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

Abstract

The present invention provides a negative electrode active material for a lithium secondary battery, the negative electrode active material for a lithium secondary battery comprising silicon oxide (SiO x ,0

Description

Technical Field

[0001] This invention relates to a negative electrode active material for secondary batteries and its preparation method. Background Technology

[0002] With the increasing global warming problem in modern society, the demand for corresponding environmentally friendly technologies has increased dramatically. In particular, with the growing technological needs related to electric vehicles and energy storage systems (ESS), the demand for lithium-ion batteries, as an energy storage device, has surged. Therefore, research is underway to improve the energy density of lithium-ion batteries.

[0003] However, commercially available lithium-ion batteries typically use graphite active materials such as natural graphite and artificial graphite. Due to the low theoretical capacity of graphite (372 mAh / g), the energy density of the batteries is low. Therefore, research is underway to improve the energy density by developing new anode materials.

[0004] As a solution to this problem, Si-based materials with high theoretical capacity (3580 mAh / g) are emerging. However, these Si-based materials suffer from a drawback: large volume expansion (up to 400%) during repeated charge-discharge cycles leads to deterioration in battery life characteristics. Therefore, as a method to address the large volume expansion problem of Si materials, SiO2, which has a lower volume expansion rate compared to Si, has been developed. x Material. This SiO x The material exhibits excellent lifetime characteristics due to its low volume expansion rate, but its inherent low initial efficiency (initial coulombic efficiency, ICE) caused by the formation of an irreversible phase in the early stage makes it difficult to apply to lithium secondary batteries. Summary of the Invention

[0005] The technical problem to be solved by the present invention

[0006] The purpose of this invention is to provide a negative electrode active material that can improve initial efficiency and capacity while improving lifetime characteristics.

[0007] Another object of the present invention is to provide a negative electrode active material that, by removing lithium compounds remaining on the surface of lithium-pretreated silicon oxide particles, inhibits the rise of slurry pH and side reactions with electrolyte during charge and discharge, and improves the stability and lifespan characteristics of the slurry.

[0008] Technical means to solve technical problems

[0009] This invention provides a negative electrode active material for lithium secondary batteries, wherein the negative electrode active material for lithium secondary batteries comprises silicon oxide (SiO2). x, a complex (0 < x ≤ 2), the silicon oxide complex comprising a phosphorus oxide containing an alkali metal or alkaline earth metal and a phosphorus oxide containing aluminum.

[0010] According to one embodiment, the complex may have a weight ratio of aluminum (Al) to phosphorus (P) (Al / P) of 0.8 or less.

[0011] According to one embodiment, the complex may have a weight ratio of aluminum (Al) to phosphorus (P) (Al / P) of 0.1 to 0.6.

[0012] According to one embodiment, the negative electrode active material for a lithium secondary battery may include a phosphorus oxide containing an alkali metal or alkaline earth metal represented by the following Chemical Formula 1.

[0013] [Chemical Formula 1]

[0014] M x P y O z

[0015] (In Chemical Formula 1, 1 ≤ x ≤ 4, 1 ≤ y ≤ 4, 0 < z ≤ 7, and M includes one or more selected from Li, Na, Mg, and K.)

[0016] According to one embodiment, the phosphorus oxide containing aluminum may include one or more selected from AlPO4, Al(PO3)3, Al(H2PO4)3, Al2P6O 18 and Al4(P4O 12 )3.

[0017] According to one embodiment, at least a part of the silicon oxide may further include at least one lithium silicate selected from Li2SiO3, Li2Si2O5, and Li4SiO4.

[0018] According to one embodiment, the content of the lithium silicate may be 10 - 95 parts by weight relative to 100 parts by weight of the silicon oxide.

[0019] According to one embodiment, the complex may further include amorphous carbon.

[0020] According to one embodiment, the negative electrode active material for a lithium secondary battery may further include one or more graphite-based materials selected from natural graphite and artificial graphite.

[0021] The present invention also provides a method for preparing a negative electrode active material for lithium secondary batteries, comprising: a) a pretreatment step, mixing a silicon compound and an alkali metal precursor or an alkaline earth metal precursor and performing heat treatment to dope the silicon compound with metal; and b) a composite step, mixing the metal-doped silicon compound with a phosphorus oxide precursor and an aluminum salt precursor and performing heat treatment to prepare a silicon oxide composite.

[0022] According to one embodiment, the alkali metal precursor or alkaline earth metal precursor in the pretreatment step a) may be a hydride, hydroxide, oxide, carbonate, metal particle or combination thereof selected from one or more metals selected from Li, Na, Mg and K.

[0023] According to one embodiment, the pretreatment step a) can be heat-treated for 1-12 hours in an inert atmosphere at 500-1000°C.

[0024] According to one implementation scheme, the composite process b) can be carried out by mechanochemical treatment.

[0025] According to one embodiment, the composite process b) can be heat-treated for 1-12 hours at 200-600°C under an inert atmosphere.

[0026] The present invention also provides a lithium secondary battery, the lithium secondary battery comprising: a negative electrode containing a negative electrode active material according to a specific embodiment of the present invention; and a positive electrode.

[0027] Invention Effects

[0028] The negative electrode active material for lithium secondary batteries of the present invention has the advantage of solving the problems of initial efficiency and capacity degradation.

[0029] Furthermore, by suppressing the expansion of silicon oxide particles caused by the charging and discharging process, the stability and lifespan characteristics of the battery can be improved.

[0030] Furthermore, removing residual metal compounds from the surface of pretreated silicon oxide particles and stabilizing the surface of active material particles can improve slurry stability and battery life characteristics. Attached Figure Description

[0031] Figure 1 and Figure 2 This is a figure showing the results of scanning electron microscopy-energy dispersive X-ray spectrometer (SEM-EDX) analysis of the silicon oxide composite prepared according to Example 1 of the present invention.

