Electrochemical device and electronic device

Abstract

The present invention relates to 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, the positive electrode active material layer includes a positive electrode active material, and the positive electrode active material includes a first positive electrode active material and a second positive electrode active material. After the electrochemical device is fully discharged, the Raman spectrum of the positive electrode active material layer has a first characteristic peak at a wavelength of 398 cm -1 ~408 cm -1 and a second characteristic peak at a wavelength of 940 cm -1 ~960 cm -1 . The second positive electrode active material contains aluminum element. The electrochemical device simultaneously has both a high energy density and good high-temperature cycle characteristics.

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] In recent years, electrochemical devices represented by lithium-ion batteries have advantages such as high operating voltage, environmental friendliness, small volume, light weight, and long cycle life, and are rapidly developing in the fields of portable household appliances, new energy vehicles, and large-scale energy storage. Lithium iron phosphate has excellent cycle characteristics and safety performance, so it is widely used as a cathode material for electrochemical devices such as lithium-ion batteries. As the popularization speed of new energy vehicles accelerates, due to the demand for longer cruising ranges, the requirements for the energy density, cycle characteristics, etc. of the battery are further increasing.

Summary of the Invention

[0003] An object of the present invention is to provide an electrochemical device and an electronic device in order to improve the energy density of the electrochemical device and improve its high-temperature cycle characteristics.

[0004] A first aspect of the present invention provides an electrochemical device, the electrochemical device includes a positive electrode, a negative electrode, and an electrolyte, the positive electrode includes a positive electrode active material layer, the positive electrode active material layer includes a positive electrode active material, the positive electrode active material includes a first positive electrode active material and a second positive electrode active material, and after the electrochemical device is completely discharged, the Raman spectrum of the positive electrode active material layer is Wavenumber 398 cm -1 ~408 cm -1 has a first characteristic peak at Wavenumber 940 cm -1 ~960 cm -1It has a second characteristic peak, and the second positive electrode active material contains an aluminum element. The first characteristic peak is the characteristic peak of the second positive electrode active material, the second characteristic peak is the characteristic peak of the first positive electrode active material, the second positive electrode active material has a higher capacity per gram, and the aluminum element can enhance the stability of the manganese-oxygen bond in the second positive electrode active material during the cycling process, endow the positive electrode active material layer with relatively excellent structural stability, increase the energy density of the electrochemical device, and improve its high-temperature cycling characteristics.

[0005] In the Several embodiment of the present invention, after the electrochemical device is fully discharged, the Raman spectrum of the positive electrode active material layer is Wavenumber 591 cm -1 ~611 cm -1 and has a third characteristic peak, and the full width at half maximum of the third characteristic peak is 15 cm -1 ~60 cm -1 and the third characteristic peak is the characteristic peak of the second positive electrode active material. When the full width at half maximum of the third characteristic peak is within the above range, it is shown that the interior of the second positive electrode active material has a stable crystal structure, can suppress the phase transition of the material structure during the cycling process, improve the structural stability of the material, and improve the cycling characteristics of the electrochemical device.

[0006] In the Several embodiment of the present invention, the full width at half maximum of the first characteristic peak is 15 cm -1 ~60 cm -1 and the full width at half maximum of the second characteristic peak is 5 cm -1 ~25 cm -1 and the full width at half maximum of the first characteristic peak is larger than that of the second characteristic peak. Since the crystallinity of the second positive electrode active material is lower than that of the first positive electrode active material, its full width at half maximum is relatively large, the full width at half maximum of the first positive electrode active material is relatively small, the crystallinity is good, and the structural change during the charge-discharge process is small. The active ions inside the second positive electrode active material compensate for the loss of active ions on the surface of the negative electrode active material, ensure the transport of active ions, and are beneficial to the improvement of the cycling characteristics of the electrochemical device.

[0007] In the SeveralIn an embodiment, the first positive electrode active material contains iron element, and the second positive electrode active material contains manganese element. The second positive electrode active material has a higher capacity per gram and can endow the electrochemical device with a higher discharge specific capacity. A synergistic effect occurs between the first positive electrode active material and the second positive electrode active material. During the charge and discharge process of the electrochemical device, the active ions in the second positive electrode active material can desorb from it, effectively compensating for the irreversible loss of the active ions on the surface of the negative electrode active material. The remaining active ions can be inserted into the first positive electrode active material, effectively improving the capacity of the positive electrode active material and the cycle performance of the electrochemical device.

[0008] In the embodiment of the present invention Several the positive electrode active material layer contains manganese element, and the mass fraction ω Al of aluminum element satisfies 0.1% ≤ ω Al ≤ 5% with respect to the mass of manganese element in the positive electrode active material layer. When the mass fraction of aluminum element satisfies the above relational expression, the stability of the manganese-oxygen bond in the second positive electrode active material can be enhanced, and further the cycle performance of the electrochemical device can be improved.

[0009] In the embodiment of the present invention Several the mass fraction ω Mn of manganese element and the mass fraction ω Fe of iron element satisfy 0.01% ≤ ω Mn / ω Fe ≤ 30%, preferably 1% ≤ ω Mn / ω Fe ≤ 25% with respect to the mass of the positive electrode active material layer. When the mass fractions of manganese element and iron element are within the above ranges, the energy density of the electrochemical device can be further increased and its cycle performance can be improved.

[0010] In the embodiment of the present invention SeveralIn an embodiment, the positive electrode active material layer contains element M, and the element M is at least one selected from the group consisting of Nb, Mg, Ti, W, Ga, Zr, Y, V, Sr, Mo, Cr, Sn, La, and Ce. Adding element M to the second positive electrode active material can enhance the stability of the manganese-oxygen bond inside the material, suppress the elution of the manganese element, further improve the cycle characteristics of the electrochemical device, and increase its energy density.

[0011] In the Several embodiment of the present invention, the mass fraction ω M of element M satisfies 0.03% < ω M ≤ 2.5% with respect to the mass of the positive electrode active material layer. When the mass fraction of element M is within this range, the cycle characteristics of the electrochemical device can be more effectively improved, and its energy density can be increased.

