Silicon-based active material for lithium secondary battery, and secondary battery anode material using same

Abstract

The present invention relates to a pre-lithiation method for a silicon-based active material, and a silicon-based active material pre-lithiated thereby, the method comprising the steps of: (S1) immersing a silicon-based active material in a pre-lithiation solution comprising an organic solvent and a lithium-hydrocarbon molecular complex; (S2) washing same with the solvent and drying same, thereby obtaining a powder; and (S3) heat-treating the powder at a temperature of 400-800°C under an inert gas atmosphere.

Description

Silicon-based active material for lithium secondary batteries and secondary battery anode material using the same

[0001] The present invention relates to a silicon-based active material for a lithium secondary battery and a secondary battery negative electrode material using the same.

[0002] Lithium secondary batteries offer advantages such as high energy density, lightweight, high-power yet stable discharge characteristics, and stability over a wide temperature range. These advantages have led to their widespread use in small home appliances and precision instruments. Their use in mid- to large-sized lithium secondary batteries is also rapidly increasing. Accordingly, silicon-based anode materials, which can dramatically increase capacity compared to commercial graphite anodes, are attracting attention.

[0003] However, silicon-based anode materials have low initial efficiency and therefore have high irreversible capacity in the first cycle, which limits the reversible capacity during actual battery operation, making commercialization difficult. To overcome this, high-efficiency technologies such as pre-lithiation methods are required.

[0004] Previously reported pre-lithiation methods for silicon-based anode materials have high costs and safety issues, such as directly contacting lithium metal or creating a temporary cell, electrochemically inserting lithium, and then disassembling the cell to recover the recovered electrode.

[0005] Furthermore, the existing prelithiation method is SiO x Lithium is inserted into Si and SiO2, which constitute the system material, to form lithium silicide (Li). x Si) and lithium silicate are formed simultaneously, but the lithium silicide has poor stability in the atmosphere and moisture, and can cause side reactions with solvents or water during slurry production, which limits the commercialization of the active material.

[0006]

[0007] Accordingly, the inventor of the present invention completed the present invention in order to solve the problems of the existing pre-lithiation method as described above.

[0008] The present invention has been devised to solve the above problems, and 0.5 V (vs Li / Li + ) and silicon oxide system (SiO) with lithium-hydrocarbon molecular complexes having redox potentials below x , 0 <x<2) 음극재 간의 자발적인 전하전달 반응을 통해, 활물질에 리튬을 균일하게 삽입하는 것이 가능한 사전리튬화 용액을 처리하고, 이후, 적절한 조건의 열처리를 가하여 대기 및 수분 안정성이 크게 향상된 실리콘산화물계 음극재의 사전리튬화 방법 및 이로부터 사전리튬화된 실리콘계 음극 활물질을 제공하는 것을 목적으로 한다.

[0009]

[0010] However, the problems to be solved by the present invention are not limited to the problems mentioned above, and other problems not mentioned can be clearly understood by a person having ordinary skill in the relevant technical field from the description below.

[0011] According to one embodiment of the present invention, there is provided a step (S1) of immersing a silicon-based active material in a prelithiation solution comprising an organic solvent and a lithium-hydrocarbon molecule complex;

[0012] Step (S2) of obtaining a powder by washing and drying with the above solvent; and

[0013] A step (S3) of heat-treating the above powder at a temperature of 400°C to 800°C under an atmosphere of an inert gas;

[0014] A method for prelithiation of a silicon-based active material including a .

[0015]

[0016] According to one embodiment of the present invention, a silicon-based active material pre-lithiated according to the above pre-lithiation method is provided, which comprises a composite of lithium silicon oxide of Li2SiO3 having a size of 12 nm or less and silicon having a size of 5 nm or less.

[0017]

[0018] According to one embodiment of the present invention, a negative electrode is provided, comprising the pre-lithiated silicon-based active material; a conductive material; and a binder.

[0019]

[0020] According to one embodiment of the present invention, a lithium secondary battery is provided, including the negative electrode; the positive electrode; and the electrolyte.

[0021]

[0022] According to one embodiment of the present invention, a capacitor is provided, including a cathode; an anode; and an electrolyte.

[0023] A pre-lithiation method according to one embodiment of the present invention enables safe and uniform lithiation through a solution process, suppresses the growth of silicon crystal grains under relatively low temperature conditions, and selectively forms a desired phase. Accordingly, a secondary battery including a pre-lithiated negative active material has the advantage of exhibiting high initial coulombic efficiency and a long lifespan. In addition, the active material pre-lithiated using the pre-lithiation method can exhibit stability in the air and moisture.

[0024] Figure 1 shows a schematic diagram of a pre-lithiation solution and a cathode pre-lithiation technology utilizing the same according to one embodiment of the present invention.

[0025] Figure 2 is a diagram showing the composition of lithium silicon oxide through a ternary phase equilibrium.

[0026] Figure 3 is a drawing showing the results of observing XRD diffraction patterns according to the amount of lithium supplied.

[0027] Figure 4 is a diagram showing the electrochemical performance of an electrode according to the amount of lithium supplied.

[0028] FIG. 5 is a diagram showing dQ / dV analysis according to one embodiment of the present invention.

[0029] Figure 6 is a diagram showing the change in half-width on XRD according to the amount of lithium supplied.

