Secondary battery, preparation method, and electrical apparatus

Abstract

The present application provides a secondary battery, a preparation method, and an electrical apparatus. The secondary battery comprises a positive electrode plate and an electrolyte. The positive electrode plate comprises 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 comprises a lithium-containing transition metal oxide. The lithium-containing transition metal oxide and the electrolyte both comprise L metal cations, and the ion radius of the L metal cations is greater than that of Li ions.

Description

Secondary battery, preparation method and power-using device

[0001] Cross-references

[0002] This application refers to Chinese patent application No. 202410397227.8, filed on April 2, 2024, entitled “Secondary Battery, Preparation Method and Electrical Device”, which is incorporated into this application in its entirety by reference. Technical Field

[0003] The present application relates to the technical field of secondary batteries, and in particular to a secondary battery, a preparation method, and an electrical device. Background Art

[0004] In recent years, secondary batteries have been widely used in energy storage systems such as hydropower, thermal, wind, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and other fields. With the widespread use of secondary batteries, higher requirements have been placed on their cycle performance and service life.

[0005] How to further improve the cycle life of secondary batteries is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] The present application has been made in view of the above-mentioned problems, and an object of the present application is to provide a secondary battery having a long cycle life.

[0007] The first aspect of the present application provides a secondary battery, comprising a positive electrode plate and an electrolyte, the positive electrode plate comprising a positive electrode current collector and a positive electrode film layer arranged 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-containing transition metal oxide, the lithium-containing transition metal oxide and the electrolyte both comprising L metal cations, the ionic radius of the L metal cations being greater than the ionic radius of the Li ions.

[0008] The secondary battery includes L metal cations in the electrolyte, so that the L metal ions are embedded in the positive electrode active material through the electrochemical process, play a supporting role in the lithium-containing transition metal oxide, expand the interlayer spacing between the lithium layers in the crystal structure, and increase the migration barrier of the transition metal (especially the transition metal with an ion radius close to that of lithium ions, such as nickel ions) in the lithium-containing transition metal oxide to the lithium layer, thereby reducing the probability of the transition metal ions entering the lithium layer, thereby alleviating the mixed discharge phenomenon and improving the cycle life of the battery. Moreover, the positive electrode active material doped by the electrochemical process has few residual impurities outside the bulk phase, and the L ions are able to efficiently enter and evenly distribute in the bulk phase of the lithium-containing transition metal oxide, thereby improving the raw material utilization rate and reducing the residual content of impurities outside the bulk phase of the active material. Furthermore, the electrolyte also includes L metal cations, so that the L metal cations can enter the lithium-containing transition metal oxide during the long cycle process, reducing the lithium-nickel mixed discharge in the late cycle, and achieving further improvement in the battery cycle stability.

[0009] The secondary battery includes L metal cations in the electrolyte, so that the L metal ions are embedded in the positive electrode active material through the electrochemical process, play a supporting role in the lithium-containing transition metal oxide, expand the interlayer spacing between the lithium layers in the crystal structure, and increase the migration barrier of the transition metal (especially the transition metal with an ion radius close to that of lithium ions, such as nickel ions) in the lithium-containing transition metal oxide to the lithium layer, thereby reducing the probability of the transition metal ions entering the lithium layer, thereby alleviating the mixed discharge phenomenon and improving the cycle life of the battery. Moreover, the positive electrode active material doped by the electrochemical process has few residual impurities outside the bulk phase, and the L ions are able to efficiently enter and evenly distribute in the bulk phase of the lithium-containing transition metal oxide, thereby improving the raw material utilization rate and reducing the residual content of impurities outside the bulk phase of the active material. Furthermore, the electrolyte also includes L metal cations, so that the L metal cations can enter the lithium-containing transition metal oxide during the long cycle process, reducing the lithium-nickel mixed discharge in the late cycle, and achieving further improvement in the battery cycle stability.

[0010] In any embodiment, L comprises one or more of Na, K, Ca, Mg, and Cs.

[0011] The above-mentioned L element has a suitable ionic radius, which can not only enter the lithium layer of the lithium-containing transition metal oxide, but also has an ionic radius larger than that of lithium ions, and can play a "supporting" role in the lithium layer, reduce cation mixing, and improve the cycle life of the secondary battery.

[0012] In any embodiment, the molar ratio of the L element to the lithium element in the lithium-containing transition metal oxide bulk phase is 0.01:100-10:100.

[0013] In any embodiment, the molar ratio of the L element to the lithium element in the lithium-containing transition metal oxide bulk phase is 0.3:100-4:100.

[0014] The molar ratio of L element to lithium element in the lithium-containing transition metal oxide bulk phase within the above range can not only fully exert the effect of L element doping in reducing lithium-nickel mixing, but also ensure the stability of the crystal structure, thereby comprehensively improving the cycle stability of the secondary battery.

[0015] In any embodiment, the X-ray diffraction pattern of the lithium-containing transition metal oxide includes a diffraction peak of the (003) crystal plane and a diffraction peak of the (104) crystal plane, and the ratio of the peak intensity I(003) of the diffraction peak of the (003) crystal plane to the peak intensity I(104) of the diffraction peak of the (104) crystal plane is 1.40 to 1.80.

[0016] The I(003) / I(104) of the lithium-containing transition metal oxide is within the above range, indicating that the material has a low degree of cation mixing and lattice distortion, which is beneficial to improving the battery cycle life.

[0017] In any embodiment, based on the total mass of the positive electrode active material, the mass proportion of the X element outside the bulk of the positive electrode active material is 0% to 0.5%.

[0018] In any embodiment, based on the total mass of the positive electrode active material, the mass proportion of the X element outside the bulk of the positive electrode active material is 0.0001% to 0.2%.

[0019] The content of L element outside the bulk phase in the positive electrode active material in the embodiment of the present application is extremely low, which can reduce the impurity content outside the bulk phase of the positive electrode active material, improve the utilization rate of raw materials, reduce the degree of side reactions of the secondary battery, and improve the cycle stability of the secondary battery.

[0020] In any embodiment, in the particles of the positive electrode active material, the molar percentage of the L element of the positive electrode active material relative to all elements in the particles is A1; in a local slice of the positive electrode active material particle, the molar percentage of the L element of the positive electrode active material relative to all elements in the local slice is B1; A1 and B1 satisfy: 50%≤B1 / A1≤100%.

[0021] The L element is evenly distributed in the positive electrode active material with B1 / A1 within the above range. The L element can fully exert its effectiveness at a low addition amount, play a supporting role for the lithium layer, reduce cation mixing, and improve the cycle life of the secondary battery.

