Battery cell, battery, and electric device

Abstract

The present application relates to the technical field of lithium batteries. Provided are a battery cell, a battery, and an electric device. A negative electrode active material in a negative electrode sheet of the battery cell comprises silicon; and a positive electrode sheet comprises a positive electrode current collector, and a first positive electrode active layer and a second positive electrode active layer that are sequentially stacked on a surface of the positive electrode current collector, wherein a first positive electrode active material of the first positive electrode active layer comprises a first polycrystalline material, and a second positive electrode active material of the second positive electrode active layer comprises a second polycrystalline material and a second single-crystal material. The battery cell satisfies: W1 being greater than W2, wherein W1 is the content by mass of the first polycrystalline material based on the mass of the first positive electrode active material, and W2 is the content by mass of the second polycrystalline material based on the mass of the second positive electrode active material. The battery cell, the battery, and the electric device in the embodiments of the present application can mitigate the problem of cracking of positive electrode active materials, thereby improving the cycle life of cells while balancing the energy density.

Description

A battery cell, a battery, and an electrical device.

[0001] Cross-referencing

[0002] This application claims priority to Chinese Patent Application No. 202510355702.X, filed on March 25, 2025, entitled “A Battery Cell, Battery and Electrical Device”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] Silicon-carbon anode batteries have a large volume expansion of the silicon-carbon anode, which can squeeze the active material in the positive electrode, easily causing the active material to crack and severely deteriorating the cycle life of the cell.

[0004] To address these issues, the traditional approach is to reduce the compaction density of the positive electrode to alleviate the compression between active material particles. However, this approach degrades the energy density of the battery cell. Summary of the Invention

[0005] This application is made in view of the above-mentioned problems, and its purpose is to provide a battery cell, a battery and an electrical device that can improve the cracking problem of the positive electrode active material, improve the cycle life of the cell, and take into account the energy density.

[0006] To achieve the above objectives, a first aspect of this application provides a battery cell, including a positive electrode sheet and a negative electrode sheet. The negative electrode sheet includes a negative electrode active material, which is a silicon-based material and includes silicon element. The positive electrode sheet includes a positive electrode current collector and a positive electrode active layer. The positive electrode active layer includes a first positive electrode active layer and a second positive electrode active layer sequentially stacked on the surface of the positive electrode current collector. The first positive electrode active layer includes a first positive electrode active material, and the second positive electrode active layer includes a second positive electrode active material. The first positive electrode active material includes a first polycrystalline material, and the second positive electrode active material includes a second polycrystalline material and a second monocrystalline material.

[0007] A single battery cell satisfies the following condition: W1 is greater than W2.

[0008] Wherein, W1 is the mass content of the first polycrystalline material, based on the mass of the first positive electrode active material; W2 is the mass content of the second polycrystalline material, based on the mass of the second positive electrode active material.

[0009] Therefore, this application uses silicon as the negative electrode to improve the energy density of the battery. At the same time, the positive electrode adopts a LOM design, and the mass ratio of polycrystalline material in the second positive active layer near the surface of the positive electrode is lower than that in the first positive active layer near the positive current collector. That is, with the same amount of polycrystalline material, the surface of the positive electrode contains less polycrystalline material, which can improve the cracking problem of polycrystalline material on the surface of the positive electrode, improve the cycle life of the cell, and take into account the energy density.

[0010] In any embodiment, the negative electrode sheet includes a negative current collector and a negative electrode active layer. Based on the mass of the negative electrode active layer, the mass content of silicon element is 0.5% to 20%, optionally 3% to 10%; and W2 is 10% to 80%, optionally 30% to 60%. By including a certain amount of silicon element in the negative electrode sheet, the energy density of the battery is improved. At the same time, by combining polycrystalline materials and monocrystalline materials in the second positive electrode active layer in a specific ratio, the second positive electrode active layer can achieve both high kinetics and less polycrystalline material cracking.

[0011] In any embodiment, the first positive electrode active material further includes a first single-crystal material. The second positive electrode active layer contains both polycrystalline and single-crystal materials, which not only reduces the damage to the current collector caused by polycrystalline materials with large particle sizes, but also reduces the difference in lithium-ion transport capacity between the two layers by reducing the damage to the material caused by local overcharging or over-discharging, thereby improving the performance of the battery.

[0012] In any embodiment, W1 is 50% to 100%, and can be selected as 60% to 80%. By combining the monocrystalline material and / or polycrystalline material in the first positive electrode active layer in a specific ratio, the cracking problem of polycrystalline material can be mitigated, and the damage of polycrystalline particles to the positive electrode current collector can be improved.

[0013] In any embodiment, the positive electrode active material includes a first positive electrode active material and a second positive electrode active material. Based on the total mass of the positive electrode active material, the total mass content of the first polycrystalline material and the second polycrystalline material is 70% to 90%, and / or, based on the total mass of the positive electrode active material, the total mass content of the first single-crystal material and the second single-crystal material is 10% to 30%. Using a certain proportion of single-crystal material and a certain proportion of polycrystalline material in combination can combine the advantages of both, enabling the positive electrode active layer to simultaneously possess high energy density and stability.

[0014] In any embodiment, based on the mass meter of the positive electrode active material, the mass content of the first polycrystalline material is denoted as W3, and the mass content of the second polycrystalline material is denoted as W4, where W4 is less than W3. By placing more mass of polycrystalline material in the first positive electrode active layer near the positive electrode current collector, and the second positive electrode active layer near the surface of the positive electrode sheet containing less mass of polycrystalline material, the cracking problem of the polycrystalline material on the surface of the positive electrode sheet can be further improved.

[0015] In any implementation, W4 is 5% to 40%.

[0016] In any implementation, W3 is 30% to 65%.

[0017] In any embodiment, the Dv50 of the first polycrystalline material and the Dv50 of the second polycrystalline material are each independently 8μm to 10μm.

[0018] In any embodiment, the Dv50 of the first single crystal material and the Dv50 of the second single crystal material are each independently 3μm to 5μm.

[0019] In any embodiment, the first positive electrode active layer includes a first conductive agent, and the second positive electrode active layer includes a second conductive agent.

[0020] The battery cell must meet the following condition: W5 is less than W6.

[0021] Wherein, W5 represents the mass content of the first conductive agent, based on the mass of the first positive electrode active layer, and W6 represents the mass content of the second conductive agent, based on the mass of the second positive electrode active layer.

[0022] And / or, the conductivity of the second conductive agent is greater than that of the first conductive agent. By increasing the content of the conductive agent in the second positive electrode active layer relative to the first positive electrode active layer and / or using a conductive agent with better conductivity, the stability of the conductive network after cracking of the polycrystalline material on the surface of the positive electrode sheet can be improved.

[0023] In any implementation, W6 is 1.0% to 2.0%, and / or W5 is 0.5% to 1.0%.