[0030] Figure 7 is a diagram showing the results of calculating the crystal size of silicon and lithium silicon oxide using XRD results.

[0031] Figure 8 is a diagram showing the trend of initial Coulomb efficiency according to changes in lithium composition.

[0032] Figure 9 is a diagram showing the life characteristics according to changes in lithium composition.

[0033] Figure 10 is a diagram showing XRD results for lithium silicon oxide phase formation according to heat treatment temperature.

[0034] Figure 11 is a diagram showing the performance difference according to the solvent (THF, 2-meTHF) during solution treatment at room temperature.

[0035] FIG. 12 is a drawing showing the results of evaluating performance when naphthalene is used as a hydrocarbon molecule according to one embodiment of the present invention.

[0036] FIG. 13 is a diagram showing a selected area diffraction (SAD) pattern analysis using a transmission electron microscope (TEM) for a pre-lithiated silicon-based active material according to one embodiment of the present invention.

[0037] FIG. 14 is a drawing showing TEM diffraction DF images of (111)Si and (200)Li2SiO3 crystal planes for a pre-lithiated silicon-based active material according to one embodiment of the present invention.

[0038] Figure 15 is a diagram showing the results of achieving high Coulomb efficiency through optimization of the composition (ratio of active material) of the electrode.

[0039] FIG. 16 is a drawing showing the results of evaluating the performance of a graphite / silicon oxide composite cathode according to one embodiment of the present invention.

[0040] Hereinafter, embodiments are described in detail with reference to the attached drawings. However, the embodiments may be modified in various ways, and the scope of the patent application is not limited or restricted by these embodiments. It should be understood that all modifications, equivalents, or alternatives to the embodiments are included within the scope of the patent application.

[0041] The terms used in the examples are for illustrative purposes only and should not be construed as limiting. Singular expressions include plural expressions unless the context clearly dictates otherwise. In this specification, terms such as "comprise" or "have" are intended to indicate the presence of a feature, number, step, operation, component, part, or combination thereof described in the specification, but should be understood to not preclude the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0042] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by a person of ordinary skill in the art to which the embodiments pertain. Terms defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and shall not be interpreted in an idealized or overly formal sense unless explicitly defined herein.

[0043] In addition, when describing with reference to the attached drawings, identical components will be assigned the same reference numerals regardless of the drawing numbers, and redundant descriptions thereof will be omitted. When describing embodiments, if a detailed description of a related known technology is judged to unnecessarily obscure the gist of the embodiment, the detailed description will be omitted.

[0044]

[0045] According to one embodiment of the present invention, there is provided a step (S1) of immersing a silicon-based active material in a prelithiation solution comprising an organic solvent and a lithium-hydrocarbon molecule complex;

[0046] Step (S2) of obtaining a powder by washing and drying with the above solvent; and

[0047] A step (S3) of heat-treating the above powder at a temperature of 400°C to 800°C under an atmosphere of an inert gas;

[0048] A method for prelithiation of a silicon-based active material including a .

[0049]

[0050] Silicon-based negative electrode materials have a problem of high irreversible capacity in the first cycle due to low initial efficiency, and therefore, the silicon-based active material used in the above pre-lithiation method is SiO x (0 <x<2) 을 포함하는 것일 수 있다.

[0051]

[0052] A method for pre-lithiation of a silicon-based active material according to one embodiment of the present invention is simple in that it is performed by immersing the silicon-based active material in a pre-lithiation solution, and has the advantage of being able to uniformly insert lithium into the silicon-based active material through a more uniform reaction compared to existing pre-lithiation methods such as a solid-state mixing method. The immersion process may be performed at a temperature of, for example, -10 to 80°C. Preferably, it may be performed at a temperature of 10 to 50°C. In the temperature range of -10 to 80°C, the redox potential of the complex typically decreases, and the enhanced reducing power may improve the initial Coulombic efficiency. If it is performed at a temperature below -10°C, the redox potential may become excessively high, preventing the pre-lithiation reaction from occurring. If it is performed at a temperature exceeding 80°C, precipitation of lithium metal may occur, which is not preferable.

[0053] The above immersion process can be performed for 0.01 to 1440 minutes, preferably for 1 to 600 minutes, and more preferably for 5 to 240 minutes. The total mass of lithium ions in the solution can be adjusted from 1 to 18 wt% based on the silicon oxide active material, and the time can be shortened under high temperature conditions with high reducing power to complete the lithium insertion reaction from the lithium-hydrocarbon molecule complex to the silicon oxide, and the time can be adjusted to be long under room temperature and low temperature.

[0054] Meanwhile, since the time required for sufficient reaction may vary depending on the size of the active material particles, it is desirable to observe the change in initial efficiency over time and determine the reaction time at which the initial efficiency no longer improves.

[0055] In one embodiment of the present invention, for example, a rapid lithium insertion reaction is induced at a temperature of 60 degrees or higher for 1 hour, and then the temperature is lowered to room temperature to allow the remaining lithium insertion reaction to occur for a sufficient period of time, but the temperature and time are not limited thereto.

[0056]

[0057] Meanwhile, the organic solvent used in the above S1 step may include a cyclic ether solvent, a linear ether solvent, etc.

