Negative electrode active material, method for producing the same, and lithium secondary battery including the same

Abstract

The present invention relates to a negative electrode active material comprising metal particles that include a core and a shell surrounding the core and whose surfaces are entirely or partially coated with an alkali metal-containing substance, a method for producing the same, and a lithium secondary battery including the same.

Description

[Technical Field]

[0001] The present invention relates to a negative electrode active material, a manufacturing method thereof, and a lithium secondary battery including the same, and more particularly to a high-power negative electrode active material incorporating metal particles whose surfaces are entirely or partially coated with an alkali metal-containing substance, a manufacturing method thereof, and a lithium secondary battery including the same. [Background technology]

[0002] Lithium ion batteries (LIBs) have high energy density and are easy to design, and are used as the main power source for mobile electronic devices. In the future, their range of applications will be further expanded to include electric vehicles and power storage devices for renewable energy sources.

[0003] In order to apply LIBs to new fields, there is a continuous demand for research into LIB materials with higher energy density and longer lifespan.

[0004] In particular, when it comes to negative electrode materials, research has been progressing on a variety of substances, including carbon, silicon, tin, and germanium.

[0005] Among these, silicon-based anode materials have attracted much attention because they have a much higher energy density than currently commercially available graphite anode materials.

[0006] However, silicon-based anode materials have fatal disadvantages, such as the formation of an unstable SEI layer due to a side reaction between the silicon surface and the electrolyte, which reduces electrochemical properties, and the internal stress caused by the sudden volume expansion that occurs during charging and discharging, which can cause the electrode material to shatter.

[0007] To solve this problem, much research has been conducted into improving the reversibility of silicon-based negative electrode materials through various surface treatments, and in particular, methods of coating or compounding carbon materials on the surface have been widely studied.

[0008] On the other hand, various surface treatments using carbon materials require complex and expensive processes, and although surface treatments using carbon materials have improved some of the lifespan characteristics of silicon-based anode materials, the ionic conductivity of silicon-based anode materials has been low, limiting the improvement of output characteristics required to realize high-speed charge / discharge LIBs, which have recently seen increasing demand.

[0009] In other words, conventional surface treatments using carbon materials combined silicon-based anode materials with carbon without improving their low ionic conductivity, making it difficult to achieve the output characteristics required for high-speed charge / discharge LIBs.

[0010] Therefore, there is a current demand for technological development related to the surface treatment of high-capacity silicon-based negative electrode active materials that suppresses the volume expansion of silicon-based negative electrode materials while improving the low ionic conductivity of silicon-based negative electrode materials. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Republic of Korea Patent Publication No. 2019-0101807 [Patent Document 2] U.S. Patent No. 8,158,282 Summary of the Invention [Problem to be solved by the invention]

[0012] Therefore, an object of the present invention is to provide a negative electrode active material for a high-power secondary battery that has high capacity and high energy density, and is capable of stable charge / discharge behavior under high current density.

[0013] Another object of the present invention is to provide a method for producing the negative electrode active material with high efficiency and low cost.

[0014] Another object of the present invention is to provide an electrode and a lithium secondary battery containing the negative electrode active material.

[0015] However, the problems to be solved by the present application are not limited to those mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the following description. [Means for solving the problem]

[0016] One aspect of the present application is a polymerizable composition comprising a core and a shell surrounding the core, The metal particles have a surface that is entirely or partially coated with an alkali metal-containing material, the metal particles include one or more selected from the group consisting of Mg, Al, Si, Ca, Fe, Mg, Mn, Co, Ni, Zn, and Ge; The alkali metal-containing substance is represented by the following formula 1: A negative electrode active material is provided. A x M y O z (chemical 1) In the above-mentioned Chemical Formula 1, A is at least one selected from the group consisting of Li, Na, and K; M is at least one selected from the group consisting of Mg, Al, Si, Ca, Fe, Mg, Mn, Co, Ni, Zn, and Ge; 0.1≦x≦2.0, 0≦y≦2.0, and 0≦z≦2.0.

[0017] Another aspect of the present application is a process comprising the steps of milling and spray drying metal particles and an alkali metal precursor to produce an alkali metal-metal particle precursor; mixing the alkali metal-metal particle precursor, amorphous carbon, and crystalline carbon to form a composite; a heat treatment step, the metal particles include any one or more selected from Si, Al, Ti, Mn, Ni, Cu, V, Zr, Mn, Co, Fe, and Nb; The alkali metal precursor includes at least one selected from the group consisting of Li, Na, and K. A method for producing a negative electrode active material is provided.

[0018] Yet another aspect of the present application is a negative electrode active material comprising: An electrode is provided.

[0019] Yet another aspect of the present application is a battery comprising a negative electrode including the negative electrode active material; a positive electrode positioned opposite the negative electrode; and an electrolyte disposed between the negative electrode and the positive electrode. [Effects of the Invention]

[0020] The negative electrode active material according to the present invention has the effect of providing a high-power secondary battery that has high capacity and high energy density, and is capable of stable charge / discharge behavior under high current density.

