Negative electrode active material and method for producing the same

Abstract

To provide a negative electrode active material that can improve initial efficiency and increase battery capacity, achieve sufficient battery cycle characteristics, and increase stability during mass production slurry production, and a manufacturing method that can manufacture such a negative electrode active material.SOLUTION: A negative electrode active material includes negative electrode active material particles, the negative electrode active material particles include silicon compound particles containing Li silicate, an intermediate layer covering the surface of the silicon compound particles, and including a Li compound different from the Li silicate adjacent to a portion of the surface of the silicon compound particle, and / or a metal oxide and / or a metal hydroxide adjacent to at least a portion of the surface of the silicon compound particle, and an outermost carbon layer covering the intermediate layer.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a negative electrode active material and a method for producing the negative electrode active material. [Background technology]

[0002] In recent years, small electronic devices such as mobile terminals have become widespread, and there is a strong demand for further miniaturization, weight reduction, and longer life. In response to such market demands, development of secondary batteries that are small, lightweight, and capable of achieving high energy density has been progressing. The application of these secondary batteries is being considered not only for small electronic devices but also for large electronic devices such as automobiles and power storage systems such as those for homes.

[0003] Among these, lithium-ion secondary batteries are attracting great attention because they can be easily made small and have a high capacity, and can provide a higher energy density than lead-acid batteries or nickel-cadmium batteries.

[0004] The lithium ion secondary battery includes a positive electrode, a negative electrode, a separator, and an electrolyte solution, and the negative electrode contains a negative electrode active material involved in charge and discharge reactions.

[0005] While carbon-based active materials are widely used as negative electrode active materials, recent market demands have called for further improvements in battery capacity. To improve battery capacity, the use of silicon as a negative electrode active material is being considered. This is because the theoretical capacity of silicon (4199 mAh / g) is more than 10 times greater than that of graphite (372 mAh / g), and a significant improvement in battery capacity can be expected. The development of silicon materials as negative electrode active materials is being considered not only for silicon itself, but also for compounds such as alloys and oxides. Furthermore, the form of the active material is being considered, ranging from the standard coated type for carbon-based active materials to an integrated type in which the material is deposited directly on the current collector.

[0006] However, when silicon is used as the main raw material for the negative electrode active material, the negative electrode active material expands and contracts during charging and discharging, making it prone to cracking, mainly near the surface of the negative electrode active material. Furthermore, ionic substances are generated within the active material, making it prone to cracking. When the surface layer of the negative electrode active material cracks, a new surface is created, increasing the reactive area of ​​the active material. At this time, the electrolyte decomposes on the new surface, and a coating made of the electrolyte decomposition product is formed on the new surface, consuming the electrolyte. This can lead to a decrease in cycle performance.

[0007] To date, various studies have been conducted on negative electrode materials and electrode configurations for lithium-ion secondary batteries that are primarily made of silicon materials in order to improve the initial battery efficiency and cycle characteristics.

[0008] Specifically, to achieve good cycle characteristics and high safety, silicon and amorphous silicon dioxide are simultaneously deposited using a vapor phase method (see, for example, Patent Document 1). Furthermore, to achieve high battery capacity and safety, a carbon material (electron conductor) is provided on the surface layer of silicon oxide particles (see, for example, Patent Document 2). Furthermore, to improve cycle characteristics and achieve high input / output characteristics, an active material containing silicon and oxygen is prepared, and an active material layer with a high oxygen ratio near the current collector is formed (see, for example, Patent Document 3). Furthermore, to improve cycle characteristics, oxygen is incorporated into the silicon active material, and the silicon active material is formed so that the average oxygen content is 40 at% or less and the oxygen content is higher near the current collector (see, for example, Patent Document 4).

[0009] In addition, in order to improve the initial charge / discharge efficiency, Si phase, SiO2, M y Nanocomposites containing SiO O metal oxides are used (see, for example, Patent Document 5). x(0.8 ≤ x ≤ 1.5, particle size range = 1 μm to 50 μm) is mixed with a carbon material and fired at high temperature (see, for example, Patent Document 6). Further, in order to improve cycle characteristics, the molar ratio of oxygen to silicon in the negative electrode active material is set to 0.1 to 1.2, and the active material is controlled within a range where the difference between the maximum value and the minimum value of the molar ratio in the vicinity of the interface between the active material and the current collector is 0.4 or less (see, for example, Patent Document 7). Further, in order to improve the battery load characteristics, a metal oxide containing lithium is used (see, for example, Patent Document 8). Further, in order to improve cycle characteristics, a hydrophobic layer such as a silane compound is formed on the surface layer of the silicon material (see, for example, Patent Document 9). Further, in order to improve cycle characteristics, silicon oxide is used, and conductivity is imparted by forming a graphite film on its surface layer (see, for example, Patent Document 10). In Patent Document 10, regarding the shift value obtained from the RAMAN spectrum of the graphite film, broad peaks appear at 1330 cm -1 and 1580 cm -1 , and the intensity ratio I 1330 / I 1580 is such that 1.5 < I 1330 / I 1580 < 3. Further, in order to improve high battery capacity and cycle characteristics, particles having a silicon microcrystalline phase dispersed in silicon dioxide are used (see, for example, Patent Document 11). Further, in order to improve overcharge and overdischarge characteristics, a silicon oxide in which the atomic ratio of silicon to oxygen is controlled to 1:y (0 < y < 2) is used (see, for example, Patent Document 12).

[0010] The lithium ion secondary battery using silicon oxide was shipped by Hitachi Maxell in June 2010 for a rectangular secondary battery for smartphones that adopted a nanosilicon composite (see, for example, Non-Patent Document 1). The silicon oxide proposed by Hohl is Si 0+ ~Si 4+It is a composite material with various oxidation states (see Non-Patent Document 2). Kapaklis has also proposed a disproportionated structure in which silicon oxide is separated into Si and SiO2 by applying a thermal load (see Non-Patent Document 3). Miyachi et al. have focused on Si and SiO2, which contribute to charge and discharge, among silicon oxides with disproportionated structures (see Non-Patent Document 4), and Yamada et al. have proposed the following reaction formula between silicon oxide and Li (see Non-Patent Document 5):

[0011] 2SiO(Si+SiO2) + 6.85Li + + 6.85e - → 1.4Li 3.75 Si + 0.4Li4SiO4 + 0.2SiO2

[0012] The above reaction formula shows that Si and SiO2 that make up silicon oxide react with Li, and are separated into Li silicide, Li silicate, and some unreacted SiO2.

[0013] The Li silicate produced here is irreversible, and once formed, it is considered to be a stable substance that does not release Li. The capacity per mass calculated from this reaction formula is close to the experimental value, and is recognized as the reaction mechanism of silicon oxide. Kim et al. have defined the irreversible component, Li silicate, associated with the charge and discharge of silicon oxide as Li4SiO4, and 7 Li-MAS-NMR and 29 The identification was carried out using Si-MAS-NMR (see Non-Patent Document 6).

[0014] This irreversible capacity is the weakest point of silicon oxide, and improvement is required. Kim et al. have used a Li pre-doping method to form Li silicate in advance, which significantly improved the initial efficiency of the battery and produced a negative electrode that can withstand practical use (see Non-Patent Document 7).

[0015] Furthermore, instead of doping the electrode with Li, a method of treating the powder has also been proposed, which has achieved an improvement in irreversible capacity (see Patent Document 13).

[0016] In addition, to improve the water resistance of the obtained Li-doped material, Al isopropoxide was used as a material to deposit AlO in the upper layer of the C layer. x It is coated (see Patent Document 14). [Prior art documents] [Patent documents]

[0017] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-185127 [Patent Document 2] Japanese Patent Application Laid-Open No. 2002-042806 [Patent Document 3] Japanese Patent Application Laid-Open No. 2006-164954 [Patent Document 4] Japanese Patent Application Laid-Open No. 2006-114454 [Patent Document 5] Japanese Patent Application Laid-Open No. 2009-070825 [Patent Document 6] Japanese Patent Application Laid-Open No. 2008-282819 [Patent Document 7] Japanese Patent Application Laid-Open No. 2008-251369 [Patent Document 8] Japanese Patent Application Laid-Open No. 2008-177346 [Patent Document 9] Japanese Patent Application Laid-Open No. 2007-234255 [Patent Document 10] Japanese Patent Application Laid-Open No. 2009-212074 [Patent Document 11] Japanese Patent Application Laid-Open No. 2009-205950 [Patent Document 12] Japanese Patent Application Publication No. 06-325765 [Patent Document 13] Japanese Patent Application Laid-Open No. 2015-156355 [Patent Document 14] Japanese Patent Application Laid-Open No. 2017-10645 [Non-patent literature]

[0018] [Non-Patent Document 1] The official journal of the Battery Industry Association of Japan, "Denchi", May 1, 2010 issue, page 10 [Non-Patent Document 2] A. Hohl, T. Wieder, P. A. van Aken, T. E. Weirich, G. Denninger, M. Vidal, S. Oswald, C. Deneke, J. Mayer, and H. Fuess: J. Non-Cryst. Solids, 320, (2003), 255. [Non-Patent Document 3] V. Kapaklis, J. Non-Crystalline Solids, 354 (2008) 612 [Non-Patent Document 4] Mariko Miyachi, Hironori Yamamoto, and Hidemasa Kawai, J. Electrochem. Soc. 2007 volume 154, issue 4, A376 - A380 [Non-Patent Document 5] M. Yamada, M. Inaba, A. Ueda, K. Matsumoto, T. Iwasaki, T. Ohzuku, J.Electrochem. Soc., 159, A1630 (2012) [Non-Patent Document 6] Taeahn Kim, Sangjin Park, and Seung M. Oh, J. Electrochem. Soc. volume 154, (2007), A1112 - A1117. [Non-Patent Document 7] Hye Jin Kim, Sunghun Choi, Seung Jong Lee, Myung Won Seo, Jae Goo Lee, Erhan Deniz, Yong Ju Lee, Eun Kyung Kim, and Jang Wook Choi,. Nano Lett. 2016, 16, 282 - 288. [Summary of the Invention] [Problems to be Solved by the Invention]

[0019] As mentioned above, compact electronic devices, such as mobile terminals, have become increasingly sophisticated and multifunctional in recent years, necessitating increased battery capacity for their primary power source: lithium-ion secondary batteries. One solution to this problem is the development of lithium-ion secondary batteries with anodes primarily made of silicon materials. Furthermore, lithium-ion secondary batteries using silicon materials are expected to have initial charge-discharge and cycle characteristics comparable to those of lithium-ion secondary batteries using carbon-based active materials. Therefore, the use of modified (Li-doped) silicon oxides, which have been modified by the insertion and partial desorption of Li, as anode active materials has improved cycle characteristics and initial charge-discharge characteristics. However, when Li-inserted anode materials are used in the electrode fabrication process, various problems arise, such as a decrease in the viscosity of the binder (thickener) due to partial elution of the Li component into the slurry.

[0020] To address these issues, we have developed an AlO x Although they investigated coating the slurry with a layer (Patent Document 14), the shear force applied during stirring to create a slurry resulted in the film peeling off, reducing the effectiveness by half. In particular, when creating a slurry in a small machine with a capacity of a few liters, the shear force was small and there were no problems, but when moving to a mass-production machine on a larger scale, they found that it was no longer possible to maintain the stability of the slurry for two days.