[0022] In any embodiment, the composition of the lithium-containing transition metal oxide is as shown in Formula I: Li a L x Ni b Co c Mn d M (1-b-c-d)O e R f Formula I

[0023] Wherein, L is a metal element, the ionic radius of the L cation is larger than the ionic radius of the Li ion, M includes one or more of Mg, Zr, Al, B, Ta, Mo, W, Nb, Sb, and La, R includes one or more of F, S, and P, 0 <a≤2,0≤b≤1,0≤c≤1,0≤d≤1,0<b+c+d≤1,0<e≤3,0≤f<2,0<x≤0.1。

[0024] In any embodiment, the lithium-containing transition metal oxide includes Li 0.99 Na 0.01 Ni 0.92 Co 0.07 Mn 0.01 O2、Li 0.95 Na 0.05 Ni 0.92 Co 0.07 Mn 0.01 O2、Li 0.95 Na 0.05 Ni 0.55 Co 0.07 Mn 0.38 O2、Li 0.99 Na 0.01 Ni 0.55 Co 0.07 Mn 0.38 O2、Li 0.90 Na 0.1 Ni 0.92 Co 0.07 Mn 0.01 O2、Li 0.99 Na 0.01 Ni 0.92 Co 0.06 Mn 0.01 Mg 0.01 O2、Li 0.99 Na 0.01 Ni 0.92 Co 0.06 Mn 0.01 Al 0.01 O2、Li 0.99 Na 0.01 NiO2、Li 0.99 Na 0.01 One or more of CoO2.

[0025] In any embodiment, based on the total mass of the electrolyte, the mass proportion of lithium element in the electrolyte is 0.005%-5%; and based on the total mass of the electrolyte, the mass proportion of L element in the electrolyte is 0.002%-10%.

[0026] In any embodiment, the electrolyte includes a first electrolyte salt containing lithium ions and a second electrolyte salt containing L ions, the first electrolyte salt including lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonyl imide, lithium bistrifluoromethanesulfonyl imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, lithium tetrafluorooxalatophosphate, or one or more thereof; and

[0027] The second electrolyte salt includes one or more of sodium hexafluorophosphate, sodium perchlorate, sodium hexafluoroarsenate, sodium tetrafluoroborate, sodium difluorophosphate, sodium bisoxalatoborate, sodium difluorooxalatoborate, sodium tetrafluorooxalatophosphate, sodium bisfluorosulfonylimide, and sodium bistrifluoromethylsulfonylimide.

[0028] In any embodiment, the L element in the lithium-containing transition metal oxide in the secondary battery is in-situ doped by an electrochemical method.

[0029] In secondary batteries, the in-situ embedding of L cations in the positive electrode active material is achieved by utilizing electrochemical processes, which can achieve uniform distribution of the L element in the lithium-containing transition metal oxide and reduce the residual L element outside the lithium-containing transition metal oxide bulk. At low doping levels, the "supporting" role of the L metal cations can be fully exerted, the mixing phenomenon is alleviated, and the cycle life of the battery can be effectively improved at low doping levels of the L element.

[0030] The second aspect of the present application provides a method for preparing a secondary battery, comprising: providing a battery cell to be filled with liquid; injecting a first electrolyte to form the battery; injecting a second electrolyte and discharging the battery at a first discharge rate to obtain a secondary battery; the secondary battery comprises a positive electrode plate, the positive electrode plate comprises a positive electrode current collector and a positive electrode film layer arranged 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-containing transition metal oxide, the lithium-containing transition metal oxide and the second electrolyte comprise L metal cations, and the ionic radius of the L metal cations is greater than the ionic radius of the Li ions.

[0031] By injecting a second electrolyte including L metal cations during the secondary injection process, the L metal cations can be embedded in the crystal lattice of the positive electrode active material during the discharge process at the first discharge rate, thereby realizing the doping of L metal cations in the lithium-containing transition metal oxide, expanding the interlayer spacing between lithium layers in the crystal structure, and reducing the probability of transition metal ions entering the lithium layer, thereby alleviating the mixing phenomenon and improving the cycle life of the battery.

[0032] In any embodiment, L comprises one or more of Na, K, Mg, Cs, and Ca.

[0033] In any embodiment, the molar concentration M of L ions in the second electrolyte satisfies: 0.001 mol / L≤M≤5 mol / L.

[0034] The molar concentration M of L ions in the second electrolyte satisfies the above range, which can achieve uniform dispersion of L ions in the electrolyte and rapid migration of L ions, and is beneficial to increasing the doping content of L metal cations in the lithium-containing metal oxide.

[0035] In any embodiment, the first discharge rate Q satisfies: Q≤2C.

[0036] In any embodiment, 0.05C <Q≤0.5C。

[0037] The first discharge rate within the above range is beneficial to increasing the doping amount of L metal in the lithium-containing transition metal oxide.

[0038] In any embodiment, injecting the second electrolyte and discharging at the first discharge rate to obtain a secondary battery specifically includes: injecting the second electrolyte, shaking evenly, discharging at the first discharge rate to a voltage lower limit, standing for a certain period of time and then aging to obtain a secondary battery; wherein the voltage lower limit is 2.8V.

[0039] During the oscillation process, the second electrolyte can fully infiltrate the positive electrode plate, which is beneficial to increasing the doping amount and doping uniformity of the L metal cation in the positive electrode active material.

[0040] In any embodiment, the standing time W during the standing time satisfies the following relationship: 8 hours ≤ W ≤ 72 hours.

[0041] The standing time within the above range is beneficial to the uniform diffusion of L metal ions in the positive electrode active material and can further improve the uniformity of the distribution of L metal ions in the lithium-containing metal oxide; it will not cause the electrolyte to be exposed to the external environment for too long, thereby affecting the overall performance.

[0042] In any embodiment, the second electrolyte includes one or more of sodium hexafluorophosphate, sodium perchlorate, sodium hexafluoroarsenate, sodium tetrafluoroborate, sodium difluorophosphate, sodium bisoxalatoborate, sodium difluorooxalatoborate, sodium tetrafluorooxalatophosphate, sodium bis(fluorosulfonyl)imide, and sodium bis(trifluoromethylsulfonyl)imide.

[0043] In any embodiment, the first electrolyte includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0044] A third aspect of the present application provides an electrical device, comprising a secondary battery according to any embodiment or a secondary battery prepared by a preparation method according to any embodiment. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] FIG1 is a distribution diagram of sodium element in a cross section of a positive electrode active material particle according to one embodiment of the present application;

[0046] FIG2 is a comparison of X-ray diffraction patterns of the positive electrode sheets of an embodiment of the present application and a comparative example;

[0047] FIG3 is a schematic diagram of a secondary battery according to an embodiment of the present application;

[0048] FIG4 is an exploded view of the secondary battery according to one embodiment of the present application shown in FIG3 ;

[0049] FIG5 is a schematic diagram of a battery module according to an embodiment of the present application;

[0050] FIG6 is a schematic diagram of a battery pack according to an embodiment of the present application;

[0051] FIG7 is an exploded view of the battery pack shown in FIG6 according to an embodiment of the present application;

[0052] FIG8 is a schematic diagram of an electric device using a secondary battery as a power source according to an embodiment of the present application.

