Electrochemical device and electronic device

Abstract

The present invention provides an electrochemical device and an electronic device. The electrochemical device includes a positive electrode, a negative electrode, and an electrolytic solution. The positive electrode includes a positive electrode active material layer, and the positive electrode active material layer includes a first powder and a second powder. After the electrochemical device is completely discharged, the X-ray diffraction analysis spectrum of the positive electrode active material layer has a first diffraction peak at a position where the diffraction angle 2θ is 17.3° to 19.3°, and a second diffraction peak at a position where the diffraction angle 2θ is 19.8° to 21.8°. The electrochemical device provided by the present invention simultaneously has a high discharge specific capacity and a long cycle life.

Description

Technical Field

[0001] The present invention belongs to the field of electrochemical technology, and specifically relates to an electrochemical device and an electronic device.

Background Art

[0002] Electrochemical devices such as lithium-ion batteries are widely used in all aspects of current life due to advantages such as high operating voltage, long cycle life, environmental friendliness, and light weight. In recent years, lithium-ion batteries have been developing rapidly in the fields of new energy vehicles and large-scale energy storage. With the accelerating popularization speed of new energy vehicles, the requirement for a longer cruising range puts forward higher requirements for the energy density, cycle performance, etc. of the battery. For example, in current lithium-ion batteries, materials such as lithium iron phosphate have excellent cycle performance and safety performance, so they are widely used as cathode materials. However, materials such as lithium iron phosphate have a much lower energy density compared to nickel cobalt manganese ternary materials, and the cruising range of new energy vehicles decreases. Therefore, it is necessary to further study cathode active materials that can improve the energy density and cycle performance of the battery.

Summary of the Invention

[0003] The object of the present invention is to provide an electrochemical device and an electronic device, which can improve the discharge specific capacity of the electrochemical device, have a high energy density, and improve the cycle performance.

[0004] A first aspect of the present invention provides an 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, 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 where the diffraction angle 2θ is 17.3° to 19.3° and a second diffraction peak at a position where the diffraction angle 2θ is 19.8° to 21.8°, the first powder comprising elemental iron and the second powder comprising elemental manganese. The first diffraction peak is a diffraction peak corresponding to the second powder, and the second diffraction peak is a diffraction peak corresponding to the first powder. The second powder having the first diffraction peak can provide a high capacity per gram, and the first powder having the second diffraction peak can provide good structural stability and charge / discharge reversibility. The two types of powders can exert a good synergistic effect in the positive electrode active material layer, providing the positive electrode active material layer with a high capacity per gram, excellent structural stability and charge / discharge reversibility, improving the discharge specific capacity and energy density of the electrochemical device, and improving the cycle performance. In any embodiment of the present invention, the peak intensity I A and the peak intensity I of the second diffraction peak B is 0 A / I B ≦0.3, preferably 0.05≦I A / I B ≦0.25. The peak intensity I A and the peak intensity of the second diffraction peak I B When the above relationship is satisfied, the structure and content of the second powder and the structure and content of the first powder satisfy a certain relationship. In this case, the second powder and the first powder have a better synergistic effect, which can ensure the ion transport inside the electrochemical device, improve the electrical performance, effectively improve the discharge specific capacity of the electrochemical device, improve the cycle performance, and make it have a high energy density.

[0005] In any embodiment of the present invention, the mass content ω of elemental manganese relative to the mass of the positive electrode active material layer is Mn and the mass content of iron element ω Fe ​is 0.01% ≤ ω Mn / ω Fe ≤ 30%, preferably 0.05% ≤ ω Mn / ω Fe ≤ 25%. A higher mass content ω Mn of the manganese element indicates a higher mass content of the second powder in the positive electrode active material. Since the second powder has a high capacity per gram, at this time, the electrochemical device has a high discharge specific capacity. When ω Mn / ω Fe is within the above range, the cycle performance of the electrochemical device can be effectively improved, the discharge specific capacity can be improved, and a high energy density can be achieved.

[0006] In any embodiment of the present invention, the second powder has a stepped form. In the positive electrode active material layer, the second powder having a stepped form can be more favorably combined with the first powder having an olivine structure, improving the uniformity of the positive electrode active material layer, being advantageous for the occlusion and desorption of active ions, further improving the discharge specific capacity of the electrochemical device, and achieving a high energy density.

[0007] In any embodiment of the present invention, the second powder contains element M, and the element M contains 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 the manganese-oxygen bond, suppress the elution of manganese, and further improve the cycle performance of the electrochemical device. At the same time, element M can also improve the content of desorbable active ions in the second powder, further improve the discharge specific capacity of the electrochemical device, and achieve a high energy density.

[0008] In any embodiment of the present invention, with respect to the mass of the second powder, the mass content ω M of the element M and the mass content ω Mn of the manganese element are 0.01% < ω M / ω Mn ≤ 4%, preferably 0.02% < ω M / ω Mn ≤ 3.5%. The mass content ω of element MM and the mass content ratio ω of the manganese element Mn being within an appropriate range is advantageous for further improving the stability of the manganese-oxygen bond and suppressing the elution of the manganese element. It is also advantageous for setting the content of desorbable active ions in the second powder within an appropriate range, further improving the discharge specific capacity of the electrochemical device, improving the cycle performance of the electrochemical device, and giving the electrochemical device a high energy density.

[0009] In any embodiment of the present invention, the compression density of the positive electrode active material layer is 2.0 g / cm 3 ~2.8 g / cm 3 and preferably 2.2 g / cm 3 ~2.6 g / cm 3 Controlling the compression density of the positive electrode active material layer within an appropriate range is advantageous for further improving the cycle performance of the electrochemical device and further improving the discharge specific capacity.

[0010] In any embodiment of the present invention, the single-sided coating weight of the positive electrode active material layer is 100 mg / 1540.25 mm 2 ~500 mg / 1540.25 mm 2 and preferably 150 mg / 1540.25 mm 2 ~450 mg / 1540.25 mm 2 Controlling the single-sided coating weight of the positive electrode active material layer within an appropriate range is advantageous for further improving the cycle performance of the electrochemical device and improving the discharge specific capacity.