[0012] In the Several embodiment of the present invention, the electrolytic solution contains an additive, and the additive contains a fluorocarbonate and / or an inorganic lithium salt. The fluorocarbonate and / or the inorganic lithium salt helps to form a dense and stable interfacial film on the surface of the positive electrode active material, further strengthens the protection of the positive electrode active material, and improves the cycle characteristics of the electrochemical device.

[0013] In the Several embodiment of the present invention, the mass fraction of the additive is 0.01% - 10% with respect to the mass of the electrolytic solution. When the mass fraction of the additive in the electrolytic solution is within an appropriate range, it helps to form an interfacial film with an appropriate thickness on the surface of the positive electrode active material, has a low impedance at the same time, and further improves the cycle characteristics of the electrochemical device.

[0014] In the Several embodiment of the present invention, the fluorocarbonate contains at least one of fluoroethylene carbonate and fluoropropylene carbonate.

[0015] In the SeveralIn an embodiment, the inorganic lithium salt includes at least one of lithium difluorophosphate and lithium tetrafluoroborate.

[0016] In the present invention Several In an embodiment, the mass fraction of the fluorocarbonate is 0.01% to 8% with respect to the mass of the electrolytic solution.

[0017] In the present invention Several In an embodiment, the mass fraction of the fluorocarbonate is 0.01% to 5% with respect to the mass of the electrolytic solution.

[0018] In the present invention Several In an embodiment, the mass fraction of the inorganic lithium salt is 0.01% to 3% with respect to the mass of the electrolytic solution.

[0019] In the present invention Several In an embodiment, the mass fraction of the inorganic lithium salt is 0.01% to 1.5% with respect to the mass of the electrolytic solution.

[0020] The second aspect of the present invention provides an electronic device including the electrochemical device of the first aspect of the present invention.

Brief Description of the Drawings

[0021]

Figure 1

Embodiments for Carrying Out the Invention

[0022] 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 in accordance with the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. The related embodiments described in this specification are exemplary and are used to provide a basic understanding of the present invention. The embodiments 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 provided embodiments, all other embodiments obtained by those skilled in the art without creative efforts fall within the protection scope of the present invention.

[0023] For the sake of brevity, this specification specifically discloses only some numerical ranges. However, any lower limit can form a range that is not clearly described in combination with any upper limit, and any lower limit can form a range that is not clearly described in combination with other lower limits. Similarly, any upper limit can form a range that is not clearly described in combination with any other upper limit. Also, each individually disclosed point or single numerical value itself can be combined with any other point or single numerical value as a lower limit or an upper limit, or combined with other lower limits or upper limits to form a range that is not clearly described.

[0024] In the description of this specification, unless otherwise specified, "above" and "below" include the corresponding numerical values.

[0025] Unless otherwise specified, the terms used in this specification have the well-known meanings generally understood by those skilled in the art. Unless otherwise specified, the numerical values of each parameter described in the present invention can be measured by various measurement methods commonly used in the art (for example, measurement can be performed according to the methods shown in the embodiments of the present invention).

[0026] A list of items connected by the terms "at least one of", "at least one of", "at least one of", or other similar terms means any combination of the listed items. For example, if items A and B are listed, the phrase "at least one of A and B" means only A, only B, or both A and B. In another example, if items A, B, and C are listed, the phrase "at least one of A, B, and 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 element or multiple elements. Item B may include a single element or multiple elements. Item C may include a single element or multiple elements.

[0027] Electrochemical device A first aspect of an embodiment of the present invention provides an electrochemical device, which includes any device that causes an electrochemical reaction to convert chemical energy and electrical energy into each other. Specific examples include, but are not limited to, lithium-ion batteries.

[0028] The electrochemical device of the present invention includes a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a positive electrode active material layer, the positive electrode active material layer includes a positive electrode active material, the positive electrode active material includes a first positive electrode active material and a second positive electrode active material, and after the electrochemical device is completely discharged, the Raman spectrum of the positive electrode active material layer is Wavenumber 398 cm -1 ~408 cm -1 has a first characteristic peak at, Wavenumber 940 cm -1 ~960 cm -1 has a second characteristic peak at, and the second positive electrode active material contains an aluminum element. The Raman spectrum of the positive electrode active material layer is Wavenumber 398 cm -1 ~408 cm -1 has a first characteristic peak at, Wavenumber 940 cm -1 ~960 cm -1It has a second characteristic peak, where the first characteristic peak is the characteristic peak corresponding to the second positive electrode active material, and the second characteristic peak is the characteristic peak corresponding to the first positive electrode active material. Since the second positive electrode active material has a relatively high capacity per gram, the positive electrode active material containing the second positive electrode active material and the first positive electrode active material also has a relatively high capacity per gram, which is further advantageous for improving the energy density of the electrochemical device. The second positive electrode active material contains an aluminum element, and the aluminum element can improve the variation of the bond length of the manganese-oxygen bond in the second positive electrode active material during the cycling process, strengthen the stability of the manganese-oxygen bond, and further improve the cycling performance of the electrochemical device. At the same time, due to the synergistic effect of the first positive electrode active material and the second positive electrode active material, the positive electrode active material layer can have relatively excellent structural stability, and the electrochemical device can have a high energy density and high-temperature cycling performance.

[0029] In some embodiments of the present invention, Wavenumber 398 cm -1 ~408 cm -1 The first characteristic peak is the characteristic peak caused by the stretching vibration of the Mn-O bond in the second positive electrode active material, Wavenumber 940 cm -1 ~960 cm -1 The second characteristic peak is the characteristic peak of the internal mode of (PO4) in the first positive electrode active material. 3-

[0030] In the present invention, the fully discharged state of the electrochemical device means that the electrochemical device is charged to 3.65 V at a constant current of 0.2 C, and then charged at a constant voltage until the current reaches 0.05 C, left standing for 5 min, and then discharged to 2.5 V at a constant current of 0.2 C. According to the above charge-discharge process, after two cycles, the obtained electrochemical device is in a fully discharged state.