[0053] Explanation of reference numerals: 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 secondary battery; 51 housing; 52 electrode assembly; 53 cover plate. DETAILED DESCRIPTION

[0054] Below, the embodiments of the secondary battery, preparation method and electrical device of the present application are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0055] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0056] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0057] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0058] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0059] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0060] Unless otherwise specified, the term "or" is used in this application to be inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0061] As the market's requirements for the capacity of lithium secondary batteries increase, the transition metal content in the positive electrode active materials of lithium secondary batteries continues to increase. However, divalent transition metal cations (especially nickel ions with a particle size similar to that of lithium ions) are easily migrated to the lithium layer to occupy the spatial sites of lithium ions during the recycling of secondary batteries. When the degree of mixing is high, a large number of divalent transition metal cations occupying the lithium layer will be oxidized to trivalent transition metal ions with a smaller ion radius during the charging process of the battery cell, resulting in the collapse of the crystal structure of the positive electrode active material, which causes the cycle life of the secondary battery to drop sharply.

[0062] [Secondary battery]

[0063] Based on this, the present application provides a secondary battery comprising a positive electrode plate and an electrolyte, wherein the positive electrode plate comprises a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, the positive electrode film layer comprises a lithium-containing transition metal oxide, and both the lithium-containing transition metal oxide and the electrolyte comprise L metal cations, and the ionic radius of the L metal cations is greater than the ionic radius of the Li ions.

[0064] The metal components in the lithium-containing transition metal oxide and the electrolyte can be tested by any known method in the art. As an example, reference can be made to EPA 6010D-2014 and the test can be performed by inductively coupled plasma atomic emission spectrometry, for example, by plasma atomic emission (ICP-OES, instrument model: Thermo ICAP7400) for characterization. The ionic radius of the L metal cation can be obtained by consulting a reference book after determining the type of element. In some embodiments, the positive electrode active material in the secondary battery can detect L metal cations before long cycling. As an example, L metal cations can be detected in the positive electrode active material before the secondary battery cycles 10 or 100 times.

[0065] The secondary battery includes L metal cations in the electrolyte, so that the L metal ions are embedded in the positive electrode active material through the electrochemical process, play a supporting role in the lithium-containing transition metal oxide, expand the interlayer spacing between the lithium layers in the crystal structure, and increase the migration barrier of the transition metal (especially the transition metal with an ion radius close to that of lithium ions, such as nickel ions) in the lithium-containing transition metal oxide to the lithium layer, thereby reducing the probability of the transition metal ions entering the lithium layer, thereby alleviating the mixed discharge phenomenon and improving the cycle life of the battery. Moreover, the positive electrode active material doped by the electrochemical process has few residual impurities outside the bulk phase, and the L ions are able to efficiently enter and evenly distribute in the bulk phase of the lithium-containing transition metal oxide, thereby improving the raw material utilization rate and reducing the residual content of impurities outside the bulk phase of the active material. Furthermore, the electrolyte also includes L metal cations, so that the L metal cations can enter the lithium-containing transition metal oxide during the long cycle process, reducing the lithium-nickel mixed discharge in the late cycle, and achieving further improvement in the battery cycle stability.

[0066] In some embodiments, L comprises one or more of Na, K, Ca, Mg, and Cs.

[0067] The above-mentioned L element has a suitable ionic radius, which can not only enter the lithium layer of the lithium-containing transition metal oxide, but also has an ionic radius larger than that of lithium ions, and can play a "supporting" role in the lithium layer, reduce cation mixing, and improve the cycle life of the secondary battery.

[0068] In some embodiments, the L metal cations in the lithium-containing transition metal oxide are located in the lithium layers of the lattice structure.

[0069] In some embodiments, the molar ratio of the L element to the lithium element in the lithium-containing transition metal oxide bulk phase is 0.01:100-10:100.

[0070] In some embodiments, the molar ratio of the L element to the lithium element in the lithium-containing transition metal oxide bulk phase is 0.3:100-4:100.

[0071] The molar ratio of L element to lithium element in the lithium-containing transition metal oxide phase can be selected as 0.01:100, 0.1:100, 0.2:100, 0.3:100, 0.4:100, 0.5:100, 0.6:100, 0.7:100, 0.8:100, 0.9:100, 1:100, 2:100, 3:100, 4:100, 5:100, 6:100, 7:100, 8:100, 9:100, 10:100 or any numerical range between the two.

[0072] The L element in the positive electrode active material typically consists of two components: one component that was not successfully incorporated into the bulk phase of the lithium-containing transition metal oxide during the preparation process and is located outside the bulk phase of the lithium-containing transition metal oxide, for example, remaining on the surface of the lithium-containing transition metal oxide; and the other component that is incorporated into the bulk phase of the lithium-containing transition metal oxide. The molar ratio of the L element to the lithium element in the bulk phase of the lithium-containing transition metal oxide can be determined by any test method known in the art. As an example, referring to EPA 6010D-2014, the mass of the L element and the lithium element in the washed positive electrode active material is measured by inductively coupled plasma atomic emission spectrometry, and the molar ratio can be obtained by converting the mass to a molar amount. It can be understood that the washing process removes the L element outside the bulk phase of the positive electrode active material, thereby obtaining the L element and lithium content located in the bulk phase of the lithium-containing transition metal oxide. Specifically, 0.4 grams (g) of the lithium-containing transition metal oxide is weighed, washed and dried, and then 10 milliliters (ml) of aqua regia (50% concentration) is added. The mixture was then placed on a plate at 180 degrees Celsius (°C) and heated for 30 minutes (min). After digestion on the plate, the volume was fixed to 100 mL and a standard curve method was used to quantitatively test the L element and lithium element in the bulk phase of the lithium-containing transition metal oxide to obtain the contents of the L element and lithium element in the bulk phase, thereby calculating the molar ratio of the L element to the lithium element in the bulk phase.

[0073] The molar ratio of L element to lithium element in the lithium-containing transition metal oxide bulk phase within the above range can not only fully exert the effect of L element doping in reducing lithium-nickel mixing, but also ensure the stability of the crystal structure, thereby comprehensively improving the cycle stability of the secondary battery.

[0074] In some embodiments, the X-ray diffraction pattern of the lithium-containing transition metal oxide includes a diffraction peak of the (003) crystal plane and a diffraction peak of the (104) crystal plane, and the ratio of the peak intensity I(003) of the diffraction peak of the (003) crystal plane to the peak intensity I(104) of the diffraction peak of the (104) crystal plane is 1.40 to 1.80.