[0021] In addition, there is an effect that the negative electrode active material can be produced with high efficiency and low cost. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a schematic diagram illustrating a core-shell structured negative electrode active material according to one embodiment of the present invention. [Figure 2a] FIG. 2a is a scanning electron microscope (SEM) photograph of the negative electrode active material according to Example 1 of the present invention. [Figure 2b] FIG. 2b is a scanning electron microscope (SEM) photograph of the negative electrode active material according to Example 1 of the present invention. [Figure 2c] FIG. 2c is a scanning electron microscope (SEM) photograph of the negative electrode active material according to Example 1 of the present invention. [Figure 3a]FIG. 3a is a transmission electron microscope (TEM) photograph of the negative electrode active material according to Example 1 of the present invention. [Figure 3b] FIG. 3b is a transmission electron microscope (TEM) photograph of the negative electrode active material according to Example 1 of the present invention. [Figure 4a] FIG. 4a shows the result of an energy dispersive X-ray spectroscopy (EDS) line scan analysis of a cross section of the negative electrode active material according to Example 1 of the present invention. [Figure 4b] FIG. 4b shows the result of an energy dispersive X-ray spectroscopy (EDS) line scan analysis of a cross section of the negative active material according to Example 1 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0023] The terms and words used in this specification and claims should not be interpreted in a limited way to their ordinary or dictionary meanings, but should be interpreted in a way that is consistent with the technical idea of ​​the present invention, in accordance with the principle that the inventor can appropriately define the concept of the term in order to best describe his or her invention.

[0024] Therefore, it should be understood that the configuration of the embodiment described in this specification is merely one of the most preferred embodiments of the present invention and does not represent the entire technical idea of ​​the present invention, and that there may be various equivalents and modifications that can replace them at the time of this application.

[0025] In this specification, the singular includes the plural unless the context clearly indicates otherwise. It should be understood that in this specification, the terms "comprise," "comprise," or "have" are intended to specify the presence of embodied features, numbers, steps, components, or combinations thereof, but do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0026] As shown in FIG. 1, an anode active material according to one embodiment of the present application includes metal particles each including a core and a shell surrounding the core, the metal particles having a surface entirely or partially coated with an alkali metal-containing material, the metal particles including at least one element selected from the group consisting of Mg, Al, Si, Ca, Fe, Mg, Mn, Co, Ni, Zn, and Ge, and the alkali metal-containing material being represented by Chemical Formula 1 below. A x M y O z (chemical 1) In the above-mentioned Chemical Formula 1, A is at least one selected from the group consisting of Li, Na, and K; M is at least one selected from the group consisting of Mg, Al, Si, Ca, Fe, Mg, Mn, Co, Ni, Zn, and Ge; 0.1≦x≦2.0, 0≦y≦2.0, and 0≦z≦2.0.

[0027] The surfaces of the metal particles of the negative electrode active material are partially or entirely coated with the alkali metal-containing material.

[0028] For example, the alkali metal-containing material may coat 30% or more, 40% or more, 50% or more, 60% or more, 70% or more, 80% or more, 90% or more, or 100% of the surface of the metal particles, and the degree of coating can be adjusted by changing process conditions during the preparation of the negative electrode active material.

[0029] The metal particles having the surface coated with the alkali metal-containing material may be contained in both the core and the shell, and the content of the alkali metal in the core and the shell can be adjusted by changing the process conditions during production.

[0030] For example, the metal particles having the surface coated with the alkali metal-containing material are contained in a relatively larger amount in the core than in the shell.

[0031] The alkali metal-containing material coated on the surface of the metal particles has high ionic conductivity, which facilitates the electrochemical reaction of the metal and improves the rate capability. The improved rate capability also improves the high-rate charge / discharge and fast charge performance of the battery.

[0032] In one embodiment, the metal particles may be silicon (Si)-containing particles, and may be any one or more selected from the group consisting of silicon particles, silicon oxide particles, silicon carbide particles, and silicon alloy particles.

[0033] The silicon-containing particles are represented by the following formula 2. SiOx(0≦x≦0.5) (Chemical 2)

[0034] In the formula 2, if x is greater than 0.5, it may have a detrimental effect on the battery capacity and efficiency. That is, lithium ions react with oxygen to form Li2O, Li-silicate (Li x Si y O z As a result, the lithium ions that reacted with the anode material cannot return to the electrolyte or cathode material and are trapped inside the anode, preventing the battery from achieving full capacity and reducing efficiency.

[0035] Furthermore, for example, the silicon carbide may be SiC, and the silicon alloy may be, for example, a Si-Z alloy (where Z is one or more elements selected from alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, and combinations thereof, and is not Si).

[0036] The silicon (Si)-containing particles may have an average particle size (D50) of 50 to 1,000 nm, and preferably 600 to 900 nm.

[0037] If the average particle size of the silicon-containing particles exceeds 1,000 nm, a high battery capacity can be obtained, but the battery life will be significantly shortened. If the average particle size of the silicon-containing particles is less than 50 nm, the battery capacity and efficiency will be low and the manufacturing costs will be high.

[0038] In one embodiment, the crystal grain size of the metal particles may be 5 to 50 nm, and preferably 10 to 20 nm.

[0039] If the crystal grain size of the metal particles is less than 5 nm, it is advantageous in terms of battery life but disadvantageous in realizing capacity, and if the crystal grain size exceeds 50 nm, it may be disadvantageous in terms of battery manufacturing costs and life stability.