[0058] Specific examples of the cyclic ether solvent may include at least one selected from the group consisting of tetrahydropyran, dioxolane, methyldioxolane, dimethyldioxolane, vinyldioxolane, methoxydioxolane, ethylmethyldioxolane, oxane, dioxane, trioxane, tetrahydrofuran, methyltetrahydrofuran, dimethyltetrahydrofuran, dimethoxytetrahydrofuran, ethoxytetrahydrofuran, ethyltetrahydrofuran, methyltetrahydropyran, dimethyltetrahydropyran, dihydropyran, tetrahydropyran, hexamethylene oxide, furan, dihydrofuran, dimethoxybenzene, and dimethyloxetane.

[0059] In addition, specific examples of the linear ether solvent may include at least one selected from the group consisting of dimethyl ether, diethyl ether, ethyl methyl ether, ethyl propyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, diisobutyl ether, ethyl tert-butyl ether, dimethoxymethane, trimethoxymethane, dimethoxyethane, diethoxyethane, dimethoxypropane, diethylene glycol dimethyl ether, diethylene glycol ethyl methyl ether, diethylene glycol isopropyl methyl ether, diethylene glycol butyl methyl ether, diethylene glycol diethyl ether, diethylene glycol tert-butyl ethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, ethylene glycol ethyl methyl ether, ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, and methoxypropane.

[0060] Among them, considering the superiority of the initial Coulombic efficiency in the first cycle of the pre-lithiated electrode, 2-methyltetrahydrofuran among the organic solvents can be considered preferable.

[0061]

[0062] Meanwhile, the lithium-hydrocarbon complex in the above S1 step is lithium-to-Li (vs Li / Li) + ) may have a redox potential of 0.5 V or less. By having the redox potential as described above, sufficient reducing power for prelithiation can be exhibited, and not only successful chemical prelithiation is possible even in a composite negative electrode including a silicon-based active material, but lithium can be uniformly inserted throughout the electrode.

[0063] The hydrocarbon molecule of the lithium-hydrocarbon complex may specifically include at least one selected from the group consisting of biphenyl, naphthalene, anthracene, phenanthrene, tetracene, diphenylanthracene, perylene, pyrene, triphenylene, bianthryl, terphenyl, quaterphenyl, and stilbene, and the hydrocarbon molecule may be substituted or unsubstituted with at least one substituent selected from the group consisting of an alkyl group having 1 to 4 carbon atoms, benzene, fluorine, and chlorine.

[0064]

[0065] The above step S2 may correspond to a step of obtaining a powder by washing with the same organic solvent as used in the above step S1 and then drying. Through this, a pre-lithiated powder of higher purity can be obtained.

[0066]

[0067] Afterwards, a heat treatment process is performed on the powder obtained by the above method (S3).

[0068] The existing pre-lithiation method uses a method of forming lithium silicide and lithium silicate simultaneously by inserting lithium without distinction between Si and SiO2, which constitute the silicon-based active material. However, the lithium silicide thus produced has problems in that it has poor stability in the atmosphere and moisture, and can cause side reactions with water during slurry production.

[0069] Accordingly, the present invention converts a composite composed of lithium silicide and lithium silicate into a composite composed of silicon and lithium silicate by performing the heat treatment process of the above-mentioned S3 step, thereby obtaining a high-value-added, high-performance active material having high initial efficiency, reversible capacity, atmospheric stability, and processability.

[0070] More specifically, through Fig. 2, silicon oxide is silicon oxide SiO x For example, if lithium is inserted into the silicon oxide, the Li composition changes along the central red line at room temperature. Afterwards, if heat treatment is performed at a specific composition, phase separation occurs at the vertex of the corresponding region, and the overall system becomes stable. Meanwhile, as an example, before heat treatment, Li y Si + Li z When the green dot material that exists in the SiO2 state undergoes heat treatment, it is converted into a mixed state of Li2SiO3, Li2Si2O5, and Si.

[0071] However, in the case of compounds with excessive lithium content, such as Li4SiO4 or more, among lithium silicon oxides, application to the electrode manufacturing process is impossible due to reactivity with moisture, so only when lithium is supplied in the solid line area of ​​the central red line and heated, a stable state in which lithium silicon oxide and silicon are mixed can be achieved. That is, silicon oxide SiO x (0 <x<2)에, 도 2 에 표시된 노란색 영역에 해당하는 적절한 양의 리튬이 추가되었을 때 대기와 수분에 안정한 리튬실리콘산화물 / 실리콘 복합체 형성을 유도할 수 있다.

[0072] Meanwhile, the heat treatment process in the S3 step may be performed specifically in an atmosphere of an inert gas such as nitrogen or argon (Ar) at a temperature range of 400°C to 800°C for 0.1 to 12 hours, and preferably, may be performed at a temperature of 450°C or higher and 700°C or lower for 0.5 to 6 hours.

[0073] When heat treatment is performed at a temperature below 400°C, as shown in Fig. 10, even if the same amount of lithium is supplied, the formation of the Li2SiO3 phase is limited, and from a temperature of 500°C or higher, the Li2SiO3 phase can be primarily formed together with the Si phase. In other words, it can be seen that in order to form the Li2SiO3 phase exhibiting high initial Coulombic efficiency, heat treatment above an appropriate temperature is required after pre-lithiation.

[0074]

[0075] Meanwhile, from the perspective of the heat treatment process (S3) as described above, the lithium content of the lithium-hydrocarbon molecular complex may be 5 to 15 mass% relative to the mass of the silicon-based active material, more preferably 5 to 12.5 mass%, and even more preferably 6.5 to 12.5 mass%.

