Electrode, method for preparing electrode and battery

Abstract

The present application discloses an electrode, a method for preparing the electrode, and a battery. The electrode comprises n layers of pole sheets stacked in sequence; wherein the pole sheet layer close to the separator side of the battery is the first layer, and the pole sheet layer close to the current collector side of the battery is the nth layer, and n is a natural number greater than or equal to 2; the electrode material of the pole sheet layer of the first layer comprises a first particle, and the electrode material of each pole sheet layer of the second to nth layers comprises at least a first particle and a second particle, respectively, and the average particle size of the first particle is greater than the average particle size of the second particle; the porosity of each pole sheet layer gradually increases along the direction from the nth layer to the first layer. The technical solution disclosed in the present application improves the compaction density of the electrode and the diffusion efficiency of lithium ions, and improves the volume energy density and kinetic performance of the electrode.

Description

Technical Field

[0001] The present application relates to the technical field of battery components, and more specifically, to an electrode, a method for preparing the electrode, and a battery. Background Art

[0002] Lithium-ion power battery is a new type of high-energy battery that can be recharged. It mainly relies on the movement of lithium ions between the positive and negative electrodes to work. It has the advantages of high energy, high battery voltage, wide operating temperature range, and long storage life. It has been widely used in military and civilian small electrical appliances.

[0003] With the promotion of energy vehicles, the application of lithium-ion power batteries in the automotive field has become more and more extensive. The volume energy density of lithium-ion power batteries is very critical to their use in the whole vehicle. In the existing technology, the volume energy density of the battery is usually improved by increasing the compaction density of the electrode. However, the ultimate compaction density of the electrode is usually affected by the true density of the material itself. At the same time, under high compaction, the porosity of the electrode will become extremely low, especially the surface of the electrode, where the pores are easily blocked, making it difficult for lithium ions to diffuse, resulting in a significant reduction in the kinetic performance of the electrode. Summary of the invention

[0004] One object of the present application is to provide a new technical solution for an electrode, a method for preparing an electrode and a battery.

[0005] According to a first aspect of the present application, an electrode is provided, comprising:

[0006] n layers of pole pieces stacked in sequence;

[0007] The electrode layer close to the separator side of the battery is the first layer, and the electrode layer close to the current collector side of the battery is the nth layer, where n is a natural number greater than or equal to 2;

[0008] The electrode material of the first electrode layer includes first particles, and the electrode material of each electrode layer of the second to n layers includes at least first particles and second particles, respectively, and the average particle size of the first particles is greater than the average particle size of the second particles;

[0009] The porosity of each pole piece layer gradually increases along the direction from the nth layer to the first layer.

[0010] Optionally, the number of first particles included in the pole piece layer of the xth layer in the electrode material of the layer accounts for [-x / (2n-2)+(2n-1) / (2n-2)];

[0011] Wherein, x is a natural number less than or equal to n.

[0012] Optionally, the average particle size of the first particles is in the range of 0.90 to 1.60 μm, and the average particle size of the second particles is in the range of 0.25 to 0.70 μm.

[0013] Optionally, the average particle size of the first particles is in the range of 1.0 to 1.2 μm, and the average particle size of the second particles is in the range of 0.35 to 0.55 μm.

[0014] Optionally, the radius of the first particle is R, and the radius of the second particle is less than or equal to 0.414R.

[0015] Optionally, each of the pole piece layers from the 2nd to the nth layer further includes third particles, and the radius of the third particles is less than or equal to 0.225R.

[0016] Optionally, the particle size of the first particles and the particle size of the second particles used in the x-th layer of the pole piece layer meet the following conditions:

[0017] 1 / d 11 =[a*d x1 2 +(1-a)d x2 2 ] / [a*d x1 3 +(1-a)d x2 3 ];

[0018] Wherein, x is a natural number greater than 1 and less than or equal to 2, a is the ratio of the number of the first particles in the xth layer to the electrode material in the layer; d 11 represents the particle size of the first particles of the first pole piece layer, d x1 represents the particle size of the first particles of the pole piece layer of the xth layer; d x2 Represents the particle size of the second particles in the xth layer.