[0040] In one embodiment, the alkali metal-containing compound may be a compound in which A in the formula (1) is Li and y is 1. For example, the alkali metal-containing compound may be a compound in which A in the formula (1) is Li and y is 1. x It may also be M.

[0041] In one embodiment, the core may additionally comprise amorphous carbon and the shell may comprise crystalline carbon.

[0042] That is, the shell may be a carbon-based shell and may be mostly made of crystalline carbon, and the additional carbon component of the core may be mostly made of amorphous carbon.

[0043] Additionally, the carbon-based shell may contain a small amount of amorphous carbon, and the core may contain a small amount of crystalline carbon.

[0044] When the core contains a small amount of crystalline carbon, the specific gravity of graphite may increase and the specific gravity of amorphous carbon may decrease with increasing distance from the center of the core.

[0045] The carbon component added to the carbonaceous shell and core may serve to mitigate volume expansion of metal particles whose surfaces are entirely or partially coated with an alkali metal-containing material during charging and discharging.

[0046] The core amorphous carbon may be located between and surround the metal particles whose surfaces are wholly or partially coated with the alkali metal-containing material, i.e., the amorphous carbon forms a matrix and the core has metal particles whose surfaces are wholly or partially coated with the alkali metal-containing material dispersed therein.

[0047] Meanwhile, the core of the negative electrode active material has voids formed therein, and the internal pores of the core can reduce the initial irreversible capacity of the battery and help alleviate the volume expansion of Si.

[0048] The volume of the voids formed in the core may be 0.01 to 0.5 cc / g, and the specific gravity of the voids may decrease as they are located farther from the center of the core.

[0049] A method for manufacturing a negative electrode active material according to another aspect of the present application may include the steps of pulverizing metal particles and an alkali metal precursor and spray-drying them to prepare an alkali metal-metal particle precursor, mixing the alkali metal-metal particle precursor, amorphous carbon, and crystalline carbon to form a composite, and heat-treating the composite.

[0050] The metal particles may include one or more selected from the group consisting of Si, Al, Ti, Mn, Ni, Cu, V, Zr, Mn, Co, Fe, and Nb, and the alkali metal precursor may include one or more selected from the group consisting of Li, Na, and K.

[0051] The alkali metal precursor is positioned on the metal particles during the spray drying process, and the entire or part of the surface of the metal particles is coated with an alkali metal-containing material during the heat treatment process.

[0052] In one embodiment, the alkali metal precursor may be any one or more selected from the group consisting of Li2CO3, LiOH, hydrate of LiOH, NaOH, hydrate of NaOH, KOH, hydrate of KOH, lithium acetate, lithium isopropoxide, LiCl, and Li2O.

[0053] The amorphous carbon may be at least one selected from the group consisting of coal-based pitch, mesophase pitch, petroleum-based pitch, tar, coal-based oil, petroleum-based heavy oil, organic synthetic pitch, sucrose, naphthalene resin, polyvinyl alcohol resin, furfuryl alcohol resin, polyacrylonitrile resin, polyamide resin, phenol resin, furan resin, cellulose resin, styrene resin, epoxy resin, vinyl chloride resin, block copolymer, polyol, and polyimide resin. The crystalline carbon may be at least one selected from the group consisting of natural graphite, artificial graphite, expanded graphite, graphene, carbon black, and fullerene.

[0054] Natural graphite is graphite that is naturally produced and includes flake graphite, highly crystalline graphite, and amorphous (microcrystalline or cryptocrystalline; amorphous) graphite. Artificial graphite is artificially synthesized graphite made by heating amorphous carbon to high temperatures and includes primary or electrographite, secondary graphite, and graphite fiber.

[0055] Expanded graphite is made by intercalating chemicals such as acids or alkalis between the layers of graphite and then heating them to expand the vertical layers of the molecular structure. Graphene consists of a single layer or multiple single layers of graphite.

[0056] Carbon black is a crystalline material with less regularity than graphite, and can be converted into graphite by heating carbon black at approximately 3,000°C for a long period of time. Fullerene is a carbon mixture containing at least 3 wt% fullerene, a polyhedral bundle-shaped compound consisting of 60 or more carbon atoms. The first carbon-based material can be one type of crystalline carbon or a combination of two or more types. For example, natural graphite or artificial graphite can be used. The crystalline carbon can be in the form of spheres, plates, fibers, tubes, or powder.

[0057] Preferably, pitch can be used as the amorphous carbon. The pitch has a softening point of 100 to 250°C, and in particular, petroleum-based or coal-based pitch with a QI (Quinolone Insoluble) content of 5% by weight or less, more preferably 1% by weight or less, can be used.

[0058] On the other hand, natural graphite can be preferably used as the crystalline carbon. The purity of the graphite to be used is high-purity, with a fixed carbon content of 99% by weight or more, more preferably 99.95% by weight or more.

[0059] Furthermore, flake graphite can be suitable for increasing electrical conductivity by contacting with silicon.

[0060] In one embodiment, the conjugation step is carried out by a physical method.

[0061] The physical method may include any one or more selected from the group consisting of high energy processes such as milling, stirring, mixing, and compression.

[0062] For example, the compounding step can be performed by ball milling. In particular, a planetary ball mill can efficiently mix and grind the mixture by rotating and revolving the composition in a non-contact manner.

