Secondary battery, electric device, positive electrode active material, and preparation method therefor

Abstract

A secondary battery, an electric device, a positive electrode active material, and a preparation method therefor. The secondary battery comprises a positive electrode sheet; the positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector; the positive electrode film layer comprises a positive electrode active material; the positive electrode active material comprises a lithium transition metal oxide; the lithium transition metal oxide comprises a nickel element and comprises at least one of a cobalt element, a manganese element and an aluminum element; based on 1 mole of the lithium transition metal oxide, the molar content of a lithium element is 1.01-1.15; and the lithium transition metal oxide further comprises a doping element, and the doping element comprises at least one of Mo, W, Ta, Nb, Sb, Ti, and Zr.

Description

Secondary battery, power consuming device, positive electrode active material, and method for manufacturing the same

[0001] Cross Reference to Related Applications

[0002] The present disclosure is based on and claims priority to Chinese Patent Application No. 202411047272.7, filed on July 31, 2024, entitled “Secondary battery, power consuming device, positive electrode active material, and method for manufacturing the same,” the entire contents of which are incorporated herein by reference. TECHNICAL FIELD

[0003] The present disclosure relates to the technical field of batteries, and in particular to a secondary battery, a power consuming device, a positive electrode active material, and a method for manufacturing the same. BACKGROUND

[0004] In recent years, with the application range of secondary batteries becoming more and more extensive, secondary batteries are widely used in energy storage power supply systems such as hydropower, thermal power, wind power, and solar power stations, and in multiple fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, aerospace, etc. With the rapid development of electric vehicles and portable electronic devices, the demand for rechargeable lithium ion batteries is increasing.

[0005] However, the cycle stability of the current secondary batteries still needs to be improved. SUMMARY

[0006] The present disclosure is made in view of the above-mentioned problems, and aims to provide a secondary battery, a power consuming device, a positive electrode active material, and a method for manufacturing the same. The secondary battery has excellent cycle stability.

[0007] To achieve the above-mentioned purpose, a first aspect of the present disclosure provides a secondary battery, the secondary battery comprising a positive electrode sheet, the positive electrode sheet comprising a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, the positive electrode film layer comprising a positive electrode active material, the positive electrode active material comprising a lithium transition metal oxide, the lithium transition metal oxide comprising a nickel element and at least one of a cobalt element, a manganese element, and an aluminum element; a molar content of a lithium element is 1.01-1.15 with respect to 1 mole of the lithium transition metal oxide; and the lithium transition metal oxide further comprises a doping element, the doping element comprising at least one of Mo, W, Ta, Nb, Sb, Ti, and Zr.

[0008] The secondary battery of the present disclosure has excellent cycle stability.

[0009] In some embodiments, in the lithium transition metal oxide, a point 1 is taken within a range of 1 nm from a surface of the grain boundary, a point 2 is taken by extending 10 nm from the point 1 in the extending direction, a point 3 is taken by further extending 10 nm from the point 2 in the extending direction, the atomic occupancy of the doping element with respect to all metal elements except lithium at the points 1, 2 and 3 is measured respectively as X1, X2 and X3, and X1, X2 and X3 satisfy the following formula (1),

[0010] wherein X=(X1+X2+X3) / 3.

[0011] By making X1, X2 and X3 satisfy the above relationship, the doping element is uniformly distributed in the bulk phase of the lithium transition metal oxide, which is beneficial to improve the structural stability of the material and improve the cycle performance.

[0012] In some embodiments, 0.5%<X1<1%, 0.5%<X2<1%, 0.5%<X3<1%. Thereby, it is more beneficial to improve the structural stability of the material and improve the cycle performance.

[0013] In some embodiments, the chemical formula of the lithium transition metal oxide is Li 1+x (Ni a M1 1-a-b M2 b ) 1-x O2, wherein M1 includes at least one of Co, Mn and Al, M2 includes at least one of Mo, W, Ta, Nb, Sb, Ti and Zr, 0.01≤x≤0.15, 0.8≤a<1.0, 0.005≤b≤0.02.

[0014] The secondary battery, by using the above lithium transition metal oxide as the positive electrode active material, is beneficial to improve the specific capacity and structural stability, thereby being more beneficial to improve the energy density and cycle performance of the secondary battery.

[0015] In some embodiments, the chemical formula of the lithium transition metal oxide is Li 1+x (Ni a Co d M3 1-a-b-d M2 b ) 1-x O2, wherein M3 includes at least one of Mn and Al, M2 includes at least one of Mo, W, Ta, Nb, Sb, Ti and Zr, 0.01≤x≤0.15, 0.8≤a<1.0, 0.005≤b≤0.02, 0<d≤0.05. Thereby, it is more beneficial to balance high energy density and excellent cycle stability.

[0016] In some embodiments, the molar content of lithium is 1.02-1.10 relative to 1 mole of lithium transition metal oxide. Thus, it is more conducive to improving the cycle performance.

[0017] In some embodiments, the doping element includes Mo and / or W. Thus, not only the electrochemical performance can be improved, but also the structural stability of the material and the safety of the battery can be comprehensively improved.

[0018] In some embodiments, the lithium transition metal oxide has a layered crystal structure, and the space group is R-3m type. Thus, it is more conducive to improving the ion transport performance and the energy density.

[0019] In some embodiments, in the R-3m space group of the lithium transition metal oxide, lithium and nickel exist at the 3a position, and lithium and nickel exist at the 3b position. The atomic proportion of lithium at the 3b position is 1%-20%, which is more conducive to improving the structural stability.

[0020] In some embodiments, the intensity ratio I (003) / I (104) In 1.20-1.35, wherein in the X-ray diffraction pattern with an X-ray wavelength of 8.3° to 8.4° at a 2θ angle, and the 104 crystal face diffraction peak is at a 2θ angle of 19.3° to 19.4°. I (003) / I (104) and the structural order degree. The present disclosure is more conducive to improving the structural stability of the material by making I (003) / I (104) In the above range, the lithium transition metal oxide has a good layered structure and a low lattice distortion, which is more conducive to improving the structural stability of the material, thereby being conducive to maintaining the performance of the battery during long-term cycling.

[0021] In some embodiments, the lithium transition metal oxide is a secondary sphere of radial primary particles in the SEM image. Thus, during the charging and discharging process of the battery, the refined particles help to reduce the stress caused by the volume change, shorten the lithium ion transport path, thereby inhibiting the rupture of the secondary particles caused by the anisotropy of the primary particles, and improving the cycle stability of the battery.

[0022] In some embodiments, in the lithium transition metal oxide, the molar content of nickel is 80% or more relative to all metal elements except lithium. Thus, the energy density of the battery can be further improved.

[0023] In some embodiments, in the lithium transition metal oxide, the molar content of nickel is 90% or more relative to all metal elements except lithium. Thus, the energy density of the battery can be further improved.

[0024] In some embodiments, the capacity retention rate of the secondary battery is 93% or more after 100 cycles of the cycle performance test at a rate of 1C in a voltage range of 2.8V-4.3V.

[0025] In some embodiments, the capacity retention rate of the secondary battery first increases at the beginning of the cycle.

[0026] The second aspect of the present disclosure provides a power consumption device comprising the secondary battery of any of the above embodiments.

[0027] The power consumption device of the present disclosure comprises the secondary battery provided by the present disclosure, and thus has at least the same advantages as the secondary battery.

[0028] The third aspect of the present disclosure provides a positive electrode active material, the positive electrode active material comprising a lithium transition metal oxide, the lithium transition metal oxide comprising a nickel element and comprising at least one of a cobalt element, a manganese element and an aluminum element; the molar content of a lithium element is 1.01-1.15 with respect to 1 mole of the lithium transition metal oxide; and the lithium transition metal oxide further comprises a doping element, the doping element comprising at least one of Mo, W, Ta, Nb, Sb, Ti and Zr.

