CN118825256A - A positive electrode material and a battery and an electric device containing the same - Google Patents

Abstract

The application relates to a multi-cation positive electrode material, which has a general formula of Li _aL_xNi_bCo_cMn_dM_{(1‑b‑c‑d)}O_eN_f or mLi₂MnO₃·(1-m)Li_aL_xNi_bCo_cMn_dM_{(1‑b‑c‑d)}O_eN_f,, wherein L ions are cations with a radius larger than that of Li ions, M comprises at least one of Mg, zr, al, B, ta, mo, W, nb, sb, la, N comprises at least one of F, S and P, 0 < a < 1,0 < b < 1,0 < c < 1,0 < d < 1,0 < b+c+d < 1,0 < e < 2,0 < f < 2,0 < M < 1,0 < x < 0.8, a+x=1, e+f=2, and the following relational expression is satisfied: 2.5 x 10 ^‑6≤x/v≤2.5×10^‑3, wherein v is the gram capacity of the polycationic positive electrode material. The application also relates to a lithium ion battery containing the positive electrode material and an electric device containing the lithium ion battery.

Description

A positive electrode material and a battery and an electric device containing the same

Technical Field

The present application relates to the field of battery technology, and in particular to a positive electrode material and a battery and an electrical device containing the same.

Background Art

Lithium-ion batteries are now widely used in pure electric vehicles, hybrid electric vehicles, smart grids and other fields. With the large-scale application of lithium-ion batteries, the field has also put forward higher requirements for their energy density, rate performance and safety performance. With the increase in people's demand for lithium-ion energy density, layered positive electrode materials have gradually developed from the earliest low-nickel materials to today's high-nickel and lithium-rich manganese-based high-gram capacity materials. However, due to factors such as lithium-nickel mixing, the structural stability of high-nickel and lithium-rich manganese-based materials is poor, which seriously affects the cycle performance of the battery cell.

Therefore, there is still a need in the art to develop a new active material for a positive electrode, which has improved stability to suppress lithium-nickel mixing and has high gram capacity and good cycle performance.

Summary of the invention

The present application is made in view of the above-mentioned problems, and its purpose is to provide a positive electrode active material which can have improved stability at a high gram capacity and effectively inhibit lithium-nickel mixing, thereby solving the technical problem in the prior art that the poor stability of the positive electrode material adversely affects the cycle performance of the battery cell.

In order to achieve the above-mentioned object, the first aspect of the present application provides a multi-cation positive electrode material, wherein the general formula of the positive electrode material is Li _a L _x Ni _b Co _c Mn _d M _(1-bcd) O _e N _f or mLi ₂ MnO ₃ ·(1-m)Li _a L _x Ni _b Co _c Mn _d M _(1-bcd) O _e N _f , wherein the L ion is a cation having a radius larger than that of the Li ion, M includes at least one of Mg, Zr, Al, B, Ta, Mo, W, Nb, Sb, and La, N includes at least one of F, S, and P, 0＜a＜1, 0≤b＜1, 0≤c＜1, 0≤d＜1, 0＜b+c+d≤1, 0＜e≤2, 0≤f＜2, 0＜m＜1, 0＜x≤0.8, a+x＝1, e+f＝2,

And the following relationship is satisfied:

2.5×10 ^-6 ≤x/v≤2.5×10 ^-3 , wherein v is the gram capacity of the multi-cation positive electrode material.

By replacing part of the lithium in the layered positive electrode material with cations with a larger ionic radius, the layered structure is supported, lithium-nickel mixing is suppressed, and material stability is improved. In addition, by setting the ratio of the molar amount of the doped cations with a larger ionic radius to the gram capacity of the positive electrode material, the cycle life of the lithium-ion battery containing the positive electrode material can be effectively adjusted.

In any embodiment, 0.001<x≤0.5, preferably 0.003<x≤0.05. In any embodiment, in the multi-cation positive electrode material, x and v satisfy the following formula: 2.5×10 ^-5 ≤x/v≤2.5×10 ^-4 . By further adjusting the ratio of x/v, the stability of the positive electrode material can be further improved.

In any embodiment, the gram capacity v of the multi-cation positive electrode material satisfies 120 mAh/g≤v≤300 mAh/g.

In any embodiment, the elements of the L ions include at least one of alkali metal elements, alkaline earth metal elements, transition metal elements, and other metal elements of the main group except lithium. In a further embodiment, the alkali metal elements include at least one of Na, K, Rb, and Cs; the alkaline earth metal elements include at least one of Mg, Ca, and Sr; the transition metal elements include Y; and the other metal elements of the main group include Bi. In a further embodiment, the elements of the L ions include at least two of Na, K, Rb, and Cs; optionally, the molar ratio of each of the at least two elements is greater than 0.5%, based on the molar amount of Li ions.

In any embodiment, in the multi-cation positive electrode material, a satisfies 0.5≤a＜1; optionally, 0.8≤a＜1.