[0021] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide an anode active material that can improve initial efficiency and increase battery capacity, realize sufficient battery cycle characteristics, and enhance stability when mass-produced as a slurry, and a manufacturing method for manufacturing such an anode active material. [Means for solving the problem]

[0022] In order to solve the above problems, the present invention provides a negative electrode active material including negative electrode active material particles, The negative electrode active material particles are Silicon compound particles containing Li silicate; An intermediate layer that coats the surface of the silicon compound particle, a Li compound different from the Li silicate adjacent to a portion of the surface of the silicon compound particle; and / or a metal oxide and / or metal hydroxide adjacent to at least a portion of the surface of the silicon compound particle; a middle layer including a carbon layer as an outermost layer covering the intermediate layer; The present invention provides a negative electrode active material characterized by having the following formula:

[0023] The negative electrode active material of the present invention contains negative electrode active material particles that include silicon compound particles containing Li silicate, and therefore can improve battery capacity.

[0024] Furthermore, in the negative electrode active material of the present invention, the silicon compound particles contain Li silicate, and the surfaces of the silicon compound particles are coated with an intermediate layer, which contains a Li compound other than the Li silicate adjacent to a portion of the surface of the silicon compound particles, and / or a metal oxide and / or metal hydroxide adjacent to at least a portion of the surface of the silicon compound particles, and the intermediate layer is coated with a carbon layer that provides conductivity. This improves stability when forming a slurry for mass production, while also achieving excellent Li diffusibility and conductivity within the bulk. By improving Li diffusibility, initial efficiency, battery cycle characteristics, and input characteristics can be improved.

[0025] As a result, the negative electrode active material of the present invention can improve the initial efficiency and increase the battery capacity, and can achieve sufficient battery cycle characteristics while enhancing stability when made into a mass-produced slurry.

[0026] At least a portion of the silicon compound particles preferably contains, as the Li silicate, at least one selected from the group consisting of Li2SiO3, Li4SiO4, and Li6Si2O7.

[0027] Such a material is obtained by modifying the SiO2 component portion in silicon compound particles, which becomes unstable when lithium is inserted and extracted during charging and discharging of the battery, into a different lithium silicate in advance, thereby reducing the irreversible capacity that occurs during charging.

[0028] The intermediate layer preferably contains the Li compound, and the Li compound is preferably a composite compound containing Li, C, and O.

[0029] A composite compound containing Li, C, and O has excellent Li permeability. Therefore, when the intermediate layer contains such a Li compound, the Li diffusibility can be further improved. Further improvement in the Li diffusibility can further improve the initial efficiency, battery cycle characteristics, and input characteristics.

[0030] In this case, for example, the composite compound containing Li, C, and O has an OC=O structure in at least a part thereof in the C1s waveform obtained from the XPS spectrum.

[0031] The complex compound containing Li, C, and O may, for example, have an OC=O structure at least in part.

[0032] It is preferable that the intermediate layer contains the metal oxide and / or metal hydroxide, and that the metal oxide and / or metal hydroxide contains at least one element selected from the group consisting of aluminum, magnesium, titanium, zirconium, calcium, and niobium.

[0033] If the intermediate layer that coats the surface of the silicon compound particles contains such a cation, excellent adhesion and excellent water resistance can be more reliably exhibited.

[0034] In this case, it is preferable that the thickness of the metal oxide and / or metal hydroxide in the intermediate layer is 0.1 nm or more and 10 nm or less.

[0035] If the thickness of the metal oxide and / or metal hydroxide in the intermediate layer is within this range, the film thickness can be easily controlled and sufficient Li permeability can be exhibited.

[0036] It is particularly preferable that the intermediate layer contains the Li compound and the metal oxide and / or metal hydroxide, and that the metal oxide and / or metal hydroxide coats the Li compound.

[0037] Metal oxides and / or metal hydroxides can exhibit superior water resistance. Furthermore, Li compounds other than Li silicates do not have as high water resistance, but they have excellent Li permeability. Therefore, if the negative electrode active material particles contain both a Li compound other than Li silicate and a metal oxide and / or metal hydroxide, and include an intermediate layer in which the metal oxide and / or metal hydroxide coats the Li compound other than Li silicate, the negative electrode active material particles can exhibit superior Li diffusibility within the bulk while further improving stability during mass-production slurry formation.

[0038] The negative electrode active material particles have a peak attributable to a Si(111) crystal plane obtained by X-ray diffraction using Cu-Kα radiation before charging and discharging the negative electrode active material particles, the crystallite size corresponding to the crystal plane is 5.0 nm or less, and the ratio A / B of the intensity A of the peak attributable to the Si(111) crystal plane to the intensity B of the peak attributable to the Li2SiO3(111) crystal plane satisfies the following formula (1): 0.4≦A / B≦1.0 (1) It is preferable that the above condition is satisfied.

[0039] A negative electrode active material containing such negative electrode active material particles can achieve a high battery capacity while reducing the irreversible capacity.

[0040] The negative electrode active material particles preferably have a median diameter of 4.5 μm or more and 15 μm or less.

[0041] If the median diameter of the negative electrode active material particles is within this range, it is possible to prevent the reaction with the electrolyte from being accelerated, and also to prevent the loss of electronic contacts due to the expansion of the active material during charge and discharge.

[0042] The present invention also provides a method for producing a negative electrode active material containing negative electrode active material particles, comprising: General formula SiO x a step of preparing silicon oxide particles represented by (0.5≦x≦1.6); intercalating Li into the silicon oxide particles to produce silicon compound particles containing Li silicate; On the surface of the silicon compound particles, a Li compound different from the Li silicate adjacent to a portion of the surface of the silicon compound particle; and / or a metal oxide and / or metal hydroxide adjacent to at least a portion of the surface of the silicon compound particle; forming an intermediate layer comprising: forming an outermost carbon layer that covers the intermediate layer to obtain negative electrode active material particles; a step of producing a negative electrode active material using the negative electrode active material particles; The present invention provides a method for producing a negative electrode active material, comprising:

[0043] The negative electrode active material produced by such a production method contains negative electrode active material particles that include silicon compound particles containing Li silicate, and therefore can improve battery capacity.

[0044] Furthermore, in the negative electrode active material produced by this production method, the silicon compound particles contain Li silicate, and the surfaces of the silicon compound particles are coated with an intermediate layer, which contains a Li compound other than the Li silicate adjacent to a portion of the surface of the silicon compound particles, and / or a metal oxide and / or metal hydroxide adjacent to at least a portion of the surface of the silicon compound particles, and the intermediate layer is coated with a carbon layer that provides conductivity. This improves stability when mass-produced as a slurry, while also achieving excellent Li diffusibility and conductivity within the bulk. By improving Li diffusibility, initial efficiency, battery cycle characteristics, and input characteristics can be improved.

[0045] As a result, the negative electrode active material produced by the method for producing a negative electrode active material of the present invention can improve initial efficiency and increase battery capacity, and can achieve sufficient battery cycle characteristics while increasing stability when mass-produced as a slurry.

[0046] In the step of preparing silicon compound particles containing Li silicate, silicon compound particles containing the Li compound on the surface are prepared, In the step of forming the intermediate layer, removing a portion of the Li compound present on the surface of the silicon compound particles; It is preferable to form the intermediate layer containing the metal oxide and / or metal hydroxide and the Li compound by coating a portion of the surface of the silicon compound particle and the surface of the Li compound with a metal oxide and / or metal hydroxide.

[0047] According to the method for producing a negative electrode active material according to this preferred embodiment, it is possible to produce a negative electrode active material in which the intermediate layer contains both a Li compound other than Li silicate and a metal oxide and / or a metal hydroxide, and the Li compound is coated with the metal oxide and / or metal hydroxide.

[0048] Metal oxides and / or metal hydroxides can exhibit superior water resistance. Furthermore, Li compounds other than Li silicates do not have as high water resistance, but they have excellent Li permeability. Therefore, the production method according to this preferred embodiment can produce a negative electrode active material that exhibits superior Li diffusivity in the bulk while further improving stability during mass production of a slurry.

[0049] In this case, for example, in the step of forming the intermediate layer, the metal oxide and / or the metal hydroxide can be formed by hydrolysis and dehydration condensation of a metal alkoxide.

[0050] The metal oxide and / or the metal hydroxide can be formed, for example, by hydrolysis and dehydration condensation of a metal alkoxide. [Effects of the Invention]

[0051] As described above, the negative electrode active material of the present invention can improve the initial efficiency and increase the battery capacity, and can achieve sufficient battery cycle characteristics while improving stability when made into a mass-produced slurry.

[0052] Furthermore, the method for producing a negative electrode active material of the present invention can improve initial efficiency and increase battery capacity, and can produce a negative electrode active material that can achieve sufficient battery cycle characteristics and exhibit high stability when mass-produced into a slurry. [Brief explanation of the drawings]

[0053] [Figure 1] 1 is a schematic partial cross-sectional view of a negative electrode active material particle included in an example of the negative electrode active material of the present invention. [Figure 2] FIG. 2 is a schematic partial cross-sectional view of a negative electrode active material particle contained in another example of the negative electrode active material of the present invention. [Figure 3] FIG. 2 is a schematic partial cross-sectional view of a negative electrode active material particle included in yet another example of the negative electrode active material of the present invention. [Figure 4] 1 is a schematic cross-sectional view showing an example of the configuration of a negative electrode containing the negative electrode active material of the present invention. [Figure 5] FIG. 1 is an exploded view showing an example of the configuration of a lithium ion secondary battery (laminate film type) equipped with a negative electrode containing the negative electrode active material of the present invention. [Figure 6] 10 is a schematic partial cross-sectional view of a negative electrode active material particle contained in the negative electrode active material of Comparative Example 4. FIG. [Figure 7] 10 is a part of an XPS spectrum of the negative electrode active material particles contained in the negative electrode active material of Example 16 after etching six times. [Figure 8] 1 shows a part of an XPS spectrum of the outermost layer of a negative electrode active material particle of the negative electrode active material of Example 1 and an XPS spectrum after etching three times. DETAILED DESCRIPTION OF THE INVENTION

[0054] As mentioned above, one method for increasing the battery capacity of lithium-ion secondary batteries is to use a silicon oxide-based anode. It is desirable for lithium-ion secondary batteries using silicon oxide to exhibit initial charge-discharge characteristics comparable to those of lithium-ion secondary batteries using carbon-based active materials. Furthermore, Li-doped SiO2, which can improve the initial charge-discharge characteristics, is also desirable for its cycle characteristics to be comparable to those of carbon-based active materials. However, no anode active material has been proposed that can provide a satisfactory pot life for mass-produced slurries.

[0055] Therefore, the present inventors have conducted extensive research to obtain a negative electrode active material that, when used as a negative electrode active material for a secondary battery, is easy to handle, exhibits high cycle characteristics, improves initial charge / discharge characteristics, and results in an increased battery capacity. As a result, they have found that by coating the surfaces of silicon compound particles containing Li silicate with an intermediate layer containing a Li compound other than Li silicate adjacent to a portion of the surface of the silicon compound particles and / or a metal oxide and / or metal hydroxide adjacent to at least a portion of the surface of the silicon compound particles, and coating the intermediate layer with an outermost carbon layer that imparts conductivity, it is possible to obtain excellent Li diffusivity and conductivity in the bulk while improving stability during mass production slurry formation, and have completed the present invention.

[0056] That is, the present invention provides a negative electrode active material containing negative electrode active material particles, The negative electrode active material particles are Silicon compound particles containing Li silicate; An intermediate layer that coats the surface of the silicon compound particle, a Li compound different from the Li silicate adjacent to a portion of the surface of the silicon compound particle; and / or a metal oxide and / or metal hydroxide adjacent to at least a portion of the surface of the silicon compound particle; a middle layer including a carbon layer as an outermost layer covering the intermediate layer; The negative electrode active material is characterized by having the following:

[0057] The present invention also provides a method for producing a negative electrode active material containing negative electrode active material particles, comprising: General formula SiO x a step of preparing silicon oxide particles represented by (0.5≦x≦1.6); intercalating Li into the silicon oxide particles to produce silicon compound particles containing Li silicate; On the surface of the silicon compound particles, a Li compound different from the Li silicate adjacent to a portion of the surface of the silicon compound particle; and / or a metal oxide and / or metal hydroxide adjacent to at least a portion of the surface of the silicon compound particle; forming an intermediate layer comprising: forming an outermost carbon layer that covers the intermediate layer to obtain negative electrode active material particles; a step of producing a negative electrode active material using the negative electrode active material particles; Also provided is a method for producing a negative electrode active material, comprising:

[0058] The present invention will be described in detail below, but the present invention is not limited thereto.