[0024] In any embodiment, the second conductive agent includes a linear conductive agent or a layered conductive agent, and may be selected from one or more of carbon nanotubes, graphene, metal nanotubes, and carbon fibers, and / or...

[0025] The first conductive agent includes a dot-like conductive agent, which may be one or more of carbon black, acetylene black, and graphite.

[0026] In any embodiment, when the battery cell is 100% charged, the compaction density of the positive electrode active layer is 3.3~3.7 g / cm³. 3 .

[0027] In any embodiment, the areal density of a single side of the positive electrode active layer is 245~280 mg / 1540.25 mm. 2 Available in 245~260mg / 1540.25mm. 2 Based on the above-mentioned arrangement of polycrystalline materials, by controlling the areal density of the cathode, the lithium-ion transport path distance of the cathode can be improved, thereby enhancing cell dynamics.

[0028] The first single-crystal material and the second single-crystal material each independently include the formula Li a1 Ni b1 Co c1 M1 d1 O e1 A1 f1 ;

[0029] The first polycrystalline material and the second polycrystalline material each independently include the formula Li a2 Ni b2 Co c2 M2 d2 O e2 A2 f2 ;

[0030] Wherein, 0 < a1 ≤ 1.2, 0.5 ≤ b1 < 1; 0 < c1 < 1; 0 < d1 < 1; 1 ≤ e1 ≤ 2; 0 ≤ f1 ≤ 1, M1 includes but is not limited to one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and A1 includes but is not limited to one or more of N, F, S and Cl;

[0031] 0 < a2 ≤ 1.2, 0.5 ≤ b2 < 1; 0 < c2 < 1; 0 < d2 < 1; 1 ≤ e2 ≤ 2; 0 ≤ f2 ≤ 1, M2 includes but is not limited to one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and A2 includes but is not limited to one or more of N, F, S and Cl.

[0032] In any embodiment, the first positive electrode active layer includes a first binder, and the mass content of the first binder is 0.8% to 1.0%, optionally 1.0% to 1.5%, based on the mass of the first positive electrode active layer. By increasing the binder content of the first positive electrode active layer to encapsulate large-diameter polycrystalline material particles, the uneven damage to the current collector caused by the polycrystalline material in the first positive electrode active layer can be improved.

[0033] In any embodiment, the battery cell is a cylindrical cell. The cylindrical cell system improves the energy density of the battery, while the aforementioned LOM design for the positive electrode improves the cracking problem of the polycrystalline material on the surface of the positive electrode, increases the cycle life of the cell, and balances energy density.

[0034] A second aspect of this application also provides a battery, including the battery cell of the first aspect.

[0035] A third aspect of this application also provides an electrical device, including the battery of the first aspect, the battery being used to provide electrical energy. Attached Figure Description

[0036] Figure 1 is a schematic diagram of a battery cell according to one embodiment of this application.

[0037] Figure 2 is an exploded view of a battery cell according to an embodiment of this application shown in Figure 1.

[0038] Figure 3 is a schematic diagram of a battery module according to one embodiment of this application.

[0039] Figure 4 is a schematic diagram of a battery pack according to one embodiment of this application.

[0040] Figure 5 is an exploded view of the battery pack of one embodiment of this application shown in Figure 4.

[0041] Figure 6 is a schematic diagram of an electrical device in which a single battery cell is used as a power source according to an embodiment of this application.

[0042] Explanation of reference numerals in the attached figures:

[0043] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Battery cell; 51 Housing; 52 Electrode assembly; 53 Top cover assembly. Embodiments of the present invention

[0044] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the battery cell, battery, and power-consuming device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0045] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for a specific parameter, it is also expected that ranges of 60~110 and 80~120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this application, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0046] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0047] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0048] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0049] Polycrystalline materials offer advantages such as short lithium-ion transport distance, good kinetics, and high powder pressure; however, they are prone to breakage under stress and have poor cycle stability. Monocrystalline materials, on the other hand, are less prone to cracking and have high cycle stability, but suffer from long internal lithium-ion diffusion paths and poor kinetics. Generally, to balance cycle performance and energy density, positive electrode active materials often incorporate both polycrystalline and monocrystalline materials. Furthermore, with increasing market demand for energy density, silicon is being considered for the introduction of silicon into the negative electrode active layer. However, the volume expansion caused by silicon further complicates the battery system environment. Considering the respective advantages and disadvantages of monocrystalline and polycrystalline materials, effectively utilizing both materials in complex silicon-containing battery systems to achieve a battery with high energy density and high cycle performance is a crucial technical problem that needs to be solved by those skilled in the art.

[0050] Based on this, the first aspect of the present application provides a battery cell including a positive electrode sheet and a negative electrode sheet. The negative electrode sheet includes a negative electrode active material, which includes a silicon-based material and silicon element. The positive electrode sheet includes a positive electrode current collector and a positive electrode active layer. The positive electrode active layer includes a first positive electrode active layer and a second positive electrode active layer sequentially stacked on the surface of the positive electrode current collector. The first positive electrode active layer includes a first positive electrode active material, and the second positive electrode active layer includes a second positive electrode active material. The first positive electrode active material includes a first polycrystalline material, and the second positive electrode active material includes a second polycrystalline material and a second monocrystalline material.

[0051] A single battery cell satisfies the following condition: W1 is greater than W2.

[0052] Wherein, W1 is the mass content of the first polycrystalline material, based on the mass of the first positive electrode active material; W2 is the mass content of the second polycrystalline material, based on the mass of the second positive electrode active material.

[0053] In this application, polycrystalline materials are mostly particles formed by the aggregation of a large number of micro- and nano-sized single particles, while single-crystal materials refer to single particles that have no aggregation or almost no aggregation.

[0054] In embodiments of this application, the silicon-based material may include at least one of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy. Here, elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy can refer to either silicon-based materials or the form in which silicon exists in the negative electrode of the battery after formation. The silicon oxide SiOx, where 0 < x ≤ 2, is used because the bonding mode between silicon atoms and oxygen atoms in the negative electrode film is diverse, and can be SiO, SiO2, etc. 1.2At least one of SiO2 or other possible silicon oxides. Here, silicon-carbon composite can refer to the form in which silicon exists in the negative electrode of a battery after formation. Silicon-carbon composite can also be a silicon-carbon composite formed by certain chemical reactions between silicon and carbon within a single battery cell. It can also be formed by a physical mixture of elemental silicon and elemental carbon, for example, where elemental carbon includes a porous framework, and elemental silicon is located in the pores of the porous framework or on its surface. Silicon-carbon composite can also be formed by coating a carbon layer onto the surface of elemental silicon.

