Electrochemical devices and electronic devices

Abstract

An electrochemical device and an electronic device, the electrochemical device comprising a positive electrode, a negative electrode and an electrolyte, the positive electrode comprising a positive electrode active material layer, the positive electrode active material layer comprising a first powder and a second powder, wherein, after the electrochemical device is fully discharged, an X-ray diffraction analysis spectrum of the positive electrode active material layer has a first diffraction peak at a position of diffraction angle 2θ of 17.3° to 19.3°, and has a second diffraction peak at a position of diffraction angle 2θ of 19.8° to 21.8°. The electrochemical device has both high discharge specific capacity and long cycle life.

Description

Technical Field

[0001] This application belongs to the field of electrochemical technology, specifically relating to an electrochemical device and an electronic device. Background Technology

[0002] Electrochemical devices such as lithium-ion batteries are widely used in all aspects of modern life due to their advantages such as high operating voltage, long cycle life, environmental friendliness, and light weight. In recent years, lithium-ion batteries have seen rapid development in the fields of new energy vehicles and large-scale energy storage. With the accelerating popularization of new energy vehicles, the demand for longer driving ranges has placed higher requirements on the energy density and cycle performance of batteries. For example, in current lithium-ion batteries, materials such as lithium iron phosphate are widely used as cathode materials due to their excellent cycle performance and safety performance. However, compared with nickel-cobalt-manganese ternary materials, lithium iron phosphate and other materials have a much lower energy density, resulting in a reduction in the driving range of new energy vehicles. Therefore, further research is needed on cathode active materials that can improve battery energy density and cycle performance. Summary of the Invention

[0003] The purpose of this application is to provide an electrochemical device and an electronic device, which aim to improve the discharge specific capacity of the electrochemical device, giving it a higher energy density and enhancing its cycle performance.

[0004] This application provides an electrochemical device comprising: a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a positive electrode active material layer, which comprises a first powder and a second powder. After full discharge, the X-ray diffraction pattern of the positive electrode active material layer exhibits a first diffraction peak at a diffraction angle 2θ of 17.3° to 19.3° and a second diffraction peak at a diffraction angle 2θ of 19.8° to 21.8°. The first powder comprises iron, and the second powder comprises manganese. The first diffraction peak corresponds to the second powder, and the second diffraction peak corresponds to the first powder. The second powder with the first diffraction peak can provide a higher specific capacity, while the first powder with the second diffraction peak can provide good structural stability and charge-discharge reversibility. The two powders can play a good synergistic effect in the positive electrode active material layer, so that the positive electrode active material layer has high specific capacity, better structural stability and charge-discharge reversibility, improve the discharge specific capacity and energy density of the electrochemical device and enhance its cycle performance.

[0005] In any embodiment of this application, the peak intensity I of the first diffraction peak A The peak intensity I of the second diffraction peak B Satisfy: 0 < I A / I B ≤0.3, preferably, 0.05≤I A / IB ≤0.25. When the peak intensity IA of the first diffraction peak is equal to the peak intensity I of the second diffraction peak... B When the above relationship is satisfied, it indicates that the structure and content of the second powder and the structure and content of the first powder satisfy a certain relationship. At this time, the second powder and the first powder have a better synergistic effect, which ensures ion transport inside the electrochemical device and improves electrical performance, effectively improves the discharge specific capacity of the electrochemical device and enhances its cycle performance, so that it has a higher energy density.

[0006] In any embodiment of this application, the mass percentage ω of manganese element is based on the mass of the positive electrode active material layer. Mn With the mass percentage of iron ω Fe Satisfy: 0.01% ≤ ω Mn / ω Fe ≤30%, preferably, 0.05%≤ω Mn / ω Fe ≤25%. Manganese content (ω) by mass. Mn The higher the ω, the higher the mass percentage of the second powder in the positive electrode active material. Since the second powder has a high specific capacity, the electrochemical device exhibits a high discharge specific capacity. Mn / ω Fe Within the aforementioned range, the cycle performance of electrochemical devices can be effectively improved and their discharge specific capacity increased, resulting in higher energy density.

[0007] In any embodiment of this application, the second powder has a stepped morphology. In the positive electrode active material layer, the second powder with a stepped morphology can better combine with the first powder with an olivine structure, improving the uniformity of the positive electrode active material layer, which is beneficial for the insertion and extraction of active ions, further improving the discharge specific capacity of the electrochemical device and giving it a higher energy density.

[0008] In any embodiment of this application, the second powder contains element M, wherein element M includes at least one selected from Al, Ti, Cr, Ce, Nb, Y, and Mg. Adding element M to the second powder can enhance the stability of manganese-oxygen bonds, inhibit manganese dissolution, and further improve the cycle performance of the electrochemical device. Simultaneously, element M can also increase the content of extractable active ions in the second powder, further enhancing the discharge specific capacity of the electrochemical device and giving it a higher energy density.

[0009] In any embodiment of this application, the mass percentage ω of element M is determined based on the mass of the second powder. M With the mass percentage of manganese ω Mn Satisfy: 0.01% < ω M / ω Mn≤4%, preferably, 0.02% < ω M / ω Mn ≤3.5%. The mass percentage ω of element M. M With the mass percentage of manganese ω Mn When the ratio is within a suitable range, it is beneficial to further improve the stability of manganese-oxygen bonds and inhibit the dissolution of manganese; it is also beneficial to keep the content of active ions that can be inserted and removed in the second powder within a suitable range, further improving the discharge specific capacity of the electrochemical device and enhancing the cycle performance of the electrochemical device, so that the electrochemical device has a high energy density.

[0010] In any embodiment of this application, the compaction density of the positive electrode active material layer is 2.0 g / cm³. 3 Up to 2.8 g / cm 3 The preferred value is 2.2 g / cm³. 3 Up to 2.6 g / cm 3 Controlling the compaction density of the positive electrode active material layer within a suitable range is beneficial for further improving the cycle performance and discharge specific capacity of the electrochemical device.

[0011] In any embodiment of this application, the single-sided coating weight of the positive electrode active material layer is 100 mg / 1540.25 mm. 2 Up to 500mg / 1540.25mm 2 The preferred concentration is 150mg / 1540.25mm. 2 Up to 450mg / 1540.25mm 2 Controlling the single-sided coating weight of the positive electrode active material layer within a suitable range is beneficial for further improving the cycle performance and discharge specific capacity of the electrochemical device.