[0031] In some embodiments of the present invention, the full width at half maximum of the first characteristic peak may be 15 cm -1 ~60 cm -1 and the full width at half maximum of the second characteristic peak may be 5 cm -1 ~25 cm -1It may also be that the full width at half maximum of the first characteristic peak is larger than the full width at half maximum of the second characteristic peak. For example, the full width at half maximum of the first characteristic peak is 15 cm -1 , 25 cm -1 , 38 cm -1 , 45 cm -1 , 52 cm -1 , or 60 cm -1 and may also be within the range consisting of any of the above numerical values. The full width at half maximum of the second characteristic peak is 5 cm -1 , 8 cm -1 , 12 cm -1 , 16 cm -1 , 22 cm -1 , or 25 cm -1 and may also be within the range consisting of any of the above numerical values. Since the crystallinity of the second positive electrode active material is lower than that of the first positive electrode active material, its full width at half maximum is relatively large, the full width at half maximum of the first positive electrode active material is relatively small, the crystallinity is good, and the structural change during the charge and discharge process is small. The active ions inside the second positive electrode active material can compensate for the loss of active ions on the surface of the negative electrode active material and can also reinsert sufficient active ions into the second positive electrode active material, ensuring the transport of active ions, which is advantageous for improving the cycle characteristics of the electrochemical device.

[0032] In some embodiments of the present invention, after the electrochemical device is fully discharged, the Raman spectrum of the positive electrode active material layer is Wavenumber 591 cm -1 ~611 cm -1 has a third characteristic peak, and the full width at half maximum of the third characteristic peak may be 15 cm -1 ~60 cm -1 and may also be within the range consisting of any of the above numerical values. For example, the full width at half maximum of the third characteristic peak is 15 cm -1 , 25 cm -1 , 40 cm -1 , 45 cm -1 , 54 cm -1 , or 60 cm -1Or it may be within a range consisting of any of the above numerical values. When the full width at half maximum of the third characteristic peak is within the above range, it has been shown that the interior of the second positive electrode active material has a stable crystal structure, suppressing the phase transition of the material structure during the cycling process, enhancing the structural stability of the material, and improving the cycling characteristics of the electrochemical device.

[0033] In the electrochemical device of the present invention, the third characteristic peak is a characteristic peak corresponding to the second positive electrode active material. As can be seen from FIG. 1, the Raman spectrum of the positive electrode active material layer of Example 1 provided in the present invention includes a first characteristic peak, a second characteristic peak, and a third characteristic peak.

[0034] In the present invention, the Raman spectrum of the positive electrode active material layer, and the full width at half maximum of the first characteristic peak, the second characteristic peak, and the third characteristic peak have meanings known in the art and can be measured using methods known in the art. For example, the lithium ion battery is charged to 3.65 V at a constant current of 0.2 C, then charged at a constant voltage until the current becomes 0.05 C, left standing for 5 min, then discharged to 2.5 V at a constant current of 0.2 C, cycled twice in this way, and after completion, the lithium ion battery is disassembled, the positive electrode plate is taken out, the positive electrode plate is immersed in DMC (dimethyl carbonate) for 30 min, and after removing the electrolyte solution and by-products on the surface of the positive electrode plate, it is dried in a ventilation hood for 4 hours. The dried positive electrode plate is sliced using an ion milling device (JEOL - IB - 09010CP), measured using a Raman spectrometer (model number HR Evolution), in the wavenumber range of 150 to 1200 cm -1 -1, a range of 2 cm × 2 cm is selected, the average value of the spectrum is taken, and a figure of the Raman spectrum is obtained. The full width at half maximum refers to the total width of the band when the height of the band of the characteristic peak is half of the maximum height, that is, the width of the peak when the height of the peak is half.

[0035] In some embodiments, the first positive electrode active material contains iron element, and the second positive electrode active material contains manganese element. The first positive electrode active material in the positive electrode active material contains an olivine structure, and its structure is relatively stable. In the charge and discharge process of the electrochemical device, the volume change is small, that is, the influence of the insertion and desorption of active ions on the structure of the first positive electrode active material is small, and it has good charge and discharge reversibility. The second positive electrode active material has a relatively high capacity per gram and can endow the electrochemical device with a relatively high discharge specific capacity. The electrochemical device of the present invention can fully exert the synergistic effect between the first positive electrode active material and the second positive electrode active material. In the charge and discharge process of the electrochemical device, the active ions in the second positive electrode active material desorb from it, and some of the active ions deposit on the negative electrode, which can effectively compensate for the irreversible loss of the active ions on the surface of the negative electrode active material due to the repair of the SEI film. The remaining active ions can be inserted into the first positive electrode active material, and the cycle characteristics of the electrochemical device can be improved.

[0036] In some embodiments, the first positive electrode active material includes, but is not limited to, lithium iron phosphate, a composite material of lithium iron phosphate and carbon.

[0037] In some embodiments, the positive electrode active material layer contains manganese element, and the mass fraction ω Al of aluminum element satisfies 0.1% ≦ ω Al ≦ 5% with respect to the mass of manganese element in the positive electrode active material layer. For example, the mass fraction ω Al of aluminum element satisfies 0.15% ≦ ω Al ≦ 5%, 0.8% ≦ ω Al ≦ 5%, 1.2% ≦ ω Al ≦ 5%, 2.6% ≦ ω Al ≦ 5%, 3.5% ≦ ω Al ≦ 5%, 4% ≦ ω Al ≦ 5%, 0.2% ≦ ω Al ≦ 4%, 0.9% ≦ ω Al ≦ 4%, 1.5% ≦ ω Al ≦ 4%, 2.5% ≦ ω Al ≦ 4%, 3% ≦ ω Al ≦ 4%, 0.3% ≦ ωAl ≤3%, 1% ≤ ω Al ≤3%, 1.6% ≤ ω Al ≤3%, 0.8% ≤ ω Al ≤2%, or 0.1% ≤ ω Al satisfies ≤1%. Preferably, the mass fraction ω of the aluminum element Al is such that 0.3% ≤ ω with respect to the mass of the manganese element in the positive electrode active material layer Al ≤3%. The aluminum element is closely related to the peak position of the first characteristic peak of the second positive electrode active material. When the mass fraction of the aluminum element satisfies the above relational expression, the peak position of the first characteristic peak shifts to the right, strengthening the stability of the manganese-oxygen bond in the second positive electrode active material, and further improving the high-temperature cycle characteristics of the electrochemical device. If the doping amount of the aluminum element in the second positive electrode active material is too large, the aluminum element occupies the active positions of the active ions, resulting in a decrease in the capacity per gram of the second positive electrode active material, which is disadvantageous for improving the energy density of the electrochemical device.