[0055] The mass ratio of monocrystalline and polycrystalline materials in a certain area within the positive electrode active layer can be detected using equipment and methods known in the art. An example is as follows: For the powder scraped from the layer away from the current collector, the powder is thoroughly washed with acetone to remove binders and dispersants, then filtered and dried to obtain powder (i.e., the second positive electrode active material). 0.05g of the uniformly mixed powder is dissolved in 40ml of anhydrous ethanol, and then an appropriate amount of dispersant is added and stirred until a suspension is obtained. 2ml of the suspension is mixed with 2ml of anhydrous ethanol and then subjected to ultrasonic treatment at a power of 480W for 5 minutes, resulting in a uniformly dispersed suspension. An appropriate amount of the middle layer suspension is then subjected to transmission electron microscopy (TEM). Spherical particles are defined as polycrystalline materials, while other non-spherical irregular particles are defined as monocrystalline materials. Referring to the above definitions, the projection area S of the polycrystalline and monocrystalline materials in the TEM image is calculated, and the equivalent circle diameter R of the polycrystalline or monocrystalline material is obtained using the equivalent circle method. Multiple transmission electron microscopy (TEM) tests were performed within the same test area in different regions to obtain the average equivalent circle diameters of the polycrystalline and single-crystal materials, denoted as R1 and R2. The quantities of polycrystalline and single-crystal materials within the test area were also counted, denoted as N1 and N2. Therefore, the mass content W2 of the second polycrystalline material in the second positive electrode active material is (N1*R1). 3 ) / (N1*R1³+N2*R2 3 (Assuming that polycrystalline and monocrystalline materials have the same density). Similarly, for the powder scraped near the current collector layer (first positive electrode active layer), the mass content W1 of the first polycrystalline material in the first positive electrode active material can be calculated.

[0056] This application introduces silicon into the negative electrode active material and includes both polycrystalline and monocrystalline materials in the positive electrode active material, which is beneficial for obtaining batteries with high energy density and good cycle performance. However, silicon in the negative electrode active material expands significantly during cycling, which can compress the positive electrode sheet and easily cause cracking of the material particles on the surface of the positive electrode sheet, affecting the cycle performance of the battery. Furthermore, the closer to the negative electrode sheet, the greater the stress on the positive electrode particles, leading to more severe damage. As mentioned earlier, compared to monocrystalline materials, polycrystalline materials are more prone to damage under stress, resulting in a more severe deterioration of the battery's cycle performance. Therefore, this application employs a double-layer design for the positive electrode sheet, where the mass content W2 of the polycrystalline material in the second positive electrode active layer (upper layer) closer to the negative electrode sheet is less than the mass content W1 of the polycrystalline material in the first positive electrode active layer (lower layer) closer to the positive current collector. In other words, the mass concentration of polycrystalline material in the upper layer is low, while the mass concentration in the lower layer is high. Placing more easily damaged polycrystalline materials in the lower layer, away from the negative electrode, can improve the cracking problem of polycrystalline materials on the surface of the positive electrode, reduce material loss caused by cracking, and alleviate the side reactions between the cracked polycrystalline material particles and the electrolyte, effectively improving the cycle life of the battery cell.

[0057] Compared to the direct physical mixing of single-crystal and polycrystalline materials in a single-layer structure, this application distributes more of the easily damaged polycrystalline material in the lower layer structure away from the negative electrode sheet. This can reduce the stress caused by silicon elements in the negative electrode sheet on the polycrystalline particles of the positive electrode sheet, improve the cracking problem of polycrystalline material on the surface of the positive electrode sheet, reduce material loss caused by cracking, and improve cycle performance.

[0058] Compared to a second positive electrode active layer composed entirely of single-crystal particles, the second positive electrode active layer of this application, located away from the current collector, contains both single-crystal and polycrystalline materials. On one hand, the presence of both single-crystal and polycrystalline materials in the second positive electrode active layer, through the combination of large-diameter polycrystalline particles and small-diameter single-crystal materials, achieves a certain gradation, which can improve the compaction density of the positive electrode active layer and increase the energy density of the battery. On the other hand, if the second positive electrode active layer near the electrolyte is entirely composed of single-crystal materials, the lithium-ion diffusion path of single-crystal materials is relatively long, resulting in poor kinetic performance of the positive electrode active layer and affecting the cycle performance and specific capacity of the battery. In contrast, the second positive electrode active layer of this application, located near the electrolyte, contains a small amount of polycrystalline material, which can improve the kinetic performance of the second positive electrode active layer near the electrolyte and enhance the cycle performance and energy density of the battery.

[0059] Compared to the case where the mass content of the first polycrystalline material in the first positive electrode active layer is less than the mass content of the second polycrystalline material in the second positive electrode active layer (i.e., W1 is less than W2), the technical solution of this application can reduce the stress caused by silicon elements in the negative electrode sheet on the polycrystalline particles of the positive electrode sheet, improve the cracking problem of polycrystalline material on the surface of the positive electrode sheet, reduce material loss caused by cracking, and improve cycle performance.

[0060] In some implementations, the first positive electrode active material does not include single-crystal materials.

[0061] In some embodiments, the negative electrode includes a negative current collector and a negative active layer. Based on the mass of the negative active layer, the mass content of silicon element is 0.5% to 20%, optionally 3% to 10%; and W2 is 10% to 80%, optionally 30% to 60%.

[0062] In some embodiments, based on the mass of the negative electrode active material, the mass percentage of silicon can be selected as 0.5%, 1%, 2%, 3%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, 20%, or the midpoint of any two of the above values.

[0063] The mass content of silicon in the negative electrode film is a well-known concept in the art and can be detected using well-known equipment and methods. For example, the negative electrode sheet can be immersed in a solvent such as water to separate the negative electrode active material from the negative electrode current collector. The various substances in the negative electrode film can be obtained by filtration and used as a test sample. The silicon content can be obtained by using an ICAP7400 inductively coupled plasma atomic emission spectrometer from Thermo Fisher Scientific, USA, in accordance with the GB / T30902-2014 standard.

[0064] Because a higher silicon content in the negative electrode leads to greater expansion of the negative electrode system, it is more prone to causing extrusion cracking of the polycrystalline material on the positive electrode surface. Therefore, the silicon content in the negative electrode is negatively correlated with the proportion of polycrystalline material in the second active material layer (upper layer) of the positive electrode. Moreover, since polycrystalline materials have stronger lithium-ion transport capabilities than single-crystal materials, when the positive electrode adopts a LOM design and the mass concentration of polycrystalline material in the upper second positive electrode active layer is reduced, the proportion of polycrystalline material decreases and the proportion of single-crystal material increases. This relatively weakens the lithium-ion transport capability of the upper layer, limiting the overall lithium-ion transport capability of the positive electrode. To balance the kinetics of the negative electrode and the upper layer of the positive electrode with the degree of polycrystalline material cracking, this application embodiment controls the silicon content in the negative electrode and the proportion of single-crystal and polycrystalline materials in the upper layer of the positive electrode.

[0065] In some embodiments, the first positive electrode active material further includes a first single crystal material.

[0066] In some implementations, W1 is 50% to 100%, and can be 60% to 80%. For example, W1 is 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 100%, or an intermediate value within any two of the above ranges.

