Lithium-rich manganese-based cathode materials with surface modification and lithium-ion secondary batteries

Abstract

The present invention provides a surface-modified lithium-rich manganese-based cathode material and a lithium-ion secondary battery. In the present invention, when the functional material is charged to a high voltage and driven by the potential, reactive oxygen species such as O2, O2 ‑ , O ‑ and oxygen oligomers O n‑ etc. are absorbed and embedded into the lattice interstitial sites, and when discharged to a low potential, the reactive oxygen is released and returns to the lithium-rich manganese-based cathode material again, forming a reversible closed loop for the utilization of reactive oxygen. In the surface-modified lithium-rich manganese-based cathode material provided by the present invention, the application of the surface functional material inhibits the oxidative precipitation of lattice oxygen in the lithium-rich manganese-based cathode material in the high-voltage delithiated state. This cathode material can reversibly electrochemically deintercalate / embed oxygen controllably at different potentials, significantly improving the cycle stability and thermal stability of the material in a high-temperature and high-voltage environment.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion secondary batteries, and particularly relates to a surface and interface modified lithium-rich manganese-based cathode material and a lithium-ion secondary battery. Background Art

[0002] Lithium-rich manganese-based cathode materials are considered to be one of the key cathode materials for next-generation lithium-ion batteries due to their high energy density and low cost. As is well known, when the lithium-rich manganese-based cathode is charged to a voltage of 4.8 V or higher, a specific capacity of up to 250-400 mAh / g can be output, which is one of the cathode materials of lithium-ion batteries with the highest known specific capacity. However, due to many defects existing in lithium-rich manganese-based cathode materials, such as low Coulomb efficiency, poor rate performance, poor cycle stability, and attenuation of the cycle median voltage, there are still severe challenges in promoting market application.

[0003] The above problems are closely related to the lattice oxygen activity of lithium-rich manganese-based cathode materials in a high-voltage operating environment. Due to the oxidation, migration, and loss of lattice oxygen, the transition layer metal ions migrate and serious side reactions of electrolyte oxidation and gas generation occur at the surface and interface. To solve the above problems, researchers have used various methods to modify the materials, such as regulating the transition metal components, regulating the synthesis process, element doping, surface coating, and surface chemical treatment.

[0004] However, it should be noted that although coating has been proven to have a certain effect in suppressing the corrosion of the electrode interface by the electrolyte and deteriorating the surface and interface structure, when the material is charged to a high voltage or a high lithium deintercalation state, the lattice oxygen of the layered material will oxidize and precipitate, and it is difficult to effectively suppress it through general coating materials. Most coating materials only consider physically blocking the electrolyte and the high-voltage cathode under the condition of ensuring appropriate electronic conductivity and lithium-ion diffusion channels. More importantly, the activity of lattice oxygen in lithium-rich manganese-based cathode materials is crucial for the release of high capacity of the materials. If the reversible electrochemical deintercalation / insertion of oxygen between the coating material and the lithium-rich manganese-based cathode material can be realized at different potentials, the loss of oxygen can be reduced, the reversible utilization of active oxygen can be ensured, and at the same time, the formation of active oxygen into oxygen and its escape to the interface to react with the electrolyte to cause significant deterioration of the cycle stability and thermal stability of the battery system can be avoided.

[0005] Therefore, providing a cathode material that can realize the reversible electrochemical deintercalation / insertion of oxygen between the coating material and the lithium-rich manganese-based cathode material at different potentials becomes a problem to be solved. Summary of the Invention

[0006] In view of this, the technical problem to be solved by the present invention is to provide a surface and interface modified lithium-rich manganese-based cathode material and a lithium-ion secondary battery. In the surface and interface modified lithium-rich manganese-based cathode material provided by the present invention, the application of the surface functional material inhibits the oxidative precipitation of lattice oxygen in the high-voltage delithiated state of the lithium-rich manganese-based cathode material, and significantly improves the cycle stability and thermal stability of the material in a high-temperature and high-voltage environment.

[0007] The present invention provides a surface and interface modified lithium-rich manganese-based cathode material, including a lithium-rich manganese-based cathode material core and a functional material layer coated on the surface of the lithium-rich manganese-based cathode material core. The chemical general formula of the functional material is shown in Chemical Formula (1):

[0008] R’ a R” b M c A’ d A” e Chemical Formula (1)

[0009] In Chemical Formula (1), R’ is one or more of alkali metals or alkaline earth metals Li, Na, K, Rb, Cs, Mg, Ca, Sr, and Ba;

[0010] R” is one or more of lanthanide rare earth elements La, Ce, Pr, Nd, Po, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Sc, Y;

[0011] M is one or more of transition metal elements Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Cd, and Ta that can change in multiple valence states;

[0012] A’ is O;

[0013] A” is one or more of S, Se, Te, F, Cl, Br, and I;

[0014] In the functional material, the valence state of element M includes the non-highest valence state of element M, and / or, when forming a battery with metallic lithium as the negative electrode, there are oxidation-reduction peaks in the cyclic voltammogram curve in the potential range of 2.0 - 5.0V;

[0015] Ions M with a valence of +w in element M W and ions M with a valence of +(w + 1) w+1 The molar ratio satisfies Equation 1:

[0016] C M w : C M w+1 = (1 - (V - U) × a) : (n - 1 + (V - U) × a) (Equation 1)

[0017] The mixed valence states (V hybrid ) of the multivalent ions of element M satisfy the relational expression of Equation 2:

[0018] V hybrid = W + 1 + (V × a - U × a - 1) / n (Equation 2)

[0019] In Equation 1 and Equation 2, C M w and C M w+1 are the molar ratios of M W to M w+1 respectively;

[0020] U is the valence of element R'; V is the valence of element R"; W is the valence of element M; n is the ratio of the stoichiometric coefficients of the elements in chemical formula (1); U, V, W, and n are all positive integers greater than zero;

[0021] a is the content of element R', and its assignment range satisfies the relational expression of Equation 3:

[0022] 0 ≤ a ≤ 1 / 2 (V-U-1) (Equation 3)

[0023] In Equation 3, a is the content of element R', U is the valence of element R'; V is the valence of element R"; U and V are positive integers greater than zero;

[0024] The theoretically electrochemically controllable maximum oxygen deintercalation / insertion content in the lattice of the functional material satisfies the relational expression of Equation 4:

[0025] O intercal. = (1 - V × a + U × a) × c / (2 × n) (Equation 4)

[0026] In the formula, O intercal. is the theoretically electrochemically controllable maximum oxygen deintercalation / insertion content in the lattice of the functional material, U is the valence of element R'; V is the valence of element R"; n is the ratio of the stoichiometric coefficients of the elements in chemical formula (1), U, V, and n are positive integers greater than zero; a is the content of element R', and its assignment range satisfies the relational expression of Equation 3;

[0027] Assuming that the valences of elements R', R", M, A', and A" are U, V, W, X, and Y respectively, then in the chemical general formula R' a R" b M c A' d A" e , a, b, c, d, and e satisfy the relational expressions of Equation 5 and Equation 6:

[0028] a × U + b × V + c × W = d × X + e × Y (Equation 5)

[0029] (a + b):c:(d + e) = (n + 1):n:(3n + 1) (Equation 6)

[0030] In Equation 5 and Equation 6, U, V, W, X, Y, and n are positive integers greater than zero; a, b, c, d are rational real numbers greater than or equal to zero, including decimals; e = 0.

[0031] Preferably, when the functional material is assembled into a battery with metallic lithium as the negative electrode, when charged to above 4.0V, there is a phenomenon that the peak intensity at 174 cm -1 and 380 cm -1 in the Raman spectrum weakens or the peak disappears.

[0032] Preferably, when the functional material is assembled into a battery with metallic lithium as the negative electrode for charge and discharge, there is an oxidation characteristic peak above 4.40V on the voltage-capacity differential curve dQ / dV or the cyclic voltammogram curve;

[0033] Alternatively, after the functional material forms a battery with a reversible hydrogen electrode (RHE) as the reference electrode in an alkaline aqueous solution, there is an oxidation-reduction characteristic peak in the 1.2 - 2.0V interval on the voltage-capacity differential curve dQ / dV or the cyclic voltammogram curve.

