An electrochemical device and an electronic device

Abstract

The application provides an electrochemical device and an electronic device, comprising a positive electrode, the positive electrode comprising a positive electrode current collector and a positive electrode active material layer arranged on at least one surface of the positive electrode current collector, the positive electrode active material layer comprising a lithium manganese oxide, the lithium manganese oxide comprising an aluminum element and a sodium element, the content of the aluminum element being A% and the content of the sodium element being B% based on the weight of the positive electrode active material, and satisfying 0.01<=A<=2 and 0.001<=B<=1. The application can improve the cycle performance of the electrochemical device, especially the cycle performance under high temperature conditions, and can also improve the high-temperature storage performance of the electrochemical device.

Description

[0001] This application is a divisional application of the Chinese Patent Application No. 202180002480.3, filed on August 11, 2021, and entitled "An Electrochemical Device and Electronic Device". TECHNICAL FIELD

[0002] The present application relates to the technical field of electrochemistry, in particular to an electrochemical device and electronic device. BACKGROUND

[0003] Lithium ion batteries have many advantages such as large volume and mass energy density, long cycle life, high nominal voltage, low self-discharge rate, small size, light weight, etc., and have been widely used in the field of consumer electronics. With the rapid development of electric vehicles and mobile electronic devices in recent years, the market has put forward higher requirements for lithium ion batteries, for example, lithium ion batteries are required to be stable at high temperatures.

[0004] However, the specific capacity of the current lithium ion battery decays seriously at high temperatures, because high temperature promotes the occurrence of side reactions inside the lithium ion battery, which destroys the structure of the positive active material and affects the stability and service life of the lithium ion battery. Therefore, there is an urgent need for a lithium ion battery with long service life at high temperature. SUMMARY

[0005] The purpose of the present application is to provide an electrochemical device and electronic device to improve the high-temperature cycle performance of the electrochemical device. The specific technical solutions are as follows:

[0006] The first aspect of the present application provides an electrochemical device, comprising a positive electrode, the positive electrode comprising a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, the positive electrode active material layer comprising lithium manganese oxide, the lithium manganese oxide comprising aluminum element and sodium element, the content of aluminum element being A% and the content of sodium element being B% based on the weight of the positive electrode active material, satisfying 0.01≤A≤2 and 0.001≤B≤1.

[0007] The positive electrode active material layer of the present application contains lithium manganese oxide, and the lithium manganese oxide contains aluminum element and sodium element. By controlling the content of aluminum element and sodium element within the above range, the dissolution of manganese (Mn) can be reduced, thereby improving the high-temperature cycle performance of the electrochemical device. Without being limited to any theory, this can be due to the fact that the aluminum element within the above content range can enhance the stability of Mn-O bond in the lithium manganese oxide, improve the crystal structure of the lithium manganese oxide, and reduce the Jahn-Tellen effect of manganese element; the sodium element as an impurity element has little effect on the high-temperature cycle performance of the electrochemical device when within the above content range. Therefore, overall, the present application can reduce the dissolution of Mn and reduce the effect of sodium element on the performance of the positive electrode by controlling the content of aluminum element and sodium element within the above range, thereby improving the cycle performance and storage capacity retention performance of the electrochemical device.

[0008] The lithium manganese oxide of the present application can include, but is not limited to, modified LiMn2O4 (hereinafter referred to as modified LMO). The modification method of the lithium manganese oxide of the present application is not particularly limited, for example, an aluminum-containing compound can be added during the synthesis of LiMn2O4, so that the lithium manganese oxide of the present application contains aluminum element.

[0009] The positive electrode active material layer of the present application can be provided on at least one surface of the positive electrode current collector, for example, the positive electrode active material layer is provided on one surface of the positive electrode current collector, or the positive electrode active material layer is provided on both surfaces of the positive electrode current collector.

[0010] In an embodiment of the present application, the electrochemical device of the present application satisfies at least one of conditions (a) or (b): (a) 0.011≤A+B≤2.5; (b) 0.1≤A / B≤125.

[0011] In an embodiment of the present application, 0.03≤A+B<2, 2

[0012] By controlling the sum of the content of aluminum element and the content of sodium element in the positive electrode active material, i.e. the value of A+B, within the above range, and / or controlling the ratio of the content of aluminum element to the content of sodium element in the positive electrode active material, i.e. the value of A / B, within the above range, an electrochemical device with excellent high-temperature cycle performance and storage capacity retention performance can be obtained.

[0013] In an embodiment of the present application, the lithium manganese oxide of the present application further contains niobium element, and the content of the niobium element is C% based on the weight of the positive electrode active material, satisfying 0

[0014] Without being bound to any theory, the inventors of the present application found that the niobium element in the above content range can further improve the crystal structure of the lithium manganese oxide, so that the number of active crystal faces (111) exposed on the surface of the lithium manganese oxide is reduced, i.e., the number of active crystal faces (111) in contact with the electrolyte is reduced, thereby reducing the side reaction between the electrolyte and the surface of the lithium manganese oxide, further reducing the Mn elution, and thus improving the high-temperature cycle performance and storage capacity retention performance of the electrochemical device. During the modification of the lithium manganese oxide, the content of the niobium element in the positive electrode active material layer can be controlled by adding a niobium-containing compound and by controlling the addition amount of the niobium-containing compound.

[0015] In an embodiment of the present application, the electrochemical device of the present application satisfies at least one of conditions (c) to (d): (c) 0.011 < A+C ≤ 2.8; (d) 0.011 ≤ A+B+C ≤ 3.3; (e) 0 < C / B ≤ 40. Without being bound to any theory, by controlling the value of the sum of the content of the aluminum element and the content of the niobium element in the positive electrode active material, i.e., A+C, within the above range, and / or, by controlling the value of the sum of the content of the aluminum element, the content of the sodium element and the content of the niobium element in the positive electrode active material, i.e., A+B+C, within the above range, and / or, by controlling the value of the ratio of the content of the niobium element to the content of the sodium element in the positive electrode active material, i.e., C / B, within the above range, an electrochemical device with excellent high-temperature cycle performance and storage capacity retention performance can be obtained.

[0016] In an embodiment of the present application, 0.07 ≤ A+C ≤ 2.3.

[0017] By controlling the value of the sum of the content of the aluminum element and the content of the niobium element in the positive electrode active material, i.e., A+C, within the above range, more excellent high-temperature cycle performance and storage capacity retention performance can be obtained. In an embodiment of the present application, when the positive electrode sheet powder of the present application is tested by X-ray diffraction (XRD), the lithium manganese oxide satisfies at least one of conditions (f) to (g): (f) the lithium manganese oxide has a first diffraction peak corresponding to the (111) crystal face at 18° to 20°, and the peak intensity of the first diffraction peak is I(111); (g) the lithium manganese oxide has a second diffraction peak corresponding to the (400) crystal face at 43° to 45°, and the peak intensity of the second diffraction peak is I(400); (h) the lithium manganese oxide has a third diffraction peak corresponding to the (440) crystal face at 63° to 65°, and the peak intensity of the third diffraction peak is I(440).

[0018] In an embodiment of the present application, the electrochemical device of the present application satisfies at least one of conditions (i) to (j): (i) 0.25 < I(400) / I(111) < 0.55; (j) 0.35 < I(440) / I(400) < 0.55.

