WO2022198614A1

WO2022198614A1 - Negative electrode material, preparation method therefor, electrochemical device, and electronic device

Info

Publication number: WO2022198614A1
Application number: PCT/CN2021/083157
Authority: WO
Inventors: 苏俊铭
Original assignee: 宁德新能源科技有限公司
Priority date: 2021-03-26
Filing date: 2021-03-26
Publication date: 2022-09-29
Also published as: CN114097108A

Abstract

A negative electrode material, a preparation method therefor, an electrochemical device, and an electronic device; the negative electrode material comprises a silicon-based material, and the surface of a silicon-based material particle is provided with a metal element; the metal element comprises at least one among Ge, Al, Zn, Sn, Sb, Bi, Fe, Mg, Ti, Cr, Mn, Co, Ni, Cu, or Pb. The negative electrode material provided by the present application can effectively improve the electrical conductivity of the material, improve the cyclic performance of the negative electrode material, and reduce the expansion rate of a battery.

Description

Anode material and preparation method thereof, electrochemical device and electronic device

technical field

The present application relates to the technical field of anode materials, and in particular, to anode materials and preparation methods thereof, electrochemical devices and electronic devices.

Background technique

At present, silicon-based anode materials have a gram capacity as high as 1500mAh/g to 4200mAh/g, and are considered to be the most promising next-generation lithium-ion anode materials. However, the electrical conductivity of silicon (resistivity>10 ⁸ Ω.cm) is low. In order to improve the electrical conductivity of silicon materials, silicon materials are usually compounded with carbon materials to increase the electrical conductivity. However, when silicon-carbon composite is used, it is easy to increase the oxygen content of the material, and the increase of the oxygen content in the negative electrode material will directly lead to a decrease in the first effect of the negative electrode material. In addition, the silicon material has a volume expansion of about 300% during the charge and discharge process and generates an unstable solid electrolyte interfacial film (SEI), and the silicon anode material will pulverize and fall off the current collector during the charge and discharge process, making the active material The loss of electrical contact with the current collector results in poor electrochemical performance, capacity decay, and decreased cycle stability, which hinders its further application to a certain extent. The low electrical conductivity of the existing silicon-based anode materials limits its charge/discharge efficiency, low initial efficiency and poor cycle performance.

Application content

In view of this, the present application proposes a negative electrode material and a preparation method thereof, an electrochemical device and an electronic device. The negative electrode material can effectively improve the electrical conductivity of the material, improve the cycle performance of the negative electrode material, and reduce the expansion rate of the battery.

In a first aspect, the present application provides a negative electrode material, the negative electrode material includes a silicon-based material, and the surfaces of the silicon-based material particles have metal elements; the metal elements include Ge, Al, Zn, Sn, Sb, Bi, At least one of Fe, Mg, Ti, Cr, Mn, Co, Ni, Cu or Pb.

With reference to the first aspect, in a feasible embodiment, the molar content of the silicon element in the silicon-based material is n _Si and the molar content of the metal element is n _Me , and the ratio of n _Me /n _Si satisfies the relationship : 0.005< _nMe / _nSi <1.0.

With reference to the first aspect, in a feasible embodiment, the metal element is located in the area from the surface of the silicon-based material particle to d um, the radius of the silicon-based material particle is r um, and the ratio of d/r satisfies the relationship : 0.01<d/r<0.80.

With reference to the first aspect, in a feasible embodiment, the silicon-based material includes at least one of silicon element, silicon-carbon composite material, silicon-graphite-carbon composite material, silicon oxide, and silicon oxide-carbon composite material A sort of.

With reference to the first aspect, in a feasible embodiment, the metal element exists in the form of embedding the metal element in the silicon-based material, a solid solution alloy formed by the metal element and the silicon element, and a mutual dissolution formed by the metal element and the silicon element. At least one of the amorphous alloys formed by bulk or metal elements and silicon elements.

In a second aspect, the present application provides a method for preparing a negative electrode material, the method comprising the following steps:

The silicon-based material particles are added to the mixed solution of water and ethanol containing metal oxide, and the precursor is obtained by drying after mixing uniformly;

The precursor is heat-treated under the protection of an inert atmosphere or a reducing atmosphere, so that metal elements are doped into the surfaces of the silicon-based material particles to obtain a negative electrode material.