[0034] Preferably, when the functional material is assembled into a battery with metallic lithium as the negative electrode for charge and discharge, there are deintercalation / insertion lithium oxidation-reduction peaks in the 0.001V - 3.0V interval on the voltage-capacity differential curve dQ / dV or the cyclic voltammogram curve;

[0035] and / or, when the functional material is assembled into a battery with metallic lithium as the negative electrode, the lithium ion diffusion coefficient measured by variable sweep rate cyclic voltammetry is higher than 10 -13 cm 2 / s.

[0036] Preferably, after the functional material is pressed into a powder cake with a diameter of 13 mm under a stress of 10 MPa, the electronic conductivity of the powder cake measured by four-probe method is higher than 10 mS / cm.

[0037] Preferably, when the surface-modified lithium-rich manganese-based cathode material is assembled into a battery with metallic lithium as the negative electrode and charged and discharged in the 2.0 - 4.8V interval in the first cycle, X-ray photoelectron spectroscopy (XPS) analysis is performed on O, F, and P on the surface of the positive electrode plate. The peak intensities of the O1s 531.2 eV ROLi organic peak, the F1s 685.0 eV LiF peak, and the P2p 136.4 eV Li x PO y F z peak are lower than those of the surface-unmodified lithium-rich manganese-based cathode material;

[0038] And / or, the surface interface modified lithium-rich manganese-based cathode material is assembled into a battery with metallic lithium as the anode, and the charge and discharge are carried out in the voltage range of 2.0 - 4.8V in the first cycle, and the oxygen content detected by differential electrochemical mass spectrometry (DEMS) is less than 100 umol / mg.

[0039] Preferably, the chemical general formula of the core of the lithium-rich manganese-based cathode material is Li 1+x Mn y Ni z Co m O2, where 1 + x + y + z + m = 2, 0 ≤ x ≤ 2, 0 < y ≤ 1, 0 ≤ z, m ≤ 1.

[0040] The present invention also provides a preparation method of the above lithium-rich manganese-based cathode material, including the following steps:

[0041] S1: Mix the lithium-rich manganese-based precursor with the lithium source, and obtain the core of the lithium-rich manganese-based cathode material through a first sintering.

[0042] S2: Mix the nanoparticle slurry of the functional material with the core of the lithium-rich manganese-based cathode material and then dry to obtain a powder.

[0043] S3: Perform a high-temperature secondary sintering on the powder to obtain the surface interface modified lithium-rich manganese-based cathode material.

[0044] The present invention also provides a lithium-ion secondary battery, including the above surface interface modified lithium-rich manganese-based cathode material.

[0045] Compared with the prior art, the present invention provides a surface interface modified lithium-rich manganese-based cathode material and a lithium-ion secondary battery. The present invention uses the functional material to absorb and embed active oxygen substances, such as O2, O2 - , O - and oxygen oligomers O n- etc. into the lattice interstices from the surface interface of the lithium-rich manganese-based cathode material particles when charging to a high voltage under the driving of the electric potential, and release the active oxygen when discharging to a low potential, so that it returns to the lithium-rich manganese-based cathode material again, forming a reversible closed loop for the utilization of active oxygen. In the surface interface modified lithium-rich manganese-based cathode material provided by the present invention, the application of the surface functional material inhibits the oxidative precipitation of lattice oxygen in the high-voltage delithiated state of the lithium-rich manganese-based cathode material, and the cathode material can reversibly electrochemically deintercalate / insert oxygen at different controllable potentials, significantly improving the cycle stability and thermal stability of the material in a high-temperature and high-voltage environment. Description of the Drawings

[0046] Figure 1 It is a schematic diagram of the electrochemical deintercalation / insertion of oxygen and the transmission of lithium ions between the functional material and the lithium-rich manganese-based cathode material during the charging process;

[0047] Figure 2Charge-discharge curves of the batteries with the functional materials of Examples 1-4 using metallic lithium as the negative electrode (vs. Li + / Li);

[0048] Figure 3 Cyclic voltammograms of the batteries with the functional materials of Examples 1-4 using metallic lithium as the negative electrode (vs. Li + / Li) in the voltage range of 2.0 V - 5.0 V;

[0049] Figure 4 Cyclic voltammograms of Example 4 with the functional materials using the reversible hydrogen electrode (RHE) as the reference electrode in the voltage range of 1.2 V - 2.0 V;

[0050] Figure 5 Cyclic voltammograms of the batteries with the functional materials of Examples 1-4 using metallic lithium as the negative electrode (vs. Li + / Li) in the voltage range of 0.001 V - 3.0 V;

[0051] Figure 6 Raman spectra of the functional materials obtained by disassembling the battery of Example 4 with the functional materials using metallic lithium as the negative electrode (vs. Li + / Li) after charging to different voltages;

[0052] Figure 7 Electronic conductivities of the compacts obtained by pressing the functional materials of Examples 1-4 into compacts with a diameter of 13 mm under a stress of 10 MPa and measured by the four-probe method;

[0053] Figure 8 SEM images of the functional materials of Examples 1-4;

[0054] Figure 9 XPS spectra of the Li-rich manganese-based cathode materials of Example 6 and Comparative Example 1 at different voltages during charge-discharge processes;

[0055] Figure 10 Gas component change diagrams detected by DEMS during the charge-discharge processes of the Li-rich manganese-based cathode materials of Example 6 and Comparative Example 1;

[0056] Figure 11 DSC curves of the positive electrode powder and the electrolyte after charging the surface and interface modified Li-rich manganese-based cathode materials of Example 6 and Comparative Example 1 to 4.8 V;

[0057] Figure 12 Cyclic capacity retention rate diagrams of the Li-rich manganese-based cathode materials of Example 6 and Comparative Example 1 at 45 °C in the voltage range of 2.0 V - 4.8 V;

[0058] Figure 13Capacity retention rate graphs of the lithium-rich manganese-based cathode material at different rates between 2.0V and 4.8V for Example 6 and Comparative Example 1. Detailed implementation manners

[0059] The present invention provides a functional material having both electronic conductivity, electrochemically controllable oxygen ion deintercalation / insertion, and lithium ion electrochemical activity, including elemental composition, chemical general formula characteristics, elemental valence characteristics, and functional characteristics of oxygen deintercalation / insertion, etc.

[0060] Among them, the chemical general formula of the functional material is:

[0061] R’ a R” b M c A’ d A” e Chemical formula (1)

[0062] In the chemical formula (1), R’ is one or more of alkali metals or alkaline earth metals Li, Na, K, Rb, Cs, Mg, Ca, Sr, and Ba;

[0063] R” is one or more of lanthanide rare earth elements La, Ce, Pr, Nd, Po, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Sc, Y;

[0064] M is one or more of transition metal elements Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Cd, and Ta that can change in multiple valence states;

[0065] A’ is O;

[0066] A” is one or more of S, Se, Te, F, Cl, Br, and I.

[0067] Preferably, R’ is selected from one or more of Li, Na, K, Ca, Sr, and Ba;

[0068] Preferably, R” is selected from one or more of lanthanide rare earth elements La, Ce, Pr, Nd, and Sc, Y;

[0069] Preferably, M is one or more of transition metal elements Ti, V, Cr, Mn, Fe, Co, Ni, and Cu;

[0070] Preferably, A” is one or more of S, Se, Te, and F;

[0071] Assume that the valence states of the elements R’, R”, M, A’, and A” are U, V, W, X, and Y respectively, then the chemical general formula R’ a R” b Mc A’ d A” e wherein, a, b, c, d, and e satisfy the relational expressions of Formula 5 and Formula 6:

[0072] a×U + b×V + c×W = d×X + e×Y (Formula 5)

[0073] (a + b):c:(d + e) = (n + 1):n:(3n + 1) (Formula 6)

[0074] wherein, U, V, W, X, Y, and n in the formula are positive integers greater than zero; a, b, c, d are rational real numbers greater than or equal to zero, including decimals; e = 0.