[0029] Through the positive electrode active material of the present disclosure, the secondary battery can have excellent cycle stability.

[0030] In some embodiments, in the lithium transition metal oxide, a point 1 is taken within a range of 1 nm from the surface of the grain boundary in the extension direction from the grain boundary to the bulk phase, a point 2 is taken as 10 nm in the extension direction from the point 1, and a point 3 is taken as 10 nm in the extension direction from the point 2, the atomic occupancy of the doping element with respect to all metal elements except lithium is measured at the point 1, the point 2 and the point 3, respectively, and is X1, X2 and X3, respectively, then X1, X2 and X3 satisfy the following formula (1),

[0031] wherein X=(X1+X2+X3) / 3.

[0032] By making X1, X2 and X3 satisfy the above relationship, the doping element is uniformly distributed in the bulk phase of the lithium transition metal oxide, which is further conducive to improving the structural stability of the material.

[0033] In some embodiments, 0.5%<X1<1%, 0.5%<X2<1%, and 0.5%<X3<1%. Thus, it is more conducive to improving the structural stability of the material and improving the cycle performance.

[0034] In some embodiments, the chemical formula of the lithium transition metal oxide is Li 1+x (Nia M1 1-a-b M2 b ) 1-x O2, wherein M1 includes at least one of Co, Mn and Al, M2 includes at least one of Mo, W, Ta, Nb, Sb, Ti, Zr, 0.01≤x≤0.15, 0.8≤a<1.0, 0.005≤b≤0.02.

[0035] The lithium transition metal oxide as the positive active material can improve the specific capacity and structural stability, thereby being more conducive to improving the energy density and cycle performance of the secondary battery.

[0036] In some embodiments, the chemical formula of the lithium transition metal oxide is Li 1+x (Ni a Co d M3 1-a-b-d M2 b ) 1-x O2, wherein M3 includes at least one of Mn and Al, M2 includes at least one of Mo, W, Ta, Nb, Sb, Ti, Zr, 0.01≤x≤0.15, 0.8≤a<1.0, 0.005≤b≤0.02, 0<d≤0.05. Thus, it is more conducive to balance high energy density and excellent cycle stability.

[0037] In some embodiments, the molar content of lithium element is 1.02-1.10 relative to 1 mole of the lithium transition metal oxide. Thus, it is more conducive to improving the cycle performance of the battery.

[0038] In some embodiments, the doping element includes Mo and / or W. Thus, not only the electrochemical performance can be improved, but also the structural stability of the material and the safety of the battery can be comprehensively improved.

[0039] In some embodiments, the lithium transition metal oxide has a layered crystal structure, and the space group is R-3m type. Thus, it is more conducive to improving the ion transport performance and energy density.

[0040] In some embodiments, in the R-3m space group of the lithium transition metal oxide, lithium element and nickel element exist in the 3a position, lithium element and nickel element exist in the 3b position, and the atomic proportion of lithium element in the 3b position is 1%-20%, which is more conducive to improving the structural stability.

[0041] In some embodiments, the intensity ratio I (003) / I (104) is 1.20-1.35, wherein the X-ray wavelength is In the X-ray diffraction pattern of the lithium transition metal oxide, the diffraction peak of the 003 crystal face is at a 2θ angle of 8.3° to 8.4°, and the diffraction peak of the 104 crystal face is at a 2θ angle of 19.3° to 19.4°. By making I (003) / I (104) Within the above range, the lithium transition metal oxide has a good layered structure and a low lattice distortion, which is more conducive to improving the structural stability of the material, thereby being conducive to maintaining the performance of the battery during long-term cycling.

[0042] In some embodiments, the lithium transition metal oxide is a secondary sphere of the primary radial particles in the SEM image. Thus, during the charging and discharging of the battery, the refined particles help to alleviate the stress caused by volume change, shorten the lithium ion transmission path, thereby inhibiting the rupture of the secondary particles caused by the anisotropy of the primary particles, and improving the cycle stability of the battery.

[0043] In some embodiments, in the lithium transition metal oxide, the molar content of the nickel element is 80% or more relative to all metal elements other than lithium. This can further improve the energy density of the battery.

[0044] In some embodiments, in the lithium transition metal oxide, the molar content of the nickel element is 90% or more relative to all metal elements other than lithium. This can further improve the energy density of the battery.

[0045] A fourth aspect of the present disclosure provides a preparation method of a positive electrode active material, comprising: mixing a precursor represented by a chemical formula Ni c M1 1-c (OH)2, a lithium source, and a doping source containing a doping element, and sintering at a temperature of 660°C to 780°C, wherein M1 includes at least one of Co, Mn, and Al, 0.8≤c<1.0, the molar ratio of the precursor to lithium in the lithium source is 1:(1.04-1.2), and the doping element is at least one of Mo, W, Ta, Nb, Sb, Ti, and Zr. The positive electrode active material prepared by the above preparation method has high specific capacity and excellent structural stability, and can enable the secondary battery to have high energy density and excellent cycle performance.

[0046] In some embodiments, the chemical formula of the precursor is Ni c Co e M3 1-e-c (OH)2, wherein M3 includes at least one of Mn and Al, 0.8≤c<1.0, and 0<e≤0.05. This is conducive to preparing a lithium transition metal oxide with more stable structure.

[0047] In some embodiments, the molar ratio of the precursor to the doping element in the doping source is 1:(0.005-0.02). Thereby, it is more advantageous to produce a lithium transition metal oxide having a more stable structure.

[0048] In some embodiments, the doping element includes Mo and / or W.

[0049] In some embodiments, the doping source containing the doping element includes at least one of MoO3, Li2MoO4, Mo(OH)3, and Li2WO4. The doping source has a suitable melting point, and the non-doping element can be completely volatilized, thereby being more advantageous to produce a material having a stable structure.

[0050] In some embodiments, the sintering temperature is 680°C to 740°C. Thereby, it is more advantageous to control the I (003) / I (104) In a suitable range, the stability of the obtained positive electrode active material can be further improved.

[0051] In some embodiments, the sintering time is 6 hours to 20 hours. Thereby, it is further advantageous to control the I (003) / I (104) In a suitable range.

[0052] In some embodiments, the lithium source includes at least one of lithium hydroxide, lithium carbonate, lithium nitrate, and hydrates thereof. BRIEF DESCRIPTION OF DRAWINGS

[0053] FIG. 1 is a schematic view of a battery cell according to an embodiment of the present disclosure.

[0054] FIG. 2 is an exploded view of the battery cell according to an embodiment of the present disclosure.

[0055] FIG. 3 is a schematic view of a battery module according to an embodiment of the present disclosure.

[0056] FIG. 4 is a schematic view of a battery pack according to an embodiment of the present disclosure.

[0057] FIG. 5 is an exploded view of the battery pack according to an embodiment of the present disclosure.

[0058] FIG. 6 is a schematic view of a power-using device using a secondary battery as a power source according to an embodiment of the present disclosure.

[0059] FIG. 7 shows a scanning electron microscope (SEM) image of the positive electrode active material produced in Example 1 and Comparative Example 1.

[0060] FIG. 8 shows a cross-sectional scanning electron microscope image and an element distribution table of the positive electrode active material produced in Example 1 and Comparative Example 2.

[0061] FIG. 9 shows an X-ray diffraction pattern (XRD pattern) of the positive electrode active material prepared in Example 1.

[0062] FIG. 10 shows a spherical aberration-corrected transmission electron microscope image of the positive electrode active material prepared in Example 1.