In conjunction with the second aspect, in a feasible implementation manner, the method satisfies at least one of the following conditions (1) to (3):

(1) The heat treatment temperature is 500°C to 1200°C;

(2) the holding time of described heat treatment is 1h to 10h;

(3) The reducing atmosphere includes at least one of nitrogen, argon, helium, and hydrogen.

In a third aspect, the present application provides a negative electrode sheet, comprising a negative electrode current collector and a negative electrode active material layer disposed on the surface of the negative electrode current collector, the negative electrode active material layer comprising the negative electrode material described in the first aspect or the above The negative electrode material prepared by the preparation method described in the second aspect.

In a fourth aspect, the present application provides an electrochemical device comprising a negative electrode active material layer, characterized in that the negative electrode active material layer comprises the negative electrode material described in the first aspect or the preparation method described in the second aspect above. obtained negative electrode material.

With reference to the fourth aspect, in a feasible implementation manner, the electrochemical device is a lithium-ion battery.

In a fifth aspect, the present application provides an electronic device comprising the electrochemical device of the fourth aspect.

Compared with the prior art, the present application at least has the following beneficial effects:

The negative electrode material provided by the present application can improve the interface properties of the silicon-based material, reduce its reactivity with the electrolyte, greatly reduce the formation of SEI film, and improve the utilization rate of active lithium ions by doping metal elements on the surface of the silicon-based material. , to improve the first efficiency of the battery; the doped metal elements can provide high electronic conductivity sites in the bulk phase for the silicon-based material, improve the electronic conductivity of the material, and reduce the impedance of the material and the battery; the coexistence of metal elements and silicon-based material particles, It can increase the phase interface or form an alloy, improve the lattice structure, directly reduce the energy barrier of lithium ions and silicon to form an alloy, improve the kinetic rate of lithium deintercalation, and improve the ionic conductivity.

Description of drawings

FIG. 1 is a schematic structural diagram of a negative electrode material provided in an embodiment of the present application.

Detailed ways

The following are preferred implementations of the embodiments of the present application. It should be pointed out that for those skilled in the art, without departing from the principles of the embodiments of the present application, several improvements and modifications can be made. These improvements and modification are also regarded as the protection scope of the embodiments of the present application.

For the sake of brevity, only some numerical ranges are expressly disclosed herein. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with any other lower limit to form an unspecified range, and likewise any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, every point or single value between the endpoints of a range is included within the range, even if not expressly recited. Thus, each point or single value may serve as its own lower or upper limit in combination with any other point or single value or with other lower or upper limits to form a range not expressly recited.

In the description herein, it should be noted that, unless otherwise specified, “above” and “below” are inclusive of the numbers, and the meaning of “multiple” in “one or more” means two or more.

The above summary of this application is not intended to describe each disclosed embodiment or every implementation in this application. The following description illustrates exemplary embodiments in more detail. In various places throughout this application, guidance is provided through a series of examples, which examples can be used in various combinations. In various instances, the enumeration is merely a representative group and should not be construed as exhaustive.

In a first aspect, an embodiment of the present application provides a negative electrode material, the negative electrode material includes a silicon-based material, and the surfaces of the silicon-based material particles have metal elements; the metal elements include Ge, Al, Zn, Sn, Sb , at least one of Bi, Fe, Mg, Ti, Cr, Mn, Co, Ni, Cu or Pb.

The negative electrode material provided by the present application can improve the interface properties of the silicon-based material, reduce its reactivity with the electrolyte, greatly reduce the formation of SEI film, and improve the utilization rate of active lithium ions by doping metal elements on the surface of the silicon-based material. , to improve the first efficiency of the battery; the doped metal can provide silicon with high electronic conductivity sites in the bulk phase, improve the electronic conductivity of the material, and reduce the impedance of the material and the battery; the coexistence of metal elements and silicon-based material particles can increase the phase The interface or the formation of alloys can improve the lattice structure, directly reduce the energy barrier of lithium ions and silicon to form alloys, improve the kinetic rate of lithium deintercalation, and improve the ionic conductivity.

