JP2012182115A - Method for manufacturing negative electrode active material for electricity storage device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a negative electrode active material for an electricity storage device showing excellent initial charge-discharge characteristics.SOLUTION: In the method for manufacturing a negative electrode active material for an electricity storage device, an oxide material composed of a compound containing at least S and P, and a lithium-containing material are brought into contact with each other in an organic solvent to include lithium in the oxide material. The oxide material and the lithium-containing material are preferably mixed in the organic solvent, or the oxide material and the lithium-containing material are preferably bonded by compression before being dipped into the organic solvent.

Description

  The present invention relates to a method for producing a negative electrode material for an electricity storage device such as a lithium ion secondary battery used in, for example, a portable electronic device or an electric vehicle.

  In recent years, with the spread of portable personal computers and mobile phones, there is an increasing demand for higher capacity and smaller size of power storage devices such as lithium ion secondary batteries. If the capacity of the electricity storage device is increased, it will be easy to reduce the size of the battery material. Therefore, there is an urgent need to develop an electrode material for the electricity storage device with a higher capacity.

For example, high-potential type LiCoO ₂ , LiCo _1-x Ni _x O ₂ , LiNiO ₂ , LiMn ₂ O _{4 and the} like are widely used as positive electrode materials for lithium ion secondary batteries. On the other hand, a carbonaceous material is generally used as the negative electrode material. These materials function as an electrode active material that reversibly occludes and releases lithium ions by charging and discharging, and a so-called rocking chair type non-aqueous secondary battery that is electrochemically connected by a non-aqueous electrolyte or solid electrolyte. Constitute.

  Examples of the carbonaceous material used for the negative electrode material include graphitic carbon material, pitch coke, fibrous carbon, and high-capacity soft carbon fired at a low temperature. However, since the carbon material has a relatively small lithium insertion capacity, there is a problem that the battery capacity is low. Specifically, even if a stoichiometric amount of lithium insertion capacity can be realized, the battery capacity of the carbon material is limited to about 372 mAh / g.

  Therefore, a method using an oxide material such as SnO as a negative electrode active material capable of inserting and extracting lithium ions and having a high capacity density exceeding that of a carbonaceous material has been proposed (Patent Documents 1 to 4). reference). For example, a binder or a conductive additive is added to the negative electrode active material made of the oxide material, and the negative electrode active material is used as a negative electrode by applying it to the surface of a metal foil or the like that serves as a current collector. This negative electrode is a 3-3.6V class, and can produce an electrical storage device with larger charge / discharge capacity than a negative electrode using a carbonaceous material. Moreover, it is said that there is almost no dendrite generation in a practical use area, and it is considered extremely safe.

Japanese Patent No. 2887632 Japanese Patent No. 3498380 Japanese Patent No. 3890671 Japanese Patent No. 3605866

  An electricity storage device using an oxide material such as SnO as a negative electrode has a problem that the charge / discharge efficiency of the initial cycle (ratio of the initial discharge capacity to the initial charge capacity) is low. This is considered to be because part of lithium in the positive electrode material is consumed in an irreversible reaction for reducing an oxide material such as SnO in the first charging process.

  This invention is made | formed in view of the above situations, and it aims at providing the manufacturing method of the negative electrode active material for electrical storage devices which has a favorable initial stage charge / discharge characteristic.

  The present invention relates to an anode active material for an electricity storage device, wherein lithium is inserted into an oxide material by bringing an oxide material composed of a compound containing at least Sn and P into contact with a lithium-containing substance in an organic solvent. It relates to the manufacturing method.

  For example, as an example of a non-aqueous secondary battery, it is known that a lithium ion secondary battery undergoes the following reaction at a negative electrode made of an oxide material such as SnO during charging and discharging.

Sn ^{x +} + xe ⁻ + xLi ⁺ → Sn + xLi ⁺ (1)
Sn + yLi ⁺ + ye ⁻ ← → Li _y Sn (2)

First, during the first charge, a reaction in which Sn ^{x +} ions accept electrons and produce metal Sn occurs irreversibly (formula (1)). Subsequently, the produced metal Sn is combined with lithium ions moved from the positive electrode through the electrolytic solution or the solid electrolyte and electrons supplied from the circuit to form a Sn-Li alloy (formula (2)). The reaction occurs as a reversible reaction that proceeds rightward during charging and proceeds leftward during discharging.

Here, paying attention to the reaction of the formula (1) generated at the time of the initial charge, the electrons necessary for generating metal Sn from Sn ^{x +} ions are usually supplied from a positive electrode (for example, LiFePO ₄ ) through a conductive wire. When the positive electrode emits electrons, lithium ions are simultaneously released (consumed) into the electrolyte for charge compensation.

  In the present invention, by inserting lithium in advance into an oxide material composed of a compound containing at least Sn and P, the lithium is used as an electron supply source before the first charge, and the reaction of the above formula (1) Can be advanced. As a result, it is possible to produce a negative electrode active material for an electricity storage device that is excellent in initial charge / discharge efficiency. In particular, by bringing an oxide material and a lithium-containing substance into contact with each other in an organic solvent, the oxide material and the lithium-containing substance are electrically connected to each other, so that lithium can be efficiently inserted into the oxide material. Become.

