JPWO2016067577A1 - Negative electrode active material, negative electrode and battery - Google Patents

Abstract

Provided is a negative electrode active material excellent in charge / discharge capacity and cycle characteristics. The negative electrode active material (100) includes specific particles (110) and a binding part (120). The specific particles (110) contain a plurality of charge / discharge phases, a constrained phase, and a plurality of ceramic particles. The charge / discharge phase is composed of one or more selected from the group consisting of Si, Sn and Zn, and has an average crystal grain size of 10 to 200 nm. The constrained phase is one or more elements selected from the group consisting of Group 2 elements, transition elements, Group 12 elements, Group 13 elements, and Group 14 elements (however, charge-discharge phase elements and C And a solid solution or an intermetallic compound composed of elements contained in the charge / discharge phase, in which the charge / discharge phase is dispersed. The ceramic particles are dispersed at least in the charge / discharge phase, have an average particle diameter of 0.01 to 0.1 μm, and are contained in an amount of 1 to 10% by mass with respect to the total mass of the specific particles (110).

Description

  The present invention relates to a negative electrode active material, a negative electrode, and a battery.

  In recent years, small electronic devices such as home video cameras, notebook computers, and smartphones have become widespread. With the widespread use of these small electronic devices, higher battery capacity and higher cycle characteristics are required.

  A secondary battery represented by a lithium ion battery uses a graphite-based negative electrode active material. However, a graphite-based negative electrode active material has limitations in increasing capacity and cycle characteristics.

  Therefore, an alloy-based negative electrode active material having a higher capacity than a graphite-based negative electrode active material has attracted attention. As the alloy-based negative electrode active material, silicon (Si) -based negative electrode active material, tin (Sn) -based negative electrode active material, and zinc (Zn) -based negative electrode active material are known. Various studies have been made on the above alloy-based negative electrode active material materials for practical use of a more compact and long-life lithium ion battery.

  However, the alloy-based negative electrode active material repeatedly repeats large expansion and contraction during charging and discharging. Therefore, the capacity of the alloy-based negative electrode active material is likely to deteriorate. The volume expansion / contraction rate of graphite accompanying charging is about 12%. On the other hand, the volume expansion / contraction rate of Si alone or Sn accompanying charging is about 400%. For this reason, when the negative electrode plate of Sn alone is repeatedly charged and discharged, remarkable expansion and contraction occur, and cracks and cracks occur in the negative electrode plate containing the negative electrode active material. In this case, the capacity of the negative electrode is significantly reduced. This is because part of the negative electrode active material is liberated by volume expansion and contraction, and the negative electrode plate loses electronic conductivity.

  Japanese Patent Laying-Open No. 2001-243946 (Patent Document 1) discloses a non-aqueous electrolyte secondary battery that can suppress deterioration of capacity. This battery includes a negative electrode including a negative electrode material made of composite particles in which the whole or part of the periphery of a core particle made of solid phase A is coated with solid phase B. The solid phase A contains at least one of silicon, tin, and zinc as a constituent element. The solid phase B is selected from the group consisting of silicon, tin, and zinc, which are constituent elements of the solid phase A, and the group 2 element, transition element, group 12 element, group 13 element, and group 14 element of the periodic table. A solid solution or an intermetallic compound with at least one element (except for the constituent element of solid phase A and carbon). The composite particles contain ceramics.

  In Patent Document 1, the solid phase A gives a high capacity. Solid phase B suppresses expansion associated with charging of solid phase A. Therefore, collapse of the solid phase A is suppressed and cycle characteristics are improved. Furthermore, since the ceramic suppresses the propagation of cracks, the cycle characteristics are improved.

JP 2001-243946 A

  However, even if the negative electrode active material disclosed in Patent Document 1 is used, the cycle characteristics may be low.

  An object of the present invention is to provide a negative electrode active material excellent in charge / discharge capacity and cycle characteristics.