As an optional technical solution of the present application, the molar content of the silicon element in the silicon-based material is n _Si and the molar content of the metal element is n _Me , and the ratio of n _Me /n _Si satisfies the relationship: 0.005<n _Me /n _Si <1.0. Specifically, the value range of n _Me /n _Si may specifically be 0.005, 0.008, 0.01, 0.05, 0.08, 0.1, 0.14, 0.15, 0.16, 0.3, 0.5, 0.6, 0.7 or 0.8, etc., of course, it can also be the above Other values within the range are not limited here. When n _Me /n _Si is too large, it means that the silicon-based material is doped with too many metal elements, the gram capacity of the negative electrode material decreases, and the production cost increases; when n _Me /n _Si is too small, it means that the silicon-based material is doped If the metal element is too small, the first effect of the negative electrode material and the electrochemical performance of the battery are reduced. Preferably, _0.059≤nMe / _nSi≤0.629 .

As shown in FIG. 1, the metal element is located in the area from the surface of the silicon-based material particle to d um, the radius of the silicon-based material particle is r um, and the ratio of d/r satisfies the relationship: 0.01<d/r<0.80 .

Optionally, the value range of d/r may specifically be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.1, 0.15, 0.2, 0.25, 0.3, 0.5, 0.6 or 0.7, etc., of course, it may also be the above range Other values within are not limited here. When the value of d/r is too large, it means that the doping depth of metal elements in the silicon-based material is too large, the doped metal elements on the surface of the silicon-based material are relatively less, and the effect of doping metal elements on the expansion of the silicon-based material is reduced. , the battery expansion rate increases; when the value of d/r is too small, it means that the doping depth of metal elements in the silicon-based material is too small, and the first effect of the negative electrode material decreases.

As an optional technical solution of the present application, the silicon-based material includes silicon element, metal element, oxygen element and carbon element. That is, in the silicon-based material particles, there may also be oxygen and carbon elements.

As an optional technical solution of the present application, the silicon-based material includes at least one of silicon element, silicon-carbon composite material, silicon-graphite-carbon composite material, silicon oxide, and silicon oxide-carbon composite material.

As an optional technical solution of the present application, the existence form of the metal element includes the metal element embedded in the silicon-based material, the solid solution alloy formed by the metal element and the silicon element, the mutual solution formed by the metal element and the silicon element, or the metal element and the metal element. At least one of the amorphous alloys formed by silicon element.

As an optional technical solution of the present application, the particle size of the negative electrode material ranges from 1um to 100um, specifically 1um, 5um, 10um, 15um, 20um, 30um, 40um, 50um, 60um, 70um, 80um, 90um or 100um etc., but are not limited to the recited values, other non-recited values within the range of values also apply.

Step S10, adding the silicon-based material particles into a mixed solution of water and ethanol containing metal oxides, mixing uniformly, and drying to obtain a precursor;

In step S20, the precursor is heat-treated under the protection of an inert atmosphere or a reducing atmosphere, so that metal elements are doped into the surface of the silicon-based material particles to obtain a negative electrode material.

In the above scheme, by mixing the metal oxide with the silicon-based material, the metal oxide on the surface of the silicon-based material can be doped into the silicon-based material particles under heat treatment, thereby improving the interface properties of the silicon-based material, Reduce its reactivity with the electrolyte, greatly reduce the formation of SEI film, improve the utilization rate of active lithium ions, and improve the first efficiency of the battery; the doped metal can provide silicon with high electronic conductivity sites in the bulk phase and improve the electronic properties of the material. The electrical conductivity reduces the impedance of the material and the battery; the coexistence of metal elements and silicon-based material particles can increase the phase interface or form an alloy, improve the lattice structure, directly reduce the energy barrier for the formation of alloys between lithium ions and silicon, and improve the material's ability to deintercalate lithium. Kinetic rate, increasing ionic conductivity.

As an optional technical solution of the present application, the proportional relationship between the silicon-based material and the addition amount of the metal oxide MeO at least satisfies: _0.005≤nMe / _nSi≤1.0 . Understandably, in the preparation process, the amount of metal oxide added can be appropriately increased to ensure that the doping reaction is fully performed.

