JP2015176676A - Negative electrode material of power storage device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power storage device excellent in various performances.SOLUTION: A negative electrode 12 of a power storage device includes a collector 18 and a plurality of particles 22 firmly fixed to the surface of the collector 18. The particles 22 are formed of an Si-based alloy. The alloy contains two or more elements selected from the group consisting of Cr, Al, Sn, Ti, Zr, Hf, V, Nb, Ta, Mo, W, Mn, Fe, Co, Ni, Cu, C, B, P, Ag, Zn, In, Ga, Ge, Pb, Bi, S and Se, with the remainder being Si and inevitable impurities. The alloy contains Cr. The ratio of (Cr%/(Cr%+Ti%+Al%+Sn%+TCF%+TNF%)) is 0.05 or more. The alloy contains Al and/or Sn. The ratio of ((Al%+Sn%)/(Cr%+Ti%+Al%+Sn%+TCF%+TNF%)) is 0.002 or more and 0.400 or less.

Description

  The present invention relates to a material suitable for a negative electrode of a power storage device such as a lithium ion secondary battery, an all solid lithium ion secondary battery, or a hybrid capacitor.

  Conventionally, a powder made of a carbon material has been used as a negative electrode active material of a lithium secondary battery. However, the theoretical capacity of the carbon material is as low as 372 mAh / g, and there is a limit to further increasing the capacity. On the other hand, in recent years, application of metal materials having higher theoretical capacity than carbon materials such as Sn, Al, and Si has been studied and put into practical use. In particular, Si has a theoretical capacity exceeding 4000 mAh / g and is a promising material. When a metal material that changes to carbon is used as a negative electrode active material for a lithium ion secondary battery, there is a problem that a cycle life is short although a high capacity is obtained.

  In response to this problem, many methods have been proposed in which various elements are added to Si to form a Si alloy powder instead of pure Si powder to obtain a fine structure. In Patent Document 1, a short amount of Si phase is obtained by adding an amount of eutectic or a higher amount of hypereutectic elements such as Co and solidifying it at a cooling rate of 100 ° C./s or more. An alloy powder having an axial particle size of 5 μm or less is obtained. The cycle life is improved by using such an Si alloy powder having a fine Si phase. That is, by producing a silicide that does not occlude and release Li, an effect of suppressing volume change during Li occlusion and release of a fine Si phase is obtained.

Furthermore, the inventors have developed a cycle life improvement technique by applying such a Si alloy, and as an alloy having a finer structure and having a better cycle life, the inventor disclosed in Patent Document 2 a predetermined Cr, Ti It has been proposed that a fine eutectic structure of Si phase and CrSi ₂ phase can be obtained by adding Al and Sn. This Patent Document 2 has found that Cr is particularly excellent as an additive element to Si.

  On the other hand, the Si alloy powder used for the negative electrode of a lithium ion secondary battery is often used by being pulverized to a few μm or less by a ball mill or the like, or by reducing crystallinity. Furthermore, as in Patent Document 4-6, when processing by a ball mill, a carbon material, conductive metal powder, and oxide powder are introduced, and these are combined with Si alloy powder to further improve charge and discharge. A method for realizing the characteristics has been proposed.

JP 2001-297757 A JP2012-150910A JP2013-84549A JP 2012-178344 A JP2012-113945A JP2013-191529A

54th Battery Symposium, Abstracts of Lectures, (2013) P138

  The present invention is based on the technique of Patent Document 2, and further establishes a technique for improving charge / discharge characteristics. In addition, there are changes in the peripheral technology of the present invention as described below. That is, in recent years, the environment surrounding Si-based negative electrode materials for lithium-ion batteries has changed greatly. Conductive materials and binders in the negative electrode, as well as improvements in electrolytes, electrolytes, separators, and positive electrode materials, etc. Improvement of the whole battery structure which supplements the low cycle life characteristic which is the biggest fault of negative electrode material is examined actively (for example, patent document 3 etc. are mentioned). In such a situation, even when the same Si alloy is used as the negative electrode active material, the number of cases where the cycle life is improved has increased. In Patent Document 2, it has been described that when the amount of Cr, Ti, Al, and Sn added exceeds 21%, the cycle life is reduced. In some cases, even higher levels are available. However, when the addition amount of these additive elements is increased, other problems also occur. That is, when the addition amount of these additional elements increases, the remaining Si amount decreases, and the initial Coulomb efficiency decreases as shown in Non-Patent Document 1, for example.

  Similar problems occur in power storage devices other than lithium ion secondary batteries.

  An object of the present invention is to provide a material from which a negative electrode for an electricity storage device having excellent discharge capacity, cycle life, initial Coulomb efficiency, and negative electrode expansion coefficient can be obtained.