[0012] In any embodiment of this application, the electrolyte contains an additive, which includes at least one of unsaturated carbonates and sulfur-containing oxygen double bond compounds; based on the mass of the electrolyte, the mass percentage of the additive is 0.01% to 5%. When the additive is added to the electrolyte of this application, the additive can decompose on the surface of the positive electrode to form an interfacial protective film, improving the oxidation resistance of the positive electrode active material and further enhancing the cycle performance of the electrochemical device; the additive can also form a dense and stable interfacial film on the surface of the negative electrode active material, helping to reduce the ion transport impedance at the negative electrode interface, and further enhancing the cycle performance of the electrochemical device. When the mass percentage of the additive in the electrolyte is within a suitable range, it can effectively improve the cycle performance of the electrochemical device.

[0013] In any embodiment of this application, the unsaturated carbonate includes at least one of vinylene carbonate and ethylene ethylene carbonate;

[0014] In any embodiment of this application, the sulfur-containing oxygen double bond compound includes at least one of 1,3-propanesulfonate lactone, propenesulfonate lactone, and vinylene sulfate.

[0015] In any embodiment of this application, the mass percentage of the additive is 0.05% to 4% based on the mass of the electrolyte.

[0016] A second aspect of this application provides an electronic device that includes the electrochemical device of the first aspect of this application.

[0017] In this application, the positive electrode active material layer includes a first powder and a second powder. After the electrochemical device is fully discharged, the X-ray diffraction pattern of the positive electrode active material layer shows a first diffraction peak at a diffraction angle of 2θ between 17.3° and 19.3°, and a second diffraction peak at a diffraction angle of 2θ between 19.8° and 21.8°. The first powder includes iron, and the second powder includes manganese. The second powder with the first diffraction peak provides higher specific capacity, while the first powder with the second diffraction peak provides good structural stability and charge-discharge reversibility. The two powders exhibit a good synergistic effect in the positive electrode active material layer, resulting in high specific capacity, superior structural stability, and charge-discharge reversibility, thereby improving the discharge specific capacity and energy density of the electrochemical device and enhancing its cycle performance. Attached Figure Description

[0018] Figure 1 This is the X-ray diffraction spectrum of the positive electrode active material layer in Example 1.

[0019] Figure 2 This is an enlarged X-ray diffraction pattern of the positive electrode active material layer in Example 1. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of this application. The embodiments described herein are illustrative in nature and are used to provide a basic understanding of this application. The embodiments of this application should not be construed as limiting this application. Based on the technical solutions and embodiments provided in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0021] For the sake of brevity, this article only discloses a few specific numerical ranges. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, just as any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value or with other lower or upper limits to form an unspecified range.

[0022] In this description, unless otherwise stated, "above" and "below" include the stated number.

[0023] Unless otherwise stated, the terms used in this application have their common meanings as commonly understood by those skilled in the art. Unless otherwise stated, the values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this application).

[0024] The list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms can mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another instance, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single component or multiple components. Item B may contain a single component or multiple components. Item C may contain a single component or multiple components.

[0025] In existing lithium-ion batteries that use lithium iron phosphate as the cathode material, due to the poor conductivity of lithium iron phosphate, the high capacity of lithium-ion batteries is generally achieved by reducing the particle size of lithium iron phosphate. However, the smaller particle size results in a smaller compaction of lithium iron phosphate material, which leads to a decrease in battery energy density.

[0026] To address the aforementioned issues, the inventors conducted extensive research that effectively improved the discharge specific capacity of the cathode material and the compaction density of the cathode sheet, thereby significantly enhancing the energy density and cycle performance of the electrochemical device.

[0027] Electrochemical device

[0028] A first aspect of this application provides an electrochemical device, including any device in which an electrochemical reaction occurs to interconvert chemical energy and electrical energy, specific examples of which include, but are not limited to, lithium-ion batteries or sodium-ion batteries.

[0029] The electrochemical device of this application includes a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a positive electrode active material layer, which includes a first powder and a second powder. After the electrochemical device is fully discharged, the X-ray diffraction pattern of the positive electrode active material layer has a first diffraction peak at a diffraction angle 2θ of 17.3° to 19.3° and a second diffraction peak at a diffraction angle 2θ of 19.8° to 21.8°.

[0030] In this application, a fully discharged electrochemical device refers to an electrochemical device that is charged at a constant current of 0.2C to 3.65V, then charged at a constant voltage to a current of 0.05C, left to stand for 5 minutes, and then discharged at a constant current of 0.2C to 2.5V. After repeating the above charge and discharge process twice, the resulting electrochemical device is in a fully discharged state.

[0031] In the electrochemical device of this application, the X-ray diffraction pattern of the positive electrode active material layer exhibits a first diffraction peak at a diffraction angle 2θ of 17.3° to 19.3° and a second diffraction peak at a diffraction angle 2θ of 19.8° to 21.8°. The first diffraction peak corresponds to the second powder, and the second diffraction peak corresponds to the first powder. The second powder with the first diffraction peak provides higher specific capacity, while the first powder with the second diffraction peak provides good structural stability and charge-discharge reversibility. The two powders exhibit a good synergistic effect in the positive electrode active material layer, resulting in high specific capacity, superior structural stability, and charge-discharge reversibility. This improves the discharge specific capacity of the electrochemical device, giving it higher energy density and enhanced cycle performance.

[0032] In the electrochemical device of this application, the first powder comprises iron, and the second powder comprises manganese. In this application, the first powder in the positive electrode active material layer comprises an olivine structure, which is relatively stable and exhibits minimal volume change during the charge-discharge process of the electrochemical device. This means that the insertion and extraction of active ions such as lithium ions have minimal impact on the structure of the first powder, resulting in good charge-discharge reversibility. The second powder in the positive electrode active material layer has a high specific capacity, enabling the electrochemical device to have a high discharge specific capacity. The electrochemical device of this application can fully utilize the synergistic effect between the first and second powders in the positive electrode active material layer. During the charge-discharge process of the electrochemical device, active lithium in the second powder is extracted. A portion of the active lithium can be deposited on the negative electrode, effectively compensating for the irreversible loss of active lithium on the surface of the negative electrode active material caused by repairing the SEI film. The remaining active lithium can be inserted into the first powder, effectively improving the cycle performance of the electrochemical device.

