Lithium ion secondary battery and electric equipment

Abstract

The invention provides a lithium ion secondary battery and electric equipment. The lithium ion secondary battery comprises a current collector and a positive electrode active material layer, the positive electrode active material layer comprises a first positive electrode active material and a second positive electrode active material, and the first positive electrode active material comprises one or two of a lithium-rich manganese-based material and lithium phosphate; the second positive electrode active material comprises lithium nickel cobalt manganese oxide; the positive electrode active material layer comprises a first positive electrode active material region close to the tab and a second positive electrode active material region far away from the tab, and the mass fraction of the second positive electrode active material in the first positive electrode active material region is greater than that of the second positive electrode active material in the second positive electrode active material region. According to the lithium ion secondary battery, the second positive electrode active material with relatively high content and relatively good dynamic performance is arranged in the first positive electrode active material region, so that polarization and impedance near a tab are reduced, and the rate capability and the cycle performance of the lithium ion secondary battery are improved.

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, specifically to a lithium-ion secondary battery and its electrical equipment. Background Technology

[0002] Batteries, as a new generation of energy storage and conversion devices, are widely used in portable electronic devices, electric vehicles, and other fields. With the development and advancement of battery technology, comprehensively improving battery performance, including range, cycle life, and rate capability, has become an important task for the industry.

[0003] Currently, mainstream positive electrode active materials such as lithium phosphate and lithium-rich manganese-based materials have poor kinetic performance, which affects the rate performance of the battery. In addition, the polarization in the region near the tab on the positive electrode is more severe, which leads to the battery capacity not being effectively released and the lifespan being shortened. Summary of the Invention

[0004] In view of this, the main technical problem to be solved by this application is how to improve the rate performance and cycle performance of lithium-ion secondary batteries.

[0005] To address the aforementioned technical problems, a first aspect of this application provides a lithium-ion secondary battery. The lithium-ion secondary battery includes a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a current collector and a positive active material layer disposed on the surface of the current collector. The current collector includes a main body and a tab located on one side of the main body. The main body includes a first region and a second region, with the first region located between the second region and the tab. The positive active material layer includes a positive active material, comprising a first positive active material and a second positive active material. The first positive active material includes one or both of lithium-rich manganese-based materials and lithium phosphate. The second positive active material includes lithium nickel cobalt manganese oxide. The positive active material layer includes a first positive active material region and a second positive active material region, with the first positive active material region located in the first region and the second positive active material region located in the second region. The mass fraction of the second positive active material in the positive active material of the first positive active material region is greater than the mass fraction of the second positive active material in the positive active material of the second positive active material region.

[0006] In the embodiments of this application, lithium-rich manganese-based materials and lithium phosphate are used in combination with lithium nickel cobalt manganese oxide, either separately or simultaneously, in the positive electrode active material layer. The positive electrode active material layer is partitioned, with different mass fractions of lithium nickel cobalt manganese oxide in different positive electrode active material layers. Specifically, a higher mass fraction of lithium nickel cobalt manganese oxide is set in the first region, and a lower mass fraction is set in the second region. Lithium nickel cobalt manganese oxide has high electronic conductivity and ion diffusion coefficient, enabling the battery to respond quickly to current changes during high-rate charging and discharging. By using a configuration with a higher mass fraction of lithium nickel cobalt manganese oxide in the first region, the first positive electrode active material region near the tab side has higher electronic conductivity and ion diffusion coefficient, improving the transport between charge and lithium ions, thereby mitigating the polarization phenomenon caused by the high current density in the first region near the tab. In this embodiment, lithium-rich manganese-based materials and lithium phosphate are used in combination with lithium nickel cobalt manganese oxide, either separately or simultaneously. This allows the positive electrode active material layer to possess the good stability of lithium phosphate and / or the high energy density of lithium-rich manganese-based materials, while also having high electronic conductivity and ion diffusion coefficient. This improves the polarization and impedance growth phenomena at high rates, thereby enhancing the overall rate performance and cycle performance of the battery.

[0007] In some embodiments, the mass fraction of the second positive electrode active material in the positive electrode active material of the first positive electrode active material region is w1, where 55% ≤ w1 ≤ 70%.

[0008] In the embodiments of this application, by setting the mass ratio of lithium nickel cobalt manganese oxide in the first positive electrode active material region within a specific range, the positive electrode active composite material near the tab side has good rate performance and cycle performance, while also having high energy density and stability.

[0009] In some embodiments, the mass fraction of the second positive electrode active material in the positive electrode active material of the second positive electrode active material region is w2, where 30% ≤ w2 ≤ 50%.

[0010] In the embodiments of this application, by setting the mass ratio of lithium nickel cobalt manganese oxide in the second positive electrode active material region within a specific range, the active composite material in the large area of ​​the positive electrode sheet has good rate performance and cycle performance, while also having high energy density and stability.

[0011] In some embodiments, the width of the first positive electrode active material region accounts for 20% to 30% of the width of the main body of the current collector, and the width of the second positive electrode active material region accounts for 70% to 80% of the width of the main body of the current collector.

[0012] In the embodiments of this application, by setting the width ratio of the first positive electrode active material region and the width ratio of the second positive electrode active material region within a specific range, more material with good kinetic performance is coated in the area with high current density in the current collector body, and less material with good kinetic performance is coated in the area with low current density in the current collector body. This is beneficial to improve the rate performance and cycle performance of the battery, while also having good energy density and stability.

[0013] In some embodiments, lithium-rich manganese-based materials include those with the structural formula nLi₂MnO₃·(1-n)LiNi. a Mn b M1 1-a-b The material of O2, wherein 0.1≤n≤0.3, 0.3≤a≤0.8, 0.2≤b≤0.5, and M1 includes one or more combinations of Na, Mg, Al, Ca, Ba, V, Zn, Ti, Fe, Co, Cr, Nb, W, Mo, Zr, Ta and Hf.

[0014] In the embodiments of this application, by including a specific molecular formula in the lithium-rich manganese-based material, the lithium-rich manganese-based material can have better electrochemical performance.