[0032] Figure 3 It is a diagram showing the X-ray diffraction (XRD) analysis results of the silicon oxide composite prepared according to Example 1 of the present invention. Detailed implementation manners

[0033] By referring to the accompanying drawings and the embodiments described in detail, the advantages and features of the present invention and the methods for realizing them can be clearly understood. However, the present invention is not limited to the embodiments disclosed below, but can be implemented in various different ways. These embodiments are provided to completely disclose the present invention and fully explain the scope of the invention to those skilled in the art. The present invention is only limited by the scope of the claims. The specific embodiments of the present invention are described in detail by referring to the accompanying drawings. Irrespective of the drawings, the same reference numerals represent the same components, and "and / or" includes all combinations of each of the mentioned items and more than one item.

[0034] Unless otherwise defined, all terms (including technical terms and scientific terms) used in this specification may have the same meanings as those commonly understood by those skilled in the technical field to which the present invention pertains. Throughout the specification, unless otherwise specifically stated to the contrary, describing that a certain part "comprises" or "includes" a certain component means that other components may also be included, rather than excluding other components. In addition, unless otherwise specifically stated, the singular form also includes the plural form.

[0035] In this specification, when describing that a part such as a layer, a film, a region, a plate, etc. is "on" or "above" another part, this includes not only the case of being "directly" "on" another part, but also the case of having other parts in between.

[0036] In this specification, the average particle size may refer to D50, where D50 refers to the particle diameter when the cumulative volume reaches 50% from the small particle size when measuring the particle size distribution by the laser scattering method. Among them, D50 can be sampled according to the KS A ISO 13320-1 standard and the particle size distribution can be measured using a Mastersizer 3000 from Malvern Corporation. Specifically, ethanol can be used as a solvent, and an ultrasonic disperser can be used for dispersion when necessary, and then the volume density can be measured.

[0037] The present invention provides a negative electrode active material for a lithium secondary battery, and the negative electrode active material for a lithium secondary battery contains a silicon oxide (SiO x , 0 < x ≤ 2) composite, and the silicon oxide composite contains a phosphorus oxide containing an alkali metal or an alkaline earth metal and a phosphorus oxide containing aluminum.

[0038] The composite may have a core-shell structure comprising: a core containing the silicon oxide; and a shell located on the core and containing a phosphorus oxide containing an alkali metal or alkaline earth metal and a phosphorus oxide containing aluminum.

[0039] The silicon oxide contains a metal compound, which, as an example, may be one or more selected from MOH and MCO3. The metal M in the metal compound may be an alkali metal or an alkaline earth metal; specifically, metal M may be one or more selected from Li, Na, Mg, and K. This metal compound remains on the surface of the pretreated silicon compound; it is a residual metal compound that did not react during pretreatment and is a substance that is inevitably generated during the pretreatment of the silicon compound.

[0040] When the metal compound is dissolved in the solvent during the preparation of the negative electrode slurry containing the negative electrode active material, it may cause the pH of the negative electrode slurry to rise. The rise in pH causes the polymer binder, which is an essential component of the slurry, to shrink its chains. Therefore, the viscosity of the slurry may decrease, which may lead to a decrease in the adhesion between the current collector and the negative electrode active material layer.

[0041] Furthermore, the dissolution of the aforementioned metal compounds in the negative electrode slurry may oxidize the Si component of the silicon oxide, which is the active material, and generate gas, which may lead to a decrease in the stability and performance of the negative electrode slurry.

[0042] This invention prepares a core-shell structured silicon oxide composite containing a shell, wherein the shell is located on the core and comprises phosphorus oxides containing alkali metals or alkaline earth metals and phosphorus oxides containing aluminum. Therefore, the metal compounds can be effectively removed, thereby solving the aforementioned problems. Specifically, the content of the metal compounds in the composite can be reduced to less than 5% by weight, specifically to 0.1-1.5% by weight, thus substantially completely removing the metal compounds. Furthermore, stabilizing the surface structure of the composite can improve the capacity and lifespan characteristics of the battery.

[0043] At least a portion of the silicon oxide may also contain at least one lithium silicate selected from Li2SiO3, Li2Si2O5 and Li4SiO4.

[0044] When the Li2SiO3 phase is formed, less Si is consumed compared to lithium silicates such as Li2Si2O5, thereby improving capacity characteristics and reducing the severe volume change of Si during battery cycle life, which is beneficial for improving lifespan characteristics. On the other hand, the Li4SiO4 phase has high reactivity with water, making it difficult to adjust the physical properties of the slurry during electrode manufacturing, and is therefore not preferred.

[0045] The content of lithium silicate relative to 100 parts by weight of the silicon oxide can be 10-95 parts by weight, preferably 30-90 parts by weight, and more preferably 50-90 parts by weight. Within the above content range, the formation of the initial irreversible phase of the silicon oxide that occurs during initial charge and discharge can be suppressed, thereby increasing the initial efficiency and capacity.

[0046] Furthermore, relative to 100 parts by weight of the silicon oxide, the content of Li4SiO4 can be 25 parts by weight or less, preferably 10 parts by weight or less, more preferably 5 parts by weight or less, and even more preferably less than 1 part by weight. Li4SiO4 has irreversible properties relative to Li ions and is susceptible to moisture, therefore it is not preferred as an active material for a negative electrode using a water-based binder. Within the range of the Li4SiO4 phase, the water resistance of the negative electrode slurry can be improved.

[0047] The lithium silicate is formed by mixing and reacting the silicon oxide with a lithium-containing metal compound through heat treatment. Unreacted residual metal compounds may remain on the surface of the silicon oxide. During the formation of the aforementioned high-content lithium silicate, the content of these residual metal compounds increases proportionally, potentially leading to more severe problems such as increased pH and gas generation in the negative electrode slurry.