[0011] In any embodiment of the present invention, the electrolyte contains an additive, the additive contains at least one of an unsaturated carbonate ester and a sulfur-oxygen double bond-containing compound, and the mass content rate of the additive is 0.01% to 5% based on the mass of the electrolyte. When the additive is added to the electrolyte of the present invention, the additive decomposes 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 improving the cycle performance of the electrochemical device. The additive forms a dense and stable interfacial film on the surface of the negative electrode active material, which is advantageous for reducing the impedance of ion transport at the negative electrode interface and can also further improve the cycle performance of the electrochemical device. When the mass content rate of the additive in the electrolyte is within an appropriate range, the cycle performance of the electrochemical device can be effectively improved.

[0012] In any embodiment of the present invention, the unsaturated carbonate ester contains at least one of vinylene carbonate and vinyl ethylene carbonate.

[0013] In any embodiment of the present invention, the sulfur-oxygen double bond-containing compound contains at least one of 1,3-propane sultone, propene sultone, and vinylene sulfate.

[0014] In any embodiment of the present invention, the mass content rate of the additive is 0.05% to 4% based on the mass of the electrolyte.

[0015] In a second aspect of the present invention, an electronic device including the electrochemical device of the first aspect of the present invention is provided.

[0016] In the present invention, the positive electrode active material layer contains a first powder and a second powder. After the electrochemical device is fully discharged, the X-ray diffraction analysis spectrum of the positive electrode active material layer has a first diffraction peak at a position where the diffraction angle 2θ is 17.3° to 19.3°, and a second diffraction peak at a position where the diffraction angle 2θ is 19.8° to 21.8°. The first powder contains iron element, and the second powder contains manganese element. The second powder having the first diffraction peak can provide a high capacity per gram, and the first powder having the second diffraction peak can provide good structural stability and charge-discharge reversibility. The two kinds of powders can exert a good synergistic effect in the positive electrode active material layer, endowing the positive electrode active material layer with a high capacity per gram, excellent structural stability and charge-discharge reversibility, improving the discharge specific capacity and energy density of the electrochemical device, and improving the cycle performance.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0018] In order to make the objectives, technical solutions, and advantages of the present invention clearer, the following will clearly and completely describe the technical solutions of the present invention with reference to the examples. It is obvious that the described examples are only a part of the examples of the present invention, not all of them. The relevant examples described here are illustrative and are used to provide a basic understanding of the present invention. The examples of the present invention should not be construed as limiting the present invention. Based on the technical solutions provided by the present invention and the examples given, other examples that can be obtained by those skilled in the art without creative efforts all fall within the scope of the claims of the present invention.

[0019] For the sake of clarity, this specification specifically discloses only several numerical ranges. However, any lower limit can be combined with any upper limit to form ranges that are not explicitly stated. And any lower limit can be combined with other lower limits to form ranges that are not explicitly stated. Similarly, any upper limit can be combined with any other upper limit to form ranges that are not explicitly stated. Also, each individually disclosed point or individual numerical value itself can be combined with any other point or individual numerical value as a lower limit or upper limit, or combined with other lower limits or upper limits, to form ranges that are not explicitly stated.

[0020] In the description of this specification, unless otherwise specified, "above" and "below" include the reference quantity.

[0021] Unless otherwise specified, the terms used in the present invention have the well-known meanings commonly understood by those skilled in the art. Unless otherwise specified, the numerical values of each parameter mentioned in the present invention can be measured by various measurement methods commonly used in the art (for example, they can be measured according to the methods shown in the embodiments of the present invention).

[0022] The enumeration of items connected by terms such as "at least one of", "at least one of", "at least one kind of" or other similar terms means any combination of the enumerated items. For example, when items A and B are enumerated, the notation "at least one of A, B" means only A, only B, or A and B. In other examples, when items A, B, and C are enumerated, the notation "at least one of A, B, C" means only A, 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 include a single component or multiple components. Item B may include a single component or multiple components. Item C may include a single component or multiple components.

[0023] In a prior lithium-ion battery using lithium iron phosphate as a cathode material, since the conductivity of lithium iron phosphate is poor, in order to obtain a lithium-ion battery having a high capacity, it is common to reduce the particle size of lithium iron phosphate. However, a lithium iron phosphate material with a small particle size has a small compression density, reducing the battery energy density.

[0024] To solve the above problems, the inventor has effectively improved the discharge specific capacity of the cathode material and the compression density of the cathode sheet through extensive studies, and realized a significant improvement in the energy density and cycle performance of the electrochemical device. Electrochemical device

[0025] The first aspect of the embodiment of the present invention provides an electrochemical device, including any device that causes an electrochemical reaction to mutually convert chemical energy and electrical energy. Specific examples include, but are not limited to, lithium-ion batteries or sodium-ion batteries.

[0026] The electrochemical device in the present invention includes a cathode, an anode, and an electrolyte. The cathode includes a cathode active material layer. The cathode active material layer includes a first powder and a second powder. After the electrochemical device is fully discharged, the X-ray diffraction analysis spectrum of the cathode active material layer has a first diffraction peak at a position where the diffraction angle 2θ is 17.3° - 19.3°, and a second diffraction peak at a position where the diffraction angle 2θ is 19.8° - 21.8°.

[0027] In the present invention, a fully discharged electrochemical device means that the electrochemical device is charged at a constant current to 3.65V at 0.2C, then charged at a constant voltage until the current reaches 0.05C, left standing for 5 minutes, and then discharged at a constant current to 2.5V at 0.2C. After cycling twice according to this charge-discharge process, the obtained electrochemical device is in a fully discharged state.

[0028] In the electrochemical device of the present invention, the X-ray diffraction analysis spectrum of the positive electrode active material layer has a first diffraction peak at a position where the diffraction angle 2θ is 17.3° to 19.3°, and a second diffraction peak at a position where the diffraction angle 2θ is 19.8° to 21.8°. The first diffraction peak corresponds to the diffraction peak of the second powder, and the second diffraction peak corresponds to the diffraction peak of the first powder. The second powder having the first diffraction peak can provide a high capacity per gram, and the first powder having the second diffraction peak can provide good structural stability and charge-discharge reversibility. The two types of powders can exhibit a good synergistic effect in the positive electrode active material layer, endowing the positive electrode active material layer with a high capacity per gram, excellent structural stability and charge-discharge reversibility, improving the discharge specific capacity of the electrochemical device, endowing it with a high energy density, and improving the cycle performance.