[0059] <Negative electrode active material> The negative electrode active material of the present invention (hereinafter also referred to as silicon-based negative electrode active material) contains negative electrode active material particles (hereinafter also referred to as silicon-based negative electrode active material particles) containing silicon compound particles, and therefore can improve battery capacity.

[0060] Furthermore, by forming Li silicate on at least a portion of the silicon compound particles, the slurry can be stabilized before application, and the use of a stable slurry leads to the production of a good electrode and improved battery characteristics. However, it has been found that such a slurry does not have sufficient long-term storage stability, and the formed Li silicate slowly dissolves in the slurry over time.

[0061] During the formation of Li-silicate, for example, applying a thermal load can enlarge the crystalline phase of the Li-silicate, which reduces the amount of Li dissolved in the slurry, but at the same time, the crystallinity of the Si increases. The formation of such highly crystalline Si significantly reduces the battery performance.

[0062] Furthermore, when the Li silicate phase becomes enlarged, the diffusibility of Li is significantly reduced, which deteriorates the battery characteristics.

[0063] Therefore, by making the Li silicate crystal phase as small as possible and suppressing the crystallization of Si and the enlargement of the Li silicate phase, a Li silicate phase that dissolves slowly in water is produced.

[0064] As a result, satisfactory battery characteristics were obtained, but in the electrode formation process, particularly in the preparation of the slurry, if the slurry was left for a long time, the binder would deteriorate and the battery characteristics would deteriorate, so it was necessary to apply the slurry as soon as possible after its preparation.

[0065] Therefore, the inventors have developed a material that can achieve excellent Li diffusivity within the bulk while improving stability when mass-produced as a slurry. The material is made by coating the surface of silicon compound particles containing Li silicate with an intermediate layer containing a Li compound other than Li silicate adjacent to a portion of the surface of the silicon compound particles, and / or a metal oxide and / or metal hydroxide adjacent to at least a portion of the surface of the silicon compound particles, and by coating the intermediate layer with an outermost carbon layer that confers conductivity.

[0066] In the negative electrode active material of the present invention, the silicon compound particles contain Li silicate, and the surfaces of the silicon compound particles are coated with an intermediate layer, which contains a Li compound other than Li silicate adjacent to a portion of the surface of the silicon compound particles, and / or a metal oxide and / or metal hydroxide adjacent to at least a portion of the surface of the silicon compound particles, and the intermediate layer is coated with an outermost carbon layer.

[0067] The metal oxide and / or metal hydroxide can exhibit excellent water resistance. Therefore, by including the metal oxide and / or metal hydroxide adjacent to at least a portion of the surface of the silicon compound particle, the intermediate layer can improve the water resistance of the negative electrode active material without significantly inhibiting Li permeability, and can improve stability during mass production slurry formation. Furthermore, the coexistence of the metal oxide and metal hydroxide can further exhibit excellent stability and excellent Li permeability.

[0068] In the negative electrode active material of the present invention, the Li compound other than Li silicate is, for example, a composite compound containing Li, C, and O. Such a composite compound may be, for example, a material synthesized by condensation during heat treatment of a decomposition product of a solvent used in the production of negative electrode active material particles, and may partially have a carboxylic acid structure (OC=O).

[0069] Although such a Li compound does not have a particularly high water resistance, by being contained in the intermediate layer so as to be adjacent to a part of the surface of the silicon compound particle, the stability of the negative electrode active material can be improved when it is mass-produced as a slurry. Furthermore, since such a Li compound has excellent Li permeability, an intermediate layer containing such a Li compound can exhibit excellent Li permeability.

[0070] The outermost carbon layer covering the intermediate layer can provide electrical conductivity.

[0071] As a result, the negative electrode active material of the present invention can have excellent Li diffusivity and conductivity in the bulk while improving stability when mass-produced as a slurry. By improving Li diffusivity, the initial efficiency, battery cycle characteristics, and input characteristics can be improved.

[0072] Therefore, the negative electrode active material of the present invention can improve the initial efficiency and increase the battery capacity, and can achieve sufficient battery cycle characteristics while enhancing stability when made into a mass-produced slurry.

[0073] The negative electrode active material of the present invention will be described in more detail below.

[0074] The negative electrode active material of the present invention can be used, for example, as a negative electrode active material for non-aqueous electrolyte secondary batteries, particularly for lithium ion secondary batteries.

[0075] FIG. 1 shows a schematic partial cross-sectional view of a negative electrode active material particle contained in an example of the negative electrode active material of the present invention.

[0076] The negative electrode active material particles 1 shown in FIG. 1 contain silicon compound particles 2. The silicon compound particles 2 can be said to be a silicon oxide material containing a silicon compound containing oxygen. The ratio of silicon to oxygen constituting this silicon oxide is SiO xThe range of 0.8≦x≦1.2 is preferred. If x is 0.8 or more, the oxygen ratio is higher than that of silicon alone, resulting in better cycle characteristics. If x is 1.2 or less, the resistance of the silicon oxide does not become too high, which is preferable. Among these, SiO x In the composition, it is preferable that x is close to 1, because high cycle characteristics can be obtained. Note that the composition of the silicon compound in the present invention does not necessarily mean 100% purity, and may contain trace amounts of impurity elements.

[0077] In addition, as an example, SiO x The figure shows an aspect in which a Si phase 3 is contained in a particle 2.

[0078] Furthermore, in the negative electrode active material of the present invention, the silicon compound particles 2 contain Li silicate. Specifically, it is preferable that at least a portion of the silicon compound particles 2 contains at least one selected from the group consisting of Li2SiO3, Li4SiO4, and Li6SiO7. More specifically, it is more preferable that the silicon compound particles 2 contain Li2SiO3. In such a material, the SiO2 component in the silicon oxide, which becomes unstable during lithium insertion and desorption during battery charge and discharge, has been previously modified into a different lithium silicate, thereby reducing the irreversible capacity generated during charge. Furthermore, by enlarging the Li silicate within a range that suppresses Si crystal growth, it is possible to reduce the irreversible capacity associated with charge and discharge. Therefore, among the Li silicates formed in the bulk, it is desirable that Li2SiO3 be crystalline.

[0079] However, if it becomes too large, it will no longer contribute to charging and discharging, so there is an optimum range.

[0080] When slurried, Li4SiO4 and Li6Si2O7 are more unstable than Li2SiO3 due to their high solubility in water, but they can be used effectively by improving the stability of mass-produced slurries using the intermediate layer described below.

[0081] In this case, Li4SiO4 has the best Li diffusibility, and it is desirable to use it in combination with Li2SiO3, which has high structural stability.

[0082] Furthermore, Li silicates such as Li2SiO3, Li4SiO4, and Li6Si2O7 contained inside the bulk of silicon oxide particles can be quantified by NMR (Nuclear Magnetic Resonance). NMR measurements can be performed, for example, under the following conditions. 29 Si-MAS-NMR (Magic Angle Spinning Nuclear Magnetic Resonance) Equipment: Bruker 700 NMR spectrometer, Probe: 4mm HR-MAS rotor 50μL, Sample rotation speed: 10kHz, ·Measurement environment temperature: 25℃.

[0083] The degree of Li silicate enlargement and the degree of Si crystallization can be confirmed by XRD (X-ray diffraction). A Bruker D8 ADVANCE X-ray diffractometer can be used. For example, the X-ray source is Cu Kα radiation, and a Ni filter is used. Measurements are performed from 10 to 40° with an output of 40 kV / 40 mA, a slit width of 0.3°, a step width of 0.008°, and a counting time of 0.15 seconds per step.

[0084] The negative electrode active material particles 1 further include an intermediate layer 4 that covers the surface of the silicon compound particles 2, and a carbon layer 7 that covers the surface of the intermediate layer 4 and is the outermost layer.

[0085] The intermediate layer 4 contained in the negative electrode active material 1 of the present invention contains a Li compound 5 different from the Li silicate adjacent to a portion of the surface of the silicon compound particle 2, and / or a metal oxide and / or metal hydroxide 6 adjacent to at least a portion of the surface of the silicon compound particle 2.

[0086] In the example shown in FIG. 1, the intermediate layer 4 contains both a Li compound 5 different from a Li silicate and a metal oxide and / or metal hydroxide 6 .

[0087] Alternatively, as in the example shown in FIG. 2, the intermediate layer 4 may contain only a Li compound 5 other than Li silicate.

[0088] Alternatively, as in the example shown in FIG. 3, the intermediate layer 4 may contain only a metal oxide and / or a metal hydroxide 6.

[0089] The metal oxide and / or metal hydroxide 6 can exhibit excellent water resistance. Therefore, by including the metal oxide and / or metal hydroxide 6 adjacent to at least a portion of the surface of the silicon compound particles 2, the intermediate layer 4 can improve the water resistance of the negative electrode active material without significantly impeding Li permeability, thereby improving stability during mass production slurry formation. For example, if an alumina layer is present in the intermediate layer, Li-AlOx is generated during the first charge, and this substance allows Li to pass through smoothly, so the presence of an alumina layer is not necessary, but the presence of an alumina layer can have a better effect on Li permeability.

[0090] For example, metal oxides can be produced by hydrolysis and dehydration condensation of metal alkoxides. In the process of forming a metal oxide layer using metal alkoxides, heat treatment at 100°C or higher is performed, but there is a high possibility that a hydroxide layer will remain in part of the bulk.

[0091] Such metal oxide layers can exhibit good stability and good Li permeability.

[0092] The Li compound 5 used in the present invention, which is different from Li silicate, is, for example, a composite compound containing Li, C, and O. Such a composite compound may be, for example, a material synthesized by condensation during heat treatment of a decomposition product of a solvent used in the production of negative electrode active material particles, and may partially have a carboxylic acid structure (OC=O).

[0093] Li, C, and O having a carboxylic acid structure have an OC=O structure at least in part in the C1s waveform obtained from an XPS (X-ray photoelectron spectroscopy) spectrum.

[0094] Although the Li compound 5 different from Li silicate does not have a particularly high water resistance, it can improve the stability of the negative electrode active material when it is mass-produced as a slurry by being contained in the intermediate layer 4 so as to be adjacent to a part of the surface of the silicon compound particles 2. Furthermore, since such Li compound 5 has excellent Li permeability, the intermediate layer 4 containing such a Li compound can exhibit excellent Li permeability.

[0095] The outermost carbon layer 7 covering the intermediate layer 4 can provide electrical conductivity.

[0096] By including the negative electrode active material particles 1 having such a structure, the negative electrode active material of the present invention can achieve excellent Li diffusivity and conductivity in the bulk while improving stability during mass production of a slurry. The improved Li diffusivity can improve initial efficiency, battery cycle characteristics, and input characteristics.

[0097] The negative electrode active material of the present invention can improve stability when mass-produced into a slurry, even when the intermediate layer 4 contains only the Li compound 5 as shown in Fig. 2, or when the intermediate layer 4 contains only the metal oxide and / or metal hydroxide 6 as shown in Fig. 3. However, when the intermediate layer 4 contains both the Li compound 5 and the metal oxide and / or metal hydroxide 6, and the metal oxide and / or metal hydroxide 6 coats the Li compound 5, as shown in Fig. 1, the negative electrode active material of the present invention can enjoy the effects of both the Li compound 5 and the metal oxide and / or metal hydroxide 6, and can therefore exhibit better Li diffusibility in the bulk while further improving stability when mass-produced into a slurry.