[0048] The silicon oxide composite of one embodiment of the present invention can effectively remove the aforementioned high content of residual metal compounds by converting them into phosphorus oxides containing alkali metals or alkaline earth metals. Therefore, initial performance can be improved by using a high content of lithium silicate, and problems caused by residual metal compounds during the formation of the lithium silicate can be effectively suppressed.

[0049] The content of silicon oxide relative to 100 parts by weight of the composite can be 80-99 parts by weight, preferably 90-99 parts by weight, and more preferably 95-99 parts by weight.

[0050] The average particle size of the silicon oxide in the composite can be 2-30 μm, preferably 5-10 μm.

[0051] The shell located on the core may contain phosphorus oxides containing alkali metals or alkaline earth metals, as well as phosphorus oxides containing aluminum. In this case, the phosphorus oxides containing alkali metals or alkaline earth metals can be converted from the metal compounds.

[0052] Specifically, the metal compound may remain inside the silicon oxide particles or in the fine cracks present on the particle surface. Therefore, when the phosphorus oxide containing alkali metals or alkaline earth metals is transformed by the metal compound, the shell can form a gradient in which the concentration of the phosphorus oxide containing alkali metals or alkaline earth metals increases towards the core. More specifically, the shell may have a concentration gradient in which the concentration of the phosphorus oxide containing alkali metals or alkaline earth metals increases in the thickness direction (from the surface of the shell to the interface between the shell and the core). In this case, the concentration can increase continuously or discontinuously (stepwise) in the thickness direction.

[0053] As an example, since the phosphorus oxide containing alkali metals or alkaline earth metals originates from metal compounds remaining in silicon oxide particles, the shell can comprise an inner shell and an outer shell, the inner shell containing phosphorus oxides containing alkali metals or alkaline earth metals, and the outer shell containing phosphorus oxides containing aluminum. In this case, the shell can also comprise an intermediate shell located between the inner and outer shells, and containing a mixture of phosphorus oxides containing alkali metals or alkaline earth metals and phosphorus oxides containing aluminum.

[0054] The concentration gradient of the shell effectively inhibits the dissolution of the metal compound in the slurry, thereby suppressing the oxidation of the silicon component in the core. Furthermore, when the metal compound is added externally alone to form phosphorus oxides containing alkali or alkaline earth metals, it is difficult to form a shell with the aforementioned concentration gradient. Instead, a gradient may form where the concentration of the phosphorus oxides containing alkali or alkaline earth metals increases in the opposite direction towards the surface of the shell. Alternatively, individual phosphorus oxide particles containing alkali or alkaline earth metals may be synthesized instead of the core-shell structured composite particles, thus failing to exhibit the aforementioned effects.

[0055] In order to effectively suppress the leaching of metal compounds contained in the silicon oxide in the core to the outside in an aqueous slurry environment, the average thickness of the shell can be 0.1-100 nm, preferably 1-10 nm, and more preferably 2-5 nm.

[0056] Furthermore, the phosphorus oxides containing alkali metals or alkaline earth metals and the phosphorus oxides containing aluminum are not limited to being contained in the shell of the complex, but may also be contained inside the core.

[0057] The complex may contain phosphorus oxides containing alkali metals or alkaline earth metals, represented by the following chemical formula 1'.

[0058] [Chemical Formula 1']

[0059] M x1 R x2 P y O z

[0060] In the chemical formula 1', 1 ≤ x1 ≤ 4, 0 ≤ x2 ≤ 3, 1 ≤ x1 + x2 ≤ 4, 1 ≤ y ≤ 4, 0 < z ≤ 7, M is one or more selected from Li, Na, Mg, and K, R is a monovalent substituent and is one or more selected from hydrogen, C1-C4 alkoxy, C1-C4 alkylcarbonyloxy, C6-C12 aryloxy, and C6-C12 arylcarbonyloxy.

[0061] Specifically, the phosphorus oxide containing an alkali metal or an alkaline earth metal can be represented by Chemical Formula 1.

[0062] [Chemical Formula 1]

[0063] M x P y O z

[0064] In Chemical Formula 1, 1 ≤ x ≤ 4, 1 ≤ y ≤ 4, 0 < z ≤ 7, and M is one or more selected from Li, Na, Mg, and K.

[0065] As specific examples, the phosphorus oxide containing an alkali metal or an alkaline earth metal can include one or more selected from Li3PO4, Li4P2O7, LiH2PO4, and CH3COOP(O)(OK)(OLi).

[0066] The phosphorus oxide containing aluminum can include one or more selected from AlPO4, Al(PO3)3, Al(H2PO4)3, Al2P6O 18 and Al4(P4O 12 )3.

[0067] The weight ratio of aluminum (Al) to phosphorus (P) in the composite including a core and a shell can be 0.8 or less, specifically 0.1 to 0.6, 0.2 to 0.4, or 0.2 to 0.35. Within the above range, the metal compound contained in the above silicon oxide is effectively converted into a phosphorus oxide containing an alkali metal or an alkaline earth metal, so that the metal compound can be effectively removed, and the surface structure of the composite can be stabilized. At this time, the contents of phosphorus (P) and aluminum (Al) elements in the composite can be measured by analysis using an Inductively Coupled Plasma Spectrometer (ICP).

[0068] The content of aluminum-containing phosphorus oxides in the composite is preferably less than the content of phosphorus oxides containing alkali metals or alkaline earth metals. Specifically, the content of aluminum-containing phosphorus oxides can be less than 2% by weight, specifically 0.1-1.8% by weight, preferably 0.5-1% by weight. Within the above range, the excellent adhesive properties and coatability of aluminum-containing phosphorus oxides are effectively exhibited, thereby forming a uniform shell on the surface of the core.