In any embodiment, in the multi-cation positive electrode material, 0.05≤b≤0.98, and 0.05≤c≤0.85.

A second aspect of the present application provides a lithium ion battery, comprising a positive electrode, wherein the positive electrode comprises the positive electrode material according to the first aspect of the present application.

In any embodiment, the lithium ion battery comprises a negative electrode, and the negative electrode active material of the negative electrode comprises at least one of graphite, hard carbon and soft carbon.

A third aspect of the present application provides an electrical device, which includes the lithium-ion battery according to the second aspect of the present application.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the technical solution of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application, and for ordinary technicians in this field, other drawings can be obtained based on the drawings without creative work.

FIG. 1 is a schematic diagram of a lithium-ion secondary battery in one embodiment of the present application.

FIG. 2 is an exploded view of the lithium ion secondary battery in one embodiment of the present application shown in FIG. 1 .

FIG. 3 is a schematic diagram of a battery pack in one embodiment of the present application.

FIG. 4 is an exploded view of the battery pack shown in FIG. 3 according to an embodiment of the present application.

FIG. 5 is a schematic diagram of a device in which a battery pack is used as a power source in one embodiment of the present application.

Description of Reference Numerals

1 Battery Pack

2 Upper cabinet

3 Lower cabinet

4 Battery Module

5 Lithium-ion secondary battery

51 Shell

52 Electrode assembly

53 Cover

DETAILED DESCRIPTION

For simplicity, the present application specifically discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an undefined range; and any lower limit can be combined with other lower limits to form an undefined range, and any upper limit can be combined with any other upper limit to form an undefined range. In addition, each separately disclosed point or single value can itself be combined as a lower limit or upper limit with any other point or single value or with other lower limits or upper limits to form an undefined range.

As people's demand for lithium-ion energy density increases, layered cathode materials have gradually developed from the earliest low-nickel materials to today's high-nickel and lithium-rich manganese-based materials with high gram capacity. However, due to factors such as lithium-nickel mixing, the structural stability of high-nickel and lithium-rich manganese-based materials is poor, which seriously affects the cycle performance of the battery cell. For example, during the charging process, the low-valent nickel in the transition metal layer will migrate to occupy the vacancies of lithium ions, causing the structure of the high-gram capacity cathode material to be destroyed and its stability and safety performance to deteriorate.

The inventors have found that by doping a certain amount of cations with a radius larger than the Li ion radius in the positive electrode material for lithium-ion batteries to replace part of the lithium ions, the doped cations can play a role in supporting the layered structure because their ion radius is larger than the ion radius of lithium, thereby inhibiting the mixing of lithium and nickel and improving the stability of the material. However, the doping amount of the above cations and the gram capacity of the positive electrode material must meet a certain relationship in order to achieve a satisfactory stabilization effect of the doped element.

Specifically, the first aspect of the present application provides a multi-cation positive electrode material, the general formula of the positive electrode material is Li _a L _x Ni _b Co _c Mn _d M _(1-bcd) O _e N _f or mLi ₂ MnO ₃ ·(1-m)Li _a L _x Ni _b Co _c Mn _d M _(1-bcd) O _e N _f , wherein the L ion is a cation having a radius greater than that of the Li ion, M includes at least one of Mg, Zr, Al, B, Ta, Mo, W, Nb, Sb, and La, N includes at least one of F, S, and P, 0＜a＜1, 0≤b＜1, 0≤c＜1, 0≤d＜1, 0＜b+c+d≤1, 0＜e≤2, 0≤f＜2, 0＜m＜1, 0＜x≤0.8, a+x＝1, e+f＝2,

And the following relationship is satisfied:

2.5×10 ^-6 ≤x/v≤2.5×10 ^-3 , wherein v is the gram capacity of the multi-cation positive electrode material.

Without being limited to any specific theory, the inventors believe that by partially replacing the lithium ions in the positive electrode material with cations L whose ionic radius is larger than that of the Li ion, the larger ionic radius of these elements hinders the occupation of the lithium ion vacancies by nickel ions to a certain extent, preventing the layered structure of the positive electrode material from being transformed into a spinel structure, thereby helping to improve the stability of the layered structure. In addition, the larger ionic radius of these cations also increases the ion diffusion channel, which helps to improve the rate performance of the material. However, the doping amount of these elements needs to be controlled within a certain range, especially relative to the gram capacity of the positive electrode material, too little doping amount is not enough to achieve the supporting effect, and too much doping amount will hinder ion transmission and reduce the gram capacity. For example, for multi-cation positive electrode materials that meet the relationship of 2.5× ^10-6≤x /v≤2.5× ^10-3 , on the one hand, elements such as sodium ions or potassium ions in the new positive electrode material that are larger than the lithium radius can play a supporting role at the lithium position, enhance the mixed discharge energy barrier, prevent the layered cathode Li/Ni mixed discharge from intensifying, and enhance the stability of the layered structure and thus improve the cycle performance. The multi-cation positive electrode material can also be embedded in the negative electrode material, wherein the ions with larger ionic radius play a supporting role in the graphite, thereby reducing the expansion/contraction of the graphite caused by the ions with smaller ionic radius during the embedding/extraction process, which is beneficial to improve the stability of the SEI film and reduce the consumption of active lithium. When x/v<2.5× ^10-6 in the positive electrode material, the number of doped ions is insufficient and cannot play a supporting role, and the improvement effect is not obvious. When x/v>2.5× ^10-3 in the positive electrode material, a large number of doped ions with larger radius will hinder the transmission of lithium ions, aggravate the side reaction between the electrolyte and the interface, increase the impedance, and reduce the gram capacity of the material, and the improvement of life is also difficult to achieve. The gram capacity of the positive electrode material can be measured by the following method: make a button cell, charge at a constant voltage after a constant current of 0.1C, and then discharge at 0.1C, measure the capacity, and divide it by the mass of the active material to obtain the gram capacity. In the present invention, unless otherwise specified, the gram capacity of the positive electrode material refers to the gram capacity measured at 25°C.