[0019] Optionally, the number of the pole sheet layers ranges from 2 to 10 layers, and the number of the second particles included in the electrode material of each pole sheet layer except the first layer gradually decreases along the direction from the side close to the current collector to the side close to the separator.

[0020] Optionally, the electrode material includes a positive electrode material, and the positive electrode material is at least one of lithium iron phosphate, lithium nickel cobalt manganese oxide and lithium manganate.

[0021] Optionally, the electrode material includes a negative electrode material, and the negative electrode material is at least one of artificial graphite, natural graphite, lithium titanate, soft carbon and hard carbon.

[0022] According to a second aspect of the present application, there is provided a method for preparing the electrode according to the first aspect, comprising the following steps:

[0023] Fully mixing the electrode material with the conductive agent and the binder to form a mixture;

[0024] heating the mixture to make the binder molten;

[0025] Solidifying the molten binder, and wrapping the electrode material with the solidified binder to obtain a powdery substance;

[0026] Processing the powdered material to form the pole piece layer;

[0027] According to the above method, by adjusting the amount of the first particles and the second particles in each layer of the pole piece layer, multiple layers of the pole piece layer with different porosities are prepared;

[0028] According to the size of the porosity, multiple electrode sheets are stacked and fused in sequence to obtain the electrode.

[0029] Optionally, solidifying the binder in a molten state includes solidifying the binder into a fiber state through an electrostatic spinning process.

[0030] Optionally, the process of sequentially stacking and fusing the plurality of pole pieces comprises: a hot pressing process.

[0031] According to a third aspect of the present application, a battery is provided, comprising the electrode described in the first aspect.

[0032] Optionally, the battery comprises: a first current collector, a first electrode, a separator, a second electrode and a second current collector which are arranged in sequence, and an electrolyte is arranged between the first electrode and the second electrode and the separator respectively.

[0033] According to one embodiment of the present disclosure, the pole sheet layer of the separator side layer is prepared by first particles, and the remaining pole sheet layers are prepared by first particles and second particles of different particle sizes, thereby improving the compaction density of the electrode. At the same time, the multi-layer arrangement of the pole sheet layer, and the arrangement of each pole sheet layer so that the porosity gradually increases along the direction from the current collector side layer to the separator side layer, improves the diffusion efficiency of lithium ions and improves the kinetic performance of the electrode.

[0034] Other features and advantages of the present application will become apparent from the following detailed description of exemplary embodiments of the present application with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the application and, together with the description, serve to explain the principles of the application.

[0036] Figure 1 It is a schematic diagram of an electrode and its preparation process in this application.

[0037] Figure 2 is a schematic diagram of a battery in this application.

[0038] Description of reference numerals:

[0039] 1-first electrode; 11-first particle; 12-second particle; 13-first layer; 14-nth layer; 2-second electrode; 3-separator; 4-first current collector; 5-second current collector; 6-electrolyte. DETAILED DESCRIPTION

[0040] Various exemplary embodiments of the present application will now be described in detail with reference to the accompanying drawings. It should be noted that unless otherwise specifically stated, the relative arrangement of components and steps, numerical expressions and numerical values ​​set forth in these embodiments do not limit the scope of the present application.

[0041] The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the present application, its application, or uses.

[0042] Technologies, methods, and equipment known to ordinary technicians in the relevant art may not be discussed in detail, but where appropriate, the technologies, methods, and equipment should be considered as part of the specification.

[0043] In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not limiting. Therefore, other examples of the exemplary embodiments may have different values.

[0044] It should be noted that like reference numerals and letters refer to similar items in the following figures, and therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0045] In the prior art, the volume energy density of the battery is usually increased by increasing the compaction density of the electrode, but the high compaction density of the electrode will reduce the porosity of the electrode, especially the pores on the surface of the electrode are easily blocked. The amount of electrode pores directly affects the charge and discharge performance of the battery. If the porosity is low or blocked, it will affect the movement of lithium ions, resulting in a significant reduction in the kinetic performance of the electrode. Therefore, the electrode structure not only needs to have high pressure, but also needs to have a reasonable pore structure. Among them, porosity refers to the percentage of the pore volume in the material to the total volume of the material in its natural state.