[0033] In some embodiments, the peak intensity I of the first diffraction peak A The peak intensity I of the second diffraction peak BSatisfy: 0 < I A / I B ≤0.3. For example, the peak intensity I of the first diffraction peak. A The peak intensity I of the second diffraction peak B Satisfy: 0.05≤I A / I B ≤0.3, 0.1≤I A / I B ≤0.3, 0.15≤I A / I B ≤0.3, 0.2≤I A / I B ≤0.3, 0.25≤I A / I B ≤0.3, 0.05≤I A / I B ≤0.25, 0.1≤I A / I B ≤0.25, 0.15≤I A / I B ≤0.25, 0.2≤I A / I B ≤0.25, 0.05≤I A / I B ≤0.2, 0.1≤I A / I B ≤0.2, 0.15≤I A / I B ≤0.2, 0.05≤I A / I B ≤0.15 or 0.05≤I A / I B ≤0.1. Preferably, the peak intensity I of the first diffraction peak is... A The peak intensity I of the second diffraction peak B Satisfy: 0.05≤I A / I B ≤0.25.

[0034] In this application, the peak intensity I of the first diffraction peak A Peak intensity I of the second diffraction peak B The ratio is related to the structure and content of the second powder and the structure and content of the first powder. When the peak intensity I of the first diffraction peak... A The peak intensity I of the second diffraction peak BWhen the above relationship is satisfied, it indicates that the structure and content of the second powder and the structure and content of the first powder satisfy a certain relationship. At this time, the second powder and the first powder have a better synergistic effect. The active lithium in the second powder can not only effectively compensate for the loss of active lithium on the surface of the negative electrode active material, but also efficiently embed into the first powder, ensuring ion transport inside the electrochemical device and improving electrical performance, effectively improving the discharge specific capacity of the electrochemical device and enhancing its cycle performance.

[0035] In this application, the X-ray diffraction pattern of the positive electrode active material layer and the peak intensities of the first and second diffraction peaks have meanings known in the art and can be tested using methods known in the art. For example, the lithium-ion battery is charged at a constant current of 0.2C to 3.65V, then charged at a constant voltage to a current of 0.05C, left to stand for 5 minutes, and then discharged at a constant current of 0.2C to 2.5V. This charging and discharging process is repeated twice (at which point the battery is in a fully discharged state). After completion, the lithium-ion battery is disassembled, the positive electrode is removed, and the positive electrode is immersed in dimethyl carbonate (DMC) for 30 minutes to remove the electrolyte and byproducts on the surface of the positive electrode. Then, it is dried in a fume hood for 4 hours, and the dried positive electrode active material layer is scraped off with a scraper to obtain the positive electrode active material layer powder. The positive electrode active material powder was placed in the sample stage of an XRD instrument (model Bruker D8). A scan rate of 2° / min and a scan angle range of 10° to 90° were used to obtain the XRD diffraction pattern. The peak positions and intensities of the first and second diffraction peaks of the positive electrode active material were calculated from the XRD diffraction pattern to obtain I0. A / I B .

[0036] In some embodiments, the mass percentage ω of manganese element is determined based on the mass of the positive electrode active material. Mn With the mass percentage of iron ω Fe Satisfy: 0.01% ≤ ω Mn / ω Fe ≤30%. For example, the mass percentage of manganese ω Mn With the mass percentage of iron ω Fe Satisfy: 0.05% ≤ ω Mn / ω Fe ≤30%, 0.1%≤ω Mn / ω Fe ≤30%, 0.5%≤ω Mn / ω Fe ≤30%, 1%≤ω Mn / ω Fe ≤30%, 5%≤ω Mn / ω Fe ≤30%, 10%≤ω Mn / ω Fe ≤30%, 15%≤ωMn / h Fe ≤30%,20%≤ω Mn / h Fe ≤30%,25%≤ω Mn / h Fe ≤30%,0.05%≤ω Mn / h Fe ≤25%,0.1%≤ω Mn / h Fe ≤25%,0.5%≤ω Mn / h Fe ≤25%,1%≤ω Mn / h Fe ≤25%,5%≤ω Mn / h Fe ≤25%,10%≤ω Mn / h Fe ≤25%,15%≤ω Mn / h Fe ≤25%,20%≤ω Mn / h Fe ≤25%,0.05%≤ω Mn / h Fe ≤20%,0.1%≤ω Mn / h Fe ≤20%,0.5%≤ω Mn / h Fe ≤20%,1%≤ω Mn / h Fe ≤20%,5%≤ω Mn / h Fe ≤20%,10%≤ω Mn / h Fe ≤20%,15%≤ω Mn / h Fe ≤20%,0.05%≤ω Mn / h Fe ≤15%,0.1%≤ω Mn / h Fe ≤15%,0.5%≤ω Mn / h Fe ≤15%,1%≤ω Mn / h Fe ≤15%,5%≤ω Mn / h Fe ≤15%,10%≤ω Mn / h Fe ≤15%,0.05%≤ω Mn / h Fe ≤10%,0.1%≤ω Mn / h Fe ≤10%,0.5%≤ωMn / ω Fe ≤10%, 1%≤ω Mn / ω Fe ≤10%, 5%≤ω Mn / ω Fe ≤10%, 0.05%≤ω Mn / ω Fe ≤5%, 0.1%≤ω Mn / ω Fe ≤5%, 0.5%≤ω Mn / ω Fe ≤5%, 1%≤ω Mn / ω Fe ≤5%, 0.05%≤ω Mn / ω Fe ≤1%, 0.1%≤ω Mn / ω Fe ≤1% or 0.05% ≤ω Mn / ω Fe ≤0.1%. Preferably, the mass percentage of manganese is ω. Mn With the mass percentage of iron ω Fe Satisfy: 0.05% ≤ ω Mn / ω Fe ≤25%.

[0037] In this application, the mass percentage of manganese element ω Mn With the mass percentage of iron ω Fe These represent the mass percentages of the second and first powders in the positive electrode active material layer, respectively. The mass percentage of manganese is ω. Mn A higher percentage indicates a higher mass content of the second powder in the positive electrode active material layer. Based on the higher specific capacity of the second powder, the electrochemical device exhibits a higher discharge specific capacity. Not intending to be limited by any theory, the inventors discovered that because the active lithium in the second powder is released and deposited onto the negative electrode during the cycling process of the electrochemical device, compensating for the loss of active lithium on the surface of the negative electrode active material, a higher mass percentage of the second powder in the positive electrode active material layer provides more readily available active lithium. This not only effectively compensates for the loss of active lithium on the surface of the negative electrode active material but also allows sufficient active lithium to be reinserted into the first powder, ensuring the transport of active ions and effectively improving the cycle capacity retention rate of the electrochemical device, thus enhancing its cycle performance.