[0098] 1, a Li compound 5 is adjacent to a portion of the surface of a silicon compound particle 2. In addition, a metal oxide and / or metal hydroxide 6 is adjacent to a portion of the surface of the silicon compound particle 2, specifically, a portion not adjacent to the Li compound 5, and coats the Li compound 5.

[0099] On the other hand, for example, as described in Patent Document 14, when the surface of silicon compound particles is coated with a carbon layer and the surface of the carbon layer is coated with a metal oxide as an outermost layer, there is no problem when forming a slurry using a small device, but for the reasons explained above, the stability is reduced when forming a mass-produced slurry.

[0100] The presence of the Li compound 5 and the metal oxide and / or metal hydroxide 6 in the negative electrode active material particles 1 can be confirmed by X-ray photoelectron spectroscopy (XPS).

[0101] The metal oxide and / or metal hydroxide 6 preferably contains at least one element selected from the group consisting of aluminum, magnesium, titanium, zirconium, calcium, and niobium.

[0102] If the intermediate layer 4 that coats the surface of the silicon compound particle 2 contains such a cation, it is possible to more reliably exhibit excellent adhesion and excellent water resistance.

[0103] Furthermore, it is preferable that the thickness of the metal oxide and / or metal hydroxide 6 in the intermediate layer 4 is 0.1 nm or more and 10 nm or less.

[0104] If the thickness of the metal oxide and / or metal hydroxide 6 in the intermediate layer 4 is within this range, the film thickness can be easily controlled and sufficient Li permeability can be exhibited.

[0105] The thickness of the metal oxide and / or metal hydroxide 6 can be measured by the following procedure. First, the metal elements are quantified by inductively coupled plasma (ICP) analysis, and the volume is calculated from the known specific gravity (density). Furthermore, the particle size of the median diameter D50 is determined from the particle size distribution of the powder, and the surface area is calculated by representing it as a sphere. Assuming that the metal oxide is uniformly coated over this area, the thickness of the metal oxide and / or metal hydroxide 6 can be calculated.

[0106] The negative electrode active material particles 1 contained in the negative electrode active material of the present invention have a peak attributable to a Si(111) crystal plane obtained by X-ray diffraction using Cu-Kα radiation before charging and discharging the negative electrode active material particles 1, the crystallite size corresponding to the crystal plane is 5.0 nm or less, and the ratio A / B of the intensity A of the peak attributable to the Si(111) crystal plane to the intensity B of the peak attributable to the Li2SiO3(111) crystal plane satisfies the following formula (1): 0.4≦A / B≦1.0 (1) It is preferable that the above condition is satisfied.

[0107] A negative electrode active material containing such negative electrode active material particles 1 can achieve high battery capacity while reducing irreversible capacity.

[0108] The negative electrode active material particles 1 preferably have a median diameter of 4.5 μm or more and 15 μm or less.

[0109] If the median diameter of the negative electrode active material particles 1 is within this range, it is possible to prevent the reaction with the electrolyte from being accelerated and to prevent the loss of electronic contacts due to the expansion of the active material during charge and discharge. The median diameter of the negative electrode active material particles 1 can be measured using a laser diffraction particle size distribution analyzer.

[0110] <Method of manufacturing negative electrode active material> The method for producing a negative electrode active material of the present invention is a method for producing a negative electrode active material including negative electrode active material particles, General formula SiO x a step of preparing silicon oxide particles represented by (0.5≦x≦1.6); intercalating Li into the silicon oxide particles to produce silicon compound particles containing Li silicate; On the surface of the silicon compound particles, a Li compound different from the Li silicate adjacent to a portion of the surface of the silicon compound particle; and / or a metal oxide and / or metal hydroxide adjacent to at least a portion of the surface of the silicon compound particle; forming an intermediate layer comprising: forming an outermost carbon layer that covers the intermediate layer to obtain negative electrode active material particles; a step of producing a negative electrode active material using the negative electrode active material particles; Includes.

[0111] The above-described manufacturing method can produce the negative electrode active material of the present invention described above. However, the negative electrode active material of the present invention may also be produced by a manufacturing method other than the manufacturing method described here.

[0112] A specific example of the method for producing the negative electrode active material of the present invention will be described below.

[0113] [Step of producing silicon oxide particles] First, silicon oxide particles (silicon oxide particles) containing a silicon compound containing oxygen are prepared. In the following, SiO X The case where silicon oxide represented by (0.5≦x≦1.6) is used will be explained.

[0114] First, a raw material that generates silicon oxide gas is heated in the presence of an inert gas under reduced pressure at a temperature range of 900°C to 1600°C to generate silicon oxide gas. The raw material can be a mixture of metal silicon powder and silicon dioxide powder. Considering the presence of oxygen on the surface of the metal silicon powder and trace amounts of oxygen in the reactor, the molar ratio of the mixture is preferably in the range of 0.9<metal silicon powder / silicon dioxide powder<1.2.

[0115] The generated silicon oxide gas is solidified and deposited on the adsorption plate. Next, the temperature inside the reactor is lowered to 100°C or less, and the silicon oxide deposit is removed and pulverized using a ball mill, jet mill, or the like to produce powder. In this manner, silicon oxide particles can be produced. The Si crystallites in the silicon oxide particles can be controlled by changing the vaporization temperature of the raw material that generates the silicon oxide gas, or by heat treatment after the silicon oxide particles are produced.

[0116] [Step of producing silicon compound particles containing Li silicate] Next, Li is inserted into the silicon oxide particles prepared as described above. This produces silicon compound particles containing Li silicate. That is, Li silicate is produced inside the silicon oxide particles. The insertion of Li is preferably carried out by an electrochemical method or an oxidation-reduction method.

[0117] In the modification by the oxidation-reduction method (Li insertion), for example, lithium can be inserted by first immersing silicon oxide particles in Solution A, which is prepared by dissolving lithium in an ether solvent, to obtain silicon compound particles containing Li silicate. Solution A may further contain a polycyclic aromatic compound or a linear polyphenylene compound.

[0118] After lithium insertion, the silicon compound particles can be immersed in Solution B containing a polycyclic aromatic compound or its derivative to release active lithium from the silicon compound particles. The solvent for Solution B can be, for example, an ether-based solvent, a ketone-based solvent, an ester-based solvent, an alcohol-based solvent, an amine-based solvent, or a mixture thereof. Alternatively, after immersion in Solution A, the resulting silicon compound particles can be heat-treated under an inert gas. The heat treatment can stabilize the Li compound. The particles can then be washed with alcohol, alkaline water containing dissolved lithium carbonate, a weak acid, or pure water.

[0119] Examples of ether solvents that can be used in solution A include diethyl ether, tert-butyl methyl ether, tetrahydrofuran, dioxane, 1,2-dimethoxyethane, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and mixtures thereof. Among these, tetrahydrofuran, dioxane, and 1,2-dimethoxyethane are particularly preferred. These solvents are preferably dehydrated and deoxygenated.

[0120] Furthermore, the polycyclic aromatic compound contained in solution A may be one or more of naphthalene, anthracene, phenanthrene, naphthacene, pentacene, pyrene, picene, triphenylene, coronene, chrysene, and derivatives thereof, and the linear polyphenylene compound may be one or more of biphenyl, terphenyl, and derivatives thereof.

[0121] The polycyclic aromatic compound contained in solution B may be one or more of naphthalene, anthracene, phenanthrene, naphthacene, pentacene, pyrene, picene, triphenylene, coronene, chrysene, and derivatives thereof.

[0122] As the ether solvent for solution B, diethyl ether, tert-butyl methyl ether, tetrahydrofuran, dioxane, 1,2-dimethoxyethane, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and the like can be used.

[0123] As the ketone solvent, acetone, acetophenone, etc. can be used.

[0124] Examples of the ester solvent that can be used include methyl formate, methyl acetate, ethyl acetate, propyl acetate, and isopropyl acetate.

[0125] As the alcohol-based solvent, methanol, ethanol, propanol, isopropyl alcohol, and the like can be used.

[0126] As the amine solvent, methylamine, ethylamine, ethylenediamine, etc. can be used.

[0127] The silicon compound particles obtained in this step may have a surface layer covered with decomposition products of the solution used in the Li intercalation process.

[0128] [Step of forming an intermediate layer on the surface of silicon compound particles] Next, an intermediate layer is formed on the surface of the silicon compound particle. The intermediate layer may contain both a Li compound 5 different from Li silicate adjacent to a portion of the surface of the silicon compound particle 2 and a metal oxide and / or metal hydroxide 6 adjacent to at least a portion of the surface of the silicon compound particle 2, as shown in Figure 1, or may contain only the Li compound 5 as shown in Figure 2, or may contain only the metal oxide and / or metal hydroxide 6 as shown in Figure 3.

[0129] Hereinafter, examples of methods for forming the intermediate layer 4 shown in FIGS. 1 to 3 will be described.

[0130] (In the case of Figure 1) When forming the intermediate layer 4 shown in FIG. 1, first, in the step of preparing the silicon compound particles 2 containing Li silicate, silicon compound particles 2 containing a Li compound on the surface are prepared.

[0131] Next, a portion of the Li compound present on the surface of the silicon compound particle 2 is removed. For example, the silicon compound particle 2 is thoroughly washed with solution B selected from the examples given above to form particles having a surface carbon content (C component in the Li compound other than Li silicate) of 0.5 mass % or less relative to the entire particle. As a result, a Li compound 5 other than Li silicate adjacent to a portion of the surface of the silicon compound particle 2 is obtained, as shown in FIG. 1.

[0132] Next, a part of the surface of the silicon compound particles 2 and the surface of the Li compound 5 are coated with a metal oxide and / or metal hydroxide 6 .

[0133] It is preferable to form a metal oxide and / or metal hydroxide 6 by hydrolysis and dehydration condensation of a metal alkoxide. Note that, in the process of forming a metal oxide layer using a metal alkoxide, if a heat treatment is performed at 100°C or higher, there is a high possibility that a hydroxide layer will remain in part of the bulk.

[0134] For example, it is preferable to form the metal oxide and / or metal hydroxide 6 using a metal alkoxide such as Al-i-propoxide, Mg-methoxide, Ca-i-propoxide, Ca-methoxide, Al-tert-butoxide, Al-sec-butoxide, Al-i-propoxide, Al-n-butoxide, Zr-n-butoxide, Ti-tert-butoxide, Ti-i-propoxide, Ti-n-butoxide, Nb-i-propoxide, or Nb-n-butoxide. If the surface of the silicon compound particle 2 is coated with an intermediate layer 4 containing a metal oxide and / or metal hydroxide 6 formed using these as starting materials, excellent water resistance can be more reliably exhibited.

[0135] More specifically, the metal oxide and / or metal hydroxide 6 can be formed, for example, by the following procedure.

[0136] The silicon compound particles 2 thoroughly washed as described above are placed in a solution in which solution B selected from the examples given above and metal alkoxide are dispersed, and the solution is thoroughly stirred. As an example, the following method is proposed.

[0137] The mixture is stirred in a 200 mL beaker on a hot plate at 100°C, 500 rpm, and for 3 hours. The raw materials used were 50 g of Li-SiO , 0.25 g of Al(Oi-Pr) (0.5% relative to the silicon compound particles), and 100 mL of diglyme.

[0138] The powder obtained after stirring is filtered and dried at a temperature in the range of 100°C to 400°C, thereby obtaining an intermediate layer 4 containing a Li compound 5 and a metal oxide and / or metal hydroxide 6 as shown in FIG.

[0139] (Example in Figure 2) When forming the intermediate layer 4 shown in FIG. 2, first, in the step of preparing the silicon compound particles 2 containing Li silicate, silicon compound particles 2 containing a Li compound on the surface are prepared.

