Positive electrode active material, electrochemical device and electronic device containing the positive electrode active material

Abstract

The present invention provides a positive electrode active material (10), and an electrochemical device and an electronic device each including the positive electrode active material (10), wherein the positive electrode active material (10) includes the elements Mn and Al, and the positive electrode active material (10) particles include a first region (11) close to a surface of the positive electrode active material (10) particle and a second region (12) away from the surface of the positive electrode active material (10) particle, wherein a molar ratio of Al / Mn in the first region (11) is a1 and a molar ratio of Al / Mn in the second region (12) is a2, and a1 and a2 satisfy 1.1≦a1 / a2≦100. The positive electrode active material (10) provided by the present invention not only effectively improves the manganese elution phenomenon of the positive electrode by concentrating Al in the region close to the surface of the positive electrode active material (10) and thereby improves the cycle characteristics and storage characteristics of the electrochemical device, but also simultaneously reduces the total Al content in the positive electrode active material and maintains the specific capacity of the positive electrode pieces, thereby improving the overall characteristics of the electrochemical device.

Description

[Technical Field]

[0001] The present invention relates to the field of electrochemistry, and in particular to a positive electrode active material, and an electrochemical device and an electronic device that include the positive electrode active material. [Background technology]

[0002] Lithium-ion batteries have the advantages of high energy density, long cycle life, no memory effect, etc., and are therefore widely used in devices such as wearable devices, smartphones, unmanned aerial vehicles, electric vehicles, and large-scale energy storage. Lithium-ion batteries have become the new green chemical power source with the most potential for development in the world today, but at the same time, the requirements for the overall properties of lithium-ion batteries are becoming higher.

[0003] The cathode active material in lithium-ion batteries is an important parameter that affects the performance of lithium-ion batteries. Lithium manganese oxide, a cathode active material, is widely used in lithium-ion batteries. However, the Mn in lithium manganese oxide is 3+ is prone to disproportionation reactions, and Mn 2+ This causes the dissolution of Mn, which then migrates to the negative electrode through the electrolyte, destroying the solid electrolyte interface (SEI), causing a loss of active lithium, and deteriorating the cycle characteristics of the lithium-ion battery. 2+ While improving the elution of the positive electrode, this often leads to a decrease in the specific capacity of the positive electrode and a deterioration in the cycle characteristics or storage characteristics of the electrochemical device, resulting in a decrease in the overall characteristics of the electrochemical device. Summary of the Invention

[0004] An object of the present invention is to provide a positive electrode active material capable of improving the overall characteristics of an electrochemical device, and an electrochemical device and an electronic device each including the positive electrode active material.

[0005] A first aspect of the present invention provides a cathode active material containing Mn and Al elements, wherein the cathode active material particles include a first region close to the surface of the cathode active material particles and a second region remote from the surface of the cathode active material particles. When the molar ratio of Al / Mn in the first region is a1 and the molar ratio of Al / Mn in the second region is a2, a1 and a2 satisfy the relationship 1.1≦a1 / a2≦100, preferably 5≦a1 / a2≦90. The value of a1 / a2 can be 1.1, 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, or 100, or any range consisting of the above values. Here, the first region refers to the portion of the cathode active material particles that is dissolved after washing with 2.4 mol / L sulfuric acid for 6 hours, and the second region refers to the portion of the cathode active material particles that is not dissolved after washing with 2.4 mol / L sulfuric acid for 6 hours.

[0006] The inventors have discovered that by adjusting the ratio a1 / a2 between the Al / Mn molar ratio a1 in the first region and the Al / Mn molar ratio a2 in the second region within the above range, the Al in the positive electrode active material is concentrated in a region close to the surface of the positive electrode active material, thereby effectively improving the manganese elution phenomenon in the positive electrode and improving the cycle characteristics and storage characteristics of the electrochemical device. At the same time, the total Al content in the positive electrode active material can be reduced, allowing the positive electrode to maintain a high specific capacity and improving the overall characteristics of the electrochemical device.

[0007] Specifically, if the value of a1 / a2 is too small (e.g., less than 1.1), the Al / Mn molar ratios in the first and second regions are nearly identical, or the Al / Mn molar ratio in the first region is smaller than that in the second region. This means that the Al in the positive electrode active material is primarily concentrated inside the positive electrode active material particles. As a result, the manganese elution phenomenon in the positive electrode is barely improved, which is detrimental to improving the cycle and storage characteristics of the electrochemical device. As the value of a1 / a2 gradually increases, the Al in the resulting positive electrode active material is primarily concentrated on the surface of the positive electrode active material particles. This can contribute to maintaining the specific capacity of the positive electrode while improving manganese elution from the positive electrode. However, if the value of a1 / a2 is too large (e.g., greater than 100), i.e., if the Al / Mn molar ratio a1 in the first region is too large, the total Al content in the positive electrode active material increases, resulting in a decrease in the specific capacity of the positive electrode. Adjusting the value of a1 / a2 within the above range contributes to simultaneously improving the cycle characteristics and storage characteristics of the electrochemical device, and also allows the positive electrode to maintain a high specific capacity, thereby improving the overall characteristics of the electrochemical device.

[0008] In some embodiments of the present invention, the Al content in the first region is 0.01% to 0.5% by mass relative to the mass of the positive electrode active material. For example, the Al content in the first region can be 0.01%, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, or 0.5%, or any range therebetween. Adjusting the Al content in the first region to fall within the above range improves manganese elution from the positive electrode while contributing to maintaining a high specific capacity of the positive electrode, thereby improving the overall performance of the electrochemical device.

[0009] In some embodiments of the present invention, the positive electrode active material is selected from lithium manganese oxides (LMOs) containing Al element.

[0010] In some embodiments of the present invention, the Al / Mn molar ratio a1 in the first region is 1% to 30%, preferably 5% to 30%, and / or the Al / Mn molar ratio a2 in the second region is 0.05% to 5%. For example, the Al / Mn molar ratio a1 in the first region can be 1%, 5%, 10%, 15%, 20%, 25%, or 30%, or any range of values ​​therein. For example, the Al / Mn molar ratio a2 in the second region can be 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, or 0.5%, or any range of values ​​therein.

[0011] If the Al / Mn molar ratio a1 in the first region is too small (e.g., less than 1%), it is not possible to improve the cyclability and storage performance of the electrochemical device by improving the manganese elution phenomenon in the positive electrode. Furthermore, the introduction of Al reduces the specific capacity of the positive electrode to some extent. If the Al / Mn molar ratio a1 in the first region is too large (e.g., greater than 30%), the total Al content in the positive electrode active material increases, reducing the specific capacity of the positive electrode. If the Al / Mn molar ratio a2 in the second region is too small (e.g., less than 0.05%) or too large (e.g., greater than 0.5%), it is detrimental to improving the cyclability and storage performance of the electrochemical device. Adjusting the Al / Mn molar ratio a1 in the first region and / or the Al / Mn molar ratio a2 in the second region within the range of the present invention can simultaneously improve the cyclability and storage performance of the electrochemical device while maintaining a high specific capacity of the positive electrode, thereby contributing to improving the overall performance of the electrochemical device.