[0038] In some embodiments, the mass fraction ω of the manganese element Mn and the mass fraction ω of the iron element Fe satisfy 0.01% ≤ ω with respect to the mass of the positive electrode active material layer Mn / ω Fe ≤30%. The mass fraction ω of the manganese element Mn and the mass fraction ω of the iron element Fe can reflect the mass fractions of the second positive electrode active material and the first positive electrode active material in the positive electrode active material. The mass fraction ω of the manganese element MnThe higher the mass fraction of the second positive electrode active material in the positive electrode active material, the higher the mass fraction of the second positive electrode active material in the positive electrode active material, and the second positive electrode active material has a high capacity per gram, so that the electrochemical device has a high discharge specific capacity. The active ions of the second positive electrode active material can be desorbed from it and deposited on the negative electrode during the cycle process of the electrochemical device, and can compensate for the loss of active ions on the surface of the negative electrode active material. A high mass fraction of the second positive electrode active material in the positive electrode active material can provide more desorbable active ions, which can not only effectively compensate for the loss of active ions on the surface of the negative electrode active material, but also allow sufficient active ions to be reinserted into the second positive electrode active material, ensure the transport of active ions, and effectively increase the cycle capacity retention rate of the electrochemical device, increase its energy density, and improve its cycle characteristics. Compared with the first positive electrode active material, the mass fraction of the second positive electrode active material should not be too high. If the mass fraction of the second positive electrode active material is too high, it will provide too many detachable and compensable active ions. If the amount is greater than the amount of active ions that can be reinserted into the positive electrode active material layer, the internal resistance will increase and the discharge specific capacity of the electrochemical device will decrease. Therefore, the mass fraction of the second positive electrode active material and the first positive electrode active material in the positive electrode active material, i.e., the mass fraction ω of elemental manganese, Mn and the mass fraction of iron, ω Fe By controlling the amount of the charge and the charge concentration within the above range, the cycle characteristics of the electrochemical device can be effectively improved and the energy density thereof can be increased.

[0039] In some embodiments, the mass fraction of elemental manganese, ω Mn and the mass fraction of iron, ω Fe 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%≦ωMn / 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% ≤ ωMn / 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 fraction ω Mn of the manganese element and the mass fraction ω Fe of the iron element satisfy 1% ≤ ω Mn / ω Fe ≤ 25%, and at this time, the electrochemical device has better cycle characteristics and high energy density.

[0040] In some embodiments, the positive electrode active material layer contains element M, and the element M is at least one selected from the group consisting of Nb, Mg, Ti, W, Ga, Zr 、Y , V, Sr, Mo, Cr, Sn, La, and Ce. For example, the element M may be Nb, may be Ga, may be Mo, may be V, may be W and Y, or may be La and Ce. The element M may be any one or more of the above elements. Adding element M to the second positive electrode active material can enhance the stability of the manganese-oxygen bond inside the material, suppress the elution of the manganese element, and further improve the high-temperature cycle characteristics of the electrochemical device. At the same time, element M can also increase the content of desorbable active ions in the second positive electrode active material, desorb sufficient active ions from the second positive electrode active material to supplement the loss of active ions on the surface of the negative electrode active material, and reinsert sufficient active ions into the positive electrode active material layer, further increasing the capacity and energy density of the electrochemical device.

[0041] In some embodiments, the mass fraction ω of element M M satisfies 0.03% < ω M ≤ 2.5% with respect to the mass of the positive electrode active material layer. For example, the mass fraction ω of element M M satisfies 0.05% ≤ ω M ≤ 1.5%, 0.1% ≤ ω M ≤ 1.5%, 0.5% ≤ ω M ≤ 1.5%, 1% ≤ ω M ≤ 1.5%, 0.05% ≤ ω M ≤ 1%, 0.1% ≤ ω M ≤ 1% or 0.5% ≤ ω M ≤ 1%. When the mass fraction ω of element M M satisfies 0.03% < ω M ≤ 2.5%, it is advantageous for further improving the stability of the manganese-oxygen bond, suppressing the elution of manganese, and making the content of desorbable lithium in the second positive electrode active material fall within an appropriate range. It can have sufficient active ions to compensate for the loss of active ions on the surface of the negative electrode active material in the second positive electrode active material, and can have sufficient active ions to reinsert into the positive electrode active material layer, further increasing the energy density of the electrochemical device and improving the high-temperature cycle characteristics of the electrochemical device. In some embodiments, the mass fraction ω of element M M satisfies 0.03% < ω M ≤ 1.5% with respect to the mass of the positive electrode active material layer, which is advantageous for improving the energy density of the electrochemical device and the high-temperature cycle characteristics of the electrochemical device.

[0042] In the present invention, the types of elements in the positive electrode active material layer can be measured using methods known in the art. For example, the positive electrode sheet obtained by disassembling a lithium-ion battery is dried, and the dried positive electrode sheet is sliced using an ion milling device (JEOL-IB-09010CP), and then the cross-section of the slice is observed using a scanning electron microscope (SEM) to search for particles in the cross-section. After measurement using an energy dispersive spectrometer (EDS), the types of elements in the positive electrode active material layer are determined.