[0069] Furthermore, the aluminum-containing phosphorus oxide can be formed by the reaction of a phosphorus oxide precursor and an aluminum salt precursor. In this case, it is preferable to add an excess of the phosphorus oxide precursor. The excess phosphorus oxide precursor reacts with the metal compound contained in the silicon oxide to convert it into a phosphorus oxide containing an alkali metal or alkaline earth metal, thereby maximizing the stabilization effect on the surface structure of the composite. At this time, the content of the phosphorus oxide containing an alkali metal or alkaline earth metal in the composite can be 0.1-7% by weight, preferably 0.5-5% by weight, and more preferably 1-3% by weight.

[0070] The composite may also contain amorphous carbon. Examples of amorphous carbon include soft carbon or hard carbon, mesophase pitch carbides, calcined coke, etc. Amorphous carbon may form the outermost coating of the composite.

[0071] The content of amorphous carbon relative to 100 parts by weight of the composite can be 3-25 parts by weight, preferably 4-15 parts by weight, and more preferably 5-10 parts by weight. Within the above range, the electrical conductivity of the composite particles can be improved, and the volume expansion of the negative electrode active material containing the composite can be reduced during charging.

[0072] The content of the complex can be 10-100 parts by weight relative to 100 parts by weight of the negative electrode active material, preferably 15-100 parts by weight, and as an example, it can be 100 parts by weight.

[0073] The negative electrode active material may further include one or more graphite-based materials selected from natural graphite and artificial graphite. Specifically, the graphite-based material is a material capable of reversibly inserting / deintercalating lithium ions and may be amorphous, plate-like, flake-like, spherical, or fibrous.

[0074] The present invention also provides a method for preparing a negative electrode active material for a lithium secondary battery, which includes: a) a pretreatment step of mixing a silicon compound with an alkali metal precursor or an alkaline earth metal precursor and performing heat treatment to dope the metal in the silicon compound; and b) a composite step of mixing the silicon compound doped with the metal with a phosphorus oxide precursor and an aluminum salt precursor and performing heat treatment to prepare a silicon oxide composite.

[0075] The step a) is a pretreatment step of the silicon compound, and this step can be divided into: the first step of preparing the silicon compound; and the second step of doping the silicon compound with the metal to prepare a pretreated silicon oxide.

[0076] In the first step, the mixing ratio of Si powder and SiO2 powder can be appropriately adjusted and mixed to form the prepared silicon compound particles (Si in SiO x , 0 < x ≤ 2) of Si and O molar ratio, and then heat treatment is performed at a temperature of 500 - 1600 °C for 1 - 12 hours or 1 - 8 hours under an inert atmosphere and reduced pressure to prepare. The prepared silicon compound can be made into silicon compound particles by pulverization.

[0077] The second step is a step of doping the prepared silicon compound particles with the metal. By mixing with an alkali metal precursor or an alkaline earth metal precursor and performing heat treatment, a negative electrode active material containing at least one lithium silicate selected from Li2SiO3, Li2Si2O5, and Li4SiO4 in at least a part of the silicon oxide can be prepared.

[0078] Specifically, in the mixing, the silicon compound and the alkali metal precursor or the alkaline earth metal precursor can be mixed so that the molar ratio of metal / Si is 0.3 to 1.0, preferably 0.3 to 0.8, and more preferably 0.4 to 0.8.

[0079] The alkali metal precursor or the alkaline earth metal precursor can be a hydride, hydroxide, oxide, carbonate, metal particle of one or more metals selected from Li, Na, Mg, and K, or a combination thereof. Preferably, it can be a lithium precursor containing one or more selected from LiOH, Li, LiH, Li2O, and Li2CO3.

[0080] Then, the mixture can be heat-treated at 500 - 1000 °C, preferably at 500 - 700 °C, for 1 - 12 hours under an inert atmosphere. When using a metal doping process by an electrochemical method or a redox method, metal silicate can be easily formed, but under the heat treatment conditions, the production rate of metal silicate (such as Li2SiO3) having a more excellent effect of reducing the volume increase of the silicon oxide can be increased, so it is beneficial to improve the life characteristics.

[0081] The silicon oxide prepared by step a) may contain a residual metal precursor, which contains one or more of LiOH, Li, LiH, Li2O and Li2CO3.

[0082] Step b) is a composite step of silicon oxide doped with metal, which can be divided into: a first step of mixing the silicon oxide with a phosphorus oxide precursor and an aluminum salt precursor; and a second step of heat treatment.

[0083] In the first step, the silicon oxide, phosphorus oxide precursor, and aluminum salt precursor prepared in step a) can be mixed via a solid-phase reaction without the use of a solvent. Specifically, the mixing can be carried out by dry mixing under shear stress and centrifugal force, and preferably by mechanochemical treatment.

[0084] The mechanochemical process is a method of preparing composite particles by applying compressive and shear forces to two or more different particles to make them adhere to each other. This can be achieved using a Hosokawa Micron Mechanofusion system powder composite equipment. Preferably, the difference in circumferential speed between the roller and the internal components is 10-50 m / s, the distance between them is 1-100 mm, and the processing time is 30-120 minutes.

[0085] The phosphorus oxide precursor is not particularly limited as long as it contains a phosphoric acid moiety, but it is preferred to contain one or more of NH4H2PO4, (NH4)2HPO4 and H3PO4.

[0086] The aluminum salt precursor is not particularly limited, but it is preferred to contain one or more selected from Al(NO3)3, NH4Al(SO4)2, AlCl3, AlF3 and Al(OH)3.

[0087] In preparing a silicon oxide composite having the composition ratio desired by the present invention, the weight ratio of the phosphorus oxide precursor to the aluminum salt precursor may be from 1:0.5 to 1:2, preferably from 1:0.8 to 1:1.2.

[0088] The second step is a heat treatment step, which can be carried out in an inert atmosphere at a temperature of 200-600°C for 1-12 hours or 1-8 hours. Within the above range, the residual metal precursor contained in the silicon oxide can be converted into a phosphorus oxide containing an alkali metal or alkaline earth metal, thereby obtaining a silicon oxide composite having the desired aluminum (Al) to phosphorus (P) weight ratio (Al / P) of the present invention.