  In the present invention, the amount of additive elements such as Cr, Ti, Al, and Sn is made higher than that of Patent Document 2, and Al and / or Sn are contained as essential elements, thereby suppressing the above-described decrease in initial Coulomb efficiency. It has been found out that it can be done and has led to the invention. Furthermore, by increasing the total amount of all the additive elements, an effect of remarkably suppressing the increase in the thickness of the negative electrode accompanying charging / discharging is also found, and the Si alloy powder is more excellent in overall characteristics than Patent Document 2.

The negative electrode material of the electricity storage device according to the present invention is made of a Si-based alloy. This alloy includes Cr, Al, Sn, Ti, Zr, Hf, V, Nb, Ta, Mo, W, Mn, Fe, Co, Ni, Cu, C, B, P, Ag, Zn, In, Ga, It contains two or more elements selected from the group consisting of Ge, Pb, Bi, S and Se. The balance is Si and inevitable impurities. When TCF (%) is defined by the following formula (I) and TNF (%) is defined by the following formula (II), this alloy satisfies the following formulas (1) to (6).
(I) TCF% = Zr% + Hf% + V% + Nb% + Ta% + Mo% + W% + Mn% + Fe% + Co% + Ni% / 2 + Cu% / 3
(II) TNF% = C% + B% + P% + Ag% + Zn% + In% + Ga% + Ge% + Pb% + Bi% + S% + Se%
(1) 25% <Cr% + Ti% + Al% + Sn% + TCF% + TNF% ≦ 40%
(2) 0.05 ≦ Cr% / (Cr% + Ti% + Al% + Sn% + TCF% + TNF%)
(3) 0.002 ≦ (Al% + Sn%) / (Cr% + Ti% + Al% + Sn% + TCF% + TNF%) ≦ 0.400
(4) 4.8 × (Cr% + Ti% + TCF%) + (Al% + Sn% + TNF%) ≦ 135%
(5) TCF% <10%
(6) TNF% ≦ 5%

  Preferably, the negative electrode material is obtained by cooling and solidifying the molten alloy at a rate of 100 ° C./s or more.

  Preferably, the negative electrode material is obtained by stirring at least an alloy powder and hard spheres in a container and pulverizing the powder.

The negative electrode of the electricity storage device according to the present invention includes a current collector and a large number of particles fixed to the surface of the current collector. The particles are made of a Si-based alloy. This alloy includes Cr, Al, Sn, Ti, Zr, Hf, V, Nb, Ta, Mo, W, Mn, Fe, Co, Ni, Cu, C, B, P, Ag, Zn, In, Ga, It contains two or more elements selected from the group consisting of Ge, Pb, Bi, S and Se. The balance is Si and inevitable impurities. When TCF (%) is defined by the following formula (I) and TNF (%) is defined by the following formula (II), this alloy satisfies the following formulas (1) to (6).
(I) TCF% = Zr% + Hf% + V% + Nb% + Ta% + Mo% + W% + Mn% + Fe% + Co% + Ni% / 2 + Cu% / 3
(II) TNF% = C% + B% + P% + Ag% + Zn% + In% + Ga% + Ge% + Pb% + Bi% + S% + Se%
(1) 25% <Cr% + Ti% + Al% + Sn% + TCF% + TNF% ≦ 40%
(2) 0.05 ≦ Cr% / (Cr% + Ti% + Al% + Sn% + TCF% + TNF%)
(3) 0.002 ≦ (Al% + Sn%) / (Cr% + Ti% + Al% + Sn% + TCF% + TNF%) ≦ 0.400
(4) 4.8 × (Cr% + Ti% + TCF%) + (Al% + Sn% + TNF%) ≦ 135%
(5) TCF% <10%
(6) TNF% ≦ 5%

The electricity storage device according to the present invention includes a positive electrode and a negative electrode. The negative electrode includes a current collector and a large number of particles fixed to the surface of the current collector. These particles are made of a Si-based alloy. This alloy includes Cr, Al, Sn, Ti, Zr, Hf, V, Nb, Ta, Mo, W, Mn, Fe, Co, Ni, Cu, C, B, P, Ag, Zn, In, Ga, It contains two or more elements selected from the group consisting of Ge, Pb, Bi, S and Se. The balance is Si and inevitable impurities. When TCF (%) is defined by the following formula (I) and TNF (%) is defined by the following formula (II), this alloy satisfies the following formulas (1) to (6).
(I) TCF% = Zr% + Hf% + V% + Nb% + Ta% + Mo% + W% + Mn% + Fe% + Co% + Ni% / 2 + Cu% / 3
(II) TNF% = C% + B% + P% + Ag% + Zn% + In% + Ga% + Ge% + Pb% + Bi% + S% + Se%
(1) 25% <Cr% + Ti% + Al% + Sn% + TCF% + TNF% ≦ 40%
(2) 0.05 ≦ Cr% / (Cr% + Ti% + Al% + Sn% + TCF% + TNF%)
(3) 0.002 ≦ (Al% + Sn%) / (Cr% + Ti% + Al% + Sn% + TCF% + TNF%) ≦ 0.400
(4) 4.8 × (Cr% + Ti% + TCF%) + (Al% + Sn% + TNF%) ≦ 135%
(5) TCF% <10%
(6) TNF% ≦ 5%

  The negative electrode containing the material according to the present invention is excellent in discharge capacity, cycle life, initial Coulomb efficiency, and negative electrode expansion coefficient.