[0063] FIG. 11 shows a capacity retention curve of the battery prepared in Example 1, Comparative Example 1, and Comparative Example 2.

[0064] BRIEF DESCRIPTION OF DRAWINGS DETAILED DESCRIPTION

[0065] Hereinafter, embodiments of the secondary battery, the power-using device, the positive electrode active material, and the method of manufacturing the same according to the present disclosure are specifically disclosed in detail with appropriate reference to the accompanying drawings. However, there can be cases where unnecessary detailed descriptions are omitted. For example, there can be cases where detailed descriptions of matters well known to those skilled in the art, repeated descriptions of actually identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the accompanying drawings and the following description are provided so that those skilled in the art can fully understand the present disclosure, and are not intended to limit the subject matter recited in the claims.

[0066] The "range" disclosed in the present disclosure is defined in the form of a lower limit and an upper limit, a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The range defined in this way can be inclusive or exclusive of the end values, and can be arbitrarily combined, i.e., any lower limit can be combined with any upper limit to form a range. For example, if the ranges 60-120 and 80-110 are listed for a particular parameter, it is understood that the ranges 60-110 and 80-120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, the following ranges can all be contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In the present disclosure, unless otherwise stated, a numerical range "a-b" represents a shorthand manner of describing any integer combination of the range between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been listed herein, and "0-5" is just a shorthand notation for these numerical combinations. In addition, when it is stated that a certain parameter is an integer ≥ 2, it is equivalent to disclose that the parameter is, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0067] If not specifically stated, all embodiments of the present disclosure and optional embodiments can be combined with each other to form new technical solutions.

[0068] If not specifically stated, all technical features of the present disclosure and optional technical features can be combined with each other to form new technical solutions.

[0069] If not specifically stated, all steps of the present disclosure can be performed in sequence or randomly, and preferably in sequence. For example, a method comprises steps (a) and (b) means that the method can comprise steps (a) and (b) performed in sequence, or steps (b) and (a) performed in sequence. For example, it is mentioned that the method can further comprise step (c), which means that step (c) can be added to the method in any order. For example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0070] At present, lithium transition metal oxides with a layered crystal structure are widely used as positive electrode materials in power batteries for new energy vehicles. However, during the synthesis process, it is difficult for such materials to form a phase that meets the stoichiometric ratio, and they are usually in a lithium-deficient state. When the charge cut-off voltage is to 4.3V (vs. Li / Li+), severe active oxygen loss and transition metal migration occur inside the particles, thereby causing poor cycle stability of the material, especially when the nickel content is increased to obtain higher energy density. In view of this, it has been reported that the cycle stability of the material can be improved by doping, but in the obtained material, the doping elements are mostly distributed on the surface of the material in the form of grain boundary segregation, and the lattice distortion and distortion of the bulk structure occur during the charging process, affecting the improvement of the cycle stability.

[0071] Based on this, the present disclosure provides a secondary battery, a power consumption device, a positive electrode active material, and a preparation method thereof. The secondary battery has excellent cycle stability. The present disclosure and exemplary embodiments are described in more detail below.

[0072] Secondary battery

[0073] The present disclosure provides a secondary battery. The term "battery" mentioned herein refers to a battery cell, a battery module, or a battery pack. The following are described respectively.

[0074] Generally, a battery cell comprises a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During the charging and discharging process of the battery, active ions are embedded and extracted between the positive electrode sheet and the negative electrode sheet. The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet, mainly playing a role in preventing short circuit between the positive and negative electrodes, while allowing ions to pass through.

[0075] The secondary battery of the present disclosure includes a positive electrode sheet, the positive electrode sheet including a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, the positive electrode film layer including a positive electrode active material, the positive electrode active material including a lithium transition metal oxide, the lithium transition metal oxide including a nickel element and including at least one of a cobalt element, a manganese element, and an aluminum element; a molar content of a lithium element is 1.01-1.15 with respect to 1 mole of the lithium transition metal oxide; and the lithium transition metal oxide further includes a doping element, the doping element including at least one of Mo, W, Ta, Nb, Sb, Ti, and Zr.

[0076] The positive electrode active material described above in the secondary battery of the present disclosure is a micro-lithium-rich and doped positive electrode material, by making the molar content of the lithium element 1.01-1.15, the material is “micro-lithium-rich”, a micro-excess of lithium ions is introduced into the transition metal layer, and in turn, the repulsion of the transition metal layer to the doping element is reduced, by making the doping element at least one of Mo, W, Ta, Nb, Sb, Ti, and Zr into the transition metal layer, these doping elements exhibit a high valence state, can produce strong interaction with oxygen ions, can improve the doping concentration in the bulk phase, enhance the structural stability, and greatly improve the cycle performance of the battery.

[0077] Exemplarily, the molar content of the lithium element is 1.01, 1.02, 1.04, 1.06, 1.08, 1.10, 1.12, 1.14, 1.15, or a value between a range formed by any two of the numerical values, with respect to 1 mole of the lithium transition metal oxide.

[0078] In some embodiments, the molar content of the lithium element is 1.02-1.10 with respect to 1 mole of the lithium transition metal oxide. Thereby, it is more conducive to improving the cycle performance.

[0079] In the present disclosure, the molar content of the metal element in the lithium transition metal oxide is the meaning known in the art, which can be determined by instruments and methods known in the art. Exemplarily, the US EPA / 6010D-2014 inductively coupled plasma atomic emission spectrometry can be referred to, and the testing instrument can use, for example, ICP-OES, Thermo ICAP7400. The lithium transition metal oxide can be a raw material, or can be obtained from the lithium transition metal oxide obtained by disassembling and separating the secondary battery.

[0080] In some embodiments, in the lithium transition metal oxide, a point 1 is taken within a range of 1 nm from the surface of the grain boundary, a point 2 is taken by extending 10 nm from the point 1 in the extending direction, a point 3 is taken by further extending 10 nm from the point 2 in the extending direction, the atomic occupancy of the doping element relative to all metal elements except lithium at the points 1, 2 and 3 is measured respectively as X1, X2 and X3, and X1, X2 and X3 satisfy the following formula (1),

[0081] wherein X=(X1+X2+X3) / 3.

[0082] By making the atomic occupancy X1, X2 and X3 of the doping element satisfy the above formula (1), it is shown that the doping element is uniformly distributed in the bulk phase of the lithium transition metal oxide, which is beneficial to further improve the structural stability of the positive electrode material, thereby improving the cycle stability of the battery.

[0083] Exemplarily, 0.1, 0.2, 0.3, 0.4, 0.49 or a value between any two of the values. In some embodiments,

[0084] The atomic occupancy of the doping element at the above points can be determined by instruments and methods known in the art. For example, sample preparation can be performed by ultrasonic drop sampling or ultrathin sectioning, and the atomic occupancy of the doping element at each point can be obtained by electron microscopy combined with energy dispersive spectrometer.

[0085] In some embodiments, 0.5% < X1 < 1%, 0.5% < X2 < 1%, 0.5% < X3 < 1%. Thus, it is shown that the doping element is distributed to the interior of the material until the bulk phase, which is beneficial to improve the structural stability of the positive electrode material.

[0086] In some embodiments, the chemical formula of the lithium transition metal oxide is Li 1+x (Ni a M1 1-a-b M2 b ) 1-x O2, wherein M1 includes at least one of Co, Mn and Al, M2 includes at least one of Mo, W, Ta, Nb, Sb, Ti, Zr, 0.01≤x≤0.15, 0.8≤a<1.0, 0.005≤b≤0.02. The secondary battery using the lithium transition metal oxide represented by the above chemical formula as the positive electrode active material has high specific capacity and excellent structural stability, thereby being more beneficial to improve the cycle performance and energy density of the secondary battery.