[0019] Without being bound to any theory, the inventors of the present application found that by controlling I(400) / I(111) within the above range, and / or controlling I(440) / I(400) within the above range, the crystal structure of lithium manganese oxide can be further improved, so that the number of active crystal faces (111) of lithium manganese oxide exposed on the surface is reduced, thereby reducing the side reaction of electrolyte with the surface of lithium manganese oxide, further reducing Mn elution, and improving the high-temperature cycle performance and storage capacity retention performance of the electrochemical device.

[0020] In an embodiment of the present application, the positive electrode active material layer can further comprise lithium nickel cobalt manganese acid oxide, and the weight percentage of the cobalt element in the positive electrode active material is less than or equal to 15% based on the weight of the positive electrode active material.

[0021] The lithium nickel cobalt manganese acid oxide in the positive electrode active material layer of the present application can further comprise residual alkali (such as Li2CO3 or LiOH) on the surface of the lithium nickel cobalt manganese acid oxide, which can react with hydrofluoric acid (HF) in the electrolyte to reduce the acidity of the electrolyte, further reduce Mn elution, and thereby improve the high-temperature cycle performance and storage capacity retention performance of the electrochemical device. Therefore, by controlling the weight percentage of cobalt in the positive electrode active material to be less than or equal to 15% based on the weight of the positive electrode active material in the present application, the production cost can be reduced while further improving the high-temperature cycle performance and storage capacity retention performance of the electrochemical device.

[0022] In an embodiment of the present application, the molar ratio of nickel element to manganese element in the positive electrode active material layer is 0.02:1 to 0.7:1, and the molar ratio of cobalt element to manganese element is less than or equal to 0.3:1.

[0023] By controlling the molar ratio of nickel element to manganese element and the molar ratio of cobalt element to manganese element in the positive electrode active material layer within the above range, the nickel element, manganese element and cobalt element in the positive electrode active material layer can be reasonably configured, thereby obtaining an electrochemical device with excellent high-temperature cycle performance and storage capacity retention performance.

[0024] In an embodiment of the present application, the positive electrode active material layer can further comprise lithium iron phosphate (LiFePO4, LFP), wherein the average particle size of the lithium iron phosphate is smaller than the average particle size of the lithium manganese oxide.

[0025] Without being bound to any theory, since the particle size of lithium iron phosphate is small, there is lithium iron phosphate on at least part of the surface of lithium manganese oxide, i.e. the lithium manganese oxide can be partially coated with lithium iron phosphate, or completely coated, thereby inhibiting the side reaction on the surface of lithium manganese oxide, and further improving the high-temperature cycle performance and storage capacity retention performance of the electrochemical device.

[0026] In an embodiment of the present application, the molar ratio of iron element to manganese element in the positive electrode active material layer is 0.02:1 to 0.25:1.

[0027] By controlling the molar ratio of iron element to manganese element in the positive electrode active material layer within the above range, the iron element and the manganese element in the positive electrode active material layer can be reasonably configured, the surface side reaction of lithium manganese oxide is inhibited, and thus the high-temperature cycle performance and the storage capacity retention performance of the electrochemical device are further improved.

[0028] In an embodiment of the present application, the weight percentage content of lithium iron phosphate in the positive electrode active material layer is ≤30% based on the weight of the positive electrode active material layer.

[0029] Without being limited to any theory, when the content of lithium iron phosphate is too high in the positive electrode active material layer (for example, higher than 30%), the energy density of the electrochemical device is affected. By controlling the weight percentage content of lithium iron phosphate in the positive electrode active material layer within the above range, the electrochemical device can have high energy density while further improving the high-temperature cycle performance and the storage capacity retention performance of the electrochemical device.

[0030] In an embodiment of the present application, the compaction density P of the positive electrode active material layer is 2.7 g / cm 3 ≤P≤4.0 g / cm 3 Without being limited to any theory, when the compaction density of the positive electrode active material layer is too low (for example, lower than 2.7 g / cm 3 ), the improvement of the energy density of the electrochemical device is not conducive; when the compaction density of the positive electrode active material layer is too high (for example, higher than 4.0 g / cm 3 ), the positive electrode is more prone to brittle fracture, which is not conducive to the safety of the electrochemical device. By controlling the compaction density of the positive electrode active material layer within the above range, the electrochemical device can have high energy density while having excellent safety.

[0031] The present application provides an electrochemical device and an electronic device, the positive electrode of the electrochemical device comprising a positive electrode current collector and a positive electrode active material layer arranged on at least one surface of the positive electrode current collector, the positive electrode active material layer comprising lithium manganese oxide, wherein the lithium manganese oxide comprises aluminum element and sodium element, by controlling the content A% of aluminum element and the content B% of sodium element in the positive electrode active material to satisfy 0.01≤A≤2, 0.001≤B≤1, the crystal structure of the lithium manganese oxide can be improved, the dissolution of manganese element is reduced, the cycle performance of the electrochemical device, especially under high-temperature conditions, is improved, and the high-temperature storage performance of the electrochemical device is also improved. BRIEF DESCRIPTION OF DRAWINGS

[0032] In order to more clearly illustrate the technical solutions of the present application and the prior art, the drawings required to be used in the embodiments and the prior art are briefly introduced as follows. Obviously, the drawings in the following description only represent some of the embodiments of the present application, rather than all the embodiments.

[0033] Figure 1 XRD pattern of the positive electrode tab powder of Example 35 of the present application. DETAILED DESCRIPTION

[0034] In order to make the objects, technical solutions, and advantages of the present application clearer, the present application is further described in detail below with reference to the drawings and embodiments. Obviously, the described embodiments only represent some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other technical solutions obtained by those skilled in the art belong to the scope of protection of the present application.

[0035] It should be noted that in the specific embodiments of the present application, the present application is explained by taking lithium-ion batteries as examples of electrochemical devices, but the electrochemical devices of the present application are not limited to lithium-ion batteries.

[0036] The first aspect of the present application provides an electrochemical device, comprising a positive electrode, the positive electrode comprising a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, the positive electrode active material layer comprising a lithium manganese oxide, the lithium manganese oxide comprising an aluminum element and a sodium element, the content of the aluminum element being A% and the content of the sodium element being B% based on the total weight of the positive electrode active material, satisfying 0.01≤A≤2 and 0.001≤B≤1. In an embodiment of the present application, 0.49≤A≤1.8 and 0.001≤B<0.5.

[0037] The positive electrode active material layer of the present application comprises a lithium manganese oxide, and the lithium manganese oxide comprises an aluminum element and a sodium element. By controlling the content of the aluminum element and the sodium element within the above range, the dissolution of manganese (Mn) can be reduced, thereby improving the high-temperature cycle performance of the electrochemical device. Without being limited to any theory, this may be because the aluminum element within the above content range can enhance the stability of the Mn-O bond in the lithium manganese oxide, improve the crystal structure of the lithium manganese oxide, and reduce the Jahn-Tellen effect of the manganese element; the sodium element as an impurity element almost has no effect on the high-temperature cycle performance of the electrochemical device when within the above content range. Therefore, overall, the present application can reduce the dissolution of Mn and reduce the effect of the sodium element on the performance of the positive electrode by controlling the content of the aluminum element and the sodium element within the above range, thereby improving the cycle performance and storage capacity retention performance of the electrochemical device.