  The negative electrode active material of this embodiment includes specific particles and a binding part. The specific particles contain a plurality of charge / discharge phases, a constrained phase, and a plurality of ceramic particles. The charge / discharge phase is composed of one or more selected from the group consisting of Si, Sn and Zn, and has an average crystal grain size of 10 to 200 nm. The constrained phase is one or more elements selected from the group consisting of Group 2 elements, transition elements, Group 12 elements, Group 13 elements, and Group 14 elements (however, charge-discharge phase elements and C And a solid solution or an intermetallic compound composed of elements contained in the charge / discharge phase, in which the charge / discharge phase is dispersed. The ceramic particles are dispersed at least in the charge / discharge phase, have an average particle diameter of 0.01 to 0.1 μm, and are contained in an amount of 1 to 10% by mass with respect to the total mass of the specific particles. In X-ray diffraction using CuKα rays, the half-value width of the peak of the constrained phase is 0.30 to 0.65 °. The binding part contains at least one of non-graphitic carbon and a carbon precursor as a main component, and binds specific particles to each other.

  The negative electrode active material according to the present embodiment is excellent in charge / discharge capacity and cycle characteristics.

FIG. 1 is a cross-sectional view of the electrode active material according to the present embodiment.

  The negative electrode active material of this embodiment includes specific particles and a binding part. The specific particles contain a plurality of charge / discharge phases, a constrained phase, and a plurality of ceramic particles. The charge / discharge phase is composed of one or more selected from the group consisting of Si, Sn and Zn, and has an average crystal grain size of 10 to 200 nm. The constrained phase is one or more elements selected from the group consisting of Group 2 elements, transition elements, Group 12 elements, Group 13 elements, and Group 14 elements (however, charge-discharge phase elements and C And a solid solution or an intermetallic compound composed of elements contained in the charge / discharge phase, in which the charge / discharge phase is dispersed. The ceramic particles are dispersed at least in the charge / discharge phase, have an average particle diameter of 0.01 to 0.1 μm, and are contained in an amount of 1 to 10% by mass with respect to the total mass of the specific particles. In X-ray diffraction using CuKα rays, the half-value width of the peak of the constrained phase is 0.30 to 0.65 °. The binding part contains at least one of non-graphitic carbon and a carbon precursor as a main component, and binds specific particles to each other.

  In the negative electrode active material of this embodiment, the charge / discharge phase absorbs and releases metal ions typified by lithium (Li). That is, the charge / discharge phase increases the capacity. Furthermore, a restraint phase suppresses the volume change (expansion and shrinkage | contraction) of the charging / discharging phase accompanying charging. By the way, when the restraint phase has a large amount of strain, the amount of strain further increases by suppressing the volume change (expansion and contraction) of the charge / discharge phase. In this case, a part of the restraint phase is detached early or collapses. As a result, the cycle characteristics of the negative electrode active material are deteriorated.

  In the present embodiment, the amount of strain in the constrained phase is reduced in advance by performing a heat treatment described later. As a result, the diffraction peak half-value width of the constrained phase, which is an index of the strain amount, can be lowered to 0.65 ° or less. Since the strain in the constrained phase is small, the cycle characteristics are enhanced.

  By the way, in order to improve cycle characteristics, it is preferable that the crystal grains of the charge / discharge phase are fine. If the crystal grains are fine, the strength of the charge / discharge phase is increased. In this case, even if charging / discharging is repeated and the charging / discharging phase repeats expansion and contraction, it is possible to suppress part of the charging / discharging phase from being separated or collapsed.

  However, when heat treatment is performed in order to reduce the strain amount of the constrained phase, the crystal grains in the charge / discharge phase tend to be coarse. Therefore, in this embodiment, fine ceramic particles are dispersed at least in the charge / discharge phase. Thereby, even if it is a case where heat processing is performed, the coarsening of a crystal grain is suppressed by ceramic particles. As a result, the average grain size of the crystal grains in the charge / discharge phase is suppressed to 10 to 200 nm, and fine crystal grains can be maintained. Therefore, cycle characteristics are improved.

  Preferably, the binding part is non-graphitic carbon.

  In this case, the capacity maintenance rate of the metal ion secondary battery is further improved.

  Preferably, the ratio of the total mass of the specific particles to the total sum of the total mass of the specific particles and the mass of the binding portion (hereinafter also referred to as the ratio RP) is 91.0 to 99.5%.

  In this case, the capacity maintenance rate of the metal ion secondary battery is further improved.

