer 2 will experience different expansion, resulting in different stresses, and a certain thickness is required for stress relief. If the third composite active layer 3 is too thick, the volume change buffering will not be further improved, and due to the low specific capacity of the negative electrode contained, the energy density of the battery cell will be affected. Based on this, in some preferred embodiments, the thickness of the third composite active layer 3 is H3, 1μm < H3 < 60μm. For example, as an example, H3 = 2μm, 5μm, 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, 55μm, or within a range consisting of any of the above values.

[0105] Preferably, 1 μm

[0106] The negative electrode sheet of the present application can be prepared according to the following steps: ​​

[0107] Providing a first negative electrode slurry, a second negative electrode slurry, and a third negative electrode slurry;

[0108] The first negative electrode slurry, the second negative electrode slurry and the third negative electrode slurry are sequentially coated on the surface of the current collector and dried to form a first composite active layer, a second composite active layer and a third composite active layer respectively.

[0109] This preparation method is not only simple and easy to industrialize, but also minimizes the volume change of the first and third composite active layers during the lithium insertion process in the resulting battery electrode. This effectively mitigates the volume change gradient between the second composite active layer, the current collector, and the electrolyte layer, stabilizes the electrode structure, and improves the cycling performance of all-solid-state batteries. Furthermore, the first and third composite active layers are relatively thin, minimizing their impact on the overall energy density of the battery.

[0110] The solid electrolyte content in the third negative electrode slurry is no less than that in the first and second negative electrode slurries. By introducing a sufficient amount of solid electrolyte into the third composite active layer, sufficient pathways are provided for lithium ions to enter the second and first composite active layers, improving the uniformity of lithium insertion and expansion across each layer.

[0111] In some embodiments, the current collector has two surfaces that are opposite to each other in the thickness direction, and the active material layer may be disposed on one surface of the current collector or on both surfaces of the current collector. For example, the current collector has two surfaces that are opposite to each other in the thickness direction, and the active material layer may be disposed on either one or both of the two opposing surfaces of the current collector.

[0112] It is understood that the active material layer of the present application may include only three composite active layers that reduce the volume change gradient, or, based on the three layers, composite active layers that reduce the volume change gradient may be further added or inserted on one or both sides of the composite active layer with the largest gram capacity. Furthermore, along the thickness direction of the negative electrode sheet, the gram capacity of each composite active layer decreases outward from both sides of the composite active layer with the largest gram capacity.

[0113] Considering the manufacturing process and bonding strength, the preferred number of layers of the composite active layer may be three.

[0114] The present application also provides a battery, which includes the negative electrode plate provided in the above embodiment.

[0115] The above-mentioned battery can be a solid-state battery or an all-solid-state battery.

[0116] In some embodiments, the solid-state battery of the present application includes a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte layer. During the battery's charge and discharge process, active ions are intercalated and released between the positive and negative electrode sheets. The solid electrolyte layer conducts ions between the positive and negative electrode sheets and isolates them from each other, preventing short circuits between the positive and negative electrodes.

[0117] The present application also provides an electronic device, which includes the battery provided by the above embodiment.

[0118] The electronic devices of the present application are not particularly limited and can be any electronic device known in the art. In some embodiments, the electronic devices may include, but are not limited to, laptop computers, pen-based computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD televisions, portable cleaners, portable CD players, mini-discs, transceivers, electronic notepads, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, power-assisted bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors.

[0119] The stability of electrode structures is well known in the industry and can be measured using well-known instrumentation methods. For example, the porosity of the active material layer after full discharge can be measured using X-ray nanostructured tomography or mercury intrusion porosimetry. By comparing the porosity of different electrode sheets, the differences in electrode structure stability can be determined.

[0120] The following examples describe the present disclosure in more detail. These examples are intended for illustrative purposes only, as various modifications and variations within the scope of the present disclosure will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further processing. The instruments used in the examples are commercially available.

[0121] Example 1

[0122] Preparation of negative electrode sheet

[0123] The negative electrode active material Sn / C, the electrolyte Li6PS5Cl, the conductive agent VGCF, and the binder PvDF were added to butyl butyrate in a mass ratio of 70:27:1:2 and mixed evenly to prepare a first negative electrode slurry and a third negative electrode slurry.