  Note that lithium is normally considered to be inserted into an oxide material in a state of being ionized into lithium ions and electrons.

  Second, in the method for producing a negative electrode active material for an electricity storage device of the present invention, it is preferable to mix an oxide material and a lithium-containing material in an organic solvent.

  According to this method, the opportunity for contact between the oxide material and the lithium-containing substance is increased, and lithium can be efficiently inserted in a short time.

  Thirdly, in the method for producing a negative electrode active material for an electricity storage device of the present invention, it is preferable that the oxide material and the lithium-containing substance are immersed in an organic solvent in a pressure-bonded state.

  According to this method, since the contact area between the oxide material and the lithium-containing substance is increased, lithium can be efficiently inserted into the oxide material.

  Fourth, in the method for producing a negative electrode active material for an electricity storage device of the present invention, it is preferable to contact the oxide material and the lithium-containing material in an inert atmosphere.

  According to this method, it is possible to suppress the risk of ignition of the lithium-containing material. Moreover, it can suppress that a lithium containing material is oxidized or Sn reduced in the negative electrode active material is oxidized again. As a result, it is possible to improve the initial charge / discharge efficiency of the negative electrode active material.

  Fifth, in the method for producing a negative electrode active material for an electricity storage device of the present invention, the organic solvent is preferably a carbonate.

  Since carbonate ester has a relatively high electrical conductivity, lithium ions can be easily transferred to an oxide material, and as a result, lithium can be efficiently inserted in a short time.

  Sixth, in the method for producing a negative electrode active material for an electricity storage device of the present invention, the organic solvent is preferably an organic electrolytic solution containing a lithium salt.

  According to this method, lithium ions can be easily transferred to the oxide material, and as a result, lithium can be efficiently inserted in a short time.

Seventhly, in the method for producing a negative electrode active material for an electricity storage device of the present invention, the oxide material preferably contains SnO 45 to 95% and P ₂ O _{5 5 to} 55% in terms of a composition.

  Eighth, in the method for producing a negative electrode active material for an electricity storage device of the present invention, the oxide material is preferably an amorphous material.

  Ninthly, the present invention relates to a negative electrode active material for an electricity storage device manufactured by any one of the above methods.

  Tenth, the negative electrode active material for an electricity storage device of the present invention preferably has metal Sn particles dispersed in an oxide material. The negative electrode active material for an electricity storage device having such a configuration is preferable because of excellent initial charge / discharge efficiency.

  Eleventh, in the negative electrode active material for an electricity storage device of the present invention, a diffraction line having a peak position at a 2θ value of 29 to 33 ° is detected in a diffraction line profile obtained by powder X-ray diffraction measurement using CuKα rays. It is preferable. In a diffraction line profile obtained by powder X-ray diffraction measurement using CuKα ray, a diffraction line having a peak position at 2θ value of 29 to 33 ° is a metal crystal phase of metal Sn (tetragonal system, space group I41 / amd ( 141)), indicating that metal Sn particles are formed in the oxide material.

Twelfth, the negative electrode active material for an electricity storage device of the present invention, as represented by mol% based on oxides _{terms, SnO 10~70%, Li 2 O} 15~70%, P 2 O 5 1.5~45% and _{MnO + CuO + ZnO + B 2} O 3 + MgO + CaO + Al 2 O 3 + SiO 2 + R '2 O (R' , characterized in that it contains a is Na, shows a K or Cs) 0 to 45%.

It is a diffraction-line profile obtained by the powder X-ray-diffraction measurement about the negative electrode active material obtained by Examples 10-12 and the comparative example using a CuK alpha ray.

  In the method for producing a negative electrode active material for an electricity storage device of the present invention, lithium is inserted into an oxide material by bringing an oxide material composed of a compound containing at least Sn and P into contact with a lithium-containing material in an organic solvent. It is characterized by.

By using a material made of a compound containing at least Sn and P as the oxide material, a negative electrode active material having a high capacity and excellent cycle characteristics can be easily obtained. Specifically, the composition preferably contains SnO 45 to 95% and P ₂ O _{5 5 to} 55% in terms of mol%. The reason for limiting the composition in this way will be described below. In the description of the composition below, “%” means “mol%” unless otherwise specified.

SnO in the oxide material is an active material component that becomes a site for occluding and releasing lithium ions. The SnO content is preferably 45 to 95%, 50 to 90%, 55 to 87%, 60 to 85%, 68 to 83%, particularly 71 to 82%. When the content of SnO is less than 45%, the charge / discharge capacity per unit mass of the oxide material is reduced, and as a result, the charge / discharge capacity of the negative electrode active material is also reduced. On the other hand, if the content of SnO is more than 95%, the amorphous component in the oxide decreases, so the volume change accompanying the insertion and extraction of lithium ions during charge / discharge cannot be mitigated, and the discharge capacity increases rapidly. May decrease. Incidentally, SnO ingredient content in the present invention, the tin oxide component other than SnO (SnO _2, etc.) also refers to that summed in terms of SnO.

