JP6536301B2 - Coated negative electrode active material - Google Patents

Description

  The present invention relates to a coated negative electrode active material whose resistance is reduced while suppressing heat generation.

  With the rapid spread of information related devices such as personal computers, video cameras and mobile phones and communication devices in recent years, development of batteries used as the power source is regarded as important. Also, in the automobile industry and the like, development of high-power and high-capacity batteries for electric vehicles or hybrid vehicles is in progress. Among various batteries, lithium batteries are currently attracting attention from the viewpoint of high energy density.

  Since lithium batteries currently on the market use an electrolytic solution containing a flammable organic solvent, a structure for attachment of a safety device for preventing temperature rise at the time of short circuit and short circuit prevention is required. On the other hand, a lithium battery in which the battery is totally solidified by changing the electrolytic solution to a solid electrolyte layer does not use a flammable organic solvent in the battery, so the safety device can be simplified, and the manufacturing cost and productivity It is considered to be excellent.

  On the other hand, techniques for coating the surface of an active material with an oxide are known. For example, Patent Document 1 discloses a negative electrode for a power storage device in which a part of a particulate negative electrode active material is covered with a film having an insulating property and lithium ion conductivity. Furthermore, the use of graphite as a negative electrode active material is described, and as a film, an oxide film of any one of niobium, titanium, vanadium, tantalum, tungsten, zirconium, molybdenum, hafnium, chromium, aluminum or silicon, or It is described that an oxide film containing any one and lithium is used. Moreover, the sol-gel method is described as a manufacturing method of a film. This technique is aimed at suppressing the electrochemical decomposition of the electrolyte and the like in the negative electrode.

  Patent Document 2 discloses a method of producing a positive electrode active material for a non-aqueous secondary battery in which a film is formed on the surface of a lithium transition metal complex oxide particle by an atomic layer deposition method, and at least one of a precursor and a coreactant A method of manufacture characterized in reducing the amount is disclosed. This technique is intended to form a film which can uniformly and thinly coat the surface of lithium transition metal complex oxide particles and which does not lose charge and discharge characteristics.

Patent Document 3 discloses a lithium ion battery including an electrolyte solution, including a passivation protector disposed on the surface of the anode, wherein the passivation protector is a thin film deposition layer, and the thickness of the passivation protector is 1 nm to 1 μm. A battery is disclosed. Furthermore, the use of aluminum oxide (Al ₂ O ₃ ) or the like as a passivation protector is described, and an atomic layer deposition method is described as a method of manufacturing the passivation protector. This technology aims to provide a lithium ion battery that can operate at high temperatures.

Patent Document 4 discloses a rechargeable lithium battery cell having an SO ₂ -based electrolyte and a specific positive electrode active material. Furthermore, as a method of surface-coating an active material, atomic layer deposition is described, the surface-coating includes Al ₂ O _{3 and the} like, and carbon is described as an example of a negative electrode active material. This technique is intended to improve power density and the like.

  Patent Document 5 comprises a carbon material and lithium titanium oxide (LTO), the average particle size of LTO to the average particle size of the carbon material is within a specific range, and the LTO is distributed on the surface of the carbon material Anode materials are disclosed. This technique is aimed at obtaining low internal resistance, high conductivity and excellent output characteristics.

JP, 2013-232403, A JP, 2014-170656, A JP, 2014-143375, A JP, 2013-519968, A JP, 2010-531041, A

  For example, patent document 1 is a technique regarding the battery which mainly used the electrolyte solution. In a battery using an electrolytic solution, for example, decomposition of the electrolytic solution occurs at the time of first charge, and a film (SEI film) is formed on the surface of the negative electrode active material. Since the SEI film usually has an insulating property, it is possible to suppress the decomposition of the electrolyte in subsequent charge and discharge.

  On the other hand, the solid electrolyte material used for the all solid lithium battery generally has less decomposition reaction than the electrolytic solution. Therefore, it is estimated that the SEI film is not sufficiently formed on the surface of the negative electrode active material. As a result, when, for example, the battery temperature rises for some reason, a reaction between the negative electrode active material and the solid electrolyte material may occur to generate heat.

  Further, in Patent Document 1, a film is formed on the surface of graphite by a sol-gel method. However, in the conventional sol-gel method, it is difficult to control the thickness of the film, and the particle size of the oxide constituting the film is also relatively large. As a result, although the heat generation due to the reaction between the negative electrode active material and the solid electrolyte material can be suppressed, the resistance is increased.