[0124] The negative electrode active material Si / C, the electrolyte Li6PS5Cl, the conductive agent VGCF, and the binder PvDF were added to butyl butyrate in a mass ratio of 75:22:1:2 and mixed evenly to prepare a second negative electrode slurry.

[0125] Each negative electrode slurry was uniformly coated on the current collector carbon-coated copper foil in turn, dried at 85°C, and then die-cut to make negative electrode sheets.

[0126] Preparation of positive electrode

[0127] The positive electrode active material ternary material nickel cobalt manganese oxide (NCM90505), electrolyte Li6PS5Cl, conductive agent VGCF, and binder PvDF were mixed evenly in a mass ratio of 67:31:1:1 and added to the solvent butyl butyrate to prepare a positive electrode slurry; the positive electrode slurry was evenly coated on the positive electrode current collector aluminum foil, dried at 85°C, cold pressed, and then die-cut to make a positive electrode sheet.

[0128] Preparation of solid electrolyte membrane

[0129] The sulfide solid electrolyte Li6PS5Cl and the binder PIB were mixed evenly in a mass ratio of 96:4 and added to butyl butyrate to prepare a solid electrolyte slurry. The solid electrolyte slurry was evenly coated on aluminum foil, dried at 85°C, and then die-cut to prepare a solid electrolyte membrane.

[0130] All-solid-state battery assembly

[0131] The negative electrode sheet, solid electrolyte membrane and positive electrode sheet prepared above are stacked in sequence, pressed and sealed, and assembled into an all-solid-state battery.

[0132] Examples 2 to 11

[0133] The preparation methods of the all-solid-state batteries of Examples 2 to 11 are similar to those of Example 1, except that the relevant parameters of the composite active layer in the negative electrode plate are adjusted. The specific parameters are detailed in Table 1 below.

[0134] Example 12

[0135] Example 12 is similar to Example 5, except that no electrolyte is added, and the mass ratio of the negative electrode active material, the conductive agent, and the binder is 97:1:2.

[0136] Example 13

[0137] Example 13 is similar to Example 6, except that no electrolyte is added, and the mass ratio of the negative electrode active material, the conductive agent, and the binder is 97:1:2.

[0138] Example 14

[0139] Example 14 is similar to Example 3, except that no electrolyte is added, and the mass ratio of the negative electrode active material, the conductive agent, and the binder is 97:1:2.

[0140] Example 15

[0141] Example 15 is similar to Example 7, except that no electrolyte is added, and the mass ratio of the negative electrode active material, the conductive agent, and the binder is 97:1:2.

[0142] Comparative Example 1

[0143] Comparative Example 1 is similar to Example 1, except that the negative electrode active materials of the first composite active layer, the third composite active layer, and the second composite active layer are all Si / C.

[0144] Comparative Example 2

[0145] Comparative Example 2 is similar to Example 1, except that the negative electrode active material of the second composite active layer is P / C, and the negative electrode lithium insertion voltage of the first composite active layer and the third composite active layer in the active material layer is lower than that of the second composite active layer.

[0146] Comparative Example 3

[0147] Comparative Example 3 is similar to Example 1, except that the central symmetry deviation of the negative electrode active material of the second composite active layer in the active material layer reaches 25%.

[0148] Table 1

[0149]

[0150] Note: In Table 1, “S” stands for “Example”, for example: “S1” stands for “Example 1”, and “D” stands for “Comparative Example”, for example: “D1” stands for “Comparative Example 1”.

[0151] Sn / C represents a tin-carbon composite in tin-based materials; Si / Sn / C represents a silicon-tin-carbon composite, which can be classified as either a tin-based material or a silicon-based material; SnSi represents a silicon-tin alloy material in tin-based materials; P / C+LTO represents a mixture of a phosphorus-carbon composite and lithium titanate particles in a phosphorus-based material; Si / C represents a silicon-carbon composite.

[0152] Test section

[0153] (1) Lithium-ion battery negative electrode structure stability test

[0154] The test samples were fully discharged and cycled batteries. The test method was ex-situ measurement. The test location was the interface with the largest expansion rate difference between the composite active layers of the negative electrode and between the composite active layer and the electrolyte layer. The test was conducted from the inner layer with the higher expansion rate to the surface of the layer with the lower expansion rate. The test area was 10μm×10μm×10μm. The test equipment was an X-ray nano-layer tomography scan, and the porosity of the active material layer after full discharge was calculated. By measuring the porosity of different electrode pieces, the structural stability differences of different samples were evaluated.

