Pole piece, battery and electronic equipment

Abstract

The embodiment of the invention provides a pole piece, a battery and electronic equipment. The pole piece comprises a current collector and an active material layer arranged on the current collector, the active material layer comprises i-level particles, and i is a positive integer greater than or equal to 2; the particle size of the ith-level particles is smaller than that of the (i-1) th-level particles, the ith-level particles are filled among the (i-1) th-level particles, the ith-level particles at least comprise silicon carbon particles with the particle size of d, and the (i-1) th-level particles at least comprise first graphite particles with the particle size of D; wherein under the condition that i is equal to 2, # imgabs0 # is met, and delta V is the change rate of the volume of the silicon carbon particles in the charging state relative to the initial volume.

Description

Technical Field

[0001] The present application belongs to the field of communication technology, and specifically relates to a pole piece, a battery and an electronic device. Background Art

[0002] As users pursue the ultimate user experience, the functions of electronic devices such as mobile phones and tablets are becoming more and more abundant, and the power consumption of electronic devices is also increasing. Correspondingly, the energy density requirements for batteries in electronic devices are also getting higher and higher. In specific applications, adding silicon to the battery pole piece, especially adding silicon to the negative electrode piece of the battery, is an important means to improve the battery energy density.

[0003] However, because silicon storage of lithium mainly relies on alloying reactions, the volume expansion of pure silicon particles in alloying reactions is about 400%, far exceeding the 20% volume change rate of graphite embedded lithium. In recent years, new silicon-carbon materials have deposited silicon particles in a porous carbon matrix, and through the large amount of pore volume reserved in the carbon matrix, the expansion of silicon-carbon particles has been effectively reduced to 100-120%.

[0004] However, even if the new silicon carbon is expected to reduce volume expansion to 100%, it is still much higher than the general level of graphite system. The expansion of silicon carbon particles will lead to the failure of the negative electrode conductive network and the rapid consumption of negative electrode electrolyte, which will seriously affect the health of the battery. Summary of the invention

[0005] The present application aims to provide a pole piece, a battery and an electronic device to solve the problem that the negative pole piece in the existing battery is prone to failure and reduces the health of the battery.

[0006] In order to solve the above technical problems, this application is implemented as follows:

[0007] In a first aspect, the present application discloses a pole piece, the pole piece comprising: a current collector and an active material layer disposed on the current collector, the active material layer comprising i-level particles, i being a positive integer greater than or equal to 2;

[0008] The particle size of the i-th level particles is smaller than the particle size of the i-1-th level particles, and the i-th level particles are filled between the i-1-th level particles, the i-th level particles at least include silicon-carbon particles with a particle size of d, and the i-1-th level particles at least include first graphite particles with a particle size of D;

[0009] Among them, when i is equal to 2, it satisfies:

[0010]

[0011] Wherein, the ΔV is the rate of change of the volume of the silicon-carbon particles in the charged state relative to the initial volume.

[0012] In a second aspect, the present application further discloses a battery, comprising: a pole piece as described in any one of the above items.

[0013] In a third aspect, the present application further discloses an electronic device, which includes: the above-mentioned battery.

[0014] In an embodiment of the present application, the first-level particles may include at least first graphite particles, and the first graphite particles may serve as skeleton particles of the active material layer. When the active material layer includes secondary particles, and the second-level particles include at least silicon-carbon particles, the rate of change ΔV of the volume of the silicon-carbon particles in the charged state relative to the initial volume may be considered, so that the particle size d and ΔV of the silicon-carbon particles and the particle size D of the first graphite particles meet certain requirements. Thus, in the charged state, even if the volume of the silicon-carbon particles expands, it will not interfere with the first graphite particles serving as the skeleton. In this way, the chemical expansion of the pole piece can be reduced, and the cycle capacity retention rate of the pole piece can be improved. Furthermore, the health of the battery to which the pole piece is applied can be improved.

[0015] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0017] Figure 1 is a schematic diagram of the structure of a pole piece described in an embodiment of the present application;

[0018] Figure 2 is a schematic diagram of the structure in which particles in the pole piece described in the embodiment of the present application are stacked according to a regular tetrahedron stacking model;

[0019] Figure 3 is a schematic diagram of the structure in which particles in the pole piece described in the embodiment of the present application are stacked according to the prismatic stacking model;

[0020] Figure 4 It is a schematic diagram of the structure in which particles in the pole piece described in the embodiment of the present application are stacked according to the pyramid stacking model.