  This invention is made in view of the said situation, and makes it a main purpose to provide the covering negative electrode active material which reduced resistance, suppressing heat_generation | fever.

  In order to solve the above problems, in the present invention, a coated negative electrode active material used for an all solid lithium battery, which is a negative electrode active material having a graphite structure, and structural defects of the above graphite structure on the surface of the negative electrode active material A coated portion for coating the coated portion, wherein the coated portion is made of aluminum oxide, the coated portion is in the form of particles, and the average particle diameter of the coated portion is 2 nm or less. Provide an active material.

  According to the present invention, the covering portion for covering the structural defect portion is a particulate aluminum oxide, and further, since the average particle diameter of the covering portion is small, the covering negative electrode active with reduced resistance while suppressing heat generation. It can be a substance.

  The coated negative electrode active material of the present invention has an effect that resistance can be reduced while suppressing heat generation.

It is a schematic sectional drawing which shows an example of the coated negative electrode active material of this invention. It is a schematic sectional drawing explaining the coated negative electrode active material of this invention. It is a SEM image of the sample obtained by Example 1 and Comparative Example 1. It is a result of calorific value and reaction resistance with respect to the samples obtained in Example 1 and Comparative Examples 1 to 4. It is an atomic force microscope (AFM) image which demonstrates the selectivity in atomic layer deposition (ALD method).

  Hereinafter, the coated negative electrode active material of the present invention will be described in detail. FIG. 1 is a schematic cross-sectional view showing an example of the coated negative electrode active material of the present invention. The coated negative electrode active material 10 in FIG. 1 has a negative electrode active material 1 having a graphite structure, and a covering portion 2 for covering a structural defect portion of the graphite structure on the surface of the negative electrode active material 1. In the present invention, the coating portion 2 is made of aluminum oxide, the coating portion 2 is in the form of particles, and the average particle diameter of the coating portion 2 is not more than a specific value.

According to the present invention, the covering portion for covering the structural defect portion is a particulate aluminum oxide, and further, since the average particle diameter of the covering portion is small, the covering negative electrode active with reduced resistance while suppressing heat generation. It can be a substance. Here, the "graphite structure" refers to a layered structure in which a hexagonal mesh plane of carbon is stacked. Of the four carbon valence electrons, three form an SP ² hybrid orbital to form a hexagonal network plane, and the remaining one (π electron) forms van der Waals bonds in the stacking direction. Moreover, "a structural defect part" means the hexagonal mesh end in a graphite structure, and, specifically, an edge part, a point defect part, etc. are mentioned. The structural defect part is a place where lithium intercalation and deintercalation occur, and at the same time is also a reaction starting point with the solid electrolyte material.

  In the present invention, by covering the structural defect portion with minute aluminum oxide particles, resistance can be reduced while suppressing heat generation. In the conventional sol-gel method, since it is difficult to control the thickness of the covering portion, for example, as shown in FIG. 2A, the aluminum oxide constituting the covering portion 2 covering the structural defect portion (edge portion) 3 The particle size of is relatively large. As a result, although the heat generation due to the reaction of the negative electrode active material 1 and the solid electrolyte material (not shown) can be suppressed, the resistance is increased.

  On the other hand, in the present invention, as shown in FIG. 2 (b), a minute covering portion 2 (particles of aluminum oxide) is provided on the structural defect portion (edge portion) 3. As a result, the resistance can be reduced while suppressing heat generation due to the reaction of the negative electrode active material 1 and the solid electrolyte material (not shown). As described above, the solid electrolyte material used for the all solid lithium battery generally has less decomposition reaction than the electrolytic solution. Therefore, it is estimated that the SEI film is not sufficiently formed on the surface of the negative electrode active material. As a result, when, for example, the battery temperature rises for some reason, a reaction between the negative electrode active material and the solid electrolyte material may occur to generate heat. On the other hand, in the present invention, the resistance can be reduced while suppressing heat generation by providing the covering portion (insulating portion) slightly in advance as the reaction starting point of the negative electrode active material and the solid electrolyte material. .