[0063] Balls that can be used in ball milling may be, for example, zirconia balls, and there is no limitation on the type of ball. The size of the ball may be, for example, about 0.3 to 10 mm, but is not limited to this.

[0064] On the other hand, the reaction time for the composite step is 1 minute to 24 hours, the reaction temperature is 40 to 250° C., and the reaction atmosphere is air or an inert atmosphere.

[0065] The heat treatment step may be performed at a temperature of 700 to 1,100°C.

[0066] The heat treatment time is not particularly limited, but is carried out for a period ranging from 10 minutes to 5 hours, for example.

[0067] According to yet another aspect of the present application, an electrode may include the negative electrode active material, and a lithium secondary battery may include an electrode including the negative electrode active material as a negative electrode, a positive electrode positioned opposite the negative electrode, and an electrolyte disposed between the negative electrode and the positive electrode.

[0068] The negative electrode includes the negative electrode active material. For example, the negative electrode active material, a binder, and optionally a conductive agent are mixed in a solvent to prepare a negative electrode active material composition, which is then molded into a predetermined shape or coated on a current collector such as copper foil.

[0069] In addition to the above-described negative electrode active material, the negative electrode may further include a negative electrode active material commonly used in the art as a negative electrode active material for lithium batteries. Commonly used negative electrode active materials may include, for example, at least one selected from the group consisting of lithium metal, metals capable of being alloyed with lithium, transition metal oxides, non-transition metal oxides, and carbon-based materials.

[0070] For example, the metal capable of alloying with lithium may be Si, Sn, Al, Ge, Pb, Bi, Sb, a Si-Y alloy (wherein Y is an alkali metal, alkaline earth metal, Group 13 element, Group 14 element, transition metal, rare earth element, or a combination thereof, and is not Si), or a Sn-Y alloy (wherein Y is an alkali metal, alkaline earth metal, Group 13 to Group 16 element, transition metal, rare earth element, or a combination thereof, and is not Sn). The element Y may be Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Bi, S, Se, Te, Po, or a combination thereof.

[0071] For example, the transition metal oxide may be lithium titanium oxide, vanadium oxide, lithium vanadium oxide, or the like.

[0072] For example, the non-transition metal oxide may be SnO2, SiOx (0 < x ≤ 2), etc. The carbon-based material may be crystalline carbon, amorphous carbon, or a mixture thereof. The crystalline carbon may be graphite such as amorphous, plate-like, flaky, spherical or fibrous natural graphite or artificial graphite, and the amorphous carbon may be soft carbon (low-temperature calcined carbon) or hard carbon, mesophase pitch carbide, calcined coke, etc.

[0073] When the negative electrode active material and the carbon-based material are used together, the oxidation reaction of the silicon-based active material can be suppressed, the SEI film can be effectively formed to form a stable film, the electric conductivity can be improved, and the charge and discharge characteristics of lithium can be further improved.

[0074] The ordinary negative electrode active material may be mixed and blended with the above-described negative electrode active material, coated on the surface of the above-described negative electrode active material, or used in any other combined form.

[0075] The binder used in the negative electrode active material composition is a component that helps to bind the negative electrode active material and the conductive agent, etc., and to bind to the current collector, and is added in an amount of 1 to 50 parts by weight based on 100 parts by weight of the negative electrode active material. For example, the binder can be added in the range of 1 to 30 parts by weight, 1 to 20 parts by weight, or 1 to 15 parts by weight based on 100 parts by weight of the negative electrode active material.

[0076] Examples of such binders include polyvinylidene fluoride, polyvinylidene chloride, polybenzimidazole, polyimide, polyvinyl acetate, polyacrylonitrile, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polystyrene, polymethyl methacrylate, polyaniline, acrylonitrile butadiene styrene, phenolic resins, epoxy resins, polyethylene terephthalate, polytetrafluoroethylene, polyphenylsulfide, polyamideimide, polyetherimide, polyethylene sulfone, polyamide, polyacetal, polyphenylene oxide, polybutylene terephthalate, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butadiene rubber, fluororubber, and various copolymers.

[0077] The negative electrode may further include a conductive agent to provide a conductive path to the negative electrode active material and further improve electrical conductivity.

[0078] The conductive agent can be any of those commonly used in lithium batteries, including carbon-based materials such as carbon black, acetylene black, ketjen black, and carbon fiber (e.g., vapor-grown carbon fiber); metal-based materials such as metal powder or metal fiber of copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives, or conductive materials containing mixtures thereof. The amount of conductive agent can be adjusted appropriately. For example, the weight ratio of the negative electrode active material to the conductive agent is in the range of 99:1 to 90:10.

[0079] The solvent may be N-methylpyrrolidone (NMP), acetone, water, etc. The content of the solvent is 1 to 10 parts by weight based on 100 parts by weight of the negative electrode active material. When the content of the solvent is within this range, the process of forming the active material layer is easy.

[0080] The current collector is generally formed to a thickness of 3 to 500 μm. The current collector is not particularly limited as long as it is conductive and does not induce chemical changes in the battery, and examples that can be used include copper, stainless steel, aluminum, nickel, titanium, baked carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloys.