[0075] When n = 1, the chemical general formula is (R’ a’ R” b’ )2M(A’ d’ A” e’ )4, wherein a’ + b’ = 1, d’ + e’ = 1;

[0076] When n = 2, the chemical general formula is (R’ a’ R” b’ )3M2(A’ d’ A” e’ )7, wherein a’ + b’ = 1, d’ + e’ = 1;

[0077] When n = 3, the chemical general formula is (R’ a’ R” b’ )4M3(A’ d’ A” e’ ) 10 , wherein a’ + b’ = 1, d’ + e’ = 1;

[0078] When n = 100, the chemical general formula is (R’ a’ R” b’ ) 101 M 100 (A’ d’ A” e’ ) 301 , wherein a’ + b’ = 1, d’ + e’ = 1;

[0079] According to the chemical general formula and the preferred elements, the following is only for example and not for limitation. The functional material can be Pr2CuO4, Pr3Cu2O7, Pr4Cu3O 10 、Pr 101 Cu 100 O 301 、Pr2NiO4、Pr3Ni2O7、Pr4Ni3O 10 、Pr 101 Ni100 O 301 , Pr2FeO4, Pr2CoO4, Pr2MnO4, Sm2NiO4, Sc2NiO4, Y2NiO4, Nd2NiO4, Nd3Ni2O7, Nd4Ni3O 10 , Nd 101 Ni 100 O 301 , Sr 0.1 Pr 1.8 CuO4, Sr 0.2 Pr 2.8 Cu2O7, Sr 0.5 Pr 1.5 CuO4, Sr 0.4 Pr 3.6 Cu3O 10 , SrPr 99 Cu 100 O 301 , Li 0.1 Pr 1.8 CuO4, Li 0.2 Pr 2.8 Cu2O7, Li 0.2 Pr 1.8 CuO4, Li 0.4 Pr 3.6 Cu3O 10 , Li 0.2 Pr 1.8 Cu 0.5 Fe 0.5 O4, Li 0.2 Pr 1.8 Cu 0.5 Mn 0.5 O4, Li 0.5 Pr 100.5 Cu 100 O 301 , Li 0.2 Pr 1.8 Cu 0.33 Fe 0.33 -Mn 0.34 O4, Li 0.2 Pr 1.6 Ce 0.2 one or more of Pr2CeCuO4.

[0080] In the chemical general formula, the content of R' and the value assignment of n will affect the valence state of the M element. The change in its content can lead to the formation of a mixed state of multivalent ions of the M element. At the same time, the content of electrochemically controllable oxygen deintercalation / insertion in the lattice of the functional material is controlled by the mixed valence of the multivalent ions of the M element.

[0081] In the functional material, the valence of element M includes the non-highest valence state of element M, and / or, when a battery with metallic lithium as the negative electrode is charged and discharged, there are redox peaks in the cyclic voltammetry curve in the potential range of 2.0 - 5.0V;

[0082] Ions M with a valence of +w in element M W And ions M with a valence of +(w + 1) w+1 The molar ratio satisfies the relationship of formula 1:

[0083] C M w : C M w+1 =(1 - (V - U)×a) : (n - 1 + (V - U)×a) (Formula 1)

[0084] The mixed valence state (V hybrid ) of the multivalent ions of element M satisfies the relationship of formula 2:

[0085] V hybrid =W + 1 + (V×a - U×a - 1) / n (Formula 2)

[0086] In formula 1 and formula 2, C M w 、C M w+1 Are respectively the amount-of-substance ratios of M W And M w+1 ;

[0087] U is the valence of element R'; V is the valence of element R"; W is the valence of element M; n is the stoichiometric ratio of elements in chemical formula (1); U, V, W, and n are all positive integers greater than zero;

[0088] a is the content of element R', and its assignment range satisfies the relationship of formula 3:

[0089] 0 ≤ a ≤ 1 / 2 (V-U-1) (Formula 3)

[0090] In formula 3, a is the content of element R', U is the valence of element R'; V is the valence of element R"; U and V are positive integers greater than zero;

[0091] The theoretically electrochemically controllable maximum oxygen deintercalation / insertion content in the lattice of the functional material satisfies the relationship of formula 4:

[0092] O intercal. =(1 - V×a + U×a)×c / (2×n) (Formula 4)

[0093] In the formula, O intercal.It is the maximum theoretically electrochemically controllable oxygen deintercalation / insertion content in the lattice of the functional material. U is the valence of element R'; V is the valence of element R"; n is the stoichiometric ratio of elements in chemical formula (1), and U, V, and n are positive integers greater than zero; a is the content of element R', and its assignment range satisfies the relationship of formula 3.

[0094] The following will give an exemplary introduction to the content of formulas 1 to 4, which should not be understood as a limiting case.

[0095] Taking n = 1, Pr2NiO4 as an example, U = 0, V = 3, a = 0, b = 2, c = 1, (d + e) = 4. At this time, Ni(M) is a mixed-valence ion, C M w : C M w+1 = (1 - (V - U)×a) : (n - 1 + (V - U)×a) is:

[0096] C Ni 2+ : C Ni 3+ = (1 - (3 - 0)×0) : (1 - 1 + (3 - 0)×0) = 1 : 0

[0097] The mixed valence state (V hybrid ) of the multivalent ions of Ni element is:

[0098] V hybrid = W + 1 + (V×a - U×a - 1) / n = 2 + 1 + (3×0 - 0×0 - 1) / 1 = 2

[0099] The maximum theoretically electrochemically controllable oxygen deintercalation / insertion content in the lattice of the functional material is:

[0100] O intercal. = (1 - V×a + U×a)×c / (2×n) = (1 - 3×0 + 0×0)×1 / (2×1) = 0.5

[0101] For further example, introducing R' = Li, then the chemical general formula is Li a Pr b NiO4. At this time, U = 1, V = 3, a + b = 2, and the specific range needs to be determined according to the limiting range of a; c = 1. First, calculate the value range of a through the calculation formula 0 ≤ a ≤ 1 / 2 (V-U-1) Calculate the value range of a:

[0102] 0 ≤ a ≤ 1 / 2 (3-1-1)

[0103] That is, 0 ≤ a ≤ 0.5.

[0104] Taking a = 0.2, at this time the chemical formula of the functional material is Li 0.2 Pr1.8 NiO4, the proportion C of mixed-valence ions present in Ni(M) M w : C M w+1 =(1 - (V - U)×a) : (n - 1 + (V - U)×a) is:

[0105] C Ni 2+ : C Ni 3+ =(1 - (3 - 1)×0.2) : (1 - 1 + (3 - 1)×0.2)=0.6 : 0.4

[0106] The mixed valence (V hybrid ) of Ni multivalent ions is:

[0107] V hybrid =W + 1 + (V×a - U×a - 1) / n = 2 + 1 + (3×0.2 - 1×0.2 - 1) / 1 = 2.4

[0108] The theoretically electrochemically controllable maximum de- / intercalation oxygen content in the lattice of the functional material is:

[0109] O intercal. =(1 - V×a + U×a)·c / (2×n)=(1 - 3×0.2 + 1×0.2)×1 / (2×1)=0.3

[0110] For further example, replacing R' = Li with Sr, the chemical general formula is Sr a La b NiO4, at this time U = 2, V = 3, a + b = 2, the specific range needs to be taken according to the defined range of a; c = 1, first calculate the value range of a through the calculation formula 0 ≤ a ≤ 1 / 2 (V-U-1) Calculate the value range of a:

[0111] 0 ≤ a ≤ 1 / 2 (3-2-1)

[0112] That is, 0 ≤ a ≤ 1.

[0113] Taking a = 0.2, at this time the chemical formula of the functional material is Sr 0.2 Pr 1.8 NiO4, the proportion C of mixed-valence ions present in Ni(M) M w : C M w+1 =(1 - (V - U)×a) : (n - 1 + (V - U)×a) is:

[0114] C Ni 2+ : C Ni3+ =(1 - (3 - 2)×0.2) : (1 - 1 + (3 - 2)×0.2) = 0.8 : 0.2

[0115] The mixed valence state (V hybrid ) of Ni element polyvalent ions is as follows:

[0116] V hybrid = W + 1 + (V×a - U×a - 1) / n = 2 + 1 + (3×0.2 - 2×0.2 - 1) / 1 = 2.2

[0117] The theoretically electrochemically controllable maximum de / insertion oxygen content in the lattice of the functional material is:

[0118] O intercal. = (1 - V×a + U×a)×c / (2×n) = (1 - 3×0.2 + 2×0.2)×1 / (2×1) = 0.4

[0119] Similarly, if a = 0.5 is taken, the chemical formula of the functional material is Sr 0.5 Pr 1.5 NiO4, C Ni 2+ : C Ni 3+ = 0.5 : 0.5, V hybrid = 2.5, O intercal. = 0.25; if a = 1 is taken, the chemical formula of the functional material is SrPrNiO4, and the proportion C Ni 2+ : C Ni 3+ = 0 : 1, V hybrid = 3, O intercal. = 0. At this time, SrLaNiO4 theoretically cannot absorb oxygen components from the outside and insert them into the lattice, and its inhibitory effect on the oxidation precipitation of lattice oxygen on the surface and interface of the high-voltage lithium-rich manganese-based cathode material is also limited; therefore, the design of the type and content of R' element has a great influence on whether the functional material can electrochemically de / insert oxygen.