[0038] The lithium manganese oxide of the present application can include, but is not limited to, modified LiMn2O4 (hereinafter referred to as modified LMO). The method of modifying the lithium manganese oxide of the present application is not particularly limited, for example, an aluminum-containing compound can be added during the synthesis of LiMn2O4, so that the lithium manganese oxide of the present application contains aluminum element.

[0039] The positive electrode active material layer of the present application can be provided on at least one surface of the positive electrode current collector, for example, the positive electrode active material layer is provided on one surface of the positive electrode current collector, or the positive electrode active material layer is provided on both surfaces of the positive electrode current collector.

[0040] In an embodiment of the present application, the electrochemical device of the present application satisfies at least one of conditions (a) or (b): (a) 0.011≤A+B≤2.5; (b) 0.1≤A / B≤125. In some embodiments, A+B can be 0.011, 0.03, 0.05, 0.07, 0.1, 0.3, 0.5, 0.9, 1.0, 1.1, 1.3, 1.5, 1.7, 1.9, 2.0, 2.5, or a range between any two of the above values. In an embodiment of the present application, A / B can be 0.1, 0.3, 0.5, 0.7, 0.9, 1.0, 3.0, 5.0, 7.0, 10, 15, 20, 25, 40, 60, 80, 100, 110, 120, 125, or a range between any two of the above values.

[0041] Without being bound to any theory, the present application is able to obtain an electrochemical device with excellent high-temperature cycle performance and storage capacity retention performance by controlling the sum of the content of aluminum element and the content of sodium element in the positive electrode active material, i.e. the value of A+B is within the above range, and / or controlling the ratio of the content of aluminum element to the content of sodium element in the positive electrode active material, i.e. the value of A / B is within the above range. When A / B is too large, the improvement in cycle performance of the electrochemical device is limited, and when the value of A / B is too small, the reversible capacity of the electrochemical device can be affected.

[0042] In an embodiment of the present application, the lithium manganese oxide further contains niobium element, and the content of the niobium element is C% based on the total weight of the positive electrode active material, satisfying 0

[0043] Without being bound to any theory, the inventors of the present application found that the niobium element in the above content range can further improve the crystal structure of lithium manganese oxide, so that the number of active crystal faces (111) of lithium manganese oxide exposed to the outside is reduced, i.e. the number of active crystal faces (111) in contact with the electrolyte is reduced, thereby reducing the side reaction of the electrolyte with the surface of the lithium manganese oxide, further reducing the Mn elution, thereby improving the high-temperature cycle performance and storage capacity retention performance of the electrochemical device. During the modification of the lithium manganese oxide, the content of the niobium element in the positive electrode active material layer can be controlled by adding a niobium-containing compound and controlling the addition amount of the niobium-containing compound. The niobium-containing compound is not particularly limited in the present application, and for example, can include but is not limited to: Nb2O5, NbF5.

[0044] In an embodiment of the present application, the electrochemical device of the present application satisfies the condition 0.01≤A+C≤2.8. In some embodiments, 0.011≤A+C≤2. In some embodiments, 0.07≤A+C≤2.3. In some embodiments, 0.01≤A+C≤1.6. In some embodiments, A+C can be 0.011, 0.03, 0.05, 0.07, 0.09, 0.1, 0.3, 0.5, 0.7, 0.9, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.2, 2.4, 2.6, 2.8, or a range consisting of any two of the above values.

[0045] By controlling the sum of the content of aluminum element and niobium element in the positive electrode active material, i.e. the value of A+C in the above range, the performance of the electrochemical device is in a relatively optimal state, when the value of A+C is too high, the cycle performance improvement of the electrochemical device is limited, and it may affect the reversible capacity of the electrochemical device.

[0046] In an embodiment of the present application, the electrochemical device of the present application satisfies the condition 0.011≤A+B+C≤3.3 In some embodiments, 0.1≤A+B+C≤2.0. In some embodiments, A+B+C can be 0.011, 0.05, 0.07, 0.1, 0.3, 0.5, 0.7, 0.9, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.5, 3.0, 3.3, or a range consisting of any two of the above values.

[0047] By controlling the value of A+B+C in the above range, the electrochemical device has relatively optimal cycle performance and storage performance.

[0048] In an embodiment of the present application, the electrochemical device of the present application satisfies the condition 0 < C / B ≤ 40. In some embodiments, 0 < C / B ≤ 10. In some embodiments, 0 < C / B ≤ 5. In some embodiments, 0 < C / B ≤ 3. In some embodiments, C / B can be 0.0001, 0.0005, 0.001, 0.003, 0.005, 0.007, 0.009, 0.01, 0.03, 0.05, 0.07, 0.09, 0.1, 0.3, 0.5, 0.7, 0.9, 1.0, 1.2, 1.5, 1.7, 1.9, 2.0, 3.0, 5.0, 7.0, 9.0, 10.0, 15, 20, 25, 30, 35, 40 or a range between any two of the above values.

[0049] By controlling the value of C / B within the above range, an electrochemical device with excellent high-temperature cycle performance and storage capacity retention performance can be obtained. When the value of C / B is too high, the cycle performance of the electrochemical device can be affected. When the value of C / B is too low, the protection of the (111) active crystal plane of lithium manganese oxide is less, the inhibition of Mn dissolution is limited, and the loss of reversible capacity of the electrochemical device can be increased.

[0050] In an embodiment of the present application, when the positive electrode sheet powder of the present application is tested by X-ray diffraction (XRD), the lithium manganese oxide has a first diffraction peak corresponding to the (111) crystal plane at 18° to 20°, and the peak intensity of the first diffraction peak is I(111).

[0051] In an embodiment of the present application, when the positive electrode sheet powder of the present application is tested by X-ray diffraction (XRD), the lithium manganese oxide has a second diffraction peak corresponding to the (400) crystal plane at 43° to 45°, and the peak intensity of the second diffraction peak is I(400).

[0052] In an embodiment of the present application, when the positive electrode sheet powder of the present application is tested by X-ray diffraction (XRD), the lithium manganese oxide has a third diffraction peak corresponding to the (440) crystal plane at 63° to 65°, and the peak intensity of the third diffraction peak is I(440).

[0053] The positive electrode sheet of the present application comprises a positive electrode active material layer, and the positive electrode active material layer contains a positive electrode active material. The main component of the positive electrode active material is lithium manganese oxide. The lithium manganese oxide of the present application contains (111) crystal plane, (400) crystal plane and (440) crystal plane as shown by XRD test.

[0054] In an embodiment of the present application, the electrochemical device of the present application satisfies the condition 0.25 < I(400) / I(111) < 0.55.

[0055] In one embodiment of the present application, the electrochemical device of the present application satisfies 0.35 < I(440) / I(400) < 0.55.

[0056] Without being bound to any theory, by controlling I(400) / I(111) within the above range, and / or controlling I(440) / I(400) within the above range, the crystal structure of the lithium manganese oxide can be further improved, such that the number of active crystal planes (111) of the lithium manganese oxide exposed on the surface is reduced, thereby reducing the side reaction of the electrolyte with the surface of the lithium manganese oxide, further reducing Mn elution, and improving the high-temperature cycle performance and storage capacity retention performance of the electrochemical device.

