A secondary battery

Abstract

The application discloses a secondary battery, and belongs to the technical field of batteries.The secondary battery disclosed by the application takes lithium nickel manganese oxide particles as positive active materials, controls the primary particle size of the particles, sets a gradient for the internal and external proportions of trivalent manganese ions and tetravalent manganese ions in the particles, and further introduces doped elements, so that the defects of a traditional spinel lithium nickel manganese oxide system secondary battery can be effectively overcome, the secondary battery has good rate performance, excellent high-temperature storage performance and good comprehensive performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a secondary battery. BACKGROUND

[0002] Spinel lithium nickel manganese oxide material has high voltage platform and energy density, and also has high theoretical capacity, is widely available and low in cost. However, due to the existence of ordered phase and disordered phase in spinel lithium nickel manganese oxide from the structural phase, the manganese ions in disordered phase lithium nickel manganese oxide exist in disproportionation reaction, and then the manganese ion dissolution phenomenon is prone to occur, the structural stability is poor, the SEI film is damaged when it is applied to a secondary battery, which is not conducive to the charge and discharge stability of the secondary battery, resulting in low discharge capacity under large rate conditions; on the other hand, the basic conductivity of ordered phase lithium nickel manganese oxide is not high, and the internal resistance is high, in the charging process, the trivalent manganese ions in lithium nickel manganese oxide will be oxidized to tetravalent manganese ions, thereby generating strong internal stress, eventually leading to the rupture and even pulverization of the material particles, resulting in poor storage stability of lithium nickel manganese oxide particles and reduced battery life, especially under high temperature conditions. Therefore, when spinel lithium nickel manganese oxide is used in a secondary battery, there is a large room for improvement in discharge performance, storage performance and the like under large rate conditions. SUMMARY

[0003] The purpose of the present application is to overcome the deficiencies in the prior art and provide a secondary battery, the secondary battery described in the present application uses lithium nickel manganese oxide particles as the positive active material, controls the primary particle size of the particles, sets a gradient for the internal and external proportions of trivalent manganese ions and tetravalent manganese ions in the particles, and also introduces a doping element, which can effectively overcome the defects of traditional spinel lithium nickel manganese oxide system secondary batteries, not only has good rate performance, but also excellent storage performance and good comprehensive performance.

[0004] To achieve the above-mentioned purpose, in the first aspect of the present application, the present application provides a secondary battery, the secondary battery comprises a positive electrode sheet, the positive electrode sheet comprises a positive electrode active material layer, the positive electrode active material layer contains a positive electrode active material, and the positive electrode active material comprises lithium nickel manganese oxide particles;

[0005] The primary particle size of the lithium nickel manganese oxide particles is 1-8 μm;

[0006] The lithium nickel manganese oxide particles comprise trivalent manganese ions and tetravalent manganese ions;

[0007] The lithium nickel manganese oxide particles satisfy:

[0008] X1=90-99%, X2=98.5-99.99%, and X1X2;

[0009] X1 is the mole ratio content of the tetravalent manganese ions in the total moles of the trivalent manganese ions and the tetravalent manganese ions at a depth of 5 nm on the surface of the lithium nickel-manganese oxide particles, and X2 is the mole ratio content of the tetravalent manganese ions in the total moles of the trivalent manganese ions and the tetravalent manganese ions at a depth of 100 nm on the surface of the lithium nickel-manganese oxide particles.

[0010] The lithium nickel-manganese oxide particles contain a doping element, and the doping element includes at least one of Co, Cr, Fe, Al, Nb, Mo, Ta, W, Ti, Zr, V, Ta, Si, Mg, Sc, Cu, Zn, Ga, Sr, Y, Ru, Sn, Sb, Na, and P.

[0011] In a second aspect of the present application, the present application also provides a power-using device including the secondary battery, which is used as a power supply in the power-using device.

[0012] The present application has the following beneficial effects:

[0013] The present application provides a secondary battery. The secondary battery described in the present application uses lithium nickel-manganese oxide particles as a positive electrode active material. By controlling the primary particle size of the particles and setting a gradient for the internal and external proportions of the trivalent manganese ions and the tetravalent manganese ions in the particles, and by introducing a doping element, the defects of the conventional spinel-type lithium nickel-manganese oxide system secondary battery can be effectively overcome. The secondary battery has good high-temperature storage stability, and has a good capacity retention rate under a large rate discharge condition. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 FIG. 1 is an electron microscope diagram of the junction between the inner core and the shell of the lithium nickel-manganese oxide particles in the secondary battery described in the present application. DETAILED DESCRIPTION

[0015] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are some but not all of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0016] In the present application, the technical features described in an open manner include a closed technical solution composed of the listed features, and also include an open technical solution containing the listed features.

[0017] In the present application, when referring to a numerical interval, unless otherwise specified, the numerical interval is considered to be continuous and includes the minimum and maximum values of the range, as well as every value between the minimum and maximum values. Further, when the range refers to integers, every integer between the minimum and maximum values of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges can be combined. In other words, unless otherwise indicated, all ranges disclosed herein are to be understood as including any and all sub-ranges subsumed therein.

[0018] The present application is further illustrated below with specific examples:

[0019] A secondary battery includes a positive electrode tab including a positive electrode active material layer containing a positive electrode active material, the positive electrode active material including lithium nickel manganese oxide particles;

[0020] The primary particle size of the lithium nickel manganese oxide particles is 1-8 μm;

[0021] The lithium nickel manganese oxide particles include trivalent manganese ions and tetravalent manganese ions;

[0022] The lithium nickel manganese oxide particles satisfy:

[0023] X1=90-99%, X2=98.5-99.99%, and X1X2;

[0024] wherein X1is the mole ratio content of tetravalent manganese ions in the total moles of trivalent manganese ions and tetravalent manganese ions of the lithium nickel manganese oxide particles at a depth of 5 nm from the surface, and X2is the mole ratio content of tetravalent manganese ions in the total moles of trivalent manganese ions and tetravalent manganese ions of the lithium nickel manganese oxide particles at a depth of 100 nm from the surface;

[0025] The lithium nickel manganese oxide particles contain a doping element, the doping element including at least one of Co, Cr, Fe, Al, Nb, Mo, Ta, W, Ti, Zr, V, Ta, Si, Mg, Sc, Cu, Zn, Ga, Sr, Y, Ru, Sn, Sb, Na, P.

[0026] In some embodiments, the primary particle size of the lithium nickel manganese oxide particles is one or a range of values of any two of 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm.

[0027] In some embodiments, X1 is one of or a range value of any two of 90%, 91%, 91.5%, 92%, 92.5%, 93%, 93.5%, 94%, 94.5%, 95%, 96%, 97%, 98%, 98.5%, 99%.

[0028] In some embodiments, X2 is one of or a range value of any two of 98.5%, 98.6%, 98.8%, 98.89%, 99%, 99.1%, 99.3%, 99.5%, 99.8%, 99.9%, 99.99%.