[0046] like Figure 1 to Figure 2As shown, in order to solve the above technical problems, the present application provides an electrode, comprising n layers of electrode layers stacked in sequence; wherein the electrode layer close to the side of the battery's diaphragm is the first layer 13, and the electrode layer close to the side of the battery's current collector is the nth layer 14, and n is a natural number greater than or equal to 2; the electrode material of the electrode layer of the first layer 13 includes first particles 11, and the electrode material of each layer of the electrode layer from the second to the nth layer includes at least first particles 11 and second particles 12, respectively, and the average particle size of the first particles 11 is greater than the average particle size of the second particles 12; the porosity of each layer of the electrode layer gradually increases along the direction from the nth layer 14 to the first layer 13.

[0047] Specifically, in this embodiment, the electrode is a structure in which multiple layers (n layers) of pole sheets are stacked (n is a natural number greater than or equal to 2, that is, the electrode can include 2 layers, 3 layers, or even more layers, and this application does not limit this). This structure is conducive to distinguishing the characteristics of each pole sheet layer. After the multiple pole sheets are stacked, the electrode materials of the pole sheets of the first layer 13 and the pole sheets of the nth layer 14 located on both sides of the electrode are determined (when the electrode is applied to a battery, a current collector and a diaphragm are usually set on both sides of the electrode, the pole sheet layer close to the current collector is the nth layer 14, and the pole sheet layer close to the diaphragm is the first layer 13). The electrode material includes first particles 11 and second particles 12, wherein the average particle size of the first particles 11 is greater than the average particle size of the second particles 12. The electrode material of the first layer 13 pole sheet layers can include only the first particles 11, and the electrode materials of the remaining pole sheet layers (2nd to nth layers) can include the first particles 11 (large particles) and the second particles 12 (small particles). The combination of large particles and small particles allows small particles to fill the gaps between large particles, achieving a higher high compaction density. The remaining electrode layers refer to the other electrode layers except the first layer 13, that is, if the electrode has a total of 2 electrode layers, the remaining electrode layers are the second electrode layers, and the electrode material of the second electrode layer includes at least the first particles 11 and the second particles 12; if the electrode has 3 electrode layers, the remaining electrode layers are the second and third electrode layers, and the second and third electrode layers respectively include at least the first particles 11 and the second particles 12, and so on.

[0048] In addition, by adjusting the number of large and small particles in the remaining electrode layers (the 2nd to nth layers), the porosity of each electrode layer can be controlled to gradually increase along the direction from the nth layer 14 to the first layer 13, that is, the electrode layer of the nth layer 14 has the lowest porosity, while the diaphragm layer side has larger pores and higher porosity, so as to facilitate the diffusion of lithium ions, so that the electrode has a lower impedance and a higher discharge retention rate. Moreover, the more layers of the electrode layer, the more uniform the gradient distribution of the pores (that is, the law of the gradual increase of the porosity along the direction from the nth layer 14 to the first layer 13), and the more conducive to the diffusion of lithium ions. Among them, the particle size of the first particle 11 selected for each electrode layer can be different, and accordingly, the particle size of the second particle 12 selected for the 2nd to nth layers can also be different, so as to facilitate the construction of different porosities for each electrode layer. The diffusion of lithium ions is restricted by the layer with lower porosity. When the electrode includes n electrode layers, from the perspective of porosity and compaction, in actual production, the proportion of the first particles 11 (large particles) in the first electrode layer 13 and the nth electrode layer 14 can be determined first, and then the porosity of the middle electrode layer can be adjusted to present a uniform gradient.

[0049] In summary, the electrode in this embodiment has a high compaction density, which improves the volume energy density of the lithium-ion battery. The gradient change law of the porosity between the first layer 13 of the pole piece layer and the nth layer 14 of the pole piece layer makes the electrode in this solution have high dynamic performance at the same time.

[0050] Optionally, the number of the first particles 11 included in the x-th electrode layer accounts for a in the electrode material of the layer, then:

[0051] a=m(first particle) / m(total particles)=[-x / (2n-2)+(2n-1) / (2n-2)];(1)

[0052] Wherein, n is a natural number greater than or equal to 2, x is a natural number less than or equal to n, and m is the number of particles.