[0076] As shown in Fig. 2, depending on the amount of lithium supplied, Li2Si2O5, Li2SiO3, and Li4SiO4 phases are formed together with the silicon phase after heat treatment. In particular, as shown in Fig. 3, when the amount of lithium is 5 mass% or more and 12.5 mass% or less based on the mass of the silicon-based active material, not only is unstable Li4SiO4 not formed in the air, but also the size of the peak (25°) of the Li2Si2O5 phase with low efficiency is formed relatively small compared to the size of the peak (27°) of the Li2SiO3 phase. In contrast, when the amount is 2.5 mass%, the size of the peak (25°) of the Li2Si2O5 phase with low efficiency is formed relatively large compared to the size of the peak (27°) of the Li2SiO3 phase. In addition, when the amount of lithium supplied is excessive, the crystallinity of silicon is strengthened, resulting in an increase in the size of crystal grains, and as shown in the 15 mass% graph of Fig. 4, a flat section appears on the charge / discharge graph (capacity / voltage), resulting in a decrease in capacity and life characteristics.

[0077]

[0078] According to one embodiment of the present invention, a prelithiated silicon-based active material is provided, which comprises a composite of lithium silicon oxide of Li2SiO3 having a size of 12 nm or less and silicon having a size of 5 nm or less.

[0079] Preferably, the particle size of the lithium silicon oxide of the Li2SiO3 may be 10 nm or less, and the particle size of the silicon may be 5 nm or less. If the particle size exceeds the above range, a phenomenon in which the reversible capacity and life characteristics are reduced may occur.

[0080] Meanwhile, the complex may optionally additionally include Li2Si2O5 in addition to Li2SiO3 as a lithium silicon oxide, and may preferably include Li2Si2O5 in a smaller amount than Li2SiO3.

[0081]

[0082] According to one embodiment of the present invention, a negative electrode including a silicon-based active material pre-lithiated by the above-described pre-lithiation method; a conductive material; and a binder; can be manufactured, and further, a lithium secondary battery including a negative electrode; a positive electrode; and an electrolyte manufactured in this manner can be provided.

[0083] In this case, the ratio of the silicon-based active material may be 70% by weight or more compared to the total weight of the active material, conductive material, and binder constituting the negative electrode.

[0084] In addition, the above-mentioned pre-lithiated silicon-based active material includes not only a silicon composite including lithium silicon oxide and silicon, but also amorphous carbon, hard carbon, soft carbon (SiO x / C, SiO x -C or SiO x @C form; the above SiO x / C or SiO x -C form means a simple mixed, complexed or carbon coated form, and the SiO x @C form may mean a carbon-coated form), and may include graphite, and at this time, the content ratio of the graphite to the silicon composite is not particularly limited, but may be, for example, 95:5 to 5:95, and the content of the silicon composite based on the total active material weight may be, for example, about 5 wt% to about 50 wt%, preferably 5 wt% to 30 wt%. Furthermore, as an additional example of the silicon-based active material, a form additionally including magnesium (Mg) (Mg-SiO x , Mg-doped SiO x , Mg-SiO x / C, Mg-doped SiO x / C, Mg-SiO x -C, Mg-doped SiO x-C) may be a silicon-based active material. The silicon-based active material may be Mg-SiO x or Mg-SiO x In the case of a silicon-based active material in the form of / C, the content of Mg included therein may be 13 wt% or less based on the total weight of the active material.

[0085]

[0086] Hereinafter, the composition and resulting effects of the present invention will be described in more detail through examples and comparative examples. However, these examples are intended to more specifically illustrate the present invention, and the scope of the present invention is not limited to these examples.

[0087]

[0088] -Example

[0089] 1. Manufacturing example: Manufacturing of pre-lithiation solution and pre-lithiation method (Fig. 1)

[0090] A 2-methyltetrahydrofuran (2-meTHF) solution containing 1 M aromatic hydrocarbon (biphenyl) and lithium ions was prepared, and silicon oxide (SiO) was added to the solution. x , 0 <x<2)을 담지하여 리튬화를 시켰다. 이를 통해, 상기 SiO x Lithium was simultaneously inserted into the Si and SiO2 domains constituting the composite, converting it into a composite of lithium silicide and lithium silicate.

[0091] After recovering the lithiated silicon oxide composite powder from the solution, it was washed with 2-meTHF solvent to remove residual lithium and biphenyl.

[0092] Afterwards, the lithiated powder was heat-treated by heating it at 400 to 800°C for 0.5 to 6 hours in an argon atmosphere, and a stabilized powder in the form of a silicon and lithium silicate complex was obtained.

[0093]

[0094] 2. Test Example 1: Observation of XRD diffraction patterns according to lithium supply amount (Fig. 3)

[0095] Silicon oxide (SiO x ) Pre-lithiation was performed by immersing the active material in a 1M biphenyl-lithium solution based on 2-methyltetrahydrofuran containing 2.5 to 17.5 mass% of lithium relative to its mass.

[0096] Afterwards, the powder obtained by washing with the same solvent was heated in an argon atmosphere and then subjected to X-ray diffraction analysis (XRD).