In particular, in the present invention, by using, for example, atomic layer deposition (ALD), it is possible to obtain a coated negative electrode active material having a coating portion that selectively covers structural defects. “Selectably coat” means the ratio (S _A ) of the area (S _A ) of the structural defect part covered by the cover to the whole area (S _B ) covered by the cover on the surface of the negative electrode active material It is said that / S _B ) is 90% or more. S _A / _{S B} is preferably 95% or more, more preferably 99% or more. The reason why the coating can be selectively formed by the ALD method is presumed to be due to the high reactivity of the structural defect (the reactivity of the functional group present in the structural defect) and the selective reaction with the precursor. . In the conventional sol-gel method, in principle, it is difficult to selectively form the covering portion.
Hereinafter, the coated negative electrode active material of the present invention will be described for each constitution.

1. Negative Electrode Active Material The negative electrode active material in the present invention is usually a carbon material having a graphite structure. The carbon material may have at least a graphite structure. Examples of the negative electrode active material include graphite (graphite) such as natural graphite and artificial graphite, non-graphitizable carbon (hard carbon), graphitizable carbon (soft carbon) and the like. In addition, the negative electrode active material may be an active material having an amorphous carbon layer on the surface. Further, BET specific surface area of the negative electrode active material is preferably within a range of, for example, ^{2m 2} / ^g~8m 2 / g. When the BET specific surface area is too large, side reactions such as decomposition reaction may be activated during charge and discharge. The D / G ratio of the negative electrode active material is, for example, in the range of 0.1 to 1.2.

As a shape of a negative electrode active material, particle shape can be mentioned, for example. As particulate form, spherical form and fibrous form can be mentioned, for example. The average particle size (D ₅₀ ) of the negative electrode active material is not particularly limited, but is, for example, in the range of 0.1 μm to ₅₀ μm, and preferably in the range of 1 μm to 20 μm. The average particle size (D ₅₀ ) of the negative electrode active material can be determined, for example, from the result of particle size distribution measurement by a laser diffraction scattering method.

2. Covering Part The covering part in the present invention is a part which covers at least a structural defect part of the graphite structure on the surface of the negative electrode active material. In particular, in the present invention, the covering portion preferably selectively covers the structural defect portion. Moreover, a coating | coated part is comprised from aluminum oxide. The ratio of the aluminum oxide contained in the coated portion is, for example, 50 mol% or more, preferably 70 mol% or more, and more preferably 90 mol% or more. The composition of the aluminum oxide is not particularly limited as long as it is a composition containing an Al element and an O element, but is usually represented by Al ₂ O ₃ .

  Moreover, the covering part in the present invention is usually particulate. As particulate form, spherical shape can be mentioned, for example. The average particle diameter of the coated portion is usually 2 nm or less, and may be 1.8 nm or less. On the other hand, the average particle diameter of the covering portion is, for example, 0.1 nm or more, and may be 0.5 nm or more. The average particle size of the coated portion can be determined, for example, by observation with a scanning electron microscope. The number of samples (N) is preferably larger, preferably 10 or more, and more preferably 100 or more.

3. Coated Negative Electrode Active Material The coated negative electrode active material of the present invention has the above-described negative electrode active material and a coated portion. The average particle diameter of the coated negative electrode active material is not particularly limited, but since the average particle diameter of the coated portion is very small, it can be approximated to the above-described average particle diameter of the negative electrode active material. Therefore, the average particle diameter of the coated negative electrode active material is preferably in the same range as the above-described average particle diameter of the negative electrode active material.

  Although the manufacturing method of the coated negative electrode active material of this invention is not specifically limited, For example, an atomic layer deposition method (ALD method) can be mentioned. The atomic layer deposition method is, for example, a method of depositing a target compound one molecule at a time by alternately using an organometallic precursor and a nonmetallic precursor. In addition, by using atomic layer deposition, it is possible to form a covering that selectively covers structural defects. In the present invention, a method for producing a coated negative electrode active material used for an all solid lithium battery, which selectively forms the structural defect of the graphite structure on the surface of the negative electrode active material having a graphite structure by atomic layer deposition. A coated portion forming step of forming a coated portion, wherein the coated portion is a particulate aluminum oxide, and the coated particle has an average particle diameter of 2 nm or less. It is also possible to provide a manufacturing method of

  In the ALD method, a precursor containing Al and a precursor containing O are generally used. Examples of the precursor containing Al include trimethylaluminum and the like. As the precursor containing O, for example, water (water vapor) can be mentioned.