[0038] Not intending to be limited by any theory, the inventors also discovered that the mass percentage of the second powder should not be too high compared to the first powder. When the mass percentage of the second powder is too high, it can provide too much lithium that can be extracted and compensated. When this exceeds the amount of lithium that can be re-intercalated into the positive electrode active material layer, it leads to increased internal resistance and reduces the discharge specific capacity of the electrochemical device. Therefore, by adjusting the mass percentage of the second powder and the first powder in the positive electrode active material layer, i.e., the mass percentage of manganese ω... Mn With the mass percentage of iron ω Fe By controlling the energy within the above range, the cycle performance of the electrochemical device can be effectively improved and its discharge specific capacity increased, giving it a higher energy density.

[0039] In some embodiments, the second powder has a stepped morphology. In the positive electrode active material layer, the second powder with a stepped morphology can better combine with the first powder, which includes an olivine structure, improving the uniformity of the positive electrode active material layer, which is beneficial for the insertion and extraction of active ions, and can further improve the discharge specific capacity of the electrochemical device, giving it a higher energy density.

[0040] In this application, the morphology of the second powder can be measured by the following method: disassembling a lithium-ion battery to obtain a positive electrode sheet, drying the positive electrode sheet, performing liquid nitrogen brittle fracture on the dried positive electrode sheet, and then observing the cross-section of the positive electrode sheet (i.e., the cross-section in the thickness direction of the positive electrode active material layer) using a scanning electron microscope (SEM) to observe and analyze the morphology of the second powder. In some embodiments, the second powder contains element M, wherein element M includes at least one of Al, Ti, Cr, Ce, Nb, Y, and Mg. After adding element M to the second powder, element M can improve the stability of manganese-oxygen bonds. The improved stability of manganese-oxygen bonds can inhibit the dissolution of manganese, further improving the cycle performance of the electrochemical device. At the same time, element M can also increase the content of lithium that can be extracted and intercalated in the second powder, so that there is enough lithium in the second powder to be extracted to compensate for the loss of active lithium on the surface of the negative electrode active material, while there is still enough active lithium to be intercalated back into the positive electrode active material layer, further improving the discharge specific capacity of the electrochemical device and giving it a higher energy density.

[0041] The positive electrode sheet is obtained by disassembling the lithium-ion battery. The positive electrode sheet is dried and then subjected to liquid nitrogen embrittlement to obtain the cross section. The cross section of the positive electrode sheet (i.e., the cross section in the thickness direction of the positive electrode active material layer) is then observed using a scanning electron microscope (SEM). The second powder can be observed and analyzed. The type and content of M element and Mn element in the second powder are analyzed using an elemental analyzer (EDS).

[0042] In some embodiments, the mass percentage ω of element M is determined based on the mass of the second powder.M With the mass percentage of manganese ω Mn Satisfy: 0.01% < ω M / ω Mn ≤4%. For example, the mass percentage ω of element M. M With the mass percentage of manganese ω Mn Satisfy: 0.05% ≤ ω M / ω Mn ≤4%, 0.1%≤ω M / ω Mn ≤4%, 0.5%≤ω M / ω Mn ≤4%, 1%≤ω M / ω Mn ≤4%, 1.5%≤ω M / ω Mn ≤4%, 2%≤ω M / ω Mn ≤4%, 2.5%≤ω M / ω Mn ≤4%, 3%≤ω M / ω Mn ≤4%, 3.5%≤ω M / ω Mn ≤4%, 0.05%≤ω M / ω Mn ≤3.5%, 0.1%≤ω M / ω Mn ≤3.5%, 0.5%≤ω M / ω Mn ≤3.5%, 1%≤ω M / ω Mn ≤3.5%, 1.5%≤ω M / ω Mn ≤3.5%, 2%≤ω M / ω Mn ≤3.5%, 2.5%≤ω M / ω Mn ≤3.5%, 3%≤ω M / ω Mn ≤3.5%, 0.05%≤ω M / ω Mn ≤3%, 0.1%≤ω M / ω Mn ≤3%, 0.5%≤ω M / ω Mn ≤3%, 1%≤ω M / ω Mn ≤3%, 1.5%≤ω M / ω Mn ≤3%, 2%≤ω M / ωMn ≤3%, 2.5%≤ω M / ω Mn ≤3%, 0.05%≤ω M / ω Mn ≤2.5%, 0.1%≤ω M / ω Mn ≤2.5%, 0.5%≤ω M / ω Mn ≤2.5%, 1%≤ω M / ω Mn ≤2.5%, 1.5%≤ω M / ω Mn ≤2.5%, 2%≤ω M / ω Mn ≤2.5%, 0.05%≤ω M / ω Mn ≤2%, 0.1%≤ω M / ω Mn ≤2%, 0.5%≤ω M / ω Mn ≤2%, 1%≤ω M / ω Mn ≤2%, 1.5%≤ω M / ω Mn ≤2%, 0.05%≤ω M / ω Mn ≤1.5%, 0.1%≤ω M / ω Mn ≤1.5%, 0.5%≤ω M / ω Mn ≤1.5%, 1%≤ω M / ω Mn ≤1.5%, 0.05%≤ω M / ω Mn ≤1%, 0.1%≤ω M / ω Mn ≤1%, 0.5%≤ω M / ω Mn ≤1%. Preferably, the mass percentage ω of element M is... M With the mass percentage of manganese ω Mn Satisfy: 0.02% < ω M / ω Mn ≤3.5%.

[0043] Mass percentage of element M ω M With the mass percentage of manganese ω MnWhen the ratio is within a suitable range, it is beneficial to further improve the stability of manganese-oxygen bonds and inhibit the dissolution of manganese. It is also beneficial to keep the content of lithium that can be inserted and extracted in the second powder within a suitable range. This ensures that there is enough lithium in the second powder to compensate for the loss of active lithium on the surface of the negative electrode active material, and that there is enough active lithium to be reinserted into the positive electrode active material layer, thereby further improving the discharge specific capacity of the electrochemical device, giving it a higher energy density, and improving the cycle performance of the electrochemical device.