[0012] In some embodiments of the present invention, the positive electrode active material is (a) the molar ratio of Al / Mn in the positive electrode active material is 0.1% to 10%, preferably 2% to 10%; (b) Mn element is Mn 3+ and Mn 4+ and Mn in the second region. 3+ / Mn 4+ Mn in the first region relative to the molar ratio of 3+ / Mn 4+When the molar ratio of the above is e, e is 0.8 to 0.95; (c) the positive electrode active material further contains Li, and when the molar ratio of Li / Mn in the first region is b1 and the molar ratio of Li / Mn in the second region is b2, b1 and b2 satisfy 1≦b1 / b2≦2, preferably 1.1≦b1 / b2≦2; At least one of the following conditions is satisfied. For example, the Al / Mn molar ratio in the positive electrode active material can be 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%, or can be within any range of the above values. For example, the value of e can be 0.8, 0.83, 0.85, 0.87, 0.9, 0.92, or 0.95, or can be within any range of the above values. For example, the value of b1 / b2 can be 1, 1.1, 1.2, 1.4, 1.6, 1.8, or 2, or can be within any range of the above values.

[0013] If the Al / Mn molar ratio in the positive electrode active material is too small (e.g., less than 0.1%), the manganese elution phenomenon from the positive electrode is hardly improved, and the cycle and storage characteristics of the electrochemical device are hardly improved. If the Al / Mn molar ratio in the positive electrode active material is too large (e.g., more than 10%), the specific capacity of the positive electrode decreases. Adjusting the Al / Mn molar ratio in the positive electrode active material within the above range contributes to improving the cycle and storage characteristics of the electrochemical device, and allows the positive electrode to maintain a high specific capacity, thereby improving the overall characteristics of the electrochemical device.

[0014] In some embodiments of the present invention, the mass percentage of Al is 0.005% to 0.1% relative to the mass of the positive electrode active material. For example, the mass percentage of Al in the positive electrode active material can be 0.005%, 0.01%, 0.02%, 0.05%, 0.08%, or 0.1%, or any range therebetween. Adjusting the mass percentage of Al in the positive electrode active material to fall within the above range improves manganese elution from the positive electrode while contributing to maintaining a high specific capacity of the positive electrode, thereby improving the overall performance of the electrochemical device.

[0015] In some embodiments of the present invention, the mass percentage of Mn is 1.0% to 1.2% relative to the mass of the positive electrode active material. Adjusting the mass percentage of Mn in the positive electrode active material to fall within this range contributes to improving manganese elution from the positive electrode while maintaining a high specific capacity of the positive electrode, thereby improving the overall performance of the electrochemical device.

[0016] Mn in the second region 3+ / Mn 4+ Mn in the first region relative to the molar ratio of 3+ / Mn 4+ When the molar ratio e of the first region is within the range of the present invention, it contributes to improving the manganese elution phenomenon and improves the cycle characteristics and storage characteristics of the electrochemical device. 3+ / Mn 4+ and the molar ratio of Mn in the second region 3+ / Mn 4+ The molar ratio of Mn in the first region is not particularly limited as long as it satisfies the range of e. 3+ / Mn 4+ The molar ratio of Mn in the second region is 15% to 55%. 3+ / Mn 4+ The molar ratio of is 30% to 70%.

[0017] By setting the ratio b1 / b2 between the Li / Mn molar ratio b1 in the first region and the Li / Mn molar ratio b2 in the second region within the above range, the Li / Mn molar ratio b1 in the first region is larger than the Li / Mn molar ratio b2 in the second region, which can improve the cycle characteristics of the electrochemical device and contribute to maintaining a high specific capacity of the positive electrode.

[0018] In some embodiments of the present invention, the Li / Mn molar ratio b1 in the first region is 58% to 98%, and the Li / Mn molar ratio b2 in the second region is 55% to 60%. For example, the Li / Mn molar ratio b1 in the first region can be 58%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 98%, or any range thereof. The Li / Mn molar ratio b2 in the second region can be 55%, 55.5%, 56%, 56.5%, 57%, 57.5%, 58%, 58.5%, 59%, 59.5%, or 60%, or any range thereof. Adjusting the Li / Mn molar ratio b1 in the first region and the Li / Mn molar ratio b2 in the second region to fall within the above ranges can improve the cycle characteristics of the electrochemical device and contribute to maintaining a high specific capacity of the positive electrode.

[0019] In some embodiments of the present invention, the positive electrode active material further comprises an M1 element, wherein the M1 element comprises at least one of Ni, Co, Nb, Mo, V, W, Zr, Mg, Ti, La, Y, and B elements, and the positive electrode active material comprises (d) the molar ratio of M1 / Mn is 0.1% to 5%; (e) the molar ratio of Al / M1 is 1 to 10; For example, the molar ratio of M1 / Mn can be 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%, or any range of values ​​therein. For example, the molar ratio of Al / M1 can be 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 6, 7, 8, 9, or 10, or any range of values ​​therein.

[0020] When the positive electrode active material contains the M1 element and the molar ratio of M1 / Mn and / or the molar ratio of Al / M1 is within the above range, the storage characteristics of the electrochemical device can be improved and the specific capacity of the positive electrode can be maintained high.

[0021] In some embodiments of the present invention, the positive electrode active material further comprises an M2 element, the M2 element including F and / or S, and the M2 element is present in a mass percentage of 0.1% to 2% relative to the mass of the positive electrode active material. For example, the M2 element may be present in a mass percentage of 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, or 2%, or in any range consisting of the above values.

[0022] If the mass percentage of the M2 element is too low (e.g., less than 0.1%), the characteristics of the electrochemical device are hardly improved. As the mass percentage of the M2 element increases, it can contribute to improving the specific capacity of the positive electrode. However, if the mass percentage of the M2 element is too high (e.g., more than 2%), the cycle characteristics of the electrochemical device deteriorate. Adjusting the mass percentage of the M2 element within the above range can improve the cycle characteristics of the electrochemical device and contribute to maintaining a high specific capacity of the positive electrode.

[0023] In some embodiments of the present invention, the M2 element includes an F element, and when the molar ratio of F / Mn in the first region is d1 and the molar ratio of F / Mn in the second region is d2, d1 and d2 satisfy the relationship 3≦d1 / d2≦50, preferably 3≦d1 / d2≦25. For example, the value of d1 / d2 can be 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, or 50, or any range consisting of the above numerical values.

[0024] Introducing the M2 element into the positive electrode active material can improve the cycle characteristics of the electrochemical device, but excessive M2 element affects the specific capacity of the positive electrode. By adjusting the value of d1 / d2 within the range of the present invention and making the F / Mn molar ratio d1 in the first region greater than the F / Mn molar ratio d2 in the second region, i.e., by concentrating the F element in the surface region of the positive electrode active material, the cycle characteristics of the electrochemical device can be improved while maintaining a high specific capacity of the positive electrode. In the present invention, the F / Mn molar ratio d1 in the first region and the F / Mn molar ratio d2 in the second region are not particularly limited as long as they satisfy the d1 / d2 range. For example, the F / Mn molar ratio d1 in the first region is 1% to 2.5%, and the F / Mn molar ratio d2 in the second region is 0.05% to 0.5%.