[0057] In one embodiment of the present application, the positive electrode active material further comprises an M element, the M element comprising at least one of Cu, Fe, Mg, Ti, Zr, Zn, W, Sr, Y. In some embodiments, the M element can comprise Mg, and at least one of Cu, Fe, Ti, Zr, Zn, W, Sr, Y.

[0058] In one embodiment of the present application, the content of the M element is less than or equal to 5% based on the weight of the positive electrode active material. In some embodiments, the content of the M element can be 0.01%, 0.03%, 0.05%, 0.07%, 0.1%, 0.3%, 0.5%, 0.7%, 1.0%, 2.0%, 3.0%, 5.0%, or a range consisting of any two of the above values.

[0059] In one embodiment of the present application, the positive electrode active material further comprises an X element, the X element comprising at least one of S, P, B, F, or Cl.

[0060] In one embodiment of the present application, the content of the X element is less than or equal to 3% based on the weight of the positive electrode active material. In some embodiments, the content of the X element can be 0.01%, 0.03%, 0.05%, 0.07%, 0.1%, 0.3%, 0.5%, 0.7%, 1.0%, 2.0%, 3.0%, or a range consisting of any two of the above values.

[0061] In one embodiment of the present application, the positive electrode active material layer can further comprise a lithium nickel cobalt manganese acid oxide, and the weight percentage content of cobalt is less than or equal to 15% based on the weight of the positive electrode active material.

[0062] Without being limited to any theory, the positive electrode active material layer of the present application can also contain lithium nickel cobalt manganese acid oxide. Residual alkali (e.g., Li2CO3 or LiOH) on the surface of the lithium nickel cobalt manganese acid oxide can react with hydrofluoric acid (HF) in the electrolyte, reducing the acidity of the electrolyte and further reducing the dissolution of Mn, thereby improving the high-temperature cycle performance and storage capacity retention performance of the electrochemical device. When the content of cobalt is too high, it will lead to an increase in the production cost of the electrochemical device. Therefore, in the present application, the weight percentage of cobalt in the lithium nickel cobalt manganese acid oxide is controlled to be less than or equal to 15% based on the weight of the positive electrode active material, which can further improve the high-temperature cycle performance and storage capacity retention performance of the electrochemical device while reducing the production cost.

[0063] The lithium nickel cobalt manganese acid oxide of the present application is not particularly limited as long as it can achieve the purpose of the present application, for example, the lithium nickel cobalt manganese acid oxide can be lithium nickel cobalt manganese oxide (hereinafter referred to as NCM). The lithium nickel cobalt manganese oxide can be single-crystal lithium nickel cobalt manganese oxide or polycrystalline lithium nickel cobalt manganese oxide.

[0064] In an embodiment of the present application, the molar ratio of nickel element to manganese element in the positive electrode active material layer is 0.02:1 to 0.7:1.

[0065] In an embodiment of the present application, the molar ratio of cobalt element to manganese element in the positive electrode active material layer is less than or equal to 0.3:1.

[0066] In the present application, by controlling the molar ratio of nickel element to manganese element and the molar ratio of cobalt element to manganese element in the positive electrode active material layer within the above range, the nickel element, manganese element and cobalt element in the positive electrode active material layer can be reasonably configured, thereby obtaining an electrochemical device with excellent high-temperature cycle performance and storage capacity retention performance.

[0067] In an embodiment of the present application, the positive electrode active material layer can also contain lithium iron phosphate (LiFePO4, i.e., LFP), wherein the average particle size of the lithium iron phosphate is smaller than the average particle size of the lithium manganese oxide.

[0068] In an embodiment of the present application, the average particle size of the lithium iron phosphate is less than or equal to 2 μm. In some embodiments, the average particle size of the lithium iron phosphate is less than or equal to 1.8 μm. In some embodiments, the average particle size of the lithium iron phosphate is less than or equal to 1.5 μm. In some embodiments, the average particle size of the lithium iron phosphate is less than or equal to 1.2 μm. In some embodiments, the average particle size of the lithium iron phosphate is less than or equal to 1.0 μm.

[0069] One embodiment of the present application utilizes the small particle size characteristics of lithium iron phosphate, so that at least part of the surface of the lithium manganese oxide is covered with lithium iron phosphate, i.e., the lithium manganese oxide can be partially or completely coated with lithium iron phosphate, thereby inhibiting the side reactions on the surface of the lithium manganese oxide and further improving the high-temperature cycle performance and storage capacity retention performance of the electrochemical device.

[0070] In one embodiment of the present application, the molar ratio of iron to manganese in the positive electrode active material layer is 0.02:1 to 0.25:1. In some embodiments, the molar ratio of iron to manganese in the positive electrode active material layer is 0.03:1 to 0.13:1. In some embodiments, the molar ratio of iron to manganese in the positive electrode active material layer is 0.05:1 to 0.12:1. In some embodiments, the molar ratio of iron to manganese in the positive electrode active material layer is 0.03:1 to 0.13:1.

[0071] By controlling the molar ratio of iron to manganese in the positive electrode active material layer within the above range, the iron and manganese in the positive electrode active material layer can be reasonably configured, the side reactions on the surface of the lithium manganese oxide can be inhibited, and the high-temperature cycle performance and storage capacity retention performance of the electrochemical device can be further improved.

[0072] In one embodiment of the present application, the weight percentage of lithium iron phosphate in the positive electrode active material layer is ≤30%, based on the weight of the positive electrode active material layer.

[0073] Without being limited to any theory, when the content of lithium iron phosphate is too high (e.g., higher than 30%) in the positive electrode active material layer, the energy density of the electrochemical device is affected. By controlling the weight percentage of lithium iron phosphate in the positive electrode active material layer within the above range, the electrochemical device can have a high energy density while further improving the high-temperature cycle performance and storage capacity retention performance of the electrochemical device.

[0074] In one embodiment of the present application, the compaction density P of the positive electrode active material layer is 2.7 g / cm 3 ≤P≤4.0 g / cm 3 Without being limited to any theory, when the compaction density of the positive electrode active material layer is too low (e.g., lower than 2.7 g / cm 3 ), the energy density of the electrochemical device is not conducive to improvement; when the compaction density of the positive electrode active material layer is too high (e.g., higher than 4.0 g / cm 3 ), the positive electrode is more prone to brittle fracture, which is not conducive to the safety of the electrochemical device. By controlling the compaction density of the positive electrode active material layer within the above range, the electrochemical device can have a high energy density while having excellent safety.

[0075] The preparation method of the lithium manganese oxide is not particularly limited in the present application, and any known preparation method in the art can be used. For example, the above-mentioned lithium manganese oxide, i.e., modified LMO, can be obtained by adding an aluminum-containing compound (e.g., Al2O3, Al(OH)3, AlF3) into LiMn2O4 during the synthesis of the lithium manganese oxide. In addition, the content of aluminum in the lithium manganese oxide can be adjusted, e.g., by controlling the amount of the aluminum-containing compound added, so as to change the content of aluminum in the positive active material layer. The content of sodium in the precursor of LiMn2O4 can be adjusted, so as to change the content of sodium in the positive active material layer. The adjustment process is not particularly limited in the present application, as long as the purpose of the present application can be achieved.