[0075] The X-ray diffraction pattern of the lithium-containing transition metal oxide can be obtained by X-ray diffractometer testing. As an example, the X-ray diffractometer can be selected as Shimadzu X-ray diffractometer XRD-7000. The peak intensity of the diffraction peak can be represented by the maximum height of the diffraction peak in the XRD pattern. The (003) crystal plane corresponds to the lattice plane with Miller index (003), and the (104) crystal plane corresponds to the lattice plane with Miller index (104). The ratio of the peak intensity I(003) of the diffraction peak of the (003) crystal plane to the peak intensity I(104) of the diffraction peak of the (104) crystal plane can reflect the degree of cation mixing in the lithium-containing transition metal oxide, especially the degree of lithium-nickel mixing. The larger the value of I(003) / I(104), the lower the degree of cation mixing.

[0076] In the embodiment of the present application, the I(003) / I(104) of the lithium-containing transition metal oxide satisfies 1.40 to 1.80; optionally 1.45 to 1.60; optionally 1.48 to 1.55. Illustratively, I(003) / I(104) can be selected as 1.40, 1.41, 1.42, 1.43, 1.44, 1.45, 1.46, 1.47, 1.48, 1.49, 1.50, 1.51, 1.52, 1.53, 1.54, 1.55, 1.56, 1.57, 1.58, 1.59, 1.60, 1.61, 1.62, 1.63, 1.64, 1.65, 1.66, 1.67, 1.68, 1.69, 1.70, 1.71, 1.72, 1.73, 1.74, 1.75, 1.76, 1.77, 1.78, 1.79, 1.80 or any range of values ​​therebetween.

[0077] The I(003) / I(104) of the lithium-containing transition metal oxide is within the above range, indicating that the material has a low degree of cation mixing and lattice distortion, which is beneficial to improving the battery cycle life.

[0078] In some embodiments, based on the total mass of the positive electrode active material, the mass proportion of the L element outside the bulk of the positive electrode active material is 0%-0.5%.

[0079] In some embodiments, based on the total mass of the positive electrode active material, the mass proportion of the L element outside the bulk of the positive electrode active material is 0.0001%-0.2%.

[0080] In some embodiments, based on the total mass of the positive electrode active material, the mass proportion of the L element located outside the bulk of the positive electrode active material can be selected as 0%, 0.01%, 0.05%, 0.1%, 2%, 0.3%, 0.4%, 0.5% or any numerical range therebetween.

[0081] Based on the total mass of the positive electrode active material, the mass fraction of the L element located outside the bulk phase of the positive electrode active material can be tested by any test method known in the art. As an example, referring to EPA 6010D-2014, the mass content of the L element in each of the positive electrode active material and the positive electrode active material after washing is tested by inductively coupled plasma atomic emission spectrometry, and the difference between the two is used as the mass fraction of the L element outside the bulk phase of the positive electrode active material. Specifically, first weigh ml g (for example, 0.4 g) of the positive electrode active material and add 10 ml (50% concentration) of aqua regia thereto. Then place it on a 180°C plate and heat it for 30 minutes; after digestion on the plate, dilute to a volume of 100 mL and use the standard curve method to perform quantitative testing of the L element to obtain the total mass of the L element in the positive electrode active material sample m2, and use m2 / m1 as the total mass content a of the L element in the positive electrode active material. Then weigh m3 (e.g., 0.4 g) of the positive electrode active material and remove any residual L elements, such as L sources, outside the bulk of the positive electrode active material through a water washing process (using water as a detergent to wash the positive electrode active material). After washing, the positive electrode active material is dried to remove the detergent water. 10 ml (50% concentration) of aqua regia is added to the dried positive electrode active material, which is then heated on a 180°C plate for 30 minutes. After digestion on the plate, the volume is fixed to 100 mL, and a standard curve method is used for quantitative analysis of the L element to obtain the total mass m4 of the L element in the bulk of the positive electrode active material. m4 / m3 is used as the mass content b of the L element in the bulk of the positive electrode active material. Let ab be the mass ratio of the L element located outside the bulk of the positive electrode active material based on the total mass of the positive electrode active material.

[0082] During the solid-phase sintering process, to ensure sufficient doping of the L element, the actual amount of L source added is often slightly higher than the theoretical value actually required. Therefore, the lithium-containing transition metal oxide prepared using the solid-phase sintering method generally has a relatively large amount of L source remaining outside the bulk phase. The positive electrode active material in the embodiments of the present application has an extremely low content of L element outside the bulk phase, which can reduce the impurity content of the positive electrode active material, improve the utilization rate of the raw materials, reduce the degree of side reactions in the secondary battery, and improve the cycle stability of the secondary battery.

[0083] In some embodiments, in the particles of the positive electrode active material, the molar percentage of the L element of the positive electrode active material relative to all elements in the particles is A1; in a local slice of the positive electrode active material particle, the molar percentage of the L element of the positive electrode active material relative to all elements in the local slice is B1; A1 and B1 satisfy: 50%≤B1 / A1≤100%.

[0084] In the particles of the positive electrode active material, the molar percentage A1 of the L element of the positive electrode active material relative to all the elements in the particles can be obtained by testing in any way known in the art. As an example, the particles of the positive electrode active material are subjected to elemental analysis by a transmission electron microscope combined with an energy spectrum to obtain the molar percentage A1 of the L element in the positive electrode active material particles. In a local section of the positive electrode active material particles, the molar percentage B1 of the L element of the positive electrode active material relative to all the elements in the local section can be obtained by testing in any way known in the art. As an example, the positive electrode particles are cut or ground by a focused ion beam (FIB) to obtain a thinned local section of the particle (within 1 micron thickness), and the section is subjected to elemental analysis by a transmission electron microscope combined with an energy spectrum to obtain the molar percentage of the L element in the local section of the positive electrode active material particles.

[0085] In some embodiments, B1 / A1 can be selected as 50%, 60%, 70%, 80%, 90%, 100% or any range therebetween.

[0086] The L element is evenly distributed in the positive electrode active material with B1 / A1 within the above range. The L element can fully exert its effectiveness at a low addition amount, play a supporting role for the lithium layer, reduce cation mixing, and improve the cycle life of the secondary battery.

[0087] In some embodiments, the composition of the lithium-containing transition metal oxide is as shown in Formula I: Li a L x Ni b Co c Mn d M (1-b-c-d) O e R f Formula I

[0088] Wherein, L is a metal element, the ionic radius of the L cation is larger than the ionic radius of the Li ion, M includes one or more of Mg, Zr, Al, B, Ta, Mo, W, Nb, Sb, and La, R includes one or more of F, S, and P, 0 <a≤2,0≤b≤1,0≤c≤1,0≤d≤1,0<b+c+d≤1,0<e≤3,0≤f<2,0<x≤0.1。

[0089] In some embodiments, x can be 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.010, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, or a range consisting of any two of the foregoing values.

[0090] In some embodiments, 0 ≤ b ≤ 1; alternatively, 0.55 ≤ b ≤ 1 or 0.9 ≤ b ≤ 1. When the nickel content is within the above range, the specific capacity of the positive electrode active material is relatively high; and combined with the doping of the L element, the crystal structure stability of the positive electrode active material is highly stable, which is conducive to further improving the cycle performance of the battery cell.