[0021] Reference numerals: 10 - current collector, 11 - active material layer. DETAILED DESCRIPTION

[0022] Embodiments of the present invention will be described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0023] The term "first" or "second" in the specification and claims of the present application may include one or more of the features explicitly or implicitly. In the description of the present invention, unless otherwise specified, "plurality" means two or more. In addition, "and / or" in the specification and claims means at least one of the connected objects, and the character " / " generally means that the objects connected before and after are in an "or" relationship.

[0024] In the description of the present invention, it is to be understood that the terms “center”, “longitudinal”, “lateral”, “length”, “width”, “thickness”, “up”, “down”, “front”, “back”, “left”, “right”, “vertical”, “horizontal”, “top”, “bottom”, “inside”, “outside”, “clockwise”, “counterclockwise”, “axial”, “radial”, “circumferential”, etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0025] In the description of the present invention, it should be noted that, 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 it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0026] The embodiment of the present application provides a pole piece, which can be used for a lithium-ion battery. Specifically, the pole piece described in the embodiment of the present application can be a positive pole piece of the lithium-ion battery, or a negative pole piece of the lithium-ion battery. The embodiment of the present application is only described by taking the pole piece as the negative pole piece of the lithium-ion battery as an example, and the pole piece as the positive pole piece of the lithium-ion battery can be implemented by reference.

[0027] Reference Figure 1 , shows a schematic diagram of the structure of a pole piece according to an embodiment of the present application, such as Figure 1 As shown, the pole piece may specifically include: a current collector 10 and an active material layer 11 disposed on the current collector 10, the active material layer 11 may specifically include i-level particles, i is a positive integer greater than or equal to 2; the particle size of the i-level particles is smaller than the particle size of the i-1-level particles, and the i-level particles are filled between the i-1-level particles, the i-level particles at least include silicon-carbon particles with a particle size of d, and the i-1-level particles at least include first graphite particles with a particle size of D; wherein, when i is equal to 2, the following is satisfied:

[0028]

[0029] Wherein, the ΔV is the rate of change of the volume of the silicon-carbon particles in the charged state relative to the initial volume.

[0030] In an embodiment of the present application, the first-level particles may include at least first graphite particles, and the first graphite particles may serve as skeleton particles of the active material layer 11. When the active material layer 11 includes secondary particles, and the second-level particles include at least silicon-carbon particles, the rate of change ΔV of the volume of the silicon-carbon particles in the charged state relative to the initial volume may be considered, so that the particle size d and ΔV of the silicon-carbon particles and the particle size D of the first graphite particles meet certain requirements. Thus, in the charged state, even if the volume of the silicon-carbon particles expands, it will not interfere with the first graphite particles serving as the skeleton. In this way, the chemical expansion of the pole piece can be reduced, and the cycle capacity retention rate of the pole piece can be improved. Furthermore, the health of the battery to which the pole piece is applied can be improved.

[0031] It should be noted that in the embodiments of the present application, the filling theory of the i-level particles 11 in the active material layer needs to be based on the following assumptions: First, the particles are regular spheres. Secondly, the particles are replaced by the normal distribution curve with the equal-diameter D50, where the D50 is the particle size corresponding to the cumulative particle size distribution percentage of a sample reaching 50%. Its physical meaning is that particles with a particle size larger than it account for 50%, and particles with a particle size smaller than it also account for 50%. D50 is also called the median diameter or median particle size. D50 is often used to indicate the average particle size of a powder.

[0032] Specifically, the material of the particles of the active material layer 11 may include but is not limited to graphite, hard carbon, soft carbon, silicon carbon, silicon oxygen, lithium titanate, etc. The present embodiment of the application does not specifically limit the material of the particles. In the embodiment of the present application, the particle size of the first-level particles as the skeleton and the particle size of one or more second-level particles as fillers satisfy a certain formula relationship, thereby reducing the chemical expansion of the pole piece and improving the cycle capacity retention rate.