  The amount of each precursor used is appropriately selected according to the composition of aluminum oxide and the properties of each precursor. Further, the reaction temperature in the ALD method is not particularly limited, but is, for example, in the range of 150 ° C. to 350 ° C.

  The coated negative electrode active material of the present invention is usually used in an all solid lithium battery. Therefore, in the present invention, it is an all solid lithium battery having a positive electrode active material layer, a negative electrode active material layer, and a solid electrolyte layer formed between the positive electrode active material layer and the negative electrode active material layer. It is also possible to provide an all solid lithium battery characterized in that the negative electrode active material layer contains the above-mentioned coated negative electrode active material. Usually, at least one of the solid electrolyte material contained in the negative electrode active material layer and the solid electrolyte material contained in the solid electrolyte layer is in contact with the coated negative electrode active material.

  The negative electrode active material layer may at least contain a negative electrode active material and may further contain a solid electrolyte material. The negative electrode active material is as described above. On the other hand, examples of solid electrolyte materials include inorganic solid electrolyte materials such as sulfide solid electrolyte materials, oxide solid electrolyte materials, nitride solid electrolyte materials, and halide solid electrolyte materials.

As a sulfide solid electrolyte material, for example, Li ₂ S-P ₂ S ₅ , Li ₂ S-P ₂ S ₅ -LiI, Li ₂ S-P ₂ S ₅ -LiCl, Li ₂ S-P ₂ S _{5- LiBr, Li 2 S-P 2} S 5 -Li 2 O, Li 2 S-P 2 S 5 -Li 2 O-LiI, Li 2 S-SiS 2, Li 2 S-SiS 2 -LiI, Li 2 S- _{SiS 2 -LiBr, Li 2 S-} SiS 2 -LiCl, Li 2 S-SiS 2 -B 2 S 3 -LiI, Li 2 S-SiS 2 -P 2 S 5 -LiI, Li 2 S-B 2 S 3 , Li ₂ S—P ₂ S ₅ —Z _m S _n (where m and n are positive numbers, and Z is any of Ge, Zn, and Ga.), Li ₂ S—GeS ₂ , Li ₂ S— _{SiS 2 -Li 3 PO 4, Li} 2 S-SiS 2 -Li x MO (However, x, y is a positive number .M is, P, Si, Ge, B , Al, Ga, either an _In.), May be mentioned Li ₁₀ GeP _{2 S 12} or the like.

In particular, the sulfide solid electrolyte material preferably includes an ion conductor containing Li, A (A is at least one of P, Si, Ge, Al and B), and S. Furthermore, the above ion conductor has an anion structure (PS ₄ ^3- structure, SiS ₄ ^4- structure, GeS ₄ ^4- structure, AlS ₃ ^3- structure, BS ₃ ^3- structure) of ortho composition as a main component of anion It is preferable to have. This is because a sulfide solid electrolyte material having high chemical stability can be obtained. It is preferable that it is 70 mol% or more with respect to the total anion structure in an ion conductor, and, as for the ratio of the anion structure of an ortho composition, it is more preferable that it is 90 mol% or more. The proportion of the anion structure of the ortho composition can be determined by Raman spectroscopy, NMR, XPS or the like.

  The sulfide solid electrolyte material preferably contains at least one of LiI, LiBr and LiCl in addition to the above ion conductor. At least a portion of LiI, LiBr and LiCl is usually present in the structure of the ion conductor as a LiI component, a LiBr component and a LiCl component, respectively. The sulfide solid electrolyte material may or may not have a peak of LiI in X-ray diffraction measurement, but the latter is preferable. It is because Li ion conductivity is high. The same applies to LiBr and LiCl in this respect. The proportion of LiX (X = I, Cl, Br) in the sulfide solid electrolyte material is, for example, in the range of 10 mol% to 30 mol%, and preferably in the range of 15 mol% to 25 mol%. The proportion of LiX refers to the proportion of the total of LiX contained in the sulfide solid electrolyte material.

The positive electrode active material layer may at least contain a positive electrode active material and may further contain a solid electrolyte material. As a positive electrode active material, an oxide active material can be mentioned, for example. Specific examples of the oxide active material include rock salt layered type active materials such as LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , LiVO ₂ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , and LiMn ₂ O _4. And spinel type active materials such as Li (Ni _0.5 Mn _1.5 ) O ₄ , and olivine type active materials such as LiFePO ₄ , LiMnPO ₄ , LiNiPO ₄ , LiCuPO _{4, and the} like. On the other hand, the solid electrolyte layer is not particularly limited as long as it is a layer containing at least a solid electrolyte material.