[0029] In the electrochemical device of the present invention, the first powder contains iron element, and the second powder contains manganese element. In the present invention, the first powder in the positive electrode active material layer has an olivine structure, and its structure is relatively stable. During the charge-discharge process of the electrochemical device, the volume change is small, that is, the insertion and desorption of active ions such as lithium ions have little influence on the structure of the first powder, and it has good charge-discharge reversibility. The second powder in the positive electrode active material layer has a high capacity per gram, endowing the electrochemical device with a high discharge specific capacity. The electrochemical device of the present invention can fully exert the synergistic effect between the first powder and the second powder in the positive electrode active material layer. During the charge-discharge process of the electrochemical device, the active lithium in the second powder desorbs from the second powder, and part of the active lithium deposits on the negative electrode, which can effectively compensate for the irreversible loss of the active lithium on the surface of the negative electrode active material due to the repair of the SEI film. The other active lithium can be inserted into the first powder, effectively improving the cycle performance of the electrochemical device.

[0030] In some embodiments, the peak intensity I of the first diffraction peak A and the peak intensity I of the second diffraction peak B satisfy 0 < I A / I B ≤ 0.3. For example, the peak intensity I of the first diffraction peakA and 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 A and the peak intensity I of the second diffraction peak B satisfy 0.05 ≦ I A / I B ≦ 0.25.

[0031] In the present invention, the ratio of the peak intensity I of the first diffraction peak A to the peak intensity I of the second diffraction peak B is related to the structure and content of the second powder, and the structure and content of the first powder. The peak intensity I of the first diffraction peak A and the peak intensity I of the second diffraction peak BWhen the above relational expression is satisfied, it is expressed that the structure and content of the second powder and the structure and content of the first powder satisfy a certain relationship. In this case, the second powder and the first powder have a more excellent 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 occlude into the first powder, guarantee the ion transport inside the electrochemical device, improve the electrical performance, effectively improve the discharge specific capacity of the electrochemical device, and improve the cycle performance.

[0032] In the present invention, the X-ray diffraction analysis spectrum of the positive electrode active material layer, and the peak intensities of the first diffraction peak and the second diffraction peak have meanings known in the art and can be measured by methods known in the art. For example, the lithium ion battery is charged at a constant current of 0.2C to 3.65V, and then charged at a constant voltage until the current becomes 0.05C, left standing for 5 minutes, and then discharged at a constant current of 0.2C to 2.5V according to the charge-discharge process and cycled twice (at this time, the battery is in a fully discharged state). Then, the lithium ion battery is disassembled, the positive electrode plate is taken out, the positive electrode plate is immersed in dimethyl carbonate (DMC) for 30 minutes to remove the electrolyte and by-products on the surface of the positive electrode plate, and then dried in a draft for 4 hours. The dried positive electrode active material layer is scraped off with a doctor blade to obtain a positive electrode active material layer powder. The positive electrode active material layer powder is placed on the sample stage of an XRD measuring device (model number: Bruker D8), and an XRD diffraction spectrum is obtained using a scanning speed of 2° / min and a scanning angle range of 10° to 90°. In the XRD diffraction spectrum, the peak positions and peak intensities of the first diffraction peak and the second diffraction peak of the positive electrode active material are calculated, and I A / I B is obtained.

[0033] In some embodiments, with respect to the mass of the positive electrode active material, the mass content ratio ω Mn of the manganese element and the mass content ratio ω Fe of the iron element satisfy 0.01% ≦ ω Mn / ω Fe ≦ 30%. For example, the mass content ratio ω Mn of the manganese element and the mass content ratio ω Feis 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% ≤ ω Mn / ω Fe ≤ 30%, 20% ≤ ω Mn / ω Fe ≤ 30%, 25% ≤ ω Mn / ω Fe ≤ 30%, 0.05% ≤ ω Mn / ω Fe ≤ 25%, 0.1% ≤ ω Mn / ω Fe ≤ 25%, 0.5% ≤ ω Mn / ω Fe ≤ 25%, 1% ≤ ω Mn / ω Fe ≤ 25%, 5% ≤ ω Mn / ω Fe ≤ 25%, 10% ≤ ω Mn / ω Fe ≤ 25%, 15% ≤ ω Mn / ω Fe ≤ 25%, 20% ≤ ω Mn / ω Fe ≤ 25%, 0.05% ≤ ω Mn / ω Fe ≤ 20%, 0.1% ≤ ω Mn / ω Fe ≤ 20%, 0.5% ≤ ω Mn / ω Fe ≤ 20%, 1% ≤ ω Mn / ω Fe ≤ 20%, 5% ≤ ω Mn / ω Fe ≤ 20%, 10% ≤ ω Mn / ω Fe ≤ 20%, 15% ≤ ω Mn / ω Fe ≤ 20%, 0.05% ≤ ω Mn / ω Fe ≤ 15%, 0.1% ≤ ω Mn / ω Fe≤15%, 0.5%≤ω Mn / ω Fe ≤15%, 1%≤ω Mn / ω Fe ≤15%, 5%≤ω Mn / ω Fe ≤15%, 10%≤ω Mn / ω Fe ≤15%, 0.05%≤ω Mn / ω Fe ≤10%, 0.1%≤ω Mn / ω Fe ≤10%, 0.5%≤ω Mn / 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 satisfies ≤0.1%. Preferably, the mass content ratio ω of the manganese element Mn and the mass content ratio ω of the iron element Fe is 0.05%≤ω Mn / ω Fe satisfies ≤25%.

[0034] In the present invention, the mass content ratio ω of the manganese element Mn and the mass content ratio ω of the iron element Fe respectively represent the mass content ratios in the positive electrode active material layer of the second powder and the first powder. The mass content ratio ω of the manganese element MnThe higher it is, the higher the mass content ratio of the second powder in the positive electrode active material is. Since the second powder has a high capacity per gram, at this time, the electrochemical device has a high discharge specific capacity. Without being limited to any theory, the active lithium in the second powder desorbs and deposits on the negative electrode during the cycling process of the electrochemical device to compensate for the loss of active lithium on the surface of the negative electrode active material. Therefore, when the mass content ratio of the second powder in the positive electrode active material layer is high, a large amount of desorbable active lithium can be provided, not only can the loss of active lithium on the surface of the negative electrode active material be effectively compensated, but also sufficient active lithium can return to the first powder and be occluded, ensuring the transport of active ions, effectively improving the cycle capacity retention rate of the electrochemical device, and improving the cycle performance, which the inventor has found.