[0033] In the embodiment of the present application, the electrode sheet may be a negative electrode sheet. Generally, when the energy density of the battery needs to be increased, it is only necessary to perform silicon doping in the negative electrode sheet of the battery, that is, the negative electrode sheet of the battery is prone to the problem of rapid consumption of the electrode liquid caused by the expansion of silicon-carbon particles. Therefore, it is only necessary to apply the technical solution described in the embodiment of the present application to the negative electrode sheet of the battery.

[0034] It should be noted that, in a specific application, the electrode may also be a positive electrode of a battery, and the embodiment of the present application may not limit the specific content of the electrode.

[0035] In a specific application, the particle stacking model may specifically include: at least one of a regular tetrahedron stacking model, a prism stacking model, and a pyramid stacking model.

[0036] Reference Figure 2 , shows a schematic diagram of the structure of the particles in the pole piece according to the regular tetrahedron stacking model described in the embodiment of the present application, such as Figure 2 As shown, the first-level particles are stacked in a regular tetrahedral structure, and the second-level particles can be filled between the first-level particles.

[0037] In practical applications, the tetrahedral stacking model is the loosest stacking model for particle arrangement. In a skeleton with the particle size of the first-level particles as D, the maximum particle size d of the second-level particles can be:

[0038]

[0039] Solving formula 2, we can get:

[0040]

[0041] From Formula 3, we can know that when the particle size of the second-level particles filled in the skeleton with the particle size of the first-level particles as D is d≤0.732D, the volume will not change significantly compared with the original simple cubic stacking.

[0042] Reference Figure 3 , shows a schematic diagram of the structure of the particles in the pole piece according to the prismatic stacking model described in the embodiment of the present application. Figure 3 As shown, the first-stage particles are stacked in a prism structure, and the second-stage particles can be filled between the first-stage particles.

[0043] In practical applications, in the prismatic packing model, when the particles are arranged and packed most densely, in a skeleton with the particle size of the first-level particles as D, the maximum particle size d of the second-level particles can be:

[0044] d=0.414D (Formula 4)

[0045] From Formula 4, we can know that when the second-level particles with a particle size of d≤0.414D are filled in a skeleton with a first-level particle size of D, the volume will not change significantly compared to the original prism space stacking.

[0046] Reference Figure 4 , shows a schematic diagram of the structure of the particles in the pole piece according to the pyramid stacking model described in the embodiment of the present application. Figure 3 As shown, the first-stage particles are stacked in a pyramidal structure, and the second-stage particles can be filled between the first-stage particles.

[0047] In practical applications, in the pyramid stacking model, when the particles are arranged and stacked most densely, in a skeleton with a particle size of the first-level particles as D, the maximum particle size d of the second-level particles can be:

[0048] d=0.155D (Formula 5)

[0049] From Formula 5, we can know that when the second-level particles with a particle size of d≤0.155D are filled in a skeleton with a first-level particle size of D, the volume will not change significantly compared to the original pyramid space stacking.

[0050] It should be pointed out that, unlike the pursuit of densest packing, as the particle size of small particle active materials decreases, the specific surface area increases, which leads to the intensification of side reactions with the electrolyte and deterioration of the cycle. Therefore, the grading level should be controlled at 2 as much as possible, and the particle size of small particles should be comprehensively selected from multiple dimensions such as dynamics, cycle performance and compaction density.

[0051] In the embodiment of the present application, when both the first-level particles and the second-level particles in the active material layer of the pole piece are graphite particles, the active material layer can be a graphite system. In the active material layer of the pole piece, when silicon-carbon particles are used as second-level particles to effectively fill the skeleton of the first-level particles, the active material layer can be a silicon-doped system. In practical applications, the silicon-doped system is destroyed during chemical expansion due to the unique expansion characteristics of silicon-carbon particles after they are added as secondary particles.

[0052] For example, the particle size of silicon-carbon particles is currently usually selected as a material with D50=8um. From Formula 3 in the gradation structure above, it can be seen that when the first-level graphite particles with D=13um are selected as the skeleton, the particle size d=9.5um of the regular tetrahedral structure that can be filled in the gaps. In the case where the second-level particles are graphite particles, the graphite particles of 7.5um meet the above standards and can fill the regular tetrahedral pores. In the case where the second-level particles are silicon-carbon particles, the initial state d=8um can fill the regular tetrahedral gaps of the first-level graphite particles, so through effective filling, the compaction density and physical rebound are increased and decreased respectively.