Ceramic particles are particles mainly composed of ceramics. “Main component” means that the volume fraction of ceramics in the particles is 50% or more. Preferably, the ceramic particles are one or more selected from the group consisting of Al ₂ O ₃ , MgO, ZrO ₂ , Y ₂ O ₃ , TiO ₂ , La ₂ O ₃ and CeO ₂ . The ceramics may be non-oxide ceramics such as CrN, TiN, TaN, AlN, BN, Si ₃ N ₄ , NbN, ZrB, TaB ₂ , MoB ₂ , WC, VC, TiC, SiC, and HfC.

  For example, the charge / discharge phase of the negative electrode active material is made of Si, and the constraining phase is made of one or more metal silicides. The metal silicide may contain Ni and / or Ti.

  The electrode according to the present embodiment includes the negative electrode active material described above. The battery according to the present embodiment includes the above-described negative electrode.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

[Negative electrode active material]
FIG. 1 is a cross-sectional view of a negative electrode active material 100 according to the present embodiment. Referring to FIG. 1, negative electrode active material 100 includes specific particles 110 and binding portions 120.

[Specific particles]
The specific particle 110 can reversibly absorb and release a metal ion typified by Li. The specific particles 110 contain a plurality of charge / discharge phases, a constrained phase, and a plurality of ceramic particles.

[Charge / discharge phase]
The charge / discharge phase is composed of one or more selected from the group consisting of silicon (Si), tin (Sn), and zinc (Zn). These elements absorb and release metal ions. That is, the charge / discharge phase increases the charge / discharge capacity of the negative electrode active material.

  The average crystal grain size of the charge / discharge phase crystal grains is 10 to 200 nm. In this embodiment, the charge / discharge phase crystal grains are fine. If the average crystal grain size is 200 nm or less, the diffusion distance of metal ions in the charge / discharge phase is short, and stress concentration associated with absorption and release of metal ions is reduced. In this case, even if the charge / discharge phase repeatedly expands and contracts with charge / discharge, the charge / discharge phase is prevented from being partially detached or collapsed. A preferable upper limit of the average crystal grain size is 100 nm, more preferably 80 nm, and further preferably 50 nm.

  The average crystal grain size of the charge / discharge phase crystal grains is measured by the following method. A sample for microstructural observation is prepared from specific particles. The prepared sample is observed with a transmission electron microscope (TEM), and the average crystal grain size is determined.

[Restricted Phase]
The plurality of charge / discharge phases described above are dispersed in the constraining phase. In other words, the constraining phase surrounds the charge / discharge phase. As described above, the charge / discharge phase repeats expansion and contraction. The constraining phase surrounds and constrains the charge / discharge phase, and suppresses volume changes (expansion and contraction) of the charge / discharge phase. Therefore, it is suppressed that a part of charging / discharging phase leaves | separates or collapses by the rapid volume change of a charging / discharging phase. As a result, the cycle characteristics of the negative electrode active material are enhanced.

  The constrained phase is one or more elements selected from the group consisting of Group 2 elements, transition elements, Group 12 elements, Group 13 elements and Group 14 elements in the periodic table (however, the charge / discharge phase) And a solid solution or an intermetallic compound consisting of elements contained in the charge / discharge phase. When the charge / discharge phase is a Si phase made of Si, the constraining phase is, for example, a metal silicide phase. The metal silicide phase contains, for example, Si, Ti, and Ni.

  In X-ray diffraction using CuKα rays, the half width of the diffraction peak of the constrained phase is 0.30 to 0.65 °.

  The constraining phase suppresses the volume change (expansion and contraction) of the charge / discharge phase. At this time, the restraint phase receives an external force from the charge / discharge phase. For this reason, strain is accumulated in the constraining phase with charge and discharge.

  If the amount of strain is large in the constrained phase before charge / discharge, strain is further added along with charge / discharge. As a result, a part of the restraint phase is disengaged or collapses. In this case, the cycle characteristics (capacity maintenance ratio) of the negative electrode active material are lowered. Therefore, in the constrained phase before charging / discharging, it is preferable that the amount of strain is small.

  The half width of the diffraction peak of the constrained phase is an index of the amount of strain in the constrained phase. The smaller the half width, the smaller the amount of strain in the constrained phase. If the half width exceeds 0.65 °, the amount of strain in the constrained phase is too large. In this case, the cycle characteristics of the negative electrode active material are low.