FIG. 1 is a conceptual diagram showing a lithium ion secondary battery as an electricity storage device according to an embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view showing a part of the negative electrode of the battery of FIG.

  Hereinafter, the present invention will be described in detail based on preferred embodiments with appropriate reference to the drawings.

  The lithium ion secondary battery 2 conceptually shown in FIG. 1 includes a tank 4, an electrolytic solution 6, a separator 8, a positive electrode 10, and a negative electrode 12. The electrolytic solution 6 is stored in the tank 4. This electrolytic solution 6 contains lithium ions. The separator 8 partitions the tank 4 into a positive electrode chamber 14 and a negative electrode chamber 16. The separator 8 prevents contact between the positive electrode 10 and the negative electrode 12. The separator 8 has a large number of holes (not shown). Lithium ions can pass through this hole. The positive electrode 10 is immersed in the electrolytic solution 6 in the positive electrode chamber 14. The negative electrode 12 is immersed in the electrolytic solution 6 in the negative electrode chamber 16.

  FIG. 2 shows a part of the negative electrode 12. The negative electrode 12 includes a current collector 18 and an active material layer 20. The active material layer 20 includes a large number of particles 22 (powder). Each particle 22 is fixed to another particle 22 that contacts the particle 22. The particles 22 that come into contact with the current collector 18 are fixed to the current collector 18. The active material layer 20 is porous.

  The material of the particles 22 (negative electrode material) is a Si-based alloy. This alloy has a Si phase and a compound phase. The main component of the Si phase is Si. This Si phase has a Diamond structure. Elements other than Si may be dissolved in the Si phase. As described above, Si reacts with lithium ions. Since the Si phase contains Si as a main component, the negative electrode 12 including the Si phase can occlude a large amount of lithium ions. The Si phase can increase the storage capacity of the negative electrode 12.

This alloy contains Cr. Cr forms a Si—Cr compound in the compound phase. Specific examples of the compound is CrSi _2. CrSi ₂ can cause a eutectic reaction with the Si phase. In other words, the particles 22 can be formed from a Si—CrSi ₂ eutectic alloy. In this eutectic alloy, the Si phase is extremely fine, and the CrSi ₂ phase is also extremely fine. This compound phase relieves stress caused by expansion during charge and contraction during discharge.

The CrSi ₂ phase has a hexagonal structure. The space group of CrSi ₂ phase belongs to P6 ₂ 22. This phase can suppress the volume change of the Si phase during charge and discharge. In this compound, elements such as Ti can be substituted.

The compound phase may contain Ti together with Cr. In this compound phase, a part of Cr in the Si—CrSi ₂ eutectic alloy is substituted with Ti. In other words, the compound phase includes a Si—Cr—Ti compound. Ti is presumed to increase the lattice constant of the crystal. In the particles 22 having a compound phase having a large lattice constant, it is estimated that lithium ions pass smoothly through the silicide. Further, it is estimated that a compound such as (Cr, Ti) Si ₂ improves the electrical conductivity of the particles 22.

  This alloy contains one or both of Al and Sn. Both of these elements suppress the decrease in initial Coulomb efficiency as described above. Although details are unknown about the suppression of the coulomb efficiency decrease, the following is presumed. Unlike elements belonging to Cr, Ti, and TCF, Al and Sn are unlikely to form silicides combined with Si. Therefore, when X-ray diffraction or EDX analysis is performed, it is understood that Al and Sn can be dissolved in Si or exist alone in the alloy. Both Al and Sn have higher electrical conductivity than Si and silicide, and are considered to improve the electrical conductivity in the negative electrode active material and with the conductive material.