[0029] In some embodiments, X3 is 1-10%, X3 is the mole content of the trivalent manganese ion in the total moles of the trivalent manganese ion and the tetravalent manganese ion at a depth of 5 nm on the surface of the lithium nickel manganese oxide particle.

[0030] In some embodiments, X4 is 0.01-1.5%, X4 is the mole content of the trivalent manganese ion in the total moles of the trivalent manganese ion and the tetravalent manganese ion at a depth of 100 nm on the surface of the lithium nickel manganese oxide particle.

[0031] In the technical solution of the present application, in order to balance the high-temperature storage stability and the improvement of the rate performance of the lithium nickel manganese oxide system secondary battery, when the lithium nickel manganese oxide particle is set, the particle size of the primary particle is limited, so that the particle size is not too small to cause the specific surface area of the overall material to be too large, the degree of side reaction after the electrolyte is immersed and contacted to increase, and the storage performance of the secondary battery to decrease, or the particle size is too large to cause the kinetic performance of the secondary battery to be poor; on the other hand, the content ratio of the trivalent manganese ion and the tetravalent manganese ion in the particle is designed, so that the content of the tetravalent manganese ion at different depths is in different ranges, and the content increases from outside to inside, so as to balance the ordered phase and disordered phase of the material, inhibit the excessive dissolution of the internal manganese, damage the negative electrode after the deposition of the negative electrode, so as to ensure the good interface of the negative electrode, and at the same time ensure the structural stability of the overall particle; in addition, by introducing a specific doping element into the lithium nickel manganese oxide particle, the trivalent manganese element on the surface of the particle can be effectively controlled, so as to realize the effect of disordered surface structure and ordered internal structure of the particle, and also improve the interface performance after the particle is immersed and contacted with the electrolyte, further improve the lithium storage capacity and lithium deintercalation stability of the material, through the above comprehensive modification, the low manganese dissolution of the lithium nickel manganese oxide particle can be ensured, and at the same time the side reaction of the disordered phase in the lithium nickel manganese oxide particle can be effectively inhibited, the integrity of the negative electrode interface is ensured, and at the same time the crack phenomenon of the particle caused by the stress effect in the charging process is relieved, finally the high-temperature storage stability and the large rate discharge capacity retention rate of the secondary battery are effectively improved, after a long time of high-temperature preservation, a high capacity is still reserved, and under the condition of 3C large rate discharge, the secondary battery still has a good discharge capacity.

[0032] Specifically, in the scheme of the present application, X1 and X2 of the lithium nickel manganese oxide particles can be confirmed by, but not limited to, XPS (X-ray photoelectron spectroscopy) test, and the specific method is as follows: the secondary battery is discharged to 3.5 V at 0.33 C, then the positive electrode sheet is disassembled, the sheet is soaked in dimethyl carbonate (DMC) in advance, dried at 60 ℃ for 4 h, then the positive active material layer powder is scraped out and fixed in a test mold using conductive tape, and then a NEXSAG2 type XPS etching analyzer is used for testing, and the test conditions are as follows: a 120 W monochromatic Al Kα X-ray source is used; the energy resolution is less than or equal to 0.48 eV; the test beam spot is 400 μm, and the instrument automatically supplements the test energy range according to the element to be tested, which is 632-660 eV; the etching treatment conditions are as follows: after identifying the lithium nickel manganese oxide particles, Ar ions are used for etching at a rate of 0.1 nm / s, and etching to a depth of 5 nm and 100 nm respectively, to obtain the XPS spectrum of Mn at 5 nm and the XPS spectrum of Mn at 100 nm, and the peaks are separated, specifically, the Mn spectrum is corrected with reference to the C1s spectrum peak position (284.8 eV), then the background is removed by sherly method, the XPS spectrum (Mn2p 3 / 2) in the energy range of 630-650 eV is separated, and then the initial peak of Mn 3+ is set at 643±0.5 eV, and the initial peak of Mn 4+ is set at 640±0.5 eV, and then the two peak positions are fixed, and fitting is performed, and when the fitting curve coincides with the data, the peak area of Mn 3+ at this time is recorded as S2, which is the peak area of the characteristic peak of trivalent manganese ion after the XPS characteristic peak of manganese element at the depth is separated, and the peak area of Mn 4+ is S1, which is the peak area of the characteristic peak of tetravalent manganese ion after the XPS characteristic peak of manganese element at the depth is separated; the above test and spectrum processing are performed on the test results at 5 nm and 100 nm, and S1 5nm and S2 5nm at 5 nm depth and S1 100nm and S2 100nm at 100 nm depth are obtained, respectively, then X1 is S1 5nm / (S1 5nm +S2 5nm ) at 5 nm depth, and X2 is S1 100nm / (S1 100nm +S2 100nm ) at 100 nm depth.

[0033] Specifically, in the scheme of the present application, the primary particle size of the lithium nickel manganese oxide particles can be tested by, but not limited to, the following method: the secondary battery is discharged to 3.5V at 0.33C, the positive electrode sheet is disassembled, then the positive electrode sheet is soaked in dimethyl carbonate (DMC) for 4h, dried at 60℃ for 4h, the positive electrode active material layer on the positive electrode sheet is scraped off for EDS spectrum test, the lithium nickel manganese oxide particles are identified under a magnified view by point scanning, then the particle morphology of the lithium nickel manganese oxide particles is obtained under a scanning electron microscope at 10k magnification, the primary particles of the lithium nickel manganese oxide particles are measured by the nanomeasurer software "cross line method", the sample amount is 200, and the statistical result is the primary particle size of the lithium nickel manganese oxide particles.

[0034] In some embodiments, the molar ratio of the doping element to the lithium nickel manganese cobalt oxide particles in the lithium nickel manganese oxide particles is (0.01-0.08):1, that is, 0.01-0.08 mol of the doping element is contained in each mol of the lithium nickel manganese oxide particles.

[0035] The introduction of the doping element can reduce the valence state of the manganese ions in the lithium nickel manganese oxide particles, and when the content of the doping element in the particles is preferably within the above range, the valence state of the manganese ions on the surface of the particles can be effectively reduced, the surface stability of the particles is further improved, the number of crystal structure defects in the interior of the particles is also reduced, the relative content of the ordered phase in the internal structure is increased, the charge-discharge stability and the large-rate discharge performance of the material are more excellent, and the electrochemical performance of the secondary battery is more excellent.