  If the half width of the constrained phase is 0.65 ° or less, the amount of strain in the constrained phase is sufficiently small. Therefore, the negative electrode active material has excellent cycle characteristics. The upper limit with preferable half value width is 0.50 degree, More preferably, it is 0.35 degree.

  When considering only the restraint phase, the lower limit of the half-value width is not particularly limited. The strain amount of the constrained phase is adjusted by a heat treatment described later. If the heat treatment temperature is raised, the half width can be lowered. However, if the heat treatment temperature is too high, the charge and discharge phase crystal grains become coarse. In this case, as described above, the cycle characteristics deteriorate. The lower limit of the half width in the range in which the average crystal grains of the charge / discharge phase can be maintained at 10 to 200 nm is 0.30 °. Therefore, the half width of the constrained phase is 0.30 to 0.65 °.

  The half width of the constrained phase is measured by the following method. X-ray diffraction is performed on the constrained phase of the negative electrode active material. In X-ray diffraction, CuKα rays (wavelength is 1.5418 mm) are used under the conditions of 30 kV and 100 mA. Based on the peak top method, the diffraction angle at the height at which the half height of the diffraction peak height is obtained is measured as the half width. Further, the half width derived from the X-ray diffractometer is measured using a single crystal of LaB6 (lanthanum hexaboride) (an ideal single crystal having no half width). Correction is performed by subtracting the measured half-value width inherent to the apparatus from the measured half-value width. The corrected value is defined as the half width of the diffraction peak of the constrained phase.

[Ceramic particles]
The plurality of ceramic particles are dispersed in the negative electrode active material. That is, the ceramic particles are dispersed in the charge / discharge phase and the constraining phase. The average particle diameter of the ceramic particles is 0.01 to 0.1 μm and is fine. Hereinafter, ceramic particles having an average particle diameter of 0.01 to 0.1 μm are also referred to as “fine ceramic particles”. The fine ceramic particles have the following action.

  The fine ceramic particles in the charge / discharge phase maintain the average crystal grain size of the crystal grains in the charge / discharge phase as fine as possible. As described above, in this embodiment, the amount of strain in the constrained phase is reduced by performing heat treatment. However, if heat treatment is performed, the crystal grains in the charge / discharge phase tend to be coarse. In this embodiment, the fine ceramic particles dispersed in the charge / discharge phase suppress the coarsening of crystal grains in the charge / discharge phase due to heat treatment. Therefore, the average crystal grain size of the charge / discharge phase is maintained at 10 to 200 nm.

  If the average particle size of the ceramic particles exceeds 0.1 μm, the ceramic particles are too large. In this case, it is difficult to suppress the coarsening of the charge / discharge phase crystal grains, and the average crystal grain size of the crystal grains may exceed 200 nm. Therefore, the upper limit of the average particle size of the ceramic particles is 0.1 μm. A preferable upper limit of the average particle size of the ceramic particles is 0.06 μm. The lower limit of the average particle size of the ceramic particles is not particularly limited. However, considering the production cost, the lower limit of the average particle size of the ceramic particles is 0.01 μm.

  The average particle diameter of the ceramic particles is measured by the following method. Measurement is performed using a laser diffraction / scattering type particle size distribution measuring apparatus (Microtrack FRA manufactured by Nikkiso Co., Ltd.). This measurement is performed after loosening the powder by ultrasonic waves using water as a dispersion solvent. At the time of data analysis, the refractive index of each substance provided by the measuring device manufacturer is input to obtain the particle size distribution.

  The content of ceramic particles in the specific particles is 1 to 10% by mass. If the ceramic particle content is too low, the crystal grains of the charge / discharge phase after the heat treatment become coarse. On the other hand, ceramic particles do not contribute to the charge / discharge capacity. Therefore, if the content of ceramic particles is too high, the charge / discharge capacity decreases. If the content of the ceramic particles is 1 to 10%, a high charge / discharge capacity can be obtained while maintaining fine grains of the charge / discharge phase. A preferable lower limit of the content of the ceramic particles is 2%. A preferable upper limit of the content of ceramic particles is 6%.

  The specific particles 110 may contain impurities in addition to the charge / discharge phase, the constrained phase, and the ceramic particles. The specific particles 110 may further contain other phases or particles.