[0025] In some embodiments of the present invention, the positive electrode active material further includes Nb, and when the molar ratio of Nb / Mn in the first region is c1 and the molar ratio of Nb / Mn in the second region is c2, c1 and c2 satisfy the relationship 3≦c1 / c2≦50. For example, the value of c1 / c2 can be 3, 10, 15, 20, 25, 30, 35, 40, or 45, or any range consisting of the above values.

[0026] Introducing Nb element into the positive electrode active material and setting the value of c1 / c2 within the above range can contribute to improving the cycle characteristics of the electrochemical device. In the present invention, the Nb / Mn molar ratio c1 in the first region and the Nb / Mn molar ratio c2 in the second region are not particularly limited as long as they satisfy the c1 / c2 range. For example, the Nb / Mn molar ratio c1 in the first region is 1% to 5%, and the Nb / Mn molar ratio c2 in the second region is 0.1% to 0.8%.

[0027] In some embodiments of the present invention, the positive electrode active material has a Dv99 of 15 μm to 50 μm, preferably 25 μm to 35 μm, and the particle size of the positive electrode active material is (i) Dv90 and Dv99 satisfy 5 μm≦Dv90≦30 μm, 5 μm≦Dv99−Dv90≦21 μm, preferably 8 μm≦Dv99−Dv90≦12 μm; (ii) Dv10, Dv50 and Dv99 satisfy 2 μm≦Dv10≦10 μm, 1≦(Dv99−Dv10) / Dv50≦4, preferably 4 μm≦Dv10≦7 μm, 2≦(Dv99−Dv10) / Dv50≦3; At least one of the following conditions must be met.

[0028] For example, the Dv99 of the positive electrode active material can be 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, or 50 μm, or any range consisting of the above values. For example, the Dv90 of the positive electrode active material can be 5 μm, 8 μm, 10 μm, 13 μm, 15 μm, 18 μm, 20 μm, 23 μm, 25 μm, 28 μm, or 30 μm, or any range consisting of the above values. The value of Dv99-Dv90 can be 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, or 21 μm, or any range consisting of the above values. For example, the Dv10 of the positive electrode active material can be 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm, or can be within any range consisting of the above values. The value of (Dv99-Dv10) / Dv50 can be 1, 1.5, 2, 2.5, 3, 3.5, or 4, or can be within any range consisting of the above values.

[0029] Adjusting the Dv99, Dv90 and Dv99-Dv90 values ​​of the positive electrode active material within the above ranges, or adjusting the Dv99, Dv10 and (Dv99-Dv10) / Dv50 values ​​of the positive electrode active material within the above ranges, or adjusting the Dv99, Dv90, Dv99-Dv90 values, Dv10 and (Dv99-Dv10) / Dv50 values ​​of the positive electrode active material within the above ranges, can all contribute to improving the overall characteristics of the electrochemical device.

[0030] In the present invention, the method for preparing the positive electrode active material is not particularly limited as long as the object of the present invention can be achieved. For example, the method for preparing the positive electrode active material is mixing the raw materials and performing a first firing at a temperature T1 for a firing time t1 to obtain an intermediate product; Next, adding an intermediate raw material, mixing it with the intermediate product, and performing a second firing at a temperature T2 for a firing time t2 to obtain a positive electrode active material; These may include, but are not limited to:

[0031] In the present invention, the temperature T1 and firing time t1 of the first firing and the temperature T2 and firing time t2 of the second firing are not particularly limited as long as they achieve the object of the present invention. For example, T1 is 800°C to 900°C, t1 is 35 hours to 45 hours, T2 is 450°C to 600°C, and t2 is 5 hours to 15 hours.

[0032] In the present invention, the raw materials and intermediate materials are not particularly limited as long as they achieve the object of the present invention. For example, the raw materials and intermediate materials may each independently contain at least one of MnO2, Li2CO3, and Al2O3, but are not limited thereto.

[0033] The calcination temperature and calcination time generally affect the distribution of elements in the positive electrode active material particles. For example, lowering the calcination temperature and / or shortening the calcination time results in the elements being distributed in regions closer to the surface of the positive electrode active material particles (e.g., the first region of the present invention). Raising the calcination temperature and / or extending the calcination time results in the elements being distributed in regions further from the surface of the positive electrode active material particles (e.g., the second region of the present invention).

[0034] In the present invention, the method for introducing element M1 into the positive electrode active material is not particularly limited as long as it achieves the object of the present invention, and for example, a compound containing M1 can be added during preparation of the positive electrode active material. In the present invention, the compound containing M1 is not particularly limited as long as it achieves the object of the present invention, and can include, but is not limited to, at least one of MgO, nickel acetate, TiO2, ZrO2, Nb2O5, MoO3, VO5, WO3, and YO3.

[0035] In the present invention, the method for introducing element M2 into the positive electrode active material is not particularly limited as long as it achieves the object of the present invention, and for example, a compound containing M2 can be added during preparation of the positive electrode active material. In the present invention, the compound containing M2 is not particularly limited as long as it achieves the object of the present invention, and can include, for example, at least one of MnS and LiF, but is not limited thereto.

[0036] A second aspect of the present invention provides an electrochemical device including a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode includes the positive electrode active material according to any one of the embodiments of the present invention, the positive electrode includes a positive electrode layer and a positive electrode current collector, the positive electrode layer includes a first positive electrode layer and a second positive electrode layer, the first positive electrode layer is located between the second positive electrode layer and the positive electrode current collector, and the first positive electrode layer has a higher Mn element content than the second positive electrode layer. The fact that the first positive electrode layer has a higher Mn element content than the second positive electrode layer contributes to reducing manganese elution from the positive electrode and improving the cycle and storage characteristics of the electrochemical device.

[0037] In some embodiments of the present invention, the electrolyte is (iii) the electrolyte solution contains a chain carbonate, the chain carbonate being 20% ​​to 60% by mass, and the chain carbonate includes at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), and ethyl methyl carbonate (EMC); (iv) the electrolytic solution contains a benzene-containing compound, and the benzene-containing compound is present in a mass percentage of 0.01% to 5%, preferably 0.01% to 3%, and more preferably 1% to 3%, and the benzene-containing compound contains at least one of biphenyl (BP), fluorobenzene (FP), and cyclohexylbenzene (CHB); (v) the electrolyte solution contains polystyrene (PS), and the polystyrene content is 0.01% to 5%, preferably 0.01% to 3%, by mass percentage; At least one of the following conditions must be met.

[0038] For example, the linear carbonate may be present in a mass percentage of 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, or 60%, or in any range of the above values. For example, the benzene-containing compound may be present in a mass percentage of 0.01%, 0.05%, 0.1%, 1%, 2%, 3%, 4%, or 5%, or in any range of the above values. For example, the polystyrene may be present in a mass percentage of 0.01%, 0.05%, 0.1%, 1%, 2%, 3%, 4%, 5%, or in any range of the above values. Optionally adding at least one of the linear carbonate, benzene-containing compound, and polystyrene to the electrolyte solution, and setting the mass percentage within the above range, contributes to the formation of a synergistic effect between the positive electrode active material and the electrolyte solution, thereby improving the cycle characteristics and storage characteristics of the electrochemical device.

