Anode active material, anode including the same, secondary battery including the same, and method for manufacturing anode active material

Abstract

The present invention relates to a negative electrode active material, a negative electrode including the same, a secondary battery including the same, and a method for producing the negative electrode active material.

Description

[Technical Field]

[0001] This application claims the benefit of the filing date of Korean Patent Application No. 10-2021-0107528 filed with the Korean Intellectual Property Office on August 13, 2021, and Korean Patent Application No. 10-2022-0012082 filed with the Korean Intellectual Property Office on January 27, 2022, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a negative electrode active material, a negative electrode including the negative electrode active material, a secondary battery including the negative electrode, and a method for producing the negative electrode active material. [Background technology]

[0003] In recent years, with the rapid spread of battery-powered electronic devices such as mobile phones, laptops, and electric vehicles, the demand for secondary batteries that are small, lightweight, and have relatively high capacity has been rapidly increasing. In particular, lithium secondary batteries, which are lightweight and have high energy density, have attracted attention as power sources for portable devices. For this reason, active research and development efforts are being made to improve the performance of lithium secondary batteries.

[0004] Generally, a lithium secondary battery includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte. The positive electrode and the negative electrode may each have an active material layer formed on a current collector, the active material layer including a positive electrode active material and a negative electrode active material. Generally, the positive electrode uses a lithium-containing metal oxide such as LiCoO2 or LiMn2O4 as the positive electrode active material, and the negative electrode uses a lithium-free carbon-containing active material or a silicon-containing active material as the negative electrode active material.

[0005] Among negative electrode active materials, silicon-containing active materials have attracted attention due to their higher capacity and excellent fast charging characteristics compared to carbon-containing active materials. However, silicon-containing active materials have the disadvantage of low initial efficiency due to their large irreversible capacity caused by large volume expansion / contraction during charging / discharging.

[0006] On the one hand, among silicon-containing active materials, silicon-containing oxides, specifically SiO x In the case of silicon-containing oxides represented by (0 < x < 2), there is an advantage that the degree of volume expansion / contraction due to charge / discharge is lower compared to other silicon-containing active materials such as silicon (Si). However, there is still a drawback that the initial efficiency decreases due to the presence of irreversible capacity in the silicon-containing oxide.

[0007] In connection with this, research has been continuously conducted to reduce the irreversible capacity and improve the initial efficiency by doping or inserting metals such as Li, Al, and Mg into the silicon-containing oxide. However, in the case of a negative electrode slurry containing a metal-doped silicon-containing oxide as a negative electrode active material, there is a problem that the metal oxide formed by doping reacts with moisture to increase the pH of the negative electrode slurry and change the viscosity. That is, there is a problem that the content of the amorphous phase in the negative electrode active material increases, and the amorphous metal oxide and metal silicate react with moisture to increase the pH of the negative electrode slurry and change the viscosity, resulting in a poor state of the manufactured negative electrode and a decrease in the charge / discharge efficiency of the negative electrode.

[0008] Therefore, there is a need to develop a negative electrode active material that can improve the phase stability of the negative electrode slurry containing a silicon-containing oxide and thereby improve the charge / discharge efficiency of the manufactured negative electrode.

[0009] Korean Registered Patent No. 10-0794192 relates to a method for manufacturing a carbon-coated silicon-graphite composite negative electrode active material for a lithium secondary battery and a method for manufacturing a secondary battery including the same, but there are limitations in solving the above-described problems.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0011] The present invention relates to a negative electrode active material capable of improving the quality of a negative electrode and the charge / discharge efficiency, a negative electrode containing the negative electrode active material, a secondary battery containing the negative electrode, and a method for manufacturing the negative electrode active material.

Means for Solving the Problems

[0012] The present invention provides a negative electrode active material including particles containing a silicon-containing oxide represented by SiO x (0 < x < 2) and lithium distributed in the particles, wherein the lithium exists in one or more forms selected from (a) crystalline phase Li2Si2O5, and optionally (b) crystalline phase Li2SiO3, (c) crystalline phase Li4SiO4, or (d) amorphous phase lithium silicate, the content of the crystalline phase Li2Si2O5 is greater than the sum of the contents of the crystalline phase Li2SiO3 and the crystalline phase Li4SiO4, and the total content of the crystalline phases present in the particles is greater than the total content of the amorphous phase.

[0013] Furthermore, the present invention provides a method for manufacturing the negative electrode active material described above, including mixing particles containing a silicon-containing oxide represented by SiO x (0 < x < 2) and a lithium precursor to produce a composition for forming a negative electrode active material, and heat-treating the composition for forming a negative electrode active material at a temperature in the range of 780°C to 900°C.

[0014] In addition, the present invention provides a negative electrode including a negative electrode current collector and a negative electrode active material layer disposed on at least one side of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode material containing the negative electrode active material described above.

[0015] Furthermore, the present invention provides a secondary battery including the negative electrode described above, a positive electrode facing the negative electrode, a separator interposed between the negative electrode and the positive electrode, and an electrolyte.

Effects of the Invention

[0016] The anode active material of the present invention includes particles containing a silicon-containing oxide and lithium distributed among the particles, wherein the lithium exists in one or more forms selected from (a) crystalline phase Li2SiO5 and, optionally, (b) crystalline phase Li2SiO3, (c) crystalline phase Li4SiO4, or (d) amorphous phase lithium silicate, wherein the content of the crystalline phase Li2SiO5 is greater than the sum of the contents of the crystalline phase Li2SiO3 and the crystalline phase Li4SiO4, and the total content of the crystalline phase present in the particles is greater than the total content of the amorphous phase. The anode active material of the present invention exhibits high charge / discharge capacity and efficiency due to the predominant presence of crystalline phase Li2SiO5 in the lithium silicate, and stable slurry production is possible due to the absence of gas generation during the production of the anode slurry. In addition, according to the negative electrode active material of the present invention, the total content of the crystalline phase is greater than the total content of the amorphous phase, and the content of lithium oxide and lithium silicate that react with moisture is small. This prevents gas generation and viscosity change in the negative electrode slurry and improves the phase stability of the slurry containing the negative electrode active material. As a result, a negative electrode including the negative electrode active material and a secondary battery including the negative electrode have improved quality and improved charge / discharge efficiency.

[0017] The present invention will become more fully understood from the following detailed description and the accompanying drawings, which are provided by way of example only and are not intended to limit the invention. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a flowchart illustrating a method for manufacturing a negative electrode active material according to one embodiment of the present invention. [Figure 2] 29Si-MAS-NMR analysis results of a negative electrode active material according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0019] The terms and words used in this specification and claims should not be interpreted in a limited way to their ordinary or dictionary meanings, but should be interpreted in a way that is consistent with the technical idea of ​​the present invention, based on the principle that the inventors can appropriately define the concepts of terms in order to best explain their inventions.

[0020] The terms used in this specification are merely used to describe exemplary embodiments and are not intended to limit the present invention. The singular expressions include the plural expressions unless otherwise clearly indicated in the context.

[0021] It should be understood that in this specification, the terms "comprise," "provide," or "have" are intended to specify the presence of embodied features, numbers, steps, components, or combinations thereof, but do not preclude the possible presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0022] In this specification, the average particle size (D 50 The average particle size (D) can be defined as the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve (graph curve of particle size distribution diagram). 50 ) can be measured, for example, by the laser diffraction method. The laser diffraction method generally enables measurement of particle sizes from about several mm to the submicron range, and can provide results with high reproducibility and high resolution.

[0023] <Negative electrode active material> The negative electrode active material will be described in detail below. The present invention relates to a negative electrode active material, and more particularly to a negative electrode active material for a lithium secondary battery.

[0024] Specifically, the negative electrode active material according to the present invention is SiO xParticles containing a silicon-containing oxide represented by (0 < x < 2); and a negative electrode active material containing lithium distributed in the particles, wherein the lithium is present in one or more forms selected from (a) crystalline phase Li2Si2O5, and optionally (b) crystalline phase Li2SiO3, (c) crystalline phase Li4SiO4, or (d) amorphous phase lithium silicate, the content of the crystalline phase Li2Si2O5 is more than the sum of the contents of the crystalline phase Li2SiO3 and the crystalline phase Li4SiO4, and the total content of the crystalline phases present in the particles is more than the total content of the amorphous phase.

[0025] Conventionally, in a negative electrode active material containing a silicon-containing oxide, research has been conducted to dope or distribute lithium or the like in the negative electrode active material to remove the irreversible capacity of the silicon-containing oxide and improve the initial efficiency. However, such a negative electrode active material has a high content of crystalline phase Li2SiO3 and crystalline phase Li4SiO4 and a high content of amorphous phase. Therefore, during the production of the negative electrode slurry, specifically, the aqueous negative electrode slurry, gas generation increases due to the reaction of moisture with lithium oxide and / or lithium silicate, increasing the pH of the negative electrode slurry and reducing the phase stability. As a result, the quality of the produced negative electrode is not good, and there is a problem of a decrease in charge-discharge efficiency.

[0026] In order to solve such problems, the negative electrode active material of the present invention is SiO x Particles containing a silicon-containing oxide represented by (0 < x < 2); and a negative electrode active material containing lithium distributed in the particles, wherein the lithium is present in one or more forms selected from (a) crystalline phase Li2Si2O5, and optionally (b) crystalline phase Li2SiO3, (c) crystalline phase Li4SiO4, or (d) amorphous phase lithium silicate, the content of the crystalline phase Li2Si2O5 is more than the sum of the contents of the crystalline phase Li2SiO3 and the crystalline phase Li4SiO4, and the total content of the crystalline phases present in the particles is more than the total content of the amorphous phase.