[0087] The values of x, a, and b can be determined by using instruments and methods known in the art, for example, by the above-mentioned test method for the molar content of metal elements.

[0088] In some embodiments, the lithium transition metal oxide has a chemical formula of Li 1+x (Ni a Co d M3 1-a-b-d M2 b ) 1-x O2, wherein M3 includes at least one of Mn and Al, M2 includes at least one of Mo, W, Ta, Nb, Sb, Ti, and Zr, 0.01≤x≤0.15, 0.8≤a<1.0, 0.005≤b≤0.02, and 0<d≤0.05. Thus, it is more conducive to balance high energy density and excellent cycle stability.

[0089] In some embodiments, the doping element includes Mo and / or W. Thus, it is more conducive to refine the particles of the positive active material, so that not only the electrochemical performance can be improved, but also the structural stability of the material and the safety of the battery can be comprehensively improved.

[0090] In some embodiments, the lithium transition metal oxide has a layered crystal structure and a space group of R-3m type. Thus, it is more conducive to improve ion transport performance and energy density.

[0091] In the X-ray diffraction pattern of the lithium transition metal oxide at an X-ray wavelength of 8.3° to 8.4° and a second diffraction peak of a (104) crystal plane at a 2θ diffraction angle of 19.3° to 19.4°, belonging to the R-3m space group.

[0092] In some embodiments, in the R-3m space group of the lithium transition metal oxide, the 3a position includes lithium elements and nickel elements, the 3b position includes lithium elements and nickel elements, and the atomic proportion of lithium elements in the 3b position is 1%-20%. In the traditional ternary layered structure, Li occupies the 3a site, and transition metals Ni, Co, Mn, etc. occupy the 3b site. In the present disclosure, by doping nickel elements in the 3a site in addition to lithium elements and doping lithium elements in the 3b site in addition to nickel elements, the structural stability is more conducive to be improved. In the present disclosure, by X-ray diffraction pattern refinement of the lithium transition metal oxide, the position distribution of Ni and Li can be determined, and their occupation in the crystal lattice can be determined.

[0093] In some embodiments, the intensity ratio I (003) / I (104)In 1.20-1.35, in the X-ray diffraction pattern at an X-ray wavelength of the 003 crystal face diffraction peak is at 8.3° to 8.4°, and the 104 crystal face diffraction peak is at a 2θ angle of 19.3° to 19.4°. (003) / I (104) and the structural order degree. The present disclosure is to make I (003) / I (104) Within the above range, the lithium transition metal oxide has a good layered structure and a lower lattice distortion, which is more conducive to improving the structural stability of the material, thereby being conducive to maintaining the performance of the battery during long-term cycling.

[0094] Exemplarily, the intensity ratio I (003) / I (104) is 1.20, 1.21, 1.22, 1.23, 1.24, 1.25, 1.26, 1.28, 1.30, 1.32, 1.34, 1.35, or a value between a range consisting of any two of the above values.

[0095] In some embodiments, the lithium transition metal oxide is a secondary sphere of a radial primary particle in the SEM image. Thus, during the charging and discharging of the battery, the refined particles help to alleviate the stress caused by volume change, shorten the lithium ion transmission path, thereby inhibiting the rupture of the secondary particles caused by the anisotropy of the primary particles, and improving the cycle stability of the battery.

[0096] In some embodiments, in the lithium transition metal oxide, the molar content of the nickel element relative to all metal elements other than lithium is 80% or more. By making the content of the nickel element within the above range, the energy density of the battery can be further improved.

[0097] Exemplarily, in the lithium transition metal oxide, the molar content of the nickel element relative to all metal elements other than lithium is 80% or more, 80.5% or more, 81% or more, 82% or more, 84%, 86% or more, 88% or more, 90% or more, 91% or more, 92% or more, 93% or more, 93.5% or more, 94% or more, 94.5% or more, 95% or more, or a value between a range consisting of any two of the above values.

[0098] In some embodiments, in the lithium transition metal oxide, the molar content of the nickel element relative to all metal elements other than lithium is 90% or more. Thus, the energy density of the battery can be further improved.

[0099] In some embodiments, the capacity retention rate of the secondary battery is 93% or more after 100 cycles of the cycle performance test at a rate of 1C in a voltage range of 2.8V-4.3V.

[0100] In some embodiments, the capacity retention rate of the secondary battery increases first at the beginning of the cycle.

[0101] Method for preparing positive electrode active material

[0102] The positive electrode active material of the present disclosure can be prepared by the following method. The method comprises the following steps: mixing a precursor represented by the chemical formula Ni c M1 1-c (OH)2, a lithium source and a doping source containing a doping element, and sintering at a temperature of 660-780°C, wherein M1 comprises at least one of Co, Mn and Al, 0.8≤c<1.0, the molar ratio of the precursor to lithium in the lithium source is 1:(1.04-1.2), and the doping element is at least one of Mo, W, Ta, Nb, Sb, Ti and Zr.

[0103] By the above method, a micro-rich lithium structure in which a micro-excess of lithium ions is introduced into the nickel layer of the layered structure can be prepared, and the doping element induces the nucleation and growth of the crystal, so that the doping element can enter the bulk phase more easily. The obtained positive electrode active material can improve the energy density of the battery and improve the cycle stability, and the method can use a one-step water-washing-free traditional solid-phase synthesis process, thereby simplifying the preparation process of the positive electrode active material.

[0104] In some embodiments, the precursor is represented by the chemical formula Ni c M1 1-c (OH)2. The precursor represented by the chemical formula Ni

[0105] In some embodiments, the chemical formula of the precursor is Ni c Co e M3 1-e-c (OH)2, wherein M3 comprises at least one of Mn and Al, 0.8≤c<1.0, and 0<e≤0.05. Thus, it is beneficial to prepare a lithium transition metal oxide with a more stable structure.

[0106] In some embodiments, the molar ratio of the precursor to the doping element in the doping source is 1:(0.005-0.02). Thus, it is beneficial to prepare a lithium transition metal oxide with a more stable structure.

[0107] In some embodiments, the doping element includes Mo and / or W.

[0108] In some embodiments, the doping source containing the doping element includes at least one of MoO3, Li2MoO4, Mo(OH)3, and Li2WO4. The doping source has a suitable melting point, and the non-doping element can be completely volatilized, thus more favorably producing a material with structural stability.

[0109] As an example, the lithium source can independently include one or more of lithium carbonate, lithium hydroxide, lithium oxide, lithium sulfate, lithium nitrate, lithium oxalate, lithium acetate, lithium phosphate, or lithium dihydrogen phosphate, but is not limited thereto. In some embodiments, the lithium source includes at least one of lithium hydroxide, lithium carbonate, lithium nitrate, and hydrates thereof.

[0110] As an example, the sintering temperature can be 660℃, 680℃, 700℃, 730℃, 750℃, 780℃, or a value between any two of the values. In some embodiments, the sintering temperature is 680℃ to 740℃. Alternatively, the sintering temperature is 700℃ to 720℃. Thus, more favorably, the I (003) / I (104) In a suitable range, the stability of the obtained positive electrode active material can be further improved.

[0111] In some embodiments, the sintering time is 6 hours to 20 hours. As an example, the sintering time can be 6, 8, 10, 12, 14, 16, 18, 20 hours, or a value between any two of the values. Alternatively, the sintering time is 6 hours to 15 hours. Thus, further favorably, the I (003) / I (104) In a suitable range.

[0112] As an example, the sintering temperature increase / decrease rate is 2-10℃ / min.