[0053] Now consider the chemical rebound situation:

[0054] In the graphite system, since the volume expansion ratio of the first-level particles and the second-level particles is the same, the original densely packed structure will not be destroyed.

[0055] In the silicon-doped system, the volume expansion of the silicon-carbon particles in the second-level particles is 100%, compared with the volume expansion of the graphite particles as the first-level particles or the second-level particles, which is 20%. It can be seen that the expansion of the silicon-carbon particles as the second-level particles is 5 times that of the graphite particles as the first-level particles. This uneven change in volume will have a negative impact on the close-packed structure.

[0056] According to the initial tetrahedral dense packing form of the silicon-doped pole piece mentioned above, the dense packing form will not change when the second-level particle d≤0.732D. That is, when the particle size of the first-level particle D=13um, the d of the second-level particle must meet the limit of <9.5um. When the silicon-carbon particles in the second-level particles are charged and expanded, the particle size of the initial 8um silicon-carbon particles will reach 10.1um when the volume changes by 100%, exceeding the secondary particle size limit of 9.5um. At this time, the silicon-carbon particles in the second-level particles will interfere with the skeleton formed by the first-level particles. From the dense packing structure of the regular tetrahedron, it can be seen that one silicon-carbon particle will squeeze out the eight adjacent graphite particles, the porosity of the pole piece will increase, the consumption of the conductive network and electrolyte will increase, and the capacity retention rate of the cyclic expansion will deteriorate faster.

[0057] The volume of the sphere of the first-stage particle can be expressed as:

[0058]

[0059] According to Formula 6, after the silicon-carbon particles are charged and expanded, the particle size can be

[0060] In a specific application, when the particles in the active material layer are stacked using a regular tetrahedral stacking model, according to the constraint of formula 3, in order to avoid interference between the silicon-carbon particles as the second-level particles and the first graphite particles as the first-level particles after charging and expansion, the particle size of the silicon-carbon particles after charging and expansion should be controlled. Less than or equal to 0.732D, that is, the particle size of the silicon-carbon particles after charging and expansion needs to be controlled to satisfy Formula 1.

[0061] In some optional embodiments of the present application, when i is equal to 3, the particles in the active material layer can be stacked using a prismatic stacking model. According to the constraints of formula 4, in order to avoid interference between the silicon-carbon particles as the third-level particles and the first-level graphite particles as the first-level particles after charging and expansion, the particle size of the silicon-carbon particles after charging and expansion should be controlled. Less than or equal to 0.414D, that is, it satisfies:

[0062]

[0063] Wherein, the ΔV is the rate of change of the volume of the silicon-carbon particles in the third-level particles in the charged state relative to the initial volume.

[0064] In some optional embodiments of the present application, when i is equal to 4, the particles in the active material layer can be stacked using a pyramid stacking model. According to the constraints of Formula 5, in order to avoid interference between the silicon-carbon particles as the fourth-level particles and the first graphite particles as the first-level particles after charging and expansion, the particle size of the silicon-carbon particles after charging and expansion should be controlled to be less than or equal to 0.155D, that is, satisfying:

[0065]

[0066] Wherein, the ΔV is the rate of change of the volume of the silicon-carbon particles in the fourth-level particles in the charged state relative to the initial volume.

[0067] It should be noted that the above constraints are restrictive conditions, not optimal conditions. The selection of the optimal conditions still needs to be comprehensively selected in combination with dynamics, compaction and circulation conditions. If it is a two-level gradation, formula one is preferred. If it involves multi-level gradation, that is, there are three or more levels of particles, then the second-level particles satisfy formula one, the third-level particles satisfy formula seven, and the fourth-level particles need to satisfy formula eight, and so on. Moreover, each level of particles can be one active substance or multiple active substances, which is not limited in the embodiments of the present application.