[0053] Specifically, the porosity of each layer of the pole piece layer can be achieved by adjusting the number of the first particles 11 and the second particles 12 of each layer. The gradient change of the porosity of each layer of the pole piece layer is achieved by adjusting the number of large and small particles, which is easy to achieve in actual production, and the adjustment result is relatively accurate. For example, in an electrode with two layers of pole pieces, the first particles 11 of the pole piece layer of the first layer 13 account for 100%, and the first particles 11 of the pole piece layer of the second layer account for 50%. For another example, in an electrode with four layers of pole pieces, the first particles 11 of the pole piece layer of the first layer account for 100%, the first particles 11 of the pole piece layer of the second layer account for 83.3%, the first particles 11 of the pole piece layer of the third layer account for 66.7%, and the first particles 11 of the pole piece layer of the fourth layer account for 50%. According to the above rules summarized in this application, the number of first particles 11 is set, and the number of first particles 11 of the pole piece layer of the nth layer 14 can be kept at least 50% to ensure that the porosity of each pole piece layer is not too low.

[0054] Optionally, the average particle size of the first particles 11 is in the range of 0.90 to 1.60 μm, and the average particle size of the second particles 12 is in the range of 0.25 to 0.70 μm.

[0055] Specifically, in this embodiment, the average particle size of the first particle 11 ranges from 0.90 to 1.60 μm, and the average particle size of the second particle 12 ranges from 0.25 to 0.70 μm. If the average particle size of the first particle 11 or the second particle 12 is too large, the specific surface area of ​​the particle will be smaller, the solid phase diffusion path will increase, the electrochemical reaction power of the material will be slower, and the kinetic performance of the battery will be affected. If the average particle size of the first particle 11 or the second particle 12 is too small, the specific surface area of ​​the particle will be larger, and the electrochemical active area will be larger accordingly, so that the side reactions on the surface of the particle material will become more, and the cycle performance of the battery will be impaired. Among them, the electrochemical active area refers to the site on the particle surface that can participate in the electrochemical reaction. Preferably, the average particle size of the first particle 11 ranges from 1.0 to 1.2 μm, and the average particle size of the second particle 12 ranges from 0.35 to 0.55 μm.

[0056] Optionally, the radius of the first particle 11 is R, and the radius of the second particle 12 is less than or equal to 0.414R.

[0057] Specifically, in this embodiment, the electrode materials used can be approximately regarded as spherical particles. Particles of the same particle size will still have pores between the particles even in the case of dense packing. If smaller particles are filled in the pores, the compaction of the material can be further improved. That is, in the case of dense packing of the first particle 11, if the radius of the first particle 11 is R, then the maximum radius that the pore of the first particle 11 can accommodate is 0.414R. Therefore, when the radius of the second particle 12 is r≤0.414R, it can be smoothly filled into the pores between the first particles 11. The material combined in this way has ultra-high compaction, and this ultra-high compaction combined material can be used as the pole piece layer of the nth layer 14, and then the filling amount of the second particle 12 (small particle) can be gradually reduced from the pole piece layer of the nth layer 14 to the pole piece layer of the first layer 13, so as to gradually increase the porosity of each layer and construct a gradient pore structure that is conducive to the diffusion of lithium ions. Such an electrode structure can take into account both high compaction and high particle diffusion efficiency.

[0058] Optionally, each of the 2nd to nth pole piece layers further includes third particles, and the maximum radius of the third particles is less than or equal to 0.225R.

[0059] Specifically, in this embodiment, in addition to the first particle 11 used in the pole piece layer of the first layer 13, the remaining pole piece layers can also be prepared by using three different sizes of granular materials. For example, the pole piece layer of the nth layer 14 can be prepared by using the first particle 11, the second particle 12 and the third particle. At this time, analogous to the two granular materials in the above embodiment, the maximum radius of the third particle is 0.225R. The pole piece layer constructed using three different sizes of granular materials has a higher compaction. After adjusting the material of the pole piece layer of the nth layer 14, the filling amount of the second particle 12 and / or the third particle can be gradually reduced from the pole piece layer of the nth layer 14 to the pole piece layer of the first layer 13, so as to gradually increase the porosity of each layer and construct a gradient pore structure that is conducive to the diffusion of lithium ions. The use of three granular materials can not only make the compaction density of the electrode larger, but also make it more convenient to adjust the gradient of the porosity change, which is conducive to achieving a uniform change in the pore structure of each layer.