[0027] Since the content of the crystal phase Li2Si2O5 in the lithium silicate dominates in the negative electrode active material of the present invention, the charge-discharge capacity and efficiency are high, and gas generation does not occur during the production of the negative electrode slurry, so that the production of a stable slurry is possible.

[0028] In addition, since the total content of the crystal phase is larger than the total content of the amorphous phase in the negative electrode active material of the present invention, and the content of lithium oxide and lithium silicate that react with moisture is small, gas generation and viscosity change of the negative electrode slurry can be prevented, and the phase stability of the slurry containing the negative electrode active material can be improved. Therefore, the negative electrode containing the negative electrode active material and the secondary battery containing the negative electrode have improved quality and improved charge-discharge efficiency.

[0029] The negative electrode active material according to one embodiment of the present invention contains particles containing a silicon-containing oxide represented by SiO x (0 < x < 2); and lithium distributed in the particles.

[0030] In one embodiment of the present invention, the negative electrode active material particles contain a silicon-containing oxide represented by SiO x (0 < x < 2). In the case of SiO2, since it does not react with lithium ions and cannot store lithium, it is preferable that x is within the range of 0 < x < 2. Specifically, the silicon-containing oxide may be a compound represented by SiO x (0.5 ≤ x ≤ 1.5). The SiO x (0 < x < 2) may correspond to a matrix in the negative electrode active material particles.

[0031] In one embodiment of the present invention, the average particle diameter (D 50 ) of the negative electrode active material particles may be 0.1 μm to 20 μm, preferably 1 μm to 15 μm, more preferably 2 μm to 10 μm. The D of the particles 50When the particle size is in the range of 0.1 μm to 20 μm, it contributes to the structural stability of the active material during charge and discharge, prevents the problem of an excessively large particle size resulting in an increased level of volume expansion / contraction, and prevents the problem of an excessively small particle size resulting in a decrease in initial efficiency.

[0032] In one embodiment of the present invention, the negative electrode active material particles may be included in an amount of 75 to 99 parts by weight, preferably 80 to 97 parts by weight, and more preferably 87 to 96 parts by weight, based on 100 parts by weight of the total negative electrode active material. In another embodiment, the negative electrode active material particles may be included in an amount of 91 to 92 parts by weight, based on 100 parts by weight of the total negative electrode active material. When the particles are included in an amount of 75 to 99 parts by weight, an appropriate level of lithium can be incorporated into the negative electrode active material, which is preferable in that both the charge / discharge capacity and efficiency of the negative electrode can be improved.

[0033] In one embodiment of the present invention, the lithium is distributed in the negative electrode active material particles, and the lithium distributed in the particles can eliminate the irreversible capacity of the silicon-containing oxide and contribute to improving the initial efficiency and charge / discharge efficiency of the negative electrode active material.

[0034] Specifically, the lithium may be distributed on the surface, inside, or both the surface and the inside of the negative electrode active material particles, or may be doped into the particles.

[0035] For example, when lithium is doped by an in-situ method, the lithium tends to be uniformly distributed on the surface and in the interior, whereas when it is doped by an ex-situ method, the concentration of lithium tends to be higher near the particle surface compared to the interior of the particle.

[0036] In one embodiment of the present invention, the lithium may be included in an amount of 0.5 to 25 parts by weight, preferably 1 to 15 parts by weight, based on 100 parts by weight of the total negative electrode active material. In another embodiment, the lithium may be included in an amount of 4 to 10 parts by weight, based on 100 parts by weight of the total negative electrode active material. When the amount is in the range of 0.5 to 25 parts by weight, the effect of improving the initial efficiency and charge / discharge efficiency of the negative electrode active material can be improved, which is preferable.

[0037] In one embodiment of the present invention, the lithium may be distributed in the negative electrode active material particles in the form of lithium silicate, which may eliminate the irreversible capacity of the particles and improve the initial efficiency and charge / discharge efficiency of the negative electrode active material. In this regard, silicate refers to a compound containing silicon, oxygen, and one or more metals.

[0038] Specifically, the lithium may be distributed on the surface, inside, or both the surface and the inside of the negative electrode active material particles in the form of lithium silicate, which may correspond to a matrix within the negative electrode active material particles.

[0039] Specifically, the lithium may be present in one or more forms selected from (a) crystalline phase Li2SiO5, and optionally (b) crystalline phase Li2SiO3, (c) crystalline phase Li4SiO4, or (d) amorphous phase lithium silicate, and the content of the crystalline phase Li2SiO5 is greater than the sum of the content of the crystalline phase Li2SiO3 and the content of the crystalline phase Li4SiO4.

[0040] In one embodiment of the present invention, the negative electrode active material includes crystalline phase lithium silicate, and the crystalline phase lithium silicate includes crystalline phase Li2SiO5 and crystalline phase Li2SiO3. Specifically, the lithium may be present in one or more forms selected from (a) crystalline phase Li2SiO5, (b) crystalline phase Li2SiO3, and, optionally, (c) crystalline phase Li4SiO4 or (d) amorphous phase lithium silicate.

[0041] The crystalline phase Li2Si2O5 is stable in the negative electrode active material and generates fewer side reactions with moisture, particularly in negative electrode slurries, specifically aqueous negative electrode slurries. Therefore, negative electrode slurries containing the negative electrode active material containing the crystalline phase Li2Si2O5 generate less gas due to reactions with moisture, particularly in aqueous negative electrode slurries, and prevent an increase in the pH of the negative electrode slurry, improving the phase stability of the slurry. This improves the quality of negative electrodes manufactured from the negative electrode slurries and improves charge / discharge efficiency.

[0042] In contrast, crystalline phase Li2SiO3 and crystalline phase Li4SiO4 have the problem of undergoing a side reaction with moisture in the anode slurry, which can lead to serious gas generation and by-products such as Li2O formed by the side reaction with moisture, which can increase the pH of the anode slurry, destabilize the slurry phase, and change the viscosity.

[0043] In this regard, the anode active material of the present invention has a higher content of the crystalline phase Li2SiO2O5 than the content of the crystalline phase Li2SiO3 and the content of the crystalline phase Li4SiO4, thereby smoothly eliminating the irreversible capacity of the anode active material and improving initial efficiency and charge / discharge efficiency. It also improves the phase stability of anode slurries containing the anode active material, preventing problems with low viscosity, improving anode quality, and enabling excellent charge / discharge capacity and charge / discharge efficiency. Furthermore, as described below, the anode active material of the present invention has an increased content of the crystalline phase Li2SiO2O5 and a reduced total content of the amorphous phase, thereby improving the phase stability of the anode slurries, preventing anode defects, and significantly improving charge / discharge capacity and efficiency.

[0044] In one embodiment of the present invention, the crystalline phase Li2Si2O5 may be included in an amount of 1 to 63 parts by weight, 3 to 60 parts by weight, 4 to 50 parts by weight, or 5 to 45 parts by weight, more preferably 20 to 40 parts by weight, based on a total of 100 parts by weight of the negative electrode active material particles. When the content of the crystalline phase Li2Si2O5 is in the range of 1 to 63 parts by weight, it is possible to reduce the occurrence of side reactions between the negative electrode active material and water during preparation of a negative electrode slurry, particularly an aqueous negative electrode slurry, and further improve the phase stability of the negative electrode slurry, which is preferable in terms of providing a good electrode condition and achieving stable charge / discharge capacity.

[0045] In one embodiment of the present invention, the crystalline phase Li2SiO3 may be included in an amount of 40 parts by weight or less, specifically 35 parts by weight or less, based on a total of 100 parts by weight of the negative electrode active material particles. In another embodiment, the crystalline phase Li2SiO3 may be included in an amount of 30 parts by weight or less, 25 parts by weight or less, or 20 parts by weight or less, based on a total of 100 parts by weight of the negative electrode active material particles. The lower limit of the content of the crystalline phase Li2SiO3 may be 0.1 parts by weight, 1 part by weight, 1.5 parts by weight, or 2 parts by weight.

[0046] In one embodiment of the present invention, the crystalline phase Li4SiO4 may be included in an amount of 5 parts by weight or less, specifically 3 parts by weight or less, based on 100 parts by weight of the total negative electrode active material particles. More specifically, the crystalline phase Li4SiO4 may be absent from the negative electrode active material. When the content of the crystalline phase Li4SiO4 satisfies the range of 5 parts by weight or less, this is preferable in terms of preventing the generation of by-products such as Li2O due to the reaction between the negative electrode active material and water during the preparation of a negative electrode slurry, specifically an aqueous negative electrode slurry, and the resulting increase in pH of the negative electrode slurry and the resulting deterioration of negative electrode quality.

[0047] In one embodiment of the present invention, the difference between the content of the crystalline phase Li2Si2O5 and the content of the crystalline phase Li2SiO3 may be 1 to 40 parts by weight, 5 to 40 parts by weight, 8 to 40 parts by weight, specifically 10 to 35 parts by weight, and more specifically 10 to 30 parts by weight, based on a total of 100 parts by weight of the particles. When the difference is in the range of 1 to 40 parts by weight, it is possible to improve the phase stability of the negative electrode slurry, prevent negative electrode defects, and significantly improve charge / discharge capacity and efficiency.