[0076] The positive electrode tab in the present application is not particularly limited, as long as the purpose of the present application can be achieved. For example, the positive electrode tab usually comprises a positive current collector and a positive active material layer. The positive current collector is not particularly limited, and can be any positive current collector in the art, such as an aluminum foil, an aluminum alloy foil, or a composite current collector.

[0077] The negative electrode tab in the present application is not particularly limited, as long as the purpose of the present application can be achieved. For example, the negative electrode tab usually comprises a negative current collector and a negative active material layer. The negative current collector is not particularly limited, and can be a metal foil or a porous metal plate, such as a copper, nickel, titanium, or iron foil or plate, or an alloy thereof. The negative active material layer comprises a negative active material, a conductive agent, a binder, and a thickening agent. The negative active material is not particularly limited, and can be any negative active material in the art. For example, it can comprise at least one of artificial graphite, natural graphite, mesocarbon microbeads (MCMB), soft carbon, hard carbon, silicon, silicon-carbon, SiO, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel-structured lithium titanate Li4Ti5O12, Li-Al alloy, or metallic lithium; the conductive agent can be at least one of graphite, super-conductive carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, or carbon nanofibers; the binder can be at least one of styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl butyral (PVB), water-based acrylic resin, or carboxymethyl cellulose (CMC); and the thickening agent can be carboxymethyl cellulose (CMC). 12

[0078] ​The base material of the separator of the present application includes, but is not limited to, at least one selected from polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polyimide (PI), or aramid. For example, the polyethylene includes at least one component selected from high-density polyethylene, low-density polyethylene, and ultra-high molecular weight polyethylene. In particular, polyethylene and polypropylene have excellent effects on preventing short-circuiting and can improve the stability of the electrochemical device through the shutdown effect. The base material can be a single layer structure or a variety of mixed multi-layer composite structures, with a thickness of 3 to 20 μm.

[0079] The lithium ion battery of the present application further includes an electrolyte, which can be one or more of a gel electrolyte, a solid-state electrolyte, and an electrolytic solution including a lithium salt and a non-aqueous solvent. In some embodiments of the present application, the lithium salt is selected from one or more of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, LiSiF6, LiBOB, and lithium difluoroborate. For example, the lithium salt can be selected as LiPF6because it can give a high ionic conductivity and improve the cycle characteristics. The non-aqueous solvent can be a carbonate compound, a carboxylic ester compound, an ether compound, other organic solvents, or a combination thereof. The carbonate compound can be a chain carbonate compound, a cyclic carbonate compound, a fluorinated carbonate compound, or a combination thereof. Examples of the chain carbonate compound are dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), and a combination thereof. Examples of the cyclic carbonate compound are ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinyl ethylene carbonate (VEC), and a combination thereof. Examples of the fluorinated carbonate compound are fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methyl ethylene carbonate, 1-fluoro-1-methyl ethylene carbonate, 1,2-difluoro-1-methyl ethylene carbonate, 1,1,2-trifluoro-2-methyl ethylene carbonate, trifluoromethyl ethylene carbonate, and a combination thereof. Examples of the carboxylic ester compound are methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valerolactone, methylvaleronolactone, hexanolactone, and a combination thereof. Examples of the ether compound are dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, and a combination thereof. Examples of the other organic solvents are dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidinone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphoric acid ester, and a combination thereof.

[0080] A second aspect of the present application provides an electronic device including the electrochemical device described in the above embodiments of the present application.

[0081] The electronic device of the present application is not particularly limited, and it can be any electronic device known in the art. In some embodiments, the electronic device can include, but is not limited to, a notebook computer, a pen input computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile, a portable copier, a portable printer, a head-mounted stereo headphone, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable audio player, a radio, a backup power supply, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting appliance, a toy, a game machine, a timepiece, a power tool, a flashlight, a camera, a home-use large storage battery, a lithium ion capacitor, and the like.

[0082] The process for preparing the electrochemical device is well known to those skilled in the art, and the present application is not particularly limited. For example, a lithium ion battery can be manufactured by overlapping the positive electrode and the negative electrode via a separator film, and then winding, folding, or the like, as necessary, and placing the same in a case, injecting an electrolyte into the case, and sealing. In addition, a current-preventing element, a guide plate, or the like can be placed in the case, as necessary, to prevent pressure increase, overcharge, and overdischarge in the lithium ion battery.

[0083] The present application provides an electrochemical device and an electronic device, the positive electrode of the electrochemical device comprising a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, the positive electrode active material layer comprising a lithium manganese oxide, wherein the lithium manganese oxide comprises an aluminum element and a sodium element, by controlling the content A% of the aluminum element and the content B% of the sodium element in the positive electrode active material to satisfy 0.01≤A≤2, 0.001≤B≤1, the crystal structure of the lithium manganese oxide can be improved, the dissolution of manganese elements can be reduced, the cycle performance of the electrochemical device, especially under high temperature conditions, can be improved, and the high temperature storage performance of the electrochemical device can also be improved.

[0084] Test method and equipment:

[0085] Positive electrode active material layer element content test:

[0086] The lithium ion battery discharged to a voltage of 2.8V is disassembled, and then the positive electrode active material layer on the positive electrode sheet after drying is dissolved with a mixed solvent (for example, 0.4g of positive electrode active material is dissolved with 10 ml of aqua regia (nitric acid and hydrochloric acid mixed at a ratio of 1:1) and 2ml of HF), and the volume is made to 100ml, and then an ICP (Inductively coupled plasma) analyzer is used to test the content of Al, Na, Nb, and the like in the solution.

[0087] XRD test:

[0088] The lithium ion battery discharged to a voltage of 2.8V is disassembled, and then the positive electrode sheet is taken out, the positive electrode active material layer is scraped off with a scraper to obtain a positive electrode active material layer powder, and then the positive electrode active material layer powder is placed on the sample table of an XRD testing instrument (model Bruck, D8), a scanning rate of 2° / min is used, and the scanning angle range is 10° to 90° to obtain an XRD diffraction pattern. In the XRD diffraction pattern, the characteristic peaks (111), (400), (440) of lithium manganese oxide are taken, and then the ratio of I(400) and I(111) is obtained, which is denoted as I(400) / I(111); the ratio of I(440) and I(400) is denoted as I(440) / I(400).

[0089] Particle size test in the positive electrode active material layer:

[0090] The lithium ion battery discharged to a voltage of 2.8V is disassembled, and then the dried positive electrode sheet is sliced, and then the cross section of the slice is observed using a scanning electron microscope (SEM), and the particles in the cross section are found, and then the composition of a single particle is determined using an energy dispersive spectrometer (EDS), and the particle size of a single particle is measured using the SEM, and the magnification is 1000 times, and three pictures are selected to calculate the average value. The test instrument is OXFORD EDS (X-max-20mm 2 ).