  The present invention is not limited to the above embodiment. The above embodiment is an exemplification, and it has substantially the same configuration as the technical idea described in the claims of the present invention, and any one having the same function and effect can be used. It is included in the technical scope of the invention.

  Hereinafter, the present invention will be more specifically described by way of examples.

Example 1
As a starting material, spherical graphite particles coated with amorphous carbon were prepared. Next, particles of aluminum oxide were deposited on the structural defects of the graphite particles by atomic layer deposition (ALD). First, graphite particles were placed in the chamber of the atomic layer deposition apparatus, the inside of the chamber was evacuated, and then the inside of the chamber was purged with nitrogen gas. Next, the temperature in the chamber was raised to 300 ° C. and held for 1 hour. Next, trimethylaluminum (Al (CH ₃ ) ₃ ) was used as a first precursor, introduced into the chamber together with nitrogen gas, and reacted with the surface of the graphite particles. Thereafter, the inside of the chamber was purged with nitrogen gas. Next, steam was used as a second precursor, and was introduced into the chamber together with nitrogen gas to react with the surface of the graphite particles. Thereafter, the inside of the chamber was purged with nitrogen gas. The above operation of introducing the precursor and purging with nitrogen gas was repeated a total of 10 times. Thus, a coated negative electrode active material was obtained.

Comparative Example 1
Graphite particles were used as a comparison sample without introducing the precursor and performing the above operation of purging with nitrogen gas.

Comparative Example 2
A coated negative electrode active material was obtained in the same manner as Example 1, except that the above operation of introducing the precursor and purging with nitrogen gas was repeated a total of 30 times.

Comparative Example 3
The coated negative electrode active material was produced by the sol-gel method. First, 1 × 10 ⁻⁴ mol of aluminum ethoxide and 2 × 10 ⁻⁴ mol of ethyl acetoacetate were dissolved in 2 ml of ethanol. The resulting solution was stirred and subjected to hydrolysis reaction and dehydration condensation to obtain a gel-like reaction product. Then, it baked on conditions of 500 degreeC and air | atmosphere atmosphere for 3 hours, and obtained the covering negative electrode active material.

Comparative Example 4
A coated negative electrode active material is obtained in the same manner as in Comparative Example 3, except that a solution of 1 × 10 ⁻³ mol of aluminum ethoxide and 2 × 10 ⁻³ mol of ethyl acetoacetate in 2 ml of ethanol is used. The

[Evaluation]
(SEM observation)
The samples obtained in Example 1 and Comparative Examples 1 to 4 were observed by a scanning electron microscope (SEM) to calculate the average particle size of the aluminum oxide. The average particle diameter of the aluminum oxide having a small average particle diameter was also calculated from the deposition rate. A representative SEM image is shown in FIG. Fig.3 (a) is a result of Example 1, FIG.3 (b) is an enlarged view of Fig.3 (a). On the other hand, FIG. 3 (c) is the result of Comparative Example 1, and FIG. 3 (d) is an enlarged view of FIG. 3 (c). As shown in FIG. 3B, in Example 1, white spots (deposited aluminum oxide) were confirmed on the surface of the graphite particles. On the other hand, as shown in FIG. 3 (d), no white spots were confirmed in Comparative Example 1.

(Resistance measurement)
Evaluation batteries were produced using the samples obtained in Example 1 and Comparative Examples 1 to 4. First, a negative electrode active material obtained, and a sulfide solid electrolyte material _{(LiI-Li 2 S-P} 2 S 5), the negative electrode active material: sulfide solid electrolyte material = 60: at a volume ratio of 40, the dispersion medium Was charged into dehydrated heptane. Then, it stirred for 10 minutes using the ultrasonic homogenizer. Thereafter, dehydrated heptane of the dispersion was removed using a hot stirrer at 80 ° C., and the dispersion was dried to obtain a negative electrode composite.

Next, a positive electrode active material (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , rock salt layered type active material), a conductive material (carbon black), and a sulfide solid electrolyte material (LiI-Li ₂ S) -P ₂ S ₅ ) was charged into dehydrated heptane as a dispersion medium at a volume ratio of positive electrode active material: conductive material: sulfide solid electrolyte material = 62.5: 37.5: 5. Then, it stirred for 10 minutes using the ultrasonic homogenizer. Thereafter, dehydrated heptane of the dispersion was removed using a hot stirrer at 80 ° C., and the dispersion was dried to obtain a positive electrode composite material.