[0067] When the positive electrode adopts a LOM (Lead-of-Mortar) design and the mass concentration of polycrystalline material in the lower first positive electrode active layer is increased, the proportion of polycrystalline material in the lower layer increases while the proportion of monocrystalline material decreases. If the gaps between polycrystalline material particles are not fully filled by monocrystalline material, the compaction density of the lower layer will deteriorate, and the uneven compression of the polycrystalline material particles on the positive current collector (substrate) will worsen, leading to substrate damage and exacerbating the brittleness of the positive electrode. Therefore, the embodiments of this application control the proportion of polycrystalline material in the lower first positive electrode active layer, which can effectively improve the damage to the substrate caused by polycrystalline material particles.

[0068] In some embodiments, the positive electrode active material includes a first positive electrode active material and a second positive electrode active material. Based on the total mass of the positive electrode active material, the total mass content of the first polycrystalline material and the second polycrystalline material is 70% to 90%, and / or, based on the total mass of the positive electrode active material, the total mass content of the first single-crystal material and the second single-crystal material is 10% to 30%. Exemplarily, based on the total mass of the positive electrode active material, the total mass content of the first polycrystalline material and the second polycrystalline material is 70%, 75%, 80%, 85%, 90%, or an intermediate value within any two of the above values. Exemplarily, based on the total mass of the positive electrode active material, the total mass content of the first single-crystal material and the second single-crystal material is 10%, 15%, 20%, 25%, 30%, or an intermediate value within any two of the above values.

[0069] In some implementations, based on the mass meter of the positive electrode active material, the mass content of the first polycrystalline material is denoted as W3, the mass content of the second polycrystalline material is denoted as W4, and W4 is less than W3.

[0070] In some implementations, W4 is 5% to 40%. For example, W4 is 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, or an intermediate value within a range of any two of the above values.

[0071] In some implementations, W3 is 30% to 65%. For example, W3 is 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, or an intermediate value within a range of any two of the above values.

[0072] In this embodiment, by reducing the mass concentration of polycrystalline material in the second positive electrode active layer, more mass of polycrystalline material is placed in the first positive electrode active layer, thereby further improving the cracking problem of polycrystalline material on the surface of the positive electrode sheet.

[0073] In some embodiments, the mass ratio of the second single-crystal material in the second positive electrode active layer relative to the total amount of positive electrode active material is greater than the mass ratio of the first single-crystal material in the first positive electrode active layer relative to the total amount of positive electrode active material. By placing more mass of single-crystal material in the second positive electrode active layer closer to the surface of the positive electrode sheet, the overall stability of the positive electrode material can be improved.

[0074] In some embodiments, the Dv50 of the first polycrystalline material and the Dv50 of the second polycrystalline material are each independently 8 μm to 10 μm. For example, the Dv50 of the polycrystalline material is 8 μm, 8.3 μm, 8.5 μm, 9 μm, 9.2 μm, 9.5 μm, 9.8 μm, 10 μm, or an intermediate value within any range of two of the above values.

[0075] In some embodiments, the Dv50 of the first single crystal material and the Dv50 of the second single crystal material are each independently 3μm to 5μm. For example, the Dv50 of the single crystal material is 3μm, 3.3μm, 3.5μm, 3.7μm, 4μm, 4.2μm, 4.5μm, 4.8μm, 5μm, or an intermediate value within any range of two of the above values.

[0076] In some embodiments, the first positive electrode active layer includes a first conductive agent, and the second positive electrode active layer includes a second conductive agent.

[0077] The battery cell must meet the following condition: W5 is less than W6.

[0078] Wherein, W5 represents the mass content of the first conductive agent, based on the mass of the first positive electrode active layer, and W6 represents the mass content of the second conductive agent, based on the mass of the second positive electrode active layer.

[0079] And / or, the conductivity of the second conductive agent is greater than that of the first conductive agent.

[0080] In some implementations, W6 is 1.0% to 2.0%, and / or W5 is 0.5% to 1.0%. For example, W6 is 1.0%, 1.2%, 1.5%, 1.7%, 2.0%, or an intermediate value within the range of any two of the above values; W5 is 0.5%, 0.6%, 0.7%, 0.8%, 1.0%, or an intermediate value within the range of any two of the above values.

[0081] In some embodiments, the second conductive agent includes a linear conductive agent or a layered conductive agent, and may be one or more of carbon nanotubes, graphene, metal nanotubes, and carbon fibers, and / or...

[0082] The first conductive agent includes a dot-like conductive agent, which may be one or more of carbon black, acetylene black, and graphite.

[0083] In this embodiment, by increasing the content of conductive agent in the second positive electrode active layer or by using a conductive agent with higher conductivity in the second positive electrode active layer, the stability of the conductive network after the polycrystalline particles crack can be improved, the impact of material cracking on capacity performance can be reduced, and the capacity performance of the positive electrode can be maintained. The proportion of polycrystalline material in the second positive electrode active layer is reduced, and the conductivity is worse. By increasing the amount of conductive agent and / or using a conductive agent with higher conductivity, the conductivity can be increased, the uniformity of conductivity between the upper and lower layers can be improved, and the conductivity difference can be reduced.

[0084] In some embodiments, the compaction density of the positive electrode active layer of a single battery cell at 100% charge is 3.3~3.7 g / cm³. 3 For example, the compaction density of the positive electrode active layer is 3.3 g / cm³. 3 3.4g / cm 3 3.5g / cm 3 3.6g / cm 3 3.7g / cm 3 Or the midpoint of the range formed by any two of the above values.

[0085] Compacted density can be tested using equipment and methods known in the art, for example, by disassembling and drying the positive electrode sheet and cutting it into pieces with an area of ​​1540.25 mm². 2 A circular electrode of a certain size is used. The active material is loaded on one side of the electrode (if there are two sides, one side is wiped off with alcohol). The thickness H1 is measured. Then, the active layer is completely wiped off, leaving only the current collector, and its thickness H2 is measured. The thickness of the positive electrode active layer is then H = H1 - H2 (mm). The compaction density of the positive electrode active layer is PD = CW / (H * 1540.25) (g / cm³). 3 .

[0086] In some embodiments, the areal density of a single side of the positive electrode active layer is 245~280 mg / 1540.25 mm. 2 Available in 245~260mg / 1540.25mm. 2 For example, the areal density of a single side of the positive electrode active layer is 245 mg / 1540.25 mm². 2 250mg / 1540.25mm 2 255mg / 1540.25mm 2260mg / 1540.25mm 2 270mg / 1540.25mm 2 280mg / 1540.25mm 2 Or the midpoint of the range formed by any two of the above values.

[0087] Areal density can be measured using equipment and methods known in the art, for example: after disassembling a cylindrical battery and drying the positive electrode, the electrode is cut into pieces with an area of ​​1540.25 mm². 2 The electrode is circular in size; retain one side of the electrode with active material loaded (if it is double-sided, wipe one side off with alcohol), weigh it and record the weight as W1. Then completely wipe off the active layer, leaving only the current collector, weigh it and record the weight as W2. Then the positive electrode CW = W1 - W2, unit mg / 1540.25mm². 2 .