[0091] For example, b can be 0, 0.01, 0.02, 0.05, 0.08, 0.10, 0.12, 0.15, 0.18, 0.20, 0.22, 0.25, 0.28, 0.30, 0.32, 0.35, 0.38, 0.40, 0.42, 0.45, 0.48, 0.50, 0.52, 0.55, 0.58, 0.60, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 8, 0.69, 0.70, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1 or a range consisting of any two of the above values.

[0092] In some embodiments, 0≤c≤1.

[0093] For example, c can be 0, 0.01, 0.02, 0.05, 0.08, 0.10, 0.12, 0.15, 0.18, 0.20, 0.22, 0.25, 0.28, 0.30, 0.32, 0.35, 0.38, 0.40, 0.42, 0.45, 0.48, 0.50, 0.52, 0.55, 0.58, 0.60, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 8, 0.69, 0.70, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1 or a range consisting of any two of the above values.

[0094] In some embodiments, 0≤d≤1.

[0095] Illustratively, d can be 0, 0.01, 0.02, 0.05, 0.08, 0.10, 0.12, 0.15, 0.18, 0.20, 0.22, 0.25, 0.28, 0.30, 0.32, 0.35, 0.38, 0.40, 0.42, 0.45, 0.48, 0.50, 0.52, 0.55, 0.58, 0.60, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 8, 0.69, 0.70, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1 or a range consisting of any two of the above values.

[0096] In some embodiments, 0<b+c+d≤1.

[0097] For example, b+c+d can be 0.01, 0.02, 0.05, 0.08, 0.10, 0.12, 0.15, 0.18, 0.20, 0.22, 0.25, 0.28, 0.30, 0.32, 0.35, 0.38, 0.40, 0.42, 0.45, 0.48, 0.50, 0.52, 0.55, 0.58, 0.60, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.70, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 0.91 68, 0.69, 0.70, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1 or a range consisting of any two of the above values.

[0098] In some embodiments, the lithium-containing transition metal oxide comprises one or more of Ni, Co, and Mn. In some embodiments, the lithium-containing transition metal oxide comprises a lithium-rich manganese-based material.

[0099] In some embodiments, the lithium-containing transition metal oxide includes Li 0.99 Na 0.01 Ni 0.92 Co 0.07 Mn 0.01 O2、Li 0.95 Na0.05 Ni 0.92 Co 0.07 Mn 0.01 O2、Li 0.95 Na 0.05 Ni 0.55 Co 0.07 Mn 0.38 O2、Li 0.99 Na 0.01 Ni 0.55 Co 0.07 Mn 0.38 O2、Li 0.90 Na 0.1 Ni 0.92 Co 0.07 Mn 0.01 O2、Li 0.99 Na 0.01 Ni 0.92 Co 0.06 Mn 0.01 Mg 0.01 O2、Li 0.99 Na 0.01 Ni 0.92 Co 0.06 Mn 0.01 Al 0.01 O2、Li 0.99 Na 0.01 NiO2、Li 0.99 Na 0.01 One or more of CoO2.

[0100] In some embodiments, based on the total mass of the electrolyte, the mass proportion of lithium element in the electrolyte is 0.005%-5%; and based on the total mass of the electrolyte, the mass proportion of L element in the electrolyte is 0.002%-10%.

[0101] In some embodiments, based on the total mass of the electrolyte, the mass proportion of lithium element in the electrolyte can be selected to be 0.002%-10%.

[0102] In some embodiments, based on the total mass of the electrolyte, the mass proportion of the L element in the electrolyte can be selected as 0.002%, 0.01%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or any numerical range therebetween.

[0103] In some embodiments, based on the total mass of the electrolyte, the mass fraction of lithium in the electrolyte can be selected as 0.005%, 0.01%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or any numerical range therebetween. Based on the total mass of the electrolyte, the mass fraction of lithium or L in the electrolyte can be obtained by any test method known in the art. As an example, a certain amount of sample is taken from the electrolyte, and the sample is further processed, such as filtering, concentrating or derivatizing, to facilitate mass spectrometry analysis. The pretreated sample is introduced into a mass spectrometer, and the sample is converted into charged ions by ionization. The ionized sample enters a mass analyzer, and a high-resolution mass spectrometer is used to obtain sufficiently accurate mass data of the L element. The mass of the measured L element is divided by the total mass of the electrolyte sample to obtain the mass fraction of the L element in the electrolyte based on the total mass of the electrolyte.

[0104] In some embodiments, the electrolyte includes a first electrolyte salt containing lithium ions and a second electrolyte salt containing L ions, the first electrolyte salt including lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonyl imide, lithium bistrifluoromethanesulfonyl imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium bisoxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate; and the second electrolyte salt includes sodium hexafluorophosphate, sodium perchlorate, sodium hexafluoroarsenate, sodium tetrafluoroborate, sodium difluorophosphate, sodium bisoxalatoborate, sodium difluorooxalatoborate, sodium tetrafluorooxalatophosphate, sodium bisfluorosulfonyl imide, and sodium bistrifluoromethanesulfonyl imide. One or more.

[0105] In some embodiments, the electrolyte includes a solvent, and the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl 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, cyclopentane sulfone, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0106] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0107] In some embodiments, the L element in the lithium-containing transition metal oxide in the secondary battery is in-situ doped by an electrochemical method.

[0108] Electrochemical in-situ doping refers to the in-situ embedding of L cations in the electrolyte into the positive electrode active material using an electrochemical process in a secondary battery.

[0109] The above method can achieve uniform distribution of L element in lithium-containing transition metal oxide, reduce the residual L element outside the lithium-containing transition metal oxide bulk phase, and fully exert the "support" role of L metal cations at a low doping amount, alleviate the mixing phenomenon, and effectively improve the cycle life of the battery at a low doping amount of L element.

[0110] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0111] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may 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 acrylate resin.

[0112] In some embodiments, the positive electrode film layer may further include a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0113] The second aspect of the present application provides a method for preparing a secondary battery, comprising: providing a battery cell to be filled with liquid; injecting a first electrolyte to form the battery; injecting a second electrolyte and discharging the battery at a first discharge rate to obtain a secondary battery; the secondary battery comprises a positive electrode plate, the positive electrode plate comprises a positive electrode current collector and a positive electrode film layer arranged 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-containing transition metal oxide, the lithium-containing transition metal oxide and the second electrolyte comprise L metal cations, and the ionic radius of the L metal cations is greater than the ionic radius of the Li ions.

[0114] By injecting a second electrolyte including L metal cations during the secondary injection process, the L metal cations can be embedded in the crystal lattice of the positive electrode active material during the discharge process at the first discharge rate, thereby realizing the doping of L metal cations in the lithium-containing transition metal oxide, expanding the interlayer spacing between lithium layers in the crystal structure, and reducing the probability of transition metal ions entering the lithium layer, thereby alleviating the mixing phenomenon and improving the cycle life of the battery.