[0036] It should be noted that the test method of the doping element in the lithium nickel manganese oxide particles described in the present application can be, but is not limited to, the following specific steps:

[0037] The secondary battery is discharged to 3.5V at 0.33C, then the positive electrode sheet is disassembled, the sheet is soaked in dimethyl carbonate (DMC) for 4h, dried at 60℃ for 4h, and the positive electrode active material layer powder is scraped off;

[0038] (1) 0.4g of the positive electrode active material layer powder is weighed into a polytetrafluoroethylene container, 8mL of a composite solution of hydrochloric acid and 2mL of hydrofluoric acid is added into the container, the sample is fully digested by heating at 210℃ for 30min, then heated at 160℃ for 20min, after the sample solution is cooled, ultrapure water is added to make the volume 50mL;

[0039] (2) For the doping element, 1.0g of the above sample solution is taken, 2% hydrochloric acid is added to make a 20g solution for use;

[0040] (3) According to the element to be measured, a standard solution with different concentrations of the element is configured, and the concentration can be 0.01, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 ppm, etc. The solution in step (2) is compared with the standard solution in the inductively coupled plasma emission spectrometer, and the content (ppm, one millionth, that is, mg / kg) of the element to be measured is quantitatively judged by comparing the characteristic spectrum emitted by the sample solution and the standard solution in the plasma state. Finally, the molar ratio of the doped element to the lithium nickel manganese oxide particle is calculated by conversion.

[0041] In some embodiments, X1 = 95-97%, and X2 = 99-99.9%.

[0042] In some embodiments, X3 = 3-5%, and X4 = 0.1-1%.

[0043] When X1, X2, X3, and X4 are within the range, the content of trivalent manganese ions in the disordered phase on the surface of the lithium nickel manganese oxide particle can be within a better range, further reducing the amount of manganese dissolution, ensuring the integrity of the negative electrode interface, and further improving the structure stability of the lithium nickel manganese oxide particle during charging and discharging and the discharge performance under large-rate discharge conditions.

[0044] By further optimizing the proportion of manganese ions in two valence states in the lithium nickel manganese oxide particle at a depth of 5 nm and 100 nm, the structure stability of the particle surface layer can be effectively improved, while the integrity of the internal crystal structure is also considered, ensuring further balance between the ordered phase and the disordered phase of the lithium nickel manganese oxide particle, and finally further improving the high-temperature storage performance and large-rate discharge performance of the lithium nickel manganese oxide particle when used in secondary batteries.

[0045] In some embodiments, the primary particles of the lithium nickel manganese oxide particle include a core and a shell.

[0046] When the primary particles of the lithium nickel manganese oxide particle are configured as a core-shell structure, the gradient stratification of the inside and outside of the particle can be further improved, the proportion of trivalent manganese ions and tetravalent manganese ions on different depth planes is more obvious, the dissolution degree of internal manganese elements is lower, and the structural stability of the particle after doping is better. The overall stress effect is smaller when lithium ions are deintercalated, and the stability is higher.

[0047] In some embodiments, the lithium nickel manganese oxide particle satisfies:

[0048] X7 > X4, and X8 < X2;

[0049] X7 is the mole ratio content of trivalent manganese ions at the interface between the outer shell and the inner core of the lithium nickel manganese oxide particles in the total moles of trivalent manganese ions and tetravalent manganese ions, and X8 is the mole ratio content of tetravalent manganese ions at the interface between the outer shell and the inner core of the lithium nickel manganese oxide particles in the total moles of trivalent manganese ions and tetravalent manganese ions.

[0050] Further preferably, X7 = 1-10%, and X8 = 90-99%.

[0051] Specifically, X1 + X3 = 100%, X2 + X4 = 100%, and X7 + X8 = 100%. By optimizing the ratio of trivalent manganese ions and tetravalent manganese ions in the inner core and the outer shell, the internal stress effect caused by oxidation of trivalent manganese ions and the destruction of the structural stability and integrity of the material caused by the disorder phase segregation reaction can be effectively inhibited. Based on the effect of the doping elements, better ion conduction can be achieved in the shell layer, and the application performance of the positive electrode material in the secondary battery is more optimal.

[0052] Specifically, in the present application, the X7 and X8 features of the lithium nickel manganese oxide particles can be confirmed by, but not limited to, the following method. Specifically, the secondary battery is discharged to 3.5V at 0.33C, and then the positive electrode sheet is disassembled. The positive electrode sheet is pre-soaked in dimethyl carbonate (DMC), dried at 60°C for 4h, and then the positive active material layer powder is scraped out. Then, 1g of the powder is pre-dispersed in 100mL of 98% ethanol solution, and the sample particles are observed under a TEM (transmission) electron microscope to determine whether there is a core-shell structure. If there is a core-shell structure, the thickness of the shell is measured. The remaining powder is fixed in a test mold using conductive tape, and an XPS etching analyzer of NEXSA GA type is used for testing. The test conditions are as follows: a 120W monochromatic Al Kα X-ray source is used; the energy resolution is less than or equal to 0.48 eV; the test beam spot is 400μm; according to the element to be tested, the instrument automatically supplements the test energy range to be 632-660eV; after identifying the lithium nickel manganese oxide particles, Ar ions are used for etching at an etching rate of 0.1nm / s, and the interface between the outer shell and the inner core is etched. The obtained XPS spectrum of Mn is peak-divided. Specifically, the Mn spectrum is corrected with reference to the C1s spectrum peak position (284.8eV), and then the background is removed by the sherly method. The XPS spectrum (Mn2p 3 / 2) in the energy range of 630-650eV is peak-divided, and an initial peak of Mn 3+ is set at 643±0.5eV, and a peak of Mn 4+the initial peak, two peak positions are fixed after setting the end, fitting, when the fitting curve coincides with the data, record the analysis of the valence state of the manganese element at the corresponding depth and the XPS characteristic peak at the corresponding depth at this time, then X7 is S2 / (S1+S2), X8 is S1 / (S1+S2), S1 is the peak area of the characteristic peak of tetravalent manganese ions after the peak separation of the manganese element XPS characteristic peak at the depth, and S2 is the peak area of the characteristic peak of trivalent manganese ions after the peak separation of the manganese element XPS characteristic peak at the depth.

[0053] Further preferably, the thickness of the shell is 0.5-10 nm.

[0054] Further preferably, the thickness of the shell is one of 0.5 nm, 1 nm, 1.5 nm, 2 nm, 2.5 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 9.5 nm, 10 nm or a range value of any two thereof.

[0055] When the lithium nickel-manganese oxide particles are constructed into an ordered-disordered composite structure through the design of the core-shell structure, when the thickness of the shell is in the range, not only can the lithium ion quickly and effectively penetrate the shell interface to realize transmission in the process of ion / electron conduction, but also the transition metal ions in the particles will not appear obvious dissolution phenomenon. Further, when the thickness of the shell is preferably in the above range, the influence of the disproportionation reaction of trivalent manganese ions on the dissolution of transition metal ions can be avoided, so that the high-temperature storage performance and large-rate discharge performance of the secondary battery are further improved.

[0056] Specifically, the thickness of the shell in the primary particles of the lithium nickel-manganese oxide particles can be confirmed by but not limited to the following method, and the specific method is as follows: the secondary battery is discharged to 3.5 V at 0.33 C, then the positive electrode sheet is disassembled, the sheet is soaked in dimethyl carbonate (DMC) in advance, dried at 60°C for 4 h, then the positive active material layer powder is scraped out, then 1 g of the powder is dispersed in 100 mL of 98% alcohol in advance, the sample is prepared by dropping, and whether the core-shell structure exists in the sample particles is observed under a TEM (transmission) electron microscope, as shown in FIG. 1. Figure 1 If the core-shell structure exists, 200 samples are selected to measure the thickness of the shell, and the average value of all samples is calculated, which is the thickness of the shell of the primary particles of the lithium nickel-manganese oxide particles.