[0088] Polycrystalline materials have stronger lithium-ion transport capabilities than monocrystalline materials. When the positive electrode adopts a LOM (Lead-of-Mile) design and the amount of polycrystalline material in the second positive electrode active layer is reduced, the lithium-ion transport capability of the upper layer will be relatively weakened, the kinetics of the upper layer will decrease, and the overall lithium-ion transport capability of the positive electrode will be limited. The embodiments of this application improve the lithium-ion transport path distance of the positive electrode by reducing the areal density of the positive electrode active layer, thereby enhancing the cell kinetics.

[0089] In some embodiments, the first single crystal material and the second single crystal material each independently include the formula Li a1 Ni b1 Co c1 M1 d1 O e1 A1 f1 ;

[0090] The first polycrystalline material and the second polycrystalline material each independently include the formula Li a2 Ni b2 Co c2 M2 d2 O e2 A2 f2 ;

[0091] Wherein, 0 < a1 ≤ 1.2, 0.5 ≤ b1 < 1; 0 < c1 < 1; 0 < d1 < 1; 1 ≤ e1 ≤ 2; 0 ≤ f1 ≤ 1, M1 includes but is not limited to one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and A1 includes but is not limited to one or more of N, F, S and Cl;

[0092] 0 < a2 ≤ 1.2, 0.5 ≤ b2 < 1; 0 < c2 < 1; 0 < d2 < 1; 1 ≤ e2 ≤ 2; 0 ≤ f2 ≤ 1, M2 includes but is not limited to one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and A2 includes but is not limited to one or more of N, F, S and Cl.

[0093] In some embodiments, the second positive electrode active material (second single-crystal material / or second polycrystalline material) of the second positive electrode active layer includes a ternary material NCM. Besides main elements such as Ni, Co, and Mn, the ternary material NCM also contains other doping elements. The mass percentage of Ni in the ternary material NCM relative to Ni, Co, and Mn is 50%~60%, and the mass percentage of Co in the ternary material relative to Ni, Co, and Mn is 4.5%~6.5%, optionally 6.5%~8.5%. By using a high-nickel ternary material in the second positive electrode active layer, the energy density is improved. Simultaneously increasing the Co content in the ternary material of the second positive electrode active layer can improve the rate performance of the material and enhance cell dynamics. In some embodiments, part or all of the second single-crystal material or the second polycrystalline material in the second positive electrode active material can be replaced with the aforementioned ternary material, or part or all of the second single-crystal material and the second polycrystalline material can be replaced with the aforementioned ternary material simultaneously.

[0094] When the positive electrode adopts a LOM design and the amount of polycrystalline material in the upper second positive electrode active layer is reduced, the kinetics of the upper layer decrease. In this application, by increasing the Co content in the ternary material NCM, the rate performance of the material can be improved, thus enhancing the cell kinetics.

[0095] In some embodiments, the first positive electrode active layer includes a binder. The first positive electrode active layer includes a first binder, and the mass content of the first binder, based on the mass of the first positive electrode active layer, is 0.8% to 1.0%, optionally 1.0% to 1.5%. For example, based on the mass of the first positive electrode active layer, the mass content of the first binder is 0.8%, 1.0%, 1.2%, 1.4%, 1.5%, or an intermediate value within any two of the above ranges.

[0096] When the positive electrode adopts a LOM (Lead-of-Mouth) design and the amount of polycrystalline material in the lower first positive electrode active layer is increased, the proportion of polycrystalline material in the lower layer increases while the proportion of monocrystalline material decreases. If the gaps between polycrystalline material particles are not fully filled by monocrystalline material, the compaction density of the lower layer will deteriorate, and the uneven compression of the positive electrode current collector (substrate) by the polycrystalline material particles will worsen, causing substrate damage and exacerbating the brittleness of the positive electrode. Therefore, this embodiment improves the brittleness of the electrode by increasing the binder content in the first positive electrode active layer to mitigate the uneven damage to the substrate caused by the lower layer. In other embodiments, a positive electrode undercoat layer can also be used to alleviate the degree of damage to the substrate caused by polycrystalline material particles.

[0097] In some embodiments, the battery cell is a cylindrical battery. For example, the cylindrical structure is a 4680 series cylinder with a diameter of 46 mm and a height of 70-110 mm.

[0098] Cylindrical batteries have advantages such as simple manufacturing process and low cost. However, cylindrical batteries experience greater internal stress during cycling, and the positive electrode sheet is subjected to greater stress, resulting in more severe material damage and limiting their use.

[0099] The positive electrode of this application has a double-layer structure, and the polycrystalline material near the negative electrode is relatively small, which can effectively reduce the stress damage to the material in the cylindrical battery, improve the cycle performance of the battery, and provide more possibilities for the widespread application of cylindrical batteries.

[0100] In one embodiment, the negative electrode sheet includes a negative current collector and a negative active layer, wherein the areal density (CW) of the negative active layer can be selected as 110~180 mg / 1540.25 mm². 2 .

[0101] Areal density can be detected using equipment and methods known in the art, such as the test methods listed above.

[0102] A second aspect of this application also provides a battery, including the battery cell of the foregoing embodiments.

[0103] A third aspect of this application also provides an electrical device, including the battery of the foregoing embodiment, the battery being used to provide electrical energy.

[0104] In addition, the battery cell and power device of this application will be described below with appropriate reference to the accompanying drawings.

[0105] [Battery cell]

[0106] This application does not impose any particular restrictions on the type of battery cell; for example, the battery cell can be a lithium-ion battery, etc.

[0107] Typically, a battery cell includes a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0108] This application does not impose any particular restrictions on the type of electrolyte, which can be selected according to actual needs. For example, the electrolyte can be selected from at least one of solid electrolytes and liquid electrolytes (i.e., electrolyte solutions). This applies to battery cells using electrolyte solutions, as well as some battery cells using solid electrolytes.

[0109] [Positive electrode plate]

[0110] The positive electrode used in the battery cell is the same as the positive electrode of the first aspect of this application. Therefore, the battery cell of this application has excellent cycle life while also maintaining good energy density.

[0111] The positive electrode sheet, also known as the cathode electrode sheet, includes a positive current collector and a positive active layer disposed on at least one surface of the positive current collector. The positive active layer includes a positive active material.

[0112] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0113] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0114] In some embodiments, when the battery cell is a lithium-ion battery, the positive electrode active material may be a positive electrode active material known in the art for lithium-ion batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.8 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0115] In some embodiments, to further improve the energy density of a single battery cell, the positive electrode active material for a lithium-ion battery may include materials with the general formula Li. a Ni b Co c M d O e A fone or more of lithium transition metal oxides and modified compounds thereof. 0.8≤a≤1.2, 0.5≤b<1, 0<c<1, 0<d<1, 1≤e≤2, 0≤f≤1, M is selected from one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and A is selected from one or more of N, F, S and Cl.