In some embodiments, in the multi-cation positive electrode material, x satisfies 0.001＜x≤0.5, and optionally 0.003＜x≤0.05. x represents the doping ratio of the cation L having an ion radius larger than the Li ion radius in the Li ion. By adjusting it, the stabilization effect of the cation L on the positive electrode material can be further improved.

In some embodiments, in the multi-cation positive electrode material, x and v satisfy the following formula: 2.5×10 ^-5 ≤x/v≤2.5×10 ^-4 . As described above, the ratio of the doping amount of the cation L to the gram capacity of the positive electrode material needs to be controlled within a certain range, and can be further adjusted to further enhance the stabilization effect of the positive electrode material. Within the further selected ratio range, the cycle life of the lithium ion battery containing the positive electrode material is more significantly improved.

In some embodiments, the gram capacity v of the multi-cation positive electrode material satisfies 120mAh/g≤v≤300mAh/g. When the gram capacity of the multi-cation positive electrode material is too low, the high energy density of the battery cannot be achieved; when the gram capacity is too high, the stability of the positive electrode material decreases, resulting in insufficient cycle life of the battery.

In some embodiments, in the multi-cation positive electrode material, the elements of the L ions include at least one of alkali metal elements, alkaline earth metal elements, transition metal elements, and other metal elements of the main group except lithium. Further, the alkali metal element includes at least one of Na, K, Rb, and Cs; the alkaline earth metal element includes at least one of Mg, Ca, and Sr; the transition metal element includes Y; and the other metal elements of the main group include Bi. In some embodiments, the L ions are different from other ions already present in the multi-cation positive electrode material, such as Co, Ni, Mn, and possible M ions. In some embodiments, the elements of the L ions include at least two of Na, K, Rb, and Cs, optionally at least three, and further optionally all four. Optionally, the molar ratio of each of the at least two, three, or four elements is greater than 0.5%, based on the molar amount of Li ions. In some embodiments, the molar ratio of at least two of Na, K, Rb, and Cs is greater than 0.005, for example, 0.01 to 0.25, based on the molar amount of Li ions. Specifically, the doping molar ratio of each element in the present application may include the following technical solutions: Na and K are not 0, or are greater than 0.005; Na and Rb are not 0, or are greater than 0.005; Na and Cs are not 0, or are greater than 0.005; K and Rb are not 0, or are greater than 0.005; K and Cs are not 0, or are greater than 0.005; Rb and Cs are not 0, or are greater than 0.005; Na, K and Rb are not 0, or are greater than 0.005; Na, Rb and Cs are not 0, or are greater than 0.005; Na, K and Cs are not 0, or are greater than 0.005; K, Rb and Cs are not 0, or are greater than 0.005; Na, K and Cs are not 0, or are greater than 0.005; K, Rb and Cs are not 0, or are greater than 0.005; Na, K, Rb and Cs are not 0, or are greater than 0.005, all of which are based on the molar amount of Li ions. The doping molar ratio of each element in Na, K, Rb and Cs may be the same or different. For example, the multi-cation positive electrode material of the present application may be Li _0.96 Na _0.01 K _0.01 Cs _0.01 Rb _0.01 Ni _0.8 Co _0.1 Mn _0.1 O ₂ , Li _0.94 Na _0.02 K _0.02 Cs _0.01 Rb _0.01 Ni _0.8 Co _0.1 Mn _0.1 O ₂ , Li _0.96 Na _0.02 K _0.02 Ni _0.8 Co _0.1 Mn _0.1 O ₂ or Li _0.97 K _0.01 Cs _0.01 Rb _0.01 Ni _0.8 Co _0.1 Mn _0.1 O ₂ . The value of the doping molar ratio of each element in Na, K, Rb, and Cs can be achieved by adjusting the type and amount of each element, for example, in the process of preparing the positive electrode material, by selecting specific doping elements and the relative molar amount of each added. The specific composition of the final positive electrode material can be determined by means such as ICP.