P ₂ O ₅ is a network-forming oxide and includes lithium ion storage and release sites in Sn atoms, and functions as a solid electrolyte to which lithium ions can move. The content of P ₂ O ₅ is preferably ₅ to 55%, 10 to 50%, 13 to 45%, 15 to 40%, 17 to 32, particularly 18 to 29%. If the content of P ₂ O ₅ is less than 5%, the change in volume of Sn atoms associated with insertion and extraction of lithium ions during charge / discharge cannot be alleviated, resulting in structural deterioration. Therefore, the discharge capacity decreases during repeated charge / discharge. It becomes easy. On the other hand, if the content of P ₂ O ₅ is more than 55%, the water resistance tends to deteriorate. Further, by absorbing moisture, a large amount of heterogeneous crystals (for example, SnHPO ₄ ) are formed, and the capacity is likely to decrease when repeatedly charged and discharged. Further, it is easy to form a stable crystal (for example, SnP ₂ O ₇ ) together with the Sn atom, and the influence of the coordinate bond to the Sn atom by the lone pair of electrons in the chain P ₂ O ₅ becomes stronger. . For this reason, many electrons are required to reduce Sn ions in the above formula (1), and the initial charge / discharge efficiency tends to decrease.

Incidentally, SnO / P ₂ O ₅ (molar ratio), 0.8～19,1～18, particularly preferably from 1.2 to 17. When SnO / P ₂ O ₅ is smaller than 0.8, Sn atoms in SnO are easily affected by the coordination of P ₂ O ₅ , and the initial charge / discharge efficiency tends to decrease. On the other hand, if SnO / P ₂ O ₅ is greater than 19, the discharge capacity tends to decrease when charging and discharging are repeated. This is because P ₂ O ₅ coordinated to Sn atoms in the oxide is reduced and the Sn atoms cannot be sufficiently included. As a result, the volume change of the Sn atoms associated with insertion and extraction of lithium ions cannot be relaxed. This is considered to cause structural deterioration.

In addition to the above components, various components can be further added to the oxide material. For example, MnO, CuO, ZnO, B ₂ O ₃ , MgO, CaO, Al ₂ O ₃ , SiO ₂ , R ₂ O (R represents Li, Na, K or Cs) in a total amount of 0 to 50%, 0 to 40%, 0 to 20%, 0 to 10%, particularly 0.1 to 7% can be contained. When these components increase, the structure becomes disordered and an amorphous material is easily obtained, but the phosphate network is easily cut. As a result, the volume change of the negative electrode active material accompanying charge / discharge cannot be relaxed, and the cycle characteristics may be deteriorated.

  The oxide material is preferably an amorphous material. In this case, the crystallinity of the oxide material (before lithium insertion) is preferably 95% or less, 80% or less, 70% or less, 50% or less, 40% or less, particularly 20% or less. Most preferably it is crystalline. The smaller the degree of crystallinity (the greater the proportion of the amorphous phase), the more the volume change during repeated charging / discharging can be alleviated, which is advantageous from the viewpoint of suppressing the decrease in discharge capacity. Note that “substantially amorphous” means that the crystallinity is substantially 0% (specifically, 0.1% or less). Specifically, the following CuKα ray In a powder X-ray diffraction measurement using, a crystal diffraction line is not detected.

  The degree of crystallinity is obtained from a diffraction line profile of 10 to 60 degrees as a 2θ value obtained by powder X-ray diffraction measurement using CuKα rays. Specifically, the integrated intensity obtained by peak-separating a broad diffraction line (amorphous halo) at 10 to 45 ° from the total scattering curve obtained by subtracting the background from the diffraction line profile is Ia, 10 When the total integrated intensity obtained by peak separation of each crystalline diffraction line detected at ˜60 ° is Ic, the crystallinity Xc can be obtained from the following equation.

    Xc = [Ic / (Ic + Ia)] × 100 (%)

  The shape of the oxide material is not particularly limited, and examples thereof include a bulk shape, a film shape, and a powder shape, and preferably a powder shape.

  When the oxide material is in the form of powder, the particle size is as follows: average particle size 0.1 to 10 μm and maximum particle size 75 μm or less, average particle size 0.3 to 9 μm, maximum particle size 65 μm or less, average particle size 0 It is preferable that the average particle size is 1 to 5 μm and the maximum particle size is 45 μm or less. When the average particle diameter of the oxide material is larger than 10 μm or the maximum particle diameter is larger than 75 μm, it becomes difficult to insert lithium into the powder particles of the oxide material, and as a result, the initial charge / discharge efficiency tends to be lowered. . In addition, the volume change of the negative electrode active material associated with insertion and extraction of lithium ions during charge / discharge cannot be mitigated, and the lithium ion easily peels off from the current collector. As a result, when charge / discharge is repeated, the capacity tends to be significantly reduced. On the other hand, if the average particle diameter of the powder is smaller than 0.1 μm, the powder is in a poorly dispersed state when formed into a paste, and it tends to be difficult to produce a uniform electrode.