[0097] As a result, the raw material, which only had a silicon (Si) phase with low crystallinity, was observed to have Li2Si2O5, Li2SiO3, and Li4SiO4 phases along with the silicon phase depending on the amount of lithium supplied after pre-lithiation and heat treatment. It was confirmed that the peak intensity of the silicon phase became stronger and sharper as the supply of lithium increased.

[0098] Through this, it was found that when the amount of lithium is 7.5 mass% or more and 12.5 mass% or less, the unstable Li4SiO4 phase is not formed in the atmosphere, and the low-efficiency Li2Si2O5 phase is not formed, so it is a section suitable for high efficiency.

[0099] In addition, it was found that as the amount of lithium supplied increases, the crystallinity of silicon is strengthened, thereby increasing the size of the crystal grains, and this can be confirmed to affect the electrochemical properties.

[0100]

[0101] 3. Test Example 2: Evaluation of Electrochemical Performance of Electrodes According to Lithium Supply Amount (Fig. 4)

[0102] Silicon oxide (SiO x) Prelithiation was performed by immersing the active material in a 1M biphenyl-lithium solution based on 2-methyltetrahydrofuran containing 2.5 to 17.5 mass% of lithium relative to its mass. Thereafter, the powder obtained by washing with the same solvent was heated in an argon atmosphere, and an electrode was manufactured using the powder obtained therefrom.

[0103] A CR2032 type battery was fabricated using a lithium-ion battery, a lithium metal chip punched to a diameter of 11.3 mm as a positive electrode, a lithium metal chip punched to a diameter of 16 mm as a negative electrode, and Celgard as a separator, and an electrolyte containing 5 vol% FEC additive in 1 M LiPF6EC / DEC. The battery was charged and discharged at a current density of 0.2 C in the range of a discharge bottom voltage of 30 mV and a charge top voltage of 1.2 V at a room temperature of 30°C to evaluate the initial coulombic efficiency and capacity.

[0104] As a result, the control bare silicon oxide electrode showed an initial efficiency of 72.0%, while the electrodes supplied with 8.5 mass% and 15 mass% of lithium showed initial Coulombic efficiencies of 84.9% and 85.8%, respectively, and it was confirmed that the initial Coulombic efficiency increased as the amount of lithium supplied increased.

[0105] However, it was confirmed that a plateau appeared in the electrochemical profile when 15 mass% lithium was supplied, indicating that the Si crystal grain size grew, leading to a decrease in capacity and life characteristics.

[0106]

[0107] 4. Test Example 3: dQ / dV Analysis Experiment (Fig. 5)

[0108] The voltage vs. capacity curve in the above test example 2 was differentiated to perform dQ / dV analysis.

[0109] As a result, as shown in Fig. 5, the electrodes manufactured with the Bare and 8.5 mass% samples did not show any peaks during the charging process, whereas when the lithium composition of the silicon oxide was 15 mass%, a peak was observed during discharge that was not observed at lower compositions, confirming that the crystallinity of the silicon increased. When a flat voltage occurs, the area with a low slope on the voltage curve appears as a peak on the dQ / dV curve, so the observation of the above peak can be seen as a phenomenon that should be avoided when developing a silicon-based electrode.

[0110]

[0111] 5. Test Example 4: Experiment to confirm the change in half-width on XRD according to lithium supply amount (Fig. 6)

[0112] The final powder was obtained using the same method as in the above test example 2, and X-ray diffraction analysis (XRD) was performed using this.

[0113] As a result of measuring the full width at half maximum (FWHM) of the peak observed at 47° on silicon (Si) and 38° on lithium silicon oxide (Li2SiO3) using the Lorentzian method in the XRD analysis results, it was confirmed that the full width at half maximum tended to decrease as the lithium supply increased.

[0114] Since the half-widths of both the silicon phase and the lithium silicon oxide phase tended to decrease with increasing lithium supply, it could be expected that the crystallinity of each phase was enhanced and the grain size increased.

[0115]

[0116] 6. Test Example 5: Calculation of the crystal size of silicon and lithium silicon oxide using XRD results (Fig. 7)

[0117] The final powder was obtained using the same method as in the above test example 2, and X-ray diffraction analysis (XRD) was performed using this.

[0118] The size of the crystal grains of each phase was calculated based on the FWHM of the phase-specific peaks in the XRD results.

[0119] As the lithium supply increased, a lithium-silicon oxide phase with a gradually higher lithium content was observed, while a silicon phase was continuously observed. The lithium-silicon oxide phase gradually increased in crystal size, but after 15 mass%, the increase increased rapidly. The silicon phase crystals maintained a similar size up to 12.5 mass%, but after 15 mass%, the crystal size grew rapidly to over 100 Å.

[0120] Through this, it was confirmed that the upper limit of the most suitable lithium supply amount is less than 15 mass%.

[0121]

[0122] 7. Test Example 6: Experiment to confirm the trend of initial Coulombic efficiency according to changes in lithium composition (Fig. 8)

[0123] The electrode was manufactured in the same manner as in the above test example 2, and the maximum coulombic efficiency was evaluated when the electrode composition was adjusted.

[0124] As a result, as shown in Fig. 8, it was confirmed that the initial Coulombic efficiency increased as the lithium composition in the raw silicon oxide gradually increased, and decreased again at 15 mass% or more. Through this, it was confirmed that in order to secure a high initial Coulombic efficiency of about 85% or more, lithium should preferably be supplied in an amount of 6.5 mass% or more and less than 15 mass%.