  Furthermore, conventionally, various compounds have been applied to suppress the volume expansion of the Si phase and improve the cycle life. However, in many cases, these compounds are hard and force the expansion and contraction of the Si phase. It is thought that it has the effect | action which suppresses and restricts. Such a forced suppression method provides a physical resistance to the volume change of Si, and as a result, it appears as an internal resistance when the Li storage capacity inherent in the Si phase is stored. Similarly, when the expanded Si phase releases Li, the deformation of the compound still cannot follow the contraction of the Si phase, and the Si phase receives a large physical resistance to return to the original volume, resulting in , Occluded Li cannot be released. This amount of Li that cannot be released is considered to cause a decrease in the initial Coulomb efficiency (discharge amount / charge amount × 100 (%)). Actually, as shown in Non-Patent Document 1, the number of phases other than the Si phase that forcibly suppress the volume change of the Si phase increases, the Si phase decreases, and the initial Coulomb efficiency decreases. On the other hand, Al and / or Sn added in the present invention is remarkably soft and has high ductility as compared with Si and silicide. Therefore, it is considered that resistance to volumetric shrinkage of the Si phase particularly when Li is released, and the present invention is set higher in total addition amount of Cr, Ti, etc. than Patent Document 2, and the amount of Si phase generated is reduced. Despite the small number, the decrease in the initial coulomb efficiency is considered to be small. It is presumed that such an improvement in electrical conductivity and resistance to resistance to volume shrinkage of the Si phase is a factor for suppressing a decrease in initial Coulomb efficiency due to the addition of Al and / or Sn in the present invention.

  There are also proposals to use relatively soft compounds such as Cu-based silicides and SnCu-based compounds, but Al and Sn have much lower hardness than these compounds. Furthermore, although Al and Sn are not as much as Si, as can be seen from the fact that they themselves can occlude Li, the resistance when Li moves inside the phase is much lower than the above compounds. This is also a factor that enables smooth charge and discharge, and is considered to contribute to the improvement of the initial Coulomb efficiency of the alloy of the present invention.

  Furthermore, since Al and Sn are excellent in ductility, it is considered that they also have a function of suppressing the decay of the negative electrode active material accompanying Li occlusion / release, and are presumed to be a factor of excellent cycle life. .

The alloy may contain Zr, Hf, V, Nb, Ta, Mo, W, Mn, Fe, Co, Ni or Cu. The alloy may contain two or more of these elements. These elements can replace Cr in the CrSi ₂ phase. It is presumed that the CrSi ₂ phase is refined by this substitution. The refined CrSi ₂ phase relieves stress caused by expansion during charge and contraction during discharge. This battery 2 is excellent in cycle life.

Zr, Hf, V, Nb, Ta, Mo, W, Mn, Fe, Co, Ni, and Cu are elements belonging to TCF. These elements form silicides in the alloy. These elements suppress the expansion of the negative electrode due to repeated charge and discharge. The total content of TCF is obtained by the following mathematical formula (I).
TCF% = Zr% + Hf% + V% + Nb% + Ta% + Mo% + W% + Mn% + Fe% + Co% + Ni% / 2 + Cu% / 3 (I)
Ni has the ability to suppress expansion of the negative electrode is about ½ that of other elements. Therefore, in the above formula (I), Ni% is divided by 2. Cu has the ability to suppress expansion of the negative electrode to about 1/3 of other elements. Therefore, in the above formula (I), Cu% is divided by 3. In this specification, “%” represents an atomic composition percentage (at.%) Unless otherwise specified.

  The total content of TCF is preferably less than 10%. A negative electrode having an alloy having a total content of less than 10% is excellent in cycle life. In this respect, the total content is preferably less than 5% and particularly preferably less than 2%. This total content may be zero.

  The alloy may contain C, B, P, Ag, Zn, In, Ga, Ge, Pb, Bi, S, or Se. The alloy may contain two or more of these elements. An alloy containing these elements excessively has poor charge / discharge characteristics. These elements are added as long as the charge / discharge characteristics are not significantly adversely affected.

C, B, P, Ag, Zn, In, Ga, Ge, Pb, Bi, S, and Se are elements belonging to TNF. These elements are in any of the following states (a) to (c) in the alloy.
(A) Elements belonging to TNF are dissolved in the Si phase.
(B) An element belonging to TNF forms a single phase (solid solution phase of the element).
(C) Elements belonging to TNF form compounds with elements other than Si.
The total content of TNF is obtained by the following mathematical formula (II).
TNF% = C% + B% + P% + Ag% + Zn% + In% + Ga% + Ge% + Pb% +
Bi% + S% + Se% (II)

  The total content of TNF is preferably 5% or less. A negative electrode having an alloy having a total content of 5% or less is excellent in cycle life. In this respect, the total content is preferably less than 3%, particularly preferably less than 1%. This total content may be zero.

  Alloys are Cr, Al, Sn, Ti, Zr, Hf, V, Nb, Ta, Mo, W, Mn, Fe, Co, Ni, Cu, C, B, P, Ag, Zn, In, Ga, Ge And two or more elements selected from the group consisting of Pb, Bi, S and Se. The balance of this alloy is Si and inevitable impurities.