  Here, the average particle size and the maximum particle size are D50 (50% volume cumulative diameter) and D100 (100% volume cumulative diameter) in terms of the median diameter of the primary particles, respectively, and were measured by a laser diffraction particle size distribution analyzer. Value.

  In order to obtain a powder of a predetermined size, a general pulverizer or classifier is used. For example, a mortar, a ball mill, a vibrating ball mill, a satellite ball mill, a planetary ball mill, a jet mill, a sieve, a centrifugal separator, an air classification, or the like is used.

  The oxide material is manufactured, for example, by heating and melting raw material powder to vitrify it. Here, it is preferable to melt the raw material powder in a reducing atmosphere or an inert atmosphere.

An oxide material containing Sn is likely to change the oxidation state of Sn atoms depending on melting conditions, and when melted in the air, undesired crystals such as SnO ₂ and SnP ₂ O ₇ are likely to be formed. As a result, the initial charge / discharge efficiency and cycle characteristics of the negative electrode material may be reduced. Therefore, by performing melting in a reducing atmosphere or an inert atmosphere, it is possible to suppress an increase in the valence of Sn ions in the oxide material, to suppress formation of unwanted crystals, and to be excellent in initial charge / discharge efficiency and cycle characteristics. It is possible to obtain an electricity storage device.

In order to melt in a reducing atmosphere, it is preferable to supply a reducing gas into the melting tank. The reducing gas, by _{volume%, N 2 90~99.5%, H} 2 0.5~10%, in particular N ₂ 92~99%, H ₂ is be used from 1 to 8% of the mixed gas preferable.

  When melting in an inert atmosphere, it is preferable to supply an inert gas into the melting tank. As the inert gas, it is preferable to use any of nitrogen, argon, and helium.

  The reducing gas or the inert gas may be supplied to the upper atmosphere of the molten glass in the melting tank, may be supplied directly from the bubbling nozzle into the molten glass, or both methods may be performed simultaneously.

In the above oxide material manufacturing method, by using a composite oxide as the starting raw material powder, an oxide material with less devitrified foreign matter and excellent homogeneity can be easily obtained. When the oxide material is used as a negative electrode active material, an electricity storage device with a stable discharge capacity is easily obtained. Examples of such complex oxides include stannous pyrophosphate (Sn ₂ P ₂ O ₇ ).

  Furthermore, in the method for producing a negative electrode material for an electricity storage device of the present invention, the raw material powder preferably contains a metal powder or a carbon powder. Thereby, Sn atoms in the negative electrode material can be shifted to a reduced state. As a result, the Sn valence in the negative electrode material is reduced, and the initial charge efficiency of the electricity storage device can be improved.

  As the metal powder, any one of Sn, Al, Si, and Ti is preferably used. Among these, it is preferable to use Sn, Al, and Si powders.

  Examples of the lithium-containing material used in the present invention include metallic lithium and lithium compounds such as lithium nitride. Lithium nitride is characterized by being relatively stable and easy to handle. The metal lithium may contain other metals such as aluminum. In that case, the purity of metallic lithium is preferably 90% or more, particularly 98% or more.

  The lithium-containing substance is preferably added so that the number of Li atoms is 1 to 4 mol, particularly 1.5 to 3 mol, per mol of Sn atoms in the oxide material. When the amount of the lithium-containing substance added is too small, the amount of lithium inserted into the oxide material becomes insufficient, and the initial charge / discharge characteristics tend to be inferior. On the other hand, when the amount of the lithium-containing substance added is too large, the amount that can be inserted into the oxide material is exceeded, and the material tends to be wasted.

  The shape of the lithium-containing material is not particularly limited, and examples thereof include a plate shape, a foil shape, and a powder shape. In particular, a foil shape is preferable in terms of easy handling. When the lithium-containing material is in the form of a foil, the thickness is preferably 1000 μm or less, particularly 500 μm or less. When the thickness of the lithium-containing substance exceeds 1000 μm, the specific surface area becomes small, and it tends to be difficult to efficiently insert lithium into the oxide material. On the other hand, the lower limit is not particularly limited, but if the thickness of the lithium-containing material is too small, it becomes difficult to produce the material, so that it is practically 10 μm or more, particularly 50 μm or more.

  In addition, it is preferable to use what exposed metal lithium in the air | atmosphere which has a dew point of -80--10 degreeC, or the atmosphere containing about 0.1-10 volume% of carbon dioxide. In particular, when metal lithium is cut or rolled into a sheet, it is preferable to perform the work in the above atmosphere. Thereby, a stable lithium carbonate film is formed on the surface, and deterioration of lithium due to oxygen, nitrogen, moisture and the like can be suppressed.

  Examples of the organic solvent used in the present invention include carbonate esters such as propylene carbonate, ethylene carbonate, butylene carbonate, vinylene carbonate, vinyl ethyl carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate; dimethylformamide, dimethylacetamide, dimethyl A sulfoxide, N-methylpyrrolidone, etc. are mentioned, These 1 type, or 2 or more types can be mixed and used. Of these, carbonates with high electrical conductivity are preferred. By using carbonate ester as the organic solvent, it is possible to shorten the time required for insertion of lithium into the oxide material, and it is possible to uniformly insert lithium into the oxide material. Among the carbonates, propylene carbonate having a high flash point and relatively high safety is most preferable.