[0113] As an example, the sintering can be performed in an oxygen atmosphere, but is not limited thereto. As an example, the oxygen flow rate is 0.1 L / min to 0.6 L / min.

[0114] For the positive electrode current collector, in some embodiments, the positive electrode current collector has two surfaces opposite in the thickness direction thereof, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0115] In some embodiments, the positive current collector can employ a metal foil or a composite current collector. For example, as a metal foil, an aluminum foil can be employed. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material base material (e.g., a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0116] In some embodiments, the positive electrode film layer can further optionally include a binder. As an example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylic ester resin.

[0117] In some embodiments, the positive electrode film layer can further optionally include a conductive agent. As an example, the conductive agent can include at least one of super P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0118] In some embodiments, the positive electrode tab can be prepared by dispersing the above-described positive active material and other components used to prepare the positive electrode tab, such as a conductive agent, a binder, and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on a positive current collector; and subjecting the same to processes such as drying, cold pressing, etc., to obtain the positive electrode tab.

[0119] [Negative electrode tab]

[0120] The negative electrode tab includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative active material.

[0121] As an example, the negative current collector has two surfaces opposite in the thickness direction thereof, and the negative electrode film layer is disposed on either one or both of the two opposite surfaces of the negative current collector.

[0122] In some embodiments, the negative current collector can employ a metal foil or a composite current collector. For example, as a metal foil, a copper foil can be employed. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material base layer (e.g., a base layer of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0123] In some embodiments, the negative active material can employ a negative active material for a battery known in the art. As an example, the negative active material can include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, a silicon-based material, a tin-based material, and lithium titanate, etc. The silicon-based material can include at least one of elemental silicon, a silicon oxide compound, a silicon-carbon composite, a silicon-nitrogen composite, or a silicon alloy. The tin-based material can include at least one of elemental tin, a tin oxide compound, or a tin alloy. However, the present disclosure is not limited to these materials, and other conventional materials that can be used as a battery negative active material can also be used. These negative active materials can be used alone only or in combination of two or more.

[0124] In some embodiments, the negative film layer can further optionally include a binder. The binder can include at least one of styrene butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), or carboxymethyl chitosan (CMCS).

[0125] In some embodiments, the negative film layer can further optionally include a conductive agent. The conductive agent can include at least one of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, or carbon nanofibers.

[0126] In some embodiments, the negative film layer can further optionally include other auxiliary agents, such as a thickening agent (e.g., sodium carboxymethyl cellulose (CMC-Na)) etc.

[0127] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-described components for preparing the negative electrode sheet, such as the negative active material, the conductive agent, the binder, and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry on the negative current collector, and then performing processes such as drying, cold pressing, etc. to obtain the negative electrode sheet.

[0128] [Electrolyte]

[0129] The electrolyte functions to conduct ions between the positive electrode sheet and the negative electrode sheet. The type of electrolyte is not particularly limited in the present disclosure and can be selected as needed. For example, the electrolyte can be liquid, gel, or all-solid.

[0130] In some embodiments, the electrolyte employs an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0131] In some embodiments, the electrolyte salt can include at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonylimide, lithium bis-trifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorobisoxalate borate, lithium bisoxalate borate, lithium difluorobisoxalate phosphate, or lithium tetrafluorobisoxalate phosphate.

[0132] In some embodiments, the solvent can include at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclobutane sulfone, dimethyl sulfone, methyl ethyl sulfone, or diethyl sulfone.

[0133] In some embodiments, the electrolyte solution can further optionally include an additive. For example, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and can further include an additive capable of improving certain properties of the battery, such as an additive for improving overcharge performance of the battery, an additive for improving high-temperature or low-temperature performance of the battery, etc.

[0134] [Separator]

[0135] In some embodiments, the battery cell further includes a separator. The type of separator is not particularly limited in the present disclosure and any known porous structure separator having good chemical stability and mechanical stability can be used.

[0136] In some embodiments, the material of the separator can include at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, or polyvinylidene fluoride. The separator can be a single layer film or a multi-layer composite film, and is not particularly limited. When the separator is a multi-layer composite film, the materials of the respective layers can be the same or different, and are not particularly limited.

[0137] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be made into an electrode assembly through a winding process or a stacking process.

[0138] In some embodiments, the battery cell can include an outer package. The outer package can be used to package the electrode assembly and the electrolyte described above.

[0139] In some embodiments, the outer package of the battery cell can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, or the like. The outer package of the battery cell can also be a soft package, such as a pouch soft package. The material of the soft package can be plastic, and as plastic, polypropylene, polybutylene terephthalate, polybutylene succinate, or the like can be listed.

[0140] The present disclosure does not have a particular limitation on the shape of the battery cell, which can be cylindrical, square, or any other arbitrary shape. For example, FIG. 1 is a battery cell 5 of a square structure as an example.

[0141] In some embodiments, referring to FIG. 2, the outer package can include a shell 51 and a top cover assembly 53. The shell 51 can include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening communicating with the receiving cavity, and the top cover assembly 53 can be provided on the opening to close the receiving cavity. The positive electrode tab, the negative electrode tab, and the separator film can form an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is packaged in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, which can be selected by a person skilled in the art according to specific actual needs.

[0142] In some embodiments, the battery cell can be assembled into a battery module, and the number of battery cells contained in the battery module can be one or more, and the specific number can be selected by a person skilled in the art according to the application and capacity of the battery module.

[0143] FIG. 3 is a battery module 4 as an example. Referring to FIG. 3, in the battery module 4, a plurality of battery cells 5 can be arranged in sequence along the length direction of the battery module 4. Of course, other arbitrary arrangements can also be made. Further, the plurality of battery cells 5 can be fixed by fasteners.

[0144] Optionally, the battery module 4 can also include a housing having a receiving space, and the plurality of battery cells 5 are received in the receiving space.

[0145] In some embodiments, the above-mentioned battery module can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, and the specific number can be selected by a person skilled in the art according to the application and capacity of the battery pack.

[0146] FIGS. 4 and 5 are a battery pack 1 as an example. Referring to FIGS. 4 and 5, the battery pack 1 can include a battery box and a plurality of battery modules 4 arranged in the battery box. The battery box includes an upper box body 2 and a lower box body 3, and the upper box body 2 can be provided on the lower box body 3 to form a closed space for receiving the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0147] Electric device

[0148] The present disclosure also provides an electric device. The secondary battery of the present disclosure is described below with appropriate reference to the accompanying drawings.

[0149] The electric device mentioned in the embodiments of the present disclosure includes the secondary battery provided by the present disclosure. The secondary battery can be used as a power source of the electric device, or can be used as an energy storage unit of the electric device. The electric device can include a mobile device (such as a mobile phone, a notebook computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto.

[0150] As the electric device, a battery cell, a battery module or a battery pack can be selected according to the use requirement thereof.

[0151] FIG. 6 is an electric device as an example. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the requirement of high power and high energy density of the secondary battery for the electric device, a battery pack or a battery module can be used.

[0152] The device as another example can be a mobile phone, a tablet computer, a notebook computer, etc. The device usually requires thin and light, and a battery cell can be used as a power source.

[0153] Embodiment

[0154] Hereinafter, the embodiments of the present disclosure are described. The embodiments described below are exemplary and are only used to explain the present disclosure, and cannot be understood as a limitation of the present disclosure. If the specific technology or condition is not mentioned in the embodiments, the technology or condition described in the literature in the art or according to the product instruction is used. If the reagent or instrument is not mentioned by the manufacturer, it is a conventional product that can be obtained by market purchase.