In this specification, the ratio P1 (%) is calculated by the following mathematical formula.
P1 = Cr% + Ti% + Al% + Sn% + TCF% + TNF%
The ratio P1 is preferably more than 25% and 40% or less. In the negative electrode in which the ratio P1 exceeds 25%, expansion due to repeated charge / discharge is suppressed. In this respect, the ratio P1 is more preferably greater than 27% and particularly preferably greater than 30%. The battery 2 having the negative electrode 12 with the ratio P1 of 40% or less is excellent in initial Coulomb efficiency. In this respect, the ratio P1 is more preferably less than 38%, and particularly preferably less than 35%.

  The total content of Cr and Ti in the alloy is preferably 0.05% or more and 30% or less. In an alloy having a total content of 0.05% or more, a Si phase having a small crystallite size can be obtained. In this respect, the total content is particularly preferably equal to or greater than 12%. In an alloy having a total content of 30% or less, a compound phase having a small crystallite size can be obtained. In this respect, the total content is particularly preferably equal to or less than 25%.

In the present specification, the ratio R1 is calculated by the following mathematical formula.
R1 = Cr% / (Cr% + Ti% + Al% + Sn% + TCF% + TNF%)
The ratio R1 is preferably 0.05 or more. An alloy having a ratio R1 of 0.05 or more has a fine structure. The negative electrode 12 made of this alloy has a long cycle life. In this respect, the ratio R1 is more preferably greater than 0.10 and particularly preferably greater than 0.15. As described above, in the structure in which a part of Cr is replaced with Ti, the lattice constant of the crystal is large. In this respect, the ratio R1 is preferably less than 0.90 and particularly preferably less than 0.80.

In the present specification, the ratio R2 is calculated by the following mathematical formula.
R2 = (Al% + Sn%) / (Cr% + Ti% + Al% + Sn% + TCF% + TNF%)
The ratio R2 is preferably 0.002 or more and 0.400 or less. A battery including the negative electrode 12 having the ratio R2 of 0.002 or more is excellent in initial Coulomb efficiency. In this respect, the ratio R2 is more preferably greater than 0.010, and particularly preferably greater than 0.100. An alloy having a ratio R2 of 0.400 or less can have a microstructure. In this respect, the ratio R2 is more preferably less than 0.350, and particularly preferably less than 0.300.

  The total content of Al and Sn in the alloy is preferably 0.05% or more and 15% or less. A battery including an alloy having a total content of 0.05% or more is excellent in initial Coulomb efficiency. In this respect, the total content is particularly preferably equal to or greater than 2%. An alloy having a total content of 15% or less can have a microstructure. In this respect, the total content is particularly preferably equal to or less than 10%.

In this specification, the ratio P2 (%) is calculated by the following mathematical formula.
P2 = 4.8 × (Cr% + Ti% + TCF%) + (Al% + Sn% + TNF%)
The ratio P2 is a parameter that correlates with the discharge capacity, and the discharge capacity can be predicted from the experimental results described later. By defining the upper limit of this equation, a sufficient discharge capacity can be ensured. The ratio P2 is preferably 135% or less. The negative electrode having an alloy having a ratio P2 of 135% or less has a large discharge capacity. In this respect, the ratio P2 is more preferably less than 130, and particularly preferably less than 125. The ratio P2 is preferably 100% or more.

  The particles 22 (powder) can be manufactured by a single roll cooling method, a gas atomizing method, a disk atomizing method, or the like. In order to obtain particles 22 having a small size, it is necessary to quench the molten metal (molten raw material). The cooling rate is preferably 100 ° C./s or more.

  In the single roll cooling method, a raw material is put into a quartz tube having pores at the bottom. This raw material is heated and melted by a high frequency induction furnace in an argon gas atmosphere. The raw material flowing out from the pores is dropped on the surface of the copper roll and cooled to obtain a ribbon. This ribbon is put into a pot (container) together with a ball (hard sphere). Examples of the ball material include zirconia, SUS304, and SUJ2. Examples of the pot material include zirconia, SUS304, and SUJ2. The pot is filled with argon gas and the pot is sealed. The ribbon is pulverized by milling to obtain particles 22. Examples of milling include a ball mill, a bead mill, a planetary ball mill, an attritor, and a vibrating ball mill.

  In the gas atomization method, raw materials are put into a refractory crucible having pores at the bottom. This raw material is heated and melted by a high frequency induction furnace in an argon gas atmosphere. In an argon gas atmosphere, argon gas is injected onto the raw material flowing out from the pores. The raw material is rapidly cooled and solidified to obtain a powder. This powder is put into a pot together with a ball. Examples of the ball material include zirconia, SUS304, and SUJ2. Examples of the pot material include zirconia, SUS304, and SUJ2. The pot is filled with argon gas and the pot is sealed. This powder is pulverized by milling to obtain particles 22. Examples of milling include a ball mill, a bead mill, a planetary ball mill, an attritor, and a vibrating ball mill. In this milling step, the structure can be refined and combined with carbon materials, conductive metal powders, oxide powders, and other ceramic powders.