[Binder]
The negative electrode active material 100 of the present embodiment further includes a binding part 120 that binds the specific particles 110 to each other. The binder 120 is mainly composed of at least one of non-graphitic carbon and a carbon precursor.

  The binding unit 120 binds the specific particles 110 to each other. That is, the binding part 120 is filled between the specific particles 110. The specific particles 110 are bound to each other via the binding part 120.

  The binder 120 is mainly composed of at least one of non-graphitic carbon and a carbon precursor. Here, “main component” means that the volume ratio in the binding portion 120 is 50% or more. Preferably, the volume ratio is 80% or more.

[Non-graphitic carbon]
Non-graphitic carbon is at least one of amorphous carbon and turbostratic carbon. Amorphous carbon means carbon having short-range order (on the order of several atoms to tens of atoms) and not having long-range order (on the order of hundreds to thousands of atoms). Turbulent structure carbon means carbon composed of carbon atoms having a turbulent structure parallel to the hexagonal plane direction and no crystallographic regularity in the three-dimensional direction. Turbulent structure carbon is confirmed with a transmission electron microscope (TEM) or the like.

  Non-graphitic carbon is produced by firing a thermoplastic organic material such as a thermoplastic resin. In the present embodiment, the thermoplastic resin is, for example, petroleum pitch, coal pitch, synthetic thermoplastic resin, natural thermoplastic resin, and a mixture thereof. A preferred thermoplastic resin is pitch powder. The pitch powder is melted and carbonized during the heating process. Therefore, the non-graphitic carbon produced from the pitch powder tends to bind the specific particles 110 to each other. Further, the pitch powder has a small irreversible capacity even when fired at a low temperature.

[Carbon precursor]
The carbon precursor is a material at a stage before the thermoplastic organic material is converted into non-graphitic carbon when the thermoplastic organic material is heated.

  Preferably, the binding part 120 is non-graphitic carbon. Carbon precursors are less conductive, while non-graphitic carbon is more conductive than carbon precursors. Therefore, when the binding part 120 is non-graphitic carbon, the capacity maintenance rate of the metal ion secondary battery is improved.

  The negative electrode active material 100 has a higher capacity retention rate than the negative electrode active material made of only the specific particles 110. The negative electrode active material 100 includes a binding part 120. Therefore, the area of the specific particles 110 that come into contact with the electrolytic solution is reduced, and decomposition of the electrolytic solution is suppressed. Furthermore, the binding part 120 maintains the bonds between the specific particles 110 and maintains the conductivity between the specific particles 110. For the above reasons, the negative electrode active material 100 is considered to have a high capacity retention rate. Since the negative electrode active material 100 of this embodiment contains the specific particle 110 and the binding part 120, it shows a high capacity retention rate despite the high discharge capacity.

  The binder 120 may contain other components other than non-graphitic carbon and a carbon precursor. The binder 120 may contain, for example, graphite particles, conductive carbonaceous fine particles, tin particles, and the like.

[Mass ratio of specific particles to binding part]
Preferably, the ratio RP of the total mass of the specific particles 110 to the total sum of the total mass of the specific particles 110 and the mass of the binding portion 120 is 91.0 to 99.5%.

  When the ratio RP is less than 91.0%, the discharge capacity at the first charge is reduced. This is probably because the ratio of the specific particles 110 in the negative electrode active material 100 is too small. On the other hand, if the ratio RP exceeds 99.5%, the binding by the binding portion 120 becomes low. In this case, since it becomes difficult to maintain the conductivity between the specific particles 110, the capacity maintenance rate of the negative electrode active material 100 is lowered. Furthermore, since the ratio of the binding part 120 is small, the contact area between the specific particles 110 and the electrolytic solution is increased, and it is difficult to suppress decomposition of the electrolytic solution. Therefore, the capacity retention rate of the negative electrode active material 100 is further reduced. Therefore, the preferred ratio RP is 91.0-99.5%. The minimum with preferable ratio RP is 95.0%, More preferably, it is 96.0%. The upper limit with preferable ratio RP is 98.5%, More preferably, it is 98.0%.

[Negative electrode and battery]
Preferably, the negative electrode of the present embodiment is used for a nonaqueous electrolyte secondary battery. The “non-aqueous electrolyte secondary battery” referred to in this specification is a metal ion secondary battery such as a lithium ion secondary battery, a sodium ion secondary battery, a magnesium ion secondary battery, or a calcium ion secondary battery.