In some embodiments, in the multi-cation positive electrode material, a satisfies 0.5≤a＜1; optionally, 0.8≤a＜1. a characterizes the molar ratio of lithium ions in the positive electrode material. Since a is less than 1, x is not 0, that is, at least part of the lithium ions in the positive electrode material are replaced by at least one L ion, such as Na, K, Rb and Cs. Among the alkali metal ions of the positive electrode material, the molar ratio of lithium ions is advantageously adjusted to 50% or more, more advantageously 80% or more. If the lithium ion content is too low, the lithium ion transport is hindered, resulting in a decrease in capacity and kinetics.

In some embodiments, in the polycationic positive electrode material, 0.05≤b≤0.98, and 0.05≤c≤0.85. The values of b and c can be selected in a wide range according to the desired material, without special restrictions. Usually for high gram capacity positive electrode materials, the content of Ni is relatively high, for example, b can be above 0.5, above 0.6, or even up to 0.98. The value of c can generally be 0.05 to 0.3, or 0.1 to 0.2.

M ions are cations for partially replacing Ni, Co and Mn, and include at least one of Mg, Zr, Al, B, Ta, Mo, W, Nb, Sb and La. Optionally, M ions are selected from Mg, Zr, Al, B, Ta, Mo, W, Nb, Sb or La ions. The relative molar ratio of M ions, based on the total molar amount of Ni, Co and Mn, may be 0-20%, and optionally 0-10%. N ions are ions for doping and replacing part of O ions, and include at least one of F, S and P; optionally, they are selected from F, S or P. The doping amount of N ions, based on the molar amount of O ions, may be 0-20%, and optionally 0-5%.

In some embodiments, the polycationic cathode material can be prepared by the following method: first, a conventional precursor is prepared by mixing compounds of lithium, cobalt, nickel, etc., and then the precursor is mixed with a compound of a doping element, ground and calcined, and the doped polycationic cathode material is obtained after cooling. The compound may be a salt of each element, such as a carbonate. The amount of the compound containing each element can be determined according to the final composition of the desired cathode material, for example, by the molar ratio of each element in the final composition. Lithium salts are usually added in excess to compensate for losses during calcination.

The second aspect of the present application provides a lithium ion battery, which includes a positive electrode, wherein the positive electrode comprises a multi-cation positive electrode material according to the first aspect of the present application. Typically, the positive electrode material is coated on a positive electrode current collector to form a positive electrode active material layer. In the preparation of the positive electrode sheet, the positive electrode material and the adhesive, the conductive agent, etc. can be dispersed in an organic solvent (e.g., N-methylpyrrolidone (NMP)) to form a uniform slurry, coated on the positive electrode current collector, and then dried at a high temperature. The pole piece obtained after drying can be rolled and cut into a predetermined shape. There is no particular restriction on the choice of adhesive. As an example, it can be one or more of styrene-butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyacrylic acid (PAA), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA) and polyvinyl butyral (PVB). There is no specific restriction on the type of conductive agent, and those skilled in the art can choose according to actual needs. As an example, the conductive agent for the positive electrode material can be selected from one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers. In some embodiments, the weight ratio of the positive electrode active material, the conductive agent and the binder contained in the slurry of the positive electrode sheet is 70-90:5-15:5-15, optionally 75-85:8-12:8-12.

In some embodiments, the lithium ion battery comprises a negative electrode, and the negative electrode active material of the negative electrode comprises at least one of graphite, hard carbon and soft carbon. However, there is no particular limitation on the selection of the negative electrode material, and a negative electrode material conventionally used for lithium ion batteries can be selected.

A third aspect of the present application provides an electrical device, which includes the lithium-ion battery according to the second aspect of the present application.

The composition and structure of lithium-ion batteries are explained in detail below.

The materials of each component of the lithium ion battery of the present application can be selected from a wide range. In some embodiments, the battery is particularly a lithium ion secondary battery. The battery cell of the lithium ion secondary battery is described in detail below.

Generally, lithium-ion secondary batteries include a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte. During the battery charging and discharging process, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. The separator is set between the positive electrode sheet and the negative electrode sheet to play a role of isolation. The electrolyte plays a role of conducting ions between the positive electrode sheet and the negative electrode sheet.

[Electrolyte]

The electrolyte plays the role of conducting ions between the positive electrode and the negative electrode. The electrolyte includes electrolyte salt and solvent.

In the present application, the electrolyte salt may be a common electrolyte salt in lithium ion secondary batteries, such as a lithium salt, including the lithium salt described above as a high thermal stability salt, a lithium salt as a low impedance additive, or a lithium salt that inhibits corrosion of aluminum foil. As an example, the electrolyte salt can be selected from one or more of lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium hexafluoroarsenate (LiAsF ₆ ), lithium bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium difluorophosphate (LiPO ₂ F ₂ ), lithium difluorobisoxalate phosphate (LiDFOP), lithium fluorosulfonate (LiSO ₃ F), difluorobisoxalate (NDFOP), Li ₂ F(SO ₂ N) ₂ SO ₂ F, KFSI, CsFSI, Ba(FSI) ₂ and LiFSO ₂ NSO ₂ CH ₂ CH ₂ CF ₃ .