[0089] The present invention also provides a lithium secondary battery, which includes: a negative electrode containing a negative electrode active material according to a specific embodiment of the present invention; and a positive electrode.

[0090] The negative electrode includes: a current collector; and a negative electrode active material layer located on the current collector and containing the negative electrode active material and a water-based binder.

[0091] The current collector can be selected from copper foil, nickel foil, stainless steel foil, titanium foil, foam nickel, foam copper, a polymer substrate coated with a conductive metal, and combinations thereof, but is not limited thereto.

[0092] The negative electrode active material layer can contain a negative electrode active material and a water-based binder, and can also selectively contain a conductive material.

[0093] The negative electrode active material can contain a silicon oxide (SiO x , 0 < x ≤ 2) composite, and the silicon oxide composite contains a phosphorus oxide containing an alkali metal or alkaline earth metal and a phosphorus oxide containing aluminum. At this time, the silicon oxide is SiO x , x can be a real number of 0 < x ≤ 2, specifically a real number of 0.1 ≤ x ≤ 2. In addition to containing silicon oxide, the core can also contain a composite oxide of lithium and silicon. The composite oxide of lithium and silicon can contain at least one lithium silicate selected from Li2SiO3, Li2Si2O5, and Li4SiO4.

[0094] In addition to containing the above silicon oxide composite, the negative electrode active material can also selectively contain a substance that can reversibly intercalate / deintercalate lithium ions, lithium metal, an alloy of lithium metal, a substance that can be doped and undoped in lithium, or a transition metal oxide.

[0095] As an example of the substance that can reversibly intercalate / deintercalate lithium ions, a carbon material can be cited, that is, a carbon-based negative electrode active material commonly used in lithium secondary batteries can be cited. As a representative example of the carbon-based negative electrode active material, crystalline carbon, amorphous carbon, or these substances can be used simultaneously. As an example of the crystalline carbon, graphite such as amorphous, plate-like, flaky, spherical, or fibrous natural graphite or artificial graphite can be cited. As an example of the amorphous carbon, soft carbon, hard carbon, mesophase pitch carbide, calcined coke, etc. can be cited.

[0096] The alloy of lithium metal can use an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn.

[0097] The substances that can be doped and de-doped with lithium may include silicon-based substances. For example, Si, SiO x (0 < x < 2), Si-Q alloy (where Q is an element selected from alkali metals, alkaline earth metals, group 13 elements, group 14 elements, group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof, and is not Si), Si-carbon composite, Sn, SnO2, Sn-R alloy (where R is an element selected from alkali metals, alkaline earth metals, group 13 elements, group 14 elements, group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof, and is not Sn), Sn-carbon composite, etc. Moreover, at least one of them and SiO2 can be mixed and used. The elements Q and R can be elements selected from 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, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof.

[0098] The transition metal oxide can be lithium titanate oxide.

[0099] The water-based binder serves to bond the negative electrode active material particles well to each other and to bond the negative electrode active material well to the current collector. Examples of the water-based binder may include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, various copolymers thereof, etc. Specifically, the binder may include a binder composed of carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and mixtures thereof.

[0100] The conductive material is used to impart conductivity to the electrode, and any conductive material can be used as long as it does not cause chemical changes in the constructed battery. As examples of the conductive material, a conductive material containing carbon-based substances such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber; metal-based substances such as metal powders or metal fibers of copper, nickel, aluminum, silver; conductive polymers such as polyphenylene derivatives; or mixtures thereof can be used.

[0101] Relative to the total weight of the negative electrode active material layer, the contents of the binder and the conductive material in the negative electrode active material layer can be 1-10% by weight, preferably 1-5% by weight, but are not limited thereto.

[0102] The positive electrode includes: a current collector; and a positive electrode active material layer, which is formed by coating the current collector with a positive electrode slurry containing the positive electrode active material.

[0103] The current collector can be the negative electrode current collector, or it can be a material known in the art, but the invention is not limited thereto.

[0104] The positive electrode active material layer comprises a positive electrode active material and may optionally include a binder and a conductive material. The positive electrode active material may be any positive electrode active material known in the art, for example, preferably a composite oxide of a metal selected from cobalt, manganese, nickel, and combinations thereof, and lithium, but the invention is not limited thereto.

[0105] The adhesive and conductive material may be the negative electrode adhesive and negative electrode conductive material, or may be substances known in the art, but the present invention is not limited thereto.

[0106] The lithium secondary battery may also include a separator located between the negative electrode and the positive electrode, and an electrolyte.

[0107] For example, the separator can be selected from glass fiber, polyester, polyethylene, polypropylene, polytetrafluoroethylene, or combinations thereof, and can be in the form of nonwoven or woven fabric. For example, polyolefin-based polymer separators such as polyethylene and polypropylene can be mainly used in lithium secondary batteries, and to ensure heat resistance or mechanical strength, separators coated with compositions containing ceramic components or polymeric substances can also be used, and single-layer or multi-layer structures can be selectively used, and separators known in the art can also be used, but the invention is not limited thereto.

[0108] The electrolyte contains an organic solvent and a lithium salt.

[0109] The organic solvent acts as a medium that facilitates the movement of ions participating in the electrochemical reactions of the battery. For example, carbonate-based solvents, ester-based solvents, ether-based solvents, ketone-based solvents, alcohol-based solvents, or aprotic solvents can be used. The organic solvent can be used alone or in mixtures of two or more. When using mixtures of two or more, the mixing ratio can be appropriately adjusted according to the desired battery performance. Alternatively, organic solvents known in the art can be used, but the invention is not limited thereto.