[0043] In the present invention, the measurement of the content of each element in the positive electrode active material layer can be carried out using methods known in the art. For example, the positive electrode sheet obtained by disassembling a lithium ion battery is washed with DMC, the active material layer of the positive electrode sheet washed with DMC is scraped off with a doctor blade, and dissolved in a mixed solvent (for example, for 0.4 g of the positive electrode active material layer, a mixed solvent of 10 mL of aqua regia (mixing nitric acid and hydrochloric acid at 1:1) and 2 mL of HF is used), made up to 100 mL in volume, and then the mass fraction of elements such as element Mn, Fe, Al, M, etc. in the solution is measured using an ICP (Inductively coupled plasma) analyzer.

[0044] In some embodiments, by way of example, the second positive electrode active material can be prepared using the following method. Put MnOOH into a corundum crucible, heat it up to 500 °C at a heating rate of 5 °C / min under an air atmosphere, maintain the constant temperature for 1 h to obtain anhydrous Mn3O4. Weigh anhydrous Mn3O4 and LiOH at a ratio of Li:Mn molar ratio of 1.05:1, and add nano-Al2O3 at a ratio of Al:Mn elemental mass ratio of 0.0163:1, and nano-magnesium oxide can be added at a ratio of Mg:Mn elemental mass ratio of 0.008:1. Also, element M can be added at a certain ratio, and the element M is, for example, at least one of Nb, Ti, W, Ga, Zr 、Y , V, Sr, Mo, Cr, Sn, La, and Ce. The above substances can be uniformly mixed using a sand mill to obtain a mixture precursor. Put the precursor into a corundum crucible, pass nitrogen gas at a rate of 2 m 3 / h, heat it up to 940 °C at a heating rate of 5 °C / min, maintain the constant temperature for 10 h, and naturally cool to room temperature to obtain the second positive electrode active material. However, MnO2 can be used instead of Mn3O4, and the mixing ratio with LiOH can be adjusted according to the content of Mn at the same time.

[0045] In some embodiments, the positive electrode active material layer may optionally contain a conductive agent and a binder. The specific types of the conductive agent and the binder are not particularly limited and can be selected as needed. For example, the conductive agent includes, but is 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. For example, the binder includes, but is 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).

[0046] 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.

[0047] In some embodiments, the positive electrode current collector can be a metal foil or a porous metal plate, for example, a foil or a porous plate of a metal such as aluminum, copper, nickel, titanium, silver, or an alloy thereof can be used. For example, the positive electrode current collector is an aluminum foil.

[0048] 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 either 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 either surface satisfy the range of the parameters of the present invention, it is considered to be within the protection scope of the present invention.

[0049] The positive electrode sheet can be prepared according to the conventional methods in the art. Usually, a first positive electrode active material, a second positive electrode active material, and any conductive agent and binder are dispersed in a solvent to form a uniform positive electrode slurry, and the solvent may be N-methylpyrrolidone (NMP). The positive electrode slurry is coated on the positive electrode current collector, and through processes such as drying and cold pressing, a positive electrode sheet is obtained.

[0050] The positive electrode sheet of the present invention may include 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), and the conductive undercoat layer is sandwiched between the positive electrode current collector and the positive electrode active material layer and is provided on the surface of the positive electrode current collector. In 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.

[0051] In the present invention, the electrolyte plays a role of conducting active ions between the positive electrode and the negative electrode.

[0052] In some embodiments, the electrolyte contains an additive, and the additive may include a fluorocarbonate and / or an inorganic lithium salt. For example, the additive may contain both a fluorocarbonate and an inorganic lithium salt, or may contain either a fluorocarbonate or an inorganic lithium salt.

[0053] In some embodiments, the fluorocarbonate includes at least one of fluoroethylene carbonate and fluoropropylene carbonate.

[0054] In some embodiments, the inorganic lithium salt includes at least one of lithium difluorophosphate and lithium tetrafluoroborate.

[0055] The additive contained in the electrolyte of the present invention helps to form a dense and stable interfacial film on the surface of the positive electrode active material, further enhances the protection of the positive electrode active material, suppresses side reactions between the electrolyte and the positive electrode active material, reduces the interfacial impedance, and improves the high-temperature cycle characteristics of the electrochemical device.

[0056] In some embodiments, the mass fraction of the additive is 0.01% to 10% based on the mass of the electrolyte. The mass fraction of the additive is 0.05%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7% , 8%, or 10%, or within the range consisting of any of the above numerical values.

[0057] In the present invention, when the mass fraction of the additive in the electrolyte is within an appropriate range, it helps to form an interfacial film with an appropriate thickness on the surface of the positive electrode active material, and at the same time has a low impedance, which is advantageous for improving the cycle characteristics of the electrochemical device. If the mass fraction of the additive is too small, the formation of the interfacial film on the surface of the positive electrode active material will be insufficient, affecting the performance of the electrochemical device. If the mass fraction of the additive for film formation is too high, the impedance of the electrolyte will increase, the migration rate of active ions will decrease, and the high-temperature cycle characteristics of the electrochemical device will be affected.

[0058] In some embodiments, the mass fraction of fluorocarbonate may be 0.01% to 8%, which can further improve the high-temperature cycle characteristics of the electrochemical device.

[0059] In some embodiments, the mass fraction of fluorocarbonate may be 0.01% to 5%, which can further improve the high-temperature cycle characteristics of the electrochemical device.

[0060] In some embodiments, the mass fraction of inorganic lithium salt may be 0.01% to 3%, which can further improve the high-temperature cycle characteristics of the electrochemical device.

[0061] In some embodiments, the mass fraction of the inorganic lithium salt may be 0.01% to 1.5%, and the high-temperature cycle performance of the electrochemical device can be further improved.

[0062] In some embodiments, the electrolyte includes an organic solvent and any other optional additives. The types of the organic solvent and other additives are not particularly limited and can be selected as needed.