[0081] Furthermore, the bonding strength of the negative electrode active material can be strengthened by forming minute irregularities on the surface, and the material can be used in various forms such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0082] The negative electrode active material composition thus prepared can be directly coated on a current collector to produce a negative electrode plate, or can be cast onto a separate support, peeled off from the support, and the resulting negative electrode active material film can be laminated onto a copper foil current collector to produce a negative electrode plate. The negative electrode is not limited to the above-listed forms and may have other forms.

[0083] The negative electrode active material composition can be used not only to manufacture an electrode for a lithium secondary battery, but also to manufacture a printable battery by printing it onto a flexible electrode substrate.

[0084] Separately, to prepare a positive electrode, a positive electrode active material composition is prepared by mixing a positive electrode active material, a conductive agent, a binder, and a solvent.

[0085] The positive electrode active material may be any lithium-containing metal oxide that is commonly used in the art.

[0086] For example, Li a A 1-b B b D2 (wherein 0.90≦a≦1.8 and 0≦b≦0.5); Li a E 1-b Bb O 2-c D c (wherein 0.90≦a≦1.8, 0≦b≦0.5, and 0≦c≦0.05); LiE 2-b B b O 4-c D c (wherein 0≦b≦0.5 and 0≦c≦0.05); Li a Ni 1-b-c Co b B c Dα (wherein 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, and 0<α≦2); Li a Ni 1-b-c Co b B c O 2- αFα (wherein 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, and 0<α<2); Li a Ni 1-b-c Co b B c O 2- αFα (wherein 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, and 0<α<2); Li a Ni 1-b-c Mn b B c Dα (wherein 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, and 0<α≦2); Li a Ni 1-b-c Mn b B c O 2- αFα (wherein 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, and 0<α<2); Li a Ni 1-b-c Mn b B c O 2- αFα (wherein 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, and 0<α<2); Li a Ni b E c G d O2 (wherein 0.90≦a≦1.8, 0≦b≦0.9, 0≦c≦0.5, and 0.001≦d≦0.1); Li a Ni b Coc Mn d G e O2 (wherein 0.90≦a≦1.8, 0≦b≦0.9, 0≦c≦0.5, 0≦d≦0.5, and 0.001≦e≦0.1); Li a NiG b O2 (wherein 0.90≦a≦1.8, 0.001≦b≦0.1); Li a CoG b O2 (wherein 0.90≦a≦1.8, 0.001≦b≦0.1); Li a MnG b O2 (wherein 0.90≦a≦1.8, 0.001≦b≦0.1); Li a Mn2G b O4 (wherein 0.90≦a≦1.8, 0.001≦b≦0.1); QO2; QS2; LiQS2; V2O5; LiV2O5; LiIO2; LiNiVO4; Li (3-f) J2(PO4)3(0≦f≦2);Li (3-f) Compounds expressed by any one of the chemical formulas Fe2(PO4)3(0≦f≦2);LiFePO4 can be used.

[0087] In the above chemical formula, A is Ni, Co, Mn, or a combination thereof; B is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof; D is O, F, S, P, or a combination thereof; E is Co, Mn, or a combination thereof; F is F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; Q is Ti, Mo, Mn, or a combination thereof; I is Cr, V, Fe, Sc, Y, or a combination thereof; and J is V, Cr, Mn, Co, Ni, Cu, or a combination thereof.

[0088] Of course, this compound may have a coating layer on its surface, or the compound may be mixed with a compound having a coating layer. The coating layer may include a coating element compound such as an oxide, hydroxide, oxyhydroxide, oxycarbonate, or hydroxycarbonate of the coating element. The compounds forming these coating layers may be amorphous or crystalline. Examples of the coating element included in the coating layer include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or mixtures thereof. The coating layer formation process may be performed using any coating method (e.g., spray coating, dipping, etc.) that does not adversely affect the physical properties of the positive electrode active material. This method is well understood by those skilled in the art, so a detailed description will be omitted.

[0089] For example, LiNiO2, LiCoO2, LiMn x O 2x (x=1, 2), LiNi 1-x Mn x O2(0 <x<1)、LiNi 1-x-y Co x Mn y O2 (0≦x≦0.5, 0≦y≦0.5), LiFeO2, V2O5, TiS, MoS, etc. can be used.

[0090] The conductive agent, binder, and solvent in the positive electrode active material composition may be the same as those in the negative electrode active material composition. In some cases, a plasticizer may be added to the positive electrode active material composition and the negative electrode active material composition to form pores inside the electrode plate. The amounts of the positive electrode active material, conductive agent, binder, and solvent are at levels typically used in lithium batteries.

[0091] The positive electrode current collector is not particularly limited as long as it has a thickness of 3 to 500 μm, has high conductivity without inducing chemical changes in the battery, and is made of, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. The current collector can have fine irregularities on its surface to increase the adhesive strength of the positive electrode active material, and can be in a variety of forms such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0092] The prepared positive electrode active material composition can be directly coated on a positive electrode current collector and dried to produce a positive electrode plate, or the positive electrode active material composition can be cast on a separate support, peeled off from the support, and the resulting film can be laminated on a positive electrode current collector to produce a positive electrode plate.

[0093] The positive and negative electrodes are separated by a separator, and any separator commonly used in lithium batteries can be used. In particular, separators with low resistance to ion migration and excellent electrolyte humidification are suitable. For example, the separator may be made of a material selected from glass fiber, polyester, Teflon (registered trademark), polyethylene, polypropylene, polytetrafluoroethylene (PTFE), or a combination thereof, and may be in the form of a nonwoven or woven fabric. The separator has a pore size of 0.01 to 10 μm and a thickness of 5 to 300 μm.