[0060] Optionally, the particle sizes of the first particles 11 and the second particles 12 used in the x-th electrode layer satisfy the following conditions:

[0061] 1 / d 11 =[a*d x1 2 +(1-a)d x2 2 ] / [a*d x1 3 +(1-a)d x2 3 ];(2)

[0062] Wherein, x is a natural number greater than 1 and less than or equal to 2, a is the ratio of the number of the first particles 11 in the xth layer to the electrode material in the layer; d 11 The particle size of the first particle 11 representing the first layer 13 of the pole piece, d x1 represents the particle size of the first particle 11 of the pole piece layer of the xth layer; d x2 Represents the particle size of the second particles 12 of the x-th layer.

[0063] Generally, if the particles of the electrode material become smaller, the tortuosity σ of the electrode will become larger, which is not conducive to particle diffusion. In this embodiment, when the first particles 11 and the second particles 12 are proportioned, the particle size of the first particles 11 and the second particles 12 of each layer can be adjusted to make the tortuosity σ of each electrode layer similar. That is, the particle size of the first particles 11 of the electrode layer of the first layer 13 can be different from the particle size of the first particles 11 of the remaining electrode layers of the second to n layers. When the average particle size of the first particles 11 and the second particles 12 of each electrode layer satisfies formula (2), it can ensure that the tortuosity σ of each electrode layer is similar, so that the electrode performance is more uniform, which is conducive to the diffusion of lithium ions and further improves the ion diffusion efficiency. Among them, the tortuosity σ is used to describe the parameters of the electrode pore structure. The larger the tortuosity, the more tortuous the internal pores, and the longer the path that the ions diffuse from the surface to the current collector.

[0064] Optionally, the number of electrode layers ranges from 2 to 10, and the number of second particles 12 included in the electrode materials of each electrode layer except the first layer 13 gradually decreases along the direction from the side close to the current collector to the side close to the separator.

[0065] Specifically, in this embodiment, the number of electrode layers can be selected to be 2-10 layers to construct a uniform pore structure. If the number of electrode layers is too large, the porosity change between two adjacent layers is very small, and the gradient change of too small porosity does not have a particularly obvious effect on improving lithium ion diffusion, but it has a great impact on production efficiency. Therefore, the appropriate selection of the number of layers can take into account both the gradient change of porosity and production efficiency. In addition, by adjusting the proportion of the second particles 12 in each layer, the gradient adjustment of porosity can be achieved.

[0066] Optionally, the electrode material includes a positive electrode material, and the positive electrode material is at least one of lithium iron phosphate, lithium nickel cobalt manganese oxide and lithium manganate.

[0067] Specifically, the electrode provided in this embodiment can be made of positive electrode material and used as the positive electrode of the battery, or can be made of negative electrode material and used as the negative electrode of the battery. The positive electrode material can be at least one of lithium iron phosphate, lithium nickel cobalt manganese oxide and lithium manganate; the negative electrode material can be at least one of artificial graphite, natural graphite, lithium titanate, soft carbon and hard carbon.

[0068] Several embodiments and comparative examples are given below to further illustrate the advantages of the electrode provided in the first aspect.

[0069] Embodiment 1:

[0070] A double-layer electrode scheme is adopted, and lithium iron phosphate material is selected as the electrode material. The second layer of the electrode layer uses the first particles 11 (average particle size D50 = 1.38μm) and the second particles 12 (average particle size D50 = 0.57μm) mixed in a ratio of 1:1, with a mass ratio of 93:7; the first layer 13 of the electrode layer uses the first particles 11 (average particle size D50 = 1.26μm).

[0071] Embodiment 2:

[0072] A three-layer electrode scheme is adopted, and lithium iron phosphate material is selected as the electrode material. The third layer of the pole piece layer uses the first particle 11 (average particle size D50 = 1.38μm) and the second particle 12 (average particle size D50 = 0.57μm) mixed in a 1:1 ratio, with a mass ratio of 93:7; the second layer of the pole piece layer in the middle is based on the above-mentioned design rules, the average particle size of the first particle 11 is 1.30μm, the average particle size of the second particle 12 is 0.53μm, and the mass ratio is 97:3; the first layer 13 of the pole piece layer uses the first particle 11 (average particle size D50 = 1.26μm).