[0125]

[0126] 8. Test Example 7: Experiment to confirm life characteristics according to changes in lithium composition (Fig. 9)

[0127] An electrode was manufactured in the same manner as in the above test example 2, and the life characteristics were evaluated when the electrode composition was adjusted.

[0128] As a result, as shown in Fig. 9, it was confirmed that the capacity of the active material was the largest and the lifespan was excellent when pre-lithiation treatment was not performed. When the amount of lithium supplied was 8.5 mass% or less, it was confirmed that the initial reversible capacity decreased somewhat, but the lifespan characteristics were maintained excellently. However, when the amount of lithium supplied was 15 mass% or more, it was confirmed that both the lifespan characteristics and the reversible capacity decreased rapidly. Through this, it was found that in order to secure excellent lifespan characteristics as well as improve the initial efficiency, it was found that lithium should preferably be supplied in an amount of less than 15 mass%.

[0129]

[0130] 9. Test Example 8: Experiment to confirm lithium silicon oxide phase formation according to heat treatment temperature (Fig. 10)

[0131] Silicon oxide (SiO x ) Pre-lithiation was performed by immersing the active material in a 1M biphenyl-lithium solution based on 2-methyltetrahydrofuran containing 10% by mass of lithium. Thereafter, the powder obtained by washing with the same solvent was heated in an argon atmosphere at different heat treatment temperatures, and X-ray diffraction analysis (XRD) was performed on the powder obtained therefrom.

[0132] As a result, as shown in Fig. 10, when heat treatment was performed at a temperature below 400°C, the Li2SiO3 phase was not formed even though the same amount of lithium was supplied. From a temperature above 500°C, the Li2SiO3 phase was observed together with the Si phase.

[0133] Through this, it was confirmed that heat treatment above a certain temperature after pre-lithiation is required to form a Li2SiO3 phase showing high initial Coulombic efficiency.

[0134]

[0135] 10. Test Example 9: Experiment to confirm performance differences according to solvent during solution treatment at room temperature (Fig. 11)

[0136] Silicon oxide (SiO x ) Prelithiation was performed by immersing the active material in a 1M biphenyl-lithium solution based on 2-methyltetrahydrofuran containing 8.5% by mass of lithium. Afterwards, the powder obtained by washing with the same solvent was heated in an argon atmosphere, and an electrode was manufactured using the powder obtained therefrom.

[0137] A CR2032 type battery was fabricated using a lithium-ion battery, a lithium metal chip punched to a diameter of 11.3 mm as a positive electrode, a lithium metal chip punched to a diameter of 16 mm as a negative electrode, and Celgard as a separator, and an electrolyte containing 5 vol% FEC additive in 1 M LiPF6EC / DEC. The battery was charged and discharged at a current density of 0.2 C in the range of a discharge bottom voltage of 30 mV and a charge top voltage of 1.2 V at a room temperature of 30°C to evaluate the initial coulombic efficiency and capacity.

[0138] Afterwards, the same experiment was conducted using a different solvent, tetrahydrofuran.

[0139] As a result, the initial coulombic efficiency of the pre-lithiated silicon oxide mixed electrode in the first cycle was 83.2% when treated with tetrahydrofuran solution and 86.5% when treated with 2-methyltetrahydrofuran solution. It was confirmed that the efficiency was higher when 2-methyltetrahydrofuran was used than when tetrahydrofuran solution was used in the same amount of solution, and that there was a difference in performance after treatment even when all conditions except the type of solution were the same. This is because the oxidation / reduction potential of lithium-biphenyl (Li-BP) in the tetrahydrofuran solution is higher than that in the 2-methyltetrahydrofuran solution, which reduces the driving force for lithium insertion. Accordingly, it can be seen that it is desirable to utilize 2-methyltetrahydrofuran as a solvent in order to sufficiently insert lithium in the pre-lithiated solution into the silicon-based active material.

[0140]

[0141] 11. Test Example 10: Naphthalene titration confirmation experiment (Fig. 12)

[0142] Silicon oxide (SiO x ) Prelithiation was performed by immersing the active material in a 1M lithium-naphthalene solution based on 2-methyltetrahydrofuran containing 3.5 mass% lithium relative to the mass of the active material. Thereafter, the powder obtained by washing with the same solvent was heated in an argon atmosphere, and an electrode was manufactured using the powder obtained therefrom.

[0143] A CR2032 type battery was fabricated using a lithium-ion battery, a lithium metal chip punched to a diameter of 11.3 mm as a positive electrode, a lithium metal chip punched to a diameter of 16 mm as a negative electrode, and Celgard as a separator, and an electrolyte containing 5 vol% FEC additive in 1 M LiPF6EC / DEC. The battery was charged and discharged at a room temperature of 30°C and a current density of 0.2 C and 0.5 C in the range of a discharge bottom voltage of 30 mV and a charge top voltage of 1.2 V, to evaluate the change in reversible capacity and initial coulombic efficiency.

[0144] As a result, as shown in Fig. 12, the silicon oxide mixed electrode treated with the naphthalene-based pre-lithiation solution had a capacity of 1237 mAh·g in the first cycle. -1 It showed a reversible capacity of 82.3% and an improved Coulombic efficiency of 82.3%. From this, it was confirmed that not only biphenyl but also other redox molecules can be utilized for the prelithiation of silicon oxide.