[0035] Without being limited to any theory, compared with the first powder, the mass content ratio of the second powder should not be too high. If the mass content ratio of the second powder is too high, there will be too much desorbable and compensable lithium provided, which is more than the amount of lithium that can return to the positive electrode active material layer and be occluded, increasing the internal resistance and reducing the discharge specific capacity of the electrochemical device, which the inventor has also found. Therefore, by controlling the mass content ratios of the second powder and the first powder in the positive electrode active material layer, that is, the mass content ratio ω Mn of manganese element and the mass content ratio ω Fe of iron element within the above ranges, the cycle performance of the electrochemical device can be effectively improved, the discharge specific capacity can be improved, and it can have a high energy density.

[0036] In some embodiments, the second powder has a stepped form. In the positive electrode active material layer, the second powder having a stepped form can be better compounded with the first powder containing an olivine structure, improving the uniformity of the positive electrode active material layer, being advantageous for the occlusion and desorption of active ions, further improving the discharge specific capacity of the electrochemical device, and enabling it to have a high energy density.

[0037] In the present invention, the form of the second powder can be measured by the following method. The lithium-ion battery is disassembled to obtain a positive electrode sheet, the positive electrode sheet is dried, the dried positive electrode sheet is brittle fractured using liquid nitrogen, and then, using a scanning electron microscope (SEM), 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 observed to observe and analyze the form of the second powder. In some embodiments, the second powder contains element M, and the element M contains 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 the manganese-oxygen bond, and the improvement of the stability of the manganese-oxygen bond can suppress the elution of manganese and further improve the cycle performance of the electrochemical device. At the same time, element M can also improve the content of desorbable lithium in the second powder, so that the second powder has sufficient lithium to desorb and compensate for the loss of active lithium on the surface of the negative electrode active material, and at the same time, has sufficient active lithium to return to and be occluded in the positive electrode active material layer, further improving the discharge specific capacity of the electrochemical device and giving it a high energy density.

[0038] The lithium-ion battery is disassembled to obtain a positive electrode sheet, the positive electrode sheet is dried, the dried positive electrode sheet is brittle fractured using liquid nitrogen, and then, using a scanning electron microscope (SEM), 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 observed to observe and analyze the form of the second powder. An energy dispersive spectrometer (EDS) is used to analyze the type and content of element M and the content of Mn element in the second powder.

[0039] In some embodiments, with respect to the mass of the second powder, the mass content ratio ω M of the element M and the mass content ratio ω Mn of the manganese element M satisfy 0.01% < ω Mn / ω M ≤ 4%. For example, the mass content ratio ω Mn of the element M and the mass content ratio ω M of the manganese element Mn satisfy 0.05% ≤ 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 / ω Mn ≤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% or 0.5%≤ω M / ω Mn satisfies ≤1%. Preferably, the mass content ω M of the element M and the mass content ω Mn of the manganese element are such that 0.02% < ω M / ω Mn ≤3.5%.

[0040] The ratio of the mass content ω M of the element M to the mass content ω Mn of the manganese element being within an appropriate range is advantageous for further improving the stability of the manganese-oxygen bond and suppressing the elution of the manganese element. It is also advantageous for setting the content of desorbable lithium in the second powder within an appropriate range, such that the second powder has sufficient lithium to compensate for the loss of active lithium on the surface of the negative electrode active material and has sufficient active lithium to return to and be occluded in the positive electrode active material layer, further improving the discharge specific capacity of the electrochemical device, giving it a high energy density, and improving the cycle performance of the electrochemical device.

[0041] In some embodiments, the compression density of the positive electrode active material layer is 2.0 g / cm 3 ~2.8 g / cm 3 That is, for example, the compression density of the positive electrode active material layer is 2.1 g / cm 3 , 2.2 g / cm 3 , 2.3 g / cm 3 , 2.4 g / cm 3 , 2.5 g / cm 3 , 2.6 g / cm 3 , 2.7 g / cm 3 Or it is a range consisting of any of the above numerical values. Preferably, the compression density of the positive electrode active material layer is 2.2 g / cm 3 ~2.6 g / cm 3 .

[0042] In some embodiments, the single-sided coating weight of the positive electrode active material layer is 100 mg / 1540.25 mm 2 ~500 mg / 1540.25 mm 2 That is, for example, the single-sided coating weight of the positive electrode active material layer is 100 mg / 1540.25 mm 2 , 150 mg / 1540.25 mm 2 , 200 mg / 1540.25 mm 2 , 250 mg / 1540.25 mm 2 , 3100 mg / 1540.25 mm 2 , 350 mg / 1540.25 mm 2 , 400 mg / 1540.25 mm 2 , 450 mg / 1540.25 mm 2 , 500 mg / 1540.25 mm 2 Or it is a range consisting of any of the above numerical values. Preferably, the single-sided coating weight of the positive electrode active material layer is 150 mg / 1540.25 mm 2 ~450 mg / 1540.25 mm 2 .

[0043] After adding the second powder in a stepped form to the positive electrode active material layer of the present invention, the contact between the positive electrode active materials becomes closer, and the compression density of the positive electrode active material layer can be improved, thereby giving the electrochemical device a high energy density. Controlling the single-sided coating weight and compression density of the positive electrode active material layer within an appropriate range is advantageous for the movement of electrons and active ions, thereby further improving the cycle performance of the electrochemical device and increasing the discharge specific capacity.