As an optional technical solution of the present application, the drying treatment method can be, for example, furnace drying, spray drying, vacuum drying, freeze drying, etc.,

As an optional technical solution of the present application, the temperature of the heat treatment is 500°C to 1200°C, specifically 500°C, 600°C, 700°C, 800°C, 850°C, 900°C, 950°C, 1000°C or 1200°C etc., of course other values within the above range are also possible.

The heat preservation time of the heat treatment is 1h to 10h, specifically 1h, 2h, 3h, 5h, 7h, 8h or 10h, etc., of course, other values within the above range are also possible.

Understandably, through high temperature heat treatment, the metal oxide deposited on the surface of the silicon-based material can be doped into the surface of the silicon-based material to obtain a silicon-based material doped with metal elements.

As an optional technical solution of the present application, the carbon composite treatment is carried out under the protection of a reducing atmosphere, and an inert atmosphere or a reducing atmosphere can be, for example, at least one of nitrogen, argon, helium, and hydrogen.

In a third aspect, an embodiment of the present application provides a negative electrode sheet, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer on the negative electrode current collector, the negative electrode active material layer comprises the negative electrode active material layer according to the first aspect of the present application negative electrode material.

As an optional technical solution of the present application, the negative electrode active material layer includes a binder, and the binder includes polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylic The (esterified) styrene-butadiene rubber, epoxy resin, nylon, etc., are not limited here.

As an optional technical solution of the present application, the negative electrode active material layer further includes a conductive material, and the conductive material includes natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, metal powder, metal fiber, copper, nickel, aluminum , silver or polyphenylene derivatives, etc., are not limited here.

As an optional technical solution of the present application, the negative electrode current collector includes, but is not limited to, copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, foamed copper or a polymer substrate coated with conductive metal.

In a fourth aspect, the present application further provides an electrochemical device, comprising a negative electrode active material layer, the negative electrode active material layer comprising the negative electrode material described in the first aspect or the method for preparing the negative electrode material described in the second aspect above. obtained negative electrode material.

As an optional technical solution of the present application, the electrochemical device further includes a positive electrode plate, and the positive electrode plate includes a positive electrode current collector and a positive electrode active material layer located on the positive electrode current collector.

As an optional technical solution of the present application, the positive electrode active material includes at least one of lithium cobalt oxide (LiCoO ₂ ), lithium nickel manganese cobalt ternary material, lithium iron phosphate, lithium manganese iron phosphate, and lithium manganate.

As an optional technical solution of the present application, the positive electrode active material layer further includes a binder and a conductive material. Understandably, the binder improves the bonding of the positive electrode active material particles to each other, and also improves the bonding of the positive electrode active material to the current collector.

Specifically, the binder includes polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone , at least one of polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylic (esterified) styrene-butadiene rubber, epoxy resin or nylon.

Specifically, the conductive material includes carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof. In some embodiments, the carbon-based material is selected from natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material is selected from metal powders, metal fibers, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

As an optional technical solution of the present application, the positive electrode current collector includes, but is not limited to, aluminum foil.

As an optional technical solution of the present application, the electrochemical device further includes an electrolyte, and the electrolyte includes an organic solvent, a lithium salt and an additive.

The organic solvent of the electrolytic solution according to the present application may be any organic solvent known in the prior art that can be used as a solvent of the electrolytic solution. The electrolyte used in the electrolyte solution according to the present application is not limited, and it may be any electrolyte known in the prior art. The additive for the electrolyte according to the present application may be any additive known in the art as an additive for the electrolyte.

In a specific embodiment, the organic solvent includes, but is not limited to: ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate or ethyl propionate.

In a specific embodiment, the lithium salt includes at least one of an organic lithium salt or an inorganic lithium salt.

In specific embodiments, the lithium salts include, but are not limited to: lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium difluorophosphate (LiPO ₂ F ₂ ), bistrifluoromethanesulfonimide Lithium LiN(CF ₃ SO ₂ ) ₂ (LiTFSI), Lithium Bis(fluorosulfonyl)imide Li(N(SO ₂ F) ₂ )(LiFSI), Lithium Bisoxalate Borate LiB(C ₂ O ₄ ) ₂ (LiBOB) ) or lithium difluorooxalate borate LiBF ₂ (C ₂ O ₄ ) (LiDFOB).