[0145]

[0146] 12. Test Example 11: TEM SAD (selected area diffraction) pattern confirmation experiment (Fig. 13)

[0147] Silicon oxide (SiO x ) Pre-lithiation was performed by immersing the active materials in 1M biphenyl-lithium solutions based on 2-methyltetrahydrofuran containing 8.5 mass% and 15 mass% of lithium, respectively, relative to their masses. Thereafter, the powders obtained by washing with the same solvent were heated in an argon atmosphere, and the powders obtained therefrom and the untreated raw powders were analyzed together using a transmission electron microscope (TEM).

[0148] The interplanar spacing of concentric circles revealed by selected area diffraction (SAD) analysis was measured and compared with that of possible lithium silicon oxide phases to identify the phases present in each sample.

[0149] As a result, a silicon (Si) phase was observed in the raw material sample, and in the lithium silicon oxide samples manufactured by supplying 8.5 mass% and 15 mass% of lithium, Li2SiO3 and Li4SiO4 phases were observed along with the silicon phase, respectively, confirming the presence of phases corresponding to those identified through XRD analysis.

[0150]

[0151] 13. Test Example 12: TEM diffraction DF image (Fig. 14)

[0152] Silicon oxide (SiO x ) Pre-lithiation was performed by immersing the active material in a 1M biphenyl-lithium solution based on 2-methyltetrahydrofuran containing 8.5 mass% and 15 mass% of lithium relative to the mass. Thereafter, the powder obtained by washing with the same solvent was heated in an argon atmosphere, and the powder obtained therefrom and the untreated raw powder were analyzed together using a transmission electron microscope (TEM).

[0153] After obtaining the overall SAD pattern of the material, the diffraction ring corresponding to a specific crystal plane was masked to display only the unique crystal plane of each target crystal phase as a dark field image, and the crystal grain size of the corresponding phase was confirmed through this.

[0154] (111) In the case of silicon based on the crystal plane, the grain size gradually increased from the original to the 8.5 mass% and 15 mass% samples, and the results corresponded to those expected through XRD analysis. It was confirmed that the grain size of the 15 mass% lithiated sample was excessively large, resulting in poor electrochemical performance.

[0155] (200) Based on the crystal plane, it was confirmed that the crystal grain size observed in the 8.5 mass% Li2SiO3 sample was 9.43 nm, which was similar to the XRD results.

[0156]

[0157] 14. Test Example 13: Experiment to verify high Coulombic efficiency through electrode composition control (Fig. 15)

[0158] Silicon oxide (SiO x ) Pre-lithiation was performed by immersing the active material in a 1M biphenyl-lithium solution based on 2-methyltetrahydrofuran containing 8.5% by mass of lithium. Thereafter, the powder obtained by washing with the same solvent was heated in an argon atmosphere, and the powder obtained therefrom was used to manufacture an electrode having an active material, conductive material, and binder in a weight ratio of 90:5:5.

[0159] A CR2032 type battery was fabricated using a lithium-ion battery with a diameter of 11.3 mm punched out as a positive electrode, a lithium metal chip with a diameter of 16 mm punched out as a negative electrode, and Celgard as a separator, and an electrolyte containing 5 vol% FEC additive in 1 M LiPF6EC / DEC. The battery was charged and discharged at a current density of 0.2 C in the range of a discharge bottom voltage of 30 mV and a charge top voltage of 1.2 V at a room temperature of 30°C to evaluate the maximum coulombic efficiency when the electrode composition was adjusted.

[0160] As a result, the first cycle of the pre-lithiated silicon oxide mixed electrode yielded 1564 mAh·g -1 It showed a reversible capacity of 89.0% and a Coulombic efficiency of 89.0%, and it was confirmed that when the ratio of the active material was increased to 90%, a higher Coulombic efficiency was shown than the existing conditions (active material, conductive material, and binder ratio of 70:18:12).

[0161]

[0162] 15. Test Example 14: Performance Evaluation of Graphite / Silicon Oxide Composite Cathode (Fig. 16)

[0163] Silicon oxide (SiO x) Pre-lithiation was performed by immersing the active material in a 1M biphenyl-lithium solution based on 2-methyltetrahydrofuran containing 8.5% by mass of lithium. Thereafter, the powder obtained by washing with the same solvent was heated in an argon atmosphere, and an electrode was manufactured using the powder obtained therefrom in which the active material, conductive agent, and binder were contained in a weight ratio of 2:1 of graphite and silicon oxide, and the weight ratio was 92:4:4.

[0164] A CR2032 type battery was fabricated using an electrode punched with a diameter of 11.3 mm as a positive electrode, a lithium metal chip punched with a diameter of 16 mm as a negative electrode, and Celgard as a separator, and an electrolyte containing 5 vol% FEC additive in 1 M LiPF6EC / DEC. The battery was charged and discharged at a room temperature of 30°C at a current density of 0.2 C in the range of a discharge bottom voltage of 30 mV and a charge top voltage of 1.2 V, to evaluate the coulombic efficiency according to the additional composite with graphite.

[0165] 552 mAh·g in the first cycle of graphite / lithiated silicon oxide mixed electrode -1 It showed a reversible capacity of 86.5% and a coulombic efficiency of 86.5%, and it was confirmed that an electrode manufactured with a slurry made by mixing graphite with silicon oxide after prelithiation and stabilization operated successfully.