[0015] In some embodiments, lithium nickel cobalt manganese oxide includes those with the structural formula LiNi x Co y Mn z M2 1-x-y-z The material of O2 includes 0.4 ≤ x < 0.7, 0.05 < y < 0.15, and 0.15 < z < 0.55. M2 includes one or more combinations of Al, Ti, Zr, W, Mo, Ba, and Nb. In the embodiments of this application, within the above ranges, lithium nickel cobalt manganese oxide has high energy density, as well as high electronic conductivity, ionic conductivity, and stability.

[0016] In some embodiments, lithium phosphates include those with the structural formula LiM3. c Fe 1-c The PO4 material, wherein 0 ≤ c ≤ 0.6, and M3 includes one or more combinations of Mn, Cr, Co, Cu, Ni, V, Mo, Ti, Zn, Al, Ga, Mg, B, and Nb. In the embodiments of this application, within the above range, lithium phosphate exhibits high stability, good cycle performance, and high energy density.

[0017] In some embodiments, the compaction density of the first positive electrode active material region is 2.8 g / cm³. 3 ~3.0g / cm 3 And / or, the compaction density of the second positive electrode active material region is 2.8 g / cm³.3 ~3.0g / cm 3 .

[0018] In the embodiments of this application, within the above-mentioned range, while maintaining a high energy density in the positive electrode active material layer, it also has good liquid retention capacity, thereby improving the cycle performance of the battery.

[0019] In some embodiments, the areal capacity per unit area of ​​the first positive electrode active material region is equal to that of the second positive electrode active material region.

[0020] In the embodiments of this application, within the above-mentioned range, while maintaining a high energy density in the positive electrode active material layer, it also has good liquid retention capacity, thereby improving the cycle performance of the battery.

[0021] In some embodiments, the volume average particle size Dv50 of the lithium-rich manganese-based material is 4 μm to 10 μm; and / or, the volume average particle size Dv50 of the lithium phosphate is 100 nm to 500 nm; and / or, the volume average particle size Dv50 of the lithium nickel cobalt manganese oxide is 3 μm to 6 μm.

[0022] In the embodiments of this application, by controlling the range of the volume average particle size Dv50 of the lithium-rich manganese-based material, lithium phosphate, and lithium nickel cobalt manganese oxide, the difference range of the particle size Dv50 of the lithium-rich manganese-based material, lithium phosphate, and lithium nickel cobalt manganese oxide can be effectively controlled, thereby increasing the gap occupancy ratio formed between the lithium-rich manganese-based material, lithium phosphate, and lithium nickel cobalt manganese oxide, resulting in a better combination effect and increasing the compaction density of the positive electrode active material composition, thereby improving the energy density of the positive electrode active material composition.

[0023] A second aspect of this application provides an electrical device that includes any of the lithium-ion secondary batteries provided in the first aspect. The electrical device provided in the embodiments of this application, by including any of the lithium-ion secondary batteries provided in the first aspect, has at least the same advantages as lithium-ion secondary batteries. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a schematic diagram of the structure of the positive electrode sheet provided in some embodiments of this application;

[0026] Figure 2 for Figure 1The diagram shows the structure of the positive electrode sheet along its thickness direction.

[0027] Figure 3 This is an exploded structural diagram of a battery cell provided in an embodiment of this application;

[0028] Figure 4 This is an exploded structural diagram of the battery provided in an embodiment of this application;

[0029] Figure 5 This is a schematic diagram of the structure of the electrical equipment provided in the embodiments of this application;

[0030] Explanation of icon numbers:

[0031] 1000 - Vehicle, 100 - Battery, 200 - Controller, 300 - Motor, 10 - Housing, 20 - Battery Cell, 11 - First Part, 12 - Second Part, 21 - End Cap, 22 - Housing, 23 - Cell Assembly, 21a - Electrode Terminal, 23a - Tab, 30 - Positive Electrode Sheet, 312 - Tab, 32 - Positive Active Material Layer, 31 - Current Collector, 311 - Main Body, 321 - First Positive Active Material Region, 322 - Second Positive Active Material Region, 3111 - First Region, 3112 - Second Region. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0033] The terms "first," "second," and "third" in this application are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first," "second," or "third" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified. All directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of this application are only used to explain the relative positional relationships and movements between components in a specific orientation (as shown in the figures). If the specific orientation changes, the directional indications also change accordingly. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, methods, products, or devices.

[0034] 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 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 "ab" 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.

[0035] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0036] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0037] In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0038] Currently used cathode active materials such as lithium iron phosphate have advantages such as good cycle performance and strong stability, but they have disadvantages such as relatively low energy density and poor rate performance. Lithium-rich manganese-based materials have advantages such as high energy density and low cost, but their rate performance and high-temperature cycle performance are usually relatively poor. Nickel cobalt manganese lithium and nickel cobalt manganese oxide have advantages such as high energy density and good rate performance, but their crystal structure is prone to non-uniform volume changes during long cycles, resulting in poor cycle performance and stability.

[0039] Furthermore, most positive electrode sheets currently employ integrated coating, with the same material applied to all locations on the electrode, meaning that the kinetic properties of all regions of the entire electrode are essentially consistent. However, since electrons on the entire electrode sheet must be led out or led in through the tabs during charging and discharging, the current density in the region near the tabs on the positive electrode sheet is significantly higher than the current density in the region farther from the tabs. This results in greater polarization and impedance in this region, which in turn affects the rate performance and cycle performance of the battery.

[0040] In summary, in order to solve the aforementioned problems, the first aspect of this application refers to... Figure 1 and Figure 2 , Figure 1 This is a schematic diagram of the structure of the positive electrode sheet provided in some embodiments of this application. Figure 2 for Figure 1The schematic diagram of the positive electrode sheet along its thickness direction illustrates a lithium-ion secondary battery. The lithium-ion secondary battery includes a positive electrode sheet 30, a negative electrode sheet, and an electrolyte. The positive electrode sheet 30 includes a current collector 31 and a positive active material layer 32 disposed on the surface of the current collector 31. The current collector 31 includes a main body 311 and a tab 312 located on one side of the main body. The main body 311 includes a first region 3111 and a second region 3112, with the first region 3111 located between the second region 3112 and the tab 312. The positive active material layer 32 includes a positive active material, which includes a first positive active material and... The second positive electrode active material includes one or both of the following: the first positive electrode active material includes lithium-rich manganese-based material and lithium phosphate; the second positive electrode active material includes lithium nickel cobalt manganese oxide; the positive electrode active material layer includes a first positive electrode active material region 321 and a second positive electrode active material region 322, the first positive electrode active material region 321 is located in a first region 3111, the second positive electrode active material region 322 is located in a second region 3112, and the mass fraction of the second positive electrode active material in the positive electrode active material of the first positive electrode active material region 321 is greater than the mass fraction of the second positive electrode active material in the positive electrode active material of the second positive electrode active material region 322.