[0155] (2) Average lithium insertion voltage test of lithium-ion battery negative electrode

[0156] The test sample is a lithium-ion half-cell with a lithium foil counter electrode. The test temperature is 30°C, the charge-discharge range is 0-1.5V, and the test pressure is 5MPa. The test process is as follows: First, a 0.1C capacity calibration is performed. Based on the calibrated capacity, the test sample is discharged at a constant current of 0.05C to obtain the discharge capacity and discharge energy. The average lithium insertion voltage of each negative electrode is calculated based on the formula: average lithium insertion voltage = discharge energy / discharge capacity.

[0157] (3) Lithium-ion battery cycle performance test

[0158] The test samples were full lithium-ion batteries; the test temperature was 30°C; the charge and discharge voltage range was 2.5V to 4.25V; the protection voltage range was 2.45V to 4.3V, and the test pressure was 50MPa. The test process was as follows: First, a 0.1C capacity calibration was performed. Based on the calibrated capacity, each test sample was charged at a constant current and constant voltage of 0.33C and discharged at a constant current of 0.33C for 200 charge and discharge cycles. Based on the discharge capacity data, the ratio of the 200th cycle capacity to the first cycle capacity was calculated to obtain the capacity retention rate of each test sample.

[0159] (4) Lithium-ion battery discharge capacity retention rate test

[0160] The test samples were full lithium-ion batteries; the test temperature was 30°C; the charge and discharge voltage range was 2.5V to 4.25V; the protection voltage range was 2.45V to 4.3V, and the test pressure was 50MPa. The test process was as follows: First, a 0.1C capacity calibration was performed. Based on the calibrated capacity, each test sample was charged at a constant current and constant voltage of 0.1C and discharged at a constant current of 0.33C. Based on the discharge capacity data, the ratio of the 0.33C discharge capacity to the 0.1C discharge capacity was calculated to obtain the capacity retention rate of each test sample.

[0161] The test results are shown in Table 2 and Figure 2 .

[0162] Table 2

[0163]

[0164] By comparing Examples 1 to 4 and Comparative Example 1, it can be seen that compared with Comparative Example 1, in which the three-layer composite active layer uses the same material, the negative electrode plate is not provided with a composite active layer to alleviate the volume change gradient. In Examples 1 to 4 of the present application, the three-layer composite active layer used, the second composite active layer in the middle has a greater gram capacity than the composite active layers on both sides. After cycling, the porosity of the plate is significantly reduced, and the capacity retention rate is significantly improved after 200 cycles, indicating that the negative electrode plate provided with a multi-layer composite active layer provided in the present application can improve the stability of the electrode structure.

[0165] By comparing Example 3, Example 5 to Example 7 and Comparative Example 2, it can be seen that compared with the second composite active layer in the middle of the negative electrode plate in Comparative Example 2 having a high average lithium insertion voltage, the average lithium insertion voltage of the second composite active layer in the middle of Examples 3, Examples 5 to Example 7 of the present application is lower than the average lithium insertion voltage of the composite active layers on both sides. The porosity of the plate is significantly reduced after cycling, and the capacity retention rate is significantly improved after 200 cycles, indicating that the negative electrode plate provided with a multi-layer composite active layer provided in the present application can improve the stability of the electrode structure.

[0166] It's understandable that in liquid battery anodes, lithium ions are transported through the electrolyte within the anode pores. Even if the material expands due to lithium insertion, creating gaps, as long as the electrolyte can penetrate the gaps, the ion pathways formed by the electrolyte penetration will not be cut off. Therefore, the ion pathways in liquid batteries are more tolerant to expansion. This means they are more tolerant to differences in expansion between composite active layers, and the order in which lithium is inserted into each layer in a liquid battery has little effect on the cycle capacity retention rate.

[0167] In solid-state battery anodes, lithium ions are transported through solid-solid contact between different particles. If the anode material expands excessively, cracks form at the contact interface, and the ion pathway is interrupted. Therefore, the ion pathway in solid-state batteries has a low tolerance for differential expansion. This means that lithium needs to be inserted between the composite active layers in a way that minimizes differential expansion.