[0140] Next, in the same manner as described above, a portion of the Li compound present on the surface of the silicon compound particle 2 is removed, thereby obtaining an intermediate layer 4 containing only a Li compound 5 different from the Li silicate adjacent to a portion of the surface of the silicon compound particle 2, as shown in FIG.

[0141] (Example in Figure 3) The intermediate layer 4 shown in FIG. 3 can be formed, for example, by the following procedure.

[0142] In the process of producing silicon compound particles 2 containing Li silicate, when silicon compound particles 2 containing a Li compound other than Li silicate on the surface are produced, all of the Li compounds other than Li silicate present on the surface of the silicon compound particles 2 are removed.

[0143] Next, a metal oxide and / or metal hydroxide 6 is formed on the surface of the silicon compound particle 2 by the same procedure as described above. As a result, an intermediate layer 4 containing only the metal oxide and / or metal hydroxide 6 adjacent to the surface of the silicon compound particle 2 is obtained, as shown in FIG.

[0144] [Step of forming an outermost carbon layer covering the intermediate layer to obtain negative electrode active material particles] Next, a carbon layer as the outermost layer is formed on the surface of the intermediate layer.

[0145] The method for producing the carbon layer is not particularly limited, but may be, for example, a pyrolytic CVD method. An example of a method for producing a carbon layer by the pyrolytic CVD method will be described below.

[0146] First, silicon compound particles whose surfaces are coated with an intermediate layer are placed in a furnace. Next, hydrocarbon gas is introduced into the furnace, and the temperature inside the furnace is increased. The decomposition temperature is not particularly limited, but is preferably 650°C or less, and more preferably 600°C or less. By setting the decomposition temperature to 650°C or less, unintended disproportionation of the silicon compound particles can be suppressed. After the furnace temperature is increased to a predetermined temperature, a carbon layer is formed on the surface of the intermediate layer. Furthermore, the hydrocarbon gas used as the raw material for the carbon material is not particularly limited, but is preferably C n H m In the composition, it is desirable that n≦3. If n≦3, the production cost can be reduced and the physical properties of the decomposition products can be improved.

[0147] The Li silicate produced by Li insertion (modification) using the oxidation-reduction method is Li4SiO4, but it can be converted to other Li silicates such as Li2SiO3 by CVD processing. The degree of crystallization of the Li silicate and Si changes depending on the temperature at this time. In addition, the reaction temperature during Li insertion also affects the degree of crystallization of the Li silicate and Si.

[0148] By this step, negative electrode active material particles 1 having the structure shown in, for example, FIGS. 1 to 3 can be obtained.

[0149] [Step of producing a negative electrode active material using negative electrode active material particles] The negative electrode active material particles prepared as described above are used to produce a negative electrode active material, which is an example of the negative electrode active material of the present invention.

[0150] <Negative electrode> The negative electrode active material of the present invention can be used, for example, in the negative electrode of a non-aqueous electrolyte secondary battery, particularly a lithium ion secondary battery.

[0151] Next, the configuration of a negative electrode containing the negative electrode active material of the present invention will be described using an example. FIG. 4 shows a schematic cross-sectional view of an example of a negative electrode containing the negative electrode active material of the present invention. As shown in FIG. 4, a negative electrode 10 has a configuration in which a negative electrode active material layer 12 is provided on a negative electrode current collector 11. This negative electrode active material layer 12 may be provided on both sides of the negative electrode current collector 11 as shown in FIG. 4, or may be provided on only one side. Furthermore, the negative electrode of the present invention does not necessarily require the negative electrode current collector 11.

[0152] Each component will be described below.

[0153] [Negative electrode current collector] The negative electrode current collector 11 is made of a highly conductive material that has excellent mechanical strength. Examples of conductive materials that can be used for the negative electrode current collector 11 include copper (Cu) and nickel (Ni). It is preferable that this conductive material does not form an intermetallic compound with lithium (Li).

[0154] The negative electrode current collector 11 preferably contains carbon (C) and sulfur (S) in addition to the main elements. This is because the physical strength of the negative electrode current collector 11 is improved. In particular, when the current collector has an active material layer that expands during charging, if the current collector contains the above elements, deformation of the electrode including the current collector is suppressed. The contents of the above contained elements are not particularly limited, but are preferably 100 mass ppm or less each. This is because a higher deformation suppression effect can be obtained.

[0155] The surface of the negative electrode current collector 11 may or may not be roughened. A roughened negative electrode current collector is, for example, a metal foil that has been electrolytically treated, embossed, or chemically etched. A non-roughened negative electrode current collector is, for example, a rolled metal foil.

[0156] [Negative electrode active material layer] The negative electrode active material layer 12 contains the negative electrode active material of the present invention that can absorb and release lithium ions, and may further contain other materials such as a negative electrode binder and a conductive additive from the viewpoint of battery design. The negative electrode active material contains the negative electrode active material of the present invention.

[0157] The negative electrode active material layer 12 may also contain a mixed negative electrode active material containing the negative electrode active material of the present invention (silicon-based negative electrode active material) and a carbon-based active material. This reduces the electrical resistance of the negative electrode active material layer and also alleviates the expansion stress that occurs during charging. Examples of carbon-based active materials that can be used include pyrolytic carbons, cokes, glassy carbon fibers, fired organic polymer compounds, and carbon blacks.

[0158] The negative electrode binder contained in the negative electrode active material layer 12 may be, for example, one or more of polymer materials, synthetic rubber, etc. Examples of polymer materials include polyvinylidene fluoride, polyimide, polyamideimide, aramid, polyacrylic acid, lithium polyacrylate, sodium polyacrylate, carboxymethyl cellulose, etc. Examples of synthetic rubbers include styrene butadiene rubber, fluorine-based rubber, ethylene propylene diene, etc.

[0159] As the negative electrode conductive assistant, for example, one or more of carbon materials such as carbon black, acetylene black, graphite, Ketjen black, carbon nanotubes, and carbon nanofibers can be used.

[0160] The negative electrode active material layer 12 is formed, for example, by a coating method, in which a silicon-based negative electrode active material is mixed with the binder and, if necessary, a conductive additive and a carbon-based active material, and then the mixture is dispersed in an organic solvent, water, or the like and coated.

[0161] Specifically, for example, the process is as follows. First, the negative electrode active material of the present invention prepared as described above is mixed with other materials such as a negative electrode binder and a conductive additive to form a negative electrode mixture, and then an organic solvent or water is added to form a slurry. Next, the slurry is applied to the surface of a negative electrode current collector and dried to form a negative electrode active material layer. At this time, hot pressing or the like may be performed as necessary. In this manner, a negative electrode containing the negative electrode active material of the present invention can be prepared.

[0162] The negative electrode active material of the present invention is particularly suitable for forming a slurry using water, but can also be applied to forming a slurry using an organic solvent.

[0163] <Lithium-ion secondary battery> A negative electrode containing the negative electrode active material of the present invention can be used in the negative electrode of a non-aqueous electrolyte secondary battery, for example, a lithium ion secondary battery.

[0164] Next, as a specific example of a nonaqueous electrolyte secondary battery in which the negative electrode active material of the present invention can be used, an example of a laminate film type lithium ion secondary battery will be described.

[0165] [Configuration of laminated film type secondary battery] The laminate film type lithium ion secondary battery 30 shown in FIG. 5 mainly comprises a wound electrode body 31 housed inside a sheet-like exterior member 35. This wound electrode body 31 has a separator between the positive and negative electrodes and is wound. There are also cases where the electrode body is not wound, but instead houses a laminate having a separator between the positive and negative electrodes. In either type of electrode body, a positive electrode lead 32 is attached to the positive electrode, and a negative electrode lead 33 is attached to the negative electrode. The outermost periphery of the electrode body 31 is protected by protective tape.

[0166] The positive electrode lead 32 and the negative electrode lead 33 are, for example, led out in one direction from the inside to the outside of the exterior member 35. The positive electrode lead 32 is formed of a conductive material such as aluminum, and the negative electrode lead 33 is formed of a conductive material such as nickel or copper.

[0167] The exterior member 35 is, for example, a laminate film in which a fusion layer, a metal layer, and a surface protection layer are laminated in this order, and the outer peripheral edges of the fusion layers of the two films of this laminate film are fused together or attached with an adhesive or the like so that the fusion layer faces the electrode body 31. The fusion part is, for example, a film such as polyethylene or polypropylene, and the metal part is, for example, aluminum foil. The protection layer is, for example, nylon or the like.

[0168] To prevent outside air from entering, adhesive films 34 are inserted between the exterior member 35 and each of the positive electrode lead 32 and the negative electrode lead 33. The material for these films is, for example, polyethylene, polypropylene, or polyolefin resin.

[0169] Each component will be described below.

[0170] [Positive electrode] The positive electrode has a positive electrode active material layer on one or both sides of a positive electrode current collector, similar to the negative electrode 10 in FIG.

[0171] The positive electrode current collector is made of a conductive material such as aluminum.

[0172] The positive electrode active material layer contains one or more positive electrode materials (positive electrode active materials) capable of absorbing and releasing lithium ions, and may contain other materials such as a positive electrode binder, a positive electrode conductive additive, and a dispersant depending on the design.

[0173] The positive electrode material is preferably a lithium-containing compound. Examples of the lithium-containing compound include a composite oxide made of lithium and a transition metal element, or a phosphate compound containing lithium and a transition metal element. Among these positive electrode materials, compounds containing at least one of nickel, iron, manganese, and cobalt are preferred. Their chemical formulas include, for example, Li x M1O2 or Li yIt is represented by M2PO4. In the formula, M1 and M2 represent at least one transition metal element. The values of x and y vary depending on the charge and discharge state of the battery, but are generally represented by 0.05 ≦ x ≦ 1.10 and 0.05 ≦ y ≦ 1.10.

[0174] Examples of the composite oxide having lithium and a transition metal element include, for example, lithium cobalt composite oxide (Li x [[ID=,6]]CoO2), lithium nickel composite oxide (Li x NiO2), lithium nickel cobalt composite oxide, and the like. Examples of the lithium nickel cobalt composite oxide include, for example, lithium nickel cobalt aluminum composite oxide (NCA) and lithium nickel cobalt manganese composite oxide (NCM). <00,00712>

[0175] Examples of the phosphate compound having lithium and a transition metal element include, for example, lithium iron phosphate compound (LiFePO4) or lithium iron manganese phosphate compound (LiFe 1-u Mn u PO4 (0 < u < 1)), and the like. By using these positive electrode materials, a high battery capacity can be obtained, and excellent cycle characteristics can also be obtained.

[0176] As the positive electrode binder, for example, any one or more of a polymer material, a synthetic rubber, and the like can be used. Examples of the polymer material include, for example, polyvinylidene fluoride, polyimide, polyamideimide, aramid, polyacrylic acid, lithium polyacrylate, sodium polyacrylate, carboxymethyl cellulose, and the like. Examples of the synthetic rubber include, for example, styrene-butadiene rubber, fluorine rubber, ethylene propylene diene, and the like.

[0177] As the positive electrode conductive assistant, for example, any one or more of carbon materials such as carbon black, acetylene black, graphite, ketjen black, carbon nanotube, carbon nanofiber, and the like can be used.

[0178] [[ID=]27] [[ID=]28][Negative electrode] [[ID=]29] The negative electrode of the secondary battery is preferably a negative electrode containing the negative electrode active material of the present invention. The negative electrode constituting this secondary battery preferably has a negative electrode charge capacity greater than the electric capacity (charge capacity as a battery) obtained from the positive electrode active material. This can suppress the deposition of lithium metal on the negative electrode.