[0048] The confirmation and content of the crystalline phase lithium silicate of the crystalline phase Li2SiO3, crystalline phase Li4SiO4, or crystalline phase Li2Si2O5 can be determined by X-ray diffraction analysis using an X-ray diffraction profile or 29 Si-MAS-NMR( 29 Si-Magic Angle Spinning-Nuclear Magnetic Resonance, 29 It can be measured by analysis via Si-magic angle spinning-nuclear magnetic resonance).

[0049] Among them, 29 Si-MAS-NMR analysis is a type of solid-state NMR analysis technique in which a rotor containing a sample is placed at a magic angle B with respect to a magnetic field B0. M This NMR analysis is performed by rapidly spinning at an angle (e.g., 54.74°). This allows the presence and content of crystalline phase Li2SiO3, crystalline phase Li4SiO4, crystalline phase Li2Si2O5, crystalline phase Si, crystalline phase SiO2, and amorphous phase contained in the negative electrode active material of the present invention to be determined.

[0050] In one embodiment of the present invention, 29 During Si-MAS-NMR analysis, the height of peak p1 of Li2SiO3 appearing in the chemical shift peaks between -70 ppm and -80 ppm may be smaller than the height of peak p2 of Li2Si2O5 appearing in the chemical shift peaks between -90 ppm and -100 ppm.

[0051] In one embodiment of the present invention, 29 In Si-MAS-NMR analysis, the ratio (p2 / p1) of the height of the peak p2 of Li2SiO3 appearing at a chemical shift peak between -90 ppm and -100 ppm to the height of the peak p1 of Li2SiO3 appearing at a chemical shift peak between -70 ppm and -80 ppm may be greater than 0.1 and less than 6.5, greater than 1 and less than 6.5, or greater than 1.5 and less than 5, specifically greater than 2 and less than 4. When the ratio is greater than 0.1 and less than 6.5, the negative electrode active material contains a sufficient amount of crystalline Li2SiO5, reducing gas generation due to a side reaction between the negative electrode active material and moisture and preventing an increase in pH due to by-products generated by the side reaction with moisture, thereby improving the phase stability of the slurry, thereby improving the quality of negative electrodes manufactured from the negative electrode slurry and improving charge / discharge efficiency.

[0052] In one embodiment of the present invention, 29 During Si-MAS-NMR analysis, the peak p3 of Li4SiO4, which appears among the chemical shift peaks at -60 ppm to -69 ppm, may not be present. This is preferable in terms of preventing the generation of by-products such as Li2O due to a side reaction between Li4SiO4 in the negative electrode active material and moisture, the resulting increase in pH of the negative electrode slurry, and the resulting deterioration of the negative electrode quality.

[0053] The contents of the crystalline phase Li2SiO3, crystalline phase Li4SiO4, and crystalline phase Li2Si2O5 can be adjusted by, but not limited to, performing a heat treatment process, adjusting the heat treatment temperature, or performing an acid treatment process in the method for manufacturing a negative electrode active material described below.

[0054] FIG. 2 shows a negative electrode active material according to one embodiment of the present invention. 29 1 shows the results of Si-MAS-NMR analysis of the negative electrode active material according to one embodiment of the present invention. 29During Si-MAS-NMR analysis, the height of the peak p1 of Li2SiO3 appearing between -70 ppm and -80 ppm may be smaller than the height of the peak p2 of Li2Si2O5 appearing between -90 ppm and -100 ppm.

[0055] In one embodiment of the present invention, the negative electrode active material may contain crystalline SiO2 in an amount of less than 5 parts by weight, specifically less than 4 parts by weight, based on 100 parts by weight of the particles. In another embodiment, the negative electrode active material may contain crystalline SiO2 in an amount of 3 parts by weight or less. Preferably, the negative electrode active material may contain crystalline SiO2 in an amount of 1 part by weight or less, based on 100 parts by weight of the particles. When the amount of crystalline SiO2 is less than 5 parts by weight, the negative electrode is easily charged and discharged, and the charge / discharge capacity and efficiency are improved.

[0056] In one embodiment of the present invention, the negative electrode active material may include crystalline phase Si in an amount of 10 to 50 parts by weight, 20 to 40 parts by weight, or 26 to 35 parts by weight, based on a total of 100 parts by weight of the particles. When the content of the crystalline phase Si is in the range of 10 to 50 parts by weight, the negative electrode is easily charged and discharged, and the charge / discharge capacity and efficiency are improved.

[0057] In one embodiment of the present invention, the total content of crystalline phases present in the particles is greater than the total content of amorphous phases. The total content of crystalline phases refers to the total content of all crystalline phases present in the particles, including crystalline phase Si, crystalline phase SiO, crystalline phase LiSiO, crystalline phase LiSiO, crystalline phase LiSiO, crystalline phase LiSiO, and crystalline phase LiSiO. The total content of amorphous phases refers to the content excluding the total content of crystalline phases present in the particles. That is, the total content of amorphous phases refers to the sum of the content of all amorphous phases present in the particles, including amorphous phase SiO as well as amorphous phase lithium silicate.

[0058] The negative electrode active material of the present invention has a total content of crystalline phases present in the particles that is greater than the total content of amorphous phases. This is advantageous in terms of reducing the content of amorphous phase lithium silicate and the like, which are highly reactive with water, during the preparation of a negative electrode slurry, specifically an aqueous negative electrode slurry, and preventing the generation of by-products such as LiO due to side reactions with water, which in turn increases the pH of the negative electrode slurry and leads to poor quality of the negative electrode.

[0059] In one embodiment of the present invention, the total content of the crystalline phases present in the particles may be more than 50 parts by weight and not more than 80 parts by weight, more than 50 parts by weight and not more than 75 parts by weight, 55 parts by weight or more and not more than 75 parts by weight, 60 parts by weight or more and not more than 70 parts by weight, 64 parts by weight or more and not more than 68 parts by weight, or 64 parts by weight or more and not more than 66 parts by weight, based on a total of 100 parts by weight of the particles.

[0060] In one embodiment of the present invention, the total content of the amorphous phase present in the particles may be 20 parts by weight to 50 parts by weight, 25 parts by weight to 50 parts by weight, 25 parts by weight to 45 parts by weight, 30 parts by weight to 40 parts by weight, 32 parts by weight to 36 parts by weight, or 34 parts by weight to 36 parts by weight, based on 100 parts by weight of the total particles.

[0061] In one embodiment of the present invention, the difference between the total content of the crystalline phase and the total content of the amorphous phase present in the particles may be 10 parts by weight to 60 parts by weight, 20 parts by weight to 50 parts by weight, 25 parts by weight to 40 parts by weight, 28 parts by weight to 36 parts by weight, or 30 parts by weight to 36 parts by weight, based on a total of 100 parts by weight of the particles.

[0062] In one embodiment of the present invention, the ratio of the total weight of the crystalline phase to the total weight of the amorphous phase present in the particles (total weight of the crystalline phase:total weight of the amorphous phase) may be 55:45 to 75:25, or may be 60:40 to 70:30.

[0063] When the contents of the crystalline phase and amorphous phase present in the particles satisfy the above ranges, the contents of the crystalline phase and amorphous phase present in the negative electrode active material can be appropriately adjusted, and the content of amorphous phase lithium silicate, which has high reactivity with water, can be reduced during the preparation of a negative electrode slurry (specifically, an aqueous negative electrode slurry). This reduces the generation of by-products such as LiO due to side reactions with water, and the resulting increase in pH and change in viscosity of the negative electrode slurry. This is advantageous in that it does not excessively increase the content of crystalline phase SiO, which hinders the expression of charge / discharge capacity and efficiency.

[0064] Even if the content of the crystalline phase Li2Si2O5 in lithium silicate is the highest, if the total content of the crystalline phases present in the negative electrode active material does not satisfy the above range, the crystalline phases will be excessively contained in the negative electrode active material, making charge and discharge difficult, resulting in problems such as difficulty in achieving capacity / efficiency and reduced life characteristics.

[0065] The total content of the crystalline phase and the total content of the amorphous phase present in the particles can be measured by a quantitative analysis method using X-ray diffraction analysis (XRD).

[0066] The negative electrode active material of the present invention may further include a carbon layer disposed on each of the particles, which may function as a protective layer to suppress volumetric expansion of the particles and prevent side reactions with the electrolyte.

[0067] In one embodiment of the present invention, the carbon layer may be included in an amount of 0.1 to 10 parts by weight, preferably 1 to 7 parts by weight, and more preferably 3 to 5 parts by weight, based on 100 parts by weight of the total negative electrode active material. When the content of the carbon layer is in the range of 0.1 to 10 parts by weight, it is preferable in that the carbon layer can effectively control the volume expansion of the particles while preventing side reactions with the electrolyte.

[0068] In one embodiment of the present invention, the carbon layer may include at least one of amorphous carbon and crystalline carbon.

[0069] In one embodiment of the present invention, the carbon layer may be an amorphous carbon layer. Specifically, the carbon layer may be formed by chemical vapor deposition (CVD) using at least one hydrocarbon gas selected from the group consisting of methane, ethane, and acetylene.