[0039] In some embodiments of the present invention, the negative electrode comprises a negative electrode material layer, the negative electrode material layer comprises a negative electrode active material, the negative electrode active material comprises at least one of natural graphite, artificial graphite, and hard carbon, and the electrochemical device comprises: (vi) Dv10 of the negative electrode active material satisfies 2 μm≦Dv10≦10 μm, preferably 3 μm≦Dv10≦8 μm; (vii) Dv90 and Dv99 of the negative electrode active material satisfy 5 μm≦Dv90≦20 μm, 5 μm≦Dv99−Dv90≦25 μm, preferably 5 μm≦Dv90≦15 μm, 5 μm≦Dv99−Dv90≦10 μm; (viii) the orientation index (OI) of the negative electrode active material is 5 to 30, preferably 8 to 20; (ix) the degree of graphitization of the negative electrode active material is 92% to 96%, preferably 93% to 95%; At least one of the following conditions must be met.

[0040] For example, the Dv10 of the negative electrode active material can be 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm, or any range consisting of the above values. For example, the Dv90 of the negative electrode active material can be 5 μm, 8 μm, 10 μm, 13 μm, 15 μm, 18 μm, or 20 μm, or any range consisting of the above values. The value of Dv99-Dv90 can be 5 μm, 8 μm, 10 μm, 13 μm, 15 μm, 18 μm, 20 μm, 23 μm, or 25 μm, or any range consisting of the above values. For example, the OI of the negative electrode active material can be 5, 8, 10, 13, 15, 18, 20, 23, 25, 28, or 30, or any range consisting of the above values. For example, the degree of graphitization of the negative electrode active material can be 92%, 93%, 94%, 95%, or 96%, or any range between the foregoing values.

[0041] By ensuring that at least one of the Dv10 of the negative electrode active material, the Dv10, Dv90 and Dv99-Dv90 values ​​of the negative electrode active material, the OI value of the negative electrode active material, and the degree of graphitization of the negative electrode active material falls within the range of the present invention, this can contribute to the formation of a synergistic effect between the negative electrode active material, the positive electrode active material, and the electrolyte, and can contribute to improving the cycle characteristics and storage characteristics of the electrochemical device.

[0042] In some embodiments of the present invention, the electrochemical device includes a separator, and the separator has an exotherm onset temperature measured by differential scanning calorimetry (DSC) of 138°C to 145°C, preferably 141°C to 143°C, and more preferably 141°C to 142°C. For example, the separator's exotherm onset temperature measured by differential scanning calorimetry can be 138°C, 139°C, 140°C, 141°C, 142°C, 143°C, 144°C, or 145°C, or any range therebetween. Adjusting the separator's exotherm onset temperature measured by DSC within the range of the present invention contributes to the formation of a synergistic effect between the separator, the negative electrode material, the positive electrode active material, and the electrolyte, which can contribute to improving the cycle characteristics and storage characteristics of the electrochemical device.

[0043] In the present invention, the molar ratio of different elements in the positive electrode active material is calculated from the contents of the different elements obtained by disassembling an electrochemical device containing the positive electrode active material at a 0% state of charge to obtain a positive electrode and then measuring the contents of the different elements.

[0044] In the present invention, the positive electrode current collector is not particularly limited as long as it achieves the object of the present invention, and may include, for example, aluminum foil, aluminum alloy foil, and composite current collector, but is not limited thereto. In the present invention, the thickness of the positive electrode current collector is not particularly limited as long as it achieves the object of the present invention, and the thickness is, for example, 8 μm to 12 μm.

[0045] In the present invention, the positive electrode layer includes the positive electrode active material according to any of the above embodiments of the present invention, and the positive electrode layer may further include a binder. In the present invention, the binder is not particularly limited as long as it achieves the object of the present invention, and may include, for example, at least one of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, polyimide, polyamide imide, styrene-butadiene rubber, and polyvinylidene fluoride, but is not limited thereto.

[0046] In the present invention, the positive electrode material layer may further include a conductive agent. The conductive agent may be any material that achieves the objectives of the present invention and may include, but is not limited to, at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, Ketjen black, graphene, metal materials, and conductive polymers. The carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The carbon fibers may include, but are not limited to, vapor-grown carbon fibers (VGCF) and / or nanocarbon fibers. The metal material may include, but is not limited to, metal powder and / or metal fibers. Specifically, the metal may include, but is not limited to, at least one of copper, nickel, aluminum, and silver. The conductive polymer may include, but is not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, and polypyrrole.

[0047] Optionally, the positive electrode may further include a conductive layer, and the conductive layer is located between the positive electrode current collector and the positive electrode material layer. In the present invention, the composition of the conductive layer is not particularly limited and may be a conductive layer commonly used in the field, for example, it may include the conductive agent and the binder, but is not limited thereto.

[0048] In the present invention, the negative electrode may include a negative electrode current collector. The negative electrode current collector of the present invention is not particularly limited as long as it achieves the object of the present invention, and may include, but is not limited to, copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or a composite current collector. In the present invention, the thickness of the negative electrode current collector is not particularly limited as long as it achieves the object of the present invention, and may be, for example, 4 μm to 12 μm. In the present invention, the negative electrode material layer may be provided on one surface in the thickness direction of the negative electrode current collector, or on both surfaces in the thickness direction of the negative electrode current collector. Note that the "surface" may be the entire region of the negative electrode current collector, or may be a partial region of the negative electrode current collector. The present invention is not particularly limited as long as it achieves the object of the present invention.

[0049] In the present invention, the negative electrode material layer may further include a conductive agent. In the present invention, the conductive agent is not particularly limited as long as it achieves the object of the present invention, and may include, for example, at least one of the conductive agents described above, but is not limited thereto.

[0050] In the present invention, the negative electrode material layer may further include a binder. In the present invention, the binder is not particularly limited as long as it achieves the object of the present invention, and may include, for example, at least one of the binders described above, but is not limited thereto.

[0051] Optionally, the negative electrode may further include a conductive layer, and the conductive layer is located between the negative electrode current collector and the negative electrode material layer. In the present invention, the composition of the conductive layer is not particularly limited and may be a conductive layer commonly used in the field, and the conductive layer may include, but is not limited to, the conductive agent and the binder.

[0052] In the present invention, the separator may be any material that achieves the objectives of the present invention and is not particularly limited. For example, the separator may include at least one of polyethylene (PE), polypropylene (PP), polytetrafluoroethylene-based polyolefin (PO) separators, polyester films (e.g., polyethylene terephthalate (PET) films), cellulose films, polyimide films (PI), polyamide films (PA), spandex, aramid films, woven films, nonwoven films (nonwoven fabrics), microporous films, composite films, separator films, laminate films, and spun films, but is not limited thereto. PP is preferred. The separator of the present invention may have a porous structure, and the pore size is not particularly limited as long as the objectives of the present invention are achieved, and is, for example, 0.01 μm to 1 μm. The thickness of the separator is not particularly limited as long as the objectives of the present invention are achieved, and is, for example, 5 μm to 500 μm, preferably 25 μm.

[0053] For example, the separator may include a substrate layer and a surface treatment layer. The substrate layer may be a porous nonwoven fabric, a membrane, or a composite membrane, and the material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate, polyimide, etc., but is not limited to these. Optionally, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be used. Optionally, a surface treatment layer is provided on at least one surface of the substrate layer, and the surface treatment layer may be a polymer layer or an inorganic layer, or may be a mixed layer made of a polymer and an inorganic material.