[0091] Positive electrode active material layer compaction density test:

[0092] The lithium ion battery discharged to a voltage of 2.8V is disassembled, and then the positive electrode sheet is taken out, and the positive electrode sheet is soaked in DMC (dimethyl carbonate) for 30 min, and the electrolyte and by-products on the surface of the positive electrode sheet are removed, and then the positive electrode sheet is dried in a fume hood for 4 hours, and then the dried positive electrode sheet is taken out, and 5 pieces of positive electrode sheet with a size of 5cm×5cm are selected, and the thickness of the positive electrode sheet is measured by a micrometer, and is denoted as d0; the positive electrode active material layer in the positive electrode sheet is scraped off with a scraper, and the weight of the positive electrode active material layer is weighed by a balance, and is denoted as m, and the thickness of the current collector after removing the active material is measured by a micrometer, and is denoted as d, and the compaction density of the positive electrode active material layer is calculated according to the following formula:

[0093] The compaction density P = m / [5cm×5cm×( d0-d) ], unit g / cm 3 .

[0094] The compaction density of the positive electrode active material layer is the average value of 5 pieces of positive electrode sheet.

[0095] Lithium ion battery capacity test:

[0096] Take 4 lithium ion batteries, charge at 0.5C current until the upper limit voltage is 4.2V in an environment of 25℃, then discharge at 0.2C current until the final voltage is 2.8V, calculate the discharge capacity of 0.2C first as the capacity of the lithium ion battery.

[0097] Lithium ion battery cycle performance test:

[0098] Repeat the charging and discharging of the lithium ion battery by the following steps, and calculate the discharge capacity retention rate of the lithium ion battery:

[0099] In an environment of 25℃, the first charging and discharging is carried out, charging at 0.5C current until the voltage is 4.2V, then discharging at 1C current until the final voltage is 2.8V, recording the discharge capacity, recorded as the discharge capacity of the first cycle; then repeat the above steps for 1000 times of charging and discharging cycle, record the discharge capacity of the 1000th cycle.

[0100] 25℃ cycle capacity retention rate=(discharge capacity of the 1000th cycle / discharge capacity of the first cycle) x 100%.

[0101] In an environment of 45℃, charge at 0.5C current until the voltage is 4.2V, then discharge at 1C current until the final voltage is 2.8V, record the discharge capacity, recorded as the discharge capacity of the first cycle; then repeat the above steps for 500 times of charging and discharging cycle, record the discharge capacity of the 500th cycle.

[0102] 45℃ cycle capacity retention rate=(discharge capacity of the 500th cycle / discharge capacity of the first cycle) x 100%.

[0103] Lithium ion battery high temperature storage performance test:

[0104] In an environment of 25℃, charge at 0.5C current until the upper limit voltage is 4.2V, then discharge at 1C current until the final voltage is 2.8V, record the discharge capacity, recorded as the capacity before storage;

[0105] Charge at 0.5C rate constant current to voltage 3.85V, charge at 4.2V constant voltage to current less than 0.05C, place the battery in 60℃ oven storage for 14 days, then discharge at 1C current until the final voltage is 2.8V; then charge at 0.5C current until the voltage is 4.2V, then discharge at 1C current until the voltage is 2.8V, record the discharge capacity of the battery, recorded as the capacity after storage.

[0106] Capacity retention rate of lithium ion battery = capacity after storage / capacity before storage x 100%.

[0107] Example 1

[0108] <Preparation of lithium manganese oxide>

[0109] Lithium carbonate 203.3 g (lithium content 18.71%), manganese dioxide 1000.0 g (Mn content 60.22%, Na content 0.27%), and aluminum trioxide 29.96 g (aluminum content 52.91%) were weighed and mixed in a high-speed mixer at 300 r / min for 20 min. The mixture was placed in an air kiln and heated to 820°C at a rate of 5°C / min and maintained for 24 h. After natural cooling, the lithium manganese oxide (i.e., modified LMO) was obtained by sieving through a 300-mesh sieve.

[0110] <Preparation of positive electrode sheet>

[0111] The prepared positive electrode active material, binder polyvinylidene fluoride (PVDF), conductive carbon black, and carbon nanotube (CNT) were mixed in a weight ratio of 95:2:1.8:1.2, and then NMP (N-methyl pyrrolidone) was added as a solvent to prepare a positive electrode slurry with a uniform transparent appearance and a solid content of 75% under vacuum stirring. The positive electrode slurry was uniformly coated on one surface of an aluminum foil with a thickness of 9 µm, dried at 90°C, and cold-pressed to obtain a positive electrode sheet with a total thickness of the positive electrode active material layer of 100 µm. Then, the above steps were repeated on the other surface of the positive electrode sheet to obtain a positive electrode sheet coated with positive electrode active material layers on both surfaces. The positive electrode sheet was cut into a size of 74 mm x 867 mm and the tabs were welded for later use. In the positive electrode active material layer, the aluminum content was 1.52%, the sodium content was 0.26%, and the compaction density of the positive electrode active material layer was 2.8 g / cm 3 .

[0112] <Preparation of negative electrode sheet>

[0113] The artificial graphite, butadiene styrene rubber (SBR), and carboxymethyl cellulose (CMC) were mixed in a weight ratio of 98:1:1, and then deionized water was added as a solvent to prepare a slurry with a solid content of 70% and stirred uniformly. The slurry was uniformly coated on one surface of a copper foil with a thickness of 8 µm, dried at 110°C, and cold-pressed to obtain a single-sided coated negative electrode active material layer with a thickness of 150 µm. Then, the above coating steps were repeated on the other surface of the negative electrode sheet to obtain a negative electrode sheet coated with negative electrode active material layers on both surfaces. The negative electrode sheet was cut into a size of 74 mm x 867 mm and the tabs were welded for later use.

[0114] Preparation of the separator

[0115] A polyethylene (PE) porous polymer film with a thickness of 15 μm was used as the separator.

[0116] Preparation of the electrolyte

[0117] The non-aqueous organic solvents propylene carbonate (PC), ethylene carbonate (EC), and diethyl carbonate (DEC) were mixed in a weight ratio of 1:1:1 in an environment with a water content of less than 10 ppm, and then lithium hexafluorophosphate (LiPF6) was added to the non-aqueous organic solvents, dissolved, and mixed uniformly. The molar concentration of LiPF6 in the electrolyte was 1.15 mol / L. Based on the total weight of the electrolyte, 2% of fluoroethylene carbonate, 2% of vinylene carbonate, and 1% of vinyl sulfate were added and mixed uniformly to prepare the electrolyte.

[0118] Preparation of the lithium ion battery

[0119] The positive electrode sheet, the separator, and the negative electrode sheet prepared above were stacked in order, with the separator between the positive electrode sheet and the negative electrode sheet to play a separating role, and then wound to obtain an electrode assembly. The electrode assembly was placed in an aluminum plastic film packaging bag, and then dehydrated at 80°C. The electrolyte prepared above was injected into the bag, and then the bag was vacuum sealed, left to stand, subjected to formation, and shaped to obtain the lithium ion battery.

[0120] Examples 2 to 7

[0121] The preparation method was similar to that of Example 1, except that the element contents and the lithium manganese oxide particle size were as shown in Table 1.

[0122] Example 8

[0123] The preparation method was similar to that of Example 1, except that 850.3 g of trimanganese tetraoxide was used instead of 1000.0 g of manganese dioxide, and other parameters were different, as shown in Table 1.