  In the disk atomization method, raw materials are put into a refractory crucible having pores at the bottom. This raw material is heated and melted by a high frequency induction furnace in an argon gas atmosphere. In an argon gas atmosphere, the raw material flowing out from the pores is dropped onto a disk that rotates at high speed. The rotation speed is 40000 rpm to 60000 rpm. The raw material is rapidly cooled by the disk and solidified to obtain a powder. This powder is milled. The milling described above for the gas atomization method can also be employed for disk atomization.

  Hereinafter, the effects of the present invention will be clarified by examples. However, the present invention should not be construed in a limited manner based on the description of the examples.

[Experiment A]
For the purpose of evaluating the influence of Cr, Ti, Al and Sn, an experiment was conducted using an alloy which does not contain an element belonging to TCF and does not contain an element belonging to TNF. In this experiment, a bipolar coin cell was used as a battery.

  First, raw materials having the compositions shown in Table 1 were prepared. Powders were produced from the respective raw materials by the gas atomization method described above. This powder was classified, and a powder having a particle size of 20 μm or less was used as a negative electrode particle. A 10 mass% conductive material (acetylene black), 15 mass% binder (polyimide), and 10 mass% solvent (N-methylpyrrolidone) were mixed with the particles in a mortar to obtain a slurry. This slurry was apply | coated on the copper foil which is a collector. This slurry was dried under reduced pressure using a vacuum dryer. The solvent was evaporated by this drying to obtain an active material layer. The active material layer and the copper foil were pressed with a hand press. This active material layer and copper foil were punched into a shape suitable for a coin-type cell to obtain a negative electrode.

As an electrolytic solution, a mixed solvent of ethylene carbonate and dimethoxyethane was prepared. The mass ratio of both was 5: 5. Furthermore, lithium hexafluorophosphate (LiPF ₆ ) was prepared as an electrolyte. The concentration of this electrolyte is 1 mol per liter of the electrolyte. This electrolyte was dissolved in the electrolytic solution.

  A separator and a positive electrode having a shape suitable for a coin-type cell were prepared. This positive electrode is made of lithium. The separator was immersed in the electrolytic solution under reduced pressure and allowed to stand for 5 hours to fully infiltrate the separator with the electrolytic solution.

  A negative electrode, a separator and a positive electrode were incorporated in the tank. The tank was filled with an electrolytic solution to obtain a coin-type cell.

  In Table 1 below, no. 1-11 is the composition of the negative electrode material according to the example of the present invention. 12-27 is the composition of the negative electrode material according to the comparative example.

  In the coin-type cell, charging was performed under the conditions that the temperature was 25 ° C. and the current value was 1/10 C until the potential difference between the positive electrode and the negative electrode became 0V. Thereafter, discharging was performed until the potential difference reached 2V. This charge and discharge was repeated 50 cycles. The initial discharge capacity X and the discharge capacity Y after 50 cycles of charging and discharging were measured. The ratio (maintenance rate) of the discharge capacity Y to the discharge capacity X was calculated. The discharge capacity X and the maintenance rate are shown in Table 2 below.

  The initial charge capacity and the initial discharge capacity were measured. The ratio of the initial discharge capacity to the initial charge capacity (initial coulomb efficiency) was calculated. The results are shown in Table 2 below.

  The thickness of the negative electrode active material layer and the thickness of the negative electrode active material layer after 50 cycles of charge and discharge were measured. The ratio of the thickness after charging / discharging to the initial thickness (negative electrode expansion coefficient) was calculated. The results are shown in Table 2 below.

  The cell according to Comparative Example 12 has a large negative electrode expansion coefficient because the value of the ratio P1 is small. The cell according to Comparative Example 13 is inferior in discharge capacity and inferior in initial Coulomb efficiency since the values of the ratio P1 and the ratio P2 are large. The cell according to Comparative Example 14 is inferior in capacity maintenance rate because the value of the ratio R1 is small. The cells according to Comparative Examples 15 and 16 are inferior in initial Coulomb efficiency because the value of the ratio R2 is small. The cell according to Comparative Example 17 is inferior in capacity maintenance rate because the value of the ratio R2 is large. The cell according to Comparative Example 18 is inferior in discharge capacity because the value of the ratio P2 is large. The cell according to Comparative Example 19 is inferior in negative electrode expansion coefficient because the value of the ratio P1 is small. The cell according to Comparative Example 20 is inferior in discharge capacity and inferior in initial Coulomb efficiency since the values of ratio P1 and ratio P2 are large. The cell according to Comparative Example 21 is inferior in capacity maintenance rate because the value of the ratio R1 is small. The cells according to Comparative Examples 22 and 23 are inferior in initial Coulomb efficiency because the value of the ratio R2 is small. The cell according to Comparative Example 24 is inferior in capacity maintenance rate because the value of the ratio R2 is large. The cell according to Comparative Example 25 is inferior in discharge capacity because the ratio P2 is large. The cells according to Comparative Examples 26 and 27 are inferior in capacity maintenance rate because the value of the ratio R1 is small.