  The battery of this embodiment is a nonaqueous electrolyte secondary battery. The battery includes the above-described negative electrode. A battery is provided with the negative electrode of this embodiment, a positive electrode, a separator, and electrolyte solution or electrolyte, for example.

  The shape of the battery may be a cylindrical shape, a square shape, a coin shape, a sheet shape, or the like. The battery of this embodiment may be a battery using a solid electrolyte such as a polymer battery.

[Positive electrode]
The positive electrode is, for example, a transition metal chalcogenide, vanadium oxide and its lithium (Li) compound, niobium oxide and its lithium compound, a conjugated polymer using an organic conductive material, a sheprel phase compound, activated carbon, activated carbon fiber, etc. is there.

[Electrolyte]
The electrolytic solution is generally a non-aqueous electrolytic solution in which a lithium salt as a supporting electrolyte is dissolved in an organic solvent. Examples of the lithium salt include LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAsF ₆ , LiB (C ₆ H ₅ ), LiCF ₃ SO ₃ , LiCH ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , Li (CF ₂ SO ₂ ) ₂ , LiCl, LiBr, LiI and the like. These may be used alone or in combination. The organic solvent is preferably a carbonic acid ester such as propylene carbonate, ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate. However, various other organic solvents including carboxylic acid esters and ethers can also be used. These organic solvents may be used alone or in combination.

[Separator]
The separator is installed between the positive electrode and the negative electrode. The separator serves as an insulator. Further, the separator greatly contributes to the retention of the electrolyte. The battery of this embodiment may be provided with a known separator. The separator is, for example, a polyolefin material such as polypropylene, polyethylene, a mixed cloth of both, or a porous body such as a glass filter.

[Production method]
An example of the manufacturing method of the negative electrode active material 100 of this embodiment is demonstrated. The manufacturing method of the negative electrode active material 100 includes a preparation process, a mechanical grinding process (hereinafter referred to as MG process) process, a mixing process, and a heat treatment process.

[Preparation process]
In the preparation step, a raw material containing a charge / discharge phase and a constraining phase is prepared. First, one or more elements selected from the group consisting of Si, Sn and Zn, and a group consisting of Group 2 elements, transition elements, Group 12 elements, Group 13 elements and Group 14 elements are selected. The raw material containing the 1 or more types of element (However, the element and C of a charge / discharge phase are excluded) is prepared. At this time, the blending of these elements is adjusted so that a charge / discharge phase and a constrained phase are formed. For example, when producing a negative electrode active material containing a Si phase as a charge / discharge phase and a metal silicide phase as a constraining phase, the composition of these elements is adjusted using Si, Ni, Ti, etc. as raw materials. .

  The prepared raw material is melted to produce a molten metal. The dissolution method is not particularly limited. Examples of the melting method include arc melting, high-frequency heating melting, resistance heating melting, and the like.

  Next, the molten metal is cooled to produce an ingot or slab. The cooling method is not particularly limited. The cooling method is, for example, a strip casting method (SC method). In the strip casting method, molten metal is poured onto a rotating water-cooled roll, and the molten metal is rapidly solidified. In this case, a flaky cast piece is produced. The ingot may be manufactured by casting a molten metal in a mold.

  The raw material (ingot or slab) is pulverized to produce raw materials. For example, the raw material is cut or pulverized using a hammer mill or the like to obtain a coarse powder of 100 μm or less. Further, the coarse powder is pulverized using a ball mill, an attritor, a disk mill, a jet mill, a pin mill, or the like to adjust the size (particle size) of the raw material (powder particles). The average particle diameter of the raw material is not particularly limited. The average particle diameter of the raw material is, for example, 25 to 30 μm. The pulverization of the coarse powder is preferably performed in an inert gas atmosphere or a dry atmosphere in order to suppress oxidation.

[MG treatment process]
The raw material and fine ceramic particles are mixed to produce a mixed powder. MG treatment is performed on the mixed powder. In the MG processing, for example, a ball mill is used. In the MG treatment, graphite, stearic acid, or PVP (polyvinylpyrrolidone) may be added to the mixed powder. In this case, it can suppress that the specific particle 110 produced | generated by MG process adheres to the inner wall of a ball mill. The specific particles 110 including the charge / discharge phase having fine crystal grains are manufactured by the MG treatment. The average particle diameter of the specific particles 110 is, for example, 5 to 200 μm.