[0124] Example 9

[0125] The preparation method was similar to that of Example 1, except that a niobium-containing compound Nb2O5 was added to the lithium manganese oxide, the aluminum content in the positive electrode active material layer was adjusted to 1.01%, the sodium content was adjusted to 0.26%, the niobium content was adjusted to 0.09%, and the compaction density of the positive electrode active material layer was adjusted to 3.0 g / cm 3 , and other parameters were the same as in Example 1.

[0126] Example 10

[0127] The preparation method was similar to that of Example 9, except that the element contents and the lithium manganese oxide particle size were as shown in Table 1.

[0128] Example 11

[0129] Lithium carbonate 203.3 g (lithium element content 18.71%), trimanganese tetroxide 850.3 g (Mn element content 70.82%, Na element content 0.01%), aluminum trioxide 19.10 g (aluminum element content 52.91%), and niobium pentoxide 2.87 g (niobium element content 79.46%) were weighed and mixed in a high-speed mixer at 300 r / min for 20 min. The mixture was placed in an air kiln and heated to 750°C at a rate of 5°C / min, and maintained for 24 h. After natural cooling, the mixture was taken out, sieved through a 300-mesh sieve, and then the lithium manganese oxide (i.e., modified LMO) product was obtained.

[0130] Examples 12 to 13

[0131] The preparation method was similar to that of Example 11, except that the element contents shown in Table 1 and the particle size of the lithium manganese oxide were different.

[0132] Examples 14 to 21

[0133] The preparation method was similar to that of Example 9, except that the element contents shown in Table 1 and the particle size of the lithium manganese oxide were different.

[0134] Example 22

[0135] The positive electrode active material modified LMO (its preparation method was similar to that of Example 9, except that the element contents and particle size shown in Table 1) was mixed with polycrystalline lithium nickel cobalt manganese acid oxide (LiNi 0.60 Co 0.10 Mn 0.30 O2, denoted as NCM:15.8 (601030), with an average particle size of 15.3 µm to obtain a mixture. The mixture was proportioned according to the parameters shown in Table 1, so that the molar ratio of nickel to manganese and the molar ratio of cobalt to manganese met the proportions shown in Table 1. The element contents and particle sizes in the positive electrode active material layer were as shown in Table 1. The compaction density of the positive electrode active material layer was 3.3 g / cm 3 , and otherwise the same as Example 9.

[0136] Examples 23 to 33

[0137] The preparation method was similar to that of Example 22, except that the element contents, the average particle size of the modified LMO, the type and average particle size of the polycrystalline lithium nickel cobalt manganese acid oxide, the molar ratio of nickel to manganese, and the molar ratio of cobalt to manganese were adjusted as shown in Table 1.

[0138] Example 34

[0139] The positive electrode active material modified LMO (the preparation method is similar to that in Example 11, except that the element content and particle size are shown in Table 1) and polycrystalline lithium nickel cobalt manganese oxide (LiNi) with an average particle size of 15.3 µm were used. 0.50 Co 0.20 Mn 0.30 O2, denoted as NCM:15.9 (502030), was mixed to obtain a mixture. The ratio of LMO to NCM was adjusted so that the molar ratio of nickel to manganese and the molar ratio of cobalt to manganese met the ratios shown in Table 1. The elemental content and particle size in the positive electrode active material layer are shown in Table 1. Otherwise, it is the same as in Example 11.

[0140] Example 35

[0141] Modified LMO (prepared in a similar manner to Example 11, except for the elemental content and particle size shown in Table 1) was mixed with lithium iron phosphate (LFP) with an average particle size of 1 µm to obtain a mixture. The ratio of LMO to LFP was adjusted so that the molar ratio of iron to manganese met the ratio shown in Table 1. The elemental content and particle size in the positive electrode active material layer are shown in Table 1. Otherwise, it is the same as in Example 11.

[0142] Example 36

[0143] The preparation method is similar to that of Example 35, except for the parameters shown in Table 1.

[0144] Example 37

[0145] The positive electrode active material was modified LMO (the preparation method is similar to that in Example 9, except for the element content and particle size shown in Table 1), and polycrystalline lithium nickel cobalt manganese oxide (LiNi) with an average particle size of 16.2 µm was prepared. 0.55 Co 0.15 Mn 0.30 O2 (NCM: 16.2 (551530)) and lithium iron phosphate (LFP) with an average particle size of 1µm were mixed to obtain a mixture in which the molar ratios of nickel to manganese and cobalt to manganese met the ratios shown in Table 1. The elemental content and particle size of the positive electrode active material layer are shown in Table 1. The compaction density of the positive electrode active material layer is 3.3 g / cm³. 3 Otherwise, it is the same as in Example 9.

[0146] Example 38

[0147] The positive electrode active material was modified LMO (the preparation method is similar to that in Example 11, except for the element content and particle size shown in Table 1), and a single crystal lithium nickel cobalt manganese oxide (LiNi) with an average particle size of 6.4 µm was prepared. 0.55 Co 0.15 Mn 0.30O2 (NCM: 6.4 (551530)) and lithium iron phosphate (LFP) with an average particle size of 1 µm were mixed to obtain a mixture in which the molar ratio of nickel to manganese and the molar ratio of cobalt to manganese met the ratios shown in Table 1. Otherwise, it was the same as in Example 11.

[0148] Example 39

[0149] The positive electrode active material was modified LMO (the preparation method is similar to that in Example 9, except for the element content and particle size shown in Table 1), and polycrystalline lithium nickel cobalt manganese oxide (LiNi) with an average particle size of 16.2 µm was prepared. 0.55 Co 0.15 Mn 0.30 O2 (NCM: 16.2 (551530)) and lithium iron phosphate (LFP) with a particle size of 1 µm were mixed to obtain a mixture in which the molar ratio of nickel to manganese and the molar ratio of cobalt to manganese met the ratios shown in Table 1. Otherwise, the process was the same as in Example 9.

[0150] Examples 40 to 41

[0151] The preparation method is similar to that of Example 39, except for the parameters shown in Table 1.

[0152] Comparative Example 1

[0153] Except for the positive electrode active material being LiMn2O4 without aluminum doping, everything else is the same as in Example 1.

[0154] Comparative Example 2

[0155] Except for the positive electrode active material being LiMn2O4 without aluminum doping, everything else is the same as in Example 22.

[0156] Comparative Example 3

[0157] Except for the positive electrode active material being LiMn2O4 without aluminum doping, everything else is the same as in Example 37.

[0158] Comparative Example 4

[0159] Except for adjusting the element content of the positive electrode active material as shown in Table 1, everything else is the same as in Example 9.

[0160] Comparative Example 5

[0161] Except for adjusting the element content of the positive electrode active material as shown in Table 1, everything else is the same as in Example 9.

[0162] Table 1

[0163]

[0164]

[0165] The combination of parameters among A, B, C is shown in Table 2:

[0166] Table 2

[0167]

[0168]

[0169] In Table 1 and Table 2, " / " means not containing or not measured.

[0170] As can be seen from Examples 1 to 8 and Comparative Example 1, when the lithium ion battery has the aluminum element content A% and the sodium element content B% in the positive electrode active material layer of the application, and 0.01≤A≤2, 0.001≤B≤1, the 25℃ cycle capacity retention rate, 45℃ cycle capacity retention rate and storage capacity retention rate are all significantly improved, indicating that the lithium ion battery of the application has excellent cycle performance, especially high temperature cycle performance, and excellent high temperature storage performance.