[Experiment B]
Experiments were performed using an element belonging to TCF or an alloy containing an element belonging to TNF. In this experiment, as in Experiment A, a bipolar coin-type cell was used.

  First, raw materials having the compositions shown in Tables 3 and 4 were prepared. Powders were produced from the respective raw materials by the gas atomization method described above. This powder was classified to obtain a powder having a particle size of 106 μm or less. This powder was put into a metal container together with a hard sphere made of chrome steel, mounted on a planetary ball mill apparatus, and stirred for 30 hours. The obtained powder was used as negative electrode particles. Using these particles, a coin-type cell was obtained in the same manner as in Experiment A.

  In Tables 3 and 4 below, no. 28-62 is the composition of the negative electrode material according to the example of the present invention, and No. 63-72 is the composition of the negative electrode material according to the comparative example.

  Using the coin cell, the discharge capacity, capacity retention rate, initial coulomb efficiency, and negative electrode expansion rate were measured in the same manner as in Experiment A. The results are shown in Tables 5 and 6 below.

  The cell according to Comparative Example 63 is inferior in negative electrode expansion coefficient because the value of the ratio P1 is small. The cell according to Comparative Example 64 has a large value of the ratio P1 and the ratio P2. The cell according to Comparative Example 65 is inferior in capacity maintenance rate because the ratio R1 is small. Since the cell according to Comparative Example 66 has a small ratio R2, the initial Coulomb efficiency is inferior. The cell according to Comparative Example 67 is inferior in the capacity maintenance rate because the value of the ratio R2 is large. The cell according to Comparative Example 68 is inferior in discharge capacity because the value of the ratio P2 is large. The cells according to Comparative Examples 69 and 70 are inferior in capacity retention because the total content of TCF is large. Since the cells according to Comparative Examples 71 and 72 have a large total content of TNF, the capacity retention rate is inferior.

[Experiment C]
[Example 73]
In the same manner as in Example 61 of Experiment B, a powder having a particle size of 106 μm or less was obtained. This powder and natural graphite powder were put into a metal container. The mass mixing ratio of both powders is 97/3. Further, a hard sphere made of chrome steel was put into this container, and it was attached to a planetary ball mill device and stirred for 30 hours. The obtained powder was used as negative electrode particles. Using these particles, a coin-type cell was obtained in the same manner as in Experiment A.

[Example 74]
A coin-type cell of Example 74 was obtained in the same manner as Example 73 except that zinc powder was used instead of natural graphite powder and the powder mass mixing ratio was 80/20.

[Example 75]
A coin-type cell of Example 75 was obtained in the same manner as Example 73 except that SiO ₂ powder was used instead of natural graphite powder and the powder mass mixing ratio was set to 92/8.

  Using the coin cell, the discharge capacity, capacity retention rate, initial coulomb efficiency, and negative electrode expansion rate were measured in the same manner as in Experiment A. In the cell according to Example 73, the discharge capacity was 640 mAh / g, the capacity retention rate was 96.2%, the initial Coulomb efficiency was 84.2%, and the negative electrode expansion rate was 142%. In the cell according to Example 74, the discharge capacity was 570 mAh / g, the capacity retention rate was 93.0%, the initial Coulomb efficiency was 85.0%, and the negative electrode expansion rate was 150%. Furthermore, in the cell according to Example 75, the discharge capacity was 620 mAh / g, the capacity retention rate was 94.5%, the initial Coulomb efficiency was 81.0%, and the negative electrode expansion coefficient was 138%. It was. The cells according to Examples 73 to 75 are excellent in various performances.

[Discussion]
From the results of Experiments AC, the superiority of the present invention is clear.

  The negative electrode described above can be applied not only to a lithium ion secondary battery but also to an electricity storage device such as an all solid lithium ion secondary battery or a hybrid capacitor.

2 ... Lithium ion secondary battery 6 ... Electrolyte solution 8 ... Separator 10 ... Positive electrode 12 ... Negative electrode 18 ... Current collector 20 ... Active material layer 22 ... Particle

The method for producing a negative electrode powder for an electricity storage device according to the present invention comprises:
A process for obtaining molten metal from the raw material adjusted to have the alloy composition as the negative electrode material described above
as well as
A step of cooling the molten metal at a rate of 100 ° C./s or more.
including.

According to another aspect, the method for producing a negative electrode powder for an electricity storage device according to the present invention comprises:
A step of charging at least the powder made of the negative electrode material and the hard sphere into the container.
as well as
A step of agitating at least the powder and the hard sphere in a container and pulverizing the powder
including.