[0044] In some embodiments, the compaction density of the positive electrode active material layer is 2.0 g / cm³. 3 Up to 2.8 g / cm 3 For example, the compaction density of the positive electrode active material layer is 2.1 g / cm³. 3 2.2g / cm 3 2.3g / cm 3 2.4g / cm 3 2.5g / cm 3 2.6g / cm 3 2.7g / cm 3 Or within any of the above values. Preferably, the compaction density of the positive electrode active material layer is 2.2 g / cm³. 3 Up to 2.6 g / cm 3 .

[0045] In some embodiments, the single-sided coating weight of the positive electrode active material layer is 100 mg / 1540.25 mm. 2 Up to 500mg / 1540.25mm 2 For example, the single-sided coating weight of the positive electrode active material layer is 100 mg / 1540.25 mm. 2 150mg / 1540.25mm 2 200mg / 1540.25mm 2 250mg / 1540.25mm 2 3100mg / 1540.25mm 2 350mg / 1540.25mm 2 400mg / 1540.25mm 2 450mg / 1540.25mm 2 500mg / 1540.25mm 2 Or within any of the above values. Preferably, the single-sided coating weight of the positive electrode active material layer is 150 mg / 1540.25 mm. 2 Up to 450mg / 1540.25mm 2 .

[0046] After adding a second powder with a stepped morphology to the positive electrode active material layer, the contact between the positive electrode active materials can be tighter, which can improve the compaction density of the positive electrode active material layer, thereby enabling the electrochemical device to have a higher energy density. Controlling the single-sided coating weight and compaction density of the positive electrode active material layer within a suitable range is beneficial to the migration of electrons and active ions, thereby further improving the cycle performance of the electrochemical device and increasing its discharge specific capacity.

[0047] In this application, the compaction density and single-sided coating weight of the positive electrode active material layer have meanings known in the art and can be tested using methods known in the art. For example, the dried positive electrode sheet is cut to an area of ​​1540.25 mm². 2 Five positive electrode sheets were prepared. The thickness of each positive electrode sheet was measured using a micrometer and recorded as d0 cm. The positive active material layer was scraped off from the positive electrode sheet using a scraper, and its mass was measured using a balance and recorded as m (mg). This mass represents the positive active material layer, which is 1540.25 mm thick. 2 The mass in terms of area; the thickness of the positive electrode current collector after removing the positive electrode active material layer is measured with a micrometer and recorded as dcm. The compaction density of the positive electrode active material layer is calculated according to the following formula: Compaction density P = m / [154.025 × (d0 - d)]. The compaction density of the positive electrode active material layer is the average of the compaction densities of the positive electrode active material layers in the 5 positive electrode sheets obtained above. The single-sided coating weight of the positive electrode active material layer is the average of the mass of the positive electrode active material layer in the 5 positive electrode sheets obtained above.

[0048] In some embodiments, the first powder includes, but is not limited to, lithium iron phosphate and a composite material of lithium iron phosphate and carbon.

[0049] In some embodiments, as an example, the second powder can be prepared by the following method: MnOOH is placed in an alumina crucible and heated to 500°C at a heating rate of 5°C / min under an air atmosphere and held at a constant temperature for 1 hour to obtain anhydrous Mn3O4. Anhydrous Mn3O4 and LiOH are weighed in a Li:Mn molar ratio of 1.05:1, and nano-Cr2O3 is added in a Cr:Mn elemental mass ratio of 0.008:1. The mixture is then homogenized using a sand mill to obtain a mixed precursor. The precursor is placed in an alumina crucible and heated at a rate of 2 m... 3 Nitrogen gas is introduced at a rate of 1 h, and the temperature is increased to 940℃ at a rate of 5℃ / min and maintained at a constant temperature for 10 h. After natural cooling to room temperature, a second powder containing manganese is obtained. Mn3O4 can also be replaced with MnO2, and the ratio with LiOH is adjusted according to the Mn content.

[0050] In some embodiments, the positive electrode active material layer may optionally include a conductive agent and a binder. The specific types of conductive agents and binders are not specifically limited and can be selected according to requirements. As examples, conductive agents include, but are not limited to, at least one of conductive graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. As examples, binders include, but are not limited to, at least one of styrene-butadiene rubber (SBR), water-based acrylic resin, carboxymethyl cellulose (CMC), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl butyral (PVB), ethylene-vinyl acetate copolymer (EVA), and polyvinyl alcohol (PVA).

[0051] In this application, the positive electrode is a positive electrode sheet, the positive electrode sheet further includes a positive electrode current collector, and the positive electrode active material layer is disposed on at least one surface of the positive electrode current collector.

[0052] In some embodiments, the positive current collector can be a metal foil or a porous metal plate, such as a foil or porous plate of metals or alloys thereof, such as aluminum, copper, nickel, titanium, silver, etc. As an example, the positive current collector is aluminum foil.

[0053] In some embodiments, the positive electrode current collector has two surfaces opposite each other in its thickness direction, and the positive electrode active material layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector. When the positive electrode active material layer is disposed on both surfaces of the positive electrode current collector, if the parameters of the positive electrode active material layer on either surface meet the parameter range of this application, it is considered to fall within the protection scope of this application.

[0054] The positive electrode sheet can be prepared according to conventional methods in the art. Typically, a first powder, a second powder, and optional conductive agents and binders are dispersed in a solvent, such as N-methylpyrrolidone (NMP), to form a uniform positive electrode slurry. The positive electrode slurry is then coated onto a positive electrode current collector, and the positive electrode sheet is obtained through processes such as drying and cold pressing.

[0055] The positive electrode sheet of this application does not exclude other positive electrode active materials besides the first powder and the second powder. The specific types of other positive electrode active materials are not specifically limited and can be selected according to requirements. As an example, other positive electrode active materials include, but are not limited to, at least one of lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, lithium manganese iron phosphate and carbon composites, and their respective modified compounds.

[0056] The positive electrode sheet of this application does not exclude other additional functional layers besides the positive electrode active material layer. For example, in some embodiments, the positive electrode sheet of this application further includes a conductive undercoat (e.g., composed of a conductive agent and a binder) sandwiched between the positive electrode current collector and the positive electrode active material layer and disposed on the surface of the positive electrode current collector. In other embodiments, the positive electrode sheet of this application further includes a protective layer covering the surface of the positive electrode active material layer.

[0057] In this application, the electrolyte plays a role in conducting active ions between the positive and negative electrodes.