[0179] In this example, the positive electrode active material layer is provided on a portion of both sides of the positive electrode current collector, and similarly, the negative electrode active material layer of the present invention is provided on a portion of both sides of the negative electrode current collector. In this case, for example, it is preferable that the negative electrode active material layer provided on the negative electrode current collector has a region where the opposing positive electrode active material layer is not present. This is to achieve a stable battery design.

[0180] The region where the negative electrode active material layer and the positive electrode active material layer do not face each other is hardly affected by charging and discharging, and therefore the state of the negative electrode active material layer is maintained as it was immediately after formation, allowing the composition of the negative electrode active material to be accurately determined with good reproducibility, regardless of whether charging and discharging are performed.

[0181] [Separator] The separator separates the lithium metal or the positive electrode from the negative electrode, preventing current short-circuiting due to contact between the two electrodes while allowing lithium ions to pass through. This separator is formed of a porous film made of, for example, a synthetic resin or ceramic, and may have a laminate structure in which two or more types of porous film are laminated. Examples of synthetic resins include polytetrafluoroethylene, polypropylene, and polyethylene.

[0182] [Electrolyte] At least a portion of each of the positive electrode active material layer and the negative electrode active material layer, or the separator, is impregnated with a liquid nonaqueous electrolyte (electrolyte solution). This electrolyte solution contains an electrolyte salt dissolved in a solvent and may contain other materials such as additives.

[0183] The solvent can be, for example, a non-aqueous solvent. Examples of non-aqueous solvents include ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, 1,2-dimethoxyethane, and tetrahydrofuran. Among these, it is desirable to use at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. This is because better properties can be obtained. In this case, more advantageous properties can be obtained by combining a high-viscosity solvent such as ethylene carbonate or propylene carbonate with a low-viscosity solvent such as dimethyl carbonate, ethyl methyl carbonate, or diethyl carbonate. This is because the dissociation property and ion mobility of the electrolyte salt are improved.

[0184] When an alloy-based negative electrode is used, it is particularly desirable to use a solvent containing at least one of halogenated chain carbonates or halogenated cyclic carbonates. This allows a stable coating to be formed on the surface of the negative electrode active material during charge and discharge, particularly during charging. Here, the halogenated chain carbonate is a chain carbonate having a halogen as a constituent element (i.e., at least one hydrogen atom is substituted with a halogen). Furthermore, the halogenated cyclic carbonate is a cyclic carbonate having a halogen as a constituent element (i.e., at least one hydrogen atom is substituted with a halogen).

[0185] Although the type of halogen is not particularly limited, fluorine is preferred because it forms a better coating than other halogens. Furthermore, the more halogens there are, the more desirable they are because the resulting coating is more stable and the decomposition reaction of the electrolyte is reduced.

[0186] Examples of halogenated chain carbonates include fluoromethyl methyl carbonate, difluoromethyl methyl carbonate, etc. Examples of halogenated cyclic carbonates include 4-fluoro-1,3-dioxolan-2-one, 4,5-difluoro-1,3-dioxolan-2-one, etc.

[0187] It is preferable that the solvent additive contains an unsaturated carbon-bond cyclic carbonate. This is because a stable coating is formed on the negative electrode surface during charge and discharge, and the decomposition reaction of the electrolyte can be suppressed. Examples of the unsaturated carbon-bond cyclic carbonate include vinylene carbonate and vinylethylene carbonate.

[0188] It is also preferable that the solvent additive contains sultone (cyclic sulfonic acid ester), as this improves the chemical stability of the battery. Examples of sultones include propane sultone and propene sultone.

[0189] Furthermore, it is preferable that the solvent contains an acid anhydride, because this improves the chemical stability of the electrolyte solution. Examples of acid anhydrides include propanedisulfonic acid anhydride.

[0190] The electrolyte salt may include, for example, one or more light metal salts such as lithium salts, for example, lithium hexafluorophosphate (LiPF6) and lithium tetrafluoroborate (LiBF4).

[0191] The content of the electrolyte salt is preferably 0.5 mol / kg or more and 2.5 mol / kg or less relative to the solvent, because this allows high ionic conductivity to be obtained.

[0192] [Manufacturing method of laminated film type secondary battery] The laminate film type secondary battery described above can be manufactured, for example, by the following procedure.

[0193] First, a positive electrode is fabricated using the above-described positive electrode material. First, a positive electrode active material is mixed with, if necessary, a positive electrode binder and a positive electrode conductive additive to form a positive electrode mixture, which is then dispersed in an organic solvent to form a positive electrode mixture slurry. Next, the mixture slurry is applied to a positive electrode current collector using a coating device such as a knife roll or a die coater having a die head, and then dried with hot air to obtain a positive electrode active material layer. Finally, the positive electrode active material layer is compression-molded using a roll press or the like. At this time, heating may be performed, and compression may be repeated multiple times.

[0194] Next, a negative electrode active material layer is formed on the negative electrode current collector according to the same procedure as in the production of the negative electrode 10 described above, to produce the negative electrode.

[0195] When preparing the positive and negative electrodes, active material layers are formed on both sides of the positive and negative electrode current collectors, respectively. At this time, the lengths of the active material coatings on both sides of each electrode may be different (see Figure 4).

[0196] Next, the electrolyte solution is prepared. Next, the positive electrode lead 32 is attached to the positive electrode current collector by ultrasonic welding or the like, and the negative electrode lead 33 is attached to the negative electrode current collector. Next, the positive electrode and the negative electrode are laminated with a separator interposed therebetween and then wound to produce a wound electrode body 31, and a protective tape is adhered to the outermost periphery. Next, the wound electrode body 31 is molded into a flat shape. Next, the wound electrode body 31 is sandwiched between folded film-like exterior members 35, and the insulating portions of the exterior members are bonded together by a heat fusion method. The wound electrode body 31 is encapsulated with only one side open. Next, an adhesive film 34 is inserted between the positive electrode lead 32 and the negative electrode lead 33 and the exterior member 35. Next, a predetermined amount of the prepared electrolyte solution is poured through the open portions, and vacuum impregnation is performed. After impregnation, the open portions are sealed by a vacuum heat fusion method. In this manner, a laminate film-type secondary battery 30 can be manufactured.

[0197] In the nonaqueous electrolyte secondary battery such as the laminate film type secondary battery 30 fabricated above, the negative electrode utilization rate during charge and discharge is preferably 93% or more and 99% or less. If the negative electrode utilization rate is in the range of 93% or more, the initial charge efficiency does not decrease and the battery capacity can be greatly improved. Furthermore, if the negative electrode utilization rate is in the range of 99% or less, Li precipitation does not occur and safety can be ensured. [Example]

[0198] EXAMPLES The present invention will be specifically explained below using examples and comparative examples, but the present invention is not limited to these.

[0199] (Examples 1 to 3) First, the negative electrode active material was prepared as follows. A raw material obtained by mixing metal silicon and silicon dioxide was introduced into a reactor. In this reactor, the raw material was vaporized in a vacuum atmosphere of 10 Pa and deposited on an adsorption plate. After sufficient cooling, the deposit was taken out and pulverized in a ball mill. The SiO of silicon oxide particles obtained in this way was x The value of x was 1.0.

[0200] The particle size of the silicon oxide particles was then adjusted by classification. The moisture content was then reduced to 50 ppm, and lithium was dissolved in an ether-based solvent, and the silicon oxide particles were modified by intercalating lithium using an oxidation-reduction method. This resulted in silicon compound particles containing Li silicate.

[0201] Analysis of the obtained silicon compound particles by X-ray photoelectron spectroscopy (XPS) revealed that the surfaces of the silicon compound particles were coated with a Li compound different from Li silicate.

[0202] Next, the obtained silicon compound particles were washed with diethyl ether to form particles with a surface carbon component (meaning a C component constituting a Li compound other than Li silicate) of 0.2 mass %. This removed some of the Li compound present on the surface of the silicon compound particles, leaving some behind.

[0203] Next, the thoroughly washed particles were placed in a solution of diethyl ether and Al-sec-butoxide, and thoroughly stirred at 100°C and 500 rpm for 3 hours. The powder was filtered and dried at 100°C to 400°C to form an aluminum oxide layer. This resulted in an intermediate layer that covered the surface of the silicon compound particles and contained aluminum oxide and a Li compound different from Li silicate.

[0204] Next, thermal decomposition CVD was performed at temperatures ranging from 450 to 650°C, which further coated the intermediate layer covering the surface of the silicon compound particles with a carbon layer and changed the Li silicate species contained in the silicon compound particles.

[0205] In this manner, the negative electrode active materials of Examples 1 to 3 each containing negative electrode active material particles were obtained.

[0206] When each negative electrode active material was observed by XPS (using XPS / PHI Quantera II), it was found that each negative electrode active material of Examples 1 to 3 contained negative electrode active material particles 1 having the structure described above with reference to Fig. 1. The XPS observation will be described in detail later.

[0207] Furthermore, the Li silicate contained in the negative electrode active material particles of each negative electrode active material was analyzed by NMR. The analysis conditions were as described above. The analysis results are shown in Table 1 below.

[0208] Table 1 below shows the median diameter of the negative electrode active material particles contained in each negative electrode active material, and the ratio (peak intensity ratio A / B) of the peak intensity A attributable to the Si(111) crystal plane to the peak intensity B attributable to the Li2SiO3(111) crystal plane. The intensity ratio A / B was confirmed by XRD. XRD also confirmed that the Si contained in each negative electrode active material was amorphous.

[0209] Next, the negative electrode active material (active material containing silicon compound particles coated with an intermediate layer and a carbon layer in sequence) prepared as above, graphite, conductive additive 1 (carbon nanotubes, CNT), conductive additive 2 (carbon particles with a median diameter of approximately 50 nm), sodium polyacrylate, and carboxymethyl cellulose (hereinafter referred to as CMC) were mixed in a dry mass ratio of 9.3:83.7:1:1:4:1, and then diluted with pure water to form a negative electrode mixture slurry. The materials were mixed using a mass production machine, and the slurry was obtained by applying a high shear force.

[0210] At this time, the stability of the mass-produced slurry was checked by checking the pot life, and whether it was stable after 48 hours was confirmed. This can be judged by whether hydrogen gas is released from the slurry. The results are shown in Table 3 below.

[0211] The negative electrode current collector was a 15 μm-thick electrolytic copper foil. This electrolytic copper foil contained carbon and sulfur at concentrations of 70 mass ppm each. Finally, the negative electrode mixture slurry was applied to the negative electrode current collector and dried at 100°C in a vacuum atmosphere for 1 hour. After drying, the deposition amount of the negative electrode active material layer per unit area on one side of the negative electrode (also referred to as area density) was 7.0 mg / cm. 2 It was.

[0212] [Assembling a coin battery for testing] Next, the solvents ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed, and then an electrolyte salt (lithium hexafluorophosphate: LiPF6) was dissolved to prepare an electrolyte solution. In this case, the solvent composition was EC:DMC = 30:70 by volume, and the content of the electrolyte salt was 1 mol / kg relative to the solvent. As additives, vinylene carbonate (VC) and fluoroethylene carbonate (FEC) were added in amounts of 1.0 mass% and 2.0 mass%, respectively.

[0213] Next, a coin battery was assembled as follows: First, a 1 mm thick Li foil was punched out to a diameter of 16 mm and attached to an aluminum clad.

[0214] Next, the negative electrode obtained above was punched out to a diameter of 15 mm, and this was placed opposite a Li foil attached to an aluminum clad via a separator. After injecting an electrolyte, a 2032 coin battery was fabricated. [Measurement of initial efficiency] The initial efficiency was measured under the following conditions. First, the coin battery prepared for the initial efficiency test was charged (initial charge) in CCCV mode at a charge rate equivalent to 0.03C. The CV was 0V and the cut-off current was 0.04mA. Next, CC discharge (initial discharge) was performed at a discharge rate of 0.03C and a discharge cut-off voltage of 1.2V.