[0073] Embodiment 3:

[0074] A three-layer electrode scheme is adopted, and lithium iron phosphate material is selected as the electrode material. The third layer of the pole piece layer uses the first particle 11 (average particle size D50 = 1.19μm) and the second particle 12 (average particle size D50 = 0.493μm) mixed in a 1:1 ratio, with a mass ratio of 93:7; the second layer of the pole piece layer in the middle is based on the above-mentioned design rules, the average particle size of the first particle 11 is 1.12μm, the average particle size of the second particle 12 is 0.466μm, and the mass ratio is 97:3; the first layer 13 of the pole piece layer uses the first particle 11 (average particle size D50 = 1.09μm).

[0075] Comparative Example 1:

[0076] A double-layer electrode solution is adopted, and lithium iron phosphate material is selected as the electrode material. The second layer of the electrode layer uses the first particle (average particle size D50 = 1.26μm), and the first layer of the electrode layer uses the first particle (average particle size D50 = 1.38μm) and the second particle (average particle size D50 = 0.57μm) mixed in a ratio of 1:1, with a mass ratio of 93:7;

[0077] Comparative Example 2:

[0078] A single-layer electrode solution is adopted, and lithium iron phosphate material is selected as the electrode material. The first particles (average particle size D50 = 1.38 μm) and the second particles (average particle size D50 = 0.57 μm) are mixed in a ratio of 1:1, with a mass ratio of 96:4.

[0079] Comparative Example 3:

[0080] A single-layer electrode solution is adopted, and the electrode material is lithium iron phosphate material with an average particle size of D50=1.38μm.

[0081] The following data table is obtained through the above examples and comparative examples.

[0082] Table 1

[0083] Example <![CDATA[Compaction density (g / cm 3 )]]> Example 1 2.702.65 Example 2 2.722.67 Example 3 2.682.63 Comparative Example 1 2.682.63 Comparative Example 2 2.722.67 Comparative Example 3 2.582.53

[0084] Table 1 shows the compaction density of an electrode with a width of 5 cm under a rolling pressure of 1 MPa. It can be seen that despite the addition of small particles (second particles 12), the multi-layer coating design can maintain the compaction of the electrode at a relatively high level.

[0085] Table 2

[0086] Example 0.33C discharge mixed material gram capacity (mAh / g) Example 1 137.5 Example 2 138.0 Example 3 138.2 Comparative Example 1 135.8 Comparative Example 2 137.2 Comparative Example 3 136.8

[0087] Table 2 shows the electrodes obtained by multi-layer coating according to gradient porosity design. The electrodes obtained by multi-layer coating with gradient porosity design have higher capacity under the same design parameters.

[0088] Table 3

[0089] Example DCIR(mΩ) Example 1 51.8 Example 2 50.8 Example 3 48.2 Comparative Example 1 56.9 Comparative Example 2 54.2 Comparative Example 3 53.6

[0090] Table 3 shows that under the condition of 50% SOC DC internal resistance, the electrode in the present application has lower impedance, which is beneficial to the diffusion of lithium ions.

[0091] Table 4

[0092] Example 0.2C / 2C discharge ratio Example 1 0.940 Example 2 0.959 Example 3 0.960 Comparative Example 1 0.875 Comparative Example 2 0.898 Comparative Example 3 0.918

[0093] Table 4 shows that under the condition of 0.2 / 2C discharge capacity ratio at room temperature, the electrode of the present application has a higher discharge retention rate, which is beneficial to the diffusion of lithium ions.

[0094] like Figure 1 As shown, according to the second aspect of the present application, a method for preparing the electrode according to the first aspect is provided, comprising the following steps:

[0095] Fully mixing the electrode material with the conductive agent and the binder to form a mixture;

[0096] heating the mixture to make the binder molten;

[0097] Solidifying the molten binder, and wrapping the electrode material with the solidified binder to obtain a powdery substance;

[0098] Processing the powdered material to form the pole piece layer;

[0099] According to the above method, by adjusting the number of the first particles 11 and the second particles 12 in each layer of the pole piece layer, multiple layers of the pole piece layer with different porosities are prepared;

[0100] According to the size of the porosity, multiple electrode sheets are stacked and fused in sequence to obtain the electrode.