[0058] In some embodiments, the electrolyte contains additives, including at least one of unsaturated carbonates and sulfur-containing oxygen double bond compounds.

[0059] As an example, the additives include, but are not limited to, at least one of vinylene carbonate (VC), vinyl ethylene carbonate (VEC), vinyl sulfate (DTD), propylene sulfate, vinyl sulfite (ES), 1,3-propanesulfonate lactone (PS), and propylene-1,3-sulfonate lactone (PES).

[0060] When the additive is added to the electrolyte of this application, the additive can decompose on the surface of the positive electrode to form an interfacial protective film, improve the oxidation resistance of the positive electrode active material layer, stabilize the structure of the positive electrode active material, and reduce the side reactions between the positive electrode active material layer and the electrolyte, thereby further improving the cycle performance of the electrochemical device; the additive can also form a dense and stable interfacial film on the surface of the negative electrode active material, which helps to reduce the ion transport impedance of the negative electrode interface, and can also further improve the cycle performance of the electrochemical device.

[0061] In some embodiments, the mass percentage of the additive is from 0.01% to 5% based on the mass of the electrolyte. For example, the mass percentage of the additive is 0.05%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 4%, or within any range of the above values. Preferably, the mass percentage of the additive is from 0.5% to 3%.

[0062] When the mass percentage of additives in the electrolyte is within a suitable range, it helps to form an interfacial protective film of appropriate thickness on the material surface, while also exhibiting low impedance, which is beneficial for improving the cycle performance of the electrochemical device. If the mass percentage of additives is too low, the interfacial protective film will be insufficiently formed, affecting the performance of the electrochemical device; if the mass percentage of additives is too high, it will increase the impedance of the electrolyte and decrease the migration rate of active ions, affecting the cycle performance of the electrochemical device.

[0063] In some embodiments, the electrolyte further includes an organic solvent, a lithium salt, and other optional electrolyte additives. The types of organic solvents, lithium salts, and other optional electrolyte additives are not specifically limited and can be selected as needed.

[0064] In some embodiments, as examples, the lithium salt includes, but is not limited to, at least one of LiPF6 (lithium hexafluorophosphate), LiBF4 (lithium tetrafluoroborate), LiClO4 (lithium perchlorate), LiAsF6 (lithium hexafluoroarsenate), LiFSI (lithium bis(fluorosulfonyl)imide), LiTFSI (lithium bis(trifluoromethanesulfonyl)imide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluorooxalate borate), LiBOB (lithium dioxalate borate), LiPO2F2 (lithium difluorophosphate), LiDFOP (lithium difluorodioxalate phosphate), and LiTFOP (lithium tetrafluorooxalate phosphate). One of the above lithium salts may be used alone, or two or more may be used simultaneously.

[0065] In some embodiments, as examples, the organic solvent includes, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE). One of the above organic solvents may be used alone, or two or more may be used simultaneously. Optionally, two or more of the above organic solvents may be used simultaneously.

[0066] In some embodiments, the other optional electrolyte additives may include electrolyte additives that can improve certain battery performance, such as electrolyte additives that improve battery overcharge performance, electrolyte additives that improve battery high-temperature or low-temperature performance, etc.

[0067] The electrolyte can be prepared according to conventional methods in the art. For example, an organic solvent, lithium salt, additives, and other optional electrolyte additives can be mixed evenly to obtain an electrolyte. There are no particular restrictions on the order of addition of the materials. For example, the lithium salt, additives, and other optional electrolyte additives can be added to the organic solvent and mixed evenly to obtain an electrolyte; or, the lithium salt can be added to the organic solvent first, and then the additives and other optional electrolyte additives can be added to the organic solvent and mixed evenly to obtain an electrolyte.

[0068] In this application, the negative electrode is a negative electrode sheet, which can be a lithium metal sheet or an electrode sheet comprising a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The negative electrode active material layer typically comprises a negative electrode active material and optionally a conductive agent, a binder, and a thickener.

[0069] The materials, composition, and manufacturing methods of the negative electrode used in this application may include any techniques known in the prior art.

[0070] The specific type of negative electrode active material is not limited and can be selected according to requirements. For example, negative electrode active materials include, but are not limited to, natural graphite, artificial graphite, mesophase microcarbon spheres (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composites, SiO, Li-Sn alloys, Li-Sn-O alloys, Sn, SnO, SnO2, and spinel-structured Li4Ti5O. 12 At least one of Li-Al alloys.

[0071] The specific type of conductive agent is not limited and can be selected according to needs. As an example, conductive agents include, but are not limited to, at least one of conductive graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0072] The specific type of adhesive is not limited and can be selected according to requirements. As an example, adhesives include, but are not limited to, at least one of styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl butyral (PVB), water-based acrylic resin, and carboxymethyl cellulose.

[0073] The specific type of thickener is not limited and can be selected according to needs. As an example, thickeners include, but are not limited to, sodium carboxymethyl cellulose (CMC).

[0074] However, this application is not limited to the above-mentioned materials. The negative electrode sheet of this application may also use other known materials that can be used as negative electrode active materials, conductive agents, binders and thickeners.

[0075] In some embodiments, the negative electrode current collector has two surfaces opposite each other in its 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.

[0076] The negative electrode current collector can be made of metal foil or porous metal plate, such as foil or porous plate of metals or alloys thereof, such as copper, nickel, titanium, iron, etc. As an example, the negative electrode current collector is copper foil.

[0077] The negative electrode sheet can be prepared according to conventional methods in the art. Typically, the negative electrode active material and optional conductive agent, binder and thickener are dispersed in a solvent, which can be N-methylpyrrolidone (NMP) or deionized water, to form a uniform negative electrode slurry. The negative electrode slurry is then coated onto the negative electrode current collector, and the negative electrode sheet is obtained through processes such as drying and cold pressing.

[0078] The negative electrode sheet of this application does not exclude other additional functional layers besides the negative electrode active material layer. For example, in some embodiments, the negative electrode sheet of this application further includes a conductive undercoat (e.g., composed of a conductive agent and a binder) sandwiched between the negative electrode current collector and the negative electrode active material layer and disposed on the surface of the negative electrode current collector. In other embodiments, the negative electrode sheet of this application further includes a protective layer covering the surface of the negative electrode active material layer.

[0079] In this application, the electrochemical device further includes a separator. The separator is disposed between the positive and negative electrodes, primarily serving to prevent short circuits between the positive and negative electrodes while allowing active ions to pass through. 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.