The type of solvent is not particularly limited and can be selected according to actual needs. In some embodiments, the solvent is a non-aqueous solvent. Optionally, the solvent may include one or more of linear carbonate, cyclic carbonate, and carboxylic acid ester. In some embodiments, the solvent may be selected from ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), 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), tetrahydrofuran, cyclopentane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS) and diethyl sulfone (ESE) One or more.

In some embodiments, the electrolyte may also optionally include other additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high temperature performance, and additives that improve battery low temperature performance. As an example, the additive is selected from at least one of a cyclic carbonate compound containing an unsaturated bond, a halogen-substituted cyclic carbonate compound, a sulfate compound, a sulfite compound, a sultone compound, a disulfonic acid compound, a nitrile compound, an aromatic compound, an isocyanate compound, a phosphazene compound, a cyclic anhydride compound, a phosphite compound, a phosphate compound, a borate compound, and a carboxylate compound.

[Positive electrode]

The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer includes a positive electrode active material and a conductive agent.

As an example, the positive electrode current collector has two surfaces facing each other in its thickness direction, and the positive electrode active material layer is disposed on any one or both of the two facing surfaces of the positive electrode current collector.

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

The positive electrode active material layer disposed on the surface of the positive electrode current collector includes a positive electrode active material. The positive electrode active material used in the present application may have any conventional positive electrode active material used in a secondary battery. In some embodiments, the positive electrode active material may include one or more selected from lithium transition metal oxides, lithium-containing phosphates of olivine structure, and their respective modified compounds. Examples of lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their modified compounds. Examples of lithium-containing phosphates of olivine structure may include, but are not limited to, one or more of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium iron manganese phosphate, lithium iron manganese phosphate and carbon composites, and their modified compounds. These materials can all be obtained commercially. Carbon may be coated on the surface of the positive electrode active material. The positive electrode active material may be doped to obtain a doped positive electrode active material. The doping element may include at least one selected from Na, K, Rb and Cs, but is not limited thereto.

The positive electrode active material layer may optionally include a conductive agent. However, there is no specific limitation on the type of the conductive agent, and those skilled in the art may select it according to actual needs. As an example, the conductive agent used for the positive electrode material may be selected from one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

The positive electrode active material layer also includes an aqueous binder. The aqueous binder can be selected from one or more of soluble polysaccharides and their derivatives and water-soluble or water-dispersible polymers. As an example, the aqueous binder can be methylcellulose and its salts, xanthan gum and its salts, chitosan and its salts, alginic acid and its salts; and polyethyleneimine and its salts, polyacrylamide, acrylic acid copolymers and their derivatives.

In the present application, the positive electrode sheet can be prepared according to methods known in the art. As an example, the carbon-coated positive electrode active material, the conductive agent and the aqueous binder can be dispersed in a solvent (such as water) to form a uniform positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet is obtained.

[Negative electrode]

The negative electrode sheet includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode material layer includes a negative electrode active material.

As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode material layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

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

In the lithium-ion secondary battery of the present application, the negative electrode material layer generally comprises a negative electrode active material and an optional binder, an optional conductive agent and other optional auxiliary agents, and is generally formed by coating and drying a negative electrode slurry. The negative electrode slurry coating is generally formed by dispersing the negative electrode active material and the optional conductive agent and binder in a solvent and stirring them uniformly. The solvent may be N-methylpyrrolidone (NMP) or deionized water.

The specific type of the negative electrode active material is not limited, and the active material known in the art that can be used for the negative electrode of a lithium ion secondary battery can be used, and those skilled in the art can select it according to actual needs. As an example, the negative electrode active material can be selected from one or more of graphite, soft carbon, hard carbon, mesophase carbon microspheres, carbon fibers, carbon nanotubes, elemental silicon, silicon oxides, silicon-carbon composites, and lithium titanate.

As an example, the conductive agent may be selected from one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

As an example, the binder can be selected from one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).

Other optional auxiliary agents include, for example, thickeners (such as sodium carboxymethyl cellulose (CMC-Na)).

[Diaphragm]

The lithium-ion secondary battery using an electrolyte includes a diaphragm. The diaphragm is arranged between the positive electrode plate and the negative electrode plate to play a role of isolation. The diaphragm of the present application is as described above; however, the lithium-ion battery of the present application may also further include a conventional diaphragm. There is no particular restriction on the type of conventional diaphragm, and any known porous structure diaphragm with good chemical stability and mechanical stability can be selected. In some embodiments, the material of the conventional diaphragm can be selected from one or more of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The diaphragm can be a single-layer film or a multi-layer composite film, without particular restriction. When the diaphragm is a multi-layer composite film, the materials of each layer can be the same or different, without particular restriction.