[0120] For further example, when n = 3, since a is not affected by n and still takes a = 0.2, the chemical formula of the functional material is Sr 0.2 Pr 3.8 Ni3O 10 , U = 2, V = 3, b = 3.8, c = 3, d + e = 10; the proportion C M w : C M w+1 = (1 - (V - U)×a) : (n - 1 + (V - U)×a) is as follows:

[0121] C Ni 2+ : C Ni 3+ =(1 - (3 - 2)×0.2) : (3 - 1 + (3 - 2)×0.2)=0.8 : 2.2

[0122] The mixed valence states (V hybrid ) of Ni multivalent ions are as follows:

[0123] V hybrid =W + 1 + (V×a - U×a - 1) / n = 2 + 1 + (3×0.2 - 2×0.2 - 1) / 3 = 2.73

[0124] The functional material Sr 0.2 Pr 3.8 Ni3O 10 The theoretically electrochemically controllable maximum oxygen deintercalation / insertion content in the lattice is:

[0125] O intercal. =(1 - V×a + U×a)×c / (2×n)=(1 - 3×0.2 + 2×0.2)×3 / (2×3)=0.4

[0126] Similarly, if n = 50, the chemical formula of the functional material at this time is Sr 0.2 Pr 50.8 Ni 50 O 151 , and the proportion C Ni 2+ : C Ni 3+ =0.8 : 49.2, V hybrid =2.98, O intercal. =0.4;

[0127] If n = 100, the chemical formula of the functional material is Sr 0.2 Pr 100.8 Ni 101 O 301 , and the proportion C Ni 2+ : C Ni 3+ =0.8 : 99.2, V hybrid =2.99, O intercal. =0.4.

[0128] The functional material provided by the present invention has both electronic conductivity, electrochemically controllable oxygen ion deintercalation / insertion, and lithium ion electrochemical activity.

[0129] In the present invention, among the synthetic raw materials of the functional material, the metal element medium can be an oxide, carbonate, acetate, oxalate, sulfate, etc.; the non-metal element medium can be a halide, oxide or elemental simple substance, etc.

[0130] Preferably, the metal element medium can be an oxide, and the non-metal element medium can be a halide or elemental simple substance.

[0131] The functional material is obtained by high-temperature sintering according to the stoichiometric ratio required by the calculation formula. The sintering temperature is 600-1200 °C, which can be 600, 700, 800, 900, 1000, 1100, 1200, or any value between 600-1200 °C. Preferably, it is any value between 800-1200 °C. The sintering time is 2-20 hours, which can be 2, 4, 6, 12, 15, 18, 20, or any value between 2-20 hours. Preferably, it is any value between 6-12 hours.

[0132] For elements such as sulfur (S) and iodine (I) that are easily oxidized, the oxygen partial pressure needs to be controlled during sintering, and the oxygen content is controlled below 2% (Vol.). In other cases where no special instructions are given, the sintering atmosphere is air.

[0133] The sintered functional material is first subjected to particle crushing by a high-energy vibration mill, and the particle D50 is controlled to be 6-9 μm. Then, it is further ground by a sand mill into nanoparticles with a particle size D50 of 20-200 nm, D max ≤1 μm nanoparticle slurry. The slurry solvent can be an oil-based system such as N-methylpyrrolidone (NMP), tetrahydrofuran (THF), and N,N-dimethylformamide (DMF), or a deionized water-based system.

[0134] Preferably, D50 is controlled to be 20-100 nm, and the slurry solvent is N-methylpyrrolidone (NMP).

[0135] The prepared functional material is assembled into a battery with metallic lithium as the negative electrode (vs. Li + / Li) and then charged and discharged. It satisfies that there is an oxidation characteristic peak above 4.40 V on the voltage-capacity differential curve dQ / dV or cyclic voltammogram. When assembled into a battery with a reversible hydrogen electrode (RHE) as the reference electrode in an alkaline aqueous solution, there is an oxidation-reduction characteristic peak in the 1.2-2.0 V interval of the voltage-capacity differential curve dQ / dV or cyclic voltammogram.

[0136] When the prepared functional material is assembled into a battery with metallic lithium as the negative electrode and charged to above 4.0 V, the Raman spectrum has peaks at 174 cm -1 and 380 cm -1 where the peak intensities are significantly weakened or the peaks disappear.

[0137] The prepared functional material is assembled into a battery with metallic lithium as the negative electrode, and there are lithium deintercalation / insertion redox peaks during cyclic voltammetry testing in the range of 0.001 V - 3.0 V.

[0138] The prepared functional material is assembled into a battery with metallic lithium as the negative electrode, and the lithium ion diffusion coefficient measured by variable scan rate cyclic voltammetry is higher than 10 -13 cm 2 / s.

[0139] After the functional material is pressed into a powder cake with a diameter of 13 mm under a stress of 10 MPa, the electronic conductivity of the powder cake measured by four-probe method is higher than 10 mS / cm.

[0140] In the present invention, the surface and interface modified lithium-rich manganese-based cathode material includes a lithium-rich manganese-based cathode material core and a functional material layer coated on the surface of the lithium-rich manganese-based cathode material core.

[0141] Among them, the present invention does not have any special restrictions on the type of the lithium-rich manganese-based cathode material core, and any lithium-rich manganese-based cathode material known to those skilled in the art can be used. Preferably, the chemical general formula of the core of the lithium-rich manganese-based cathode material is Li 1+x Mn y Ni z Co m O2, where 1 + x + y + z + m = 2, 0 ≤ x ≤ 2, 0 < y ≤ 1, 0 ≤ z, m ≤ 1.

[0142] The surface and interface modified lithium-rich manganese-based cathode material provided by the present invention realizes controllable oxygen reversible electrochemical deintercalation / insertion of the coating material and the lithium-rich manganese-based cathode material at different potentials, reduces the loss of oxygen, ensures the reversible utilization of active oxygen, and at the same time avoids the formation of oxygen by active oxygen and its escape to the interface to react with the electrolyte, realizing the high-temperature and high-voltage cycle stability and thermal stability of the material.

[0143] In the present invention, the preparation method of the lithium-rich manganese-based cathode material includes the following steps:

[0144] S1: Mix the lithium-rich manganese-based precursor and the lithium source, and obtain the lithium-rich manganese-based cathode material through a first sintering; among them, the present invention does not have any special restrictions on the mixing method, and any raw material mixing method known to those skilled in the art can be used. In the present invention, ball milling mixing is preferably used. The first high-temperature sintering temperature is 600 - 900 °C, which can be 600, 700, 800, 900, or any value between 600 - 900 °C, and the sintering time is 2 - 10 h, which can be 2, 3, 4, 5, 6, 7, 8, 9, 10, or any value between 2 - 10 h;

[0145] In some preferred embodiments of the present invention, the lithium-rich manganese-based cathode material is prepared by ball-milling and uniformly mixing a precursor with an appropriate amount of a lithium source, followed by three-stage sintering temperature regimes: a low temperature of 250-400°C for 2-4 hours, a medium temperature of 600-700°C for 10-15 hours, and a high temperature of 800-900°C for 2-10 hours.

[0146] S2: The nanoparticle slurry of the functional material is mixed with the lithium-rich manganese-based cathode material and then dried to obtain a powder. In the present invention, there are no special restrictions on the preparation method of the nanoparticle slurry of the functional material, and any slurry preparation method known to those skilled in the art can be used. In the present invention, the slurry is preferably obtained by a sand milling method. In the present invention, the mass ratio of the coated nano-functional material in the powder is 0.1 wt.% to 5.0 wt.%, and can be 0.1 wt.%, 0.3 wt.%, 0.5 wt.%, 0.7 wt.%, 1 wt.%, 1.5 wt.%, 2 wt.%, 2.5 wt.%, 3 wt.%, 3.5 wt.%, 4 wt.%, 4.5 wt.%, 5 wt.%, or any value between 0.1 wt.% and 5.0 wt.%, preferably any value between 0.5 wt.% and 2.0 wt.%.