[0115] In some embodiments, L includes one or more of Na, K, Mg, Cs, and Ca.

[0116] In some embodiments, the molar concentration M of L ions in the second electrolyte satisfies: 0.001 moles per liter (mol / L)≤M≤5 mol / L.

[0117] In some embodiments, the molar concentration M of L ions in the second electrolyte can be selected as: 0.001 mol / L, 0.1 mol / L, 0.5 mol / L, 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L and any numerical range therebetween.

[0118] The molar concentration M of L ions in the second electrolyte satisfies the above range, which can achieve uniform dispersion of L ions in the electrolyte and rapid migration of L ions, and is beneficial to increasing the doping content of L metal cations in the lithium-containing metal oxide.

[0119] In some embodiments, the first discharge rate Q satisfies: Q≤2C.

[0120] In some embodiments, the first discharge rate can be selected as 0.01C, 0.05C, 0.06C, 0.07C, 0.08C, 0.09C, 0.1C, 0.2C, 0.3C, 0.4C, 0.5C, 1C, 1.5C, 2C or any range of values ​​therebetween.

[0121] In some embodiments, 0.05C <Q≤0.5C。

[0122] The first discharge rate within the above range is beneficial to increasing the doping amount of L metal in the lithium-containing transition metal oxide.

[0123] In some embodiments, the injecting of the second electrolyte and discharging at a first discharge rate to obtain a secondary battery specifically includes: injecting the second electrolyte, shaking evenly, discharging at the first discharge rate to a voltage lower limit, and aging after standing for a certain period of time to obtain a secondary battery; wherein the voltage lower limit is 2.8 volts (V).

[0124] In some embodiments, the shaking method includes one or more of ultrasonic shaking method and mechanical shaking method.

[0125] During the oscillation process, the second electrolyte can fully infiltrate the positive electrode plate, which is beneficial to increasing the doping amount and doping uniformity of the L metal cation in the positive electrode active material.

[0126] In some embodiments, the standing time W in the standing time satisfies: 8 hours ≤ W ≤ 72 hours, in hours.

[0127] In some embodiments, W can be selected as 8 hours, 10 hours, 15 hours, 20 hours, 25 hours, 30 hours, 35 hours, 40 hours, 45 hours, 50 hours, 55 hours, 60 hours, 65 hours, 70 hours, 72 hours, or any range therebetween.

[0128] The standing time within the above range is beneficial to the uniform diffusion of L metal ions in the positive electrode active material and can further improve the uniformity of the distribution of L metal ions in the lithium-containing metal oxide; it will not cause the electrolyte to be exposed to the external environment for too long, thereby affecting the overall performance.

[0129] In some embodiments, the second electrolyte includes one or more of sodium hexafluorophosphate, sodium perchlorate, sodium hexafluoroarsenate, sodium tetrafluoroborate, sodium difluorophosphate, sodium bisoxalatoborate, sodium difluorooxalatoborate, sodium tetrafluorooxalatophosphate, sodium bis(fluorosulfonyl)imide, and sodium bis(trifluoromethylsulfonyl)imide.

[0130] In some embodiments, the first electrolyte includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0131] [Negative electrode]

[0132] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0133] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0134] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0135] In some embodiments, the negative electrode film layer may further include a binder. For example, the binder may be selected from 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), and carboxymethyl chitosan (CMCS).

[0136] In some embodiments, the negative electrode film layer may further include a conductive agent. For example, the conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0137] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0138] In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0139] [Isolation film]

[0140] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0141] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0142] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0143] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0144] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the secondary battery can be a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0145] In this application, the shape of the secondary battery includes but is not limited to cylindrical, square or any other shape. For example, FIG3 shows a secondary battery 5 with a square structure as an example.

[0146] In some embodiments, referring to Figure 4, the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may 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 connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can be formed into an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0147] In some embodiments, secondary batteries can be assembled into a battery module. The number of secondary batteries contained in the battery module can be one or more. The specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0148] Figure 5 shows an example battery module 4. Referring to Figure 5 , within the battery module 4, multiple secondary batteries 5 may be arranged sequentially along the length of the battery module 4. Of course, any other arrangement is also possible. Furthermore, the multiple secondary batteries 5 may be secured together using fasteners.

[0149] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.

[0150] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0151] Figures 6 and 7 illustrate an example battery pack 1. Referring to Figures 6 and 7 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be positioned over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0152] In addition, the present application also provides an electric device, which includes at least one of the secondary battery, battery module, or battery pack provided in the present application. The secondary battery, battery module, or battery pack can be used as a power source for the electric device, and can also be used as an energy storage unit for the electric device. The electric device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited thereto.

[0153] As an electrical device, a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

[0154] Figure 8 shows an example of an electric device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery, a battery pack or battery module can be used.

[0155] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0156] Example

[0157] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0158] 1. Preparation method

[0159] Example 1:

[0160] 1) Preparation of positive electrode sheet

[0161] First, nickel acetate, cobalt acetate, and manganese acetate (92:7:1) were added to deionized water and stirred to obtain a transition metal salt solution. The coprecipitant, an alkali metal salt solution, was quickly poured into the transition metal salt solution and the reaction continued for 9 hours. The mixture was then allowed to age for 4 hours to allow for primary particle growth. The product was washed three times with deionized water, dried in a blast dryer, and then vacuum-dried at 100°C for 12 hours. The dried solid was collected as the precursor.

[0162] The precursor and lithium hydroxide were mixed evenly in a molar ratio of 1:1.05 and ground. The excess lithium hydroxide was used to compensate for the loss of lithium during high-temperature calcination. The fully ground solid powder was transferred to a crucible and placed in a muffle furnace with programmed temperature. The calcination procedure was: pre-calcination from room temperature to 500℃ for 5h, and then calcined at a high temperature of 700℃ for 12h, with a heating rate of 3℃ min -1 After cooling to room temperature, the material LiNi 0.92 Co 0.07 Mn 0.01 O2.

[0163] The positive electrode active material LiNi 0.92 Co 0.07 Mn 0.01 O2, binder polyvinylidene fluoride, and conductive agent acetylene black are mixed in a weight ratio of 98:1:1, dissolved in solvent N-methylpyrrolidone (NMP) to make positive electrode slurry, and then the slurry is coated on the current collector aluminum foil. After drying, it is cold pressed, trimmed, cut into pieces, and striped to make positive electrode sheets.

[0164] 2) Preparation of negative electrode sheet

[0165] The negative electrode active material graphite, conductive agent carbon black, thickener CMC, and adhesive styrene-butadiene rubber (SBR) are mixed in a weight ratio of 96.2:0.8:1.2:0.8 and dissolved in solvent deionized water to form a negative electrode slurry, and the negative electrode slurry is obtained under the action of a vacuum mixer; the slurry is then coated on the current collector copper foil, and after drying, it is cold pressed, trimmed, cut into pieces, and striped to form a negative electrode sheet.