[0110] The lithium salt is dissolved in an organic solvent and used in the battery as a source of lithium ions to enable the basic operation of the lithium secondary battery, and is a substance that promotes the movement of lithium ions between the positive and negative electrodes. Examples of such lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiN(SO3C2F5)2, LiN(CF3SO2)2, LiC4F9SO3, LiClO4, LiAlO2, LiAlCl4, and LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2 (where x and y are natural numbers), LiCl, LiI, LiB(C2O4)2 or combinations thereof, but the invention is not limited thereto.

[0111] The concentration of the lithium salt can be used in the range of 0.1-2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, thus exhibiting excellent electrolyte performance, and lithium ions can move effectively.

[0112] Furthermore, as needed, to improve charge / discharge characteristics, flame retardant properties, etc., the electrolyte may further contain pyridine, triethyl phosphate, triethanolamine, cyclic ethers, ethylenediamine, n-glycine dimethyl ether, hexamethylphosphoric triamine, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, aluminum trichloride, etc. In some cases, to impart non-flammability, halogen-containing solvents such as carbon tetrachloride and trifluoroethylene may also be included, and to improve high-temperature storage characteristics, fluoroethylene carbonate (FEC), propene sultone (PRS), fluoropropylene carbonate (FPC), etc., may also be included.

[0113] In the method for manufacturing a lithium secondary battery according to the present invention, which achieves the objectives described above, an electrode assembly can be formed by sequentially stacking a manufactured negative electrode, a separator, and a positive electrode, and then an electrolyte is injected after placing the manufactured electrode assembly into a cylindrical or angular battery casing. Alternatively, the battery can be manufactured by immersing the stacked electrode assembly in an electrolyte and sealing the resulting product in a battery casing.

[0114] The battery casing used in this invention can be any battery casing commonly used in the art, and is not limited by the shape depending on the purpose of the battery, such as a cylindrical, angular, pouch, or coin-shaped casing.

[0115] The lithium secondary battery of the present invention can be used not only as a battery cell for powering small devices, but also preferably as a single cell in medium to large-sized battery modules comprising multiple battery cells. Preferred examples of such medium to large-sized devices include electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and energy storage systems, but are not limited thereto.

[0116] Hereinafter, preferred embodiments and comparative examples of the present invention are described. However, the following embodiments are merely preferred implementations of the present invention, and the present invention is not limited to the following embodiments.

[0117] Example

[0118] (Example 1)

[0119] Step 1: Preparation of silicon compounds

[0120] A raw material mixed with metallic silicon and silicon dioxide was introduced into a reactor, vaporized at 600°C under a vacuum of 10 Pa for 5 hours, and deposited onto an adsorption plate. After sufficient cooling, the deposit was removed and pulverized using a ball mill. The resulting silicon compound particles were SiO₂. x The value of x is 1.0. Then, by adjusting the particle size of the silicon compound particles in stages, SiO particles with an average particle size (D50) of 8 μm are obtained.

[0121] Step 2: Preparation of silicon oxide containing lithium compounds

[0122] The prepared SiO particles and LiOH powder are mixed to form a Li / Si molar ratio of 0.75 to form a mixed powder. The mixed powder and zirconia balls (1 to 20 times the volume of the mixed powder) are placed in a sealed container and shaken and mixed for 30 minutes. Afterward, the mixed powder is filtered through a 25-500 μm sieve and placed in an alumina crucible.

[0123] An alumina crucible was heat-treated at 800°C for 8 hours under a nitrogen atmosphere. The heat-treated powder was then recovered and pulverized in a mortar to prepare a silicon oxide containing lithium compounds. At this point, the average particle size of the silicon oxide was 6.7 μm.

[0124] Step 3: Preparation of silicon oxide composite

[0125] The silicon oxide composite was prepared by mixing 98 wt% of the prepared silicon oxide (D50: 6.7 μm), 1 wt% of Al(NO3)3·9H2O and 1 wt% of NH4H2PO4 and subjecting it to mechanochemical treatment for 30 minutes. Then, it was heated to 400 °C at a rate of 3 °C / min in a high-purity argon atmosphere and heat-treated at 400 °C for 4 hours.

[0126] Step 4: Manufacturing the negative electrode

[0127] A slurry is prepared by mixing 80 wt% of the prepared composite, 10 wt% of Super C, 6 wt% of carboxymethyl cellulose, and 4 wt% of styrene-butadiene rubber in distilled water. The slurry is then coated onto a Cu foil current collector, and a negative electrode is manufactured using conventional processes of drying and pressing.

[0128] Step 5: Manufacturing the half-cell

[0129] The CR2016 coin cell battery is manufactured by using the prepared negative electrode and lithium metal as the counter electrode, inserting a polyethylene (PE) separator between the negative and counter electrodes, and then injecting an electrolyte. The assembled coin cell battery is left to stand at room temperature for 3-24 hours to create a half-cell. At this time, the electrolyte is prepared by mixing 1.0 M LiPF6 as the lithium salt and 2 vol% FEC electrolyte additive in an organic solvent (EC:EMC = 3:7 vol%).

[0130] (Comparative Example 1)

[0131] Except that Al(NO3)3·9H2O as an aluminum salt precursor and NH4H2PO4 as a phosphorus oxide precursor are not added in step 3 of Example 1, the same method as in Example 1 is used.

[0132] Evaluation example

[0133] Evaluation Example 1: Analysis of the properties of silicon oxide composites

[0134] (Example 1 and Comparative Example 1)

[0135] 1) Scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX) analysis

[0136] The silicon oxide composite prepared in step 3 of Example 1 was analyzed by SEM-EDX, and the results are shown below. Figure 1 and Figure 2 middle.

[0137] from Figure 1 It can be confirmed that the obtained composite contains aluminum and phosphorus in addition to silicon and oxygen.

[0138] from Figure 2 It can be confirmed that aluminum is uniformly coated on the surface of the prepared composite particles.

[0139] 2) X-ray diffraction (XRD) analysis

[0140] XRD analysis was performed on the silicon oxide composites prepared in step 3 of Example 1 and Comparative Example 1, and the results are shown below. Figure 3 middle.