[0068] In some optional embodiments of the present application, when the i-1th level particles and the i-th level particles are stacked according to a regular tetrahedral stacking model, since every 8 first-level particles as the skeleton can accommodate 4 second-level particles as fillings, there should be restrictive requirements to meet:

[0069] P i ≥2*(P i-1,1 +P i-1,2 +…+P i-1,n ) (Formula 9)

[0070] ∑P i =1 (Formula 10)

[0071] Wherein, Pi is the proportion of the i-th level particles. In a specific application, when the proportion of the i-1-level particles and the i-th level particles satisfies Formula 9 and Formula 10, it can be considered that the i-1-level particles as the skeleton can provide enough gaps to accommodate the i-th level particles as fillers, so as to avoid excessive expansion of the volume of the active material layer and interference with the i-1-level particles as the skeleton. In this way, the chemical expansion of the pole piece can be reduced and the cycle capacity retention rate of the pole piece can be improved. Furthermore, the health of the battery using the pole piece can be improved. That is, in the pole piece of the silicon-doped system, the particle size of the silicon-carbon particles needs to be controlled to satisfy Formula 1, and the particle proportion satisfies Formula 9 and Formula 10.

[0072] In some optional embodiments of the present application, the i-th level particles may also include second graphite particles, and the initial particle size of the second graphite particles is larger than the initial particle size of the silicon-carbon particles. In specific applications, since the expansion rate of the silicon-carbon particles in the charging state is much larger than the expansion rate of the second graphite particles, the initial particle size of the second graphite particles as filling particles may be set larger than the initial particle size of the silicon-carbon particles when formula 1 is satisfied, so as to further enhance the filling and supporting effect of the second graphite particles as filling particles.

[0073] It should be noted that, in practical applications, the initial particle size of the second graphite particles may also be smaller than or equal to the initial particle size of the silicon-carbon particles, and this embodiment of the present application does not limit this.

[0074] Optionally, the first-level particles may include the first graphite particles, and the second-level particles may include the silicon-carbon particles and the second graphite particles; wherein the proportion of the first-level particles is greater than twice the proportion of the second-level particles, so that the first-level particles as the skeleton can provide enough gaps to accommodate the second-level particles as fillers, avoiding excessive expansion of the volume of the active material layer and interference with the first-level particles as the skeleton. In this way, the chemical expansion of the pole piece can be reduced and the cycle capacity retention rate of the pole piece can be improved. Furthermore, the health of the battery using the pole piece can be improved.

[0075] In the process of implementing the embodiments of the present application, in order to fully verify the technical solution provided by the present application, the inventors designed and calculated the particle size and ratio of the second-level (or multi-level) particles and the ratio of the first-level particles according to the particle size of the first-level particles by using the grading design formula that takes the expansion effect into consideration. Specifically, the following five embodiments are provided.

[0076] Example 1

[0077] Taking 3C graphite as an example, graphite (80% of the first graphite particles as the first-level particles have a particle size of 13um, and 20% of the second graphite particles as the second-level particles have a particle size of 7.5um) and silicon-carbon particles (8um) as the second-level particles are graded into a negative electrode sheet with a gram capacity of 500mAh / g (silicon-carbon content of 11%).

[0078] The critical particle size of the silicon-carbon particles as the second-level particles is calculated using Formula 3. It can be seen that: the silicon-carbon particle size> the critical particle size of the silicon-carbon particles as the second-level particles, that is, Formula 1 is not satisfied.

[0079] After compounding:

[0080] First graphite particles as first-stage particles: 71% (first graphite particles account for 80% of graphite * graphite accounts for 89% of active material);

[0081] Secondary graphite particles as secondary particles: 18% (20% of the first graphite particles in the graphite * 89% of the graphite in the active material);

[0082] Silicon carbon particles as second-level particles: 11%;

[0083] It can be seen that the proportion of first-level particles>2*the proportion of second-level particles, that is, Formula 9 is satisfied.

[0084] Example 2

[0085] Graphite (80% as first-stage first graphite particles with a particle size of 13um, 20% as second-stage second graphite particles with a particle size of 7.5um) and silicon-carbon particles (6um) as second-stage particles are graded into a negative electrode sheet with a gram capacity of 500mAh / g.

[0086] The critical particle size of silicon-carbon particles as second-level particles is calculated using Formula 3, and it can be seen that: Silicon-carbon particle size = critical particle size of silicon-carbon particles as second-level particles, that is, Formula 1 is satisfied.