[0168] Therefore, based on the design of the gram capacity gradient, this application further optimizes the average lithium insertion voltage, so that the first and third composite active layers insert lithium first, and the second composite active layer with the highest gram capacity inserts lithium later. By selecting the various materials listed in this application, the lithium insertion voltage of the second composite active layer can be lower than the lithium insertion voltages of the first and third composite active layers, thereby thermodynamically achieving the second composite active layer's later lithium insertion. This in turn causes the first and third composite active layers to expand first, reducing the volume change gradient at the interface, reducing crack generation, and maintaining stable contact for the lithium-ion battery.

[0169] If the average lithium insertion voltage is reversed, that is, the second composite active layer has a higher lithium insertion voltage, while the first and third composite active layers on either side have lower lithium insertion voltages, the second composite active layer will preferentially insert lithium, and the second composite active layer will have a higher specific capacity. In this case, the expansion difference between the composite active layers on both sides during lithium insertion will become even greater, thus failing to achieve the effect of improving the interface. This conclusion can be confirmed by the cycling results of Example 1 and Comparative Example 2 in Table 2 above.

[0170] By comparing Example 3, Example 8 to Example 11 and Comparative Example 3, it can be seen that the porosity of the electrode sheet after cycling and the capacity retention rate after 200 cycles in Comparative Example 3 are both low. The possible reason is that the centrosymmetric deviation of the negative electrode active material reaches 25%. The centrosymmetric deviation is too high, the material particles are long strips, there are sharp edges or holes, and there is a large anisotropy in expansion, which leads to local stress concentration in the composite active layer, causing the negative electrode to crack, or causing local cracks, and ultimately leading to poor capacity retention after 200 cycles. In Examples 3, 8 to 11 of the present application, the centrosymmetric deviation of the negative electrode active material is no more than 20%, the electrode sheet porosity is significantly reduced after cycling, and the capacity retention rate is significantly improved after 200 cycles, indicating that the negative electrode sheet provided with a multi-layer composite active layer provided by the present application can improve the stability of the electrode structure.

[0171] In addition, combined Figure 2 As shown, compared with Comparative Example 1, the 200-cycle capacity retention rate of the battery in Example 3 is significantly improved, indicating that the negative electrode plate provided with a buffer volume change gradient composite active layer provided in the present application can improve the cycle performance of the battery.

[0172] Examples 12-15 lacked electrolyte, which helped reduce side reactions between the negative electrode and the electrolyte (carbon-containing negative electrode materials are more susceptible to reaction with sulfide electrolytes), resulting in better cycle performance. However, due to poor lithium ion conductivity and the lack of small-particle electrolyte filling, the overall porosity was high, and the rate performance was far lower than that of the corresponding electrolyte-added Examples 3 and Examples 5-7.

[0173] In the description of this application, it should be noted that the terms "upper" and "lower" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on this application. Unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be internal communication between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to the specific circumstances.

[0174] It should be noted that, in this application, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "comprising a ..." does not exclude the presence of other identical elements in the process, method, article or device comprising the element.

[0175] The foregoing is merely a list of specific embodiments of the present application, intended to enable those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application is not limited to the embodiments shown herein, but is intended to conform to the broadest scope consistent with the principles and novel features of the present application.

Claims

1. A negative electrode plate, characterized in that: It is applied to solid-state batteries or all-solid-state batteries, including: Current collector(4); and an active material layer provided on at least one surface of the current collector (4), the active material layer comprising a first composite active layer (1), a second composite active layer (2), and a third composite active layer (3) stacked in sequence along the thickness direction of the current collector, with the first composite active layer (1) being located between the current collector (4) and the second composite active layer (2); wherein the gram capacity of the second composite active layer (2) is greater than the gram capacity of the first composite active layer (1), and the gram capacity of the second composite active layer (2) is greater than the gram capacity of the third composite active layer (3); The average lithium insertion voltage of the second composite active layer (2) is lower than the average lithium insertion voltage of the first composite active layer (1), and the average lithium insertion voltage of the second composite active layer (2) is lower than the average lithium insertion voltage of the third composite active layer (3); The gram capacity of the first composite active layer (1) is Cap1, 600<Cap1<1200mAh / g; The gram capacity of the second composite active layer (2) is Cap2, 1200<Cap2<3600mAh / g; The gram capacity of the third composite active layer (3) is Cap3, 600<Cap3<1200mAh / g; The gram capacity of the first composite active layer (1) is Cap1, the gram capacity of the second composite active layer (2) is Cap2, and the gram capacity of the third composite active layer (3) is Cap3; Cap1:Cap2=1:(1.2-3), Cap3:Cap2=1:(1.2-3); The average lithium insertion voltage of the first composite active layer (1) is U1, 0.01V<U1<1.6V; The average lithium insertion voltage of the second composite active layer (2) is U2, 0.01V<U2<0.9V; The average lithium insertion voltage of the third composite active layer (3) is U3, 0.01V<U3<1.6V; The thickness of the first composite active layer (1) is H1, 1 μm<H1<60 μm; The thickness of the second composite active layer (2) is H2, 10 μm < H2 < 100 μm; The thickness of the third composite active layer (3) is H3, 1 μm<H3<60 μm.