[0044] In the present invention, the compression density and the single-sided coating weight of the positive electrode active material layer have the meanings known in the art and can be measured by methods known in the art. For example, five dried positive electrode plates are cut into electrode plates with an area of 1540.25 mm 2 and the thickness of each positive electrode plate is measured with a micrometer with an accuracy of 0.1 μm and denoted as d0 cm. The positive electrode active material layer on the positive electrode plate is scraped off by a doctor blade, and the mass of the positive electrode active material layer is weighed with a balance and denoted as m (mg). The mass of the positive electrode active material layer with an area of 1540.25 mm 2 is used. The thickness of the positive electrode current collector from which the positive electrode active material layer has been removed is measured with a micrometer with an accuracy of 0.1 μm and denoted as d cm. The compression density of the positive electrode active material layer is calculated according to the following formula. Compression density P = m / [154.025×(d0 - d)]. The compression density of the positive electrode active material layer is the average value of the compression densities of the positive electrode active material layers in the five positive electrode plates obtained by cutting as described above. The single-sided coating weight of the positive electrode active material layer is the average value of the masses of the positive electrode active material layers in the five positive electrode plates obtained by cutting as described above.

[0045] In some embodiments, the first powder includes, but is not limited to, lithium iron phosphate and a composite material of lithium phosphate and carbon.

[0046] In some embodiments, by way of example, the second powder can be manufactured by the following method. Put MnOOH into a corundum crucible, and in an air atmosphere, heat it up to 500 °C at a heating rate of 5 °C / min, hold it at a constant temperature for 1 hour to obtain anhydrous Mn3O4. Weigh anhydrous Mn3O4 and LiOH at a ratio where the molar ratio of Li:Mn is 1.05:1. At the same time, add nano-Cr2O3 at a ratio where the elemental mass ratio of Cr:Mn is 0.008:1, and mix them uniformly by a sand mill device to obtain a mixture precursor. Place the precursor in a corundum crucible, flow nitrogen gas at a rate of 2m 3 / h, heat it up to 940 °C at a heating rate of 5 °C / min, hold it at a constant temperature for 10 h, and then naturally cool it to room temperature to obtain a second powder containing manganese element. Among them, MnO2 can be used instead of Mn3O4, and the mixing ratio with LiOH can be modified based on the Mn content.

[0047] In some embodiments, the positive electrode active material layer may further optionally include a conductive agent and a binder. There are no specific restrictions on the specific types of the conductive agent and the binder, and they can be selected according to actual requirements. By way of example, the conductive agent includes at least one of conductive graphite, superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers, but is not limited thereto. By way of example, the binder includes 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), but is not limited thereto.

[0048] In the present invention, 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 provided on at least one surface of the positive electrode current collector.

[0049] In some embodiments, the positive electrode current collector may be a metal foil material or a porous metal plate. For example, a foil material or a porous plate made of a metal such as aluminum, copper, nickel, titanium, silver, or an alloy thereof may be used. As an example, the positive electrode current collector is an aluminum foil.

[0050] In some embodiments, the positive electrode current collector has two surfaces facing each other in its thickness direction, and the positive electrode active material layer is provided on one or both of the two opposing surfaces of the positive electrode current collector. When the positive electrode active material layer is provided on the two surfaces of the positive electrode current collector, if the parameters of the positive electrode active material layer on any of the surfaces satisfy the parameter range of the present invention, it is considered to be within the protection scope of the present invention.

[0051] The positive electrode sheet can be manufactured according to the conventional methods in the art. Usually, a first powder, a second powder, an optional conductive agent, and a binder are dispersed in a solvent. The solvent may be N-methylpyrrolidone (NMP). A uniform positive electrode slurry is formed, the positive electrode slurry is applied to the positive electrode current collector, and through processes such as drying and cold pressing, a positive electrode sheet is obtained.

[0052] The positive electrode sheet of the present invention does not exclude other positive electrode active materials other than the first powder and the second powder. There are no specific restrictions on the specific types of other positive electrode active materials, and they can be selected according to actual requirements. As an example, other positive electrode active materials include at least one of lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, a composite material of lithium manganese iron phosphate and carbon, and modified compounds thereof, but are not limited thereto.

[0053] The positive electrode sheet of the present invention does not exclude other additional functional layers other than the positive electrode active material layer. For example, in some embodiments, the positive electrode sheet of the present invention further includes a conductive undercoat layer (for example, composed of a conductive agent and a binder) sandwiched between the positive electrode current collector and the positive electrode active material layer and provided on the surface of the positive electrode current collector. In some other embodiments, the positive electrode sheet of the present invention further includes a protective layer covering the surface of the positive electrode active material layer.

[0054] In the present invention, the electrolyte plays a role of conducting active ions between the positive electrode and the negative electrode.

[0055] In some embodiments, the electrolyte contains an additive, and the additive contains at least one of an unsaturated carbonate ester and a sulfur-oxygen double bond-containing compound.

[0056] As an example, the additive includes at least one of vinylene carbonate (VC), vinyl ethylene carbonate (VEC), ethylene sulfate (DTD), 1,3-propylene sulfate, ethylene sulfite (ES), 1,3-propane sultone (PS), and propene-1,3-sultone (PES), but is not limited thereto.

[0057] When the additive is added to the electrolyte of the present invention, the additive decomposes on the surface of the positive electrode to form an interfacial protective film, improves the oxidation resistance of the positive electrode active material layer, stabilizes the structure of the positive electrode active material, realizes the effect of suppressing side reactions between the positive electrode active material layer and the electrolyte, and further improves the cycle performance of the electrochemical device. The additive forms a dense and stable interfacial film on the surface of the negative electrode active material, which is advantageous for reducing the impedance of ion transport at the negative electrode interface, and can also further improve the cycle performance of the electrochemical device.

[0058] In some embodiments, based on the mass of the electrolyte, the mass content ratio of the additive is 0.01% to 5%. For example, the mass content ratio of the additive is in the range of 0.05%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 4% or any range consisting of the above numerical values. Preferably, the mass content ratio of the additive is 0.5% to 3%.

[0059] The mass content of the additive in the electrolyte being within an appropriate range is advantageous for forming an interfacial protective film with an appropriate thickness on the surface of the material, and at the same time has a low impedance, which is advantageous for improving the cycle performance of the electrochemical device. If the mass content of the additive is too small, the film formation of the interfacial protective film will be insufficient, affecting the performance of the electrochemical device. If the mass content of the additive is too high, it will increase the impedance of the electrolyte, reduce the migration rate of active ions, and affect the cycle performance of the electrochemical device.