[0054] The inorganic layer may include, but is not limited to, inorganic particles and a binder. In the present invention, the inorganic particles are not particularly limited and may include, but are not limited to, at least one of alumina, silica, magnesia, titania, hafnia, tin oxide, ceria, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. In the present invention, the binder is not particularly limited and may include, but is not limited to, at least one of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylic acid ester, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene. The polymer layer includes a polymer, and the polymer material can include, but is not limited to, at least one of polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene), etc.

[0055] In the present invention, the electrolyte may further include a lithium salt. The lithium salt is not particularly limited as long as it achieves the object of the present invention, and may include, but is not limited to, at least one of LiPF, LiBF, LiAsF, LiClO, LiB(C H ), LiCH SO, LiCF SO, LiN(SO CF), LiC(SO CF), LiSiF, LiBOB, and lithium difluoroborate. Preferably, the lithium salt includes LiPF.

[0056] In the present invention, the electrolyte solution may further include a non-aqueous solvent. The non-aqueous solvent may be any solvent that achieves the objectives of the present invention, and may include, but is not limited to, at least one of a carbonate compound, a carboxylate compound, an ether compound, and other organic solvents. The carbonate compound may include, but is not limited to, at least one of a cyclic carbonate compound and / or a fluorocarbonate compound. The cyclic carbonate may include, but is not limited to, at least one of ethylene carbonate (also known as EC), propylene carbonate (PC), butylene carbonate (BC), and vinyl ethylene carbonate (VEC). The fluorocarbonate compound can include, but is not limited to, at least one of fluoroethylene carbonate (also called fluoroethylene carbonate, abbreviated as FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, and trifluoromethylethylene carbonate. The carboxylate compound may include, but is not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, gamma-butyrolactone, decanolide, valerolactone, mevalonolactone, and caprolactone. The ether compound may include, but is not limited to, at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, and tetrahydrofuran.The other organic solvent may include, but is not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphate ester. The mass percentage of the nonaqueous solvent relative to the mass of the electrolyte solution may be 15% to 80%, for example, 15%, 20%, 30%, 40%, 50%, 60%, 70%, or 80%, or any range of the above values.

[0057] The electrochemical device of the present invention is not particularly limited and may include any device in which an electrochemical reaction occurs. In some embodiments, the electrochemical device includes, but is not limited to, a lithium metal secondary battery, a lithium ion secondary battery (lithium ion battery), a lithium polymer secondary battery, and a lithium ion polymer secondary battery.

[0058] The process for preparing an electrochemical device is well known to those skilled in the art, and the present invention is not particularly limited thereto. For example, the process may include, but is not limited to, the following steps: Laminate a positive electrode, a separator, and a negative electrode in order, and if necessary, roll or fold the laminate to obtain a wound electrode assembly. Then, place the electrode assembly in a packaging bag, inject an electrolyte into the packaging bag, and seal the bag to obtain an electrochemical device. Alternatively, laminate a positive electrode, a separator, and a negative electrode in order, and then secure the four corners of the entire laminate with tape to obtain a laminated electrode assembly. Place the electrode assembly in a packaging bag, inject an electrolyte into the packaging bag, and seal the bag to obtain an electrochemical device. Additionally, an overcurrent protection element, lead plates, etc. may be placed in the packaging bag as needed to prevent internal pressure buildup, overcharging, overdischarging, etc. within the electrochemical device.

[0059] A third aspect of the present invention provides an electronic device including an electrochemical device according to any one of the above embodiments of the present invention. The electrochemical device provided by the present invention has good cycle characteristics and storage characteristics, and the positive electrode has a higher specific capacity. Therefore, the electronic device provided by the present invention has a longer service life and good characteristics.

[0060] 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 includes, but is not limited to, a notebook computer, a pen-input computer, a mobile computer, an electronic book player, a mobile phone, a portable facsimile machine, a portable copier, a portable printer, a stereo headset, a video recorder, an LCD television, a portable vacuum cleaner, a portable CD player, a minidisc, a walkie-talkie, an electronic notebook, a calculator, a memory card, a portable tape recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, an auxiliary bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flashlight, a camera, a large household storage battery, and a lithium ion capacitor.

[0061] The present invention provides a cathode active material containing Mn and Al, wherein the cathode active material particles include a first region close to the surface of the cathode active material particles and a second region remote from the surface of the cathode active material particles, where a1 is the molar ratio of Al / Mn in the first region and a2 is the molar ratio of Al / Mn in the second region, and a1 and a2 satisfy the relationship 1.1≦a1 / a2≦100. By adjusting the Al / Mn molar ratio a1 in the first region and the ratio a1 / a2 between the Al / Mn molar ratio a1 in the first region and the Al / Mn molar ratio a2 in the second region within the above ranges, Al in the cathode active material is concentrated in the region close to the surface of the cathode active material, effectively reducing manganese elution from the positive electrode and improving the cycle and storage characteristics of the electrochemical device. At the same time, the total Al content in the cathode active material is reduced, maintaining a high specific capacity of the positive electrode and improving the overall characteristics of the electrochemical device. [Brief explanation of the drawings]

[0062] In order to more clearly describe the technical solutions of the embodiments of the present invention, the following briefly describes the drawings that need to be used in the embodiments. The drawings described below are only a part of the embodiments of the present invention, and it is obvious that those skilled in the art can obtain other embodiments based on these drawings.

[0063] [Figure 1] FIG. 1 is a cross-sectional view of a positive electrode active material particle according to some embodiments of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0064] In order to clearly illustrate the objectives, technical solutions, and advantages of the present invention, the present invention will be described in more detail below by way of examples with reference to the drawings. It is clear that the described examples are only some of the examples of the present invention, and do not cover all of the examples. All other examples obtained by those skilled in the art based on the examples of the present invention fall within the scope of protection of the present invention.

[0065] 1 shows a cross-sectional schematic diagram of a positive electrode active material particle according to some embodiments of the present invention. As can be seen from the diagram, first region 11 is a region close to the surface of a particle of positive electrode active material 10, and second region 12 is a region away from the surface of the particle of positive electrode active material 10. In the embodiments of the present invention, the present invention will be described using a lithium ion battery as an example of an electrochemical device, but the electrochemical device of the present invention is not limited to a lithium ion battery.

[0066] Example Hereinafter, the embodiments of the present invention will be described in more detail with reference to examples and comparative examples. Various tests and evaluations were performed as follows. Unless otherwise specified, "%" is based on mass.

[0067] Measurement method and equipment: Elemental content determination: a) Prepare a sulfuric acid solution with a concentration of 2.4 mol / L. b) 50 g of positive electrode active material (a lithium ion battery is fully discharged to 2.5 V, the positive electrode material layer on the positive electrode is scraped off with a ceramic knife, and the positive electrode active material layer is baked at 400°C for 5 hours to obtain the positive electrode active material) is taken, c) Mix 300 mL of sulfuric acid solution with 50 g of positive electrode active material, place on a magnetic stirrer and stir, fixing the stirring speed at 200 r / min; d) After 6 hours, the stirring is stopped and the mixture is allowed to stand, and after 4 hours of standing, the mixture is suction filtered through filter paper, the filtrate is collected, and measured using an inductively coupled plasma optical emission spectrometer (model number: Thermo ICAP6300). The molar ratios between different elements in the first region, such as the Al / Mn molar ratio, Li / Mn molar ratio, Nb / Mn molar ratio, and F / Mn molar ratio, can be calculated and obtained; e) After suction filtration, the sample was dried at 85°C for 8 hours. f) The dried sample was measured using an inductively coupled plasma optical emission spectrometer (model: Thermo ICAP6300), and the molar ratios between different elements in the second region, such as the Al / Mn molar ratio, Li / Mn molar ratio, Nb / Mn molar ratio, and F / Mn molar ratio, were calculated and obtained.