[0116] In some embodiments, by way of example, the positive electrode active material for a lithium-ion battery may include LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), LiNi 0.85 Co 0.15 Al 0.05 one or more of O2, LiFePO4 and LiMnPO4.

[0117] In some embodiments, the modified compound of each of the above positive electrode active materials may be doping modification and / or surface coating modification performed on the positive electrode active material.

[0118] As an optional technical solution of the present application, the polyanionic compound may be Li 1+x Mn 1-y A y P 1-z R z O4; wherein x is any value within the range of -0.100 to 0.100, y is any value within the range of 0.001 to 0.500, z is any value within the range of 0.001 to 0.100, A comprises one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and R comprises one or more elements selected from B, S, Si and N;

[0119] As an optional technical solution of the present application, the polyanionic compound may be Li a A e Mn 1-f B f P 1-g Cg O 4-n D n , wherein A comprises one or more elements selected from the group consisting of Zn, Al, Na, K, Mg, Nb, Mo and W; B comprises one or more elements selected from the group consisting of Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge; C comprises one or more elements selected from the group consisting of B, S, Si and N; D comprises one or more elements selected from the group consisting of S, F, Cl and Br; a is selected from the range of 0.9 to 1.1, e is selected from the range of 0.001 to 0.1, f is selected from the range of 0.001 to 0.5, g is selected from the range of 0.001 to 0.1, n is selected from the range of 0.001 to 0.1, and the second positive electrode active material is electrically neutral.

[0120] During charging and discharging of the battery, the deintercalation and consumption of Li will be accompanied, and the molar content of Li is different when the battery is discharged to different states. In the enumeration of the positive electrode material in the present application, the molar content of Li refers to the initial state of the material, that is, the state before feeding; after the positive electrode material is applied to a battery system and subjected to charge-discharge cycles, the molar content of Li will change.

[0121] In the enumeration of the positive electrode material in the present application, the molar content of O is only a theoretical state value. Lattice oxygen release will cause the molar content of oxygen to change, and the actual molar content of O will fluctuate.

[0122] As an optional technical solution of the present application, the polyanionic compound can be Na 4+x R 3-y P 4-m O 15 / C; wherein 0<x<0.5, 0<y≤0.5, 0<m≤0.2, and R comprises at least one selected from the group consisting of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Cr, Nb, Mo, In, Ga, Sn, Hf, Ta, W and Pb.

[0123] As an optional technical solution of the present application, the polyanionic compound can be Na x-a A a V y-b M b (PO4) 2-2c (DO4) 2c F z-d Q dWherein, element A represents an alkali metal element that substitutes for element Na, element M represents a metal element that substitutes for element V, element D represents a dopant element that substitutes for element P, and element Q represents a dopant element that substitutes for element F. Element D includes at least one of Si and S, and element Q includes at least one of Cl and O; 3.5≤x≤4.5, 0≤a≤0.15x, 0.8≤y≤1.1, 0≤b≤0.3y, 0≤c≤0.15, 0.8≤z≤1.1, 0≤d≤0.2z. Optionally, element A includes at least one of K and Li; element M includes at least one of Fe, Cr, Al, Sc, Ga, In, Ti, Zr, Mn, Zn, Ni, Cu, and Co.

[0124] In some embodiments, the positive electrode active layer may optionally include a binder. As an example, the first binder in the first positive electrode active layer and the second binder in the second positive electrode active layer may each independently include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0125] In some embodiments, the positive electrode active layer may optionally include a conductive agent. As an example, the first conductive agent in the first positive electrode active layer and the second conductive agent in the second positive electrode active layer may each independently include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0126] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as a first positive active material, a first conductive agent, a first binder, and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a first positive slurry; dispersing a second positive active material, a second conductive agent, a second binder, and any other components in a solvent to form a second positive slurry; sequentially coating the first positive slurry and the second positive slurry onto a positive current collector, and then obtaining the positive electrode sheet after drying, cold pressing, and other processes.

[0127] [Negative electrode plate]

[0128] The negative electrode sheet, also known as the anode sheet, includes, in some embodiments, a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector.

[0129] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0130] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0131] In some embodiments, the negative electrode film layer includes a negative electrode active material. The negative electrode active material may be any negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include silicon-based materials, and may also include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, tin-based materials, and lithium titanate, etc. Tin-based materials may be selected from at least one of elemental tin, tin oxides, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0132] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0133] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0134] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0135] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0136] In other embodiments, the current collector of the negative electrode sheet may typically include a current collector body and a base coating. The base coating may be disposed on at least one side of the current collector body. The base coating basically does not contain negative electrode active material, but may include a small amount of carbon material. However, the carbon material forms a thin coating and cannot play the role of negative electrode active material.

[0137] In some embodiments, the membrane layer may also include a binder for fixing the additive to the negative electrode sheet. The type of binder is not particularly limited, and those skilled in the art can choose flexibly according to actual needs.

[0138] [Electrolytes]

[0139] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0140] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0141] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0142] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0143] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0144] [Isolation membrane]

[0145] In some embodiments, the battery cell also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0146] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0147] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0148] In some embodiments, the battery cell may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above.

[0149] In some embodiments, the outer packaging of the battery cell can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the battery cell can also be a flexible package, such as a pouch. The material of the flexible package can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0150] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 shows a square battery cell 5 as an example.

[0151] In some embodiments, referring to FIG2, the outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be placed over the opening to close the receiving cavity. The positive electrode sheet, negative electrode sheet, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 may be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0152] In some implementations, individual battery cells can be assembled into a battery module. The number of individual battery cells contained in a battery module can be one or more, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery module.

[0153] Figure 3 shows a battery module 4 as an example. Referring to Figure 3, in the battery module 4, multiple battery cells 5 can be arranged sequentially along the length of the battery module 4. Of course, they can also be arranged in any other manner. Furthermore, the multiple battery cells 5 can be fixed in place using fasteners.

[0154] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0155] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0156] Figures 4 and 5 show a battery pack 1 as an example. Referring to Figures 4 and 5, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper box 2 and a lower box 3, with the upper box 2 covering the lower box 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0157] In addition, this application also provides an electrical device, which includes at least one of the battery cell, battery module, or battery pack provided in this application. The battery cell, battery module, or battery pack can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device may include, but is not limited to, mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0158] As an electrical device, you can choose individual battery cells, battery modules, or battery packs according to your usage requirements.

[0159] Figure 6 shows an example of an electrical device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the individual battery cells, a battery pack or battery module can be used.