[0080] In some embodiments, the material of the separator may include one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride, but is not limited to these. The separator may be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer may be the same or different. In some embodiments, a ceramic coating or a metal oxide coating may also be provided on the separator.

[0081] Electronic devices

[0082] A second aspect of the present application provides an electronic device that includes the electrochemical device of the first aspect of the present application, wherein the electrochemical device can be used as a power source in the electronic device.

[0083] The electronic device described in this application is not particularly limited and can be any electronic device known in the prior art. In some embodiments, the electronic device may include, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.

[0084] Example

[0085] The following examples describe the disclosure of this invention in more detail. These examples are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of this disclosure. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on mass, and all reagents used in the examples are commercially available or synthesized by conventional methods and can be used directly without further processing. The instruments used in the examples are also commercially available.

[0086] Example 1

[0087] Preparation of the second powder

[0088] MnOOH was placed in an alumina crucible and heated to 500℃ at a rate of 5℃ / min under air atmosphere, and held at this temperature for 1 h to obtain anhydrous Mn3O4. Anhydrous Mn3O4 and LiOH were weighed out at a Li:Mn molar ratio of 1.05:1, and nano-Cr2O3 was added at an elemental mass ratio of 0.0213:Mn. The mixture was then homogenized using a sand mill to obtain a precursor mixture. The precursor was placed in an alumina crucible and heated at a rate of 2 m... 3 Nitrogen gas is introduced at a rate of / h, and the temperature is increased to 940℃ at a heating rate of 5℃ / min and held constant for 10h. The mixture is then naturally cooled to room temperature to obtain a second powder. The surface of the second powder has a stepped structure with a width of 600nm to 700nm.

[0089] Preparation of positive electrode sheet

[0090] The first powder, lithium iron phosphate, the second powder synthesized above, the conductive agent Super P, and the binder polyvinylidene fluoride were mixed in a mass ratio of 88.32:7.68:2.4:1.6. N-methylpyrrolidone (NMP) was added, and the mixture was stirred under vacuum until it became homogeneous, obtaining a positive electrode slurry with a solid content of 70 wt%. The positive electrode slurry was uniformly coated onto one surface of a 10 μm thick aluminum foil for the positive electrode current collector. The aluminum foil was dried at 85°C to obtain a positive electrode sheet with a single-sided coating of positive active material layer with a coating thickness of 65 μm. The above steps were repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of positive active material layer. After cold pressing, cutting, and slitting, the sheet was dried under vacuum at 85°C for 4 hours to obtain a positive electrode sheet with dimensions of 74 mm × 867 mm.

[0091] Preparation of negative electrode sheet

[0092] Artificial graphite (anode active material), Super P (conductive agent), sodium carboxymethyl cellulose (CMC) (thickener), and styrene-butadiene rubber (SBR) (binder) were mixed in a mass ratio of 96.4:1.5:0.5:1.6. Deionized water was added, and the mixture was stirred under vacuum to obtain a cathode slurry with a solid content of 70 wt%. The cathode slurry was uniformly coated onto one surface of a 10 μm thick copper foil current collector. The copper foil was dried at 85 °C to obtain a cathode sheet with a single-sided coating of 63 μm thick and coated with the cathode active material. The above steps were repeated on the other surface of the aluminum foil to obtain a cathode sheet with a double-sided coating of the cathode active material. After cold pressing, cutting, and slitting, the cathode sheet was dried under vacuum at 120 °C for 12 h to obtain a cathode sheet with dimensions of 79 mm × 972 mm.

[0093] Preparation of electrolyte

[0094] A base solvent is prepared by mixing chain carbonate DEC and cyclic carbonate EC at a mass ratio of 2:1. Lithium salt LiPF6 is then added to the base solvent, dissolved, and mixed thoroughly to obtain the electrolyte. The mass percentage of LiPF6 in the electrolyte is 12.5%. A certain amount of additive (at least one of VC, VEC, DTD, PS, or PES) is then added to the electrolyte.

[0095] Preparation of the separating membrane

[0096] A water-based polyvinylidene fluoride, alumina, and polypropylene were mixed in a mass ratio of 1:8:1 and added to deionized water. The mixture was stirred to obtain a coating slurry with a solid content of 50 wt%. The coating slurry was uniformly coated onto one surface of a 5 μm thick PP film (provided by Celgard) and dried at 85°C to obtain a single-sided coated release liner with a coating thickness of 5 μm. The above steps were repeated on the other surface of the release liner to obtain a double-sided coated release liner. The release liner was then dried and cold-pressed to obtain the final release liner.

[0097] Preparation of lithium-ion batteries

[0098] The positive electrode, separator, and negative electrode prepared above are stacked in sequence, with the separator positioned between the positive and negative electrode to provide isolation. The electrode assembly is then wound to obtain an electrode assembly. The electrode assembly is placed in an aluminum-plastic film packaging bag, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, degassing, and edge trimming, a lithium-ion battery is obtained.

[0099] Examples 2 to 38 and Comparative Examples 1 to 3

[0100] The preparation method of the lithium-ion battery is similar to that in Example 1, except that the relevant parameters in the preparation process of the positive electrode and electrolyte are adjusted. For details of the parameters, please refer to Table 1. " / " indicates that the corresponding component was not added.

[0101] Test section

[0102] (1) Discharge specific capacity test of lithium-ion batteries

[0103] The lithium-ion battery was charged to 3.65V at a constant current of 0.2C, then charged to 0.05C at a constant voltage. After standing for 5 minutes, it was discharged to 2.5V at a constant current of 0.2C. The charging and discharging process was repeated twice, and the capacity of the second cycle was recorded as D0. The battery was disassembled, the positive electrode was removed, and the positive electrode was immersed in DMC (dimethyl carbonate) for 30 minutes to remove the electrolyte and by-products on the surface of the positive electrode. Then it was dried in a fume hood for 4 hours, and the electrode was calcined into powder at 400℃ in a vacuum. The mass of the powder was measured as m1.

[0104] The specific discharge capacity of a lithium-ion battery = D0 / m1.

[0105] (2) Cycle performance test of lithium-ion batteries

[0106] The lithium-ion battery was charged at 25°C with a constant current of 1C to 3.65V, then charged with a constant voltage to a current of 0.05C, left to stand for 5 minutes, and then discharged with a constant current of 1C to 2.5V. This constitutes one charge-discharge cycle, and the discharge capacity at this point is recorded as D01. The lithium-ion battery was subjected to the above charge-discharge process for 3000 cycles, and the discharge capacity of the 3000th cycle is recorded as D1.