[0147] S3: The powder obtained in S2 is subjected to high-temperature secondary sintering to obtain the surface and interface modified lithium-rich manganese-based cathode material. Among them, the temperature of the high-temperature secondary sintering is 350°C to 1000°C, and can be 350, 400, 500, 600, 700, 800, 900, 1000, or any value between 350°C and 1000°C, preferably any value between 550 and 800°C. The time is 2-8 hours, and can be 2, 3, 4, 5, 6, 7, 8, or any value between 2-8 hours, preferably any value between 2-4 hours. Among them, the atmosphere of the high-temperature secondary sintering is preferably an air atmosphere condition.

[0148] The surface and interface modified lithium-rich manganese-based cathode material is assembled into a battery with metallic lithium as the anode, and charged and discharged in the voltage range of 2.0-4.8V in the first cycle. X-ray photoelectron spectroscopy (XPS) analysis is performed on O, F, and P on the surface of the positive electrode sheet. The O1s 531.2 eV ROLi organic peak, the F1s 685.0 eV LiF peak, and the P2p 136.4 eV Li x PO y F z The peak intensity shows a significant decrease compared to the unmodified control sample.

[0149] The surface and interface modified lithium-rich manganese-based cathode material is assembled into a battery with metallic lithium as the anode, and charged and discharged in the voltage range of 2.0-4.8V in the first cycle. The oxygen content detected by differential electrochemical mass spectrometry (DEMS) is less than 100 μmol / mg.

[0150] In the present invention, TOF-SIMS analysis is performed on the above functional material-coated lithium-rich manganese-based cathode material with surface modification, and a uniform coating is formed within the range of 50 nm on the surface layer of the lithium-rich manganese-based cathode material.

[0151] See Figure 1 , Figure 1 which is a schematic diagram of the electrochemical deintercalation / insertion of oxygen and the transport of lithium ions between the functional material and the lithium-rich manganese-based cathode material during the charging process. Figure 1 In [reference], when the lithium-rich manganese-based cathode material is charged, lithium ions are removed from the layered structure and transported and diffused into the electrolyte from the lithium ion channels when passing through the coating material; when further charged to above 4.5 V, the lattice oxygen of the layered cathode material loses electrons and undergoes oxidation to form O2, O2 - , O - and oxygen oligomers O n- and other substances, which then escape to the surface interface of the cathode material; under the drive of the electric field, the functional coating material absorbs and embeds the oxygen component into the tetrahedral lattice formed by adjacent R’ or R”, and at the same time, accompanied by the oxidation state change of transition metal lithium ions, it prevents the oxygen component from further escaping to the surface interface of the cathode material to contact the electrolyte, inhibiting the oxidation and decomposition of the electrolyte by the oxygen component; during the discharging process, on the contrary, under the drive of the electric field, the functional material releases the absorbed oxygen, enabling the oxygen to participate in the reduction reaction of the cathode; the above process realizes the reversible utilization of lattice oxygen in the cathode material at high voltages, inhibits the precipitation of oxygen, and ensures the promoting effect of oxygen activity on the high-capacity characteristics of the material.

[0152] The present invention also provides a lithium-ion secondary battery, which includes a positive electrode plate, a negative electrode plate, a separator, and an electrolyte. The positive electrode plate includes the above-mentioned lithium-rich manganese-based cathode material with surface modification.

[0153] The positive electrode plate is prepared by transfer coating, extrusion coating, or gravure coating. For example, first, the positive electrode active material, binder, conductive agent, and organic solvent are mixed in a predetermined ratio. The organic solvent can be N-methylpyrrolidone (NMP). The mixed material is stirred into a homogeneous system to obtain a positive electrode slurry; then the positive electrode slurry is coated on the positive electrode current collector, and after processes such as drying and rolling, the positive electrode plate is obtained.

[0154] The negative electrode plate is prepared by transfer coating, extrusion coating, or gravure coating. For example, first, the negative electrode active material, binder, conductive agent, and solvent are mixed in a predetermined ratio. The organic solvent can be deionized water. The mixed material is stirred into a homogeneous system to obtain a negative electrode slurry; then the negative electrode slurry is coated on the negative electrode current collector, and after processes such as drying and rolling, the negative electrode plate is obtained.

[0155] The electrolyte includes a lithium salt, an additive, and a solvent, which functions to transport ions between the positive and negative electrodes;

[0156] As some examples, the solvent in the electrolyte is a non-aqueous organic solvent, such as ethylene carbonate (EC), fluoroethylene carbonate (FEC), propylene carbonate (PC), fluoropropylene carbonate (FPC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), and ethyl butyrate (EB), one or more of which are preferably two or more.

[0157] Further preferably, the solvent can be two or more of ethylene carbonate (EC), fluoroethylene carbonate (FEC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and dimethyl carbonate (DMC).

[0158] As some examples, the lithium salt in the electrolyte is a lithium compound with a relatively high ionization degree, such as lithium hexafluorophosphate (LiPF6), lithium hexafluoroarsenate (LiAsF6), lithium perchlorate (LiClO4), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0159] Preferably, the lithium salt can be lithium hexafluorophosphate (LiPF6) combined with a small amount of any one or more of the other lithium salts.

[0160] The function of the additive in the electrolyte is to form a stable solid electrolyte layer at the positive and negative electrode interfaces, reducing the continuous side reactions between the electrodes and the electrolyte at high or low voltages. The additives include salts, solid organic powders, and liquid organic substances.

[0161] As some examples, the solid organic powder additives in the electrolyte include vinylene carbonate (VC), ethylene vinylene carbonate (VEC), fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), trifluoromethyl ethylene carbonate (TFPC), methylene methanedisulfonate (MMDS), 1,3-propane sultone (1,3-PS), 1-propene-1,3-sultone (PST), and divinyl sulfite (DTD); the salts include lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiC2BF2O4), lithium difluorophosphate (LiPO2F2), lithium tetrafluoroborate (LiBF4), and lithium bis(oxalato)difluorophosphate (LiC4O8F2P); the liquid organic substances include bis(2,2,2-trifluoroethyl) carbonate (TFEC), triethyl borate (TEB), trimethoxycyclotriboroxane (TMEB), and difluoroethyl carbonate (DFDEC).

[0162] Preferably, the solid organic additive may be two or more of vinylene carbonate (VC), ethylene vinylene carbonate (VEC), methylene methanedisulfonate (MMDS), 1,3 - propane sultone (1,3 - PS), 1 - propene - 1,3 - sultone (PST), and divinyl sulfate (DTD).

[0163] More preferably, the content of the solid organic additive is 0.1 wt.% to 4 wt.%, and it can be 0.1 wt.%, 0.3 wt.%, 0.5 wt.%, 1 wt.%, 1.5 wt.%, 2 wt.%, 2.5 wt.%, 3 wt.%, 3.5 wt.%, 4 wt.%, or any value between 0.1 wt.% and 4 wt.%.

[0164] Preferably, the lithium salt additive may be, but is not limited to, one or more of lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiC2BF2O4), lithium difluorophosphate (LiPO2F2), and lithium bis(oxalato)difluorophosphate (LiC4O8F2P).

[0165] More preferably, the content of the lithium salt additive is 0.1 wt.% to 1 wt.%, and it can be 0.1 wt.%, 0.2 wt.%, 0.3 wt.%, 0.4 wt.%, 0.5 wt.%, 0.6 wt.%, 0.7 wt.%, 0.8 wt.%, 0.9 wt.%, 1 wt.%, or any value between 0.1 wt.% and 1 wt.%.

[0166] There is no particular limitation on the separator for the lithium - ion secondary battery of the embodiment of the present invention, and any well - known separator can be used, including PP film, PE film, alumina - coated separator, polymer - coated separator, and solid - electrolyte - coated separator.