[0155] Embodiment 1

[0156] Preparation of positive active material

[0157] Ni 0.95 Co 0.04 Mn 0.01The (OH)2, LiOH and doping source MoO3 were mixed uniformly (the molar ratio among the three was 1:1.1:0.01), and then the fully mixed and ground powder was added into a corundum ceramic boat, covered with a lid, and placed in a tube furnace. Pure oxygen was introduced at a flow rate of 0.5 L / min, and the temperature was raised to 700°C at a rate of 5°C / min. After being kept at 700°C for 12 hours, the temperature was lowered to room temperature at a rate of 2°C / min. After cooling, the powder was ground and broken, and then passed through a 400-mesh sieve to obtain the positive electrode active material.

[0158] Button cell preparation

[0159] The above positive electrode active material, conductive agent super-P, carbon nanotube (CNT), and polyvinylidene fluoride (PVDF) were mixed uniformly in N-methyl pyrrolidone (NMP) at a mass ratio of 98.24:0.5:0.36:0.9, and then the positive electrode slurry was prepared. The positive electrode slurry was then coated on a 13-μm Al foil. After vacuum drying at 120°C, cold pressing, and cutting and striping, the positive electrode sheet was obtained.

[0160] The separator film was a 12-μm thick polyethylene porous film.

[0161] The electrolyte was prepared by adding lithium difluoro(oxalato)borate into a mixed solvent of methyl ethyl carbonate and fluoroethylene carbonate at a volume ratio of 3:1, and mixing uniformly. The molar concentration of lithium difluoro(oxalato)borate in the electrolyte was 0.05 mol / L.

[0162] The above positive electrode sheet, separator film, electrolyte, and lithium sheet were assembled into a button cell in an argon glove box.

[0163] Examples 2-5

[0164] The positive electrode active material and button cell were prepared in the same manner as in Example 1, except that the molar ratio of Ni 0.95 Co 0.04 Mn 0.01 (OH)2, LiOH, and MoO3 was different, and the oxygen flow rate was 0.4 L / min, as shown in Table 1.

[0165] Comparative Example 1

[0166] The positive electrode active material and button cell were prepared in the same manner as in Example 1, except that MoO3 was not used, and the molar ratio of Ni 0.95 Co 0.04 Mn 0.01 (OH)2 and LiOH was 1:1.02.

[0167] Comparative Example 2

[0168] The positive active material and button cell were prepared in the same way as Example 1, except that Ni 0.95 Co 0.04 Mn 0.01 The molar ratio of (Ni(OH)2, LiOH and MoO3 was 1:1.02:0.01.

[0169] Comparative Example 3

[0170] The positive active material and button cell were prepared in the same way as Example 1, except that Ni 0.95 Co 0.04 Mn 0.01 The molar ratio of (Ni(OH)2, LiOH and MoO3 was 1:1.03:0.01.

[0171] Test of the positive active material

[0172] (1) Elemental composition analysis of the positive active material

[0173] The positive active material was dissolved with a mixed solvent (nitric acid and hydrochloric acid mixed at a volume ratio of 1:1), for example, 0.4 g of the positive active material was dissolved with 10 mL of the mixed solvent, and the volume was made up to 100 mL. The content of each metal element was then measured by ICP-OES, Thermo ICAP7400, according to US EPA 6010D-2014 inductively coupled plasma atomic emission spectrometry, and the unit was ppm, which was converted into a molar ratio. The results are shown in Table 2.

[0174] (2) Morphology characterization

[0175] Sample preparation: a toothpick was used to stick a small amount of positive active material powder and evenly spread it on the conductive carbon glue.

[0176] The Navigator-100 high-throughput scanning electron microscope (SEM) of PicoBunch Technology Co., Ltd. was used to test the morphology of the positive active material particles, and the SEM test conditions were as follows: mode BSE (backscattered detector), voltage 3KV, working distance 5mm.

[0177] Figure 7 shows the scanning electron microscope (SEM) images of the positive active materials prepared in Example 1 and Comparative Example 1. As can be seen from Figure 7, the positive active material prepared in Example 1 is a secondary ball with radial primary particles. Compared with Comparative Example 1, the primary particles of Example 1 are significantly refined.

[0178] (3) Test of the distribution of doped elements in the positive active material

[0179] Sample preparation: A small amount of positive electrode active material powder was taken and anhydrous ethanol was added as a dispersion medium. An ultrasonic water bath was used to ensure that the powder particles were fully dispersed, with a set ultrasonic time of 10-15 minutes. Then, a clean copper mesh was taken and the ultrasonic-treated powder suspension was gently dropped onto the copper mesh using a pipette or micro pipette. Finally, the copper mesh with the sample dropped on it was placed at room temperature for natural evaporation or slightly heated using a low-temperature oven to accelerate the evaporation of ethanol. The prepared TEM sample was placed in a special sample box to avoid moisture or contamination.

[0180] A cross-section of a primary particle of the positive electrode active material was observed by a JEM-ARM200F NEOARM spherical aberration-corrected transmission electron microscope from JEOL Ltd. Three points were selected by the following method: a point 1 was taken at a distance of 1 nm from the grain boundary surface in the extension direction from the grain boundary to the bulk phase, a point 2 was taken at a distance of 10 nm from the point 1 in the extension direction, and a point 3 was taken at a distance of 10 nm from the point 2 in the extension direction. The atomic fraction X1, X2 and X3 of the doping element relative to all metal elements except lithium at the points 1, 2 and 3 were measured, respectively, and calculated according to formula (1).

[0181] wherein X = (X1+X2+X3) / 3.

[0182] For example, when the doping element is Mo, the atomic fractions X1, X2 and X3 are tested by an energy dispersive spectrometer (EDS) equipped in the spherical aberration-corrected transmission electron microscope. FIG. 8 shows the cross-sectional scanning electron microscope image and element distribution table of the positive electrode active materials prepared in Example 1 and Comparative Example 2. It can be seen from FIG. 8 that the value of formula (1) calculated based on X1, X2 and X3 of the positive electrode active material of Comparative Example 2 is as high as 0.95, and X1 is much larger than X2 and X3, indicating that the doped Mo element is mainly distributed near the grain boundary, and the outline of the grain boundary observed under the spherical aberration-corrected transmission electron microscope is clear; the value of formula (1) calculated based on X1, X2 and X3 of the positive electrode active material of Example 1 is 0.18, and the doped Mo element is uniformly distributed in the bulk phase, and the outline of the grain boundary observed under the spherical aberration-corrected transmission electron microscope is blurred.

[0183] (4) X-ray diffraction test

[0184] X-ray diffraction (XRD) powder refinement spectrum was collected on the BL14B1 beamline station of the Shanghai Synchrotron Radiation Facility (SSRF) in China. A LaB6 standard sample was used as a calibrant to ensure the accuracy of the diffraction data. The X-ray wavelength was The beam energy was 18 keV.

[0185] Figure 9 shows the X-ray diffraction pattern (XRD pattern) of the positive electrode active material prepared in Example 1. As can be seen from Figure 9, by comparing with the reference pattern of LiNiO2of the standard R-3m space group, the main diffraction peak of the (003) crystal plane in the range of 2θ diffraction angle of 8.3° to 8.4° can be observed. The diffraction peak position and intensity reflect the structural order and regularity of the layer spacing of the material crystal in the c-axis direction. At the same time, the diffraction peak of the (104) crystal plane appears at the position of about 19.3° to 19.4° of 2θ diffraction angle, which is related to the a-axis and b-axis, and reflects the structural characteristics of the crystal in the horizontal plane of the crystal lattice. By dividing the (003) peak value by the (104) peak value, the I (003) / I (104) .