[0094] The lithium salt-containing non-aqueous electrolyte is composed of a non-aqueous electrolyte and lithium. The non-aqueous electrolyte may be a non-aqueous electrolytic solution, a solid electrolyte, or an inorganic solid electrolyte.

[0095] Examples of the non-aqueous electrolyte that can be used include aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0096] Examples of the organic solid electrolyte that can be used include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate ester polymers, polyagitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, and polymers containing ionic dissociative groups.

[0097] Examples of the inorganic solid electrolyte that can be used include nitrides, halides, and sulfates of Li, such as LiN, LiI, LiNI, LiN-LiI-LiOH, LiSiO, LiSiO-LiI-LiOH, LiSiS, LiSiO, LiSiO-LiI-LiOH, and LiPO-LiS-SiS.

[0098] Any lithium salt that is commonly used in lithium batteries can be used as the lithium salt. Examples of substances that are easily dissolved in the non-aqueous electrolyte include LiCl, LiBr, LiI, LiClO4, LiBF4, and LiB 10 Cl 10, LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, (CF3SO2)2NLi, lithium chloroborate, lower aliphatic lithium carboxylates, lithium tetraphenylborate, imides, and the like can be used in one or more of the following materials.

[0099] Lithium secondary batteries are classified into lithium ion batteries, lithium ion polymer batteries, and lithium polymer batteries depending on the type of separator and electrolyte used, and may be classified into cylindrical, prismatic, coin-shaped, pouch-shaped, etc. depending on the shape, and into bulk type and thin film type depending on the size.

[0100] The manufacturing methods of these batteries are well known in the art and will not be described in detail. [Example]

[0101] The present invention will be described in more detail below using examples and comparative examples, but the present invention is not limited thereto.

[0102] [Example 1] 10 parts by weight of silicon particles (D50: 15 μm), 100 parts by weight of isopropyl alcohol (IPA), 2 parts by weight of stearic acid, and 0.01 parts by weight of LiOH were mixed and put into a bead mill to form a mixture of particles with an average particle size (D 50 ) was milled to 102 nm.

[0103] The milled solution was spray dried to produce silicon precursor particles with an average particle size (D50) of 5 μm.

[0104] The silicon precursor particles, petroleum pitch, and graphite were carbonized and then placed in a compounder (manufactured by Hansol Chemical) in a weight ratio of 60:20:20, and compounded for 30 minutes. The compound was then heat-treated in an argon (Ar) gas atmosphere at 900°C for 3 hours to produce an anode active material.

[0105] [Example 2] A negative electrode active material was produced in the same manner as in Example 1, except that silicon with an average particle size (D50) of 84 nm was used.

[0106] [Example 3] A negative electrode active material was produced in the same manner as in Example 1, except that silicon with an average particle size (D50) of 136 nm was used.

[0107] [Example 4] A negative electrode active material was prepared in the same manner as in Example 1, except that the amount of LiOH added was 0.1 parts by weight.

[0108] [Example 5] A negative electrode active material was produced in the same manner as in Example 1, except that the amount of silicon particles added was 1.5 parts by weight.

[0109] [Example 6] A negative electrode active material was produced in the same manner as in Example 1, except that the amount of silicon particles added was 0.5 parts by weight.

[0110] [Example 7] A negative electrode active material was produced in the same manner as in Example 1, except that the heat treatment temperature was set to 1,250°C.

[0111] [Example 8] A negative electrode active material was produced in the same manner as in Example 1, except that the heat treatment temperature was set to 750°C.

[0112] [Comparative Example 1] A negative electrode active material was prepared in the same manner as in Example 1, except that LiOH was not added.

[0113] [Manufacturing example] Fabrication of coin half-cells The negative electrode active materials prepared in Examples 1 to 8 and Comparative Example 1, a conductive agent (Super P), and a binder (SBR-CMC) were uniformly mixed in a weight ratio of 93:3:4 to prepare a negative electrode slurry.

[0114] The prepared negative electrode slurry was coated on a copper foil current collector with a thickness of 20 μm, and the coated electrode plate was dried at 120° C. for 30 minutes and then pressed to prepare a negative electrode.

[0115] A CR2032 type coin half cell was fabricated using metallic lithium as the negative electrode and counter electrode, a PE separator as the separator, and 1.0 M LiPF6 dissolved in a mixed solvent of EC (ethylene carbonate): DEC (diethyl carbonate): DMC (dimethyl carbonate) (volume ratio 3:5:2) as the electrolyte.

[0116] Fabrication of a coin full cell The negative electrode used in the coin half-cell was used to prepare a positive electrode as follows: LiNi 0.6 Co 0.2 Mn 0.2 O2 and PVA-PAA as a binder were mixed in a 1:1 weight ratio to prepare a positive electrode slurry. The positive electrode slurry was coated onto an aluminum foil current collector with a thickness of 12 μm. The coated electrode plate was dried at 120°C for 15 minutes and then pressed to prepare a positive electrode.

[0117] A CR2032 type coin full cell was manufactured using the positive and negative electrodes, a PE separator as a separator, and an electrolyte of 1.5M LiPF6 dissolved in a mixed solvent of EC (ethylene carbonate): DEC (diethyl carbonate): DMC (dimethyl carbonate) (volume ratio 2:1:7) + FEC 20%.