[0160] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0161] Example

[0162] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0163] Example 1

[0164] (1) Preparation of positive electrode sheet

[0165] Prepare 350g of positive electrode active material, specifically 245g of polycrystalline material and 105g of single-crystal material. The polycrystalline material has the chemical formula Li(Ni) 0.92 Co 0.07 Mn 0.01 O2, Dv50 is 10μm; the chemical formula of the single crystal material is Li(Ni) 0.92 Co 0.04 Mn 0.04 O2, Dv50 is 3μm.

[0166] 140g of the first positive electrode active material, specifically 140g of polycrystalline material, along with the binder polyvinylidene fluoride (PVDF) and the conductive agent (SP:CNT=0.9:0.2), were added to a certain amount of N-methylpyrrolidone (NMP). The mass ratio of the first positive electrode active material, binder, and conductive agent was 98:1.2:0.8. The mixture was stirred in a drying room to prepare a uniform first positive electrode slurry. The thickness of the positive electrode current collector aluminum foil was 13μm. The above-mentioned first positive electrode slurry was uniformly coated on both sides of the aluminum foil to form the first positive electrode active layer. In the first positive electrode active layer, W1 is the mass content of polycrystalline material based on the first positive electrode active material, W3 is the mass content of polycrystalline material based on the positive electrode active material, and W5 is the mass content of conductive agent based on the first positive electrode active layer. In this embodiment, W1 is 100%, W3 is 40%, and W5 is 0.8%.

[0167] Next, 210g of the second positive electrode active material, specifically 105g of single-crystal material and 105g of polycrystalline material, along with the binder polyvinylidene fluoride (PVDF) and the conductive agent (SP:CNT=0.9:0.2), are added to a certain amount of N-methylpyrrolidone (NMP). The mass ratio of the second positive electrode active material, binder, and conductive agent is 98:0.8:1.2. The mixture is stirred in a drying room to prepare a uniform second positive electrode slurry. The second positive electrode slurry is then uniformly coated onto the first positive electrode active layers on both sides to form the second positive electrode active layer. In the second positive electrode active layer, W2 is the mass content of polycrystalline material based on the second positive electrode active material, W4 is the mass content of polycrystalline material based on the positive electrode active material, and W6 is the mass content of conductive agent based on the second positive electrode active layer. In this embodiment, W2 is 50%, W4 is 30%, and W6 is 1.2%.

[0168] The positive electrode sheet is made by drying.

[0169] (2) Preparation of negative electrode sheet

[0170] Graphite, nano-silicon materials, sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and conductive carbon dots are added to a certain amount of deionized water. The mass ratio of graphite: nano-silicon materials: sodium carboxymethyl cellulose: styrene-butadiene rubber: conductive agent is 85:5:2:3:5 (the mass content of silicon element is 5%). The mixture is stirred to prepare a uniform negative electrode slurry. The above negative electrode slurry is coated on copper foil to form a negative electrode active layer. After drying, a negative electrode sheet is prepared.

[0171] (3) Separating membrane: made of porous polyethylene (PE) polymer film;

[0172] (4) Electrolyte: 1 mol / L LiPF6 / (ethylene carbonate (EC) + diethyl carbonate (DEC) + dimethyl carbonate (DMC)) (volume ratio 1:1:1) + 5 wt.% fluoroethylene carbonate (FEC).

[0173] (5) Assembly:

[0174] The prepared positive electrode sheet, negative electrode sheet, and separator are wound into corresponding battery cells. The battery cells are then vacuum-dried at 90°C for 12 hours, followed by ultrasonic welding of the positive and negative electrode tabs. The positive electrode uses aluminum tabs, and the negative electrode uses copper tabs, with the tabs located on the same side of the battery cell. The battery cell with welded tabs is then placed into a square aluminum shell of suitable size, dried, and injected with electrolyte. After encapsulation, high-temperature settling, formation, secondary electrolyte injection, aging, and capacity testing, a single battery cell is obtained.

[0175] Examples 2-11 and Comparative Examples 1-4

[0176] The preparation process is roughly the same as in Example 1, except that the amount of single-crystal material and polycrystalline material used in the first positive electrode active layer and the second positive electrode active layer are different (the total amount of single-crystal material and the total amount of polycrystalline material remain unchanged), and / or the mass content of silicon element in the negative electrode active layer is different (the total amount of graphite and nano-silicon material remains unchanged), and / or the mass content of conductive agent in the second positive electrode active layer is different (the total amount of binder and conductive agent remains unchanged).

[0177] The relevant parameters of the positive and negative electrode sheets of Examples 1-11 and Comparative Examples 1-4 are shown in Tables 1-1 and 1-2 below.

[0178] In addition, the battery cells of Examples 1-11 and Comparative Examples 1-4 were subjected to performance tests. The test results are shown in Tables 1-1 and 1-2 below.

[0179] 25℃ Cyclic Test: The battery cells are charged and discharged in a constant temperature environment of 25℃ between 2.5V and 4.2V. The specific operation is as follows: charge to 4.2V at 0.5C, then charge at 4.2V at constant voltage until the current does not exceed 0.05C, let stand for 5 minutes, and then discharge to 2.5V at 0.5C. The capacity is recorded as Cm (m=1,2,3...). Repeat the above operation. The capacity retention rate is expressed by the ratio of Cm / C3. When Cm / C3×100%=80%, the corresponding number of cycles is recorded as an indicator of cycle capability. The more cycles, the better the cycle performance of the battery cell.

[0180] The battery performance of Examples 1-11 and Comparative Examples 1-4 is shown in Tables 1-1 and 1-2 below.

[0181] Table 1-1: Relevant parameters and performance test results of Examples 1-6

[0182]

[0183] Table 1-2 Relevant parameters and performance test results of Examples 7-11 and Comparative Examples 1-4

[0184]

[0185] Based on the above results, we can conclude that:

[0186] The negative electrode active material of the battery cell in Examples 1-11 includes silicon. The positive electrode active layer of the positive electrode includes a first positive electrode active layer and a second positive electrode active layer sequentially stacked on the surface of the positive electrode current collector. The first positive electrode active material of the first positive electrode active layer includes polycrystalline material, and the second positive electrode active material of the second positive electrode active layer includes polycrystalline material and monocrystalline material. W1 is the mass content of polycrystalline material in the first positive electrode active layer based on the first positive electrode active material, and W2 is the mass content of polycrystalline material in the second positive electrode active layer based on the second positive electrode active material. Under the premise that the total amount of monocrystalline material and the total amount of polycrystalline material remain unchanged (the mass ratio of monocrystalline material to polycrystalline material is 3:7), W1 is greater than W2, that is, the concentration of polycrystalline material in the second positive electrode active layer (upper layer) is less than the concentration of polycrystalline material in the first positive electrode active layer (lower layer), which can improve cycle performance.

[0187] According to Examples 1-7, the mass content of silicon in the negative electrode active layer is 0.5%-20%, which can be selected as 3%-10%; and W2 is 10%-50%, all of which can improve the cycle performance of the battery.