[0171] As can be seen from Examples 1 to 8 and Comparative Examples 1 to 3, when the positive electrode active material does not contain the lithium manganese oxide of the application (for example, Comparative Examples 1 to 3), its I(400) / I(111) and I(440) / I(400) are out of the range of the application. While the lithium ion battery with the I(400) / I(111) and I(440) / I(400) range of the application has excellent cycle performance, especially high temperature cycle performance, and excellent high temperature storage performance.

[0172] As can be seen from Examples 9 to 21 and Comparative Examples 4 to 5, when the aluminum element content in the positive electrode active material is too high (for example, Comparative Example 4), the sodium element content is too high (for example, Comparative Example 5), its I(400) / I(111) and I(440) / I(400) are out of the range of the application. While the lithium ion battery with the aluminum element and sodium element content range of the application has its 25℃ cycle capacity retention rate, 45℃ cycle capacity retention rate and storage capacity retention rate significantly improved.

[0173] As can be seen from Examples 1 to 8 and Examples 9 to 21, when the positive electrode active material layer further contains the niobium element of the application, and the content C% is within the range of the application, the high temperature storage performance of the lithium ion battery is further improved.

[0174] As can be seen from Examples 9 to 21 and Examples 22 to 34, when the positive electrode active material layer further contains lithium nickel cobalt manganese acid oxide, the 25℃ cycle capacity retention rate, 45℃ cycle capacity retention rate and storage capacity retention rate of the lithium ion battery are further improved.

[0175] As can be seen from Examples 22 to 34, the weight percentage content of cobalt in the lithium nickel cobalt manganese acid oxide has an influence on the cycle performance and high-temperature storage performance of the lithium ion battery, but as long as the content of the lithium nickel cobalt manganese acid oxide is within the range of the present application, a lithium ion battery with excellent cycle performance and high-temperature storage performance can be obtained.

[0176] As can be seen from Examples 37 to 41, when the positive electrode active material layer further contains lithium iron phosphate, the 25°C cycle capacity retention rate, the 45°C cycle capacity retention rate and the storage capacity retention rate of the lithium ion battery are further improved.

[0177] The relationship among the content of aluminum element, the content of sodium element and the content of niobium element, i.e. the A+B value, the A / B value, the A+C value, the A+B+C value and the C / B value, will also generally affect the cycle performance and high-temperature storage performance of the lithium ion battery. As can also be seen from Examples 1 to 41, as long as the parameters combined among the above A, B and C are within the range of the present application, a lithium ion battery with excellent cycle performance and high-temperature storage performance can be obtained.

[0178] The particle size of the modified LMO, the particle size of the NCM, the particle size of the LFP, the content of Co in the positive electrode active material layer, the molar ratio of Ni to Mn, the molar ratio of Co to Mn, the molar ratio of Fe to Mn and the compaction density of the positive electrode active material layer will also generally affect the cycle performance and high-temperature storage performance of the lithium ion battery. As can also be seen from Examples 1 to 41, as long as the above parameters are within the range of the present application, a lithium ion battery with excellent cycle performance and high-temperature storage performance can be obtained.

[0179] Figure 1 The XRD pattern of the positive electrode tab powder of Example 35 of the present application is shown in FIG. 1. Figure 1 As can be seen, the positive electrode active material of the present application has a first diffraction peak corresponding to the (111) crystal face at 18° to 20°, a second diffraction peak corresponding to the (400) crystal face at 43° to 45° and a third diffraction peak corresponding to the (440) crystal face at 63° to 65°, and satisfies 0.25 < I(400) / I(111) < 0.5 and 0.35 < I(440) / I(400) < 0.55.

[0180] The above description is merely preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the scope of protection of the present application.

Claims

1. An electrochemical device comprising a positive electrode, a negative electrode, a separator, and an electrolyte, the positive electrode comprising a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, the positive electrode active material layer comprising a lithium manganese oxide, the lithium manganese oxide comprising an aluminum element and a sodium element, the content of the aluminum element being A% and the content of the sodium element being B% based on the weight of the positive electrode active material, satisfying 0.01≤A≤2 and 0.001≤B≤1; the positive electrode active material layer further comprising a lithium nickel cobalt manganese acid oxide, the weight percentage content of the cobalt element being less than or equal to 15% based on the weight of the positive electrode active material. 2.The electrochemical device according to claim 1, wherein at least one of conditions (a) or (b) is satisfied: (a) 0.011≤A+B≤2.5; (b) 0.1≤A / B≤125. 3.The electrochemical device according to claim 1, wherein 0.03≤A+B<2 and 2<A / B≤125. 4.The electrochemical device according to claim 1, further comprising a niobium element, the content of the niobium element being C% based on the weight of the positive electrode active material, satisfying 0<C≤1. 5.The electrochemical device according to claim 4, wherein at least one of conditions (c) to (d) is satisfied: (c) 0.011﹤A+C≤2.8; (d) 0.011≤A+B+C≤3.3; (e) 0﹤C / B≤40. 6.The electrochemical device according to claim 4, wherein 0.07≤A+C≤2.

3. The lithium manganese oxide satisfies at least one of conditions (f) to (g) using XRD testing: (f) the lithium manganese oxide has a first diffraction peak corresponding to a (111) crystal plane at 18° to 20°, the peak intensity of the first diffraction peak being I(111); (g) the lithium manganese oxide has a second diffraction peak corresponding to a (400) crystal plane at 43° to 45°, the peak intensity of the second diffraction peak being I(400); (h) the lithium manganese oxide has a third diffraction peak corresponding to a (440) crystal plane at 63° to 65°, the peak intensity of the third diffraction peak being I(440). 8.The electrochemical device according to claim 7, wherein at least one of conditions (i) to (j) is satisfied: (i) 0.25﹤I(400) / I(111)﹤0.55; (j) 0.35﹤I(440) / I(400)﹤0.

55. The molar ratio of the nickel element to the manganese element in the positive electrode active material layer is 0.02∶1 to 0.7∶1, and the molar ratio of the cobalt element to the manganese element is less than or equal to 0.3∶1. The positive electrode active material layer further comprises lithium iron phosphate, wherein the average particle size of the lithium iron phosphate is smaller than the average particle size of the lithium manganese oxide. The molar ratio of the iron element to the manganese element in the positive electrode active material layer is 0.02∶1 to 0.25∶1.

7. The electrochemical device of claim 1, wherein, The weight percentage content of the lithium iron phosphate is ≤30% based on the weight of the positive electrode active material. 14.An electronic device comprising the electrochemical device according to any one of claims 1 to 13. ​ ​ ​ ​ ​ 9. The electrochemical device of claim 1, wherein, ​ 10. The electrochemical device according to any one of claims 1 to 9, wherein, ​ 11. The electrochemical device of claim 10, wherein, ​ 12. The electrochemical device of claim 10, wherein, ​ 13. The electrochemical device of claim 1, wherein, The compacted density P of the positive electrode active material layer is 2.7 g / cm 3 ≤ P ≤ 4.0 g / cm 3 . ​

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