[0166]

[0167] Although the embodiments described above have been described with limited drawings, those skilled in the art will appreciate that various technical modifications and variations can be applied based on the above. For example, appropriate results can still be achieved even if the described techniques are performed in a different order than described, and / or the described components are combined or combined in a different manner than described, or are replaced or substituted with other components or equivalents.

[0168] Therefore, other implementations, other embodiments, and equivalents to the claims also fall within the scope of the claims described below.

Claims

1. A step (S1) of immersing a silicon-based active material in a pre-lithiation solution containing an organic solvent and a lithium-hydrocarbon molecule complex; Step (S2) of obtaining a powder by washing and drying with the above solvent; and A step (S3) of heat-treating the above powder at a temperature of 400°C to 800°C under an atmosphere of an inert gas; A method for prelithiation of a silicon-based active material, comprising:

2. In paragraph 1, A method for prelithiating a silicon-based active material, wherein the lithium content of the lithium-hydrocarbon molecular complex is 5 to 15 mass% relative to the mass of the silicon-based active material.

3. In paragraph 1, The silicon-based active material in the above S1 step is SiO x (0 <x<2) 인, 실리콘계 활물질의 사전리튬화 방법.

4. In paragraph 1, The above organic solvent is, A method for prelithiating a silicon-based active material, comprising at least one of a cyclic ether solvent and a linear ether solvent.

5. In paragraph 4, The above cyclic ether solvent is, A method for prelithiating a silicon-based active material, comprising at least one selected from the group consisting of tetrahydropyran, dioxolane, methyldioxolane, dimethyldioxolane, vinyldioxolane, methoxydioxolane, ethylmethyldioxolane, oxane, dioxane, trioxane, tetrahydrofuran, methyltetrahydrofuran, dimethyltetrahydrofuran, dimethoxytetrahydrofuran, ethoxytetrahydrofuran, ethyltetrahydrofuran, methyltetrahydropyran, dimethyltetrahydropyran, dihydropyran, tetrahydropyran, hexamethylene oxide, furan, dihydrofuran, dimethoxybenzene, and dimethyloxetane.

6. In paragraph 4, The above linear ether solvent is, A method for prelithiating a silicon-based active material, comprising at least one selected from the group consisting of dimethyl ether, diethyl ether, ethyl methyl ether, ethyl propyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, diisobutyl ether, ethyl tert-butyl ether, dimethoxymethane, trimethoxymethane, dimethoxyethane, diethoxyethane, dimethoxypropane, diethylene glycol dimethyl ether, diethylene glycol ethyl methyl ether, diethylene glycol isopropyl methyl ether, diethylene glycol butyl methyl ether, diethylene glycol diethyl ether, diethylene glycol tert-butyl ethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, ethylene glycol ethyl methyl ether, ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, and methoxypropane.

7. In paragraph 1, The above organic solvent is, A method for prelithiating a silicon-based active material comprising 2-methyltetrahydrofuran.

8. In paragraph 1, A method for prelithiation of a silicon-based active material, wherein the lithium-hydrocarbon molecular complex has a redox potential of 0.5 V or less with respect to lithium.

9. In paragraph 1, The hydrocarbon molecules of the above lithium-hydrocarbon molecule complex are, Contains at least one selected from the group consisting of biphenyl, naphthalene, anthracene, phenanthrene, tetracene, diphenylanthracene, perylene, pyrene, triphenylene, bianthryl, terphenyl, quaterphenyl and stilbene, A method for prelithiation of a silicon-based active material, wherein the hydrocarbon molecule is substituted or unsubstituted with one or more substituents selected from the group consisting of an alkyl group having 1 to 4 carbon atoms, benzene, fluorine, and chlorine.

10. In paragraph 1, A method for pre-lithiation of a silicon-based active material, wherein the above S3 step is performed by heat treatment at a temperature of 450°C or higher and 700°C or lower. A silicon-based active material pre-lithiated according to the pre-lithiation method described in claim 1 or claim 10, comprising a composite of lithium silicon oxide of Li2SiO3 having a size of 11.12 nm or less and silicon having a size of 5 nm or less.

12. In paragraph 11, A prelithiated silicon-based active material, wherein the above complex may additionally include lithium silicon oxide of Li2Si2O5 having a size of 10 nm or less, and the content of Li2Si2O5 is less than that of Li2SiO3.

13. Pre-lithiated silicon-based active material described in Article 11; Challenge; and A cathode comprising a binder; 14. In paragraph 13, A negative electrode, wherein the proportion of the above-mentioned pre-lithiated silicon-based active material is 70 wt% or more relative to the total weight of the active material, conductive material, and binder constituting the negative electrode.

15. In paragraph 13, A negative electrode, wherein the pre-lithiated silicon-based active material further comprises one or more of graphite, amorphous carbon, hard carbon, soft carbon, and magnesium.

16. In paragraph 15, A negative electrode having a weight ratio of graphite to silicon composite among the above active materials of 95:5 to 5:

95.

17. The cathode described in Article 13; Bipolar; and A lithium secondary battery comprising an electrolyte.

18. The cathode described in Article 13; Bipolar; and A capacitor comprising an electrolyte.

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