[0186] In the ternary layered structure R-3m space group, there are 3a positions and 3b positions. Li occupies the 3a position, and transition metals occupy the 3b position, i.e. the transition metal layer. The above XRD data is imported into the Rietveld refinement software GSAS II for refinement: the initial crystal structure model is set, and the crystal structure parameters are gradually adjusted, including atomic coordinates, occupation factors, anisotropic temperature factors, etc., so that the calculated diffraction pattern matches the experimental data. Through repeated iteration optimization, the R factor (such as Rwp, Rp, χ2, etc.) is reduced to improve the fitting quality. Table 1 shows the refinement results of the XRD data of Example 1.

[0187] Table 1:

[0188] As can be seen from Table 1, in the positive electrode active material prepared in Example 1, the atomic proportion of Ni in the lithium site (3a position) is 2.36%, and the atomic proportion of lithium in the nickel site (3b position) is 5.18%, which indicates that lithium and nickel are mixed in the material, and the Li content is rich relative to the total content of transition metals, which is more conducive to improving the structural stability.

[0189] (5) Scanning transmission electron microscope

[0190] The occupation of Mo atoms in the bulk phase structure in Example 1 was tested by JEM-ARM200F NEOARM spherical aberration-corrected transmission electron microscope of JEOL Ltd., with an acceleration voltage of 200 kV. The results of Example 1 are shown on the left side of Figure 10, and the signal intensity of atoms in three regions in the transition metal layer, #1, #2, and #3, is randomly counted; the signal intensity of atoms at the arrow position is obviously enhanced, indicating that Mo atoms occupy the position of nickel atoms in the bulk phase structure.

[0191] Battery performance test

[0192] Cycle performance test

[0193] First, voltage calibration was performed according to the following steps: the button cells prepared in the above examples and comparative examples were charged at 1C constant current to 4.3V, then charged at 4.3V constant voltage until the current dropped to 0.05C, and then discharged at 1C constant current to 3.0V to obtain the first cycle discharge capacity (C0) at 30°C in a constant temperature environment.

[0194] Second, the cycle test was performed according to the following steps: the button cells were subjected to charge-discharge cycle test at 1C current density at 30°C, and the voltage interval was set to 3.0V-4.3V. This was repeated for 100 cycles to obtain the discharge capacity after 100 cycles, denoted as C100. n .

[0195] Capacity retention rate = discharge capacity after 100 cycles (C100) / first cycle discharge capacity (C0). n

[0196] Figure 11 shows the capacity retention rate curves of the batteries of Example 1 and Comparative Examples 1 and 2. As can be seen from Figure 11, after 100 cycles in 1C / 1C cycle mode, the capacity retention rate of the battery of Example 1 after 100 cycles is 98.99%, and the cycle stability is significantly improved compared with the batteries of Comparative Examples 1, 2 and 3; the capacity retention rate of the secondary battery first increases and then decreases after the start of the cycle, which may be due to the activation process of the battery in the initial cycle, and a more stable electrolyte interface film (SEI film) may be formed on the surface of the electrode material, thereby initially improving the cycle performance of the battery; however, as the number of cycles increases, the continuous growth of the electrolyte interface film may lead to an increase in the internal resistance of the battery and a gradual decrease in the activity of the electrode material, eventually causing the capacity to decrease.

[0197] Table 2:

[0198] Table 3

[0199] As shown in Tables 2 and 3, compared with Comparative Examples 1, 2 and 3, in Examples 1-5 of the present disclosure, by making the molar content of lithium element in the positive electrode active material 1.01-1.15 and including the doping element Mo, the structural stability of the positive electrode active material is significantly improved, and the capacity retention rate after 100 cycles is significantly improved.

[0200] Examples 6-11

[0201] The positive electrode active material and button cell were prepared in the same manner as Example 1, and the molar ratio of the precursor: LiOH: doping element of the doping source was 1:1.1:0.01, and the difference was that different doping sources were used in Examples 6-11, as shown in Table 4. ​

[0202] Example 12

[0203] The positive active material and button cell were prepared in the same way as Example 1, except that Example 12 used Ni 0.95 Co 0.03 Al 0.02 (OH)2as the precursor.

[0204] Example 13

[0205] The positive active material and button cell were prepared in the same way as Example 6, except that Example 13 used Ni 0.95 Co 0.03 Al 0.02 (OH)2as the precursor.

[0206] Example 14

[0207] The positive active material and button cell were prepared in the same way as Example 1, except that Example 14 used N i0.95 Mn 0.03 Al 0.02 (OH)2as the precursor.

[0208] The above Examples 6-14 were tested in the same way as described above, as shown in Table 4 and Table 5 below.

[0209] Table 4

[0210] Table 5

[0211] As shown in Table 4 and Table 5, in Examples 6-14 of the present disclosure, the doping element is Mo, W, Ta, Nb, Sb, Ti or Zr, and the capacity retention rate after 100 cycles is significantly improved.

[0212] Examples 15-20

[0213] The positive active material and button cell were prepared in the same way as Example 1, obtaining the same chemical composition of the positive active material as Example 1, except that the temperature, time and oxygen flow rate of sintering were adjusted, as shown in Table 6.

[0214] Table 6

[0215] As shown in Table 6, in Examples 15-17, the sintering temperature is in the range of 680-740°C, the sintering time is 6-15 hours, and the oxygen flow rate is between 0.3 L / min and 0.5 L / min, all of which can form a stable oxide structure and improve the capacity retention rate.

[0216] Note that the present disclosure is not limited to the above-described embodiments. The above-described embodiments are merely examples, and embodiments having substantially the same configuration, function, and effect as the technical idea of the present disclosure are included in the technical scope of the present disclosure. Furthermore, other modes constructed by combining a part of the configurations of the embodiments in a manner that a person skilled in the art can think of within the scope of the present disclosure are also included in the scope of the present disclosure.

Claims

1. A secondary battery comprising a positive electrode sheet including a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector, the positive electrode film layer including a positive electrode active material, the positive electrode active material including a lithium transition metal oxide including a nickel element and including at least one of a cobalt element, a manganese element, and an aluminum element, a molar content of a lithium element is 1.01 to 1.15 with respect to 1 mole of the lithium transition metal oxide; the lithium transition metal oxide further includes a doping element including at least one of Mo, W, Ta, Nb, Sb, Ti, and Zr.

2. The secondary battery according to claim 1, wherein In the lithium transition metal oxide, in a direction of extension from a grain boundary to a bulk phase, a point 1 is taken within a range of 1 nm from a surface of the grain boundary, a point 2 is extended by 10 nm in the direction of extension from the point 1, a point 3 is further extended by 10 nm in the direction of extension from the point 2, atomic occupancy ratios of the doping element with respect to all metal elements other than lithium at the points 1, 2, and 3 are measured, respectively, X1, X2, and X3, and the X1, X2, and X3 satisfy the following formula (1), wherein X = (X1+ X2+ X3) / 3.

3. The secondary battery according to claim 2, wherein 0.5% < X1 < 1%, 0.5% < X2 < 1%, 0.5% < X3 < 1%.

4. The secondary battery according to any one of claims 1 to 3, wherein The lithium transition metal oxide has a chemical formula of Li 1+x (Ni a M1 1-a-b M2 b ) 1-x O2, in the formula, M1 includes at least one of Co, Mn, and Al, M2 includes at least one of Mo, W, Ta, Nb, Sb, Ti, and Zr, 0.01 ≤ x ≤ 0.15, 0.8 ≤ a < 1.0, 0.005 ≤ b ≤ 0.

02.

5. The secondary battery according to claim 4, wherein The lithium transition metal oxide has a chemical formula of Li 1+x (Ni a Co d M3 1-a-b-d M2 b ) 1-x O2, in the formula, M3 includes at least one of Mn and Al, M2 includes at least one of Mo, W, Ta, Nb, Sb, Ti, and Zr, 0.01 ≤ x ≤ 0.15, 0.8 ≤ a < 1.0, 0.005 ≤ b ≤ 0.02, 0 < d ≤ 0.