[0060] In some embodiments, the electrolyte further includes an organic solvent, a lithium salt, and any other optional electrolyte additive. There are no specific restrictions on the types of the organic solvent, the lithium salt, and any other optional electrolyte additive, and they can be selected according to actual requirements.

[0061] In some embodiments, by way of example, the lithium salt includes 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 difluoro(oxalato)borate), LiBOB (lithium bis(oxalato)borate), LiPO2F2 (lithium difluorophosphate), LiDFOP (lithium difluoro(bis(oxalato))phosphate), LiTFOP (lithium tetrafluoro(oxalato)phosphate), but is not limited thereto. The above lithium salts may be used alone or two or more of them may be used simultaneously.

[0062] In some embodiments, by way of example, 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), butylene 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), ethyl methyl sulfone (EMS), and diethyl sulfone (ESE). The above organic solvent may be used alone or two or more of them may be used simultaneously. Optionally, two or more of the above organic solvents are used simultaneously.

[0063] In some embodiments, the other optional electrolyte additive may include an electrolyte additive capable of improving certain performance of the battery, such as an electrolyte additive for improving the overcharge performance of the battery, an electrolyte additive for improving the high-temperature performance or low-temperature performance of the battery, and the like.

[0064] The electrolyte can be manufactured according to conventional methods in the art. For example, an organic solvent, a lithium salt, an additive, and any other optional electrolyte additive may be uniformly mixed to obtain an electrolyte. The order of adding each material is not particularly limited. For example, the lithium salt, the additive, and any other optional electrolyte additive are added to the organic solvent and uniformly mixed to obtain an electrolyte. Alternatively, first, the lithium salt is added to the organic solvent, and then the additive and any other optional electrolyte additive are added to the organic solvent and uniformly mixed to obtain an electrolyte.

[0065] In the present invention, the negative electrode is a negative electrode sheet, which may be a metallic lithium sheet, or may be an electrode sheet including a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector. The negative electrode active material layer usually contains a negative electrode active material, an optional conductive agent, a binder, and a thickener.

[0066] The materials, structure, and manufacturing method of the negative electrode sheet used in the present invention may include any technology known in the prior art.

[0067] There are no specific restrictions on the specific type of the negative electrode active material, and it may be selected according to actual requirements. For example, the negative electrode active material includes at least one of natural graphite, artificial graphite, mesocarbon microbeads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiO, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel-structured Li4Ti5O 12 , Li-Al alloy, but is not limited thereto.

[0068] There are no specific restrictions on the specific type of the conductive agent, and it may be selected according to actual requirements. For example, the conductive agent includes at least one of conductive graphite, superconducting carbon, acetylene black, carbon black, ketjen black, carbon dot, carbon nanotube, graphene, and carbon nanofiber, but is not limited thereto.

[0069] There are no specific restrictions on the specific type of the binder, and it may be selected according to actual requirements. For example, the binder includes at least one of styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl butyral (PVB), water-based acrylic resin, and carboxymethyl cellulose, but is not limited thereto.

[0070] There are no specific restrictions on the specific types of thickeners, and they can be selected according to actual requirements. For example, the thickener includes, but is not limited to, sodium carboxymethyl cellulose (CMC).

[0071] However, the present invention is not limited to these materials, and the negative electrode sheet of the present invention may further use other well-known materials that can be used as negative electrode active materials, conductive agents, binders, and thickeners.

[0072] In some embodiments, the negative electrode current collector has two surfaces facing each other in its thickness direction, and the negative electrode film layer is provided on one or both of the two opposing surfaces of the negative electrode current collector.

[0073] The negative electrode current collector may be a metal foil material or a porous metal plate, for example, a foil material or a porous plate made of a metal such as copper, nickel, titanium, iron, or an alloy thereof. As an example, the negative electrode current collector is a copper foil.

[0074] The negative electrode sheet can be manufactured according to the conventional methods in the art. Usually, the negative electrode active material, an optional conductive agent, an adhesive, and a thickener are dispersed in a solvent. The solvent may be N-methylpyrrolidone (NMP) or deionized water. A uniform negative electrode slurry is formed, the negative electrode slurry is applied to the negative electrode current collector, and the negative electrode sheet is obtained through processes such as drying and cold pressing.

[0075] The negative electrode sheet of the present invention does not exclude other additional functional layers other than the negative electrode active material layer. For example, in some embodiments, the negative electrode sheet of the present invention further includes a conductive undercoat layer (for example, composed of a conductive agent and a binder) sandwiched between the negative electrode current collector and the negative electrode active material layer and provided on the surface of the negative electrode current collector. In some other embodiments, the negative electrode sheet of the present invention further includes a protective layer covering the surface of the negative electrode active material layer.

[0076] In the present invention, the electrochemical device further includes a separator. The separator is provided between the positive electrode plate and the negative electrode plate, mainly serving to prevent short circuit between the positive electrode and the negative electrode, and at the same time allowing active ions to pass through. The present invention is not particularly limited to the type of separator, and any well-known separator having porous structure with chemical stability and mechanical stability may be selected.

[0077] In some embodiments, the material of the separator may include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride, but is not limited thereto. 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 from each other. In some embodiments, the separator may further be provided with a ceramic coating layer or a metal oxide coating layer.

[0078] Electronic device A second aspect of the embodiment of the present invention provides an electronic device, wherein the electronic device includes the electrochemical device of the first aspect of the embodiment of the present invention, and the electrochemical device is used as a power source in the electronic device.

[0079] There is no particular limitation on the electronic device of the present invention, and it may be any well-known electronic device used in the prior art. In some embodiments, the electronic device may include a notebook computer, a pen-input computer, a mobile computer, an e-book player, a mobile phone, a mobile fax, a mobile copier, a mobile printer, a head-mounted stereo headset, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disk, a transceiver, an electronic organizer, a calculator, a memory card, a portable recorder, a radio, a backup power source, a motor, an automobile, a motorcycle, an assist bicycle, a bicycle, a lighting fixture, a toy, a game machine, a clock, a power tool, a flashlight, a camera, a large household storage battery, a lithium ion capacitor, etc., but is not limited thereto.