[0041] In the embodiments of this application, lithium-rich manganese-based materials and lithium phosphate are used in combination with lithium nickel cobalt manganese oxide, either separately or simultaneously, in the positive electrode active material layer 32. Furthermore, the positive electrode active material layer 32 is partitioned, with different mass fractions of lithium nickel cobalt manganese oxide in different positive electrode active material layers. Specifically, a higher mass fraction of lithium nickel cobalt manganese oxide is set in the first region 3111, and a lower mass fraction is set in the second region 3112. The lithium nickel cobalt manganese oxide has high electronic conductivity and ion diffusion coefficient, enabling the battery to respond quickly to current changes during high-rate charging and discharging. By using a configuration with a higher mass fraction of lithium nickel cobalt manganese oxide in the first region 3111, the first positive electrode active material region 321 near the tab side has high electronic conductivity and ion diffusion coefficient, improving the transport between charge and lithium ions, thereby mitigating the polarization phenomenon caused by the high current density in the first region 3111 near the tab 312. In this embodiment, lithium-rich manganese-based materials and lithium phosphate are used in combination with lithium nickel cobalt manganese oxide, either separately or simultaneously. This allows the positive electrode active material layer 32 to possess the good stability of lithium phosphate and / or the high energy density of lithium-rich manganese-based materials, while also having high electronic conductivity and ion diffusion coefficient. This improves the polarization and impedance growth phenomena at high rates, thereby enhancing the overall rate performance and cycle performance of the battery.

[0042] In some embodiments of this application, lithium nickel cobalt manganese oxide is used in combination with lithium-rich manganese-based material in the positive electrode active material layer 32; or, lithium nickel cobalt manganese oxide is used in combination with lithium phosphate in the positive electrode active material layer 32; or, lithium nickel cobalt manganese oxide is used in combination with lithium-rich manganese-based material and lithium phosphate in the positive electrode active material layer 32.

[0043] In some embodiments, the mass fraction of the second positive electrode active material in the positive electrode active material of the first positive electrode active material region 321 is w1, where 55% ≤ w1 ≤ 70%.

[0044] In any embodiment, the mass fraction w1 of the second positive electrode active material in the positive electrode active material of the first positive electrode active material region 321 can be 55%, 58%, 60%, 65%, 67%, 69%, 70%, etc., or a range of any two of the above values. For example, the mass fraction w1 of the second positive electrode active material in the positive electrode active material of the first positive electrode active material region 321 can be 55% to 60%, 58% to 67%, 65% to 70%, etc.

[0045] In the embodiments of this application, by setting the mass ratio of lithium nickel cobalt manganese oxide in the first positive electrode active material region 321 within a specific range, the positive electrode active composite material near the tab side has good rate performance and cycle performance, while also having high energy density and stability.

[0046] In some embodiments, the mass fraction of the second positive electrode active material in the positive electrode active material of the second positive electrode active material region 322 is w2, where 30% ≤ w2 ≤ 50%.

[0047] In any embodiment, the mass fraction w2 of the second positive electrode active material in the positive electrode active material of the second positive electrode active material region 322 can be 30%, 38%, 40%, 45%, 47%, 49%, 50%, etc., or a range of any two of the above values. For example, the mass fraction w2 of the second positive electrode active material in the positive electrode active material of the second positive electrode active material region 322 can be 30% to 38%, 40% to 47%, 45% to 50%, etc.

[0048] In the embodiments of this application, by setting the mass ratio of lithium nickel cobalt manganese oxide in the second positive electrode active material region 322 within a specific range, the active composite material in the large area of ​​the positive electrode sheet has good rate performance and cycle performance, while also having high energy density and stability.

[0049] In some embodiments, the width of the first positive electrode active material region 321 accounts for 20% to 30% of the width of the main body portion 311 of the current collector, and the width of the second positive electrode active material region 322 accounts for 70% to 80% of the width of the main body portion 311 of the current collector.

[0050] In any embodiment, the width of the first positive electrode active material region 321 may be 20%, 22%, 24%, 27%, 29%, 30%, or any range of any two of the above values, for example, the width of the first positive electrode active material region 321 may be 20%–22%, 24%–29%, 27%–30%, or any two of the above values; the width of the second positive electrode active material region 322 may be 70%, 72%, 74%, 77%, 79%, 80%, or any two of the above values, for example, the width of the second positive electrode active material region 322 may be 70%–72%, 74%–79%, 77%–80%, or any two of the above values, for example, the width of the second positive electrode active material region 322 may be 70%–72%, 74%–79%, 77%–80%, or any two of the above values.

[0051] In the embodiments of this application, by setting the width ratio of the first positive electrode active material region 321 and the width ratio of the second positive electrode active material region 322 within a specific range, more material with good kinetic performance is coated in the area with high current density in the current collector body, and less material with good kinetic performance is coated in the area with low current density in the current collector body. This is beneficial to improve the rate performance and cycle performance of the battery, while also having good energy density and stability.