[0070] In one embodiment of the present invention, when the negative electrode active material is acid-treated, lithium by-products selected from the group consisting of crystalline lithium silicate, Li2O, LiOH, and Li2CO3 are substantially absent or completely absent from the surface of the negative electrode active material. The lithium by-products increase the pH of the negative electrode slurry, lower the viscosity, and can cause the electrode condition of the negative electrode to deteriorate. Therefore, by performing an acid treatment process on the negative electrode active material to remove by-products such as lithium silicate and Li2O present on the surface of the negative electrode active material, it is possible to achieve desirable improvements in the quality of the negative electrode and the charge / discharge efficiency.

[0071] In one embodiment of the present invention, a negative electrode active material obtained by adding 0.5 g of the negative electrode active material to 50 mL of distilled water and stirring for 3 hours may have a pH at 23°C of 9 to 13, 9 to 12, 9.5 to 11.5, 10 to 11, or 10 to 10.5. When the pH of the resulting material is in the range of 9 to 13, it can be evaluated that the content of substances that cause side reactions between the negative electrode active material and water, increase the pH of the negative electrode slurry, decrease the viscosity, and reduce phase stability has been reduced to a desirable level. Therefore, when the pH of the resulting material is in the range of 9 to 13, an increase in pH due to by-products resulting from side reactions with water is prevented to a desirable level, improving the phase stability of the slurry. This improves the quality of negative electrodes manufactured from the negative electrode slurry and improves charge / discharge efficiency.

[0072] In one embodiment of the present invention, the average particle size (D 50 ) may be 0.1 μm to 20 μm, preferably 1 μm to 15 μm, and more preferably 2 μm to 10 μm. 50When the range of 0.1 μm to 20 μm is satisfied, the structural stability of the active material during charge and discharge can be achieved, preventing the problem that the volume expansion / shrinkage level increases due to excessively large particle sizes and preventing the problem that the initial efficiency decreases due to excessively low particle sizes.

[0073] In one embodiment of the present invention, during X-ray diffraction measurement using the CuKα line of the negative electrode active material, when the height of the peak of Li2Si2O5 existing in the range of diffraction angle 2θ of 24.4° to 25.0° is g1 and the height of the peak of Li2SiO3 existing in the range of diffraction angle 2θ of 18.6° to 19.2° is g2, g2 / g1 may be > 0.05. Specifically, g2 / g1 > 0.1 or g2 / g1 > 0.2 may also be acceptable.

[0074] When g2 / g1 is below the above range (for example, 0.05 or less), there is a problem that the amount of Li2SiO3 stable during charge and discharge decreases excessively, resulting in poor life performance.

[0075] The X-ray diffraction measurement of the negative electrode active material can be performed using X’Pert Pro. manufactured by PANalytical. Specifically, based on the moving average approximation curve obtained with a data specific number of 11 for the diffraction intensity values at intervals of 0.02° of the diffraction angle 2θ, the height g1 of the peak of Li2Si2O5 appearing in the range of diffraction angle 2θ of 24.4° to 25.0°, and the height g2 of the peak of Li2SiO3 appearing in the range of diffraction angle 2θ of 18.6° to 19.2° can be measured.

[0076] <Method for manufacturing negative electrode active material> The present invention provides a method for manufacturing a negative electrode active material, specifically, the method for manufacturing the negative electrode active material described above.

[0077] Specifically, the method for manufacturing the negative electrode active material includes mixing particles containing a silicon-containing oxide represented by SiO x (0 < x < 2) and a lithium precursor to produce a composition for forming a negative electrode active material; and heat-treating the composition for forming a negative electrode active material at a temperature in the range of 780°C to 900°C.

[0078] According to the method for manufacturing a negative electrode active material of the present invention, the content of the crystal phase Li2Si2O5 is more than the sum of the contents of the crystal phases Li2SiO3 and Li4SiO4, and the total content of the crystal phases present in the particles is more than the total content of the amorphous phase. Thus, it is possible to manufacture the above-described negative electrode active material. As a result, in the negative electrode active material manufactured by the method for manufacturing a negative electrode active material of the present invention, since the content of the crystal phase Li2Si2O5 in lithium silicate is predominantly present, the charge and discharge capacity and efficiency are high, gas generation due to side reactions with moisture is suppressed, and since the total content of the crystal phases is larger than the total content of the amorphous phase, when manufacturing a negative electrode slurry (specifically, an aqueous negative electrode slurry), the content of amorphous lithium silicate or the like having high reactivity with moisture is reduced, generation of by-products such as Li2O due to side reactions with moisture, an increase in the pH of the negative electrode slurry, and a change in viscosity can be prevented, and the negative electrode including the negative electrode active material and the secondary battery including the negative electrode have improved quality and improved charge and discharge efficiency.

[0079] The method for manufacturing a negative electrode active material of the present invention includes a step of mixing particles containing a silicon-containing oxide represented by SiO x (0 < x < 2) and a lithium precursor to produce a composition for forming a negative electrode active material.

[0080] In one embodiment of the present invention, the particles contain a silicon-containing oxide represented by SiO x (0 < x < 2). Since SiO2 does not react with lithium ions and cannot store lithium, it is preferable that x is within the above range. Specifically, the silicon-containing oxide may be a compound represented by SiO x (0.5 ≤ x ≤ 1.5) in terms of the structural stability of the active material.

[0081] In one embodiment of the present invention, the average particle size (D 50) may be 0.1 μm to 20 μm, preferably 1 μm to 15 μm, and more preferably 2 μm to 10 μm, in order to achieve structural stability of the active material during charge and discharge, to prevent the problem of an excessively large particle size resulting in an increased level of volume expansion / contraction, and to prevent the problem of an excessively small particle size resulting in a decrease in initial efficiency.

[0082] In one embodiment of the present invention, the lithium precursor can be subjected to a heat treatment process described below to distribute lithium in the particles. Specifically, the lithium precursor may include at least one selected from the group consisting of lithium metal, LiOH, LiH, and Li2CO3, and may include lithium metal to prevent further oxidation during the reaction between the particles and the lithium precursor. The lithium precursor may be in particulate form, specifically, lithium metal powder.

[0083] In one embodiment of the present invention, the lithium precursor may comprise stabilized lithium metal powder (SLMP).

[0084] In one embodiment of the present invention, the particles and the lithium precursor may be solid mixed. Specifically, the particles and the lithium precursor may be in a solid state during the mixing. In this case, when the negative electrode active material is formed by heat treatment (described later), the porosity and specific surface area of ​​the negative electrode active material can be controlled to appropriate levels, thereby favorably controlling the volume expansion of the negative electrode active material during charge and discharge.

[0085] In one embodiment of the present invention, the particles and the lithium precursor may be mixed while being heat-treated in an inert gas atmosphere. Specifically, the particles and the lithium precursor may be mixed while being heat-treated at a temperature in the range of 100°C to 300°C, specifically 150°C to 200°C. When mixed while being heat-treated under the above conditions, the lithium precursor and the particles are mixed more uniformly, and the reaction occurs under mild conditions in advance, allowing lithium to be uniformly distributed in the particles.

[0086] The method for producing a negative electrode active material of the present invention includes a step of heat-treating the composition for forming a negative electrode active material at a temperature in the range of 780°C to 900°C.

[0087] The heat treatment process in the above temperature range can distribute lithium in the particles, specifically, lithium can be distributed on the surface, inside, or both on the surface and inside of the particles.

[0088] The above-described negative electrode active material can be prepared by a heat treatment process within the above temperature range. Specifically, the heat treatment process within the above temperature range allows the lithium to be distributed in the particles in the form of lithium silicate, thereby eliminating the irreversible capacity of the particles and improving the initial efficiency and charge / discharge efficiency of the negative electrode active material. Specifically, the lithium may exist in one or more forms selected from (a) crystalline phase Li2SiO5, and optionally (b) crystalline phase Li2SiO3, (c) crystalline phase Li4SiO4, or (d) amorphous phase lithium silicate. In this case, in the negative electrode active material prepared by the method of the present invention, the content of the crystalline phase Li2SiO2O5 may be greater than the sum of the content of the crystalline phase Li2SiO3 and the content of the crystalline phase Li4SiO4.

[0089] Furthermore, by performing the heat treatment process within the above temperature range, the total content of the crystalline phase present in the particles may be greater than the total content of the amorphous phase. As a result, the content of lithium oxide and lithium silicate that react with moisture is reduced, which can prevent gas generation and viscosity change in the negative electrode slurry and improve the phase stability of the slurry including the negative electrode active material. As a result, the quality and charge / discharge efficiency of a negative electrode including the negative electrode active material and a secondary battery including the negative electrode are improved.

[0090] If the heat treatment process is performed at a temperature below 780°C, the amorphous phase content of the negative electrode active material prepared by the above-mentioned method increases, the crystalline phase Li2Si2O5 content decreases, and the phase stability of the negative electrode slurry decreases, resulting in an increased side reaction with water in the negative electrode slurry (specifically, an aqueous negative electrode slurry), which can lead to problems such as poor electrode condition and reduced charge / discharge efficiency.If the heat treatment process is performed at a temperature above 900°C, the crystalline phase SiO2 content increases, which acts as a resistor during charge / discharge, making charge / discharge difficult and reducing charge / discharge capacity and efficiency, which is undesirable.

[0091] Specifically, the heat treatment may be carried out at a temperature of 780°C to 890°C or 800°C to 870°C, and in the above ranges, it is preferable in that the crystalline phase lithium silicate of Li2Si2O5 is easily developed.