  The amount of water contained in the organic solvent is preferably 500 ppm or less, particularly preferably 300 ppm or less. If the amount of moisture is too large, lithium-containing substances (particularly metallic lithium) may react with moisture to produce lithium hydroxide that is corrosive to metallic materials such as current collectors. On the other hand, when the amount of water contained in the organic solvent is small, the production cost is high, and therefore, in reality, one having a concentration of 1 ppm or more, particularly 3 ppm or more is used.

In addition, it is preferable to use an organic electrolyte solution in which a lithium salt is dissolved in an organic solvent. This facilitates the movement of lithium ions to the oxide material, so that lithium can be inserted efficiently in a short time. Examples of the lithium salt include LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiCF ₃ SO ₃ , LiClO ₄ , LiBF ₄ , LiPF _{6 and the} like. Of these, LiPF ₆ is preferable because the lithium salt has a high degree of dissociation and high electrical conductivity.

  The amount of the lithium salt added is preferably 0.1 mol or more, 0.2 mol or more, particularly 0.5 mol or more per liter of the organic solvent in order to sufficiently obtain the above effect. Although there is no particular limitation on the upper limit, it is preferable that the upper limit is 5 mol or less, 3 mol or less, particularly 2 mol or less, per liter of the organic solvent, because a further effect cannot be obtained even if the amount is too large.

  As a method of bringing the oxide material and the lithium-containing substance into contact in an organic solvent, a method of mixing the oxide material and the lithium-containing substance in an organic solvent can be given. Specific examples include shear mixing (kneading). A general kneading machine such as a rotating / revolving mixer, a planetary mixer, or a three-roll mill is used for the shear mixing.

  Furthermore, it is preferable to pulverize and mix the oxide material and the lithium-containing substance in an organic solvent. According to this method, since the oxide material and the lithium-containing substance are atomized to increase the specific surface area, the opportunity of contact between both increases, and lithium can be efficiently inserted into the oxide material in a short time. It becomes possible. This makes it possible to obtain a powdered negative electrode active material in which lithium is homogeneously and sufficiently inserted. For the pulverization and mixing, a general pulverizer such as a mortar, a raking machine, a ball mill, a vibrating ball mill, a satellite ball mill, a planetary ball mill, or a jet mill is used.

  As another method of bringing the oxide material and the lithium-containing substance into contact with each other in an organic solvent, for example, a method in which the oxide material and the lithium-containing substance are pressure-bonded in advance and then immersed in an organic solvent can be used. The pressure bonding between the oxide material and the lithium-containing substance can be performed using a hand press, a press roller, or the like.

  The environment when the oxide material and the lithium-containing substance (particularly metallic lithium) are brought into contact with each other in an organic solvent is preferably in the air having a dew point of −80 to −10 ° C. or in an inert atmosphere. Is preferably in an argon atmosphere at -80 to -10 ° C. Thereby, when the oxide material and the lithium-containing substance are brought into contact with each other in an organic solvent, the lithium-containing substance is prevented from igniting and the lithium metal and the Sn metal in the oxide material are prevented from being oxidized. Can do.

  After contacting the oxide material and the lithium-containing substance in an organic solvent, it is preferable to perform aging for a certain period so that the lithium-containing substance diffuses uniformly in the oxide material. The aging conditions are not particularly limited, and are appropriately selected, for example, at 0 to 170 ° C. (preferably 20 to 120 ° C.) for 30 minutes to 60 days (preferably 1 hour to 30 days).

  In the negative electrode active material for an electricity storage device obtained by the above production method, it is preferable that metal Sn particles are dispersed in an oxide material. In this case, it is preferable because the initial charge / discharge efficiency is excellent. In addition, in the diffraction line profile obtained by the powder X-ray diffraction measurement using CuKα ray, the diffraction line having a peak position at 2θ value of 29 to 33 ° can be attributed to the metal Sn. The presence or absence of Sn particles can be confirmed.

  The peak positions of diffraction lines attributed to the metal Sn are detected at 30.6 ° (Miller index (hkl) = (200)) and 32.0 ° (Miller index (hkl) = (101)). Therefore, when metal Sn particles are present in the oxide material, two diffraction lines are detected at around 30.6 ° and around 32.0 °, but both diffraction lines overlap to form one diffraction line. It may be detected.

  The negative electrode active material for an electricity storage device of the present invention has a diffraction line profile obtained by powder X-ray diffraction measurement using CuKα rays and a half width of a diffraction line having a peak position at 2θ value of 29 to 33 ° is 0.1. It is preferably at least 0.1 °, at least 0.12 °, at least 0.15 °, at least 0.2 °, at least 0.3 °, particularly preferably at least 0.5 °. When the half width of the diffraction line is sufficiently large, the crystallite size of the metal Sn particles in the negative electrode active material is on the nano order (for example, 0.1 to 100 nm). Volume expansion is unlikely to occur, and as a result, a stable discharge capacity is easily obtained even after repeated charge and discharge. On the other hand, when the half width of the diffraction line is too small, it indicates that the size of the metal Sn particles is large (micron order or more). For this reason, when lithium ions are occluded by the charging reaction, a large volume expansion occurs locally, and the cycle characteristics tend to deteriorate.