[0087] After compounding:

[0088] First graphite particles as first-stage particles: 71%

[0089] Secondary graphite particles as 2nd grade particles: 18%

[0090] Silicon carbon particles as second-level particles: 11%;

[0091] The proportion of first-level particles>2*the proportion of second-level particles, that is, Formula 9 is satisfied.

[0092] Example 3

[0093] Graphite (80% as first-stage first graphite particles with a particle size of 13um, 20% as second-stage second graphite particles with a particle size of 7.5um) and silicon-carbon particles (5um) as second-stage particles are graded into a negative electrode sheet with a gram capacity of 500mAh / g.

[0094] The critical particle size of silicon-carbon particles as the second-level particles is calculated using Formula 3, and it can be seen that: silicon-carbon particle size < critical particle size of silicon-carbon particles as the second-level particles.

[0095] After compounding:

[0096] First graphite particles as first-stage particles: 71%

[0097] Secondary graphite particles as 2nd grade particles: 18%

[0098] Silicon carbon particles as second-level particles: 11%;

[0099] The proportion of first-level particles>2*the proportion of second-level particles, that is, Formula 9 is satisfied.

[0100] Example 4

[0101] Taking 5C graphite as an example, graphite (60% as the first graphite particles of the first level with a particle size of 13um, 40% as the second graphite particles of 7.5um as the second level particles) and silicon carbon particles (5um) as the second level particles are graded into a negative electrode sheet with a gram capacity of 500mAh / g.

[0102] The critical particle size of silicon-carbon particles as the second-level particles is calculated using Formula 3. It can be seen that: the silicon-carbon particle size is less than the critical particle size of silicon-carbon particles as the second-level particles, that is, Formula 1 is satisfied.

[0103] After compounding:

[0104] First graphite particles as first-stage particles: 53%

[0105] Secondary graphite particles as 2nd-stage particles: 36%

[0106] Silicon carbon particles as second-level particles: 11%;

[0107] The proportion of first-level particles is less than 2*the proportion of second-level particles, which means that Formula 9 is not satisfied.

[0108] Example 5

[0109] Graphite (72% as first-stage first graphite particles with a particle size of 13um, 28% as second-stage second graphite particles with a particle size of 7.5um) and silicon-carbon particles (5um) as second-stage particles are graded into a negative electrode sheet with a gram capacity of 500mAh / g.

[0110] The critical particle size of silicon-carbon particles as the second-level particles is calculated using Formula 3. It can be seen that: the silicon-carbon particle size is less than the critical particle size of silicon-carbon particles as the second-level particles, that is, Formula 1 is satisfied.

[0111] After compounding:

[0112] First graphite particles as first-stage particles: 64%

[0113] Secondary graphite particles as 2nd grade particles: 25%

[0114] Silicon carbon particles as second-level particles: 11%;

[0115] The proportion of first-level particles>2*the proportion of second-level particles, that is, Formula 9 is satisfied.

[0116] The test results are summarized in the following table:

[0117] Group Normal temperature cycle maintenance Normal temperature cycle expansion High temperature cycle maintenance High temperature cyclic expansion Example 1 80%@600cls 12%@600cls 80%@400cls 14%@400cls Example 2 82%@600cls 11%@600cls 83%@400cls 12%@400cls Example 3 84%@600cls 10%@600cls 86%@400cls 10%@400cls Example 4 78%@600cls 12%@600cls 76%@400cls 14%@400cls Example 5 82%@600cls 11%@600cls 83%@400cls 12%@400cls

[0118] As can be seen from the above table, by comparing Examples 1 to 3, when the second-level particles only include silicon-carbon particles, when the particle gradation in the active material layer satisfies both Formula 1 and Formula 9 (Examples 2 and 3), the pole piece can maintain good health and low expansion under both normal and high temperature conditions. And when the particle gradation satisfies both Formula 1 and Formula 9, the pole piece with smaller silicon-carbon particles (Example 3) can obtain better health and lower expansion.

[0119] By comparing Example 4 and Example 5, it can be seen that when the second-level particles include silicon-carbon particles and graphite particles, when the particle grading in the active material layer satisfies Formula 1 and Formula 9 (Example 5) at the same time, the pole piece can maintain good health and low expansion under both normal temperature and high temperature conditions.