[0167] To further understand the present invention, the surface - modified lithium - rich manganese - based cathode material and the lithium - ion secondary battery provided by the present invention will be described below in conjunction with embodiments, and the protection scope of the present invention is not limited by the following embodiments.

[0168] The following embodiments more specifically describe the content disclosed by the present invention. These embodiments are only for illustrative purposes, because various modifications and changes within the scope of the content disclosed by the present invention are obvious to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on weight, and all reagents used in the embodiments are commercially available or synthesized according to conventional methods and can be used directly without further treatment, and the instruments used in the embodiments are all commercially available.

[0169] Example 1

[0170] The preparation method of the surface-modified lithium-rich manganese-based positive electrode material provided in this embodiment comprises the following steps:

[0171] Lithium carbonate and nickel-cobalt-manganese precursor Ni 0.16 Co 0.16 Mn 0.68 The mixed material was placed in a box furnace, heated to 350°C at a heating rate of 5°C / min in an air atmosphere, kept warm for 2 hours, then heated to 600°C at a heating rate of 5°C / min and kept warm for 10 hours, and then heated to 850°C at a heating rate of 5°C / min and kept warm for 8 hours. After cooling, the lithium-rich manganese-based positive electrode material Li 1.2 Mn 0.54 Ni 0.13 Co 0.13 O2;

[0172] The praseodymium oxide and the copper oxide in a stoichiometric ratio are mixed uniformly, the mixture is placed in a muffle furnace, the temperature is increased to 700°C at a heating rate of 5°C / min in an air atmosphere, the temperature is kept for 24 hours, and the Pr2CuO4 functional material is obtained after cooling;

[0173] The Pr2CuO4 functional material is placed in a high-energy vibration mill to crush the particles to a particle size of about D50 = 6um, and then input into a sand mill for grinding, NMP solvent system, after grinding for 24-36 hours, the particle size D50 is controlled to be 50-200nm, and the solid content of the particles is controlled to be 10-30%, preferably the particle size is controlled to be 50nm, and the solid content is 20%;

[0174] The functional material slurry and the lithium-rich manganese-based positive electrode material were weighed according to a coating amount of 0.3 wt.%, fully dispersed in a planetary mixer for 2 h, and then dried to obtain the material;

[0175] The mixed material was placed in a muffle furnace, heated to 600°C at a heating rate of 5°C / min in an air atmosphere, kept warm for 2 hours, and after cooling, a lithium-rich manganese-based positive electrode material coated with Pr2CuO4 functional material was obtained.

[0176] Example 2

[0177] In this embodiment, the sintering temperature of the Pr2CuO4 functional material in Embodiment 1 is changed to 800°C, and the other conditions remain unchanged.

[0178] Example 3

[0179] In this embodiment, the sintering temperature of the Pr2CuO4 functional material in Embodiment 1 is changed to 900°C, and the other conditions remain unchanged.

[0180] Example 4

[0181] In this embodiment, the sintering temperature of the Pr2CuO4 functional material in Embodiment 1 is changed to 1000 °C, and the other conditions remain unchanged.

[0182] Example 5

[0183] In this embodiment, the coating amount of 0.3 wt.% in Embodiment 4 is changed to 0.5 wt.%, and the other conditions remain unchanged.

[0184] Example 6

[0185] In this embodiment, the coating amount of 0.3 wt.% in Embodiment 4 is changed to 1.0 wt.%, and the other conditions remain unchanged.

[0186] Example 7

[0187] In this embodiment, the Pr2CuO4 functional material in Embodiment 6 is changed to a Pr2NiO4 functional material, and the raw materials are praseodymium oxide and nickel oxide, and the other conditions remain unchanged.

[0188] Example 8

[0189] In this embodiment, the Pr2CuO4 functional material in Embodiment 6 is changed to a Pr2FeO4 functional material, and the raw materials are praseodymium oxide and ferrous oxide, and the other conditions remain unchanged.

[0190] Example 9

[0191] In this embodiment, the Pr2CuO4 functional material in Embodiment 6 is changed to a Pr2CoO4 functional material, and the raw materials are praseodymium oxide and cobalt oxide, and the other conditions remain unchanged.

[0192] Example 10

[0193] In this embodiment, the Pr2CuO4 functional material in Embodiment 6 is changed to a Pr2MnO4 functional material, and the raw materials are praseodymium oxide and manganese oxide, and the other conditions remain unchanged.

[0194] Example 11

[0195] In this embodiment, the Pr2CuO4 functional material in Embodiment 6 is changed to a Sm2NiO4 functional material, and the raw materials are samarium oxide and nickel oxide, and the other conditions remain unchanged.

[0196] Example 12

[0197] In this embodiment, the Pr2CuO4 functional material in Embodiment 6 is changed to a Nd2NiO4 functional material, and the raw materials are nickel oxide and neodymium oxide, and the other conditions remain unchanged.

[0198] Example 13

[0199] In this embodiment, the Pr2CuO4 functional material in Embodiment 6 is changed to a Sc2NiO4 functional material, and the raw materials are scandium oxide and nickel oxide, with the remaining conditions unchanged.

[0200] Example 14

[0201] In this embodiment, the Pr2CuO4 functional material in Embodiment 6 is changed to a Y2NiO4 functional material, and the raw materials are yttrium oxide and nickel oxide, with the remaining conditions unchanged.

[0202] Example 15

[0203] In this embodiment, the Pr2CuO4 functional material in Embodiment 6 is changed to a Li 0.2 Pr 1.8 CuO4 functional material, and the raw materials are lithium carbonate, praseodymium oxide, and copper oxide, with the remaining conditions unchanged.

[0204] Example 16

[0205] In this embodiment, the Pr2CuO4 functional material in Embodiment 6 is changed to a Li 0.5 Pr 1.5 CuO4 functional material, and the raw materials are lithium carbonate, praseodymium oxide, and copper oxide, with the remaining conditions unchanged.

[0206] Example 17

[0207] In this embodiment, the Pr2CuO4 functional material in Embodiment 6 is changed to a Sr 0.5 Pr 1.5 CuO4 functional material, and the raw materials are strontium carbonate, praseodymium oxide, and copper oxide, with the remaining conditions unchanged.

[0208] Example 18

[0209] In this embodiment, the Pr2CuO4 functional material in Embodiment 6 is changed to a SrPrCuO4 functional material, and the raw materials are strontium carbonate, praseodymium oxide, and copper oxide, with the remaining conditions unchanged.

[0210] Example 19

[0211] In this embodiment, the Pr2CuO4 functional material in Embodiment 6 is changed to a Li 0.2 Pr 1.8 Cu 0.5 Fe 0.5 O4 functional material, and the raw materials are lithium carbonate, praseodymium oxide, copper oxide, and iron oxide, with the remaining conditions unchanged.

[0212] Example 20

[0213] In this embodiment, the Pr2CuO4 functional material in Embodiment 6 is changed to Li 0.2 Pr 1.8 Cu 0.5 Mn 0.5 O4 functional material, and the raw materials are lithium carbonate, praseodymium oxide, copper oxide and manganese oxide, and the remaining conditions remain unchanged.

[0214] Example 21

[0215] In this embodiment, the Pr2CuO4 functional material in Embodiment 6 is changed to Li 0.2 Pr 1.8 Cu 0.33 Fe 0.33 -Mn 0.34 O4 functional material, and the raw materials are lithium carbonate, praseodymium oxide, copper oxide, ferrous oxide and manganese oxide, and the remaining conditions remain unchanged.

[0216] Example 22

[0217] In this embodiment, the Pr2CuO4 functional material in Embodiment 6 is changed to Li 0.2 Pr 1.6 Ce 0.2 CuO4 functional material, and the raw materials are lithium carbonate, praseodymium oxide, cerium oxide and copper oxide, and the remaining conditions remain unchanged.

[0218] Example 23

[0219] In this embodiment, the Pr2CuO4 functional material in Embodiment 6 is changed to Pr3Ni2O7 functional material, and the raw materials are praseodymium oxide and nickel oxide, and the remaining conditions remain unchanged.

[0220] Example 24

[0221] In this embodiment, the Pr2CuO4 functional material in Embodiment 6 is changed to Pr4Ni3O 10 Functional material, and the raw materials are praseodymium oxide and nickel oxide, and the remaining conditions remain unchanged.