  However, if the half width of the diffraction line attributed to the metal Sn is too large, it means that the content of the metal Sn particles is small in the oxide material. Therefore, the half width of the diffraction line is 14 ° or less, 13 °. Below, it is preferable that it is 12.5 degrees or less, 12 degrees or less, and especially 11 degrees or less.

The negative electrode active material for an electricity storage device obtained by the production method of the present invention is represented by mol% in terms of oxide, SnO 10 to 70%, Li ₂ O 15 to 70%, P ₂ O ₅ 1.5 to 45% and _{MnO + CuO + ZnO + B 2} O 3 + MgO + CaO + Al 2 O 3 + SiO 2 + R '2 O (R' is Na, shows a K or Cs) preferably contains from 0 to 45%. Here, SnO component content other than SnO Sn component (metal Sn, Li _y Sn in Sn, SnO _2, etc.) refers to a value obtained by summing in terms as SnO, Li ₂ O ingredient content is Li ₂ O Other Li components (metallic lithium, Li in Li _y Sn, etc.) are also converted as Li ₂ O and are added together.

  The negative electrode active material for an electricity storage device obtained by the production method of the present invention is used as a negative electrode material for an electricity storage device by adding a binder or a conductive additive.

  Examples of the binder include cellulose derivatives such as carboxymethylcellulose, hydroxypropylmethylcellulose, hydroxypropylcellulose, hydroxyethylcellulose, ethylcellulose, hydroxymethylcellulose, and water-soluble polymers such as polyvinyl alcohol; thermosetting polyimide, phenolic resin, epoxy resin, urea Examples thereof include thermosetting resins such as resins, melamine resins, unsaturated polyester resins, and polyurethanes; polyvinylidene fluoride.

  Examples of the conductive assistant include highly conductive carbon black such as acetylene black and ketjen black, carbon powder such as graphite, and carbon fiber.

  The negative electrode material for an electricity storage device can be used as an anode for an electricity storage device by applying it to the surface of a metal foil or the like that serves as a current collector.

  As mentioned above, although the manufacturing method of the negative electrode active material for lithium ion secondary batteries was mainly demonstrated, the negative electrode active material manufactured by the method of this invention is not limited to this, Other non-aqueous secondary batteries Furthermore, the present invention can also be applied to a hybrid capacitor in which a negative electrode material for a lithium ion secondary battery and a positive electrode material for a non-aqueous electric double layer capacitor are combined.

  A lithium ion capacitor, which is a hybrid capacitor, is one type of asymmetric capacitor that has different charge / discharge principles for a positive electrode and a negative electrode. The lithium ion capacitor has a structure in which a negative electrode for a lithium ion secondary battery and a positive electrode for an electric double layer capacitor are combined. Here, the positive electrode forms an electric double layer on the surface and is charged / discharged by utilizing a physical action (electrostatic action), whereas the negative electrode has a lithium ion chemistry similar to the lithium ion secondary battery described above. Charge and discharge by reaction (occlusion and release).

  A positive electrode material made of a carbonaceous powder having a high specific surface area such as activated carbon, polyacene, or mesophase carbon is used for the positive electrode of the lithium ion capacitor. On the other hand, a negative electrode active material produced by the method of the present invention can be used for the negative electrode.

  Hereinafter, as an example of the negative electrode material for an electricity storage device of the present invention, a method for producing a negative electrode material for a lithium ion non-aqueous secondary battery will be described in detail using examples, but the present invention is limited to these examples. It is not something.

(1) Preparation of oxide material After melting using a composite oxide of tin and phosphorus (stannous pyrophosphate: Sn ₂ P ₂ O ₇ ) as the main raw material, and other various oxides, carbonate raw materials, etc. The raw materials were prepared so that the composition of SnO was 72 mol% and P ₂ O _{5 was} 28 mol%. The raw material was put into a quartz crucible and melted at 950 ° C. for 40 minutes in a nitrogen atmosphere using an electric furnace to be vitrified.

  Next, the molten glass was cast out between a pair of rotating rollers to be molded while being rapidly cooled to obtain a film glass having a thickness of 0.1 to 2 mm. This film-like glass was pulverized at 100 rpm for 3 hours using a ball mill containing zirconia balls having a diameter of 1 to 3 cm, and then passed through a resin sieve having a mesh size of 120 μm. Material coarse powder). Subsequently, the glass coarse powder was subjected to air classification to obtain a glass powder (oxide material powder) having an average particle diameter of 2 μm and a maximum particle diameter of 28 μm.

  When the structure of the oxide material powder was identified by powder X-ray diffraction measurement, it was amorphous and no crystals were detected.

(2) Preparation of negative electrode active material (insertion of lithium into oxide material)
The obtained oxide material powder was dried in vacuum at 200 ° C. for 12 hours, and then contacted with metallic lithium under the following conditions.