[0057] In some embodiments, the primary particles of the lithium nickel-manganese oxide particles comprise an inner core and a shell, and the lithium nickel-manganese oxide particles satisfy:

[0058] 0.076≤(Cxr) / s≤1.276;

[0059] wherein r nm is the thickness of the shell, C is the unit molar amount of the doped element in the lithium nickel-manganese oxide particles, sm 2g is the specific surface area of the positive electrode active material particles.

[0060] When the core-shell structure is constructed in the primary particles of the lithium nickel manganese oxide particles, by synchronously controlling the thickness of the shell, the content of the doping elements, and the specific surface area of the overall active material particles, the lithium ion conduction efficiency and stability of the material in the positive electrode sheet can be further improved, wherein the ratio of C to s represents the distribution density of the doping elements in the particles, and by optimizing the ratio of the two, the doping effect of the surface layer of the particles can be controlled, so that the degree of change of the crystal structure of the surface layer particles is within a suitable range, the ion conductivity is improved, and the probability of transition metal ion dissolution is not increased; at the same time, by controlling the ratio of the distribution density to the shell thickness r, the concentration of the unit doping element in the shell layer can be effectively controlled, and by optimizing the three, the proportion of the internal ordered phase in the particles can be high, which can provide sufficient mechanical properties and capacity support for the material, while the proportion of the disorder in the shell is high, which can improve the transmission efficiency of the ions, optimize the kinetic performance, control the probability of transition metal ion dissolution, reduce the generation of side reactions in the secondary battery, and finally achieve better electrochemical performance.

[0061] In some embodiments, the r = 0.5-10 nm;

[0062] Further preferably, the r = 1-5 nm.

[0063] As mentioned above, the thickness of the shell in the primary particles will simultaneously affect the efficiency of lithium ion conduction and the probability of transition metal ion dissolution to some extent. When the thickness increases, the probability of transition metal ion dissolution increases due to the influence of the disproportionation reaction of the disordered phase, and if the thickness decreases, the kinetic transmission performance of the overall particles will be reduced. Therefore, when the thickness r is preferably within the above range, the balance of the particles in the above two aspects is more optimal, and the secondary battery can simultaneously improve the high-temperature storage stability and large-rate discharge performance.

[0064] In some embodiments, the s = 0.2-1.5 m 2 / g;

[0065] Further preferably, the s = 0.2 m 2 / g, 0.3 m 2 / g, 0.4 m 2 / g, 0.45 m 2 / g, 0.5 m 2 / g, 0.6 m 2 / g, 0.8 m 2 / g, 1 m 2 / g, 1.1 m 2 / g, 1.2 m 2 / g, 1.5 m 2one or any two of the range values of C = 0.01~0.08.

[0066] Further preferably, the s = 0.45~0.8m 2 / g.

[0067] When the specific surface area of the positive electrode active material particles is preferably within the above range, not only can the material be more fully infiltrated when in contact with the electrolyte, thereby facilitating better ion / electron conduction performance, but also the degree of oxidation side reaction of the electrolyte after contact is maintained at a low level, and the secondary battery has better kinetic performance and storage stability.

[0068] Specifically, the specific surface area s of the positive electrode active material particles can be confirmed by, but not limited to, BET analysis method, and the specific method is as follows: the secondary battery is discharged to 3.5V at 0.33C, then disassembled and the positive electrode plate is taken out, the positive electrode plate is dried at 60°C for 4h, then the positive electrode active material layer is scraped, 1g of powder is taken and the material is tested by BET analysis using a full-automatic specific surface and pore size analyzer, thereby obtaining the specific surface area of the lithium nickel manganese oxide particles.

[0069] In some embodiments, the C = 0.01~0.08.

[0070] Further preferably, the C = 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08 one or any two of the range values.

[0071] When the content of the doping element in the shell layer of the lithium nickel manganese oxide primary particles is preferably within the above range, not only can the structure ratio of the shell layer crystal phase be optimized to improve the ion conductivity of the shell layer, but also the dissolution degree of the transition metal ions is not affected, thereby achieving better comprehensive performance.

[0072] In some embodiments, the structural formula of the lithium nickel manganese oxide particles is Li e Ni a Mn b X c O d , wherein e = 0.98~1.02, a = 0.39~0.54, b = 1.43~1.54, c = 0.01~0.08, d = 3.85~4.4, and X is a doping element.

[0073] In application to the secondary battery described in the present application, the lithium nickel manganese oxide described in the present application can overcome the defects of structure phase stability and charge-discharge stability of the lithium nickel manganese oxide by regulating the introduction of the doping elements, the size of the primary particles and the proportion distribution of the trivalent and tetravalent manganese elements, and the range of (Cxr) / s, and finally realize good high-temperature storage stability and rate performance. At the same time, the primary particle size of the particles in the secondary battery, the manganese element distribution rule, and the range of C, r and s can be comprehensively adjusted by the process parameters of the positive electrode material during preparation, including but not limited to the type of the positive electrode material, the preparation process, etc. Specifically, for example, by setting the sintering time, the oxygen content of the calcination atmosphere, and the cooling rate when calcining the precursor hydroxide and the lithium source during the preparation of the lithium nickel manganese oxide particles, the concentration proportion of the trivalent manganese element and the tetravalent manganese element in the primary particles of the lithium nickel manganese oxide appears gradual change from inside to outside; during the calcination process, the shell thickness of the primary particles is regulated by different sintering procedures; during the preparation process, the doping element content of the shell in the primary particles is regulated by adjusting the addition amount of the doping elements and the sintering time and the cooling rate; the specific surface area of the particles is regulated by selecting different precursor materials and different sintering procedures; the particle size range of the primary particles is regulated by the post-grinding process of the material.

[0074] In addition, the above-mentioned parameter characteristics can also be relatively independently regulated by other conventional process methods and formula methods by those skilled in the art, and are not limited to the specific embodiments described and listed in the present application.

[0075] In some embodiments, the lithium nickel manganese oxide particles can be prepared by a calcination method, and the preparation method can be implemented as follows:

[0076] The precursor containing the doping substance is mixed with a lithium source, and then preheated to 900-1000℃ for primary calcination for 5-20h in an oxygen atmosphere, and then adjusted to 600-900℃ for secondary calcination for 1-30h in an oxygen atmosphere, to obtain the lithium nickel manganese oxide particles.

[0077] Specifically, the molar ratio of the precursor and the lithium source is 1:4-1:4.2;

[0078] Specifically, the structural formula of the precursor is Ni 0.25-α Mn 0.75-β X c (OH) 2-γ , X is a doping element, wherein c= ((2-γ)-2(0.25-α)-2(0.75-β)) / n, n is the valence of the doping element X, and c>0, 0.005≤α≤0.02, 0.005≤β≤0.02, 0.01≤γ<0.08;

[0079] Specifically, the lithium source includes, but is not limited to, at least one of lithium carbonate, lithium hydroxide, lithium sulfate, lithium chloride, lithium phosphate, lithium bromide, lithium iodide.