[0052] In some embodiments, lithium-rich manganese-based materials include those with the structural formula nLi₂MnO₃·(1-n)LiNi. a Mn b M1 1-a-bThe material of O2, wherein 0.1≤n≤0.3, 0.3≤a≤0.8, 0.2≤b≤0.5, and M1 includes one or more combinations of Na, Mg, Al, Ca, Ba, V, Zn, Ti, Fe, Co, Cr, Nb, W, Mo, Zr, Ta and Hf. In any embodiment, the value of n can be 0.1, 0.15, 0.2, 0.25, 0.3, etc., or a range consisting of any two of the above values, such as 0.1≤n≤0.15, 0.15≤n≤0.25, 0.25≤n≤0.3, etc.; the value of a can be 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, etc., or a range consisting of any two of the above values, such as 0.3≤a≤0.4, 0.4≤a≤0.7, 0.7≤a≤0.8, etc.; the value of b can be 0.2, 0.25, 0.3, 0.4, 0.5, etc., or a range consisting of any two of the above values, such as 0.2≤b≤0.3, 0.3≤b≤0.4, 0.4≤b≤0.5, etc. It should be noted that lithium-ion secondary batteries undergo formation and cycling processes, resulting in the consumption of lithium ions and thus a decrease in the measured lithium content in the positive electrode active material. Conversely, if lithium replenishment is performed on both the positive and negative electrode plates, the lithium content in the positive electrode active material will increase after formation and cycling. Furthermore, those skilled in the art will understand that other elements in the chemical formula of lithium-rich manganese-based materials may be lost. For example, oxygen (O) may be consumed, resulting in a decrease in the measured O content in lithium-rich manganese-based materials.

[0053] In the embodiments of this application, by including a specific molecular formula in the lithium-rich manganese-based material, the lithium-rich manganese-based material can have better electrochemical performance.

[0054] In some embodiments, lithium nickel cobalt manganese oxide includes those with the structural formula LiNi x Co y Mn z M2 1-x-y-zThe material of O2 is 0.4≤x<0.7, 0.05<y<0.15, 0.15<z<0.55, and M2 includes one or more combinations of Al, Ti, Zr, W, Mo, Ba, and Nb. In any embodiment, the value of x can be 0.4, 0.5, 0.6, 0.69, etc., or a range consisting of any two of the above values, such as 0.4≤x≤0.5, 0.4≤x≤0.6, 0.5≤x≤0.69, etc., or 0.69≤x<0.7, etc.; the value of y can be 0.051, 0.06, 0.08, 0.1, 0.12, 0.14, etc., or a range consisting of any two of the above values, such as 0.051≤y≤0.06, 0.06≤y≤0.1, 0.1<y≤0.14, etc., or 0.05<y≤0.051, 0.14≤y<0.15, etc. The value of z can be 0.151, 0.2, 0.25, 0.36, 0.47, 0.54, etc., or a range consisting of any two of the above values. For example, 0.151≤z≤0.2, 0.2<z<0.47, 0.47≤z≤0.54, etc., or 0.15<z≤0.151, 0.54≤z<0.55, etc. It should be noted that lithium-ion secondary batteries experience lithium ion consumption during formation and cycling processes, resulting in a decrease in the measured lithium content in the positive electrode active material. Simultaneously, if lithium replenishment is performed on the positive and negative electrode plates, the measured lithium content in the positive electrode active material will increase after formation and cycling. Furthermore, those skilled in the art will understand that other elements in the chemical formula of lithium nickel cobalt manganese oxide may be lost. For example, oxygen (O) may be consumed, resulting in a decrease in the measured O content in lithium nickel cobalt manganese oxide.

[0055] In the embodiments of this application, within the above-mentioned range, lithium nickel cobalt manganese oxide has high energy density, as well as high electronic conductivity, ionic conductivity and stability.

[0056] In some embodiments, lithium phosphates include those with the structural formula LiM3. c Fe 1-cThe PO4 material has a concentration of 0 ≤ c ≤ 0.6, and M3 includes one or more combinations of Mn, Cr, Co, Cu, Ni, V, Mo, Ti, Zn, Al, Ga, Mg, B, and Nb. In any embodiment, the value of c can be 0, 0.1, 0.3, 0.4, 0.5, 0.6, or a range of any two of the above values, such as 0 ≤ c ≤ 0.1, 0.1 ≤ c ≤ 0.3, 0.3 ≤ c ≤ 0.5, 0.4 ≤ c ≤ 0.6, etc. It should be noted that in the embodiments of this application, the chemical formula of lithium phosphate refers to the chemical formula of the materials used in the preparation process. Due to the formation and cycling processes in lithium-ion secondary batteries, lithium ions are consumed, resulting in a decrease in the measured lithium content in the positive electrode active material. Simultaneously, if lithium is replenished to the positive and negative electrode plates, an increase in the measured lithium content in the positive electrode active material will occur after formation and cycling processes. Furthermore, as those skilled in the art will understand, other elements in the chemical formula of lithium phosphate may be lost. For example, phosphorus (P) and oxygen (O) elements may be consumed, resulting in a decrease in the measured P content and / or O content in lithium phosphates.

[0057] In the embodiments of this application, within the above-mentioned range, lithium phosphate has high stability and cycle performance, as well as high energy density.

[0058] In some embodiments, the compaction density of the first positive electrode active material region 321 is 2.8 g / cm³. 3 ~3.0g / cm 3 And / or, the compaction density of the second positive electrode active material region 322 is 2.8 g / cm³. 3 ~3.0g / cm 3 .

[0059] In any embodiment, the compaction density of the first positive electrode active material region 321 can be 2.8 g / cm³. 3 2.85g / cm 3 2.89 g / cm 3 2.9g / cm 3 2.95g / cm 3 3.0g / cm 3 etc., or a range consisting of any two of the above values. For example, the compaction density of the first positive electrode active material region 321 can be 2.8 g / cm³. 3 ~2.85g / cm 3 2.85g / cm 3 ~2.89g / cm 3 2.89 g / cm 3 ~3.0g / cm 3The compaction density of the second positive electrode active material region 322 can be 2.8 g / cm³. 3 2.85g / cm 3 2.89 g / cm 3 2.9g / cm 3 2.95g / cm 3 3.0g / cm 3 etc., or a range consisting of any two of the above values. For example, the compaction density of the second positive electrode active material region 322 can be 2.8 g / cm³. 3 ~2.85g / cm 3 2.85g / cm 3 ~2.89g / cm 3 2.89 g / cm 3 ~3.0g / cm 3 wait.

[0060] In the embodiments of this application, the compaction density is set within the above-mentioned range. While maintaining a high energy density in the positive electrode active material layer 32, it also has good liquid retention capacity, thereby improving the cycle performance of the battery.