As the metallic lithium, a foil having a purity of 99.5% and a thickness of 500 μm cut into small pieces having a side of 0.5 to 20 mm in an environment having a dew point temperature of −40 ° C. or lower was used. In Examples 1 to 10, the lithium metal was 0.16 g per gram of the oxide material (about 4 moles of Li atoms relative to 1 mole of Sn atoms), and in Example 11, 0.12 g (1 mole of Sn atoms per gram of oxide material). In contrast, in Example 12, 0.08 g per 1 g of the oxide material (about 2 mol of Li atom relative to 1 mol of Sn atom) was added.
The ratio was added.

  In Examples 1 to 4 and 7, the organic solvent described in the table was added to the oxide material powder and metal lithium, and after pulverizing and mixing for 1 hour using an agate mortar, 3 hours (10 hours in Example 4) Aged. In Examples 1 to 4, pulverization and mixing were performed in an air atmosphere having a dew point temperature of −40 ° C. or lower. In Example 7, pulverization and mixing were performed in an argon atmosphere having a dew point temperature of −40 ° C. or lower. In Examples 10 to 12, the organic solvents described in the table were added, pulverized and mixed for 3 hours in an air atmosphere with a dew point temperature of −40 ° C. or lower using an agate mortar, and then aged for 3 days.

  In Examples 5 and 6, in an air atmosphere having a dew point temperature of −40 ° C. or lower, the oxide material powder previously immersed in the organic solvent described in the table and metallic lithium are mixed and pressed using a hand press machine. Thus, the oxide material powder and metallic lithium were pressure-bonded and then immersed in an organic solvent for 10 days for aging.

  In Examples 8 and 9, the organic solvent described in the table was added to the oxide material powder and lithium metal in an air atmosphere having a dew point temperature of −40 ° C. or lower, and the mixture was kneaded and mixed with a rotation / revolution mixer. .

  After bringing the oxide material powder into contact with the lithium metal, the organic solvent was passed through a resin sieve having an opening of 75 μm. The sample under the sieve was centrifuged at 5000 prm, and the precipitated sample was collected. The obtained sample was vacuum dried at 120 ° C. to obtain a negative electrode active material.

  In the comparative example, the oxide material was used as it was as the negative electrode active material without contacting metal lithium.

  In addition, the organic solvent of Tables 1-2 shows the following.

EC: DEC (1: 1) = an organic solvent in which ethylene carbonate and diethyl carbonate are mixed at a volume ratio of 1: 1 PC = propylene carbonate LiPF ₆ in PC = an organic system in which 1 mol / L of LiPF ₆ is dissolved in propylene carbonate Electrolyte

(3) Preparation of negative electrode After the negative electrode active material, the conductive additive and the binder obtained above were weighed in a weight percentage of 85: 5: 10 and dispersed in dehydrated N-methylpyrrolidone. The slurry was sufficiently stirred with a rotation / revolution mixer. Here, ketjen black (hereinafter abbreviated as “KB”) was used as the conductive assistant, and polyvinylidene fluoride (hereinafter abbreviated as “PVDF”) as the binder.

  Next, using a doctor blade with a gap of 100 μm, the obtained slurry was coated on a 20 μm thick copper foil as a negative electrode current collector, vacuum-dried with a dryer at 70 ° C., and then between a pair of rotating rollers. An electrode sheet was obtained by pressing through. This electrode sheet was punched to a diameter of 11 mm with an electrode punching machine and dried under reduced pressure at a temperature of 120 ° C. for 3 hours to obtain a circular working electrode (a negative electrode for a non-aqueous secondary battery).

(4) Preparation of test battery The working electrode was placed on the lower lid of the coin cell with the copper foil surface facing down, and then dried on a reduced pressure at 70 ° C. for 8 hours on a polypropylene porous membrane having a diameter of 16 mm (Hoechst Cera A separator comprising Cellguard # 2400 manufactured by Needs Co., Ltd. and metallic lithium as a counter electrode were laminated to prepare a test battery. As the electrolytic solution, 1M LiPF ₆ solution / EC: DEC = 1: 1 (EC = ethylene carbonate, DEC = diethyl carbonate) was used. The test battery was assembled in an environment with a dew point temperature of −40 ° C. or lower.

(5) Charging / discharging test The test battery is charged with CC (constant current) from 0.2 V to 0 V at 0.2 mA (occlusion of lithium ions into the negative electrode active material) and charged in the unit weight of the negative electrode active material. The charge amount (mAh / g) was obtained by obtaining the amount of electricity. Next, the battery was discharged from 0 V to 2 V at a constant current of 0.2 mA (release of lithium ions from the negative electrode active material), and the amount of electricity discharged in the unit weight of the negative electrode active material was determined to be the discharge capacity (mAh / g). Asked. Tables 1 and 2 show the results of the initial charge / discharge characteristics.