[0118] Evaluation example 1: SEM and TEM analysis The cross section of the negative active material prepared in Example 1 was analyzed by scanning electron microscope (SEM), and the results are shown in FIG. 2A.

[0119] The interface between the core and shell can be clearly observed (Fig. 2B), and the core contains Li. xIt was confirmed that Si-coated silicon particles were distributed in large numbers in the form of scale-like primary particles (Fig. 2C).

[0120] Also, Li x To more clearly confirm the shape of the Si-coated silicon particles, transmission electron microscope (TEM) analysis was performed and the results are shown in Figure 3A.

[0121] Li coating the surface of silicon particles x Si was confirmed.

[0122] Also, Li x Si crystal grains were observed (Fig. 3B).

[0123] Table 1 below shows the average grain size of silicon particles analyzed by transmission electron microscope (TEM).

[0124] [Table 1]

[0125] That is, by SEM and TEM analysis, the core-shell structure of the negative electrode active material of the present invention and Li x Si-coated silicon particles could be confirmed.

[0126] Evaluation example 2: FIB-EDS analysis The negative electrode active material prepared in Example 1 was sampled using FIB (Nova200 manufactured by FEI), and EDS line scan analysis was performed using STEM-EDS (JEOL-2200FS manufactured by JEOL) at an acceleration voltage of 20 kV.

[0127] As shown in FIG. 4A, the concentration ratios of carbon, silicon, and oxygen in the core and shell were analyzed through EDS line scanning performed along the XY line corresponding to the horizontal axis of the cross section of the negative electrode active material prepared in Example 1.

[0128] As a result of the analysis, as shown in Figure 4B, the core had relatively higher concentrations of silicon and oxygen than the shell, and the shell had a higher concentration of carbon than the core.

[0129] Through this, Li is mainly in the core x The Si-coated silicon particles are distributed, and the shell contains a smaller number of Li particles than the core. x It was confirmed that the Si contained coated silicon particles and was mostly composed of carbon.

[0130] That is, the EDS line scan analysis allowed specific identification of the core and shell components of the core-shell structured negative electrode active material of the present invention.

[0131] Evaluation example 3: Battery characteristic evaluation The battery characteristics of the coin half cells and coin full cells manufactured using the negative electrode active materials manufactured in Examples 1 to 8 and Comparative Example 1 were evaluated as follows.

[0132] A coin full cell was used to measure the life characteristics, and a coin half cell was used to evaluate other battery characteristics.

[0133] Coin half-cells prepared using the negative electrode active materials prepared in Examples 1 to 8 and Comparative Example 1 were each charged at a constant current rate of 0.1 C at 25°C until the voltage reached 0.01 V (vs. Li), and then charged at a constant voltage of 0.05 C while maintaining 0.01 V. After the cells were fully charged, they were rested for 10 minutes and then discharged at a constant current of 0.1 C until the voltage reached 1.5 V (vs. Li) (two runs, initial formation). The "C" represents the cell's discharge rate, calculated by dividing the cell's total capacity by the total discharge time.

[0134] Additionally, coin full cells prepared using negative electrodes prepared using the negative electrode active materials prepared in Examples 1 to 8 and Comparative Example 1 were each charged at a constant current rate of 0.1 C at 25°C until the voltage reached 4.2 V (vs. Li), and then charged at a constant voltage of 0.05 C while maintaining 4.2 V. After the cells were fully charged, they were allowed to rest for 10 minutes and then discharged at a constant current of 0.1 C until the voltage reached 2.7 V (vs. Li) (performed twice, initial formation).

[0135] The cell was then charged at a constant current of 1.0 C at 25°C until the voltage reached 4.2 V (vs. Li), and then at a constant voltage of 0.05 C while maintaining 4.2 V. After the coin cell was fully charged, it was left to rest for 10 minutes and then discharged at a constant current of 1.0 C until the voltage reached 2.7 V (vs. Li) (cycles 1 to 100).

[0136] The initial discharge capacity, initial efficiency and life characteristics measured for the cells using the negative electrode active materials prepared in Examples 1 to 8 and Comparative Example 1 are shown in Table 2 below.

[0137] The initial discharge capacity indicates the charge and discharge capacity in the first cycle.

[0138] The initial efficiency, life characteristics and output characteristics were calculated using the following equations 1, 2 and 3, respectively.

[0139] <Number 1> Initial efficiency [%] = [discharge capacity at 1st cycle / charge capacity at 1st cycle] x 100

[0140] <Number 2> Life characteristic [%] = [100th cycle discharge capacity / 1st cycle discharge capacity] x 100

[0141] <Number 3> Output characteristics [%] = [discharge capacity when discharged at a rate of 2.0C / discharge capacity when discharged at a rate of 0.1C] x 100

[0142] [Table 2]

[0143] Through the examples, it was confirmed that the battery characteristics can be changed by adjusting the size and amount of silicon particles, the amount of LiOH added, and the heat treatment temperature.

[0144] That is, the batteries of Examples 1 to 8 exhibited an initial discharge capacity of 1,100 to 1,330 mAh / g, an initial efficiency of 83 to 90%, a life characteristic of 75 to 90%, and an output characteristic of 70 to 85%.