[0092] The heat treatment may be performed for 1 to 12 hours, specifically 2 to 8 hours. When the heat treatment is performed for 1 to 12 hours, the lithium silicate can be uniformly distributed within the particles, thereby further improving the charge / discharge efficiency.

[0093] The heat treatment may be performed in an inert atmosphere to prevent further oxidation of the particles and the lithium precursor, specifically, in an inert atmosphere of at least one gas selected from the group consisting of nitrogen gas, argon gas, and helium gas.

[0094] The method for manufacturing a negative electrode active material according to the present invention may further include a step of subjecting the heat-treated negative electrode active material-forming composition to an acid treatment. By-products, such as lithium silicates (e.g., crystalline phase Li2SiO3, Li4SiO4, etc.) and Li2O present on the surface of the negative electrode active material due to the heat treatment process, may increase the pH of the negative electrode slurry containing the negative electrode active material, lower the viscosity, and cause a negative electrode to be defective. Therefore, by performing an acid treatment process after the heat treatment process to remove by-products, such as lithium silicates (e.g., crystalline phase Li2SiO3, Li4SiO4, etc.) and Li2O present on the surface of the negative electrode active material, it is possible to achieve desirable improvements in negative electrode quality and charge / discharge efficiency.

[0095] Specifically, the acid treatment may be performed by treating the heat-treated composition for forming a negative electrode active material with an acid aqueous solution containing at least one acid selected from the group consisting of hydrochloric acid (HCl), sulfuric acid (H2SO4), nitric acid (HNO3), and phosphoric acid (H3PO4), specifically at least one acid selected from the group consisting of hydrochloric acid (HCl), sulfuric acid (H2SO4), and nitric acid (HNO3), for 0.3 to 6 hours, specifically 0.5 to 4 hours. This is preferable in that by-products present on the surface of the negative electrode active material can be easily removed by this process.

[0096] The pH of the acid aqueous solution at 23° C. may be 3 or less, specifically 2 or less, more specifically 1 or less, in order to easily remove by-products present on the surface of the negative electrode active material.

[0097] An exemplary process for making an active negative electrode material according to one embodiment of the present invention is presented in FIG.

[0098] The method for manufacturing an anode active material according to the present invention may further include forming a carbon layer on each of the silicon-containing oxide particles before mixing the silicon-containing oxide particles with a lithium precursor. The carbon layer may be disposed or formed on the particles and function as a protective layer to appropriately control volume expansion of the anode active material during charge and discharge and to prevent side reactions with the electrolyte. Meanwhile, the carbon layer formation step may be performed before mixing the particles with a lithium precursor to prevent changes in the crystalline and amorphous phases of the anode active material.

[0099] The carbon layer may be formed by chemical vapor deposition (CVD), specifically, by using at least one hydrocarbon gas selected from the group consisting of methane, ethane, and acetylene. More specifically, the carbon layer may be formed by adding at least one hydrocarbon gas selected from the group consisting of methane, ethane, and acetylene to the acid-treated composition for forming a negative electrode active material, followed by heat treatment using chemical vapor deposition (CVD). This method allows the carbon layer to be formed uniformly on the silicon-containing oxide particles, thereby smoothly controlling the volumetric expansion of the particles and preventing side reactions with the electrolyte.

[0100] The carbon layer forming step may be performed at a temperature of 800°C to 1,100°C, preferably 850°C to 1,000°C, to prevent changes in the crystalline phase and amorphous phase in the negative electrode active material prepared in the previous step. The other carbon layers are as described above.

[0101] <Negative electrode> The present invention provides a negative electrode, specifically a negative electrode for a lithium secondary battery. In one embodiment of the present invention, the negative electrode includes the negative electrode active material described above.

[0102] The negative electrode according to the present invention includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, the negative electrode active material layer including a negative electrode material. The negative electrode material includes the above-described negative electrode active material.

[0103] The negative electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and has high conductivity. Specifically, the negative electrode current collector may include at least one selected from the group consisting of copper, stainless steel, aluminum, nickel, titanium, sintered carbon, and an aluminum-cadmium alloy, and may specifically include copper.

[0104] The negative electrode current collector may generally have a thickness of 3 μm to 500 μm. The negative electrode current collector may have a surface with fine irregularities to enhance the bonding strength of the negative electrode active material. For example, the negative electrode current collector may be used in various forms such as a film, a sheet, a foil, a mesh, a porous material, a foam, or a nonwoven fabric.

[0105] The negative electrode active material layer may be disposed on at least one surface of the negative electrode current collector. Specifically, the negative electrode active material layer may be disposed on one or both surfaces of the negative electrode current collector.

[0106] In one embodiment of the present invention, the negative electrode material may be included in an amount of 60 to 99 parts by weight, specifically 70 to 98 parts by weight, based on a total of 100 parts by weight of the negative electrode active material layer.

[0107] The negative electrode material may further include a carbon-containing active material in addition to the negative electrode active material. The carbon-containing active material may include at least one selected from the group consisting of artificial graphite, natural graphite, hard carbon, soft carbon, carbon black, graphene, and fibrous carbon, and preferably includes at least one selected from the group consisting of artificial graphite and natural graphite.

[0108] The negative electrode material may contain the above-mentioned negative electrode active material and carbon-containing active material in a weight ratio of 1:99 to 60:40, preferably 3:97 to 50:50. The negative electrode active material layer may contain a binder.

[0109] The binder may include at least one selected from the group consisting of styrene butadiene rubber (SBR), acrylonitrile butadiene rubber, acrylic rubber, butyl rubber, fluororubber, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl alcohol (PVA), polyacrylic acid (PAA), polyethylene glycol (PEG), polyacrylonitrile (PAN), and polyacryl amide (PAM), in order to further improve electrode adhesive strength and provide sufficient resistance to volume expansion / contraction of the active material. Preferably, the binder contains styrene butadiene rubber and carboxymethyl cellulose, which have high strength, excellent resistance to volume expansion / contraction of the negative electrode active material, and excellent flexibility to prevent distortion, warping, etc. of the electrode.

[0110] In one embodiment of the present invention, the binder may be included in an amount of 0.5 parts by weight to 30 parts by weight, specifically 1 part by weight to 20 parts by weight, based on a total of 100 parts by weight of the negative electrode active material layer. This range is preferable in that it can more effectively control the volume expansion of the active material.

[0111] The negative electrode active material layer may include a conductive material. The conductive material may be used to improve the conductivity of the negative electrode, and preferably does not induce chemical changes and is conductive. Specifically, the conductive material may include at least one selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, conductive fiber, carbon nanotubes (CNTs), fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives. Preferably, the conductive material may include at least one selected from carbon black and carbon nanotubes to achieve high conductivity. More preferably, the conductive material may include carbon black and carbon nanotubes.

[0112] In one embodiment of the present invention, the conductive material may be included in an amount of 0.5 to 25 parts by weight, specifically 1 to 20 parts by weight, based on a total of 100 parts by weight of the negative electrode active material layer.

[0113] In one embodiment of the present invention, the negative electrode active material layer may have a thickness of 30 μm to 100 μm, preferably 40 μm to 80 μm, in order to improve electrical contact with components in the negative electrode active material layer.

[0114] <Negative electrode slurry> The present invention provides an anode slurry containing an anode material. In one embodiment of the present invention, the negative electrode material includes the above-described negative electrode active material.

[0115] In one embodiment of the present invention, the negative electrode slurry may contain the negative electrode material, a binder, and a conductive material.

[0116] In one embodiment of the present invention, the negative electrode material may be contained in the negative electrode slurry in an amount of 60 parts by weight to 99 parts by weight, specifically 70 parts by weight to 98 parts by weight, based on 100 parts by weight of the total solid content of the negative electrode slurry.

[0117] In one embodiment of the present invention, the binder may be contained in the negative electrode slurry in an amount of 0.5 parts by weight to 30 parts by weight, specifically 1 part by weight to 20 parts by weight, based on 100 parts by weight of the total solid content of the negative electrode slurry.

[0118] In one embodiment of the present invention, the conductive material may be contained in the negative electrode slurry in an amount of 0.5 parts by weight to 25 parts by weight, specifically 1 part by weight to 20 parts by weight, based on 100 parts by weight of the total solid content of the negative electrode slurry.

[0119] The other components of the negative electrode material, the binder, and the conductive material are as described above.

[0120] The negative electrode slurry according to an embodiment of the present invention may further include a solvent for forming the negative electrode slurry. Specifically, the solvent for forming the negative electrode slurry may include at least one selected from the group consisting of distilled water, ethanol, methanol, and isopropyl alcohol, specifically distilled water, in order to facilitate dispersion of components.

[0121] In one embodiment of the present invention, the solid content weight of the negative electrode slurry may be 20 parts by weight to 75 parts by weight, specifically 30 parts by weight to 70 parts by weight, based on 100 parts by weight of the total negative electrode slurry.

[0122] In one embodiment of the present invention, the viscosity of the negative electrode slurry at 23° C. may be 500 cP to 20,000 cP, specifically 1,000 cP to 10,000 cP.

[0123] When the viscosity is in the range of 500 cP to 20,000 cP, the coating property of the negative electrode slurry is improved, and a negative electrode with excellent quality can be realized. In this case, the viscosity can be measured at 23°C using a viscometer (device name: Brookfield viscometer, manufacturer: Brookfield).

[0124] In the present invention, the pH of the negative electrode slurry at 23° C. may be 6 to 12.5, specifically 6.5 to 12.25, and more specifically 7 to 12.