[0141] from Figure 3 It can be confirmed that the composite prepared according to Example 1 contains a crystalline Li3PO4 phase.

[0142] Evaluation Example 2: Evaluation based on the characteristics of the addition ratio of phosphorus oxide precursor and aluminum salt precursor

[0143] (Examples 2 to 8)

[0144] Except for the addition of Al(NO3)3·9H2O as an aluminum salt precursor and NH4H2PO4 as a phosphorus oxide precursor in step 3 of Example 1 as shown in Table 1 below, the process was carried out in the same manner as in Example 1. At this time, the total content of the aluminum salt precursor and the phosphorus oxide precursor was 2% by weight.

[0145] (Comparative Example 2)

[0146] Except that heat treatment is not performed in step 3 of embodiment 1, the same method as in embodiment 1 is used.

[0147] (Evaluation Method)

[0148] *Analysis of gas generation rate of slurry

[0149] Prepare a slurry comprising 25% by weight of the composite prepared in step 3, 70% by weight of artificial graphite, 1.5% by weight of carboxymethyl cellulose, 2% by weight of styrene-butadiene rubber, 1.5% by weight of conductive material Super C, and having a solids content of 40% by weight.

[0150] 4 ml of the prepared slurry was injected into an airtight syringe and left at room temperature for 7 days with the injection port sealed.

[0151] Then, the gas generation rate of the slurry is calculated according to the following formula 1, and the results are shown in Table 1 below.

[0152] [Calculation Formula 1]

[0153] Gas generation rate of slurry = (Slurry volume after 1 day - Initial slurry volume) / (Initial slurry volume)

[0154] *Analysis of viscosity change over time

[0155] The initial viscosity and viscosity after 1 day of the slurries prepared in step 4 of Examples 1 to 8 and Comparative Examples 1 to 2 were measured. The rate of change of viscosity over time was calculated according to the following formula 2, and the results are shown in Table 1 below. At this time, the viscosity of the slurry was measured using a Brookfield rotational viscometer at room temperature and pressure with a viscosity of 1 s⁻¹. -1 The shear rate was measured.

[0156] [Calculation Formula 2]

[0157] Rate of change of viscosity over time = (initial viscosity - viscosity after 1 day) / initial viscosity

[0158] *Evaluation of charge and discharge performance

[0159] At room temperature (25°C), the half-cells manufactured according to Examples 1 to 8 and Comparative Examples 1 to 2 were charged at a rate of 0.1C and a constant current until the voltage reached 0.01V (vs. Li). Then, the voltage was maintained at 0.01V in constant voltage mode while being cut off at a rate of 0.01C, thereby charging at a constant voltage. The half-cells were discharged at a constant current at a rate of 0.1C until the voltage reached 1.5V (vs. Li). This charge and discharge cycle was considered as one cycle, and another charge and discharge cycle was performed in the same manner. Then, the applied current during charge and discharge was changed to 0.5C and 50 cycles were performed, with a 10-minute rest period between cycles.

[0160] The charge / discharge efficiency and discharge capacity of the first cycle in the 50 cycles are designated as the initial efficiency and initial discharge capacity, respectively. Based on the initial discharge capacity, the capacity retention rate of the 50 cycles is calculated and recorded in Table 1 below.

[0161] [Table 1]

[0162]

[0163]

[0164] The Al / P values ​​in Table 1 refer to the weight ratio (Al / P) of aluminum (Al) to phosphorus (P) in the composite as analyzed by ICP.

[0165] As can be confirmed from Table 1, a silicon oxide composite with an Al / P value of less than 0.8 was prepared when the addition ratio of aluminum salt precursor to phosphorus oxide precursor was in the range of 0.5 to 3.

[0166] Specifically, in Examples 1 to 8, where the Al / P value in the prepared silicon oxide composite was 0.8 or less, it was confirmed that the slurry exhibited a lower gas generation rate and a lower viscosity change rate over time compared to Comparative Example 1, which did not contain Al and P. This was determined to be due to the effective removal of residual lithium compounds (LiOH) contained in the silicon oxide via the following reaction formula 1, thereby suppressing gas generation caused by the dissolution of LiOH in the slurry and reducing the viscosity change rate over time.

[0167] In Comparative Example 2, a silicon oxide composite was prepared under the same addition ratio of aluminum salt precursor and phosphorus oxide precursor as in Example 1. However, since no heat treatment was performed, the Li3PO4 formation reaction according to Reaction Formula 1 did not occur, and the aluminum salt precursor and phosphorus oxide precursor added according to Reaction Formula 2 reacted with each other to form AlPO4, or may exist in the composite in a precursor state. Therefore, although it had an Al / P value similar to that of Example 1, the lack of heat treatment prevented the removal of residual lithium compounds (LiOH) contained in the silicon oxide, resulting in a large amount of dissolution in the slurry and exhibiting a high gas generation rate and viscosity change rate over time.

[0168] [Reaction Formula 1]

[0169] LiOH + (NH4)H2PO4 → Li3PO4

[0170] [Reaction 2]

[0171] Al(NO3)3·9H2O+(NH4)H2PO4→AlPO4

[0172] Furthermore, it can be confirmed that the half-cells manufactured by Examples 1 to 8 exhibit high capacity retention compared to Comparative Examples 1 to 2. This is determined to be because, through Reaction Formula 1 and Reaction Formula 2, a silicon oxide composite containing a shell comprising lithium, aluminum, and phosphorus is generated on a core surface comprising silicon oxide, thereby stabilizing the surface structure of the composite and significantly improving its charge-discharge characteristics.

[0173] Furthermore, it can be confirmed that in Examples 1 to 7, where the Al / P value is in the range of 0.1 to 0.6, improved slurry stability and initial charge-discharge characteristics are observed compared to Example 8, where the Al / P value is not in the above range. Therefore, it can be confirmed that the preferred Al / P value in the silicon oxide composite is 0.1 to 0.6.