[0061] In some embodiments, the areal capacity per unit area of ​​the first positive electrode active material region 321 and the second positive electrode active material region 322 are equal.

[0062] In the embodiments of this application, the unit areal capacity is common knowledge in the art and has a common meaning in the art, and can be measured by methods and instruments in the art.

[0063] In the embodiments of this application, within the above-mentioned range, while maintaining a high energy density in the positive electrode active material layer, it also has good liquid retention capacity, thereby improving the cycle performance of the battery.

[0064] In some embodiments, the volume average particle size Dv50 of the lithium-rich manganese-based material is 4 μm to 10 μm; and / or, the volume average particle size Dv50 of the lithium phosphate is 100 nm to 500 nm; and / or, the volume average particle size Dv50 of the lithium nickel cobalt manganese oxide is 3 μm to 6 μm.

[0065] In the embodiments of this application, the volume average particle size Dv50 is common knowledge in the art and has a common meaning in the art. It can be measured by methods and instruments in the art.

[0066] In any embodiment, the volume average particle size Dv50 of the lithium-rich manganese-based material can be 4μm, 6μm, 7μm, 9μm, 10μm, etc., or a range consisting of any two of the above values. For example, the volume average particle size Dv50 of the lithium-rich manganese-based material can be 4μm~6μm, 6μm~9μm, 9μm~10μm, etc.; the volume average particle size Dv50 of the lithium phosphate can be 100nm, 150nm, 200nm, 300nm, 400nm, 500nm, etc., or any of the above values. The range consisting of two values, for example, the volume average particle size Dv50 of lithium phosphate can be 100nm~200nm, 200nm~300nm, 300nm~500nm, etc.; the volume average particle size Dv50 of lithium nickel cobalt manganese oxide can be 3μm, 3.5μm, 4μm, 5μm, 6μm, etc., or any range consisting of two of the above values, for example, the volume average particle size Dv50 of lithium nickel cobalt manganese oxide can be 3μm~3.5μm, 3.5μm~5μm, 5μm~6μm, etc.

[0067] In the embodiments of this application, by controlling the range of the volume average particle size Dv50 of the lithium-rich manganese-based material, lithium phosphate, and lithium nickel cobalt manganese oxide, the difference range of the particle size Dv50 of the lithium-rich manganese-based material, lithium phosphate, and lithium nickel cobalt manganese oxide can be effectively controlled, thereby increasing the gap occupancy ratio formed between the lithium-rich manganese-based material, lithium phosphate, and lithium nickel cobalt manganese oxide, resulting in a better combination effect and increasing the compaction density of the positive electrode active material composition, thereby improving the energy density of the positive electrode active material composition.

[0068] A second aspect of this application provides an electrical device that includes any of the lithium-ion secondary batteries provided in the first aspect. The electrical device provided in the embodiments of this application, by including any of the lithium-ion secondary batteries provided in the first aspect, has at least the same advantages as lithium-ion secondary batteries.

[0069] In addition, the battery cell, battery and electrical device of this application will be described below with appropriate reference to the accompanying drawings.

[0070] In the embodiments of this application, a battery cell refers to the smallest unit that makes up a battery. A battery cell also includes an electrolyte and a separator. The separator is disposed between the positive and negative electrodes, primarily to prevent short circuits between the positive and negative electrodes, while also allowing ions to pass through. During the battery charging and discharging process, active ions Li... + The electrolyte moves back and forth between the positive and negative electrodes, inserting and de-inserting, while acting as a conductor for ions between them.

[0071] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, wherein the positive electrode film layer includes the positive active material composition of the above embodiments of this application.

[0072] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0073] 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.).

[0074] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0075] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0076] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0077] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes the negative electrode active material of the above embodiments.

[0078] 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.

[0079] 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.).

[0080] 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).

[0081] 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.

[0082] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0083] 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.

[0084] 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.

[0085] In some embodiments, the electrolyte includes an electrolyte salt and a solvent.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] 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.

[0090] 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.

[0091] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into a battery cell assembly using a winding or stacking process.

[0092] In some implementations, such as Figure 3 As shown, the battery cell 20 may include an outer packaging. This outer packaging can be used to encapsulate the aforementioned cell assembly 23 and electrolyte. The outer packaging includes an end cap 21, a housing 22, and other functional components.

[0093] End cap 21 refers to a component that covers the opening of housing 22 to isolate the internal environment of battery cell 20 from the external environment. The shape of end cap 21 can be adapted to the shape of housing 22 to fit it. Optionally, end cap 21 can be made of a material with certain hardness and strength (such as aluminum alloy), so that end cap 21 is not easily deformed under pressure and impact, allowing battery cell 20 to have higher structural strength and improved stability. Functional components such as electrode terminals 21a can be provided on end cap 21. Electrode terminals 21a can be used for electrical connection with cell assembly 23 to output or input electrical energy to battery cell 20. In some embodiments, end cap 21 can also be provided with a pressure relief mechanism for releasing internal pressure when the internal pressure or temperature of battery cell 20 reaches a threshold. The material of end cap 21 can also be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and this application embodiment does not impose special limitations on this. In some embodiments, an insulating element (not shown) may be provided on the inner side of the end cap 21. The insulating element can be used to isolate the electrical connection components within the housing 22 from the end cap 21 to reduce the risk of short circuits. For example, the insulating element may be made of plastic, rubber, etc.

[0094] The housing 22 is a component used to cooperate with the end cap 21 to form the internal environment of the battery cell 20. This internal environment can accommodate the cell assembly 23, electrolyte, and other components. The housing 22 and the end cap 21 can be independent components. An opening can be provided on the housing 22, and the end cap 21 can be used to close the opening to form the internal environment of the battery cell 20. Alternatively, the end cap 21 and the housing 22 can be integrated. Specifically, the end cap 21 and the housing 22 can form a common connecting surface before other components are inserted into the housing. When it is necessary to encapsulate the interior of the housing 22, the end cap 21 closes the housing 22. The housing 22 can be of various shapes and sizes, such as cuboid, cylindrical, hexagonal prism, etc. Specifically, the shape of the housing 22 can be determined according to the specific shape and size of the cell assembly 23. The material of the housing 22 can be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc. This application embodiment does not impose any special limitations on this.