[0125] When the pH of the negative electrode slurry is in the range of 6 to 12.5, the content of substances that cause a side reaction between the negative electrode active material and moisture, increase the pH of the negative electrode slurry, decrease the viscosity, and decrease the phase stability can be reduced to a preferred level. Therefore, when the pH of the negative electrode slurry at 23°C is in the range of 6 to 12.5, the negative electrode active material is prevented from increasing in pH due to by-products resulting from a side reaction with moisture, improving the phase stability of the slurry, resulting in improved quality of the negative electrode manufactured from the negative electrode slurry and improved charge / discharge efficiency.

[0126] The negative electrode may be manufactured by a method including the steps of: preparing a negative electrode slurry including a negative electrode material containing the above-described negative electrode active material; applying the negative electrode slurry onto a negative electrode current collector; and drying and rolling the applied negative electrode slurry. The negative electrode slurry may further include an additional negative electrode active material.

[0127] The additional negative electrode active material may be a compound capable of reversible intercalation and deintercalation of lithium. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, and Al alloys; and SiO. βExamples of the negative electrode active material include metal oxides capable of doping and dedoping lithium, such as SnO2, vanadium oxide, lithium titanium oxide, and lithium vanadium oxide (0<β<2); or composites containing the metallic compounds and carbonaceous materials, such as Si-C composites and Sn-C composites. A mixture of two or more of these may be used. A thin film of metallic lithium may also be used as the negative electrode active material. The carbon material may be either low-crystalline carbon or high-crystalline carbon. Typical low-crystalline carbons are soft carbon and hard carbon, while typical high-crystalline carbons are amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesocarbon microbeads, mesophase pitches, and high-temperature-calcined carbons such as petroleum or coal tar pitch-derived cokes.

[0128] The additional anode active material may be a carbon-containing anode active material. In one embodiment of the present invention, the weight ratio of the negative electrode active material and the additional negative electrode active material contained in the negative electrode slurry may be 10:90 to 90:10, specifically 10:90 to 50:50.

[0129] <Secondary battery> The present invention provides a secondary battery, specifically a lithium secondary battery, including the above-described negative electrode. Specifically, the secondary battery according to the present invention includes the above-described negative electrode; a positive electrode facing the negative electrode; a separator interposed between the negative electrode and the positive electrode; and an electrolyte.

[0130] The positive electrode may include a positive electrode current collector; and a positive electrode active material layer formed on the positive electrode current collector.

[0131] The positive electrode current collector is not particularly limited as long as it does not induce a chemical change in the battery and has high conductivity. Specifically, the positive electrode current collector may be copper, stainless steel, aluminum, nickel, titanium, fired carbon, a material obtained by surface treatment of copper or stainless steel with carbon, nickel, titanium, silver, etc., an aluminum-cadmium alloy, or the like.

[0132] The positive electrode current collector may usually have a thickness of 3 μm to 500 μm. The positive electrode current collector may form fine irregularities on its surface to strengthen the bonding force with the positive electrode active material. For example, the positive electrode current collector may be used in various forms such as a film, sheet, foil, net, porous body, foam, non-woven fabric body, etc. The positive electrode active material layer may contain a positive electrode active material.

[0133] The positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium. Specifically, it may include a lithium transition metal composite oxide containing at least one transition metal selected from nickel, cobalt, manganese, and aluminum and lithium, preferably a lithium transition metal composite oxide containing a transition metal containing nickel, cobalt, and manganese and lithium.

[0134] More specifically, examples of the lithium transition metal composite oxide include lithium-manganese-based oxides (such as LiMnO2, LiMn2O4, etc.), lithium-cobalt-based oxides (such as LiCoO2, etc.), lithium-nickel-based oxides (such as LiNiO2, etc.), lithium-nickel-manganese-based oxides (such as LiNi 1-Y Mn Y O2 (where 0 < Y < 1), LiMn 2-z Ni z O4 (where 0 < Z < 2), etc.), lithium-nickel-cobalt-based oxides (such as LiNi 1-Y1 CoY1 O2 (where 0 < Y1 < 1, etc.), lithium-manganese-cobalt-based oxides (e.g., LiCo 1-Y2 Mn Y2 O2 (where 0 < Y2 < 1), LiMn 2-z1 Co z1 O4 (where 0 < Z1 < 2, etc.), lithium-nickel-manganese-cobalt-based oxides (e.g., Li(Ni p Co q Mn r1 )O2 (where 0 < p < 1, 0 < q < 1, 0 < r1 < 1, p + q + r1 = 1), or Li(Ni p1 Co q1 Mn r2 )O4 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r2 < 2, p1 + q1 + r2 = 2, etc.), or lithium-nickel-cobalt-transition metal (M) oxides (e.g., Li(Ni p2 Co q2 Mn r3 M S2 )O2 (where M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p2, q2, r3, and s2 are atomic fractions of independent elements, 0 < p2 < 1, 0 < q2 < 1, 0 < r3 < 1, 0 < s2 < 1, p2 + q2 + r3 + s2 = 1.) etc.), and any one or two or more of these compounds may be included. Among them, in terms of improving the capacity characteristics and stability of the battery, the lithium transition metal composite oxide is LiCoO2, LiMnO2, LiNiO2, lithium nickel-manganese-cobalt oxide (e.g., Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.5 Mn 0.3 Co 0.2 )O2, Li(Ni 0.7 Mn 0.15 Co 0.15 )O2, or Li(Ni 0.8 Mn 0.1 Co 0.1 )O2 etc.), or lithium nickel cobalt aluminum oxide (e.g., Li(Ni 0.8 Co 0.15 Al0.05 )O2, etc.), and in consideration of the remarkable improvement effect by controlling the types and content ratios of constituent elements forming the lithium transition metal composite oxide, the lithium transition metal composite oxide may be Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.5 Mn 0.3 Co 0.2 )O2, Li(Ni 0.7 Mn 0.15 Co 0.15 )O2, or Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, etc., and any one of these or a mixture of two or more thereof may be used.

[0135] The positive electrode active material may be contained in the positive electrode active material layer in an amount of 80% by weight to 99% by weight, preferably 92% by weight to 98% by weight, in consideration of the positive electrode active material being able to exhibit sufficient capacity.

[0136] The positive electrode active material layer may further include a binder and / or a conductive material in addition to the positive electrode active material.

[0137] The binder is a component that aids in binding the active material and conductive material, etc., and in binding them to the current collector, and specifically may include at least one selected from the group consisting of polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, and fluororubber, and preferably polyvinylidene fluoride.

[0138] The binder may be contained in the positive electrode active material layer in an amount of 1 to 20% by weight, preferably 1.2 to 10% by weight, in order to ensure sufficient binding strength between components such as the positive electrode active material.

[0139] The conductive material may be used to supplement and improve the conductivity of the secondary battery, and is not particularly limited as long as it does not induce chemical changes and has conductivity. Specifically, the conductive material may include at least one selected from the group consisting of graphite such as natural graphite and artificial graphite; carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; conductive tubes such as carbon nanotubes; fluorocarbon powder; metal powder such as aluminum and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and polyphenylene derivatives. Preferably, the conductive material may include carbon black in order to improve conductivity.

[0140] In order to ensure sufficient conductivity, the conductive material may be contained in the positive electrode active material layer in an amount of 1 to 20% by weight, preferably 1.2 to 10% by weight.

[0141] The thickness of the positive electrode active material layer may be 30 μm to 400 μm, preferably 50 μm to 110 μm.

[0142] The positive electrode may be fabricated by coating a positive electrode slurry containing a positive electrode active material and, optionally, a binder, a conductive material, and a solvent for forming the positive electrode slurry on the positive electrode current collector, followed by drying and rolling.

[0143] The solvent for forming the positive electrode slurry may include an organic solvent such as NMP (N-methyl-2-pyrrolidone), and may be used in an amount that provides a preferred viscosity when containing the positive electrode active material, and optionally a binder and a conductive material, etc. For example, the solvent for forming the positive electrode slurry may be included in the positive electrode slurry so that the concentration of the solids, including the positive electrode active material, and optionally a binder and a conductive material, is 50 wt % to 95 wt %, preferably 70 wt % to 90 wt %.

[0144] The separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator typically used in lithium secondary batteries can be used without limitation. It is particularly preferred that the separator exhibits low resistance to electrolyte ion movement and excellent electrolyte humidification. Specifically, porous polymer films, such as those made from polyolefin-based polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminates of two or more layers thereof, may be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made from high-melting-point glass fibers or polyethylene terephthalate fibers, may also be used. To ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymeric material may be used, and it may be selectively used as a single-layer or multi-layer structure.

[0145] In addition, examples of the electrolyte used in the present invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in manufacturing secondary batteries, but are not limited to these. Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0146] The organic solvent may be used without any particular limitation as long as it can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specific examples of the organic solvent that may be used include ester-based solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether-based solvents such as dibutyl ether and tetrahydrofuran; ketone-based solvents such as cyclohexanone; aromatic hydrocarbon-based solvents such as benzene and fluorobenzene; carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (R is a C2-C20 linear, branched, or cyclic hydrocarbon group that may contain a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; and sulfolanes. Among these, carbonate-based solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and a high dielectric constant, which can improve the charge / discharge performance of a battery, and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferred. In this case, the cyclic carbonate and the linear carbonate are mixed in a volume ratio of about 1:1 to about 1:9, thereby providing excellent electrolyte performance.