[0063] In some embodiments, for example, the organic solvent includes 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), but is not limited thereto. The above organic solvent may be used alone or in combination of two or more. Optionally, the above organic solvent is used in combination of two or more.

[0064] In some embodiments, the other additives may include additives that can improve certain performance of the battery, such as additives for improving the overcharge performance of the battery, additives for improving the high-temperature or low-temperature performance of the battery, and the like.

[0065] The electrolyte can be prepared according to the conventional methods in the art. For example, additives, organic solvents, and any other optional additives can be uniformly mixed to obtain the electrolyte. The addition order of each material is not particularly limited. For example, additives and any other optional additives are added to the organic solvent and uniformly mixed to obtain the electrolyte.

[0066] In the present invention, the negative electrode is a negative electrode sheet, which may be a lithium metal 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 includes a negative electrode active material, as well as an optional conductive agent, binder, and thickener.

[0067] The materials, configurations, and manufacturing methods of the negative electrode sheets used in the present invention may include any techniques known in the prior art.

[0068] The specific type of the negative electrode active material is not particularly limited and can be selected as needed. By way of example, the negative electrode active material includes, but is not limited to, 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 , and Li-Al alloy.

[0069] The specific type of the conductive agent is not particularly limited and can be selected as needed. By way of example, the conductive agent includes, but is not limited to, at least one of conductive graphite, superconducting carbon, acetylene black, carbon black, ketjen black, carbon dot, carbon nanotube, graphene, and carbon nanofiber.

[0070] The specific type of the binder is not particularly limited and can be selected as needed. By way of example, the binder includes, but is 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.

[0071] The specific type of the thickener is not particularly limited and can be selected as needed. By way of example, the thickener includes, but is not limited to, sodium carboxymethyl cellulose (CMC -Na ).

[0072] However, the present invention is not limited to the above materials, and the negative electrode sheet of the present invention can also use other known materials used as the negative electrode active material, the conductive agent, the binder, and the thickener.

[0073] In some embodiments, the negative electrode current collector has two surfaces facing each other in its thickness direction, Negative electrode active material layer and is provided on one or both of the two opposing surfaces of the negative electrode current collector.

[0074] The negative electrode current collector can be a metal foil or a porous metal plate, and for example, a foil or a porous plate of a metal such as copper, nickel, titanium, iron or an alloy thereof can be used. By way of example, the negative electrode current collector is a copper foil.

[0075] The negative electrode sheet can be prepared according to conventional methods in the art. Usually, the negative electrode active material, and any conductive agent, binder, and thickener are dispersed in a solvent to form a uniform negative electrode slurry, and the solvent may be N-methylpyrrolidone (NMP) or deionized water. The negative electrode slurry is applied onto the negative electrode current collector, and the negative electrode sheet is obtained through processes such as drying and cold pressing.

[0076] The negative electrode sheet of the present invention may include 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), and the conductive undercoat layer is 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 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.

[0077] In the present invention, the electrochemical device further includes a separator. The separator is provided between the positive electrode sheet and the negative electrode sheet, mainly plays a role in preventing short circuit between the positive and negative electrodes, and can allow active ions to pass through. The type of the separator of the present invention is not particularly limited, and any known separator with a porous structure having good chemical stability and mechanical stability can be used.

[0078] In some embodiments, the material of the separator can include at least one 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. In some embodiments, a ceramic coating or a metal oxide coating can also be provided on the separator.

[0079] Electronic device A second aspect of the embodiments of the present invention provides an electronic device, and the electronic device includes the electrochemical device according to the first aspect of the embodiments of the present invention, and the electrochemical device can be used as a power source in the electronic device.

[0080] The electronic device of the present invention is not particularly limited and may be any known electronic device used in the prior art. In some embodiments, the electronic device may include, but is not limited to, a notebook computer, a pen-input computer, a mobile computer, an e-book player, a mobile phone, a portable facsimile machine, a portable copier, a portable printer, a 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 tape recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, an assisted bicycle, a bicycle, a lighting fixture, a toy, a game machine, a clock, a power tool, a flash, a camera, a large household battery, and a lithium ion capacitor, etc.

[0081] Example Since various modifications and changes within the scope disclosed in the present invention will be apparent to those skilled in the art, the following examples are provided to more specifically illustrate the content disclosed in the present invention, and these examples are used only for illustrative purposes. Unless otherwise specified, 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 can be obtained by synthesis by ordinary methods and can be used directly without further treatment. Also, all equipment used in the examples is commercially available.

[0082] Example 1 Preparation of positive electrode sheet LiFePO4, which is the first positive electrode active material, and the second positive electrode active material were uniformly mixed at a mass ratio of 92:8, and sintered in a nitrogen atmosphere at 300 °C for 2 h to obtain a positive electrode active material. Here, the manufacturing process of the second positive electrode active material was as follows. MnOOH was put into a corundum crucible, and the temperature was raised to 500 °C at a heating rate of 5 °C / min under an air atmosphere, and the constant temperature was maintained for 1 h to obtain anhydrous Mn3O4. Anhydrous Mn3O4 and LiOH were weighed at a ratio of Li:Mn molar ratio of 1.05:1, and nano-Al2O3 was added at a ratio of Al:Mn elemental mass ratio of 0.0163:1, and nano-magnesium oxide was added at a ratio of Mg:Mn elemental mass ratio of 0.008:1. The above substances were uniformly mixed using a sand mill to obtain a precursor mixture. The precursor was put into a corundum crucible, nitrogen gas was passed through at a rate of 2 m 3 / h, the temperature was raised to 940 °C at a heating rate of 5 °C / min, the constant temperature was maintained for 10 h, and it was naturally cooled to room temperature to obtain the second positive electrode active material.