[0215] When investigating the initial charge-discharge characteristics, the initial efficiency (hereinafter sometimes referred to as initial efficiency) was calculated. The initial efficiency was calculated using the formula: initial efficiency (%) = (initial discharge capacity / initial charge capacity) × 100. The results are shown in Table 3 below as initial efficiencies.

[0216] [Production and evaluation of lithium-ion secondary batteries] Based on the initial data obtained, the positive electrode was designed so that the negative electrode utilization rate would be 95%. The utilization rate was calculated using the following formula from the positive and negative electrode capacities obtained with the Li counter electrode. Utilization rate = (positive electrode capacity - negative electrode loss) / (negative electrode capacity - negative electrode loss) x 100 Based on this design, the lithium ion secondary batteries were manufactured in Examples 1 to 3. Battery evaluation was carried out on each of the lithium ion secondary batteries in the Examples and Comparative Examples.

[0217] The cycle characteristics were investigated as follows. First, to stabilize the battery, two charge / discharge cycles were performed at 0.2C in an atmosphere of 25°C, and the discharge capacity at the second cycle was measured. The battery cycle characteristics were calculated from the discharge capacity at the third cycle, and the battery test was stopped after 100 cycles. Charging and discharging were performed at 0.7C and 0.5C, respectively. The charging voltage was 4.3V, the discharge cut-off voltage was 2.5V, and the charge cut-off rate was 0.07C. The results are shown in Table 3 below.

[0218] (Comparative Examples 1 to 3) In Comparative Examples 1 to 3, after Li doping (insertion), a strong shear force was applied and the particles were washed three times in diethyl ether (filtered and washed three times) to remove all Li compounds other than Li silicate present on the surface of the silicon compound particles, and the negative electrode active materials of Comparative Examples 1 to 3 were obtained in the same manner as in Examples 1 to 3, except that no aluminum oxide layer was formed.

[0219] The negative electrode active materials of Comparative Examples 1 to 3 were tested in the same manner as in Example 1. As a result, as shown in Table 3, it was confirmed that the stability during mass production of slurry was significantly reduced. The mass-produced slurry was required to have a durability of at least 2 days (48 hours), and this requirement could not be met.

[0220] Comparative Example 4 In Comparative Example 4, SiO particles whose surfaces had been coated with a carbon layer by CVD at 600°C were doped with Li to obtain carbon-coated silicon compound particles. The carbon-coated silicon compound particles were then added to a dispersion of Al isopropoxide in isopropyl alcohol (IPA), stirred, and dried to form a metal oxide (aluminum oxide) layer on the carbon layer. This produced the negative electrode active material of Comparative Example 4.

[0221] A schematic diagram of the negative electrode active material particles contained in the negative electrode active material of Comparative Example 4 is shown in FIG.

[0222] The negative electrode active material particles 8 contained in the negative electrode active material of Comparative Example 4 include silicon compound particles 2 containing a Si phase 3. The silicon compound particles 2 contain Li silicate due to doping (intercalation) of lithium. The surface of the silicon compound particles 2 is coated with a carbon layer 7. The surface of the carbon layer 7 is coated with an aluminum oxide layer 6 as the outermost layer.

[0223] Between the silicon compound particles 2 and the carbon layer 7, neither a Li compound other than Li silicate nor a metal hydroxide and / or metal hydroxide is present.

[0224] The negative electrode active material of Comparative Example 4 was tested in the same manner as in Example 1. As a result, as shown in Table 3, stability during 48 hours of mass production slurrying could not be achieved. However, when the negative electrode active material of Comparative Example 4 was slurried using a small-scale machine, stability during 48 hours of slurrying could be achieved.

[0225] (Examples 1 to 3) As is clear from the results shown in Table 3, it was confirmed that Examples 1 to 3 achieved durability of 48 hours or more when mass-produced into slurries.

[0226] Furthermore, as is clear from the results shown in Table 3, the negative electrode active materials of Examples 1 to 3 were able to exhibit higher capacity retention rates than the negative electrode active materials of Comparative Examples 1 to 4, and it was found that sufficient battery cycle characteristics were achieved.

[0227] Examples 4 to 15 In Examples 4 to 15, each negative electrode active material was prepared in the same manner as in Example 1, except that the starting material (metal alkoxide species) for forming the metal oxide was changed as shown in Table 1 below.

[0228] The negative electrode active materials of Examples 4 to 15 were tested in the same manner as in Example 1. As a result, as shown in Table 3, it was confirmed that the negative electrode active materials of Examples 4 to 15, like Examples 1 to 3, were able to achieve durability of 48 hours or more when mass-produced into slurries.

[0229] Furthermore, as is clear from the results shown in Table 3, the negative electrode active materials of Examples 4 to 15 were able to exhibit higher capacity retention rates than the negative electrode active materials of Comparative Examples 1 to 4, and it was found that sufficient battery cycle characteristics were achieved.

[0230] (Examples 16 to 18) In Examples 16 to 18, each negative electrode active material was prepared in the same manner as in Example 1, except that no aluminum oxide layer was formed.

[0231] The negative electrode active materials of Examples 16 to 18 were tested in the same manner as in Example 1. As a result, as shown in Table 3, it was confirmed that the negative electrode active materials of Examples 16 to 18, like Examples 1 to 3, achieved durability of 48 hours or more when mass-produced into slurries.

[0232] Furthermore, as is clear from the results shown in Table 3, the negative electrode active materials of Examples 16 to 18 were able to exhibit higher capacity retention rates than the negative electrode active materials of Comparative Examples 1 to 4, and it was found that sufficient battery cycle characteristics were achieved.

[0233] (Examples 19 to 24) In Examples 19 to 24, each negative electrode active material was prepared in the same manner as in Example 1, except that the thickness of the aluminum oxide layer was changed by changing the amount of Al-sec-butoxide added when forming the aluminum oxide layer.

[0234] The negative electrode active materials of Examples 19 to 24 were tested in the same manner as in Example 1. As a result, as shown in Table 3, it was confirmed that the negative electrode active materials of Examples 19 to 24, like Examples 1 to 3, were able to achieve durability of 48 hours or more when mass-produced into slurries.

[0235] As is clear from the results shown in Table 3, the negative electrode active materials of Examples 19 to 24 were able to exhibit higher capacity retention rates than the negative electrode active materials of Comparative Examples 1 to 3, and were found to have achieved sufficient battery cycle characteristics. Furthermore, the negative electrode active materials of Examples 19 to 23 were able to exhibit higher capacity retention rates than the negative electrode active material of Comparative Example 4, and were found to have achieved even more sufficient battery cycle characteristics.

[0236] These results confirmed that sufficient performance was achieved even with an aluminum oxide layer of 0.1 nm. However, as the aluminum oxide layer became thicker, the cycle performance tended to decrease due to increased resistance, and it can be said that there is an optimal range.

[0237] Examples 25 to 29 In Examples 25 to 29, after forming the outermost carbon layer, the negative electrode active material particles were subjected to additional heat treatment to change the crystallinity of Si and Li silicate. Each negative electrode active material was produced in the same manner as in Example 1, except that the temperature was adjusted to a range of 600 to 700°C.

[0238] Before charging and discharging, the negative electrode active materials of Examples 25 to 29 were analyzed by X-ray diffraction (XRD) using Cu-Kα radiation.

[0239] From the XRD chart obtained by XRD analysis, the ratio A / B of the intensity A of the peak due to the Si(111) crystal plane (appearing near 2θ = 28.4°) to the intensity B of the peak due to the Li2SiO3(111) crystal plane (appearing in the range of 2θ = 17° to 21°) was calculated. In addition, the crystallite size corresponding to the Si(111) crystal plane was calculated from the peak due to the Si(111) crystal plane using Scherrer's formula.

[0240] The results based on the XRD analysis are shown in the following Table 2. Furthermore, each of the negative electrode active materials of Examples other than Examples 25 to 29 and Comparative Examples was also analyzed by XRD, and the results are shown together in the following Tables 1 and 2.

[0241] The negative electrode active materials of Examples 25 to 29 were tested in the same manner as in Example 1. As a result, as shown in Table 3, it was confirmed that the negative electrode active materials of Examples 25 to 29, like Example 1, were able to achieve durability of 48 hours or more when mass-produced into a slurry.

[0242] As is clear from the results shown in Table 3, the negative electrode active materials of Examples 25 to 29 were able to exhibit higher capacity retention rates and achieve sufficient battery cycle characteristics than the negative electrode active materials of Comparative Examples 1 to 3. Furthermore, the negative electrode active materials of Examples 26 to 29 were able to exhibit higher capacity retention rates and achieve further sufficient battery cycle characteristics than the negative electrode active material of Comparative Example 4.

[0243] Furthermore, the results of Examples 25 to 29 showed that Examples 26 to 29, in which the crystallite size corresponding to the Si(111) crystal plane was 5.0 nm or less, exhibited better cycle characteristics than Example 25, in which the crystallite size corresponding to the Si(111) crystal plane was 9.2 nm or less.

[0244] (Comparative Example 5) In Comparative Example 5, a negative electrode active material was produced in the same manner as in Example 1, except that the outermost carbon layer was not formed.

[0245] The negative electrode active material of Comparative Example 5 was tested in the same manner as in Example 1. As a result, as shown in Table 3, it was confirmed that the negative electrode active material of Comparative Example 5, like Examples 1 to 3, achieved durability of 48 hours or more when made into a mass-produced slurry.

[0246] However, as is clear from the results shown in Table 3, the negative electrode active material of Comparative Example 5 exhibited a capacity retention rate that was even inferior to the negative electrode active materials of Comparative Examples 1 to 3. This result shows that unless the outermost carbon layer is formed, the conductivity decreases and sufficient battery characteristics cannot be obtained.

[0247] Examples 30 to 36 In Examples 30 to 36, each negative electrode active material was produced in the same manner as in Example 1, except that the particle size of the silicon oxide particles was adjusted by classification to change the median diameter of the negative electrode active material particles as shown in Table 2 below. The particle sizes of the negative electrode active material particles contained in the negative electrode active materials of the other Examples and Comparative Examples are also shown in Tables 1 and 2.

[0248] The negative electrode active materials of Examples 30 to 36 were tested in the same manner as in Example 1. As a result, as shown in Table 3, it was confirmed that the negative electrode active materials of Examples 30 to 36, like Example 1, were able to achieve durability of 48 hours or more when mass-produced into a slurry.

[0249] Furthermore, as is clear from the results shown in Table 3, it was found that the negative electrode active materials of Examples 30 to 36 were able to exhibit higher capacity retention rates and achieve sufficient battery cycle characteristics than the negative electrode active materials of Comparative Examples 1 to 3. Furthermore, it was found that the negative electrode active materials of Examples 31 to 36 were able to exhibit higher capacity retention rates and achieve further sufficient battery cycle characteristics than the negative electrode active material of Comparative Example 4.

[0250] Furthermore, the results of Examples 30 to 36 show that Examples 31 to 35, in which the median diameter of the negative electrode active material particles was 4.5 nm or more and 15 nm or less, exhibited better cycle characteristics than Examples 30 and 36, in which the median diameter of the negative electrode active material particles was 4 nm or 17 nm.

[0251] (Comparative Example 6) In Comparative Example 6, silicon oxide particles were obtained in the same manner as in Example 1, and the particle size of the obtained silicon oxide particles was adjusted by classification. The silicon oxide particles thus obtained were used as the negative electrode active material of Comparative Example 6.

[0252] The negative electrode active material of Comparative Example 6 was tested in the same manner as in Example 1. As a result, as shown in Table 3, the initial efficiency was 65%. In contrast, the negative electrode active materials of Examples 1 to 36 of the present invention were able to achieve initial efficiencies of 85% or more.