[0147] The lithium salt may be any compound capable of providing lithium ions used in lithium secondary batteries. Specifically, examples of the lithium salt include LiPF, LiClO, LiAsF, LiBF, LiSbF, LiAlO, LiAlCl, LiCF, SO, LiCF, SO, LiN(CF, SO), LiN(CF, SO), LiN(CF, SO), LiCl, LiI, and LiB(C, O) . The lithium salt is preferably used at a concentration in the range of 0.1 M to 2.0 M. When the lithium salt concentration is within the range of 0.1 M to 2.0 M, the electrolyte has suitable conductivity and viscosity, resulting in excellent electrolyte performance and efficient lithium ion migration.

[0148] The secondary battery can be manufactured by a conventional method for manufacturing a secondary battery, by interposing a separator between the negative electrode and the positive electrode, and then injecting an electrolyte therein.

[0149] The secondary battery according to the present invention is useful in portable devices such as mobile phones, laptops, and digital cameras, and in electric vehicles such as hybrid electric vehicles (HEVs), and is particularly suitable as a component battery of a medium- to large-sized battery module. Accordingly, the present invention provides a medium- to large-sized battery module including the above-described secondary battery as a unit cell.

[0150] Such a medium- to large-sized battery module can be suitably applied to power sources that require high output and large capacity, such as electric vehicles, hybrid electric vehicles, and power storage devices. [Example]

[0151] The present invention may be embodied in various different forms and should not be construed as limited to the embodiments set forth herein, although the present invention may be embodied in various different forms and should not be construed as limited to the embodiments set forth herein.

[0152] Example 1 (1) Manufacturing of negative electrode active material SiO as silicon-containing oxide particles x (0.5≦x≦1.5) (average particle size (D 50 The silicon-containing oxide particles were subjected to chemical vapor deposition (CVD) at 950° C. using methane as a hydrocarbon gas to prepare silicon-containing oxide particles having a carbon layer formed thereon.

[0153] The silicon-containing oxide particles on which the carbon layer was formed and lithium metal powder as a lithium precursor were solid-phase mixed in a weight ratio of 93:7 to prepare a composition for forming a negative electrode active material.

[0154] The composition for forming a negative electrode active material was heat-treated at 850° C. for 3 hours. The heat-treated composition for forming a negative electrode active material was treated with an aqueous hydrochloric acid solution having a pH of 1 at 23° C. for 1 hour.

[0155] The material obtained by the acid treatment was used as the negative electrode active material of Example 1. The weight ratio of the silicon-containing oxide particles:lithium (Li):carbon layer in the negative electrode active material was 91.3:4.7:4.0.

[0156] (2) Preparation of negative electrode slurry A negative electrode material, a binder, and a conductive material were mixed in a weight ratio of 95:3:2 with distilled water as a solvent for forming a negative electrode slurry to prepare a negative electrode slurry (solid content: 50 wt % based on the total weight of the negative electrode slurry).

[0157] The negative electrode material is a mixture of the above-mentioned negative electrode active material and artificial graphite as a carbon-containing active material in a weight ratio of 20:80, the binder is a mixture of carboxymethyl cellulose and styrene-butadiene rubber in a weight ratio of 50:50, and the conductive material is a mixture of carbon black and carbon nanotubes in a weight ratio of 75:25.

[0158] (3) Manufacturing of the negative electrode The negative electrode current collector was a copper current collector (thickness: 20 μm). The negative electrode slurry was applied to one side of the copper current collector at a rate of 180 mg / 25 cm. 2 The coated layer was rolled and dried in a vacuum oven at 130°C for 8 hours to form a negative electrode active material layer (thickness: 50 µm), which was used as a negative electrode (thickness of negative electrode: 70 µm).

[0159] (4) Secondary battery manufacturing A lithium metal counter electrode was used as the positive electrode. A polyethylene separator was interposed between the negative electrode and the positive electrode, and an electrolyte was injected to prepare a secondary battery.

[0160] The electrolyte was an organic solvent made by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 30:70, to which vinylene carbonate was added in an amount of 0.5 wt % based on the total weight of the electrolyte, and LiPF6 was added as a lithium salt at a concentration of 1 M.

[0161] Example 2 A negative electrode active material, a negative electrode slurry, a negative electrode, and a secondary battery were manufactured in the same manner as in Example 1, except that the heat treatment was carried out at 790° C. in the manufacture of the negative electrode active material.

[0162] Example 3 The negative electrode active material, negative electrode slurry, negative electrode, and secondary battery were manufactured in the same manner as in Example 1, except that the heat treatment was carried out at 890°C in the manufacture of the negative electrode active material.

[0163] Example 4 The negative electrode active material, negative electrode slurry, negative electrode, and secondary battery were produced in the same manner as in Example 1, except that the acid treatment step was not performed in the production of the negative electrode active material.

[0164] Example 5 A negative electrode active material, a negative electrode slurry, a negative electrode, and a secondary battery were manufactured in the same manner as in Example 1, except that in the manufacture of the negative electrode active material, the heat treatment was performed at 890°C, and the heat-treated composition for forming a negative electrode active material was treated with a hydrochloric acid aqueous solution having a pH of 1 at 23°C for 30 minutes.

[0165] Example 6 A negative electrode active material, a negative electrode slurry, a negative electrode, and a secondary battery were manufactured in the same manner as in Example 1, except that in the manufacture of the negative electrode active material, the heat treatment was performed at 790°C, and the heat-treated composition for forming a negative electrode active material was treated with a hydrochloric acid aqueous solution having a pH of 1 at 23°C for 2 hours.

[0166] Comparative Example 1 The negative electrode active material, negative electrode slurry, negative electrode, and secondary battery were manufactured in the same manner as in Example 1, except that the heat treatment was carried out at 770°C in the manufacture of the negative electrode active material.

[0167] Comparative Example 2 In the preparation of the negative electrode active material, the heat treatment was carried out at 770°C, and the acid treatment step was not carried out, but the negative electrode active material, negative electrode slurry, negative electrode, and secondary battery were prepared in the same manner as in Example 1.

[0168] Comparative Example 3 In the preparation of the negative electrode active material, the negative electrode slurry, the negative electrode, and the secondary battery were prepared in the same manner as in Example 1, except that the heat treatment was carried out at 1,000°C.

[0169] Comparative Example 4 In the production of the negative electrode active material, the heat treatment was carried out at 1,000°C, and the acid treatment step was not carried out, but the negative electrode active material, negative electrode slurry, negative electrode, and secondary battery were produced in the same manner as in Example 1.

[0170] Comparative Example 5 A negative electrode active material, a negative electrode slurry, a negative electrode, and a secondary battery were manufactured in the same manner as in Comparative Example 1, except that the acid treatment was carried out for 4 hours.

[0171] The compositions of the negative electrode active materials produced in Examples 1 to 6 and Comparative Examples 1 to 5 were measured by the following method and are shown in Tables 1 and 2 below.

[0172] <Measurement of p2 / p1 and p3 / p1> In Table 2, p2 / p1 and p3 / p1 were 29 calculated as follows by Si MAS NMR analysis. (1) p2 / p1: 29 The ratio of the peak height (p2) of Li2Si2O5 to the peak height (p1) of Li2SiO3 during Si MAS NMR analysis (2) p3 / p1: 29 The ratio of the peak height (p3) of Li4SiO4 to the peak height (p1) of Li2SiO3 during Si MAS NMR analysis

[0173] (Measurement of the total content of crystalline phases Li2Si2O5, Li2SiO3, Li4SiO4, SiO2, Si, the total content of the crystalline phase, and the total content of the amorphous phase) Measurement was carried out using an XRD (X-ray diffraction) instrument (product name: D4-endavor, manufacturer: bruker). The X-ray wavelength generated by Cu Kα was used as the type and wavelength of the light source, and the wavelength (λ) of the light source was 0.15406 nm. After mixing the reference substance MgO and the negative electrode active material at a weight ratio of 20:80, it was placed in a cylindrical holder with a diameter of 2.5 cm and a height of 2.5 mm, and a flattening operation was performed with a slide glass so that the height of the sample in the holder was constant to prepare a sample for XRD analysis. The SCAN TIME was set to 1 hour 15 minutes, the measurement region was set to a region where 2θ was 10° to 90°, and the STEP TIME and STEP SIZE were set to scan 2θ by 0.02° per second. The measurement results were analyzed by Rietveld analysis using X-ray diffraction pattern analysis software to obtain the X-ray diffraction profile. By the above analysis, the total content of crystalline phases Li2Si2O5, Li2SiO3, Li4SiO4, SiO2, Si, the total content of the crystalline phase, and the total content of the amorphous phase were measured.

[0174] <Measurement of pH parameters of negative electrode active material> 0.5 g of the negative active material of each of the Examples and Comparative Examples obtained above was added to 50 mL of distilled water, stirred for 3 hours, and then filtered. The pH of the resulting mixture at 23° C. was measured.

[0175] [Table 1]

[0176] [Table 2]

[0177] Experimental Example 1: Evaluation of the phase stability of negative electrode slurry <pH evaluation experiment of negative electrode slurry> The pH of the negative electrode slurries prepared above in the Examples and Comparative Examples was measured at 23° C. and is shown in Table 3 below.