[0080] Specifically, the oxygen volume concentration of the oxygen atmosphere is 20-100%.

[0081] Specifically, after the secondary calcination, the lithium nickel manganese oxide particles are further subjected to annealing treatment, and the temperature of the annealing treatment is not higher than the temperature of the secondary calcination.

[0082] In the scheme, the person skilled in the art can regulate the size of X2 by the temperature of the primary calcination and the oxygen concentration in the oxygen atmosphere as needed, and can regulate the size of X1 by the temperature and time of the secondary sintering and by increasing the annealing treatment, but is not limited thereto.

[0083] In the present application, the preparation method of the lithium nickel manganese oxide particles is not limited, and the person skilled in the art can prepare the lithium nickel manganese oxide particles by using the above method or other methods according to conventional technical means.

[0084] For example, in addition to the above index method, the lithium nickel manganese oxide particles can also be prepared by the following preparation method:

[0085] The precursor containing the doping substance is mixed with a lithium source, and then preheated to 900-1100°C for primary calcination for 5-20h in an oxygen atmosphere. The obtained intermediate material is mixed with a trivalent manganese source, and then re-heated to 600-1000°C for secondary calcination for 1-30h in an oxygen atmosphere, to obtain the lithium nickel manganese oxide particles.

[0086] The trivalent manganese source includes manganese sesquioxide, and the molar ratio of the manganese sesquioxide to the intermediate material is (1-10):100.

[0087] In the method, X1 of the lithium nickel manganese oxide particles can be regulated by the addition amount of the trivalent manganese source, and X2 can be regulated by the calcination temperature of the primary sintering and the oxygen concentration in the oxygen atmosphere. The lithium source used includes, but is not limited to, at least one of lithium dihydrogen phosphate, lithium phosphate, lithium hydroxide, lithium carbonate, lithium nitrate, lithium oxalate, lithium citrate, lithium acetate;

[0088] In some embodiments, the secondary battery further includes an electrolyte, and the electrolyte includes a solvent and a lithium salt.

[0089] For example, in some embodiments, the solvent includes at least one of a carbonate solvent, a carboxylic acid ester solvent, an ether solvent, a sulfone solvent, a nitrile solvent, a phosphate ester solvent.

[0090] In some embodiments, the lithium salt comprises at least one of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium perchlorate, lithium tetrafluoroborate, lithium bisoxalate borate, lithium difluorooxalate borate, lithium triflate, lithium bisfluoromethanesulfonimide, lithium bis-trifluoromethanesulfonimide, lithium difluorobisoxalate phosphate, lithium tetrafluorooxalate phosphate, and the like.

[0091] In some embodiments, the concentration of the lithium salt in the electrolyte is 0.9-2 mol / L.

[0092] In some embodiments, the concentration of the lithium salt in the electrolyte is one of 0.9 mol / L, 1 mol / L, 1.2 mol / L, 1.5 mol / L, 1.8 mol / L, 2 mol / L, or a range value of any two thereof.

[0093] When the concentration of the lithium salt is preferably within the above range, the transport ability of lithium ions can be further optimized, the impedance of the overall secondary battery system can be reduced, the negative electrode potential lifting phenomenon can be improved, the probability of excessive negative electrode potential drop rate can be further reduced, and the fast charging performance of the secondary battery can be more optimal.

[0094] In addition, the electrolyte can further comprise an additive. Illustratively, the additive can comprise a negative electrode film-forming additive, can comprise a positive electrode film-forming additive, and can further comprise an additive capable of improving certain performance of the battery, such as an additive capable of improving high-temperature performance of the battery, an additive capable of improving overcharge performance of the battery, an additive capable of improving low-temperature performance of the battery, and the like.

[0095] The battery can further comprise a separator, which is located between the positive electrode sheet and the negative electrode sheet, and is used to separate the positive electrode sheet and the negative electrode sheet to prevent the positive electrode sheet and the negative electrode sheet from being in contact and short-circuiting. The separator can be any separator film material suitable for a battery in the art. Illustratively, the separator comprises at least one of polypropylene and polyethylene, but is not limited thereto.

[0096] In some embodiments, the compaction density of the positive electrode sheet is 2.8-3.4 g / cm 3 .

[0097] When the compaction density of the positive electrode sheet is within this range, the wettability of the electrolyte in the positive electrode active material layer can be improved, the contact area between the electrolyte and the positive electrode active material particles can be ensured, and excessive side reactions can be avoided while ensuring the ionic conductivity of the positive electrode active material particles.

[0098] It should be noted that the compaction density of the positive electrode sheet described in the present application can be confirmed by, but is not limited to, the following method: the secondary battery is discharged to 3.5 V at 0.33 C, then the positive electrode sheet is disassembled, the sheet is soaked in dimethyl carbonate (DMC) for 2 h, and dried at 60°C for 4 h.

[0099] The positive electrode sheet is subjected to the following operations: (1) the positive electrode sheet is cut into a 20 mm diameter disc, weighed and recorded as m1, in units of g, a 20 mm diameter disc is cut at the positive electrode sheet tab position, weighed and recorded as m2, in units of g, the active material mass on the 20 mm diameter positive electrode sheet disc is m, m = m1-m2, in units of g; (2) the thickness of the positive electrode sheet is measured by a micrometer, h1, in units of μm, the thickness of the positive electrode sheet foil is h2, in units of μm, the thickness of the positive electrode active material layer is d, d = h1-h2, in units of μm; (3) the compaction density of the positive electrode sheet can be calculated according to the formula m x 4 / (π x 0.02 x 0.02) / d.

[0100] When the primary particle size of the lithium nickel manganese oxide particles and the types of elements and manganese element distribution contained therein are optimized, the material can effectively overcome the defects of traditional spinel lithium nickel manganese oxide, and when the compaction density of the particles after being arranged into a positive electrode sheet is further optimized, the interface stability between the lithium nickel manganese oxide particles and the electrolyte is better, the lithium ion deintercalation site dispersion is higher, the activity is higher, and the comprehensive performance of the corresponding secondary battery is better after the positive electrode sheet is in contact with the electrolyte.

[0101] Further preferably, the positive electrode active material layer further comprises a binder and a conductive agent.

[0102] Further preferably, in the positive electrode active material layer, the mass ratio of the positive electrode active material, the conductive agent and the binder is (94-97.5):(0.8-2.5):(1-4).

[0103] In some embodiments, the negative electrode sheet comprises a current collector and a negative electrode active material layer, and the negative electrode active material layer comprises a negative electrode active material.

[0104] Further preferably, the negative electrode active material layer comprises a negative electrode active material, a thickening agent, a binder and a conductive agent.

[0105] Further preferably, in the negative electrode active material layer, the mass ratio of the negative electrode active material, the conductive agent, the thickening agent and the binder is (96-98):(0.5-1):(0.5-1):(2-3).