[0101] Specifically, taking the preparation of the positive electrode of the battery as an example, first select a positive electrode material of suitable particle size according to the scheme provided in the first aspect, crush the positive electrode material into particles, and fully mix it with a conductive agent and a binder to form a mixture. Among them, the positive electrode material can be selected from lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium manganate, etc.; the conductive agent includes carbon nanotubes, graphene, carbon black, carbon fiber, etc. After the mixture is heated to make the binder therein molten, it is further solidified so that the binder fully wraps the granular material to form a powdered substance. The powdered substance is processed to form a basic pole piece of a specific size and thickness. This basic pole piece is the pole piece layer ultimately used to process the electrode. According to the size of the porosity, the prepared multi-layer pole pieces are stacked and fused, and finally an electrode with high compaction and uniform porosity change is obtained.

[0102] Among them, when preparing the first layer 13 of the electrode layer, only the first particle 11 needs to be added to the electrode material, and the remaining layers can be added with the first particle 11, the second particle 12 or even the third particle according to the actual needs according to the technical solution of the first aspect. The number ratio of the first particle 11 and the second particle 12 of each electrode layer can be determined by formula (1), and the particle size of the first particle 11 and the second particle 12 of each electrode layer can be determined by formula (2). The electrode prepared by the preparation method of the present application has an ultra-high compaction density, which improves the volume energy density of the battery. The porosity of the electrode from the first layer 13 to the nth layer 14 of the electrode layer has a certain gradient change law, which can simultaneously ensure the dynamic performance of the electrode. The entire preparation process is simple and the preparation efficiency is high.

[0103] Optionally, solidifying the binder in a molten state includes solidifying the binder into a fiber state through an electrostatic spinning process.

[0104] Specifically, when curing the molten binder, the electrospinning process can be selected. Electrospinning is a special form of electrostatic atomization of polymer fluids. At this time, the atomized substances are not tiny droplets, but polymer micro jets that can run for a considerable distance and eventually solidify into fibers. This method can produce polymer filaments with nanometer diameters, making the bonding between the binder and electrode material particles more firm and uniform.

[0105] Optionally, the process of sequentially stacking and fusing the plurality of pole pieces comprises: a hot pressing process.

[0106] Specifically, the hot pressing process can achieve high compaction of the granular material on the one hand, and on the other hand make the fusion of each layer more complete, making the integrity of the electrode stronger.

[0107] According to a third aspect of the present application, a battery is provided, comprising the electrode described in the first aspect.

[0108] Optionally, the battery includes: a first current collector, a first electrode 1, a separator, a second electrode 2, and a second current collector arranged in sequence, and an electrolyte is arranged between the first electrode 1 and the second electrode 2 and the separator respectively.

[0109] like Figure 2 As shown, the battery provided in this embodiment includes a first current collector 4, a first electrode 1, a diaphragm 3, a second electrode 2, and a second current collector 5, which are arranged in sequence, and an electrolyte 6 is arranged between the first electrode 1 and the second electrode 2 and the diaphragm 3 respectively. Among them, the first electrode 1 is a negative electrode, and the second electrode 2 is a positive electrode, and both adopt the electrode structure described in the first aspect. During assembly, the pole piece layer of the first layer 13 of the first electrode 1 and the second electrode 2 is arranged close to the diaphragm 3, and the pole piece layer of the nth layer 14 is close to the first current collector 4 and the second current collector 5 respectively. The first current collector 4 can be made of copper foil, and the second current collector 5 can be made of aluminum foil. The battery in this embodiment has higher volume energy density and dynamic performance.

[0110] The above embodiments focus on the differences between the various embodiments. As long as the different optimization features between the various embodiments are not contradictory, they can be combined to form a better embodiment. Considering the simplicity of the text, they will not be repeated here.

[0111] Although some specific embodiments of the present application have been described in detail by way of example, it should be understood by those skilled in the art that the above examples are only for illustration, not for limiting the scope of the present application. It should be understood by those skilled in the art that the above embodiments may be modified without departing from the scope and spirit of the present application. The scope of the present application is defined by the appended claims.