[0083] The positive electrode active material, Super P as a conductive agent, and polyvinylidene fluoride as a binder were mixed at a mass ratio of 96:2.4:1.6, N-methylpyrrolidone (NMP) was added, and the system was stirred by a vacuum stirrer until it became uniform to obtain a positive electrode slurry. Here, the solid content concentration of the positive electrode slurry was 70 wt%. The positive electrode slurry was uniformly coated on one surface of an aluminum foil, which was a positive electrode current collector 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 and a coating layer thickness of 65 μm. The above procedure was repeated on the other surface of the aluminum foil, that is, a positive electrode sheet with positive electrode active material layers coated on both sides was obtained. 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 specification of 74 mm × 867 mm.

[0084] Preparation of negative electrode sheet Artificial graphite, which is the negative electrode active material, Super P as a conductive agent, and sodium carboxymethyl cellulose (CMC) as a thickening agent -Na) and styrene-butadiene rubber (SBR) as a binder were mixed at a mass ratio of 96.4:1.5:0.5:1.6, deionized water was added, and under the action of a vacuum stirrer, a negative electrode slurry was obtained. Here, the solid content concentration of the negative electrode slurry was 70 wt%. The negative electrode slurry was uniformly coated on one surface of a copper foil which was a negative electrode current collector with a thickness of 10 μm, and the copper foil was dried at 85°C to obtain a negative electrode sheet with a coating layer thickness of 63 μm and a negative electrode active material layer coated on one side. Copper foil The above procedure was repeated on the other surface of Copper foil , that is, a negative electrode sheet with negative electrode active material layers coated on both sides was obtained. 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 specification of 79 mm × 972 mm.

[0085] Preparation of electrolyte In a glove box with an argon atmosphere having a water content <10 ppm, chain carbonate DEC, cyclic carbonate EC, and cyclic carbonate PC were mixed at a mass ratio of 1:1:1 to obtain a base solvent. Then, lithium salt LiPF6 was added to the base solvent and dissolved, and they were uniformly mixed. Here, the mass fraction of LiPF6 was 12.5% with respect to the mass of the electrolyte. Alternatively, FEC or lithium difluorophosphate was further added to the electrolyte.

[0086] Preparation 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 slurry of a coating layer with a solid content concentration of 50 wt%. The slurry of the coating layer was uniformly coated on the surface of a PE film (provided by Celgard) with a thickness of 5 μm, and dried at 85°C to obtain a separator with a coating layer thickness of 5 μm and a coating layer coated on one side. The above procedure was repeated on the other surface of the separator, that is, a separator with coating layers coated on both sides was obtained. Then, after drying and cold pressing, a separator was obtained.

[0087] Preparation of lithium-ion battery The prepared positive electrode sheet, separator, and negative electrode sheet were stacked in sequence, with the separator positioned between the positive electrode sheet and the negative electrode sheet to serve as an isolation function. They were wound to obtain an electrode assembly. The electrode assembly was placed in an aluminum laminated film packaging bag, dried, and then an electrolytic solution was injected. After passing through processes such as vacuum sealing, standing, formation, degassing, and edge trimming, a lithium-ion battery was obtained. Here, the formation conditions were as follows. Charge to 3.3 V at a constant current of 0.02 C, and then charge to 3.6 V at a constant current of 0.1 C. Charge to 4.2 V at a constant current of 0.2 C, stand for 10 min, then discharge to 2.5 V, stand for 10 min, and then charge to 3.0 V at a constant current of 0.2 C.

[0088] Examples 2 to 25 and Comparative Examples 1 to 2 The manufacturing method of the lithium-ion battery was the same as that of Example 1 except that the relevant parameters in the preparation process of the positive electrode sheet and the electrolytic solution were adjusted. For specific parameters, refer to Table 1, where " / " indicates that the corresponding component is not present.

[0089] Measurement content (1) Measurement of the discharge specific capacity of the lithium-ion battery The lithium-ion battery was charged to 3.65 V at a constant current of 0.2 C, and then charged at a constant voltage until the current reached 0.05 C. It was left standing for 5 min, and then discharged to 2.5 V at a constant current of 0.2 C. According to the above charge-discharge process, it was cycled 2 times, and the capacity of the second cycle was recorded as D0. The lithium-ion battery was disassembled, the positive electrode sheet was taken out, the positive electrode sheet was immersed in DMC (dimethyl carbonate) for 30 min, and after removing the electrolytic solution and by-products on the surface of the positive electrode sheet, it was dried in a ventilation hood for 4 hours, and the electrode sheet was baked into powder at 400 °C in a vacuum, and its mass was weighed and recorded as m1.

[0090] The discharge specific capacity of the lithium-ion battery = D0 / m1.

[0091] (2) Measurement of the cycle characteristics of the lithium-ion battery The lithium-ion battery was charged at a constant current of 1C to 3.65V at 45°C, and then charged at a constant voltage until the current reached 0.05C, left standing for 5 minutes, and then discharged at a constant current of 1C to 2.5V. This was one charge-discharge cycle, and the discharge capacity at this time was measured and recorded as D01. According to the above charge-discharge process, the lithium-ion battery was cycled 1000 times, and the discharge capacity at the 1000th cycle was measured and recorded as D1.

[0092] The cycle capacity retention rate (%) of the lithium-ion battery = D1 / D01×100%.

[0093] Tables 1 to 3 show the results of performance measurements of Examples 1 to 25 and Comparative Examples 1 to 2.

[0094]

Table 1

[0095] Figure 1 is the Raman spectrum diagram of the positive electrode active material layer of Example 1. As can be seen from Figure 1, the positive electrode active material layer Wavenumber has a first characteristic peak at 398 cm -1 ~408 cm -1 and has a second characteristic peak at Wavenumber 940 cm -1 ~960 cm -1 and has a third characteristic peak at Wavenumber 591 cm -1 ~611 cm -1 As can be seen from the measurement results in Table 1, the full width at half maximum of the first characteristic peak of the positive electrode active material layer of Examples 1 to 7 is 20.8 cm -1 ~29.6 cm -1 and the full width at half maximum of the second characteristic peak is 10.3 cm -1This is the case. Since Comparative Example 1 does not contain the second positive electrode active material, its Raman spectrum does not have the first characteristic peak, and the discharge specific capacity and high-temperature cycle characteristics are low. The above measurement results show that when a second positive electrode active material containing aluminum element is added 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 first positive electrode active material and the second positive electrode active material, the loss of active lithium on the surface of 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 increased, and the high-temperature cycle characteristics of the lithium-ion battery can be improved.