[0222] Comparative Example 1

[0223] In this comparative example, the Pr2CuO4 functional material in Embodiment 6 is changed to Al2O3, and the remaining conditions remain unchanged.

[0224] Comparative Example 2

[0225] In this comparative example, the Pr2CuO4 functional material in Example 6 was changed to Y2O3, and the other conditions remained unchanged.

[0226] Comparative Example 3

[0227] In this comparative example, the Pr2CuO4 functional material in Example 6 was changed to TiO2, and the other conditions remained unchanged.

[0228] Comparative Example 4

[0229] In this comparative example, the Pr2CuO4 functional material in Example 6 was changed to ZrO2, and the other conditions remained unchanged.

[0230] Comparative Example 5

[0231] In this comparative example, the Pr2CuO4 functional material in Example 6 was changed to lithium titanium aluminum phosphate (LATP), and the other conditions remained unchanged.

[0232] Characterization and Analysis

[0233] Scanning electron microscope (SEM): For surface morphology characterization, a field emission electron microscope (FE-SEM, S4800) model S4800 from Hitachi, Japan was used.

[0234] X-ray photoelectron spectroscopy (XPS) test: For XPS test, an ESCALAB 250Xi photoelectron spectrometer from Thermo Fisher Scientific was used, and the light source was monochromatic Al Kα X-ray. The sample preparation process is as follows: The cycled battery was disassembled in a glove box. After taking out the positive electrode sheet, it was washed three times with DMC to remove the residual electrolyte and then placed in the transition chamber of the glove box to evacuate for 2 h to remove the solvent. The sample was transferred to the XPS instrument using a self-made sample transfer box from Thermo Fisher to avoid contact of the sample with air. The obtained test data was fitted and quantitatively analyzed using Avantage software. The energy correction of the spectral data was to correct the peak position energy value corresponding to the C-C bond (conductive additive) in the C1s spectrum to 284.8 eV.

[0235] X-ray diffraction (XRD): The equipment used for the phase characterization of the sample was an X-ray diffractometer from Bruker, Germany, with the equipment model being D8 Advance diffractometer. The used X-ray source was Cu Kα, the scanning angle range was 10 - 80°, and the scanning speed was 0.05° / min.

[0236] Time-of-flight secondary ion mass spectrometer (TOF-SIMS): PHI nano TOFⅡ from Japan, an O 2+ oxygen cluster ion source, a Cs of 0.25 - 2 keV +Cesium ion source and Ar with an energy of 2.5 - 20 keV + The argon cluster ion source is used to collect surface mass spectrometry, depth profiling, and imaging data of the sample.

[0237] Simultaneous thermal analyzer (DSC): The instrument model used is Netzsch STA499C from Germany. Before the test, the sample powder charged to 4.8 V was scraped from the current collector. 2 mg of the sample and 1 mL of the electrolyte were added to a stainless - steel high - pressure sealed crucible for testing. The heating rate was 5 °C / min, and the test temperature range was 50 - 600 °C.

[0238] Electronic conductivity: The electronic conductivity of the material was measured using a four - probe resistance analyzer RTS - 5 (Guangzhou Four - Probe). 0.1 g of the powder was placed in a 15 - mm wafer making machine, and after applying a stress of 12 kN to form a wafer, it was placed in the four - probe instrument to measure the electronic conductivity.

[0239] Differential electrochemical mass spectrometer (DEMS): An in - situ differential electrochemical mass spectrometer built using Hiden HRP - 20 from the UK was used to detect the oxygen release rate in real - time.

[0240] Raman spectroscopy (Raman): The equipment used was a ThermoFisher DXR laser micro - Raman spectrometer, with a laser wavelength of 523 nm and a measurement range of 0 - 1600 cm -1 。

[0241] Determination of oxygen de - insertion / insertion content: At 25 °C, the absolute oxygen excess stoichiometry value (σ) was determined using the reverse dichromate titration method. This method is based on treating the sample with a known excess of Fe(II) and then titrating with a standard potassium dichromate (K2Cr2O7) solution. Chemically pure Mohr's salt (Fe(NH4)2(SO4)2·6H2O) was used as the source of Fe(II), and 1:4 hydrochloric acid (HCl, chemically pure grade) was used as the solvent for the complex oxide to be analyzed. The potassium dichromate in the working solution was prepared from high - purity K2Cr2O7. The functional material powder was pre - purged with argon to prevent the release of oxygen into the atmosphere when the sample was dissolved. The powder was dissolved in HCl with Mohr's salt in an argon atmosphere, and potentiometric titration was carried out with 0.1 N standard potassium dichromate, and the potentiometric titration end - point was fixed using an ATP - 02 automatic titrator. The oxygen content in the functional material was calculated using the following formula:

[0242]

[0243] Battery Preparation:

[0244] Preparation of the electrode: The samples of the lithium-rich manganese-based cathode materials of the examples and comparative examples, acetylene black, and polyvinylidene fluoride were placed in a vacuum drying oven at 60 °C for 12 h. The dried materials were taken and added to N-methylpyrrolidone as a solvent in a mass ratio of 8:1:1 and mixed thoroughly. The uniformly dispersed slurry was evenly coated on an aluminum foil current collector in a dew point chamber. The electrode was placed in an oven at 55 °C for 5 h until the NMP was completely volatilized, and then cut into circular pieces with a diameter of 12 mm. After weighing, it was placed in a vacuum oven at 120 °C for 6 h to completely remove the water and solvent in the electrode. Finally, the dried electrode was taken out and transferred to a glove box. The areal density of the active material of the prepared electrode was about 3-5 mg / cm 2 or so.

[0245] Battery assembly: The battery was assembled in a glove box filled with argon. The used coin cell case model was R2032 (made of 304 stainless steel). The electrolyte was the electrolyte prepared in the examples and comparative examples of the present invention, FEC:EMC = 2:8 (Vol.%), 1.2 mol / L LiPF6. The separator was a 25-μm polypropylene separator, and the negative electrode was a lithium metal sheet with a diameter of 16.3 mm and a thickness of 500 μm.

[0246] Battery Testing:

[0247] Formation and grading: After the battery was assembled, it was left standing for more than 2 h to allow the electrolyte to fully infiltrate the inside of the electrode. Then, charge-discharge tests were carried out on a Land CT 3002A (Wuhan Blue Electric) charge-discharge tester. The formation and grading current density was 25 mA / g, the voltage range was 2.0-4.8 V, and the standard specific capacity C0 (mAh / g) was determined by cycling 3 times.

[0248] Cycling test: 25 °C / 45 °C, 1.0C / 1.0C, 2.0-4.8 V, 1.0C = C0 (mAh / g).

[0249] Rate test: 25 °C, 0.1C / 0.1C, 0.2C / 0.2C, 0.3C / 0.3C, 0.5C / 0.5C, 1.0C / 1.0C, 2.0C / 2.0C, 5.0C / 5.0C, 2.0-4.8 V, 1.0C = C0 (mAh / g).

[0250] EIS AC impedance test: A Zahner electrochemical workstation (Zahner, Germany) was used, and the test frequency was 5 MHz - 50 mHz, and the voltage amplitude was 10 mV.

[0251] Cyclic voltammetry test: It was tested using a CHI604E electrochemical workstation (Shanghai Chenhua Instrument Co., Ltd.). The scan was carried out at room temperature, and the scan rate was 0.1-0.6 mV / s. The oxidation-reduction peak potential was obtained through cyclic voltammetry test, and the lithium ion diffusion coefficient was obtained through variable scan rate cyclic voltammetry test.

[0252] The physical property parameters of the above-exemplified embodiments and the comparative example of the surface-modified lithium-rich manganese-based cathode material are summarized in Table 1 as follows.

[0253] Table 1

[0254]

[0255]

[0256] The electrochemical performance of the above-exemplified embodiments and the comparative example of the surface-modified lithium-rich manganese-based cathode material are summarized in Table 2 as follows.

[0257] Table 2

[0258]

[0259]

[0260] As can be seen from the above, the present invention provides a surface-modified lithium-rich manganese-based cathode material and a lithium-ion secondary battery, aiming to use a functional coating material to absorb and embed active oxygen substances, such as O 2 , O2 - , O - , and oxygen oligomers O n- , etc. into the lattice gaps at the surface and interface of the lithium-rich manganese-based cathode material particles when charging to a high voltage under the driving of the electric potential, and release active oxygen when discharging to a low potential. The lithium-rich manganese-based cathode material modified by the functional material has good electrochemical performance in the lithium-ion secondary battery.