[0106] It should be noted that the conductive agent in the positive electrode active material layer and the negative electrode active material layer is used to provide conductivity, and any conductive agent can be used without particular limitation, as long as it has suitable electronic conductivity and does not significantly cause adverse chemical changes in the battery. Exemplarily, the conductive agent in the positive electrode active material layer includes, but is not limited to, at least one of carbon nanotubes, carbon black, graphite, carbon fibers, activated carbon, mesoporous carbon, fullerenes, etc., wherein the carbon fibers are, for example, carbon nanofibers, etc.; the carbon black is, for example, SP (Super P, same below), acetylene black, Ketjen black, etc.

[0107] The thickening agent and the binder in the positive active material layer and the negative active material layer are used to improve the adhesion between the positive active material particles and the adhesion between the positive active material and the positive current collector. Any binder can be used without particular limitation as long as it has suitable binder properties and does not significantly cause adverse chemical changes in the battery. Exemplary binders in the positive active material layer include, but are not limited to, fluorine-containing polyolefin-based binders, which include, but are not limited to, polyvinylidene fluoride (PVDF), polyvinylidene fluoride copolymers, or modified (e.g., carboxylic acid, acrylic acid, acrylonitrile, etc.) derivatives thereof, etc., and the thickening agent in the negative active material layer includes, but is not limited to, carboxymethyl cellulose or a salt thereof, and the binder includes, but is not limited to, styrene-butadiene rubber.

[0108] In some embodiments, the negative active material includes at least one of natural graphite, artificial graphite, mesophase carbon microbeads (MCMB), hard carbon, soft carbon, silicon, silicon oxide SiO f (0 < f < 2, such as f = 1), silicon carbon, lithium titanate.

[0109] In some embodiments, the particle size D v50 of the negative active material in the negative active material layer is 5-20 μm.

[0110] In some embodiments, the particle size D v50 of the negative active material is one of 5 μm, 7 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm or a range value of any two thereof.

[0111] When the particle size of the negative active material is within a suitable range, the negative active material can have a moderate specific surface area, which can ensure the rapid extraction and embedding of lithium ions into the negative active material during the charge and discharge cycle, improve the high-rate discharge performance of the product, and at the same time avoid excessive irreversible capacity loss due to too small particle size of the negative active material, thereby affecting the high-temperature storage life of the product.

[0112] In some embodiments, the particle size D v50 of the negative active material in the negative active material layer can be confirmed by, but is not limited to, the following methods:

[0113] The secondary battery is discharged at 0.33C to 3.5V, disassembled and the negative electrode sheet is taken out and left to stand at room temperature for 24h, then 0.1-0.2g of the powder of the negative electrode active material layer particles on the negative electrode sheet is collected by a spatula, and then the powder is operated as follows: (1) the powder is dried at 80±5°C in a vacuum environment for 4h to remove adsorbed water, and after cooling, 100mL of anhydrous ethanol is slowly added; (2) the obtained suspension is subjected to probe ultrasonic dispersion, the probe ultrasonic power is 200W, the ultrasonic time is controlled to be 30-60s, and after ultrasonic is completed, low-speed stirring is used for standby; (3) the laser particle size tester is started, first anhydrous ethanol is injected to perform background scanning, and then the dispersed suspension is injected into the sample cell to the liquid level line; (4) the obscuration is stabilized at 12±2% by increasing or decreasing the sample amount or anhydrous ethanol; (5) the measurement is formally started, the measurement is performed for 3 times with an interval of 10s each time, and the volume cumulative distribution curve is automatically output by the instrument software, wherein the particle size corresponding to the cumulative volume distribution percentage of 50% is the Dv50 of the negative electrode active material layer particles; v50 The relative standard deviation of Dv50 monitored by the repeated measurement of the three times is required to be ≤2%, otherwise the test is re-dispersed; (6) the average value of the Dv50 values of the three effective measurements is calculated, that is, the particle size Dv50 of the negative electrode active material layer particles is obtained. v50 v50

[0114] In some embodiments, the solvent in the electrolyte includes a linear carbonate;

[0115] Specifically, the linear carbonate includes at least one of dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate;

[0116] In some embodiments, the solvent in the electrolyte further includes a carboxylic acid ester solvent;

[0117] Specifically, the carboxylic acid ester solvent includes at least one of ethyl acetate, methyl formate, and 1,4-butyrolactone;

[0118] In some embodiments, the solvent in the electrolyte further includes an ether solvent;

[0119] In some embodiments, the solvent in the electrolyte further includes a cyclic carbonate;

[0120] Specifically, the cyclic carbonate includes at least one of ethylene carbonate and propylene carbonate; and the ether solvent includes at least one of dimethyl ether of ethylene glycol and tetrahydrofuran.

[0121] Further preferably, in addition to the linear carbonate, other types of solvents are also present in the electrolyte.

[0122] ​​More specifically, the solvent includes at least one of ethylene carbonate (EC), methylene methanedisulfonate (MMDS), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), propylene carbonate (PC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), diethyl sulfone (ESE).

[0123] In some embodiments, the electrolyte further includes an additive, and the additive includes at least one of vinyl carbonate (VC), vinyl sulfate (DTD).

[0124] The application is further illustrated in the following specific examples, which should not be construed as limiting the scope of the application:

[0125] Example 1

[0126] A secondary battery, the preparation method including the following steps:

[0127] (1) Preparation of a positive electrode sheet:

[0128] (1.1) Preparation of a positive active material: mixing a precursor Ni 0.25-α Mn 0.75-β X c (OH) 2-γ and a lithium source lithium hydroxide in a molar ratio of 1:4, then pre-heating for a first calcination in an oxygen atmosphere, and then adjusting the temperature for a second calcination in the same atmosphere, to obtain the positive active material;

[0129] (1.2) Preparation of a positive electrode sheet: dispersing the positive active material, a conductive agent SP, and a binder PVDF in N-methyl pyrrolidone in a mass ratio of 97:1.5:1.5, vacuum stirring to prepare a slurry, then coating on both sides of a current collector aluminum foil, drying, cold pressing, and slitting, to obtain the positive electrode sheet;

[0130] (2) Preparation of a negative electrode sheet: dispersing a lithium source lithium hydroxide, a conductive agent SP, and a binder PVDF in N-methyl pyrrolidone in a mass ratio of 97:1.5:1.5, vacuum stirring to prepare a slurry, then coating on both sides of a current collector copper foil, drying, cold pressing, and slitting, to obtain the negative electrode sheet; v50The negative active material artificial graphite with a particle size D5.2 μm, the conductive agent SP, the binder carboxymethyl cellulose sodium, and the binder butadiene rubber are dispersed in water at a mass ratio of 96.4:0.6:0.6:2.4, a slurry is prepared by vacuum stirring, and then coated on both sides of the current collector copper foil, dried, cold-pressed, and cut, to obtain the negative electrode sheet, and the compaction density of the negative electrode sheet is 1.6 g / cm3. 3 ;

[0131] (3) Preparation of electrolyte: ethylene carbonate, diethyl carbonate, methyl ethyl carbonate, and vinylene carbonate are compounded at a mass ratio of 8:85:5:2, and then lithium hexafluorophosphate is added to prepare an electrolyte of 1 mol / L;

[0132] (4) The positive electrode sheet, the separator (commercially available PE separator), and the negative electrode sheet are stacked or wound in sequence to assemble an electric core, the electric core is placed in an outer packaging shell, electrolyte is injected after drying, vacuum packaging, standing, formation, and constant volume, to obtain the secondary battery.