[0080] Examples

[0081] The following examples are used to more specifically explain the disclosure content of the present invention. These examples are for illustrative purposes only, because it is obvious to those skilled in the art to make various modifications and changes within the scope of the disclosure content of the present invention. Unless otherwise specified, all parts, percentages, and ratios described in the following examples are based on mass. Also, all reagents used in the examples are commercially available or can be obtained by synthesis using ordinary methods, and no further treatment is required and they can be used as they are. Note that the devices used in the examples are commercially available.

[0082] Example 1 Manufacture of the second powder MnOOH was put into a corundum crucible, and the temperature was raised to 500 °C at a heating rate of 5 °C / min in an air atmosphere, and held at a constant temperature for 1 hour to obtain anhydrous Mn3O4. Anhydrous Mn3O4 and LiOH were weighed at a ratio such that the molar ratio of Li:Mn was 1.05:1. At the same time, nano-Cr2O3 was added at a ratio such that the elemental mass ratio of Cr:Mn was 0.0213:1, and they were uniformly mixed by a sand mill device to obtain a mixture precursor. The precursor was placed in a corundum crucible, nitrogen gas was flowed at a rate of 2m 3 / h, the temperature was raised to 940 °C at a heating rate of 5 °C / min, held at a constant temperature for 10 h, and naturally cooled to room temperature to obtain the second powder. The surface of the second powder has a stepped structure with a width of 600 nm to 700 nm.

[0083] Manufacture of the positive electrode sheet Lithium iron phosphate, which is the first powder, the second powder synthesized as described above, Super P which is a conductive agent, and polyvinylidene fluoride which is a binder were mixed at a mass ratio of 88.32:7.68:2.4:1.6, N-methylpyrrolidone (NMP) was added, and the mixture was stirred with a vacuum stirrer until the system became uniform to obtain a positive electrode slurry. Among them, the solid content of the positive electrode slurry was 70 wt%. The positive electrode slurry was uniformly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 10 μm, and the aluminum foil was dried at 85 °C to obtain a positive electrode sheet with a positive electrode active material layer coated on one side with a coating layer thickness of 65 μm. The above steps were repeated for the other surface of the aluminum foil to obtain a positive electrode sheet with positive electrode active material layers coated on both sides. Then, after cold pressing, cutting, and slitting, it was dried under vacuum conditions at 85 °C for 4 h to obtain a positive electrode sheet with a size of 74 mm × 867 mm.

[0084] Manufacture of negative electrode sheet Artificial graphite, which is a negative electrode active material, Super P which is a conductive agent, sodium carboxymethyl cellulose (CMC) which is a thickener, and styrene-butadiene rubber (SBR) which is a binder were mixed at a mass ratio of 96.4:1.5:0.5:1.6, added to deionized water, and a negative electrode slurry was obtained by stirring with a vacuum stirrer. Among them, the solid content of the negative electrode slurry was 70 wt%. The negative electrode slurry was uniformly coated on one surface of a negative electrode current collector copper foil with a thickness of 10 μm, and the copper foil was dried at 85 °C to obtain a negative electrode sheet with a negative electrode active material layer coated on one side with a coating layer thickness of 63 μm. The above steps were repeated for the other surface of the aluminum foil to obtain a negative electrode sheet with negative electrode active material layers coated on both sides. Then, after cold pressing, cutting, and slitting, it was dried under vacuum conditions at 120 °C for 12 h to obtain a negative electrode sheet with a size of 79 mm × 972 mm.

[0085] Manufacture of electrolyte The chain carbonate DEC and the cyclic carbonate EC were mixed at a mass ratio of 2:1 to obtain a base solvent. Then, LiPF6, which is a lithium salt, was added to the base solvent, dissolved, and uniformly mixed to obtain an electrolyte solution. Among them, based on the mass of the electrolyte solution, the mass content of LiPF6 was 12.5%. Furthermore, an additive (at least one of VC, VEC, DTD, PS, and PES) with a certain content was added to the electrolyte solution.

[0086] Manufacture of separator Aqueous polyvinylidene fluoride, aluminum oxide, and polypropylene were mixed at a mass ratio of 1:8:1, added to deionized water, and stirred to obtain a coating layer slurry with a solid content of 50 wt%. The coating layer slurry was uniformly coated on one surface of a PP film (provided by Celgard) with a thickness of 5 μm, dried at 85 °C, and a separator with a coating layer with a thickness of 5 μm coated on one side was obtained. The above steps were repeated for the other surface of the separator to obtain a separator with coating layers coated on both sides. Then, after drying and cold pressing, a separator was obtained.

[0087] Manufacture of lithium-ion battery The positive electrode sheet, separator, and negative electrode sheet obtained as manufactured above were laminated in order, with the separator positioned between the positive electrode and the negative electrode to play a role of isolation, and wound to obtain an electrode assembly. The electrode assembly was placed in an aluminum plastic film pack, and after drying, the electrolyte solution was injected, and through processes such as vacuum sealing, standing, formation, degassing, and trimming, a lithium-ion battery was obtained.

[0088] Examples 2 to 38 and Comparative Examples 1 to 3 The manufacturing method of the lithium-ion battery was similar to that of Example 1, and the difference was that the relevant parameters in the manufacturing processes of the positive electrode sheet and the electrolyte solution were adjusted. The specific parameters are shown in Table 1, and " / " indicates that the corresponding component is not contained.

[0089] Measurement part (1) Measurement of the discharge specific capacity of the lithium-ion battery The lithium-ion battery was charged at a constant current of 0.2C to 3.65V, and then charged at a constant voltage until the current reached 0.05C. After standing for 5 minutes, it was discharged at a constant current of 0.2C to 2.5V. This charge-discharge process was cycled twice, and the capacity of the second cycle was denoted as D0. The battery was disassembled, the positive electrode sheet was taken out, the positive electrode sheet was immersed in DMC (dimethyl carbonate) for 30 minutes to remove the electrolyte and by-products on the surface of the positive electrode sheet, and then dried in a draft for 4 hours. The electrode sheet was calcined into powder at 400°C in a vacuum and weighed with the mass denoted as m1. Discharge specific capacity of the lithium-ion battery = D0 / m1.