Next, the sulfide solid electrolyte material _{(LiI-Li 2 S-P} 2 S 5), placed 200mg in Macor cylinder, to obtain pellets of a solid electrolyte layer by pressing at 98 MPa. Thereafter, 200 mg of the positive electrode mixture was put on one surface of the solid electrolyte layer, and pressed at 98 MPa to obtain a positive electrode active material layer. Thereafter, 200 mg of the negative electrode mixture was put on the other surface of the solid electrolyte layer, and pressed at 98 MPa to obtain a negative electrode active material layer. A stainless steel rod was inserted into both electrodes and restrained by 1 ton to make a battery. Thus, a battery for evaluation was obtained.

  The obtained evaluation battery was aged, and then SOC (State Of Charge) was adjusted to 85%. The alternating current impedance measurement was performed in that state, and reaction resistance was measured. The results are shown in Table 1 and FIG.

(Measurement of calorific value)
The evaluation battery obtained by the above-described method was disassembled in a state of 100% SOC, and the negative electrode active material layer was taken out. The obtained negative electrode active material layer was crushed in a mortar, and differential scanning calorimetry was performed in the range from room temperature to 500 ° C. From the observed exothermic curve, the peak area showing the reduction reaction of the solid electrolyte material was determined to calculate the calorific value. The results are shown in Table 1 and FIG.

  As shown in Table 1 and FIG. 4, the calorific value of Example 1 and Comparative Example 2 was lower than the calorific value of Comparative Example 1. It is presumed that this is because a minute covering portion (aluminum oxide) is formed to cover the structural defect portion, and the reaction between the negative electrode active material and the solid electrolyte material can be suppressed.

  Moreover, the reaction resistance of Example 1 became lower than the reaction resistance of Comparative Example 1. Strictly speaking, the resistance reduction effect by providing the covering part is the resistance reducing effect due to the ion conductivity of the covering part (aluminum oxide), and the resistance increasing that the covering part inhibits the Li insertion and detachment of the active material. Although it depends on the balance with the effect, it was confirmed that when the average particle diameter of the coating portion is sufficiently small, the resistance reduction effect is dominant. On the other hand, the reaction resistance of Comparative Example 2 was higher than the reaction resistance of Comparative Example 1. It is presumed that this is because the resistance increase effect is dominant. Thus, it has been confirmed that if the average particle size of the aluminum oxide is 2 nm or less, a calorific value and reaction resistance lower than those of Comparative Example 1 can be obtained.

  Moreover, Comparative Examples 3 and 4 are the coated negative electrode active materials manufactured by the sol-gel method. Although the calorific value was less than or equal to that of Comparative Example 1, the reaction resistance increased as the average particle size of the aluminum oxide increased. Thus, in Comparative Examples 3 and 4, it was confirmed that the reaction resistance increased.

[Reference example]
Aluminum oxide particles were deposited (20 cycles, about 4 nm) on the surface of flat graphite (highly oriented pyrolytic graphite) by atomic layer deposition (ALD). The results are shown in FIG. FIG. 5A shows the result of observation of the graphite surface before the ALD method with an atomic force microscope (AFM). As shown to Fig.5 (a), a structural defect part (edge part) can be confirmed to graphite. On the other hand, FIG. 5 (b) is the result of observing the graphite surface after the ALD method with an atomic force microscope (AFM), and FIG. 5 (c) is an enlarged view of FIG. 5 (b). . As shown in FIGS. 5B and 5C, it was confirmed that the oxide was selectively deposited only on the structural defect portion (edge portion) on the graphite. Also from this result, it was confirmed that the structural defect portion of the graphite is selectively covered by using the ALD method.

1 ... negative electrode active material 2 ... coating portion 3 ... structural defect portion (edge portion)
10 ... Coated negative electrode active material

Claims (1)

A coated negative electrode active material used for an all solid lithium battery,
A negative electrode active material having a graphite structure, and a covering portion covering the structural defect portion of the graphite structure on the surface of the negative electrode active material,
The covering portion is made of aluminum oxide,
The coated negative electrode active material, wherein the coated portion is in the form of particles, and the average particle diameter of the coated portion is 2 nm or less.