[0068] Mn 3+ / Mn 4+ Molar ratio determination: X-ray photoelectron spectroscopy (XPS) revealed that Mn in the first and second regions of the positive electrode active material 3+ / Mn 4+ The molar ratio was determined.

[0069] Measurement of cycle characteristics: At 25°C, a lithium-ion battery is charged at a constant current of 0.5C up to 4.2V, then charged at a constant voltage of 0.05C at 4.2V, and then discharged at a constant current of 1C down to 2.8V. The discharge capacity is measured as D. 01 The lithium ion battery was subjected to a cycle process of "0.5C charge-1C discharge" multiple times according to the above operation steps, and the discharge capacity after the 500th cycle was measured as D1. The capacity retention rate after 500 cycles at 25°C (%) = D1 / D01 ×100%.

[0070] Determination of storage properties: After allowing the lithium-ion battery to stand for 30 minutes at 25°C, it was charged at a constant current of 0.2C to 4.2V, then charged to 0.05C at a constant voltage of 4.2V, allowed to stand for 30 minutes, and then discharged at a rate of 0.5C to 2.8V. The discharge capacity at this time was recorded as the pre-storage capacity of the lithium-ion battery. The fully charged battery was then placed in an oven at approximately 60°C and stored for approximately 7 days, after which the post-storage capacity was measured. The specific test process was as follows: The lithium-ion battery was allowed to stand for 30 minutes at 25°C, then charged at a constant current of 0.2C to 4.2V, then charged to 0.05C at a constant voltage of 4.2V, allowed to stand for 30 minutes, and then discharged at a rate of 0.5C to 2.8V. The discharge capacity at this time was recorded as the post-storage capacity of the lithium-ion battery. High-temperature storage capacity retention rate at 60°C = capacity after storage / capacity before storage × 100%. For each example or comparative example, four lithium ion batteries were measured, and the average value was used as the final result.

[0071] Measurement of specific capacitance: Button batteries were fabricated using the positive electrodes and lithium metal of the Examples or Comparative Examples. At 25°C, the button batteries were charged at a constant current and constant voltage with a charging current of 0.5 C (i.e., the current required to fully discharge the theoretical capacity in 2 hours) until the upper limit voltage reached 4.2 V. They were then discharged at a constant current of 0.2 C until the final voltage reached 2.8 V, and the initial discharge capacity was recorded. The ratio of the initial discharge capacity to the mass of the positive electrode was recorded as the specific capacity of the positive electrode. For each Example or Comparative Example, four positive electrodes were measured, and the average value was used as the final result. The mass of the positive electrode was the mass minus the mass of the positive electrode current collector. The button batteries were prepared using methods known in the art, and the electrolyte used in each Example or Comparative Example was the electrolyte used in each Example or Comparative Example.

[0072] Measurement of separator heat generation onset temperature: Measurement was performed using DSC, and a DSC curve of the separator was obtained at a temperature rise rate of 10°C / min, and the heat generation initiation temperature of the separator was obtained from the DSC curve.

[0073] Particle size measurement method: The particle size of the positive electrode active material or negative electrode active material was measured using a laser granulometer (model number: Mastersize 3000). Dv10, Dv50, Dv90, and Dv99 were the diameters at which the cumulative volume was 10%, 50%, 90%, and 99% in the volume-based particle distribution measured by the laser scattering granulometer.

[0074] Example 1-1 <Preparation of positive electrode active material> Primary firing: The raw materials MnO2, Al2O3, and Li2CO3 are mixed so that the Al / Mn molar ratio is x1 and the Li / Mn molar ratio is y1, and fired at a temperature T1 for a firing time t1 to obtain an intermediate product. Secondary firing: Al2O3, Li2CO3 and the intermediate product were further mixed and fired at a temperature T2 for a firing time t2 to obtain a positive electrode active material, which was lithium manganese oxide (LMO) containing Al element.

[0075] Here, the Al / Mn molar ratio of Al in Al2O3 added during secondary firing to Mn in the intermediate product was x2, the Li / Mn molar ratio of Li in Li2CO3 added during secondary firing to Mn in the intermediate product was y2, and the raw material MnO2 contained Al and had an Al / Mn molar ratio of x0. The positive electrode active material had a Dv99 of 45 μm, a Dv90 of 26 μm, a Dv50 of 11.2 μm, and a Dv10 of 6 μm.

[0076] <Preparation of positive electrode> The prepared positive electrode active material, acetylene black (conductive agent), and polyvinylidene fluoride (binder) were mixed in a mass ratio of 96.5:2:1.5, N-methylpyrrolidone (NMP) was added, and the mixture was uniformly stirred using a vacuum mixer to obtain a positive electrode slurry. The solids content of the positive electrode slurry was 70 wt%. The positive electrode slurry was uniformly coated onto one surface of an aluminum foil positive electrode current collector with a thickness of 12 μm, and the aluminum foil was dried at 120°C for 1 hour to obtain a positive electrode with a positive electrode material layer coated on one side. The above steps were repeated on the other side of the aluminum foil to obtain a positive electrode with a positive electrode material layer coated on both sides. Next, the mixture was cold-pressed, cut, and slit, and then dried under vacuum at 120°C for 1 hour to obtain a positive electrode measuring 74 mm x 867 mm.

[0077] <Preparation of negative electrode> The negative electrode active material (artificial graphite), conductive agent (acetylene black), binder (styrene butadiene rubber (SBR)), and thickener (sodium carboxymethyl cellulose (CMC)) were mixed in a mass ratio of 95:2:2:1, deionized water was added, and the mixture was uniformly stirred using a vacuum mixer to obtain a negative electrode slurry. The solids content of the negative electrode slurry was 75 wt%. The negative electrode slurry was uniformly coated onto one side of a 12 μm-thick copper foil negative electrode current collector, and the copper foil was dried at 120 °C to obtain a negative electrode with a 130 μm-thick coating layer on one side. The above steps were repeated on the other side of the aluminum foil to obtain a negative electrode with a double-coated negative electrode. Next, the mixture was cold-pressed, cut, and slit, and then dried under vacuum at 120 °C for 1 hour to obtain a negative electrode measuring 78 mm x 875 mm. Here, the negative electrode material has a Dv99 of 30 μm, a Dv90 of 18 μm, a Dv10 of 5 μm, an OI value of 18, and a graphitization degree of 96%.

[0078] <Preparation of electrolyte> In a glove box under a dry argon atmosphere, EC, PC, DEC, and EMC were mixed in a mass ratio of 5:1:4:7 to obtain an organic solvent, and then lithium salt LiPF6 was added to the organic solvent, dissolved, and mixed uniformly to obtain an electrolyte solution, where the mass percentage of LiPF6 in the electrolyte solution was 12.5%, and the remainder was organic solvent.