Claims

1. An electrode, used in a battery, characterized in that: include: n layers of pole pieces stacked in sequence; The electrode layer close to the separator side of the battery is the first layer, and the electrode layer close to the current collector side of the battery is the nth layer, where n is a natural number greater than or equal to 2; The electrode material of the first electrode layer includes first particles, and the electrode material of each electrode layer of the second to n layers includes at least first particles and second particles, respectively, and the average particle size of the first particles is greater than the average particle size of the second particles; And the particle size of the first particles and the particle size of the second particles used in the x-th layer of the pole piece layer meet the following conditions: 1 / d 11 =[a*d x1 2 +(1-a)d x2 2 ] / [a*d x1 3 +(1-a)d x2 3 ]; Wherein, x is greater than 1 and less than or equal to n, a is the number ratio of the first particles in the xth layer to the electrode material in the layer; d 11 represents the particle size of the first particles of the first pole piece layer, d x1 represents the particle size of the first particles of the pole piece layer of the xth layer, d x2 represents the particle size of the second particle in the xth layer, and d 11 d x1 and d x2 The unit is μm; The porosity of each pole piece layer gradually increases along the direction from the nth layer to the first layer.

2. The electrode according to claim 1, characterized in that The number of the first particles included in the pole piece layer of the xth layer in the electrode material of this layer accounts for: [-x / (2n-2)+(2n-1) / (2n-2)]; wherein x is a natural number less than or equal to n.

3. The electrode according to claim 1, characterized in that The average particle size of the first particles is in the range of 0.90 to 1.60 μm, and the average particle size of the second particles is in the range of 0.25 to 0.70 μm.

4. The electrode according to claim 3, characterized in that The average particle size of the first particles is in the range of 1.0 to 1.2 μm, and the average particle size of the second particles is in the range of 0.35 to 0.55 μm.

5. The electrode according to claim 1, characterized in that The radius of the first particle is R, and the radius of the second particle is less than or equal to 0.414R.

6. The electrode according to claim 5, characterized in that Each of the pole piece layers from the 2nd to the nth layer further includes third particles, and the radius of the third particles is less than or equal to 0.225R.

7. The electrode according to claim 1, characterized in that The number of the pole sheet layers ranges from 2 to 10, and the number of the second particles included in the electrode material of each pole sheet layer except the first layer gradually decreases along the direction from the side close to the current collector to the side close to the separator.

8. The electrode according to claim 1, characterized in that The electrode material comprises a positive electrode material, and the positive electrode material is at least one of lithium iron phosphate, lithium nickel cobalt manganese oxide and lithium manganate.

9. The electrode according to claim 1, characterized in that The electrode material includes a negative electrode material, and the negative electrode material is at least one of artificial graphite, natural graphite, lithium titanate, soft carbon and hard carbon.

10. A method for preparing an electrode, applied to the electrode according to any one of claims 1 to 9, characterized in that: The following steps are involved: Fully mixing the electrode material with the conductive agent and the binder to form a mixture; heating the mixture to make the binder molten; Solidifying the molten binder, and wrapping the electrode material with the solidified binder to obtain a powdery substance; Processing the powdered material to form the pole piece layer; According to the above method, by adjusting the amount of the first particles and the second particles in each layer of the pole piece layer, multiple layers of the pole piece layer with different porosities are prepared; According to the size of the porosity, multiple electrode sheets are stacked and fused in sequence to obtain the electrode.

11. The method for preparing an electrode according to claim 10, characterized in that: Solidifying the binder in a molten state includes solidifying the binder into a fiber state through an electrostatic spinning process.

12. The method for preparing an electrode according to claim 10, characterized in that: The process of sequentially stacking and fusing the plurality of pole pieces includes: a hot pressing process.

13. A battery, characterized in that: The electrode comprises the electrode described in any one of claims 1 to 9.

14. The battery according to claim 13, characterized in that The battery comprises: a first current collector, a first electrode, a separator, a second electrode and a second current collector which are arranged in sequence, and an electrolyte is arranged between the first electrode and the second electrode and the separator respectively.

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