In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.

In some embodiments, the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.

In some embodiments, the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, and examples of the plastic include polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square or any other shape. For example, FIG1 is a lithium-ion secondary battery 5 of a square structure as an example.

In some embodiments, referring to FIG. 2 , the outer package may include a shell 51 and a cover plate 53. Among them, the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the diaphragm can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. The number of electrode assemblies 52 contained in the lithium-ion secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

In some embodiments, lithium-ion secondary batteries can be assembled into a battery module 4, and the number of lithium-ion secondary batteries contained in the battery module 4 can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module 4. In the battery module 4, multiple lithium-ion secondary batteries 5 can be arranged in sequence along the length direction of the battery module. Of course, they can also be arranged in any other manner. Further, the multiple lithium-ion secondary batteries 5 can be fixed by fasteners. Optionally, the battery module 4 can also include a housing having a housing space, and multiple lithium-ion secondary batteries 5 are accommodated in the housing space.

In some embodiments, the lithium-ion secondary batteries 5 or battery modules 4 may be assembled into a battery pack 1 , and the number of lithium-ion secondary batteries 5 or battery modules 4 included in the battery pack 1 may be selected by those skilled in the art based on the application and capacity of the battery pack 1 .

The lithium-ion secondary battery of the present application may include a battery cell form, a battery module form, or a battery pack form. In some embodiments, the battery cells may be assembled into a battery module. In some embodiments, the battery cells may be assembled into a battery pack. In some embodiments, the battery modules may also be assembled into a battery pack.

FIG3 and FIG4 are battery packs 1 as an example. Referring to FIG3 and FIG4, the battery pack 1 may include a battery box and a plurality of battery cells disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3, and the upper box body 2 can be covered on the lower box body 3 to form a closed space for accommodating the battery cells.

In addition, the present application also provides a device, which includes a battery pack provided in the present application. The battery pack can be used as a power source for the device, and can also be used as an energy storage unit for the device. The device can be, but is not limited to, a mobile device (such as a mobile phone, a laptop computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc. As the device, a battery pack can be selected according to its usage requirements.

FIG5 is a device as an example. The device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the device's requirements for high power and high energy density of lithium-ion secondary batteries, a battery pack or a battery module may be used.

Example

Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. The reagents or instruments used that do not specify the manufacturer are all conventional products that can be obtained commercially. If not otherwise specified, all experimental steps are carried out under normal pressure.

Example 1

Preparation of high nickel-doped cathode material Li _0.96 Na _0.01 K _0.01 Cs _0.01 Rb _0.01 Ni _0.8 Co _0.1 Mn _0.1 O ₂

First, add nickel acetate, cobalt acetate and manganese acetate to deionized water in a stoichiometric ratio and stir evenly. Quickly pour the sodium carbonate solution into the transition metal salt solution, continue the reaction for 9 hours, and then let it stand for 4 hours to allow the primary particles to grow. Wash it with deionized water three times, dry it in a blast dryer, and then place it under vacuum at 100°C for 12 hours. Collect the dried solid as the precursor.

The precursor was mixed with lithium carbonate, sodium carbonate, potassium carbonate, rubidium carbonate and cesium carbonate in a molar ratio of 1:1.05:0.01:0.01:0.01:0.01, and then ground. The excess lithium carbonate was used to compensate for the loss of lithium during high-temperature calcination. The fully ground solid powder was transferred to a crucible and placed in a muffle furnace with programmed temperature rise. The calcination procedure was: pre-calcination from room temperature to 500℃ for 5h, and then calcined at a high temperature of 800℃ for 12h, with a heating rate of 3℃ min ^-1 . The resulting material was then cooled to room temperature and collected.

【Preparation of positive electrode】

The positive electrode material prepared as described above was mixed with polyvinylidene fluoride (PVDF) and conductive agent (carbon black Super P) at a mass ratio of 90:5:5, and N-methyl-pyrrolidone (NMP) was used as solvent. The amount of solvent added was adjusted to control the viscosity of the slurry to 100-20000mPa.s. The slurry was coated on the surface of aluminum foil using a coating machine, and then transferred to a vacuum drying oven for complete drying. After drying at 85°C, cold pressing was performed, and then trimming, cutting, and striping were performed, and then drying was performed at 85°C under vacuum conditions for 4 hours, and the pole ears were welded to form positive electrode sheets. The total coating amount of the positive electrode active material on the obtained pole sheet was 0.3g/ ^1540.25mm2 .

【Preparation of negative electrode sheet】

Active material graphite, conductive agent Super-P, thickener CMC and adhesive SBR are added into solvent deionized water in a mass ratio of 96.5:1.0:1.0:1.5 and mixed evenly to form anode slurry; the anode slurry is coated on the current collector copper foil and dried at 85°C, and then trimmed, cut into pieces and stripped, and then dried at 110°C under vacuum conditions for 4 hours, and the pole ears are welded to form negative electrode sheets.