[0174] Evaluation Example 3: Evaluation based on the characteristics of the added amounts of phosphorus oxide precursor and aluminum salt precursor

[0175] (Examples 9 to 15)

[0176] Except for adding Al(NO3)3·9H2O as an aluminum salt precursor and NH4H2PO4 as a phosphorus oxide precursor in step 3 of Example 1 at a weight ratio of 1:1 and the amounts shown in Table 2 below, the process was carried out in the same manner as in Example 1.

[0177] (Evaluation Method)

[0178] The gas generation rate, viscosity change rate over time, and charge / discharge performance of the slurry were evaluated using the same method as in Evaluation Example 2, and the results are shown in Table 2 below.

[0179] [Table 2]

[0180]

[0181] The total amount of precursors added refers to the total amount of aluminum salt precursors and phosphorus oxide precursors added.

[0182] As can be confirmed from Table 2, in Examples 9 to 13, where the total addition amount of aluminum salt precursor and phosphorus oxide precursor is 0.6% by weight or more, the slurry exhibits a lower gas generation rate and superior charge-discharge characteristics compared to Examples 14 and 15, where the total addition amount is less than 0.6% by weight. This indicates that within the aforementioned content range, the reactions according to Reaction Formulas 1 and 2 are carried out effectively, thereby effectively achieving the removal of residual lithium compound LiOH and the stabilization of the composite surface structure.

[0183] In Examples 12 and 13, it was determined that due to the excessive addition of the aforementioned precursors, the viscosity of the slurry changed relatively rapidly over time, and the charge / discharge performance decreased. Therefore, it can be confirmed that the preferred total addition amount of the aluminum salt precursor and the phosphorus oxide precursor is 0.6-3% by weight.

Claims

1. A negative electrode active material for a lithium secondary battery, which comprises a silicon oxide composite, in, The silicon oxide is SiO x 0 <x≤2, The silicon oxide composite comprises a phosphorus oxide containing an alkali metal or an alkaline earth metal and a phosphorus oxide containing aluminum, The phosphorus oxide containing an alkali metal or an alkaline earth metal is transformed by reacting a phosphorus oxide precursor with an alkali metal or an alkaline earth metal compound, and the alkali metal or the alkaline earth metal comprises one or more selected from Li, Na, Mg and K.

2. The negative electrode active material for lithium secondary batteries according to claim 1, wherein, The composite has a weight ratio of aluminum (Al) to phosphorus (P), Al / P, of 0.8 or less.

3. The negative electrode active material for lithium secondary batteries according to claim 2, wherein, The composite has a weight ratio of aluminum (Al) to phosphorus (P), Al / P, of 0.1 to 0.

6.

4. The negative electrode active material for lithium secondary batteries according to claim 1, wherein, Comprises a phosphorus oxide containing an alkali metal or an alkaline earth metal represented by the following Chemical Formula 1: [Chemical Formula 1] M x P y O z In the Chemical Formula 1, 1≤x≤4, 1≤y≤4, 0<z≤7, and M comprises one or more selected from Li, Na, Mg and K.

5. The negative electrode active material for lithium secondary batteries according to claim 1, wherein, The aluminum-containing phosphorus oxide comprises a group selected from AlPO4, Al(PO3)3, Al(H2PO4)3, and Al2P6O. 18 and Al4(P4O) 12 One or more of 3.

6. The negative electrode active material for lithium secondary batteries according to claim 1, wherein, At least a part of the silicon oxide further comprises at least one lithium silicate selected from Li2SiO3, Li2Si2O5 and Li4SiO4.

7. The negative electrode active material for lithium secondary batteries according to claim 6, wherein, The content of the lithium silicate is 10-95 parts by weight relative to 100 parts by weight of the silicon oxide.

8. The negative electrode active material for lithium secondary batteries according to claim 1, wherein, The composite further comprises amorphous carbon.

9. The negative electrode active material for lithium secondary batteries according to claim 1, wherein, Further comprises one or more graphite-based materials selected from natural graphite and artificial graphite.

10. A method for preparing a negative electrode active material for a lithium secondary battery, which comprises: a) A pretreatment step of mixing a silicon compound and an alkali metal precursor or an alkaline earth metal precursor and performing heat treatment to dope a metal in the silicon compound; And b) A composite step of mixing the silicon compound doped with a metal with a phosphorus oxide precursor and an aluminum salt precursor and performing heat treatment to prepare a silicon oxide composite, the silicon oxide composite comprising a phosphorus oxide containing an alkali metal or an alkaline earth metal and a phosphorus oxide containing aluminum, Wherein, the phosphorus oxide precursor comprises one or more selected from NH4H2PO4, (NH4)2HPO4 and H3PO4, and the alkali metal or the alkaline earth metal comprises one or more selected from Li, Na, Mg and K.

11. The method for preparing negative electrode active material for lithium secondary batteries according to claim 10, wherein, The alkali metal precursor or the alkaline earth metal precursor in the pretreatment step a) is a hydride, hydroxide, oxide, carbonate, metal particles or a combination thereof of one or more metals selected from Li, Na, Mg and K.

12. The method for preparing negative electrode active material for lithium secondary batteries according to claim 10, wherein, In the pretreatment step a), heat treatment is performed at 500-1000°C for 1-12 hours in an inert atmosphere.

13. The method for preparing negative electrode active material for lithium secondary batteries according to claim 10, wherein, The composite step b) is performed by mechanochemical treatment.

14. The method for preparing negative electrode active material for lithium secondary batteries according to claim 10, wherein, In the composite step b), heat treatment is performed at 200-600°C for 1-12 hours in an inert atmosphere.

15. A lithium secondary battery, comprising: A negative electrode comprising the negative electrode active material according to any one of claims 1 to 9; And a positive electrode.

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