[0166] 3) Preparation of the first electrolyte

[0167] In an argon atmosphere glove box (H2O <0.1ppm, O2 <0.1ppm), the organic solvents ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 3 / 7, LiPF6 lithium salt was added and dissolved in the organic solvent, and stirred evenly to obtain a first electrolyte with a LiPF6 concentration of 1 mol / L.

[0168] 4) Preparation of the second electrolyte

[0169] In an argon atmosphere glove box (H2O <0.1ppm, O2 <0.1ppm), the organic solvents ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 3 / 7, and NaPF6 sodium salt was added and dissolved in the organic solvent. The mixture was stirred evenly to obtain a second electrolyte with a NaPF6 concentration of 2 mol / L.

[0170] 5) Isolation film

[0171] A 9 μm polyethylene (PE) film was used as the separator.

[0172] 6) Preparation of batteries

[0173] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, so that the separator is in the middle of the positive and negative electrode sheets to isolate the positive and negative electrode sheets, and the bare battery cell is wound to obtain the electrode ear. The electrode ear is welded, and the battery cell is placed in an aluminum shell to obtain a battery cell to be injected. During the first injection, the first electrolyte lithium hexafluorophosphate is injected at a concentration of 1 mol / L. After standing at high temperature for 18 hours, the battery cell is transferred to a formation cabinet. After being formed to 55% SOC (3.7V), the second electrolyte sodium hexafluorophosphate is injected at a concentration of 2 mol / L. Ultrasonic oscillation is used until the second electrolyte fully infiltrates the positive electrode sheet, and the battery cell is discharged at a first rate constant current of 0.2C to 2.8V. After being set aside for 24 hours, it is transferred to an aging cabinet and aged at 50°C for 48 hours; after undergoing processes such as capacity division, the secondary battery prepared in Example 1 is obtained.

[0174] The I(003) / I(104) ratio of the lithium-containing transition metal oxide in the secondary battery is 1.55. The mass fraction of the Na element located outside the bulk of the positive electrode active material is 2 ppm, based on the total mass of the positive electrode active material. In the particles of the positive electrode active material, the molar percentage of the L element in the positive electrode active material relative to all elements in the particles is A1. In a local section of the positive electrode active material particle, the molar percentage of the L element in the positive electrode active material relative to all elements in the local section is B1. B1 / A1 is 55%. The mass content of Na ions in the electrolyte is 3.8%, based on the total mass of the electrolyte.

[0175] The preparation method of the battery of Example 2 is similar to that of the battery of Example 1, except that the type of sodium salt in the second electrolyte is adjusted.

[0176] The preparation method of the battery of Example 3-4 is similar to that of the battery of Example 1, except that the first discharge rate is adjusted, as shown in Table 1.

[0177] The preparation method of the battery of Example 5 is similar to that of the battery of Example 1, except that the rest time after the first rate constant current discharge is adjusted, as shown in Table 1.

[0178] The preparation method of the battery of Example 6 is similar to that of the battery of Example 4, except that the sodium salt concentration of the second electrolyte is adjusted.

[0179] The preparation methods of the batteries of Examples 7 and 8 are similar to that of the battery of Example 1, except that the type of electrolyte salt in the second electrolyte is adjusted.

[0180] Comparative Example 1

[0181] The preparation method of Comparative Example 1 is basically the same as that of Example 1, except that after the first injection to 55% SOC (3.7V), the second injection is injected with lithium hexafluorophosphate and then transferred to an aging cabinet for aging at 50°C for 48 hours; and then after the capacity separation process, the secondary battery prepared in Comparative Example 1 is obtained.

[0182] Comparative Example 2

[0183] The preparation method of Comparative Example 1 is basically the same as that of Example 1, except that after the first injection to 55% SOC (3.7V), sodium hexafluorophosphate is injected and then transferred to an aging cabinet for aging at 50°C for 48 hours; and then after the capacity separation and other processes, the secondary battery prepared in Comparative Example 1 is obtained.

[0184] Table 1

[0185] 2. Test Method

[0186] 1. Cycle stability test of secondary batteries

[0187] At 45°C, the secondary battery was allowed to stand for 30 minutes, then charged at a constant current of 0.5C to a voltage of 4.2V, further charged at a constant voltage of 4.2V to a current of 0.05C, allowed to stand for 5 minutes, and then discharged at a constant current of 0.5C to a voltage of 2.8V. This is a charge and discharge cycle process. The discharge capacity this time is the first discharge capacity of the battery. The secondary battery was subjected to a cyclic charge and discharge test according to the above method until the discharge capacity of the secondary battery decayed to 80% of the first discharge capacity, and the number of cycles of the secondary battery was recorded.

[0188] 3. Analysis of test results of various embodiments and comparative examples

[0189] Batteries of various examples and comparative examples were prepared according to the above methods, and various performance parameters were measured. The results are shown in Table 2 below.

[0190] Table 2

[0191] Please refer to Figure 1, which shows the distribution diagram of the Na element in the cross section of the positive electrode active material particles in the embodiment of the present application. As can be seen from Figure 1, the Na element is evenly distributed inside the positive electrode active material in the embodiment of the present application.

[0192] Figure 2 is a comparison of the X-ray diffraction patterns of the positive electrode sheets in the secondary batteries of the embodiment of the present application and the comparative example. As can be seen from Figure 2, the (003) crystal plane peak of the positive electrode sheet in the embodiment of the present application is shifted to the left compared with the comparative example, indicating that the lithium-nickel mixing phenomenon in the secondary battery in the embodiment of the present application is reduced compared with the comparative example.

[0193] In Comparative Example 2, an electrolyte salt containing Na metal cations was added only during the secondary injection, without undergoing a discharge process. Therefore, only Na metal cations were included in the electrolyte, and the Na metal cations were not embedded in the positive electrode active material of the fresh battery cell. From the comparison of the embodiment and the comparative example, it can be seen that the lithium-containing transition metal oxide and the electrolyte of the positive electrode plate of the secondary battery provided by the present application both include Na metal cations. The ionic radius of Na metal cations is greater than the ionic radius of Li ions, which can increase the I(003) / I(104) of the lithium-containing transition metal oxide, reduce lithium-nickel mixing, and improve the cycle stability of the secondary battery.

[0194] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A secondary battery, characterized in that: The invention comprises a positive electrode plate and an electrolyte, wherein the positive electrode plate comprises a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, wherein the positive electrode film layer comprises a positive electrode active material, wherein the positive electrode active material comprises a lithium-containing transition metal oxide, wherein both the lithium-containing transition metal oxide and the electrolyte comprise L metal cations, and the ionic radius of the L metal cations is greater than the ionic radius of the Li ions.