In a specific embodiment, the concentration of the lithium salt in the electrolyte may be 0.5 mol/L to 3 mol/L.

As an optional technical solution of the present application, the electrochemical device of the present application includes, but is not limited to: all kinds of primary batteries, secondary batteries, fuel cells, solar cells or capacitors.

In a specific embodiment, the electrochemical device is a lithium secondary battery, wherein the lithium secondary battery includes, but is not limited to, a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion secondary battery polymer secondary battery.

In a fifth aspect, an embodiment of the present application further provides an electronic device, where the electronic device includes the electrochemical device described in the fourth aspect.

As an optional technical solution of the present application, the electronic devices include, but are not limited to: notebook computers, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, headsets, etc. stereo headphones, VCRs, LCD TVs, portable cleaners, portable CD players, mini discs, transceivers, electronic notepads, calculators, memory cards, portable recorders, radios, backup power, motors, cars, motorcycles, power Bicycles, bicycles, lighting equipment, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries or lithium-ion capacitors, etc.

The preparation of lithium ion batteries is described below by taking lithium ion batteries as an example and in conjunction with specific embodiments. Those skilled in the art will understand that the preparation methods described in this application are only examples, and any other suitable preparation methods are included in the scope of this application. within the range.

1. Preparation of negative electrode materials

Disperse the silicon carbon material in a mixed solution of tin chloride in water and ethanol, stir evenly at 60 °C, and then dry the mixed solution to obtain the precursor;

The precursor was placed in an inert atmosphere and treated at a high temperature of 900° C. for 6 hours to obtain a tin-doped silicon carbon material.

Examples 1 to 13 were prepared according to the above method, and the specific parameters of Comparative Examples 1 to 6 are shown in Table 1 below.

2. Performance test of negative electrode material:

(1) Deduction test:

The negative electrode material, conductive carbon black and polymer prepared in the examples and comparative examples were added with deionized water in a mass ratio of 80:10:10 and stirred into a slurry, which was then coated with a scraper to form a coating with a thickness of 100um, and the temperature was 85°C for 12 minutes. After drying in a vacuum drying oven for 2 hours, use a punching machine in a dry environment to cut into discs with a diameter of 1 cm, use a metal lithium sheet as a counter electrode in a glove box, select a ceglad composite membrane for the separator, and add electrolyte to assemble into a buckle type battery. Use the LAND series battery test to test the charge and discharge of the battery to test its charge and discharge performance.

(2) Qualitative doping of metal elements, doping depth of doping elements, particle size test of negative electrode materials:

The types of doping elements can be known by cutting the material particles, observing the cut section by scanning SEM, and performing X-ray energy spectrum analysis. Combined with SEM backscattering, EDS mapping test or FIB-TEM test and EDS mapping analysis on the cross section of the sample particles, the doping depth d of the doping element and the radius r of the anode material particles can be obtained.

(3) Content test of doped metal elements and silicon elements:

The carbon in the sample is removed by calcining the negative electrode material particle sample in air or oxygen, and the obtained powder is digested with mixed acid and then subjected to ICP-AES test and calculation, and the amount ratio of the material doped with metal elements and silicon elements can be obtained. .

Table 1. Anode material performance parameters

*After 5 cycles of the button battery in the table, the discharge cut-off voltage is 2.0V gram capacity.

3. Preparation of Lithium Batteries

(1) Preparation of positive electrode sheet

The positive active material lithium cobalt oxide (LiCoO ₂ ), conductive carbon black, and binder polyvinylidene fluoride are mixed according to the weight ratio of 95:2.5:2.5, and N-methylpyrrolidone (NMP) is added. Under the action of a vacuum mixer Stir evenly to obtain a positive electrode slurry; uniformly coat the positive electrode slurry on the aluminum foil of the positive electrode current collector; dry the aluminum foil, and then after cold pressing, cutting and slitting, it is dried under vacuum conditions to obtain a positive electrode pole piece.