[0178] <Experiment to evaluate the viscosity of negative electrode slurry> Immediately after producing the negative electrode slurries of the Examples and Comparative Examples, the viscosities at 23°C were measured using a viscometer (device name: Brookfield viscometer, manufacturer: Brookfield). In addition, the negative electrode slurries of the Examples and Comparative Examples produced above were stored for 3 days, and then the viscosities of the negative electrode slurries at 23°C were measured.

[0179] <Measurement of gas generation amount from negative electrode slurry> The negative electrode slurries of the Examples and Comparative Examples prepared above were placed in 7 mL aluminum pouches and sealed.

[0180] The difference between the weight of the aluminum pouch containing the negative electrode slurry in air and the weight of the aluminum pouch in water at 23°C was calculated and divided by the density of water at 23°C to measure the volume of gas immediately after the production of the negative electrode slurry.

[0181] Next, the aluminum pouch containing the negative electrode slurry was stored at 60°C for 3 days, and then the difference between the weight of the aluminum pouch containing the negative electrode slurry in air and the weight of the aluminum pouch in water at 23°C was calculated, and this was divided by the density of water at 23°C to measure the volume of gas after storing the negative electrode slurry for 3 days.

[0182] The difference between the gas volume measured after storing the negative electrode slurry for 3 days and the gas volume measured immediately after producing the negative electrode slurry was defined as the amount of gas generated, and is shown in Table 3 below.

[0183] [Table 3]

[0184] Examples 1 to 3, 5, and 6 are characterized by a high content of crystalline phase Li2Si2O5, and the total content of crystalline phases present in the negative electrode active material is greater than the total content of amorphous phases. From the above configuration, it can be seen that Examples 1 to 3, 5, and 6 have low negative electrode slurries with high viscosities, little change in slurry viscosity, excellent phase stability, few side reactions, and no gas generation. It can be seen that Examples 1 to 3 have a more suitable total crystalline phase content in the negative electrode active material than Examples 5 and 6, and generate even less gas during slurry formation.

[0185] In the case of Example 4, since the acid treatment process was not performed, the pH of the slurry was higher than in Examples 1 to 3. However, since the content of crystalline phase Li2Si2O5 was greater than the sum of the content of crystalline phase Li2SiO3 and the content of crystalline phase Li4SiO4, the occurrence of side reactions with water in the aqueous negative electrode slurry was reduced, and the amount of gas generated was greater than in Examples 1 to 3, 5, and 6, but still less than in Comparative Examples 1 to 4.

[0186] In contrast, in Comparative Examples 1 to 4, the negative electrode slurry had a high pH and low viscosity, and the viscosity of the slurry changed significantly, which made it easy for side reactions to occur, resulting in gas generation and a decrease in phase stability.

[0187] In the case of Comparative Example 5, although the overall lithium content and pH were low, the content of the amorphous phase in the negative electrode active material was high, resulting in high reactivity in the slurry, and therefore it was confirmed that the viscosity of the slurry changed significantly and gas was generated.

[0188] Experimental Example 2: Evaluation of charge / discharge efficiency of secondary batteries The batteries of Examples 1 to 6 and Comparative Examples 1 to 5 were charged and discharged to evaluate the discharge capacity, initial efficiency, and capacity retention rate, and the results are shown in Table 4 below.

[0189] On the other hand, charge / discharge was performed at 0.1C in the first and second cycles, and at 0.5C from the third to the 50th cycles. Charging conditions: CC (constant current) / CV (constant voltage) (5mV / 0.005C current cut-off) Discharge condition: CC (constant current) condition 1.5V

[0190] From the results of the initial charge / discharge, the discharge capacity (mAh / g) and initial efficiency (%) were calculated. Specifically, the initial efficiency (%) was calculated as follows: Initial efficiency (%) = (discharge capacity after first discharge / first charge capacity) x 100 The capacity retention rate was calculated as follows. Capacity retention rate (%) = (50th discharge capacity / initial discharge capacity) x 100

[0191] [Table 4]

[0192] As can be seen from Table 4, Examples 1 to 6 using the negative electrode active material according to the present invention have a high content of the crystalline phase Li2Si2O5, and the total content of the crystalline phase in the negative electrode active material is greater than the total content of the amorphous phase. This reduces gas generation due to reaction with moisture in the negative electrode slurry, prevents an increase in the pH of the negative electrode slurry, and improves the phase stability of the slurry. As a result, the quality of the negative electrode manufactured from the negative electrode slurry is improved, and the charge / discharge efficiency is improved, resulting in excellent discharge capacity, initial efficiency, and capacity retention.

[0193] In contrast, in Comparative Examples 1 to 5, the content of the crystalline phase Li2Si2O5 was low or the total content of crystalline phases in the negative electrode active material was low, which made it easier for side reactions with moisture to occur in the negative electrode slurry, making the negative electrode slurry unstable and resulting in a decrease in the quality of the negative electrode, as well as in the charge / discharge capacity, initial efficiency, and capacity retention rate.

Claims

1. SiO ｘ Particles containing a silicon-containing oxide represented by (0<x<2), and a negative electrode active material containing lithium distributed in the particles, The lithium is in the crystalline phase Li ２ Si ２ O ５ and optionally (b) crystalline phase Li ２ SiO ３ , (c) crystal phase Li ４ SiO ４ or (d) amorphous phase lithium silicate; The crystalline phase Li ２ Si ２ O ５ The content of the crystalline phase Li ２ SiO ３ and the crystalline phase Li ４ SiO ４ more than the sum of the contents of the total content of crystalline phases present in said particles is greater than the total content of amorphous phases; A negative electrode active material comprising crystalline phase Si.

2. The lithium is in the crystalline phase Li ２ Si ２ O ５ , (b) crystal phase Li ２ SiO ３ and optionally (c) crystalline phase Li ４ SiO ４ or (d) amorphous-phase lithium silicate.

3. The negative electrode active material of claim 1 , wherein the total content of the crystalline phases present in the particles is more than 50 parts by weight and not more than 80 parts by weight, based on 100 parts by weight of the particles.

4. The crystalline phase Li ２ Si ２ O ５ Content and crystalline phase Li ２ SiO ３ 2. The negative electrode active material of claim 1, wherein the difference between the content of the particles and the content of the cation exchanger is 1 to 40 parts by weight based on a total of 100 parts by weight of the particles.

5. The crystalline phase Li ４ SiO ４ The negative electrode active material according to claim 1 , which does not contain

6. The negative electrode active material ２９ During Si-MAS-NMR analysis, Li appears in the chemical shift peak at -70 ppm to -80 ppm. ２ SiO ３ The height of peak p1 is the height of Li appearing in the chemical shift peak of -90 ppm to -100 ppm. ２ Si ２ O ５ The negative electrode active material according to claim 2 , wherein the height (Height) of the peak p2 is smaller than the height (Height) of the peak p2.

7. The negative electrode active material ２９ During Si-MAS-NMR analysis, Li appears in the chemical shift peak at -70 ppm to -80 ppm. ２ SiO ３ Li appears in the chemical shift peak at -90 ppm to -100 ppm relative to the height of peak p1 ２ Si ２ O ５ The negative electrode active material according to claim 2 , wherein the ratio (p2 / p1) of the heights of the peaks p2 to p1 is greater than 0.1 and not greater than 6.

5.

8. The negative electrode active material ２９ During Si-MAS-NMR analysis, Li appears in the chemical shift peak at -60 ppm to -69 ppm. ４ SiO ４ The negative electrode active material according to claim 1 , wherein peak p3 of

9. Crystal phase SiO ２ The negative electrode active material according to claim 1 , wherein the negative electrode active material contains less than 5 parts by weight based on a total of 100 parts by weight of the particles.

10. 2. The negative electrode active material of claim 1, wherein the lithium is present in an amount of 0.5 to 25 parts by weight based on 100 parts by weight of the total negative electrode active material.

11. 2. The negative electrode active material according to claim 1, wherein the negative electrode active material obtained by adding 0.5 g of the negative electrode active material to 50 mL of distilled water and stirring for 3 hours has a pH at 23°C of 9 or more and 13 or less.

12. 10. The negative electrode active material of claim 1, further comprising a carbon layer disposed on each of the particles.

13. SiO ｘ preparing a composition for forming a negative electrode active material by mixing particles containing a silicon-containing oxide represented by (0<x<2) and a lithium precursor; and The method for producing a negative electrode active material according to claim 1 , further comprising a step of heat-treating the composition for forming a negative electrode active material at a temperature in the range of 780° C. to 900° C.

14. The method of claim 13 , further comprising: treating the heat-treated composition for forming a negative electrode active material with an acid.

15. The method of claim 13 , further comprising forming a carbon layer on the particles containing silicon-containing oxide before mixing the particles containing silicon-containing oxide and the lithium precursor.

16. The method for producing a negative electrode active material according to claim 13, wherein the heat treatment is carried out for 1 hour to 12 hours.

17. The method for producing a negative electrode active material according to claim 13 , wherein the heat treatment is performed in an inert atmosphere.

18. a negative electrode current collector, and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, The negative electrode active material layer comprises a negative electrode material containing the negative electrode active material according to claim 1 .

19. The negative electrode according to claim 18 . a positive electrode facing the negative electrode; a separator interposed between the negative electrode and the positive electrode; and A secondary battery, including an electrolyte.

20. 2. The negative electrode active material according to claim 1, wherein the crystalline phase Si is contained in an amount of 10 to 50 parts by weight based on a total of 100 parts by weight of the particles.

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