[0120] In summary, the pole piece described in the embodiment of the present application may at least include the following advantages:

[0121] In an embodiment of the present application, the first-level particles may include at least first graphite particles, and the first graphite particles may serve as skeleton particles of the active material layer. When the active material layer includes secondary particles, and the second-level particles include at least silicon-carbon particles, the rate of change ΔV of the volume of the silicon-carbon particles in the charged state relative to the initial volume may be considered, so that the particle size d and ΔV of the silicon-carbon particles and the particle size D of the first graphite particles meet certain requirements. Thus, in the charged state, even if the volume of the silicon-carbon particles expands, it will not interfere with the first graphite particles serving as the skeleton. In this way, the chemical expansion of the pole piece can be reduced, and the cycle capacity retention rate of the pole piece can be improved. Furthermore, the health of the battery to which the pole piece is applied can be improved.

[0122] The present application embodiment provides a battery, and the battery may include the pole piece described in any of the above embodiments. Specifically, the battery may be a lithium battery, and the pole piece may be at least one of a positive pole piece and a negative pole piece. The present application embodiment does not limit the specific type of the pole piece.

[0123] It should be noted that in the embodiment of the present application, the structure of the pole piece is the same as the structure of the pole piece described in any of the above embodiments, and its beneficial effects are also similar, which will not be elaborated here.

[0124] The embodiment of the present application provides an electronic device, which may include the battery described in any of the above embodiments. Specifically, the electronic device may include but is not limited to at least one of a mobile phone, a tablet computer, and a wearable device, and the embodiment of the present application may not limit the specific type of the electronic device.

[0125] It should be noted that in the embodiments of the present application, the structure of the battery is the same as the structure of the battery described in any of the above embodiments, and its beneficial effects are also similar, which will not be described in detail here.

[0126] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0127] Although the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A pole piece, characterized in that: The pole piece comprises: a current collector and an active material layer disposed on the current collector, wherein the active material layer comprises i-level particles, where i is a positive integer greater than or equal to 2; The particle size of the i-th level particles is smaller than the particle size of the i-1-th level particles, and the i-th level particles are filled between the i-1-th level particles, the i-th level particles at least include silicon-carbon particles with a particle size of d, and the i-1-th level particles at least include first graphite particles with a particle size of D; Among them, when i is equal to 2, it satisfies: Wherein, the ΔV is the rate of change of the volume of the silicon-carbon particles in the charged state relative to the initial volume.

2. The pole piece according to claim 1, characterized in that: The i-1th level particles and the i-th level particles are stacked according to a regular tetrahedral stacking model, satisfying: P i ≥2*(P i-1,1 +P i-1,2 +…+P i-1,n ), ΣP i =1, Wherein, Pi is the proportion of the i-th level particles.

3. The pole piece according to claim 1, characterized in that: The i-th level particles further include second graphite particles, and the primary particle size of the second graphite particles is larger than the primary particle size of the silicon-carbon particles.

4. The pole piece according to any one of claims 1 to 3, characterized in that: When i is equal to 2, the first-level particles include the first graphite particles, and the second-level particles include the silicon-carbon particles and the second graphite particles; wherein the proportion of the first-level particles is greater than twice the proportion of the second-level particles.

5. The pole piece according to claim 1, characterized in that: The pole piece is a negative pole piece.

6. The pole piece according to claim 1, characterized in that: When i is equal to 3, it satisfies: Wherein, the ΔV is the rate of change of the volume of the silicon-carbon particles in the third-level particles in the charged state relative to the initial volume.

7. The pole piece according to claim 1, characterized in that: When i is equal to 4, it satisfies: Wherein, the ΔV is the rate of change of the volume of the silicon-carbon particles in the fourth-level particles in the charged state relative to the initial volume.

8. The pole piece according to claim 1, characterized in that: The particle stacking model includes at least one of a regular tetrahedron stacking model, a prism stacking model and a pyramid stacking model.

9. A battery, characterized in that: The battery comprises: a pole piece as claimed in any one of claims 1 to 8.

10. An electronic device, characterized in that: The electronic device comprises: the battery according to claim 9.

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