(2) Preparation of negative pole piece

The negative electrode materials, graphite, conductive agent (conductive carbon black, Super

) and the binder PAA are mixed according to the weight ratio of 70:15:5:10, deionized water is added, the solid content is controlled to be about 5wt% to 70wt%, the negative electrode slurry is obtained under the action of a vacuum mixer, and the viscosity of the slurry is adjusted. It is about 4000Pa·s to 6000Pa·s; the negative electrode slurry is evenly coated on the negative electrode current collector copper foil; the copper foil is dried, and then after cold pressing, cutting and slitting, it is dried under vacuum conditions to obtain Negative pole piece.

(3) Electrolyte

In a dry argon atmosphere glove box, add propylene carbonate (PC), ethylene carbonate (EC), and diethyl carbonate (DEC) (weight ratio of about 1:1:1) to a solvent mixed with LiPF6 is mixed uniformly, wherein the concentration of LiPF6 is about 1.15 mol/L, and about 12.5 wt% of fluoroethylene carbonate (FEC) is added and mixed uniformly to obtain an electrolyte.

(3) Isolation film

A polyethylene porous polymer film is used as the separator.

(4) Preparation of lithium ion battery

Stack the positive pole piece, the separator and the negative pole piece in order, so that the separator is placed between the positive and negative pole pieces to play the role of isolation, and then roll up to obtain a bare cell; after welding the tabs, place the bare cell on the In the outer packaging foil aluminum-plastic film, the above-prepared electrolyte is injected into the dried bare cell, and the lithium-ion battery is obtained through the processes of vacuum packaging, standing, forming, shaping, and capacity testing.

4. Performance test of lithium battery:

(1) Lithium-ion battery cycle performance test

Place the lithium-ion battery in a 45°C (25°C) incubator and let it stand for 30 minutes to make the lithium-ion battery reach a constant temperature. The lithium-ion battery that has reached a constant temperature is charged with a constant current of 0.7C to a voltage of 4.4V, and then charged with a constant voltage of 4.4V to a current of 0.025C. After standing for 5 minutes, it is discharged with a constant current of 0.5C to a voltage of 3.0V. The capacity obtained in this step is the initial capacity, and 0.7C charge/0.5C discharge is carried out for cycle test, and the capacity decay curve is obtained by taking the ratio of the capacity in each step to the initial capacity. The room temperature cycle performance of the battery was recorded as the number of cycles from 25°C to 90% of the capacity retention rate, and the number of cycles from 45°C to 80% of the capacity retention rate was recorded as the high-temperature cycle performance of the battery. The number of cycles in each case compares the cycle performance of the materials.

(2) Discharge rate test:

Place the lithium-ion battery in a 25°C incubator for 30 minutes so that the lithium-ion battery reaches a constant temperature. Discharge the lithium-ion battery that has reached a constant temperature with a constant current of 0.2C to a voltage of 3.0V, let it stand for 5 minutes, charge it with a constant current of 0.5C to a voltage of 4.45V, and then charge it with a constant voltage of 4.45V to a current of 0.05C, then let it stand. 5min, adjust the discharge rate, conduct the discharge test at 0.2C, 0.5C, 1C, 1.5C, 2.0C, respectively, to obtain the discharge capacity, and compare the capacity obtained at each rate with the capacity obtained at 0.2C. The ratio at 0.2C compares rate performance.

(3) Charging rate test:

Place the lithium-ion battery in a 25°C incubator for 30 minutes so that the lithium-ion battery reaches a constant temperature. Charge the lithium-ion battery that has reached a constant temperature to 4.45V at 0.2C, charge it to 0.05C at constant voltage and let it stand for 5 minutes, discharge it to 3.0V at 0.5C, and then let it stand for 5 minutes. , 1.5C, 2.0C for charging test, respectively obtain the charging capacity, compare the capacity obtained at each rate with the capacity obtained at 0.2C, and compare the rate performance by comparing the ratio at 2C and 0.2C.

(4) Battery full charge expansion rate test:

Use a screw micrometer to test the thickness of the fresh battery when it is half-charged (50% state of charge (SOC)). When the cycle reaches 400 cycles, the battery is in a fully charged (100% SOC) state, and then use a screw micrometer to test the thickness of the battery at this time. Comparing with the thickness of the fresh battery at the initial half-charge (50% SOC), the expansion rate of the fully charged (100% SOC) battery at this time can be obtained.