2. The secondary battery according to claim 1, wherein L includes one or more of Na, K, Ca, Mg, and Cs.

3. The secondary battery according to claim 1 or 2, characterized in that The molar ratio of the L element to the lithium element in the lithium-containing transition metal oxide bulk phase is 0.01:100-10:

100.

4. The secondary battery according to any one of claims 1 to 3, characterized in that The molar ratio of the L element to the lithium element in the lithium-containing transition metal oxide bulk phase is 0.3:100-4:

100.

5. The secondary battery according to any one of claims 1 to 4, characterized in that The X-ray diffraction pattern of the lithium-containing transition metal oxide includes a diffraction peak of the (003) crystal plane and a diffraction peak of the (104) crystal plane, and the ratio of the peak intensity I(003) of the diffraction peak of the (003) crystal plane to the peak intensity I(104) of the diffraction peak of the (104) crystal plane is 1.40 to 1.

80.

6. The secondary battery according to any one of claims 1 to 5, characterized in that Based on the total mass of the positive electrode active material, the mass proportion of the L element outside the bulk of the positive electrode active material is 0%-0.5%.

7. The secondary battery according to any one of claims 1 to 6, characterized in that Based on the total mass of the positive electrode active material, the mass proportion of the L element located outside the bulk of the positive electrode active material is 0.0001%-0.2%.

8. The secondary battery according to any one of claims 1 to 7, characterized in that In the particles of the positive electrode active material, the molar percentage of the L element of the positive electrode active material relative to all elements in the particles is A1; In a local slice of the positive electrode active material particle, the molar percentage of the L element of the positive electrode active material relative to all elements in the local slice is B1; A1 and B1 satisfy: 50% ≤ B1 / A1 ≤ 100%.

9. The secondary battery according to claim 1, wherein The composition of the lithium-containing transition metal oxide is shown in Formula I: Li a L x Ni b Co c Mn d M (1-b-c-d) O e R f Formula I Wherein, L is a metal element, the ionic radius of the L cation is larger than the ionic radius of the Li ion, M includes one or more of Mg, Zr, Al, B, Ta, Mo, W, Nb, Sb, and La, R includes one or more of F, S, and P, 0 <a≤2,0≤b≤1,0≤c≤1,0≤d≤1,0<b+c+d≤1,0<e≤3,0≤f<2,0<x≤0.1。 10. The secondary battery according to any one of claims 1 to 9, characterized in that The lithium-containing transition metal oxide includes Li 0.99 Na 0.01 Ni 0.92 Co 0.07 Mn 0.01 O2、Li 0.95 Na 0.05 Ni 0.92 Co 0.07 Mn 0.01 O2、Li 0.95 Na 0.05 Ni 0.55 Co 0.07 Mn 0.38 O2、Li 0.99 Na 0.01 Ni 0.55 Co 0.07 Mn 0.38 O2、Li 0.90 Na 0.1 Ni 0.92 Co 0.07 Mn 0.01 O2、Li 0.99 Na 0.01 Ni 0.92 Co 0.06 Mn 0.01 Mg 0.01 O2、Li 0.99 Na 0.01 Ni 0.92 Co 0.06 Mn 0.01 Al 0.01 O2、Li 0.99 Na 0.01 NiO2、Li 0.99 Na 0.01 One or more of CoO2.

11. The secondary battery according to any one of claims 1 to 10, characterized in that: Based on the total mass of the electrolyte, the mass proportion of lithium element in the electrolyte is 0.005%-5%; as well as Based on the total mass of the electrolyte, the mass proportion of the L element in the electrolyte is 0.002%-10%.

12. The secondary battery according to any one of claims 1 to 11, characterized in that: The electrolyte includes a first electrolyte salt containing lithium ions and a second electrolyte salt containing L ions, wherein the first electrolyte salt includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonyl imide, lithium bistrifluoromethanesulfonyl imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate; and The second electrolyte salt includes one or more of sodium hexafluorophosphate, sodium perchlorate, sodium hexafluoroarsenate, sodium tetrafluoroborate, sodium difluorophosphate, sodium bisoxalatoborate, sodium difluorooxalatoborate, sodium tetrafluorooxalatophosphate, sodium bis(fluorosulfonylimide), and sodium bis(trifluoromethylsulfonylimide).

13. The secondary battery according to any one of claims 1 to 12, characterized in that: The L element in the lithium-containing transition metal oxide in the secondary battery is in-situ doped by an electrochemical method.

14. A method for preparing a secondary battery, characterized in that: include: Provide battery cells to be filled with liquid; injecting the first electrolyte to form; injecting a second electrolyte and discharging at a first discharge rate to obtain a secondary battery; The secondary battery includes a positive electrode plate, which includes a positive electrode collector and a positive electrode film layer arranged on at least one surface of the positive electrode collector. The positive electrode film layer includes a positive electrode active material, and the positive electrode active material includes a lithium-containing transition metal oxide. The lithium-containing transition metal oxide and the second electrolyte include L metal cations, and the ionic radius of the L metal cations is larger than the ionic radius of the Li ions.

15. The preparation method according to claim 14, characterized in that L includes one or more of Na, K, Mg, Cs, and Ca.

16. The preparation method according to claim 14 or 15, characterized in that: The molar concentration M of L ions in the second electrolyte satisfies: 0.001 mol / L≤M≤5 mol / L.

17. The preparation method according to any one of claims 14 to 16, characterized in that The first discharge rate Q satisfies: Q≤2C.

18. The preparation method according to any one of claims 14 to 17, characterized in that 0.05C <Q≤0.5C。 19. The preparation method according to any one of claims 14 to 18, characterized in that The injecting of the second electrolyte and discharging at the first discharge rate to obtain the secondary battery specifically includes: The second electrolyte is injected, shaken evenly, discharged at a first discharge rate to a voltage lower limit, and then aged after standing for a certain period of time to obtain a secondary battery; wherein the voltage lower limit is 2.8V.

20. The preparation method according to any one of claims 14 to 19, characterized in that The standing time W in the standing for a certain period of time satisfies the following conditions: 8 hours ≤ W ≤ 72 hours.

21. The preparation method according to any one of claims 14 to 20, characterized in that The second electrolyte includes one or more of sodium hexafluorophosphate, sodium perchlorate, sodium hexafluoroarsenate, sodium tetrafluoroborate, sodium difluorophosphate, sodium bisoxalatoborate, sodium difluorooxalatoborate, sodium tetrafluorooxalatophosphate, sodium bis(fluorosulfonyl)imide, and sodium bis(trifluoromethylsulfonyl)imide.

22. The preparation method according to any one of claims 14 to 21, characterized in that The first electrolyte includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

23. An electrical device, characterized in that: A secondary battery comprising the secondary battery according to any one of claims 1 to 13 or a secondary battery prepared by the preparation method according to any one of claims 14 to 22.

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