[0079] <Preparation of separator> A porous polyethylene thin film (manufactured by Celgard) with a thickness of 7 μm was used, and the separator's heat generation initiation temperature was 141°C.

[0080] <Preparation of lithium-ion batteries> The prepared positive electrode, separator, and negative electrode were stacked in this order, and a separator was placed between the positive and negative electrodes to act as an insulator. The stack was then wound up to obtain an electrode assembly. The electrode assembly was placed in an aluminum plastic film packaging bag, dried, and then an electrolyte solution was injected. The assembly was then vacuum packaged, left to stand, formed, and side-cut, and a lithium-ion battery was obtained.

[0081] Examples 1-2 to 1-8 The same procedure as in Example 1-1 was carried out except that the preparation parameters were adjusted as shown in Table 1.

[0082] Examples 2-1 to 2-4 The same procedure as in Examples 1-4 was carried out except that the preparation parameters were adjusted as shown in Table 2.

[0083] Examples 3-1 to 3-5, 3-7 and 3-8 In <Preparation of Positive Electrode Active Material>, the same procedures as in Examples 1-4 were carried out except that the compound corresponding to the M1 element added during primary firing and its content were adjusted to prepare positive electrode active materials with the molar ratios of each element shown in Table 3.

[0084] Examples 3-6 In <Preparation of Positive Electrode Active Material>, the same procedures as in Examples 1-4 were carried out except that a compound corresponding to the M1 element was added during the primary firing so that the M1 / Mn molar ratio was 1.0%, and a compound corresponding to the M1 element was added during the secondary firing so that the molar ratio of M1 to Mn in the intermediate product was 2.6%, thereby producing a positive electrode active material having the molar ratios of each element shown in Table 3.

[0085] Examples 3-9 In <Preparation of Positive Electrode Active Material>, the same procedures as in Examples 1-4 were carried out except that during the primary firing, a compound corresponding to the M1 element was added so that the M1 / Mn molar ratio was 1.0%, and during the secondary firing, a compound corresponding to the M1 element was added so that the molar ratio of M1 to Mn in the intermediate product was 1.0%, thereby producing a positive electrode active material having the molar ratios of each element shown in Table 3.

[0086] Examples 3-10 to 3-13 The same procedures as in Examples 1-4 were carried out except that a compound corresponding to M2 was added during the primary firing so that the mass percentage of the M2 element would be the mass percentage shown in Table 3.

[0087] Examples 3-14 The same procedures as in Example 3-7 were carried out, except that a compound corresponding to M2 was added during the primary firing so that the mass percentage of the M2 element would be the mass percentage shown in Table 3.

[0088] Examples 4-1 to 4-3 The same procedure as in Examples 1-4 was carried out except that the preparation parameters were adjusted as shown in Table 4.

[0089] Examples 5-1 to 5-6 The same procedures as in Examples 1-4 were carried out except that the benzene-containing compound and PS were added according to Table 5 during the preparation of the electrolyte solution, and the related preparation parameters were adjusted.

[0090] Comparative Examples 1-1 and 1-2 The same procedure as in Examples 1-4 was carried out except that the preparation parameters were adjusted as shown in Table 1.

[0091] The relevant preparation parameters and property measurements for each example and comparative example are as shown in Tables 1 to 5.

[0092] [Table 1]

[0093] Examples 1-1 to 1-8 and Comparative Examples 1-1 and 1-2 demonstrate that, when the ratio a1 / a2 of the Al / Mn molar ratio a1 in the first region of the positive electrode active material to the Al / Mn molar ratio a2 in the second region is within the range of the present invention, the specific capacity of the positive electrode in the electrochemical device, as well as the cycle and storage characteristics of the electrochemical device, can be simultaneously improved. At the same time, when the value of e is within the range of the present invention, the resulting electrochemical device simultaneously exhibits good cycle and storage characteristics, and the positive electrode in the electrochemical device also has a higher specific capacity. Examples 1-1 to 1-8 and Comparative Example 1-1 demonstrate that, when the Al / Mn molar ratio a1 in the first region is within the range of the present invention, the resulting electrochemical device simultaneously exhibits good cycle and storage characteristics, and the positive electrode in the electrochemical device also has a high specific capacity. From Examples 1-1 to 1-8, it can be seen that when the Al / Mn molar ratio a2 in the second region and the Al / Mn molar ratio of the positive electrode active material are within the ranges of the present invention, the resulting electrochemical device simultaneously has good cycle characteristics and storage characteristics, and the positive electrode in the electrochemical device also has a high specific capacity.

[0094] [Table 2]

[0095] Examples 1-4 and 2-1 to 2-4 show that when the ratio b1 / b2 of the Li / Mn molar ratio b1 in the first region to the Li / Mn molar ratio b2 in the second region of the positive electrode active material is within the range of the present invention, the resulting electrochemical device simultaneously exhibits good cycle characteristics and storage characteristics, and the positive electrode in the electrochemical device also has a high specific capacity. As the value of b1 / b2 increases, the cycle characteristics and storage characteristics of the electrochemical device tend to gradually improve.

[0096] [Table 3]

[0097] Examples 1-4 and 3-1 to 3-14 demonstrate that the addition of the M1 element and / or M2 element can further improve the cycle and storage characteristics of an electrochemical device and the specific capacity of the positive electrode in the electrochemical device. Examples 3-1 to 3-9 demonstrate that by incorporating an M1 element within the ranges of the present invention into a positive electrode active material and ensuring that the M1 / Mn molar ratio, Al / M1 molar ratio, and c1 / c2 values ​​fall within the ranges of the present invention, the resulting electrochemical device simultaneously exhibits good cycle and storage characteristics, and the positive electrode in the electrochemical device also exhibits a high specific capacity. Examples 3-10 to 3-13 demonstrate that by incorporating an M2 element within the ranges of the present invention into a positive electrode active material and ensuring that the mass percentage of the M2 element and the d1 / d2 values ​​fall within the ranges of the present invention, the resulting electrochemical device simultaneously exhibits good cycle and storage characteristics, and the positive electrode in the electrochemical device also exhibits a high specific capacity. Examples 1-4 and 3-14 show that simultaneous introduction of the M1 element and the M2 element can further improve the cycle characteristics and storage characteristics of the electrochemical device, and the specific capacity of the positive electrode in the electrochemical device.

[0098] [Table 4]

[0099] Generally, the particle size of the positive electrode active material affects the characteristics of the electrochemical device, such as the cycle characteristics and storage characteristics. Examples 1-4 and 4-1 to 4-3 show that when the Dv90, Dv10, Dv99-Dv90, and (Dv99-Dv10) / Dv50 values ​​of the positive electrode active material are within the ranges of the present invention, the resulting electrochemical device simultaneously exhibits good cycle characteristics and storage characteristics, and the positive electrode in the electrochemical device also has a high specific capacity.