(6) Powder X-ray diffraction (powder XRD) measurement For the negative electrode active materials obtained in Examples 10 to 12 and the comparative example, RINT2000 manufactured by RIGAKU was used as a powder X-ray diffraction measurement device, and Cu-Kα rays were used as an X-ray source. The diffraction line profile was obtained by measuring each sample in an atmosphere having a dew point of −50 ° C. under the following conditions (see FIG. 1).
Tube voltage / tube current: 40 kV / 40 mA
Divergence / scattering slit: 1 °
Receiving slit: 0.15mm
Sampling width: 0.01 °
Measurement range: 10-60 °
Measurement speed: 0.1 ° / sec
Integration count: 5 times

(7) Analysis and data analysis Materials Data Inc. as analysis / quantification software. JADE Ver. Data analysis of the diffraction line profile was performed using 6.0.
First, in order to smooth the amorphous halo other than the crystalline diffraction line in the diffraction line profile in the range of 10 to 60 °, the parameter is smoothed with a parabolic filter by 99 points with a Savitzky-Golay Filter, and then within that range. The diffraction line profile was linearly fitted so that the intensity of the diffraction line profile was not negative, and the background was subtracted.
In the diffraction line profile obtained by subtracting the background, when one or more diffraction lines having peak positions at 2θ values of 29 to 33 ° are detected, the half-value width (FWHM) of each diffraction line is uniquely determined. As can be determined, the 2θ value at the peak position of each diffraction line was fixed and separated by curve fitting using the pseudo-Voight function.
In addition, when a diffraction line is observed in a diffraction line profile having a 2θ value other than 29 to 33 °, a diffraction line component whose parameter (2θ value at the peak position) is not fixed is added.
After repeatedly refining so that the fitting residual of the fitting curve obtained by curve fitting with the diffraction line profile is 20% or less, the half-value width and peak position 2θ value of each diffraction line component are obtained. It was.
Table 3 shows the results of the peak positions and half widths obtained from the diffraction line profiles in the negative electrode active materials of Examples 10 to 12 and the comparative example.

  The batteries using the negative electrode active materials of Examples 1 to 12 showed good characteristics with an initial discharge capacity of 477 mAh / g or more and an initial charge / discharge efficiency of 58.9% or more. In particular, in Examples 1 to 7 and 10 to 12, in which the contact between the oxide material and the lithium metal was performed by pulverization mixing or pressure bonding, the initial charge / discharge efficiency was as good as 63.5% or more.

  On the other hand, the initial discharge capacity of the battery using the negative electrode active material of the comparative example was as high as 570 mAh / g, but the initial charge / discharge efficiency was as low as 55.3%.

  As is clear from Table 3 and FIG. 1, in Examples 10 to 12, diffraction having a peak position at a 2θ value of 29 to 33 ° in a diffraction line profile obtained by powder X-ray diffraction measurement using CuKα rays. A line is detected, and it can be seen that metal Sn particles are dispersed in the oxide material. On the other hand, in the comparative example, since the diffraction line having the peak position at the 2θ value of 29 to 33 ° was not detected, it is considered that the metal Sn particles are not included in the oxide material.

Claims (12)

  A method for producing a negative electrode active material for an electricity storage device, wherein lithium is inserted into an oxide material by bringing an oxide material comprising a compound containing at least Sn and P into contact with a lithium-containing substance in an organic solvent.   The method for producing a negative electrode active material for an electricity storage device according to claim 1, wherein the oxide material and the lithium-containing substance are mixed in an organic solvent.   2. The method for producing a negative electrode active material for an electricity storage device according to claim 1, wherein the oxide material and the lithium-containing substance are immersed in an organic solvent in a pressure-bonded state.   The method for producing a negative electrode active material for an electricity storage device according to any one of claims 1 to 3, wherein the oxide material and the lithium-containing substance are contacted in an inert atmosphere.   The method for producing a negative electrode active material for an electricity storage device according to any one of claims 1 to 4, wherein the organic solvent is a carbonate.   The method for producing a negative electrode active material for an electricity storage device according to any one of claims 1 to 5, wherein the organic solvent is an organic electrolytic solution containing a lithium salt. Oxide material, in mol% as composition, negative electrode active material for an electricity storage device according to claim 1, SnO 45 to 95%, characterized in that it contains P ₂ O ₅ 5 to 55% to Manufacturing method.   The method for producing a negative electrode active material for an electricity storage device according to any one of claims 1 to 7, wherein the oxide material is an amorphous material.   A negative electrode active material for an electricity storage device manufactured by the method according to claim 1.   The negative electrode active material for an electricity storage device according to claim 9, wherein metal Sn particles are dispersed in the oxide material.   The power storage device according to claim 9 or 10, wherein a diffraction line having a peak position at a 2θ value of 29 to 33 ° is detected in a diffraction line profile obtained by powder X-ray diffraction measurement using a CuKα ray. Negative electrode active material. In terms of oxide-based mol%, SnO 10-70%, Li ₂ O 15-70%, P ₂ O ₅ 1.5-45% and MnO + CuO + ZnO + B ₂ O ₃ + MgO + CaO + Al ₂ O ₃ + SiO ₂ + R ′ ₂ O (R The negative electrode active material for an electricity storage device according to claim 9, wherein 0 represents Na, K, or Cs).

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