[0188] According to Examples 1-3 and Examples 8-9, W2 is 10%-66.66%, which can be selected as 30%-60%, and W1 is 71.73%-100%, all of which can improve the cycle performance of the battery.

[0189] According to Examples 1 and 10, W3 is the mass content of polycrystalline material in the first positive electrode active layer based on the positive electrode active material, and W4 is the mass content of polycrystalline material in the second positive electrode active layer based on the positive electrode active material. When W1 is greater than W2 and W4 is less than W3, that is, the amount of polycrystalline material in the upper layer is less than the amount of polycrystalline material in the lower layer, the cycle life of the battery is improved more significantly.

[0190] According to Examples 1 and 11, W5 is the mass content of the conductive agent in the first positive electrode active layer based on the first positive electrode active layer, and W6 is the mass content of the conductive agent in the second positive electrode active layer based on the second positive electrode active layer. When W5 is less than W6, that is, the conductivity of the upper layer is better than that of the lower layer, the cycle life of the battery is improved more significantly.

[0191] The cycle life of the positive electrode active layer in Comparative Example 1, which uses a conventional mixing method, is poor because the polycrystalline material in the upper layer is severely cracked, and the new interface consumes active lithium, thus worsening the cycle life.

[0192] Although the positive electrode active layer of Comparative Example 2 is coated in layers, W1 is smaller than W2 and the cycle life is worse. This is because the polycrystalline material in the upper layer cracks more severely.

[0193] Although Comparative Example 3 was coated in layers and W1 was greater than W2, the upper layer only contained single-crystal material, resulting in a poor cycle life.

[0194] Although Comparative Example 4 was coated in layers and W1 was greater than W2, the upper layer only had single-crystal material and the lower layer only had polycrystalline material, resulting in poor kinetics of the upper single crystal, easy phase transition, and poor cycle life.

[0195] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

A battery cell, wherein, The device includes a positive electrode and a negative electrode. The negative electrode includes a negative electrode active material, which is a silicon-based material containing silicon. The positive electrode includes a positive current collector and a positive electrode active layer. The positive electrode active layer includes a first positive electrode active layer and a second positive electrode active layer sequentially stacked on the surface of the positive current collector. The first positive electrode active layer includes a first positive electrode active material, and the second positive electrode active layer includes a second positive electrode active material. The first positive electrode active material includes a first polycrystalline material, and the second positive electrode active material includes a second polycrystalline material and a second single-crystal material. The battery cell satisfies: W1 is greater than W2. Wherein, W1 is the mass content of the first polycrystalline material, based on the mass of the first positive electrode active material; W2 is the mass content of the second polycrystalline material, based on the mass of the second positive electrode active material. The battery cell of claim 1, wherein, The negative electrode includes a negative current collector and a negative active layer. Based on the mass of the negative active layer, the mass content of silicon is 0.5% to 20%, and can be selected as 3% to 10%; and the W2 is 10% to 80%, and can be selected as 30% to 60%. The battery cell of claim 1, wherein, The first positive electrode active material also includes a first single crystal material. The battery cell of any one of claims 1 to 3, wherein, The W1 is 50%~100%, and can be selected as 60%~80%. The battery cell of claim 3, wherein, The positive electrode active material includes the first positive electrode active material and the second positive electrode active material. Based on the total mass of the positive electrode active material, the total mass content of the first polycrystalline material and the second polycrystalline material is 70% to 90%, and / or, based on the total mass of the positive electrode active material, the total mass content of the first single crystal material and the second single crystal material is 10% to 30%. The battery cell of claim 5, wherein, Based on the mass of the positive electrode active material, the mass content of the first polycrystalline material is recorded as W3, and the mass content of the second polycrystalline material is recorded as W4, wherein W4 is less than W3. The battery cell of claim 6, wherein, The W4 is 5%~40%. The battery cell according to claim 6 or 7, wherein The W3 is 30%~65%. The battery cell of any one of claims 1 to 8, wherein, The Dv50 of the first polycrystalline material and the Dv50 of the second polycrystalline material are each independently 8μm~10μm. The battery cell of claim 3, wherein, The Dv50 of the first single crystal material and the Dv50 of the second single crystal material are each independently 3μm~5μm. The battery cell of any one of claims 1 to 10, wherein, The first positive electrode active layer includes a first conductive agent, and the second positive electrode active layer includes a second conductive agent. The battery cell satisfies the following condition: W5 is less than W6. Wherein, W5 represents the mass content of the first conductive agent, based on the mass of the first positive electrode active layer; and W6 represents the mass content of the second conductive agent, based on the mass of the second positive electrode active layer. And / or, the conductivity of the second conductive agent is greater than the conductivity of the first conductive agent. The battery cell of claim 11, wherein, The W6 is 1.0% to 2.0%, and / or the W5 is 0.5% to 1.0%. The battery cell according to claim 11 or 12, wherein The second conductive agent includes linear or layered conductive agents, and may be one or more of carbon nanotubes, graphene, metal nanotubes, and carbon fibers, and / or... The first conductive agent includes a dot-shaped conductive agent, which may be one or more of carbon black, acetylene black, and graphite. The battery cell of any one of claims 1 to 13, wherein, The compaction density of the positive electrode active layer is 3.3-3.7 g / cm3 at 100% state of charge of the battery cell 3 . The battery cell of any one of claims 1 to 14, wherein, The areal density of the single face of the positive electrode active layer is 245 to 280 mg / 1540.25 mm 2 , and is optionally 245 to 260 mg / 1540.25 mm 2 . The battery cell according to claim 3, 9 or 10, wherein the first single crystalline material, the second single crystalline material each independently comprises the formula Li a1 Ni b1 Co c1 M1 d1 O e1 A1 f1 ; each of the first and second polycrystalline materials independently comprises the formula Li a2 Ni b2 Co c2 M2 d2 O e2 A2 f2 ; Wherein, 0 < a1 ≤ 1.2, 0.5 ≤ b1 < 1; 0 < c1 < 1; 0 < d1 < 1; 1 ≤ e1 ≤ 2; 0 ≤ f1 ≤ 1, M1 includes but is not limited to one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and A1 includes but is not limited to one or more of N, F, S and Cl; 0 < a2 ≤ 1.2, 0.5 ≤ b2 < 1; 0 < c2 < 1; 0 < d2 < 1; 1 ≤ e2 ≤ 2; 0 ≤ f2 ≤ 1, M2 includes but is not limited to one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and A2 includes but is not limited to one or more of N, F, S and Cl. The battery cell of any one of claims 1 to 16, wherein, The first positive electrode active layer includes a first binder, and based on the mass of the first positive electrode active layer, the mass content of the first binder is 0.8% to 1.0%, optionally 1.0% to 1.5%. The battery cell of claim 1, wherein, The battery cell is a cylindrical battery. A battery, wherein, Includes the battery cell as described in any one of claims 1 to 18. An electric power utilization device, wherein Includes the battery as described in claim 19, the battery being used to provide electrical energy.

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