[0096]

Table 2

[0097] As can be seen from the measurement results in Table 2 above, ω Mn / ω Fe As the value increases, the half-width of the third characteristic peak of the positive electrode active material gradually increases, and within a certain range, the larger the value of ω Mn / ω Fe , the higher the discharge specific capacity and high-temperature cycle stability of the electrochemical device. However, if the Mn content is too high, when the electrochemical device performs charge and discharge cycles at 45 °C, Mn will elute, which will further affect the high-temperature cycle characteristics of the electrochemical device.

[0098]

Table 3

[0099] As can be seen from the measurement results of Example 1 and Examples 16 to 25 in Table 3 above, when the electrolyte simultaneously contains fluorocarbonate and / or inorganic lithium salt as additives, the electrochemical device has a higher retention rate after 1000 cycles at 45°C than Example 1 that does not contain the above additives. The above results indicate that the additives in the electrolyte can form an interfacial film on the surface of the positive electrode active material, strengthen the protection of the positive electrode active material, suppress side reactions between the electrolyte and the positive electrode active material, reduce the interfacial impedance, and further improve the high-temperature cycle characteristics of the electrochemical device.

[0100] As can be understood from the above, due to the synergistic effect between the first positive electrode active material and the second positive electrode active material containing aluminum, the capacity per gram of the positive electrode active material can be greatly increased, the energy density of the electrochemical device can be increased, and its high-temperature cycle characteristics can be improved.

[0101] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Within the technical scope disclosed in the present invention, any technician proficient in the technical field can easily conceive various equivalent changes or substitutions, 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 protection scope of the claims.

Claims

1. An electrochemical device including 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 positive electrode active material, and the positive electrode active material includes a first positive electrode active material and a second positive electrode active material, After the electrochemical device is completely discharged, the Raman spectrum of the positive electrode active material layer has a first characteristic peak at a wavelength of 398 cm －１ to 408 cm －１ and has a second characteristic peak at a wavelength of 940 cm －１ to 960 cm －１ and has and the second positive electrode active material contains an aluminum element. An electrochemical device.

2. After the electrochemical device is completely discharged, the Raman spectrum of the positive electrode active material layer has a third characteristic peak at a wavelength of 591 cm －１ ~611 cm －１ and the full width at half maximum of the third characteristic peak is 15 cm －１ ~60 cm －１ The electrochemical device according to claim 1, wherein the electrochemical device is as described above.

3. The half-value width of the first characteristic peak is 15 cm －１ to 60 cm －１ and the half-value width of the second characteristic peak is 5 cm －１ to 25 cm －１ and The electrochemical device according to claim 1, wherein the half-value width of the first characteristic peak is larger than the half-value width of the second characteristic peak.

4. The electrochemical device according to claim 1, wherein the first positive electrode active material contains an iron element and the second positive electrode active material contains a manganese element.

5. The positive electrode active material layer contains a manganese element. The mass fraction ω of aluminum element Ａｌ satisfies 0.1% ≤ ω Ａｌ ≤ 5% with respect to the mass of manganese element in the positive electrode active material layer, and the electrochemical device according to claim 1.

6. The mass fraction ω of the manganese element Ｍｎ and the mass fraction ω of the iron element Ｆｅ satisfy 0.01% ≤ ω Ｍｎ / ω Ｆｅ ≤ 30% with respect to the mass of the positive electrode active material layer, the electrochemical device according to claim 4.

7. The positive electrode active material layer contains an element M, and the element M is at least one selected from the group consisting of Nb, Mg, Ti, W, Ga, Zr, W, Y, V, Sr, Mo, Cr, Sn, La, and Ce. The mass percentage ω of the element M Ｍ is such that 0.03% < ω Ｍ ≤ 2.5% with respect to the mass of the positive electrode active material layer, for the electrochemical device according to claim 1.

8. The electrolytic solution contains an additive, the additive contains a fluorocarbonate and / or an inorganic lithium salt, and the mass fraction of the additive is 0.01% to 10% with respect to the mass of the electrolytic solution. The electrochemical device according to claim 1.

9. The additive is (1) the fluorocarbonate contains at least one of fluoroethylene carbonate and fluoropropylene carbonate; (2) the inorganic lithium salt contains at least one of lithium difluorophosphate and lithium tetrafluoroborate; (3) the mass fraction of the fluorocarbonate is 0.01% to 8% with respect to the mass of the electrolytic solution; (4) the mass fraction of the inorganic lithium salt is 0.01% to 3% with respect to the mass of the electrolytic solution. The electrochemical device according to claim 8, satisfying at least one of the above.

10. The additive is (5) the mass fraction of the fluorocarbonate is 0.01% to 5% with respect to the mass of the electrolytic solution; (6) the mass fraction of the inorganic lithium salt is 0.01% to 1.5% with respect to the mass of the electrolytic solution. The electrochemical device according to claim 8 or 9, satisfying at least one of the above.

11. The electrochemical device (7) Mass fraction ω of aluminum element Ａｌ satisfies 0.3% ≤ ω Ａｌ ≤ 3% with respect to the mass of manganese element in the positive electrode active material layer, (8) The mass fraction ω of the manganese element Ｍｎ and the mass fraction ω of the iron element Ｆｅ satisfy 1% ≤ ω Ｍｎ / ω Ｆｅ ≤ 25% with respect to the mass of the positive electrode active material layer. (9) The mass fraction ω of the element M Ｍ is such that 0.03% < ω Ｍ ≤ 1.5% with respect to the mass of the positive electrode active material layer, satisfies at least one of the following. The electrochemical device according to any one of claims 1 to 10.

12. An electronic device including the electrochemical device according to any one of claims 1 to 11.

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