[0133] The preparation and parameters of each secondary battery are shown in Tables 1 and 2.

[0134] Examples 2-17

[0135] A secondary battery, which is different from Example 1 only in that the parameter conditions during preparation of the secondary battery are different, as shown in Tables 1-2, wherein the positive active material in Example 4 is further subjected to annealing treatment after secondary calcination, and the negative electrode sheet in Example 13 is prepared by replacing the negative active material with a hard carbon with a particle size D v50 19.5 μm, as shown in Table 1.

[0136] Examples 18-21

[0137] A secondary battery, which is different from Example 1 only in that the preparation method of the positive active material is as follows: the precursor Ni 0.25-α Mn 0.75-β X c (OH) 2-γ and lithium source lithium hydroxide are mixed at a molar ratio of 1:4.2, and then subjected to primary calcination by preheating in an oxygen atmosphere, and the obtained intermediate material is mixed with manganese sesquioxide powder, and then subjected to secondary calcination by adjusting the temperature in the same atmosphere, to obtain the positive active material; the preparation parameters are shown in Table 1, and the parameters of the secondary battery are shown in Table 2.

[0138] Comparative Examples 1-9 and Comparative Example 15

[0139] A secondary battery, which is different from Example 1 only in that the parameter conditions during preparation of the secondary battery are different, as shown in Tables 1-2.

[0140] Comparative Examples 10-14

[0141] A secondary battery, which differs from Example 1 only in that the preparation method of the positive electrode active material is as follows: a precursor Ni 0.25-α Mn 0.75-β X c (OH) 2-γ and lithium source lithium hydroxide are mixed in a molar ratio of 1:4.2, followed by a first calcination in advance under an oxygen atmosphere, and the obtained intermediate material is mixed with a manganese sesquioxide powder, followed by a second calcination under the same atmosphere at a temperature adjustment, to obtain the positive electrode active material; the preparation parameters are shown in Table 1, and the parameters of the secondary battery are shown in Table 2.

[0142] Table 1

[0143]

[0144] Table 1 (continued)

[0145]

[0146] Table 2

[0147]

[0148] Table 2 (continued)

[0149]

[0150] Effect Example 1

[0151] The secondary batteries obtained in each example and comparative example were tested as follows:

[0152] (1) Cycle storage performance test: each secondary battery was discharged at 0.33C to 3.5V, and after standing for 10 min, charged at 0.33C to 4.75V, and after standing for 10 min, discharged at 0.33C to 3.5V, and after standing for 10 min, the above charging and discharging cycle was repeated for 2 cycles at 0.33C, and the discharge capacity of the second cycle was recorded as Q1; then the secondary battery was charged at 0.33C to 4.75V, and then placed in a 45°C oven for storage for 30 days, and after taking out, discharged at 0.33C rate, and the discharge capacity was recorded as Q2; the storage capacity retention rate of the secondary battery was calculated according to H%=100%×Q2 / Q1;

[0153] (2) Large rate discharge test

[0154] The secondary battery was discharged at 0.33 C to 3.5 V, rested for 10 min, then charged at 0.33 C to 4.75 V, rested for 10 min, and then discharged at 0.33 C to 3.5 V, rested for 10 min, and then charged at 0.33 C and discharged at 0.33 C for 2 cycles, and the discharge capacity of the second cycle was recorded as Q1; then the secondary battery was charged at 0.33 C to 4.75 V, and then discharged at 3 C to 3.5 V, and the discharge capacity was recorded as Q1, and the capacity retention rate of the secondary battery under large-rate discharge was calculated according to the formula I = Q2 / Q1 x 100%.

[0155] The test results are shown in Table 3.

[0156] Table 3

[0157]

[0158] According to Table 3, it can be seen that:

[0159] (1) In order to balance the storage stability of the secondary battery, especially the storage performance at a higher temperature and the rate performance under a large rate condition, the particle size of the primary particles of the lithium nickel-manganese oxide particles is limited when the positive active material is selected as the lithium nickel-manganese oxide particles, so that the particles can balance the low side reaction activity after contacting with the electrolyte and the higher kinetic performance, and the content ratio of the trivalent manganese ions and the tetravalent manganese ions of the particles is designed, so that the content of the tetravalent manganese ions at different depths is in different ranges, and the content increases from the outside to the inside, so as to balance the ordered phase and disordered phase of the material, guarantee the good interface of the negative electrode, and guarantee the structural stability of the whole particle. In addition, by introducing a specific doping element into the lithium nickel-manganese oxide particles, the trivalent manganese element on the surface of the particles can be effectively controlled, so as to realize the effect of disordered surface structure and ordered internal structure of the particles, and finally balance the kinetic performance and structural stability performance during lithium ion deintercalation. The capacity retention rate of the secondary battery in the storage test can reach more than 90%, and the capacity retention rate in the rate test can reach more than 88%. In comparison, in the secondary batteries of each comparative example, the lithium nickel-manganese oxide particles are not designed to balance the particle size, manganese element setting and other factors, and cannot reach the same level as the products of the embodiments.

[0160] (2) When the proportions of tetravalent manganese ions at different depths of the lithium nickel-manganese oxide particles in the secondary battery satisfy X1 = 90-99% and X2 = 98.5-99.99%, further, X1 is optimized to be in the range of 95-97% and / or X2 is optimized to be in the range of 99-99.9%, the content of trivalent manganese ions in the disordered phase on the surface of the lithium nickel-manganese oxide particles can be in a better range, the amount of manganese dissolution is further reduced, the integrity of the negative electrode interface is ensured, and thus the structure stability during charging and discharging and the discharge performance under large-rate discharge conditions of the lithium nickel-manganese oxide particles are further improved.

[0161] (3) The introduction of the doping element can reduce the valence of manganese ions in the lithium nickel-manganese oxide particles, and when the content of the doping element in the particles is preferably in the range of (0.01-0.08):1 in terms of the molar ratio of the doping element to the lithium nickel-manganese oxide particles, the valence of manganese ions on the surface of the particles can be effectively reduced, the structure stability of the surface layer of the particles is further improved, and the number of crystal structure defects in the interior of the particles is also reduced, so that the relative content of the ordered phase in the internal structure is increased, and the charging and discharging stability and the large-rate discharge performance of the material are more excellent.