[0145] On the other hand, when comparing Example 1 with Comparative Example 1, which was prepared in the same manner as Example 1 except that LiOH was not added, it was confirmed that the battery characteristics of Comparative Example 1 were inferior to those of Example 1.

[0146] That is, in Comparative Example 1, the initial discharge capacity, initial efficiency and life characteristics were slightly decreased compared to Example 1, and in particular the output characteristics were significantly decreased.

[0147] Therefore, the alkali metal-containing material of the present invention (Li x It was confirmed that a negative electrode active material containing silicon particles coated with silicon (Si) has superior battery characteristics, especially output characteristics, compared to a negative electrode active material containing uncoated silicon particles.

[0148] The scope of the present invention is indicated by the claims that follow rather than by the above detailed description, and all modifications and variations that fall within the meaning and scope of the claims and their equivalents should be interpreted as being included within the scope of the present invention. [Industrial Applicability]

[0149] The negative electrode active material according to the present invention has the effect of providing a high-power secondary battery that has high capacity and high energy density, and is capable of stable charge / discharge behavior under high current density.

[0150] In addition, there is an effect that the negative electrode active material can be produced with high efficiency and low cost.

Claims

1. a core and a shell surrounding the core; The powder contains at least one selected from the group consisting of metal particles, silicon oxide particles, and silicon carbide particles, any one or more selected from the group consisting of metal particles, silicon oxide particles, and silicon carbide particles are entirely or partially coated with an alkali metal-containing material; The metal particles include at least one selected from the group consisting of Ti, Cu, V, Zr, Nb, Mg, Al, Si, Ca, Fe, Mn, Co, Ni, Zn, and Ge, The alkali metal-containing substance is represented by the following formula 1: the core comprises amorphous carbon and the shell comprises crystalline carbon; the amorphous carbon of the core forms a matrix; The negative electrode active material has at least one selected from the group consisting of metal particles, silicon oxide particles, and silicon carbide particles dispersed in the matrix. A x M y O z (Chem.1) In the above-mentioned Chemical Formula 1, A is at least one selected from the group consisting of Li, Na, and K; M is at least one selected from the group consisting of Ti, Cu, V, Zr, Nb, Mg, Al, Si, Ca, Fe, Mn, Co, Ni, Zn, and Ge; 0.1≦x≦2.0, 0≦y≦2.0, and 0≦z≦2.

0.

2. The metal particles are silicon (Si)-containing particles. The negative electrode active material according to claim 1 .

3. The silicon (Si)-containing particles include at least one selected from the group consisting of silicon particles and silicon alloy particles. The negative electrode active material according to claim 2 .

4. The silicon (Si)-containing particles have an average particle size (D50) of 50 to 1,000 nm. The negative electrode active material according to claim 2 .

5. The crystal grain size of the metal particles is 5 to 50 nm. The negative electrode active material according to claim 1 .

6. The alkali metal-containing material is In the above formula 1, A is Li and y is 1. The negative electrode active material according to claim 1 .

7. The silicon oxide particles are represented by the following formula 2: The negative electrode active material according to claim 1 . SiOx (0≦x≦0.5) (Chemical formula 2)

8. milling and spray drying the metal particles and alkali metal precursor to produce an alkali metal-metal particle precursor; mixing the alkali metal-metal particle precursor, amorphous carbon, and crystalline carbon to form a composite; a heat treatment step, The metal particles include one or more selected from Ti, Cu, V, Zr, Nb, Mg, Al, Si, Ca, Fe, Mn, Co, Ni, Zn, and Ge, The alkali metal precursor includes at least one selected from the group consisting of Li, Na, and K. The method for producing the negative electrode active material according to any one of claims 1 to 7.

9. The alkali metal precursor is Li 2 CO 3 , LiOH, LiOH hydrate, NaOH, NaOH hydrate, KOH, KOH hydrate, Li acetate, Li isopropoxide, LiCl, and Li 2 O, The method for producing a negative electrode active material according to claim 8 .

10. The amorphous carbon may include at least one selected from the group consisting of coal-based pitch, mesophase pitch, petroleum-based pitch, tar, coal-based oil, petroleum-based heavy oil, organic synthetic pitch, sucrose, naphthalene resin, polyvinyl alcohol resin, furfuryl alcohol resin, polyacrylonitrile resin, polyamide resin, phenol resin, furan resin, cellulose resin, styrene resin, epoxy resin, vinyl chloride resin, block copolymer, polyol, and polyimide resin, The crystalline carbon includes at least one selected from the group consisting of natural graphite, artificial graphite, expanded graphite, graphene, carbon black, and fullerene. The method for producing a negative electrode active material according to claim 8 .

11. The compounding step is carried out by any one or more selected from the group consisting of milling, stirring, mixing, and compression. The method for producing a negative electrode active material according to claim 8 .

12. The treatment temperature of the heat treatment step is 700 to 1,100°C. The method for producing a negative electrode active material according to claim 8 .

13. The negative electrode active material according to any one of claims 1 to 7, electrode.

14. A negative electrode comprising the negative electrode active material according to any one of claims 1 to 7; a positive electrode positioned opposite the negative electrode; an electrolyte disposed between the negative electrode and the positive electrode; Lithium secondary battery.

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