[0095] The casing 22 may contain one or more battery cell assemblies 23. The portions of the positive and negative electrodes that lack active material each constitute a tab 23a. The positive and negative tabs may be located together at one end of the main body or at opposite ends of the main body. During the charging and discharging process of the battery, the positive and negative active materials react with the electrolyte, and the tabs 23a connect to the electrode terminals to form a current loop.

[0096] Please refer to Figure 4The battery 100 includes a housing 10 and a battery cell 20, with the battery cell 20 housed within the housing 10. The housing 10 provides a space for the battery cell 20 and can have various structures. In some embodiments, the housing 10 may include a first portion 11 and a second portion 12, which overlap each other, collectively defining a space for accommodating the battery cell 20. The second portion 12 may be a hollow structure with one open end, and the first portion 11 may be a plate-like structure, covering the open side of the second portion 12 so that the first portion 11 and the second portion 12 together define the space. Alternatively, both the first portion 11 and the second portion 12 may be hollow structures with one open side, with the open side of the first portion 11 covering the open side of the second portion 12. Of course, the housing 10 formed by the first portion 11 and the second portion 12 can have various shapes, such as a cylinder, a cuboid, etc.

[0097] In battery 100, there can be multiple battery cells 20, which can be connected in series, parallel, or in a mixed manner. A mixed connection means that multiple battery cells 20 are connected in both series and parallel configurations. Multiple battery cells 20 can be directly connected in series, parallel, or in a mixed manner, and then the entire assembly of the multiple battery cells 20 is housed within the housing 10. Alternatively, battery 100 can also be composed of multiple battery cells 20 first connected in series, parallel, or in a mixed manner to form a battery module, and then multiple battery modules are connected in series, parallel, or in a mixed manner to form a whole, which is also housed within the housing 10. Battery 100 may also include other structures; for example, it may include a busbar component for electrical connection between the multiple battery cells 20.

[0098] In this embodiment, the battery 100 includes a lithium-ion battery as the battery cell 20. In other embodiments, the battery 100 may further include any one or more of lithium-sulfur batteries, sodium-ion batteries, and magnesium-ion batteries, but is not limited thereto. The battery cell 20 may be cylindrical, flat, cuboid, or other shapes.

[0099] In some implementations, the batteries can be assembled into battery modules, and the number of batteries contained in a battery module 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 module.

[0100] In addition, this application also provides an electrical device, which includes at least one of the battery cells and / or batteries provided in this application. The battery cells or battery packs can be used as the power source for the electrical device or as the energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., 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.

[0101] As electrical equipment, individual battery cells and / or batteries can be selected according to their usage requirements.

[0102] Figure 5 As shown, the electrical equipment is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. A partial structural diagram of one embodiment of the electrical equipment is provided. A battery 100 is internally disposed in the electrical equipment 1000, and the battery 100 can be located at the bottom, head, or tail of the electrical equipment 1000. The battery 100 can be used to power the electrical equipment 1000; for example, the battery 100 can serve as the operating power source for the electrical equipment 1000. The electrical equipment 1000 may also include a controller 200 and a motor 300. The controller 200 is used to control the battery 100 to supply power to the motor 300, for example, to meet the power requirements of the electrical equipment 1000 during startup, navigation, and operation.

[0103] In some embodiments of this application, the battery 100 can not only serve as the operating power source for the electrical device 1000, but also as the driving power source for the electrical device 1000, replacing or partially replacing fuel oil or natural gas to provide driving power for the electrical device 1000.

[0104] 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.

[0105] Example 1

[0106] Preparation of the positive electrode sheet

[0107] A positive electrode active material is formed by mixing lithium-rich manganese-based materials, lithium phosphate, and lithium nickel cobalt manganese oxide. The chemical formula of the lithium-rich manganese-based material is 0.3Li₂MnO₃·0.7LiNi. 0.5 Co 0.2 Mn 0.3 O2, the chemical formula of lithium phosphate is LiMn0.4 Fe 0.6 PO4, the chemical formula of lithium nickel cobalt manganese oxide is LiNi 0.6 Co 0.2 Mn 0.2 O2, the first positive electrode active material region and the second positive electrode active material region use positive electrode active materials with different ratios. In the positive electrode active material of the first positive electrode active material region, the mass fraction of lithium-rich manganese-based material is 22.5%, the mass fraction of lithium phosphate is 22.5%, and the mass fraction of lithium nickel cobalt manganese oxide is 55%. In the positive electrode active material of the second positive electrode active material region, the mass fraction of lithium-rich manganese-based material is 30%, the mass fraction of lithium phosphate is 30%, and the mass fraction of lithium nickel cobalt manganese oxide is 40%.

[0108] The positive electrode active material, conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) of the first positive electrode active material region are mixed in a mass ratio of 94:4:2. N-methylpyrrolidone solvent is added, and the mixture is thoroughly stirred until homogeneous, yielding the positive electrode slurry of the first positive electrode active material region. The same process is repeated for the second positive electrode active material region. The positive electrode slurry of the second positive electrode active material region is first coated onto the second region, with the width of the second region accounting for 80% of the width of the current collector body. The coating is then dried and cold-pressed. Next, the positive electrode slurry of the first positive electrode active material region is coated onto the first region, with the width of the first region accounting for 20% of the width of the current collector body. This process is repeated again, followed by a second drying and cold pressing, to obtain the positive electrode sheet.

[0109] Preparation of the negative electrode sheet

[0110] Artificial graphite, hard carbon, conductive agent acetylene black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC-Na) are added to a deionized water solvent in a mass ratio of 90:5:2:2:1 and thoroughly mixed. The mixture is then coated onto both sides of a copper foil and subjected to drying, cold pressing, and other processes to obtain the negative electrode sheet.

[0111] Preparation of Electrolyte

[0112] In an argon-atmospheric glove box, ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) were mixed uniformly in a volume ratio of 1:1:1 to obtain a solvent. LiPF6 was added and dissolved in the solvent, and the mixture was stirred evenly to obtain a 1 mol / L LiPF6 electrolyte.