Claims (5)

Made of Si alloy,
The alloy is Cr, Al, Sn, Ti, Zr, Hf, V, Nb, Ta, Mo, W, Mn, Fe, Co, Ni, Cu, C, B, P, Ag, Zn, In, Ga, Containing two or more elements selected from the group consisting of Ge, Pb, Bi, S and Se, the balance being Si and inevitable impurities,
When TCF (%) is defined by the following formula (I) and TNF (%) is defined by the following formula (II), the above-mentioned alloy satisfies the following formulas (1) to (6). .
(I) TCF% = Zr% + Hf% + V% + Nb% + Ta% + Mo% + W% + Mn% + Fe% + Co% + Ni% / 2 + Cu% / 3
(II) TNF% = C% + B% + P% + Ag% + Zn% + In% + Ga% + Ge% + Pb% + Bi% + S% + Se%
(1) 25% <Cr% + Ti% + Al% + Sn% + TCF% + TNF% ≦ 40%
(2) 0.05 ≦ Cr% / (Cr% + Ti% + Al% + Sn% + TCF% + TNF%)
(3) 0.002 ≦ (Al% + Sn%) / (Cr% + Ti% + Al% + Sn% + TCF% + TNF%) ≦ 0.400
(4) 4.8 × (Cr% + Ti% + TCF%) + (Al% + Sn% + TNF%) ≦ 135%
(5) TCF% <10%
(6) TNF% ≦ 5%   The negative electrode material according to claim 1, wherein the molten alloy is obtained by cooling and solidifying at a rate of 100 ° C./s or more.   The negative electrode material according to claim 1 or 2, which is obtained by stirring at least the powder of the alloy and the hard sphere in a container and pulverizing the powder. A current collector and a number of particles fixed to the surface of the current collector;
The particles are made of a Si-based alloy,
The alloy is Cr, Al, Sn, Ti, Zr, Hf, V, Nb, Ta, Mo, W, Mn, Fe, Co, Ni, Cu, C, B, P, Ag, Zn, In, Ga, Containing two or more elements selected from the group consisting of Ge, Pb, Bi, S and Se, the balance being Si and inevitable impurities,
When TCF (%) is defined by the following formula (I) and TNF (%) is defined by the following formula (II), the alloy satisfies the following formulas (1) to (6).
(I) TCF% = Zr% + Hf% + V% + Nb% + Ta% + Mo% + W% + Mn% + Fe% + Co% + Ni% / 2 + Cu% / 3
(II) TNF% = C% + B% + P% + Ag% + Zn% + In% + Ga% + Ge% + Pb% + Bi% + S% + Se%
(1) 25% <Cr% + Ti% + Al% + Sn% + TCF% + TNF% ≦ 40%
(2) 0.05 ≦ Cr% / (Cr% + Ti% + Al% + Sn% + TCF% + TNF%)
(3) 0.002 ≦ (Al% + Sn%) / (Cr% + Ti% + Al% + Sn% + TCF% + TNF%) ≦ 0.400
(4) 4.8 × (Cr% + Ti% + TCF%) + (Al% + Sn% + TNF%) ≦ 135%
(5) TCF% <10%
(6) TNF% ≦ 5% A positive electrode and a negative electrode,
The negative electrode comprises a current collector and a large number of particles fixed to the surface of the current collector,
The particles are made of a Si-based alloy,
The alloy is Cr, Al, Sn, Ti, Zr, Hf, V, Nb, Ta, Mo, W, Mn, Fe, Co, Ni, Cu, C, B, P, Ag, Zn, In, Ga, Containing two or more elements selected from the group consisting of Ge, Pb, Bi, S and Se, the balance being Si and inevitable impurities,
An electrical storage device in which, when TCF (%) is defined by the following formula (I) and TNF (%) is defined by the following formula (II), the alloy satisfies the following formulas (1) to (6).
(I) TCF% = Zr% + Hf% + V% + Nb% + Ta% + Mo% + W% + Mn% + Fe% + Co% + Ni% / 2 + Cu% / 3
(II) TNF% = C% + B% + P% + Ag% + Zn% + In% + Ga% + Ge% + Pb% + Bi% + S% + Se%
(1) 25% <Cr% + Ti% + Al% + Sn% + TCF% + TNF% ≦ 40%
(2) 0.05 ≦ Cr% / (Cr% + Ti% + Al% + Sn% + TCF% + TNF%)
(3) 0.002 ≦ (Al% + Sn%) / (Cr% + Ti% + Al% + Sn% + TCF% + TNF%) ≦ 0.400
(4) 4.8 × (Cr% + Ti% + TCF%) + (Al% + Sn% + TNF%) ≦ 135%
(5) TCF% <10%
(6) TNF% ≦ 5%

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