[0162] (4) In addition, according to Examples 18-21, when the lithium nickel-manganese oxide particles are constructed to have an ordered-disordered composite structure through the design of a core-shell structure, not only can the lithium ions quickly and effectively penetrate the shell interface to realize transmission in the process of ion / electron conduction, but also the transition metal ions in the particles will not appear obvious dissolution. Further, when the thickness of the shell is preferably in the above range, the influence of the disproportionation reaction of trivalent manganese ions on the dissolution of transition metal ions can be avoided, and the storage performance and high-temperature storage performance of the secondary battery are further improved.

[0163] Further, in order to explore the influence of the lithium nickel-manganese oxide particles with the shell on the performance of the secondary battery, the following examples are set:

[0164] Examples 22-48

[0165] A secondary battery, which is different from Example 1 only in that the preparation method of the positive electrode active material is as follows: the precursor Ni 0.25-α Mn 0.75-β X c (OH) 2-γ and lithium source lithium hydroxide are mixed in a molar ratio of 1:4.2, then preheated for primary calcination in an oxygen atmosphere, crushed, and then mixed with manganese sesquioxide powder, and then adjusted to temperature for secondary calcination in the same atmosphere to obtain the positive electrode active material; the preparation parameters are shown in Table 4, and the parameters of the secondary battery are shown in Table 5.

[0166] Table 4

[0167] Table 4

[0168] Table 4 (continued)

[0169]

[0170] Table 5

[0171]

[0172] Table 5 (continued)

[0173]

[0174] Example 2

[0175] The secondary battery obtained above was subjected to the same test as in Example 1, and the results are shown in Table 6.

[0176] Table 6

[0177]

[0178] As can be seen from the test results, after constructing the core-shell structure in the primary particles of the lithium nickel-manganese oxide particles, by simultaneously controlling the thickness of the shell, the content of the doping elements, and the specific surface area of the overall active material particles, the lithium ion conduction efficiency and stability of the material in the positive electrode sheet can be further improved, wherein the ratio of C to s represents the distribution density of the doping elements in the particles, by optimizing the ratio of the two, when (Cxr) / s is in the range of 0.076-1.276, the doping effect of the surface layer of the particles can be controlled, the degree of change in the crystal structure of the surface layer particles is ensured to be in the appropriate range, the ion conductivity is improved, and the probability of transition metal ion dissolution is not increased; at the same time, by controlling the ratio of the distribution density to the shell thickness r, the concentration of the unit doping elements in the shell layer can be effectively controlled, by optimizing and coordinating the three, the proportion of the internal ordered phase in the particles can be high, which provides sufficient mechanical properties and capacity support for the material, the proportion of disorder in the shell is high, which improves the transmission efficiency of ions, optimizes the kinetic performance, controls the probability of transition metal ion dissolution, reduces the generation of side reactions in the secondary battery, and finally realizes better electrochemical performance, the storage capacity retention rate of the secondary battery can reach more than 93%, and the capacity retention rate at 3C high rate can reach more than 92%.

Claims

1. A secondary battery, characterized in that, The secondary battery includes a positive electrode sheet, the positive electrode sheet includes a positive active material layer, the positive active material layer contains a positive active material, and the positive active material includes lithium nickel manganese oxide particles; The primary particle size of the lithium nickel manganese oxide particles is 1~8μm; The lithium nickel manganese oxide particles have the structural formula Li e Ni a Mn b X c O d Where e = 0.98~1.02, a = 0.39~0.54, b = 1.43~1.54, c = 0.01~0.08, d = 3.85~4.4, and X is a dopant element; The lithium nickel manganese oxide particles include trivalent manganese ions and tetravalent manganese ions; The lithium nickel manganese oxide particles satisfy the following: X1 = 90~99%, X2 = 98.5~99.99%, and X1 < X2; Where X1 is the molar percentage of tetravalent manganese ions in the total molar percentage of trivalent and tetravalent manganese ions at a depth of 5 nm on the surface of lithium nickel manganese oxide particles, and X2 is the molar percentage of tetravalent manganese ions in the total molar percentage of trivalent and tetravalent manganese ions at a depth of 100 nm on the surface of lithium nickel manganese oxide particles. X3 = 1~10%, where X3 is the molar percentage of trivalent manganese ions in the total molar content of trivalent and tetravalent manganese ions at a depth of 5nm on the surface of lithium nickel manganese oxide particles; X4 = 0.01~1.5%, where X4 is the molar percentage of trivalent manganese ions in the total molar content of trivalent and tetravalent manganese ions at a depth of 100nm on the surface of lithium nickel manganese oxide particles. The lithium nickel manganese oxide particles contain doping elements, including at least one of Co, Cr, Fe, Al, Nb, Mo, Ta, W, Ti, Zr, V, Ta, Si, Mg, Sc, Cu, Zn, Ga, Sr, Y, Ru, Sn, Sb, Na, and P.

2. The secondary battery as described in claim 1, characterized in that, X1 = 95~97%, and X2 = 99~99.9%.

3. The secondary battery as described in claim 1, characterized in that, The primary particles of the lithium nickel manganese oxide particles include a core and a shell.

4. The secondary battery as described in claim 3, characterized in that, Lithium nickel manganese oxide particles satisfy the following: X7 > X4, and X8 < X2; Where X7 represents the molar percentage of trivalent manganese ions at the interface between the outer shell and the core of lithium nickel manganese oxide particles, in the total molar percentage of trivalent and tetravalent manganese ions, and X8 represents the molar percentage of tetravalent manganese ions at the interface between the outer shell and the core of lithium nickel manganese oxide particles, in the total molar percentage of trivalent and tetravalent manganese ions.

5. The secondary battery as described in claim 4, characterized in that, X7 = 1~10%, and / or X8 = 90~99%.

6. The secondary battery as described in claim 5, characterized in that, The primary particles of the lithium nickel manganese oxide granules include a core and a shell, and the secondary battery satisfies the following: 0.076 ≤ (C × r) / s ≤ 1.276; Where r is the thickness of the outer shell of the primary lithium nickel manganese oxide particle, in nm; C is the molar amount of dopant element in each mole of lithium nickel manganese oxide particle; and s is the specific surface area of ​​the positive electrode active material particle, in m². 2 / g.

7. The secondary battery as described in claim 6, characterized in that, The r = 0.5~10 nm and / or the s = 0.2~1.5 m 2 / g, and / or, wherein C = 0.01~0.08 mol / mol.

8. The secondary battery as described in claim 1, characterized in that, The compaction density of the positive electrode sheet is 2.8~3.4 g / cm³. 3 .

9. The secondary battery as described in claim 1, characterized in that, The secondary battery further includes a negative electrode sheet, which has a negative electrode active material layer containing a negative electrode active material; the particle size D of the negative electrode active material layer particles is... v50 The anode material has a diameter of 5~20μm and / or includes at least one of natural graphite, artificial graphite, mesophase carbon microspheres, hard carbon, soft carbon, silicon, silicon oxide, silicon carbon, and lithium titanate.

10. An electrical appliance, characterized in that, The secondary battery includes the secondary battery described in any one of claims 1 to 9, wherein the secondary battery is used as a power supply in an electrical device.

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