【Preparation of electrolyte】

A mixture of ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC) was used as a non-aqueous organic solvent, wherein the mass ratio of each component was EC:PC:DEC=30:30:40, and lithium hexafluorophosphate (LiPF6) was used as a lithium salt to prepare an electrolyte with a concentration of 1M.

【Isolation film】

A 12 μm polypropylene film was used as the isolation film.

【Preparation of lithium-ion batteries】

The positive electrode sheet, the separator, and the negative electrode sheet as described above are stacked in order, with the separator being located between the positive and negative electrode sheets to play a role of isolation, and the above-mentioned electrolyte is added to assemble a stacked battery, which is the lithium-ion secondary battery of Example 1.

Example 2

Preparation of high nickel-doped cathode material Li _0.96 Na _0.04 Ni _0.8 Co _0.1 Mn _0.1 O ₂

First, add nickel acetate, cobalt acetate and manganese acetate to deionized water in a stoichiometric ratio and stir evenly. Quickly pour the sodium carbonate solution into the transition metal salt solution, continue the reaction for 9 hours, and then let it stand for 4 hours to allow the primary particles to grow. Wash it with deionized water three times, dry it in a blast dryer, and then place it under vacuum at 100°C for 12 hours. Collect the dried solid as the precursor.

The precursor was mixed with lithium carbonate and sodium carbonate in a molar ratio of 1:1.05:0.04, and then ground. The excess lithium carbonate was used to compensate for the loss of lithium during high-temperature calcination. The fully ground solid powder was transferred to a crucible and placed in a muffle furnace with programmed temperature rise. The calcination procedure was: pre-calcination from room temperature to 500°C for 5h, and then calcined at a high temperature of 800°C for 12h, with a heating rate of 3°C min ^-1 . The resulting material was then cooled to room temperature and collected.

The preparation process of the lithium ion battery of Example 2 is the same as that of Example 1, except that the positive electrode material used is the positive electrode material prepared according to Example 2.

Comparative Example 1

_Preparation of undoped _{cathode material LiNi0.8Co0.1Mn0.1O2}

First, add nickel acetate, cobalt acetate and manganese acetate to deionized water in a stoichiometric ratio and stir evenly. Quickly pour the sodium carbonate solution into the transition metal salt solution, continue the reaction for 9 hours, and then let it stand for 4 hours to allow the primary particles to grow. Wash it with deionized water three times, dry it in a blast dryer, and then place it under vacuum at 100°C for 12 hours. Collect the dried solid as the precursor.

The precursor and lithium carbonate were mixed evenly in a molar ratio of 1:1.07, and then ground. The excess lithium carbonate was used to compensate for the loss of lithium during high-temperature calcination. The fully ground solid powder was transferred to a crucible and placed in a muffle furnace for calcination. The calcination procedure was: pre-calcination from room temperature to 500°C for 5h, and then calcined at a high temperature of 800°C for 12h, with a heating rate of 3°C min ^-1 . The resulting material was then cooled to room temperature and collected.

The preparation process of the lithium ion battery of Comparative Example 1 is the same as that of Example 1, except that the positive electrode material used is the positive electrode material prepared according to Comparative Example 1.

Comparative Example 2

Preparation of positive electrode material Li _0.4 Na _0.6 Ni _0.8 Co _0.1 Mn _0.1 O ₂

First, add nickel acetate, cobalt acetate and manganese acetate to deionized water in a stoichiometric ratio and stir evenly. Quickly pour the sodium carbonate solution into the transition metal salt solution, continue the reaction for 9 hours, and then let it stand for 4 hours to allow the primary particles to grow. Wash it with deionized water three times, dry it in a blast dryer, and then place it under vacuum at 100°C for 12 hours. Collect the dried solid as the precursor.

The precursor was mixed with lithium carbonate and sodium carbonate in a molar ratio of 1:0.43:0.6, and then ground. The excess lithium carbonate was used to compensate for the loss of lithium during high-temperature calcination. The fully ground solid powder was transferred to a crucible and placed in a muffle furnace with programmed temperature rise. The calcination procedure was: pre-calcination from room temperature to 500°C for 5h, and then calcined at a high temperature of 800°C for 12h, with a heating rate of 3°C min ^-1 . The resulting material was then cooled to room temperature and collected.

The preparation process of the lithium ion battery of Comparative Example 2 is the same as that of Example 1, except that the positive electrode material used is the positive electrode material prepared according to Comparative Example 2.

Comparative Example 3

Preparation of positive electrode material Li _0.9996 Na _0.0004 Ni _0.8 Co _0.1 Mn _0.1 O ₂

First, add nickel acetate, cobalt acetate and manganese acetate to deionized water in a stoichiometric ratio and stir evenly. Quickly pour the sodium carbonate solution into the transition metal salt solution, continue the reaction for 9 hours, and then let it stand for 4 hours to allow the primary particles to grow. Wash it with deionized water three times, dry it in a blast dryer, and then place it under vacuum at 100°C for 12 hours. Collect the dried solid as the precursor.