[0261] From the comparative analysis of Example 1 and Example 4, it can be seen that for the coating materials with the same theoretical oxygen content that can be deintercalated / inserted in the lattice, the initial oxidation peak potential of Example 4 is lower, and the oxygen content monitored by DEMS is lower (60.3 mmol / g vs. 71.3 mmol / g). The cycle capacity retention rate at 45 °C for 200 th cycles is higher (75.3% vs. 69.8%), and the DSC thermal decomposition temperature is also increased (145.5 °C vs. 143.2 °C).

[0262] By comparing Example 6 with Examples 16 and 18, it is found that for the samples without the theoretical oxygen content that can be deintercalated / inserted in the lattice, the oxygen content monitored by DEMS is very high (46.4 mmol / g vs. 421.4 mmol / g), and the DSC thermal decomposition temperature decreases (146.7 °C vs. 140.2 °C), and the cycle stability at 45 °C is also significantly deteriorated (78.1% vs. 71.6%).

[0263] Comparing Examples 1-24 with Comparative Examples 1-5, for all those using the technical solutions provided by the present invention, the oxygen content monitored by DEMS was significantly reduced, the cycle stability was improved, and the thermal stability of the high delithiated state lithium-rich manganese-based cathode material was also improved.

[0264] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A surface-modified lithium-rich manganese-based cathode material, characterized in that, It includes a core of a lithium-rich manganese-based cathode material and a functional material layer coated on the surface of the lithium-rich manganese-based cathode material core. The chemical general formula of the functional material is shown in Chemical Formula (1): R’ a R” b M c A’ d A” e Chemical formula (1) In Chemical Formula (1), R' is one or more of alkali metals or alkaline earth metals Li, Na, K, Rb, Cs, Mg, Ca, Sr, and Ba; R" is one or more of lanthanide rare earth elements La, Ce, Pr, Nd, Po, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Sc, Y; M is one or more of transition metal elements Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Cd, and Ta that can change valence states; A' is O; A" is one or more of S, Se, Te, F, Cl, Br, and I; In the functional material, the valence state of the M element includes the non-highest valence state of the M element, and / or when a battery with metallic lithium as the negative electrode is formed, there are oxidation-reduction peaks in the cyclic voltammogram curve in the potential range of 2.0 - 5.0V; Ion M with a valence of +w in element M W and ion M with a valence of +(w + 1) w+1 The molar ratio satisfies the relationship of Equation 1: C M w : C M w+1 = (1 - (V - U) × a) : (n - 1 + (V - U) × a) (Equation 1) The mixed valence state (V hybrid ) of the multivalent ions of element M satisfies the relational expression of Equation 2: V hybrid = W + 1 + (V × a - U × a - 1) / n (Equation 2) In Formula 1 and Formula 2, C M w , C M w+1 are the molar ratios of M W to M w+1 respectively; U is the valence of the R' element; V is the valence of the R" element; W is the valence of the M element; n is the stoichiometric ratio of elements in Chemical Formula (1); U, V, W, and n are all positive integers greater than zero; a is the content of the R' element, and its assignment range satisfies the relationship of Equation 3: 0 ≤ a ≤ 1 / 2 (V-U-1) (Equation 3) In Equation 3, a is the content of the R' element, U is the valence of the R' element; V is the valence of the R" element; U and V are positive integers greater than zero; The theoretically electrochemically controllable maximum oxygen deintercalation / insertion content in the lattice of the functional material satisfies the relationship of Equation 4: O intercal. = (1 - V×a + U×a)×c / (2×n) (Equation 4) Where O intercal. is the maximum theoretically electrochemically controllable oxygen deintercalation / insertion content in the lattice of the functional material, U is the valence of element R', V is the valence of element R", n is the stoichiometric ratio of elements in chemical formula (1), and U, V, and n are positive integers greater than zero; a is the content of element R', and its assignment range satisfies the relationship of formula 3; Assume that the valences of elements R’, R”, M, A’ and A” are U, V, W, X and Y respectively, then the chemical general formula R’ a R” b M c A’ d A” e in which a, b, c, d and e satisfy the relational expressions of Formula 5 and Formula 6: a×U + b×V + c×W = d×X + e×Y (Equation 5) (a + b):c:(d + e)=(n + 1):n:(3n + 1) (Equation 6). In Equation 5 and Equation 6, U, V, W, X, Y, and n are positive integers greater than zero; a, b, c, and d are rational real numbers greater than or equal to zero, including decimals; e = 0.

2. The lithium-rich manganese-based cathode material according to claim 1, wherein When the functional material is assembled into a battery with metallic lithium as the negative electrode, when charging to above 4.0V, there is a phenomenon that the peak intensity at 174 cm -1 and 380 cm -1 weakens or the peak disappears in the Raman spectrum.

3. The lithium-rich manganese-based cathode material according to claim 1, characterized in that, When the functional material is assembled into a battery with metallic lithium as the negative electrode for charge and discharge, there is an oxidation characteristic peak above 4.40V in the voltage-capacity differential curve dQ / dV or the cyclic voltammogram curve; Or, after the functional material forms a battery with a reversible hydrogen electrode (RHE) as the reference electrode in an alkaline aqueous solution, there are oxidation-reduction characteristic peaks in the voltage-capacity differential curve dQ / dV or the cyclic voltammogram curve in the range of 1.2 - 2.0V; 4. The lithium-rich manganese-based cathode material according to claim 1, wherein, When the functional material is assembled into a battery with metallic lithium as the negative electrode for charge and discharge, there are lithium deintercalation / insertion oxidation-reduction peaks in the voltage-capacity differential curve dQ / dV or the cyclic voltammogram curve in the range of 0.001V - 3.0V; And / or, the functional material is assembled into a battery with metallic lithium as the negative electrode, and the lithium ion diffusion coefficient measured by variable sweep rate cyclic voltammetry is higher than 10 -13 cm 2 / s.

5. The lithium-rich manganese-based cathode material according to claim 1, characterized in that, After the functional material is pressed into a powder cake with a diameter of 13mm under a stress of 10MPa, the electronic conductivity of the powder cake measured by a four-probe method is higher than 10mS / cm.

6. The lithium-rich manganese-based cathode material according to claim 1, characterized in that, The surface-modified lithium-rich manganese-based cathode material is assembled into a battery with metallic lithium as the anode, and charged and discharged in the voltage range of 2.0 - 4.8 V during the first cycle. X-ray photoelectron spectroscopy (XPS) is performed on O, F, and P on the surface of the positive electrode sheet. The organic peak of O1s at 531.2 eV is ROLi, the LiF peak of F1s at 685.0 eV, and the peak of P2p at 136.4 eV is Li x PO y F z The peak intensity is lower than that of the surface-unmodified lithium-rich manganese-based cathode material; And / or, when the surface and interface modified lithium-rich manganese-based cathode material is assembled into a battery with metallic lithium as the negative electrode, and charged and discharged in the range of 2.0 - 4.8V in the first cycle, the oxygen content detected by differential electrochemical mass spectrometry (DEMS) is less than 100umol / mg.

7. The lithium-rich manganese-based cathode material according to claim 1, wherein The chemical general formula of the core of the lithium-rich manganese-based cathode material is Li 1+x Mn y Ni z Co m O2, where 1 + x + y + z + m = 2, 0 ≤ x ≤ 2, 0 < y ≤ 1, 0 ≤ z, m ≤ 1.

8. A method for preparing a lithium-rich manganese-based cathode material according to any one of claims 1 to 7, characterized in that, It includes the following steps: S1: Mix the lithium-rich manganese-based precursor with a lithium source and perform primary sintering to obtain the core of the lithium-rich manganese-based cathode material; S2: Mix the nanoparticle slurry of the functional material with the core of the lithium-rich manganese-based cathode material and then dry it to obtain a powder; S3: Perform secondary high-temperature sintering on the powder to obtain the surface and interface modified lithium-rich manganese-based cathode material.

9. A lithium ion secondary battery, characterized in that, Comprising the surface and interface modified lithium-rich manganese-based cathode material according to any one of claims 1 to 7.

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