  The specific particles 110 of the present embodiment can be manufactured by the above preparation process and MG treatment process.

[Mixing process]
In the mixing step, the thermoplastic organic powder is dissolved in an organic solvent, and the specific particles 110 obtained in the MG treatment step are added thereto to form a mixed powder. The ratio RP in the negative electrode active material 100 is set to 91.0% to 99.5%. For this purpose, the amount of the thermoplastic organic powder to be mixed is preferably 0.1% by mass to 16.5% by mass with respect to the total amount of the specific particles 110 and the thermoplastic organic powder.

[Heat treatment process]
As described above, the negative electrode active material includes a charge / discharge phase having fine crystal grains, a constrained phase, and ceramic particles. However, many strains are introduced into the constrained phase by the MG treatment. Therefore, heat treatment is performed on the negative electrode active material to reduce the strain amount of the constrained phase. Further, heat treatment is performed to convert the thermoplastic organic powder into at least one of non-graphitic carbon and carbon precursor, thereby forming a binding part.

  In the heat treatment step, the mixed powder is heat treated at 300 to 1000 ° C. in a non-oxidizing atmosphere (inert gas atmosphere, vacuum atmosphere, etc.). If the heat treatment temperature exceeds 1000 ° C., the strain amount of the constrained phase is reduced, but the crystal grains of the charge / discharge phase are coarsened. However, in the negative electrode active material of this embodiment, by containing 1 to 10% by mass of fine ceramic particles, coarsening of crystal grains in the charge / discharge phase during heat treatment is suppressed. If the heat treatment temperature is 1000 ° C. or lower, the average crystal grain size of the charge / discharge phase can be suppressed to 200 nm or lower. If the heat treatment temperature is less than 300 ° C., the thermoplastic organic powder is not sufficiently softened, and it is difficult to bind the plurality of particles 110 to each other. Furthermore, it is difficult for the thermoplastic organic powder to be converted into at least one of non-graphitic carbon and carbon precursor, and the binding portion is difficult to be formed.

  If heat processing temperature is 300-1000 degreeC, the distortion amount of a constrained phase will be reduced and the half value width of the diffraction peak of a constrained phase will be 0.30-0.65 degree. Furthermore, the thermoplastic organic powder is sufficiently softened to bind the specific particles 110 to each other. Furthermore, the thermoplastic organic powder is converted into at least one of non-graphitic carbon and carbon precursor, and the binding portion 120 is formed. As a result, the above-described electrode active material is obtained.

  A preferred lower limit of the heat treatment temperature is 350 ° C. The upper limit with preferable heat processing temperature is 950 degreeC, More preferably, it is 900 degreeC, More preferably, it is 850 degreeC. A particularly preferable heat treatment temperature is 400 to 800 ° C.

  A preferable heat treatment time is 3.0 hours to 12 hours. A more preferable lower limit of the heat treatment time is 4.0 hours. A more preferable upper limit of the heat treatment time is 8 hours.

  When the negative electrode active material 100 includes the specific particles 110 and the binding part 120, the negative electrode active material 100 is manufactured by the above process. When the negative electrode active material 100 contains the specific particles 110 and the binding part 120 and other substances, the specific particles 110, the thermoplastic organic powder, and other substances are mixed and heat-treated in the mixing step. Thus, the negative electrode active material 100 is manufactured.

  The negative electrode active material 100 is manufactured by the above manufacturing process.

[Negative Electrode and Battery Manufacturing Method]
An example of the negative electrode manufacturing method according to the present embodiment is as follows. A negative electrode mixture is prepared by mixing a binder with the powder of the specific particles 110 described above. The binder is, for example, a water-insoluble resin such as polyvinylidene fluoride (PVDF), polymethyl methacrylate (PMMA), polytetrafluoroethylene (PTFE), etc., and is insoluble in the solvent used for the non-aqueous electrolyte of the battery. And water-soluble resins such as carboxymethyl cellulose (CMC) and vinyl alcohol (PVA), and styrene butadiene rubber (SBR).