The performance parameters of the anode materials of Examples 1 to 13 and the anode materials of Comparative Examples 1 to 6 prepared according to the above method are shown in Table 1, and the performance test results of the prepared lithium batteries are shown in Table 2.

Table 2

It can be seen from the test results of Examples 1 to 4 and Comparative Examples 1 and 2 that none of Comparative Examples 1 and 2 are doped with metal elements, while different types of silicon-based materials in Examples 1 to 4 are doped with metal elements. After that, the first effect of silicon-based materials has been improved, and the first effect and charge/discharge efficiency of batteries made of this material have been improved. According to the test results of Examples 1 to 4, it can be seen that under the condition that the doping depth and doping amount are similar, because of its low electronic conductivity, many side reactions and high oxygen content, the The first efficiency of silicon material is lower, and its gram capacity is lower, which leads to lower first efficiency of the battery; because the electronic conductivity of silicon oxide is lower than that of other materials, which leads to lower charging/discharging efficiency; but its lithium deintercalation The resulting volume change is smaller, resulting in better capacity retention and cell expansion.

According to the test results of Example 4 and Comparative Example 2, it can be seen that the Ge-doped silicon material can improve the lattice structure, increase the kinetics of lithium deintercalation, and significantly improve the first effect of the material, thereby improving the battery performance. electrochemical performance. The silicon-carbon composite materials in Examples 2 and 3 have carbon components to enhance the electronic conductivity of the silicon-carbon composite materials, so the first effects of Examples 2 and 3 are higher than those of Examples 1 and 4 and Comparative Examples 1 and 2. At the same time, due to the existence of carbon components, the capacity retention rate of the battery is improved, and the expansion rate of the battery is reduced.

The silicon element powder and silicon oxide powder in Comparative Examples 1 and 2 are not doped with the metal element Ge. Although the gram capacity of the material is not affected, the first effect is lower than that of Examples 1 and 4, and the material has no effect. The protective interface of carbon materials is prone to generate more SEI, thus deteriorating the electrochemical performance parameters such as battery first efficiency, charge/discharge rate, capacity retention rate and cell expansion rate.

According to the test data of Examples 5 to 7, the effects of different doping elements on the performance of materials and cells are illustrated. In Example 5, Si and Sn cannot form a solid solution, so the doping form of Sn element on the surface of the silicon-based material exists in the form of Sn metal element particles, and the Sn metal element can be used as the bulk phase conductor of the silicon-based material. The electronic conductivity of the battery can be improved, thereby improving the charge/discharge efficiency of the battery. In Example 6, Si and Al can form two solid solutions, so the doping form of Al on the surface of the silicon-based material exists in the form of two solid solutions, which can not only improve the electronic conductivity of the silicon material as a bulk conductive agent, but also It can improve the existence form of some Si elements, increase the rate of lithium ion deintercalation in solid solution, and improve the dynamic performance of the material. In Example 7, Si and Cu have more than 5 eutectic forms and multiple solid solutions. Because Cu has high electronic conductivity, it can increase the conductivity of the material more than Si and Al alloys. In addition, although the Cu element cannot provide capacity for lithium intercalation, resulting in a low gram capacity of the material, the doping of metal element Cu can stabilize the interface of the material, reduce the formation of SEI, and improve the first effect of silicon-based anode materials. Therefore, among Examples 5 to 7, the negative electrode material of Example 7 has the best overall performance.

According to the test data of Examples 1, 8 to 10 and Comparative Examples 3 and 4, the effect of metal doping depth on the electrochemical performance of materials and batteries is illustrated. When the doping metal elements are the same and the doping amount is similar, the gram capacity of the negative electrode material is similar; as the doping depth of the metal element increases, the doping metal element on the surface of the silicon-based material decreases, and the first effect of the material decreases. , and then the first efficiency of the battery is also reduced, but because the silicon-based material is doped with metal elements, the rate of lithium deintercalation in the silicon component is increased, thereby increasing the charge/discharge rate of the cell. However, in Comparative Example 2, the elements are doped on the outermost surface, and the performance improvement of materials and batteries is limited. In Comparative Example 3, the element doping almost penetrates into the entire base material particles, and the surface doping is less metal elements. Therefore, compared with Example 1, the first effect of the negative electrode material and battery in Comparative Example 3 is lower, but the charge/charge of the battery is low. The discharge rate is higher. In addition, because the doping distribution of metal elements is relatively uniform, the limiting effect of the surface layer on the internal volume expansion is limited, so the battery expansion rate is improved.