2. The negative electrode sheet according to claim 1, wherein: The first composite active layer (1), the second composite active layer (2) and the third composite active layer (3) all comprise a negative electrode active material, a binder and a conductive agent.

3. The negative electrode sheet according to claim 2, wherein: The negative electrode active material of the second composite active layer (2) is a centrosymmetric active material.

4. The negative electrode sheet according to claim 3, wherein: The central symmetry deviation of the negative electrode active material is ε, 0.1%≤ε≤20%.

5. The negative electrode sheet according to claim 2, wherein: The mass ratio of the negative electrode active material, the conductive agent and the binder is (30-120):1:(1-3).

6. The negative electrode sheet according to claim 2, wherein: The first composite active layer (1), the second composite active layer (2) and the third composite active layer (3) all further comprise an electrolyte.

7. The negative electrode sheet according to claim 6, wherein: The mass ratio of the negative electrode active material, the electrolyte, the conductive agent and the binder is (20-75): (6-30): 1: (1-3).

8. The negative electrode sheet according to claim 2, wherein: The negative electrode active material of the first composite active layer (1) and / or the third composite active layer (3) comprises one or more of silicon-based materials, aluminum-based materials, tin-based materials, phosphorus-based materials, lithium titanate, soft carbon and hard carbon.

9. The negative electrode sheet according to claim 8, wherein: The silicon-based material includes one or more of silicon, silicon alloy, silicon oxide, and silicon-carbon composite; And / or, the tin-based material includes one or more of tin, tin alloy, tin oxide, and tin-carbon composite; And / or, the aluminum-based material includes one or more of aluminum, aluminum alloy, and aluminum-carbon composite; And / or, the phosphorus-based material includes one or more of black phosphorus, phosphorus-carbon composites, and metal-phosphorus-carbon composites.

10. The negative electrode sheet according to claim 2, wherein: The negative electrode active material of the second composite active layer (2) includes a silicon-based material, or a silicon-based material mixed with one or more of conductive graphite, artificial graphite, natural graphite, mesophase carbon microbeads and hard carbon.

11. The negative electrode sheet according to claim 6, wherein: The electrolyte includes one or more of lithium nitride, sulfide electrolyte, hydride electrolyte and polymer electrolyte.

12. The negative electrode sheet according to claim 11, wherein: The sulfide electrolyte includes (1-x)Li2S-xP2S5, Li6PS5Cl y , one or more of Li3PS4, wherein 0≤x<0.5, 0≤y<2; and / or, the hydride comprises (1-z)LiBH4-zLiI, wherein 0≤z<1; And / or, the polymer electrolyte includes a polymer resin and a lithium salt, the polymer resin includes one or more of polyethylene oxide, polypropylene oxide, polysiloxane, and polysilsesquioxane, and the lithium salt includes one or more of LiFSI, LiTFSI, LiCF3SO3, LiC4F9SO3, and LiC4F9SO3.

13. The negative electrode sheet according to claim 2, wherein: The mass fraction of the electrolyte in the first composite active layer (1), the second composite active layer (2) and / or the third composite active layer (3) is w%, and 7%≤w%≤50%.

14. The negative electrode sheet according to claim 2, wherein: The binder includes one or more of PAN, PEO, SEBS, TAP, PTFE, PIB and PVDF.

15. The negative electrode plate according to claim 2, wherein: The conductive agent includes one or more of acetylene black, carbon black, carbon fiber, conductive graphite, graphene and carbon nanotubes.

16. A battery, characterized in that: It comprises the negative electrode sheet as claimed in any one of claims 1 to 15.

17. An electronic device, characterized in that: It comprises the battery as claimed in claim 16.

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