[0113] [Septum]

[0114] A 13μm thick polyethylene membrane was used as the separator.

[0115] Battery assembly

[0116] The separator, negative electrode, and positive electrode are arranged in the order of "separator-negative electrode-separator-positive electrode". One end of the positive electrode, negative electrode, and two separators is fixed to the discharge roller, and the other end is stacked together and fixed to the winding shaft. The winding shaft is rotated by a motor to wind the positive electrode, negative electrode, and two separators to obtain a wound cell. The wound cell is placed in an outer packaging, injected with prepared electrolyte, and then sealed, injected, formed, and vented to obtain a lithium-ion battery.

[0117] The main process parameters of Examples 2-13 and Comparative Examples 1-2 differ from those of Example 1 as shown in Tables 1 and 2. In Table 1, the first mass percentage represents the mass percentage of lithium-rich manganese-based material in the first positive electrode active material region, and the second mass percentage represents the mass percentage of lithium phosphate in the first positive electrode active material region. In Table 2, the third mass percentage represents the mass percentage of lithium-rich manganese-based material in the second positive electrode active material region, and the fourth mass percentage represents the mass percentage of lithium phosphate in the second positive electrode active material region. For experimental parameters and process steps not described in other examples and comparative examples, please refer to the above descriptions, which are consistent with the preceding text, and will not be repeated here.

[0118] The specific testing methods for the relevant parameters in the above embodiments and comparative examples are as follows:

[0119] 1. Powder compaction density test

[0120] A certain amount of powder is placed in a compaction mold, and then the mold is placed on a compaction density instrument. Different pressures are set to press the powder. After the pressure is released, the thickness of the powder under different pressures is read on the equipment, and the compaction density can be calculated from this.

[0121] 2. Volume average particle size Dv50 test

[0122] Equipment Model: Malvern 2000 (MasterSizer 2000) laser particle size analyzer; Reference Standard Procedure: GB / T19077-2016 / ISO 13320:2009; Specific Test Procedure: Take an appropriate amount of the sample to be tested (the sample concentration should be 8%-12% opacity), add 20ml of deionized water, and sonicate for 5 minutes (53KHz / 120W) to ensure complete dispersion of the sample. Then, measure the sample according to the GB / T19077-2016 / ISO 13320:2009 standard.

[0123] 3. 0.33C Capacity Test

[0124] The secondary battery was charged to 4.5V at a constant current of 0.33C under a constant temperature environment of 25℃, then charged at a constant voltage of 4.5V until the current dropped to 0.05C, and then discharged to 2.5V at a constant current of 0.33C to obtain a capacity of 0.33C.

[0125] 4. Cyclic performance test

[0126] The secondary battery was charged at a constant current of 0.33C to 4.4V under a constant temperature environment of 25℃, then charged at a constant voltage of 4.4V until the current dropped to 0.05C, and then discharged at a constant current of 0.33C to 2.8V, yielding the initial discharge capacity D1. This charging and discharging process was repeated until the 1000th cycle, yielding the discharge capacity D1000 after 1000 cycles. The capacity retention rate after 1000 cycles is calculated as D1000 / D1.

[0127] Capacity retention rate = discharge capacity after 1000 cycles (D1000) / discharge capacity in the first cycle (D1).

[0128] 5. Ratio Performance Test

[0129] The secondary battery was charged to 4.5V at a constant current of 0.33C under a constant temperature environment of 25℃, then charged at a constant voltage of 4.5V until the current dropped to 0.05C, and then discharged to 2.5V at a constant current of 0.33C to obtain a capacity of 0.33C. At 25℃, it was charged to 4.5V at a constant current of 2C, then charged at a constant voltage of 4.5V until the current dropped to 0.05C, and then discharged to 2.5V at a constant current of 0.33C to obtain a capacity of 2C.

[0130] The specific capacity retention rate of the secondary battery when the charging current changes from 0.33C to 2C is as follows:

[0131] Capacity retention rate = 2C capacity / 0.33C capacity.

[0132] 6. DC Impedance (DCR) Test

[0133] First, discharge the battery at 0.33C to 2.5V at 25℃. After resting for 30 minutes, charge it to 4.5V with a current of 0.33C, then maintain a constant voltage of 4.5V until the current is less than 0.05C. After resting for 30 minutes, discharge it to 2.5V with 0.33C. This gives the battery capacity C0. Next, charge the battery to 4.5V with a current of 0.33C, then maintain a constant voltage of 4.5V until the current is less than 0.05C. After resting for 30 minutes, discharge it to 0.5C0 capacity to adjust the battery to 50% SOC. After resting for 2 hours, the battery voltage is V1. Then discharge it with a current I (4C current) for 30 seconds. The battery voltage is V2. The DCR (in mΩ) of the battery can be obtained by using (V1-V2) / I*1000.

[0134] 7. Unit area capacity test

[0135] The area of ​​the prepared positive electrode sheet to be tested was cut into small circular pieces with a diameter of 12 mm. A lithium sheet was used as the counter electrode, and a polyethylene film as the separator. Electrolyte was injected to assemble a button cell. The button cell was charged at 0.1C to 4.55V, then charged at a constant voltage until the current dropped to 0.05C. After resting for 10 minutes, it was discharged at 0.1C to 2.0V and rested for 10 minutes. This process was repeated 3 times, and the capacity (mAh) of each charge-discharge cycle was recorded. The areal capacity A of the positive electrode sheet is calculated as: Third discharge capacity / 1.13, in mAh / cm². 2 .