According to the test data of Examples 1, 11 to 13 and Comparative Examples 1, 5, and 6, the influence of the doping amount of metal elements on the negative electrode material and the electrochemical performance of the battery is illustrated. According to Examples 11 to 13, when the doping depth of the metal element is similar, the gram capacity of the negative electrode material decreases with the increase of the doping amount of the metal element, because the gram capacity of silicon is higher than that of the doped metal element. The gram capacity is high; however, the first effect of the anode material and the electrochemical performance of the battery are both improved with the increase of the doping amount. Comparative Example 5 shows that the doping amount of the metal element is too small, and the performance of the negative electrode material and the battery is only slightly improved compared with that of Comparative Example 1. Comparative example 6 shows that the doping amount of metal elements is too high, the gram capacity of the material decreases, and the improvement effect on the electrochemical performance of the material and the battery is also reduced; and the cost of doping elements is higher than that of silicon elements, which is not conducive to practical applications. , is not conducive to reducing production costs.

Although the present application is disclosed above with preferred embodiments, it is not used to limit the claims. Any person skilled in the art can make some possible changes and modifications without departing from the concept of the present application. The scope of protection shall be subject to the scope defined by the claims of this application.

Claims

A negative electrode material, characterized in that the negative electrode material comprises a silicon-based material, and the surfaces of the silicon-based material particles have metal elements; the metal elements comprise Ge, Al, Zn, Sn, Sb, Bi, Fe, Mg , at least one of Ti, Cr, Mn, Co, Ni, Cu or Pb.
The negative electrode material according to claim 1, wherein the molar content of the silicon element in the silicon-based material is nSi and the molar content of the metal element is nMe , and the ratio of nMe / nSi satisfies the relationship : 0.005< nMe / nSi <1.0.
The negative electrode material according to claim 1, wherein the metal element is located in the area from the surface of the silicon-based material particle to d um, the radius of the silicon-based material particle is r um, and the ratio of d/r satisfies the relationship : 0.01<d/r<0.80.
The negative electrode material according to claim 1, wherein the silicon-based material comprises at least one of silicon element, silicon-carbon composite material, silicon-graphite-carbon composite material, silicon oxide, and silicon oxide-carbon composite material A sort of.
The negative electrode material according to claim 1, wherein the metal element exists in the form of a metal element embedded in a silicon-based material, a solid solution alloy formed by the metal element and the silicon element, and a mutual dissolution formed by the metal element and the silicon element. At least one of the amorphous alloys formed by bulk or metal elements and silicon elements.
A method for preparing a negative electrode material as claimed in any one of claims 1 to 5, wherein the method comprises the following steps:

The silicon-based material particles are added to the mixed solution of water and ethanol containing metal oxide, and the precursor is obtained by drying after mixing uniformly;

The precursor is heat-treated under the protection of an inert atmosphere or a reducing atmosphere, so that metal elements are doped into the surface of the silicon-based material to obtain a negative electrode material.
The preparation method according to claim 6, wherein the method satisfies at least one of the following conditions (1) to (3):

(1) The heat treatment temperature is 500°C to 1200°C;

(2) the holding time of described heat treatment is 1h to 10h;

(3) The reducing atmosphere includes at least one of nitrogen, argon, helium, and hydrogen.
A negative electrode pole piece, comprising a negative electrode current collector and a negative electrode active material layer disposed on the surface of the negative electrode current collector, wherein the negative electrode active material layer comprises the negative electrode material described in any one of claims 1 to 5 or the negative electrode material prepared by the preparation method according to any one of claims 6 to 7.
An electrochemical device comprising a negative electrode active material layer, wherein the negative electrode active material layer comprises the negative electrode material described in any one of claims 1 to 5 or the negative electrode material described in any one of claims 6 to 7 The negative electrode material prepared by the preparation method.
The electrochemical device of claim 9, wherein the electrochemical device is a lithium-ion battery.
An electronic device, characterized in that, the electronic device comprises the electrochemical device of claim 10 .