[0107] The cycle capacity retention rate (%) of a lithium-ion battery = D1 / D01 × 100%.

[0108] Tables 1 to 4 present the performance test results of Examples 1 to 38 and Comparative Examples 1 to 3.

[0109] Table 1

[0110]

[0111]

[0112] Figure 1 This is the X-ray diffraction spectrum of the positive electrode active material layer in Example 1, from... Figure 1 As can be seen, the positive electrode active material layer exhibits a first diffraction peak at positions 17.3° to 19.3° and a second diffraction peak at positions 19.8° to 21.8°. The test results in Table 1 show that adding the second powder to the positive electrode active material layer significantly improves the discharge specific capacity of the lithium-ion battery. Furthermore, through the synergistic effect between the second and first powders, the loss of active lithium on the surface of the negative electrode active material can be effectively compensated, effectively improving the energy density and cycle capacity retention rate of the lithium-ion battery, and enhancing its cycle performance.

[0113] Table 2

[0114]

[0115] The test results in Table 2 also show that by adding element M to the positive electrode active material layer and controlling its content within a suitable range, the discharge specific capacity of lithium-ion batteries and their cycle performance can be further improved.

[0116] Table 3

[0117]

[0118] The test results in Table 3 also show that by reasonably controlling the compaction density of the positive electrode active material layer and the coating weight on one side, the energy density of lithium-ion batteries can be further improved and their cycle performance can be enhanced, thus enabling lithium-ion batteries to have high discharge specific capacity and long cycle life.

[0119] Table 4

[0120] Types of additives Additive content (%) Retention rate (%) after 3000 cycles at 25℃ Example 5 VC / 94.36 Example 27 VC 2.50 95.45 Example 28 VC 1.50 95.73 Example 29 VC 3.00 95.21 Example 30 VC 4.50 94.86 Example 31 VC 0.05 94.58 Example 32 VEC 1.50 95.35 Example 33 PS 1.50 95.57 Example 34 PES 1.50 95.78 Example 35 DTD 1.50 95.41 Example 36 VC+PES 1.00+0.50 96.32 Example 37 VC+DTD 1.00+1.50 95.86 Example 38 VC+PS 1.50+1.00 95.49

[0121] The test results in Table 4 also show that when the electrolyte contains additives, it helps to form a more uniform and low-impedance interface protective film after the first charge and discharge cycle of the lithium-ion battery, improves the oxidation resistance of the positive electrode active material, prevents side reactions between the electrolyte and the positive electrode active material layer, and thus further improves the cycle performance of the lithium-ion battery.

[0122] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. An electrochemical device, comprising: Positive electrode, negative electrode, and electrolyte. The positive electrode includes a positive electrode active material layer, which comprises a first powder and a second powder. In the electrochemical device, after full discharge, the X-ray diffraction pattern of the positive electrode active material layer shows a first diffraction peak at a diffraction angle 2θ of 17.3° to 19.3°, and a second diffraction peak at a diffraction angle 2θ of 19.8° to 21.8°. The peak intensity I of the first diffraction peak is... A The peak intensity I of the second diffraction peak B Satisfy: 0 A / I B ≤0.3,​ The first powder contains iron, and the second powder contains manganese. The mass percentage ω of manganese is determined based on the mass of the positive electrode active material layer. Mn With the mass percentage of iron ω Fe Satisfy: 0.01%≤ω Mn / ω Fe ≤30%.

2. The electrochemical device according to claim 1, wherein, The second powder satisfies at least one of conditions (1) to (2): (1) The second powder contains element M, wherein element M includes at least one of Al, Ti, Cr, Ce, Nb, Y and Mg; (2) The second powder has a stepped morphology.

3. The electrochemical device according to claim 2, wherein, Based on the mass of the second powder, the mass percentage ω of element M M With the mass percentage of manganese ω Mn Satisfies: 0.01% < ω M / ω Mn ≤4%.

4. The electrochemical device according to claim 1, wherein, The positive electrode active material layer satisfies at least one of conditions (3) to (4): (3) The compaction density of the positive electrode active material layer is 2.0 g / cm³. 3 Up to 2.8 g / cm 3 ; (4) The single-sided coating weight of the positive electrode active material layer is 100 mg / 1540.25 mm. 2 Up to 500mg / 1540.25mm 2 .

5. The electrochemical device according to claim 1, wherein, The electrolyte contains additives, which include at least one of unsaturated carbonates and sulfur-containing oxygen double bond compounds. Based on the mass of the electrolyte, the additive has a mass percentage content of 0.05% to 5%.

6. The electrochemical device according to claim 5, wherein, The additive satisfies at least one of conditions (5) to (6): (5) The unsaturated carbonate includes at least one of vinylene carbonate and ethylene ethylene carbonate; (6) The sulfur-containing oxygen double bond compound includes at least one of 1,3-propanesulfonate lactone, propenesulfonate lactone and vinylene sulfate.

7. The electrochemical device according to claim 1, wherein, The electrochemical device satisfies at least one of conditions (7) to (8): (7) The peak intensity I of the first diffraction peak A The peak intensity I of the second diffraction peak B Satisfy: 0.05≤I A / I B ≤0.25; (8) Based on the mass of the positive electrode active material layer, the mass percentage of manganese element ω Mn With the mass percentage of iron ω Fe Satisfies: 0.05%≤ω Mn / ω Fe ≤25%.

8. The electrochemical device according to claim 3, wherein, Based on the mass of the second powder, the mass percentage ω of element M M With the mass percentage of manganese ω Mn Satisfies: 0.02% < ω M / ω Mn ≤3.5%.

9. The electrochemical device according to claim 1, wherein, The electrochemical device satisfies at least one of conditions (10) to (11): (10) The compaction density of the positive electrode active material layer is 2.2 g / cm³. 3 Up to 2.6 g / cm 3 ; (11) The single-sided coating weight of the positive electrode active material layer is 150 mg / 1540.25 mm. 2 Up to 450mg / 1540.25mm 2 .

10. The electrochemical device according to claim 5, wherein, Based on the mass of the electrolyte, the additive has a mass percentage content of 0.5% to 3%.

11. An electronic device comprising the electrochemical device according to any one of claims 1 to 10.

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