[0253] The conditions for each example and each comparative example are shown in Tables 1 and 2. The evaluation results for each example and each comparative example are shown in Table 3.

[0254] [Table 1]

[0255] [Table 2]

[0256] [Table 3]

[0257] Furthermore, although not shown in Table 3, the negative electrode active materials of Examples 1 to 36 were able to achieve higher capacities than conventional carbon-based negative electrode active materials.

[0258] [Observation of negative electrode active material particles using XPS] The structure of each negative electrode active material particle was observed by measuring at various depths while dry etching the surface using an XPS / PHI Quantera II (manufactured by ULVAC-PHI, Inc.).

[0259] The etching conditions were 30 minutes, an acceleration voltage of 2 kV, and an etching area of ​​2 mm x 2 mm.

[0260] FIG. 7 shows a portion of the XPS spectrum of the negative electrode active material particles contained in the negative electrode active material of Example 16 after etching was performed six times.

[0261] The spectrum shown in FIG. 7 shows multiple C1s peaks, with the peak near 284 eV corresponding to the CC structure and the peak near 290 eV (indicated by an arrow) corresponding to the O-C=O structure. Furthermore, the XPS observation results confirmed a peak corresponding to Li in a binding energy region different from that shown in FIG. 7, thereby confirming the presence of Li. That is, the intermediate layer of the negative electrode active material particles of the negative electrode active material of Example 16 contained a Li compound having an O-C=O structure. The presence of a similar Li compound was also confirmed by XPS observation of the negative electrode active material particles contained in each of the negative electrode active materials of Examples 1 to 15 and 17 to 36. Tables 1 and 2 above indicate the presence or absence of a "Li, C, O compound."

[0262] FIG. 8 shows a portion of the XPS spectrum of the outermost layer (solid line) and the XPS spectrum (dashed line) after etching was performed three times for the negative electrode active material particles contained in the negative electrode active material of Example 1.

[0263] The dashed spectrum shown in Figure 8 has a peak (indicated by an arrow) at around 74.4 eV that is not present in the solid spectrum. This peak is due to AlO x This corresponds to the peak of . Furthermore, the XPS observation of the surface layer confirmed the presence of C. These results show that the negative electrode active material contained in the negative electrode active material of Example 1 includes a carbon layer as the outermost layer and an aluminum oxide layer thereunder.

[0264] It was confirmed that the negative electrode active material particles contained in each of the negative electrode active materials of Examples 2 to 15 and 19 to 36 also contained an outermost carbon layer and an underlying metal oxide layer.

[0265] Although not shown in Tables 1 and 2, the presence of metal hydroxides in addition to metal oxides was confirmed in the intermediate layers of the negative electrode active material particles contained in the negative electrode active materials of Examples 1 to 33. This is thought to be because, although the alkoxides were converted to metal oxides by applying heat, some of them remained inside as hydroxides. Therefore, in the metal oxide columns of Tables 1 and 2, the amount of oxygen atoms relative to the metal element is represented by x.

[0266] The present specification includes the following aspects. [1] A negative electrode active material comprising negative electrode active material particles, the negative electrode active material particles comprising silicon compound particles containing Li silicate and an intermediate layer covering the surfaces of the silicon compound particles, an intermediate layer containing a Li compound other than Li silicate adjacent to a portion of the surface of the silicon compound particle, and / or a metal oxide and / or metal hydroxide adjacent to at least a portion of the surface of the silicon compound particle; and a carbon layer as an outermost layer covering the intermediate layer. A negative electrode active material characterized by having the following: [2] The negative electrode active material according to [1], wherein at least a portion of the silicon compound particles contains at least one Li silicate selected from the group consisting of Li2SiO3, Li4SiO4, and Li6Si2O7. [3] The negative electrode active material according to [1] or [2], wherein the intermediate layer contains the Li compound, and the Li compound is a composite compound containing Li, C, and O. [4] The negative electrode active material according to [3], wherein the composite compound containing Li, C, and O has an O-C=O structure in at least a part of the C1s waveform obtained from an XPS spectrum. [5] The negative electrode active material according to any one of [1] to [4], wherein the intermediate layer contains the metal oxide and / or metal hydroxide, and the metal oxide and / or metal hydroxide contains at least one element selected from the group consisting of aluminum, magnesium, titanium, zirconium, calcium, and niobium. [6] The negative electrode active material according to [5], wherein the thickness of the metal oxide and / or metal hydroxide in the intermediate layer is 0.1 nm or more and 10 nm or less. [7] The negative electrode active material according to any one of [1] to [6], wherein the intermediate layer contains the Li compound and the metal oxide and / or metal hydroxide, and the metal oxide and / or metal hydroxide coats the Li compound. [8] The negative electrode active material according to any one of [1] to [7], wherein the negative electrode active material particles have a peak attributable to a Si(111) crystal plane obtained by X-ray diffraction using Cu-Kα radiation before charging and discharging the negative electrode active material particles, the crystallite size corresponding to the crystal plane is 5.0 nm or less, and the ratio A / B of the intensity A of the peak attributable to the Si(111) crystal plane to the intensity B of the peak attributable to the Li2SiO3(111) crystal plane satisfies the following formula (1): 0.4≦A / B≦1.0 (1). [9] The negative electrode active material according to any one of [1] to [8], wherein the negative electrode active material particles have a median diameter of 4.5 μm or more and 15 μm or less.

[10] A method for producing a negative electrode active material containing negative electrode active material particles, the method comprising the steps of: xa step of inserting Li into the silicon oxide particles to prepare silicon compound particles containing Li silicate; a step of forming an intermediate layer on the surface of the silicon compound particles, the intermediate layer containing a Li compound other than Li silicate adjacent to a portion of the surface of the silicon compound particles, and / or a metal oxide and / or a metal hydroxide adjacent to at least a portion of the surface of the silicon compound particles; a step of forming an outermost carbon layer covering the intermediate layer to obtain negative electrode active material particles; and a step of producing a negative electrode active material using the negative electrode active material particles.

[11] The method for producing a negative electrode active material according to

[10] , characterized in that in the step of producing silicon compound particles containing Li silicate, silicon compound particles containing the Li compound on their surfaces are produced, and in the step of forming the intermediate layer, a portion of the Li compound present on the surfaces of the silicon compound particles is removed, and a portion of the surfaces of the silicon compound particles and the surface of the Li compound are coated with a metal oxide and / or a metal hydroxide, thereby forming the intermediate layer containing the metal oxide and / or the metal hydroxide and the Li compound.

[12] The method for producing a negative electrode active material according to

[11] , wherein in the step of forming the intermediate layer, the metal oxide and / or the metal hydroxide is formed by hydrolysis and dehydration condensation of a metal alkoxide.

[0267] The present invention is not limited to the above-described embodiments, which are merely examples, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and that provides similar effects is included within the technical scope of the present invention. [Explanation of symbols]

[0268] 1 and 8... negative electrode active material particles, 2... silicon compound particles (SiO xparticles), 3...Si phase, 4...intermediate layer, 5...Li compound, 6...metal oxide and / or metal hydroxide, 7...carbon layer, 10...negative electrode, 11...negative electrode current collector, 12...negative electrode active material layer, 30...lithium ion secondary battery (laminate film type), 31...electrode body, 32...positive electrode lead, 33...negative electrode lead, 34...adhesive film, 35...exterior member.

Claims

1. A negative electrode active material containing negative electrode active material particles, The negative electrode active material particles are Silicon compound particles containing Li silicate; an intermediate layer covering the surface of the silicon compound particle, the intermediate layer comprising a Li compound different from the Li silicate adjacent to a portion of the surface of the silicon compound particle, or the Li compound and a metal oxide and / or metal hydroxide adjacent to at least a portion of the surface of the silicon compound particle; a carbon layer as an outermost layer covering the intermediate layer; and The Li compound is a composite compound containing Li, C, and O, and the composite compound containing Li, C, and O has an O-C=O structure in at least a part thereof in a C1s waveform obtained from an XPS spectrum.

2. The silicon compound particles contain, at least in part, Li as the Li silicate. ２ SiO ３ , Li ４ SiO ４ and Li ６ Si ２ O ７ 2. The negative electrode active material according to claim 1, comprising at least one selected from the group consisting of:

3. 2. The negative electrode active material according to claim 1, wherein the intermediate layer contains the metal oxide and / or metal hydroxide, and the metal oxide and / or metal hydroxide contains at least one element selected from the group consisting of aluminum, magnesium, titanium, zirconium, calcium, and niobium.

4. 4. The negative electrode active material according to claim 3, wherein the thickness of the metal oxide and / or metal hydroxide in the intermediate layer is 0.1 nm or more and 10 nm or less.

5. 5. The negative electrode active material according to claim 1, wherein the intermediate layer contains the Li compound and the metal oxide and / or metal hydroxide, and the metal oxide and / or metal hydroxide coats the Li compound.

6. The negative electrode active material particles have a peak attributable to a Si (111) crystal plane obtained by X-ray diffraction using Cu-Kα radiation before charging and discharging the negative electrode active material particles, and the crystallite size corresponding to the crystal plane is 5.0 nm or less, and Li ２ SiO ３ The ratio A / B of the intensity A of the peak due to the Si (111) crystal plane to the intensity B of the peak due to the (111) crystal plane is expressed by the following formula (1): 0.4≦A / B≦1.0 (1) 5. The negative electrode active material according to claim 1, which satisfies the following:

7. The negative electrode active material particles have a peak attributable to a Si (111) crystal plane obtained by X-ray diffraction using Cu-Kα radiation before charging and discharging the negative electrode active material particles, and the crystallite size corresponding to the crystal plane is 5.0 nm or less, and Li ２ SiO ３ The ratio A / B of the intensity A of the peak due to the Si (111) crystal plane to the intensity B of the peak due to the (111) crystal plane is expressed by the following formula (1): 0.4≦A / B≦1.0 (1) 6. The negative electrode active material according to claim 5, wherein the negative electrode active material satisfies the above.

8. 5. The negative electrode active material according to claim 1, wherein the negative electrode active material particles have a median diameter of 4.5 μm or more and 15 μm or less.

9. A method for producing a negative electrode active material including negative electrode active material particles, comprising: General formula SiO ｘ (0.5≦x≦1.6) intercalating Li into the silicon oxide particles to prepare silicon compound particles containing Li silicate; forming an intermediate layer on the surface of the silicon compound particle, the intermediate layer comprising a Li compound different from Li silicate adjacent to a portion of the surface of the silicon compound particle, or the Li compound and a metal oxide and / or metal hydroxide adjacent to at least a portion of the surface of the silicon compound particle, the Li compound being a composite compound containing Li, C, and O, and the composite compound containing Li, C, and O having an O-C=O structure in at least a portion thereof in a C1s waveform obtained from an XPS spectrum; forming an outermost carbon layer that covers the intermediate layer to obtain negative electrode active material particles; a step of producing a negative electrode active material using the negative electrode active material particles; 2. A method for producing a negative electrode active material, comprising:

10. In the step of preparing silicon compound particles containing Li silicate, silicon compound particles containing the Li compound on their surfaces are prepared, In the step of forming the intermediate layer, removing a portion of the Li compound present on the surface of the silicon compound particles; 10. The method for producing a negative electrode active material according to claim 9, wherein the intermediate layer containing the metal oxide and / or metal hydroxide and the Li compound is formed by coating a portion of the surface of the silicon compound particle and the surface of the Li compound with a metal oxide and / or a metal hydroxide.

11. 11. The method for producing a negative electrode active material according to claim 10, wherein in the step of forming the intermediate layer, the metal oxide and / or the metal hydroxide is formed by hydrolysis and dehydration condensation of a metal alkoxide.

Images