[0090] (2) Measurement of the cycle performance of the lithium-ion battery At 25°C, the lithium-ion battery was charged at a constant current of 1C to 3.65V, and then charged at a constant voltage until the current reached 0.05C. After standing for 5 minutes, it was discharged at a constant current of 1C to 2.5V. This was regarded as one charge-discharge cycle. At this time, the discharge capacity was measured and recorded as D01. According to the above charge-discharge process, the lithium-ion battery was cycled 3000 times, and the discharge capacity of the 3000th cycle was measured and recorded as D1.

[0091] Cycle capacity retention rate of the lithium-ion battery (%) = D1 / D01×100%.

[0092] Tables 1 to 4 show the results of the performance measurements of Examples 1 to 38 and Comparative Examples 1 to 3.

[0093]

Table 1

[0094] Figure 1 is the X-ray diffraction spectrum of the positive electrode active material layer of Example 1. As can be seen from Figure 1, the positive electrode active material layer has a first diffraction peak at a position of 17.3° to 19.3°, and a second diffraction peak at a position of 19.8 to 21.8°. As can be seen from the measurement results in Table 1, after adding the second powder to the positive electrode active material layer, the discharge specific capacity of the lithium-ion battery can be significantly improved. And due to the synergistic effect between the second powder and the first powder, the loss of surface-active lithium on the negative electrode active material can be effectively compensated, the energy density and cycle capacity retention rate of the lithium-ion battery can be effectively improved, and the cycle performance of the lithium-ion battery can be improved.

[0095]

Table 2

[0096] As can be further seen from the measurement results in Table 2, by adding element M to the positive electrode active material layer and controlling its content within an appropriate range, the discharge specific capacity of the lithium-ion battery can be further improved, and the cycle performance can be improved.

[0097]

Table 3

[0098] As can be further seen from the measurement results in Table 3, by appropriately controlling the compression density and the single-sided coating weight of the positive electrode active material layer, the energy density of the lithium-ion battery can be further improved, the cycle performance can be improved, and the lithium-ion battery can be made to have a high discharge specific capacity and a long cycle life.

[0099]

Table 4

[0100] As can be further understood from the measurement results in Table 4, when the electrolytic solution contains an additive, it is advantageous for forming an interface protective film having more uniform and lower impedance after the first charge and discharge of the lithium ion battery, improving the oxidation resistance of the positive electrode active material, preventing side reactions between the electrolytic solution and the positive electrode active material layer, and further improving the cycle performance of the lithium ion battery.

[0101] The above are only specific embodiments of the present invention, and the protection scope of the present invention is not limited thereto. Those skilled in the art can easily conceive equivalent changes or substitutions within the disclosed technical scope of the present invention, and these changes or substitutions should be included within the protection scope of the present invention. Therefore, the protection scope of the present invention should conform to the scope of the claims.

Claims

1. An electrochemical device, comprising a positive electrode, a negative electrode, and an electrolytic solution, wherein the positive electrode includes a positive electrode active material layer, 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 analysis spectrum of the positive electrode active material layer has a first diffraction peak at a position where the diffraction angle 2θ is 17.3° to 19.3°, and a second diffraction peak at a position where the diffraction angle 2θ is 19.8° to 21.8°, the first powder contains iron element, and the second powder contains manganese element, an electrochemical device.

2. The peak intensity I of the first diffraction peak Ａ and the peak intensity I of the second diffraction peak Ｂ satisfy 0 < I Ａ / I Ｂ ≦ 0.

3. The electrochemical device according to claim 1

3. With respect to the mass of the positive electrode active material layer, the mass content ratio ω of manganese element Ｍｎ and the mass content ratio ω of iron element Ｆｅ satisfy 0.01% ≤ ω Ｍｎ / ω Ｆｅ ≤ 30%, the electrochemical device according to claim 1.

4. The second powder is, (1) the second powder contains an element M, and the element M contains at least one of Al, Ti, Cr, Ce, Nb, Y, and Mg, (2) the second powder has a stepped morphology, and satisfies at least one of the above, the electrochemical device according to claim 1.

5. With respect to the mass of the second powder, the mass content ratio ω of the element M Ｍ and the mass content ratio ω of the manganese element Ｍｎ are such that 0.01% < ω Ｍ / ω Ｍｎ ≦ 4%, and the electrochemical device according to claim 4

6. The positive electrode active material layer, (3) The compression density of the positive electrode active material layer is 2.0 g / cm ３ to 2.8 g / cm ３ and (4) The one-sided coating weight of the positive electrode active material layer is 100 mg / 1540.25 mm ２ to 500 mg / 1540.25 mm ２ and and satisfies at least one of the above, the electrochemical device according to claim 1.

7. The electrolytic solution contains an additive, the additive contains at least one of an unsaturated carbonate and a sulfur-oxygen double bond-containing compound, and the mass content ratio of the additive is 0.05% to 5% based on the mass of the electrolytic solution, the electrochemical device according to claim 1.

8. The additive is, (5) the unsaturated carbonate contains at least one of vinylene carbonate and vinyl ethylene carbonate, (6) the sulfur-oxygen double bond-containing compound contains at least one of 1,3-propane sultone, propene sultone, and vinylene sulfate, and satisfies at least one of the above, the electrochemical device according to claim 7.

9. (7) The peak intensity I of the first diffraction peak Ａ and the peak intensity I of the second diffraction peak Ｂ satisfy 0.05 ≦ I Ａ / I Ｂ ≦ 0.25, (8) With respect to the mass of the positive electrode active material layer, the mass content ratio ω of manganese element Ｍｎ and the mass content ratio ω of iron element Ｆｅ satisfy 0.05% ≤ ω Ｍｎ / ω Ｆｅ ≤ 25%, and (9) With respect to the mass of the second powder, the mass content ratio ω of the element M Ｍ and the mass content ratio ω of the manganese element Ｍｎ are such that 0.02% < ω Ｍ / ω Ｍｎ ≤ 3.5% is satisfied, (10) The compression density of the positive electrode active material layer is 2.2 g / cm ３ to 2.6 g / cm ３ and (11) The one-sided coating weight of the positive electrode active material layer is 150 mg / 1540.25 mm ２ to 450 mg / 1540.25 mm ２ and (12) the mass content ratio of the additive is 0.5% to 3% based on the mass of the electrolytic solution, and satisfies at least one of the above, the electrochemical device according to any one of claims 1 to 8.

10. An electronic device including the electrochemical device according to any one of claims 1 to 9.

Images