The precursor was mixed with lithium carbonate and sodium carbonate in a molar ratio of 1:1.07:0.0004, and then ground. The excess lithium carbonate was used to compensate for the loss of lithium during high-temperature calcination. The fully ground solid powder was transferred to a crucible and placed in a muffle furnace with programmed temperature rise. The calcination procedure was: pre-calcination from room temperature to 500°C for 5h, and then calcined at a high temperature of 800°C for 12h, with a heating rate of 3°C min ^-1 . The resulting material was then cooled to room temperature and collected.

The preparation process of the lithium ion battery of Comparative Example 3 is the same as that of Example 1, except that the positive electrode material used is the positive electrode material prepared according to Comparative Example 3.

【Battery performance test】

1. Gram capacity of positive electrode material

A button cell was made, charged at a constant voltage after a constant current of 0.1C, and then discharged at 0.1C. The capacity was measured and divided by the mass of the active material to obtain the gram capacity.

2. Cycle performance test:

The cycle test conditions are as follows: at 25°C and 45°C, the secondary battery is subjected to a 1C/1C cycle test with a charge and discharge voltage range of 2.8 to 4.35V, and the test is stopped when the capacity decays to 80% of the initial discharge capacity.

The lithium ion batteries prepared in Examples 1-2 and Comparative Examples 1-3 were subjected to the performance tests described above, and the test results are summarized in Table 1 below.

Table 1

It can be seen from the results in Table 1 that by using cations L with larger ionic radius to dope and replace Li ions in the positive electrode material to a certain extent, the structural stability of the positive electrode material can be effectively improved, and the cycle life of the lithium ion battery can be improved. In addition, the ratio of the molar amount of the doping element to the gram capacity needs to be controlled within a certain range. Excessive doping (Comparative Example 2) and insufficient doping (Comparative Example 3) may both lead to insufficient improvement in the cycle life of the lithium ion battery.

Although the present application has been described with reference to the embodiments, various modifications may be made thereto and parts thereof may be replaced with equivalents without departing from the scope of the present application. In particular, the various technical features mentioned in the various embodiments may be combined in any manner as long as there is no structural conflict. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims (12)

1. A multi-cation positive electrode material is provided, which has a general formula of Li _aL_xNi_bCo_cMn_dM_(1-b-c-d)O_eN_f or mLi₂MnO₃·(1-m)Li_aL_xNi_bCo_cMn_dM_(1-b-c-d)O_eN_f,, wherein L ions are cations with a radius larger than that of Li ions, M comprises at least one of Mg, zr, al, B, ta, mo, W, nb, sb, la, N comprises at least one of F, S and P, 0 < a < 1,0 < b < 1,0 < c < 1,0 < d < 1,0 < b+c+d < 1,0 < e < 2,0 < f < 2,0 < M < 1,0 < x < 0.8, a+x=1, e+f=2,

And satisfies the following relationship:

2.5 x 10 ^-6≤x/v≤2.5×10^-3, wherein v is the gram capacity of the polycationic positive electrode material.

2. The positive electrode material according to claim 1, wherein 0.001 < x.ltoreq.0.5; optionally 0.003 < x.ltoreq.0.05.

3. The positive electrode material according to claim 1 or 2, wherein x and v satisfy the following formula:

2.5×10^-5≤x/v≤2.5×10^-4。

4. The positive electrode material according to any one of claims 1 to 3, wherein a gram capacity v of the positive electrode material satisfies 120 mAh/g+.v+.300 mAh/g.

5. The positive electrode material according to any one of claims 1 to 4, wherein an element of the L ion includes at least one of an alkali metal element, an alkaline earth metal element, a transition metal element, and other metal elements of main group other than a lithium element.

6. The positive electrode material according to claim 5, wherein the alkali metal element comprises at least one of Na, K, rb, cs; the alkaline earth metal element comprises at least one of Mg, ca and Sr; the transition metal element includes Y; and the main group other metal element includes Bi.

7. The positive electrode material according to claim 5 or 6, wherein the element of L ion includes at least two of Na, K, rb, cs; preferably, the molar ratio of each of the at least two elements is greater than 0.5% based on the molar amount of Li ions.

8. The positive electrode material according to any one of claims 1 to 7, wherein a satisfies 0.5.ltoreq.a < 1; optionally, 0.8.ltoreq.a < 1.

9. The positive electrode material according to any one of claims 1 to 8, wherein 0.05+.b+.0.98, and 0.05+.c+.0.85.

10. A lithium ion battery comprising a positive electrode comprising the multi-cation positive electrode material according to any one of claims 1 to 9.

11. The lithium ion battery of claim 10, comprising a negative electrode, a negative electrode active material of the negative electrode comprising at least one of graphite, hard carbon, and soft carbon.

12. An electrical device comprising the lithium ion battery of claim 10 or 11.