[0100] [Table 5]

[0101] Generally, the type and content of components in the electrolyte of an electrochemical device affect the characteristics of the electrochemical device, such as cycle and storage characteristics. Examples 1-4, 5-1, and 5-3 demonstrate that when the electrolyte contains a benzene-containing compound and the type and mass percentage are within the range of the present invention, the resulting electrochemical device simultaneously exhibits better cycle and storage characteristics. Examples 1-4, 5-4, and 5-5 demonstrate that when the electrolyte contains PS and the mass percentage is within the range of the present invention, the resulting electrochemical device simultaneously exhibits better cycle and storage characteristics. Examples 1-4 and 5-6 demonstrate that the benzene-containing compound and PS have a beneficial additive effect, further improving the cycle and storage characteristics of the electrochemical device.

[0102] The above description is only a preferred embodiment of the present invention, and does not limit the present invention. Any amendments, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention. [Explanation of symbols]

[0103] 10 positive electrode active material, 11 first region, 12 second region.

Claims

1. Contains Mn and Al elements, the positive electrode active material particle includes a first region close to a surface of the positive electrode active material particle and a second region distant from the surface of the positive electrode active material particle, When the molar ratio of Al / Mn in the first region is a1 and the molar ratio of Al / Mn in the second region is a2, a1 and a2 satisfy 20≦a1 / a2≦90, a1 is 1% to 30%, a2 is 0.05% to 5%, The positive electrode active material is selected from lithium manganese oxides containing Al element, the molar ratio of Al / Mn in the positive electrode active material is 0.1% to 10%; Al is 0.005% to 0.1% by mass percentage relative to the mass of the positive electrode active material, The positive electrode active material, wherein Mn is present in an amount of 1.0% to 1.2% by mass percentage relative to the mass of the positive electrode active material.

2. 2. The positive electrode active material according to claim 1, wherein Al in the first region is 0.01% to 0.5% by mass percentage relative to the mass of the positive electrode active material.

3. (b) the Mn element includes Mn3+ and Mn4+, and when the ratio of the molar ratio of Mn3+ / Mn4+ in the first region to the molar ratio of Mn3+ / Mn4+ in the second region is e, e is 0.80 to 0.95; (c) the positive electrode active material contains Li, and when a molar ratio of Li / Mn in the first region is b1 and a molar ratio of Li / Mn in the second region is b2, b1 and b2 satisfy 1≦b1 / b2≦2; The positive electrode active material according to claim 1 , which satisfies at least one of the following conditions:

4. Further comprising an M1 element, wherein the M1 element comprises at least one of Ni, Co, Nb, Mo, V, W, Zr, Mg, Ti, La, Y, and B elements; The positive electrode active material is (d) the molar ratio of M1 / Mn is 0.1% to 5%; (e) the molar ratio of Al / M1 is 1 to 10; The positive electrode active material according to claim 1 , which satisfies at least one of the following conditions:

5. Further comprising an M2 element, wherein the M2 element comprises F and / or S; 2. The positive electrode active material according to claim 1, wherein the M2 element is present in an amount of 0.1% to 2% by mass based on the mass of the positive electrode active material.

6. The M2 element includes an F element, 6. The positive electrode active material according to claim 5, wherein d1 is a molar ratio of F / Mn in the first region and d2 is a molar ratio of F / Mn in the second region, and d1 and d2 satisfy 3≦d1 / d2≦50.

7. Further containing Nb element, 2. The positive electrode active material according to claim 1, wherein, when a molar ratio of Nb / Mn in the first region is c1 and a molar ratio of Nb / Mn in the second region is c2, c1 and c2 satisfy 3≦c1 / c2≦50.

8. The positive electrode active material has a Dv99 of 15 μm to 50 μm, The particle diameter of the positive electrode active material is (i) Dv90 and Dv99 satisfy 5 μm≦Dv90≦30 μm and 5 μm≦Dv99−Dv90≦21 μm, (ii) Dv10, Dv50, and Dv99 satisfy 2 μm≦Dv10≦10 μm and 1≦(Dv99−Dv10) / Dv50≦4; The positive electrode active material according to claim 1 , which satisfies at least one of the following conditions:

9. (g) a1 is 5% to 30%; (h) the molar ratio of Al / Mn in the positive electrode active material is 2% to 10%; (i) the positive electrode active material contains Li, and when a molar ratio of Li / Mn in the first region is b1 and a molar ratio of Li / Mn in the second region is b2, b1 and b2 satisfy 1.1≦b1 / b2≦2; (j) the positive electrode active material contains an M2 element, and the M2 element contains an F element, and when a molar ratio of F / Mn in the first region is d1 and a molar ratio of F / Mn in the second region is d2, d1 and d2 satisfy 3≦d1 / d2≦25; (k) the positive electrode active material has a Dv99 of 25 μm to 35 μm; (l) the particle diameter of the positive electrode active material satisfies 8 μm≦Dv99−Dv90≦12 μm; (m) the particle diameter of the positive electrode active material satisfies 4 μm≦Dv10≦7 μm and 2≦(Dv99−Dv10) / Dv50≦3; The positive electrode active material according to any one of claims 1 to 8, which satisfies at least one of the above.

10. a positive electrode, a negative electrode, and an electrolyte; The positive electrode comprises the positive electrode active material according to any one of claims 1 to 9, the positive electrode includes a positive electrode material layer and a positive electrode current collector; the positive electrode material layer includes a first positive electrode material layer and a second positive electrode material layer, the first positive electrode material layer is located between the second positive electrode material layer and the positive electrode current collector, an Mn element content in the first positive electrode material layer greater than an Mn element content in the second positive electrode material layer;

11. With respect to the mass of the electrolyte, the electrolyte is (iii) the electrolyte solution contains a chain carbonate, the chain carbonate is present in a mass percentage of 20% to 60%, and the chain carbonate contains at least one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, and ethyl methyl carbonate; (iv) the electrolytic solution contains a benzene-containing compound, the benzene-containing compound is present in a mass percentage of 0.01% to 5%, and the benzene-containing compound contains at least one of biphenyl, fluorobenzene, and cyclohexylbenzene; (v) the electrolyte solution contains polystyrene, and the polystyrene is present in an amount of 0.01% to 5% by mass; The electrochemical device according to claim 10 , which satisfies at least one of the following conditions:

12. (x) the benzene-containing compound is present in an amount of 1% to 3% by mass relative to the mass of the electrolyte; (xi) the polystyrene is present in an amount of 0.01% to 3% by mass relative to the mass of the electrolyte; The electrochemical device according to claim 11 , wherein at least one of the following is satisfied:

13. the negative electrode includes a negative electrode material layer, the negative electrode material layer includes a negative electrode active material, and the negative electrode active material includes at least one of natural graphite, artificial graphite, and hard carbon; The electrochemical device comprises: (vi) the Dv10 of the negative electrode active material satisfies 2 μm≦Dv10≦10 μm; (vii) Dv90 and Dv99 of the negative electrode active material satisfy 5 μm≦Dv90≦20 μm and 5 μm≦Dv99−Dv90≦25 μm; (viii) the orientation index of the negative electrode active material is 5 to 30; (ix) the degree of graphitization of the negative electrode active material is 92% to 96%; The electrochemical device according to claim 10 , which satisfies at least one of the following conditions:

14. the electrochemical device includes a separator; 11. The electrochemical device according to claim 10, wherein the separator has an exotherm onset temperature of 138°C to 145°C as measured by differential scanning calorimetry.

15. An electronic device comprising an electrochemical device according to any one of claims 10 to 14.

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