[0136]

[0137]

[0138]

[0139] Table 3: Performance test results of Examples 1-13 and Comparative Examples 1-2

[0140] serial number 50% SOC DCR (mΩ) 2C / 0.33C capacity retention Capacity retention after 1000 cycles Example 1 2.5 87％ 85％ Example 2 2.3 88％ 86％ Example 3 2.2 90％ 88％ Example 4 2.3 90％ 88％ Example 5 2 92％ 90％ Example 6 2.7 86％ 84％ Example 7 2.3 88％ 86％ Example 8 2.6 85％ 82％ Example 9 2.8 83％ 80％ Example 10 2.4 86％ 86％ Example 11 2.2 90％ 90％ Example 12 3 85％ 83％ Example 13 2.9 85％ 82％ Comparative Example 1 3 84％ 80％ Comparative Example 2 3 84％ 81％

[0141] A brief analysis of Tables 1-3 above is as follows: Comparing Examples 1-3 with Comparative Example 1, it is evident that increasing the mass fraction of lithium nickel cobalt manganese oxide in the first positive electrode active material region 321 can reduce the DCR of the lithium-ion battery and improve its rate performance and cycle performance. Comparing Examples 1, 4-5, and 12, it is evident that increasing the width ratio of the first positive electrode active material region 321 can reduce the DCR of the lithium-ion battery and improve its rate performance and cycle performance. Comparing Examples 1, 6-7, and 13, it is evident that increasing the mass fraction of lithium nickel cobalt manganese oxide in the second positive electrode active material region 322 can reduce the DCR of the lithium-ion battery and improve its rate performance and cycle performance. Comparing Examples 1 and 8-9, it is evident that by including both lithium-rich manganese-based materials and lithium phosphate in the first positive electrode active material, compared to materials containing only lithium-rich manganese oxide... Lithium-manganese-based materials, or materials containing only lithium phosphate, can effectively reduce the DCR of lithium-ion batteries and improve their rate performance and cycle performance. Comparisons of Examples 1-13 and Comparative Example 2 show that by setting the mass fraction of lithium nickel cobalt manganese oxide in the first positive electrode active material region 321 to be greater than that in the second positive electrode active material region 322, the DCR of lithium-ion batteries can be reduced, and the rate performance and cycle performance can be improved. Comparisons of Examples 1, 10-11, and Comparative Example 2 show that, provided the mass fraction of lithium nickel cobalt manganese oxide in the first positive electrode active material region 321 is greater than that in the second positive electrode active material region 322, different structural formulas and different Dv50 values ​​of lithium-rich manganese-based materials, lithium phosphates, and lithium nickel cobalt manganese oxides can still reduce the DCR of lithium-ion batteries and improve their rate performance and cycle performance.

[0142] The above are merely embodiments of this application and do not limit the scope of this patent application. Any equivalent structural or procedural changes made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the scope of patent protection of this application.

Claims

1. A lithium-ion secondary battery, characterized in that, The device includes a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a current collector and a positive active material layer disposed on the surface of the current collector. The current collector includes a main body and a tab located on one side of the main body. The main body includes a first region and a second region, with the first region located between the second region and the tab. The positive electrode active material layer includes a positive electrode active material, which includes a first positive electrode active material and a second positive electrode active material. The first positive electrode active material includes one or two of lithium-rich manganese-based materials and lithium phosphate; the second positive electrode active material includes lithium nickel cobalt manganese oxide. The positive electrode active material layer includes a first positive electrode active material region and a second positive electrode active material region. The first positive electrode active material region is located in a first region, and the second positive electrode active material region is located in a second region. The mass fraction of the second positive electrode active material in the positive electrode active material in the first positive electrode active material region is greater than the mass fraction of the second positive electrode active material in the positive electrode active material in the second positive electrode active material region.

2. The lithium-ion secondary battery according to claim 1, characterized in that, The mass fraction of the second positive electrode active material in the positive electrode active material of the first positive electrode active material region is w1, where 55% ≤ w1 ≤ 70%.

3. The lithium-ion secondary battery according to claim 1 or 2, characterized in that, The mass fraction of the second positive electrode active material in the positive electrode active material in the second positive electrode active material region is w2, where 30% ≤ w2 ≤ 50%.

4. The lithium-ion secondary battery according to any one of claims 1 to 3, characterized in that, The width of the first positive electrode active material region accounts for 20% to 30% of the width of the main body of the current collector, and the width of the second positive electrode active material region accounts for 70% to 80% of the width of the main body of the current collector.

5. The lithium-ion secondary battery according to any one of claims 1 to 4, characterized in that, The lithium-rich manganese-based material includes materials with the structural formula nLi₂MnO₃·(1-n)LiNi. a Mn b M1 1-a-b The material of O2, wherein 0.1≤n≤0.3, 0.3≤a≤0.8, 0.2≤b≤0.5, and M1 includes one or more combinations of Na, Mg, Al, Ca, Ba, V, Zn, Ti, Fe, Co, Cr, Nb, W, Mo, Zr, Ta and Hf.

6. The lithium-ion secondary battery according to any one of claims 1 to 5, characterized in that, The lithium nickel cobalt manganese oxide includes a structure with the formula LiNi x Co y Mn z M2 1-x-y-z The material of O2 is 0.4≤x<0.7, 0.05<y<0.15, 0.15<z<0.55, and M2 includes one or more combinations of Al, Ti, Zr, W, Mo, Ba, and Nb.

7. The lithium-ion secondary battery according to any one of claims 1 to 6, characterized in that, The lithium phosphate includes the structural formula LiM3. c Fe 1-c The material of PO4, wherein 0≤c≤0.6, and M3 includes one or more combinations of Mn, Cr, Co, Cu, Ni, V, Mo, Ti, Zn, Al, Ga, Mg, B and Nb.

8. The lithium-ion secondary battery according to any one of claims 1 to 7, characterized in that, The compaction density of the first positive electrode active material region is 2.8 g / cm³. 3 ~3.0g / cm 3 , and / or The compaction density of the second positive electrode active material region is 2.8 g / cm³. 3 ~3.0g / cm 3 .

9. The lithium-ion secondary battery according to any one of claims 1 to 8, characterized in that, The areal capacity per unit area of ​​the first positive electrode active material region is equal to that of the second positive electrode active material region.

10. The lithium-ion secondary battery according to any one of claims 1 to 9, characterized in that, The volume average particle size Dv50 of the lithium-rich manganese-based material is 4 μm to 10 μm; and / or, The volume average particle size Dv50 of the lithium phosphate is 100 nm to 500 nm; and / or, The volume average particle size Dv50 of the lithium nickel cobalt manganese oxide is 3 μm to 6 μm.

11. An electrical appliance, characterized in that, Including the lithium-ion secondary battery as described in any one of claims 1 to 10.

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