05.

6. The secondary battery according to any one of claims 1-5, wherein, a molar content of a lithium element is 1.02 to 1.10 with respect to 1 mole of the lithium transition metal oxide.

7. The secondary battery according to any one of claims 1-6, wherein, the doping element includes Mo and / or W.

8. The secondary battery according to any one of claims 1-7, wherein, the lithium transition metal oxide has a layered crystal structure, and a space group is R-3m type.

9. The secondary battery according to claim 8, wherein in the R-3m type space group of the lithium transition metal oxide, lithium elements and nickel elements exist at 3a positions, and lithium elements and nickel elements exist at 3b positions, and an atomic ratio of the lithium elements at the 3b positions is 1% to 20%.

10. The secondary battery according to claim 9, wherein The intensity ratio I of the 003 crystal face diffraction peak to the 104 crystal face diffraction peak of the lithium transition metal oxide (003) / I (104) In 1.20-1.35, wherein in the X-ray diffraction pattern at an X-ray wavelength of The 003 crystal face diffraction peak is at a 2θ angle of 8.3° to 8.4°, and the 104 crystal face diffraction peak is at a 2θ angle of 19.3° to 19.4°.

11. The secondary battery according to any one of claims 1-10, wherein, the lithium transition metal oxide is a secondary sphere of radial primary particles in an SEM image.

12. The secondary battery according to any one of claims 1-11, wherein, in the lithium transition metal oxide, a molar content of the nickel element is 80% or more with respect to all metal elements other than lithium.

13. The secondary battery according to claim 12, wherein in the lithium transition metal oxide, a molar content of the nickel element is 90% or more with respect to all metal elements other than lithium.

14. The secondary battery according to claim 13, wherein a capacity retention rate of the secondary battery is 93% or more after 100 cycles of a cycle performance test at a voltage interval of 2.8 V to 4.3 V at a rate of 1 C.

15. The secondary battery according to claim 14, wherein the capacity retention rate of the secondary battery first increases at the start of the cycle. 16.A power consuming device comprising the secondary battery according to any one of claims 1 to 15. 17.A positive electrode active material, the positive electrode active material including a lithium transition metal oxide including a nickel element and including at least one of a cobalt element, a manganese element, and an aluminum element, a molar content of a lithium element is 1.01 to 1.15 with respect to 1 mole of the lithium transition metal oxide, the lithium transition metal oxide further includes a doping element including at least one of Mo, W, Ta, Nb, Sb, Ti, and Zr.

18. The positive electrode active material according to claim 17, wherein In the lithium transition metal oxide, in a direction of extension from a grain boundary to a bulk phase, a point 1 is taken within a range of 1 nm from a surface of the grain boundary, a point 2 is extended by 10 nm in the direction from the point 1, a point 3 is further extended by 10 nm in the direction from the point 2, the atomic occupancy of the doping element with respect to all metal elements other than lithium at the points 1, 2, and 3 is measured, respectively, X1, X2, and X3, and X1, X2, and X3 satisfy the following relationship, wherein X=(X1+X2+X3) / 3.

19. The positive electrode active material according to claim 18, wherein 0.5% < X1 < 1%, 0.5% < X2 < 1%, 0.5% < X3 < 1%.

20. The positive electrode active material according to any one of claims 17 to 19, wherein The lithium transition metal oxide has a chemical formula of Li 1+x (Ni a M1 1-a-b M2 b ) 1-x O2, In the formula, M1 includes at least one of Co, Mn and Al, M2 includes at least one of Mo, W, Ta, Nb, Sb, Ti, Zr, 0.01 ≤ x ≤ 0.15, 0.8 ≤ a < 1.0, 0.005 ≤ b ≤ 0.

02.

21. The positive electrode active material according to any one of claims 17 to 20, wherein The lithium transition metal oxide has a chemical formula of Li 1+x (Ni a Co d M3 1-a-b-d M2 b ) 1-x O2, In the formula, M3 includes at least one of Mn and Al, M2 includes at least one of Mo, W, Ta, Nb, Sb, Ti, Zr, 0.01 ≤ x ≤ 0.15, 0.8 ≤ a < 1.0, 0.005 ≤ b ≤ 0.02, 0 < d ≤ 0.

05.

22. The positive electrode active material according to any one of claims 17 to 21, wherein The molar content of lithium element is 1.02-1.10 with respect to 1 mole of the lithium transition metal oxide.

23. The positive electrode active material according to any one of claims 17 to 22, wherein The doping element includes Mo and / or W.

24. The positive electrode active material according to any one of claims 17 to 23, wherein The lithium transition metal oxide has a layered crystal structure with a space group of R-3m type.

25. The positive electrode active material according to claim 24, wherein In the R-3m space group of the lithium transition metal oxide, lithium element and nickel element exist at 3a position, lithium element and nickel element exist at 3b position, and the atomic proportion of lithium element at 3b position is 1%-20%.

26. The positive electrode active material according to claim 25, wherein The intensity ratio I of the 003 crystal plane diffraction peak to the 104 crystal plane diffraction peak of the lithium transition metal oxide is 0.5 to 1.5 (003) / I (104) In 1.20-1.35, wherein in the X-ray diffraction pattern at an X-ray wavelength of 1.54 A, The 003 crystal plane diffraction peak is at a 2θ angle of 8.3° to 8.4°, and the 104 crystal plane diffraction peak is at a 2θ angle of 19.3° to 19.4°.

27. The positive electrode active material according to any one of claims 17 to 26, wherein The lithium transition metal oxide is a secondary sphere of radial primary particles in the SEM image.

28. The positive electrode active material according to any one of claims 17 to 27, wherein In the lithium transition metal oxide, the molar content of the nickel element is 80% or more with respect to all metal elements excluding lithium.

29. The positive electrode active material according to claim 28, wherein In the lithium transition metal oxide, the molar content of the nickel element is 90% or more with respect to all metal elements excluding lithium.

30. A method for preparing a positive electrode active material, comprising: The chemical formula Ni c M1 1-c The precursor represented by the chemical formula (OH)2, a lithium source, and a doping source containing a doping element are mixed, and sintering is performed at a temperature of 660°C to 780°C, In the formula, M1 includes at least one of Co, Mn and Al, 0.8 ≤ c < 1.0, The molar ratio of lithium element in the lithium source to the precursor is 1:(1.04-1.2), The doping element includes at least one of Mo, W, Ta, Nb, Sb, Ti, Zr.

31. The method of manufacturing according to claim 30, wherein, The chemical formula of the precursor is Ni c Co e M3 1-e-c (OH)2, wherein M3 includes at least one of Mn and Al, 0.8≤c<1.0, and 0<e≤0.

05.

32. The method of manufacturing according to claim 30 or 31, wherein, The molar ratio of the doping element in the doping source to the precursor is 1:(0.005-0.02).

33. The method of making according to any one of claims 30-32, wherein, The doping element includes Mo and / or W.

34. The method of manufacturing according to claim 33, wherein, The doping source containing the doping element includes at least one of MoO3, Li2MoO4, Mo(OH)3 and Li2WO4.

35. The method of making according to any one of claims 30-34, wherein, The sintering temperature is 680°C to 740°C.

36. The method of making according to any one of claims 30-35, wherein, The sintering time is 6 hours-20 hours.

37. The method of making according to any one of claims 30-36, wherein, The lithium source includes at least one of lithium hydroxide, lithium carbonate, lithium nitrate and hydrates thereof.

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