  When giving sufficient electroconductivity to a negative electrode, the electroconductive powder for improving electroconductivity is mixed with a negative electrode mixture. The conductive powder is, for example, a carbon material such as natural graphite, artificial graphite or acetylene black, or a metal such as Ni. A preferred conductive powder is a carbon material. The carbon material can occlude Li ions. Therefore, the carbon material increases not only the conductivity but also the capacity of the negative electrode. The carbon material is further excellent in liquid retention. A preferred carbon material is acetylene black.

  A solvent such as water is added to the negative electrode mixture, and if necessary, the mixture is sufficiently stirred using a homogenizer and glass beads to produce a negative electrode mixture slurry. This slurry is applied to an active material support such as rolled copper foil or electrodeposited copper foil and dried. Thereafter, the dried product is pressed as necessary. A negative electrode is manufactured by the above process.

  A laminate in which a separator and a metal Li thin plate are sequentially laminated on the negative electrode is manufactured. The laminate is placed in a case to manufacture a battery.

  Batteries with respective test numbers shown in Table 1 were produced and their characteristics were evaluated.

<Manufacture of negative electrode active material>
(1) Preparatory process In each test number, the pure raw material of Ni, Ti, and Si was accommodated in the melting crucible made from aluminum titanate. The mass ratio of Ni, Ti and Si was 22.2: 18.0: 59.8.

  After making the inside of the melting crucible an argon (Ar) atmosphere, the raw material in the melting crucible was heated to 1500 ° C. by high frequency induction heating to produce a molten metal. The produced molten metal was brought into contact with a copper water-cooled roll rotating at a peripheral speed of 90 m / min and rapidly solidified to produce a flaky slab (SC method). The cooling rate in the SC method was 500 to 2000 ° C./second. The manufactured slab was pulverized and then classified with a 63 μm sieve to produce a raw material having an average particle size of 25 to 30 μm.

(2) MG treatment process For each test number, a mixture was prepared by mixing raw materials and alumina (Al ₂ O ₃ ) powder. The average particle size of the alumina powder of each test number was 0.06 μm. A mixture of the raw material and the alumina powder in the ratio shown in Table 1 was put into a planetary ball mill (manufactured by Kurimoto Steel Co., Ltd., trade name: BX384E) and subjected to MG treatment to produce specific particles (powder). .

  Specifically, the mixture was put into a mill pot of a planetary ball mill. The material of the mill pot was SUS304, the inner diameter was 100 mm, and the depth was 67 mm. In addition, a plurality of balls were thrown into the mill pot. The material of the ball was SUS304, and the ball diameter was 4 mm. Furthermore, in order to suppress the specific particles from sticking to the ball and the inner wall of the mill pot, graphite was put into the mill pot. The mass ratio of the charged mixture, balls and graphite was mixture: graphite: ball = 35 g: 5 g: 600 g.

  In the MG treatment, the inside of the glove box was a nitrogen atmosphere (oxygen less than 1%). Further, the MG treatment was carried out for 10 hours with the rotational speed of the mill pot set to 500 rpm. After the MG treatment, specific particles were taken out in a glove box in a nitrogen atmosphere (less than 1% oxygen) and classified (63 μm).

(3) Mixing step The specific particles obtained in the MG treatment step and a coal-based pitch powder (softening point 86 ° C., average particle size 20 μm, residual carbon ratio after heating at 1000 ° C. 50%) are mixed with a rocking mixer (Aichi Electric Co., Ltd.) The mixed powder was prepared. The ratio of the mass of the coal-based pitch powder to the sum of the mass of the specific particles and the mass of the coal-based pitch powder is as shown in Table 1 in the mixing ratio of the thermoplastic organic matter powder.

(4) Heat treatment step The above mixture was put into a graphite crucible. Thereafter, the mixed powder was heated at a temperature of 200 ° C. for 1 hour in a nitrogen stream. After heating, the mixture was further heated at the temperature shown in Table 1 for 1 hour to produce a negative electrode active material. In the manufactured negative electrode active material, the ratio RP of the total mass of the specific particles to the total mass of the specific particles and the total mass of the carbon-based material (carbon precursor) derived from the coal-based pitch powder as the binding portion is shown in Table 1. It was as shown in.

(5) Measurement of average grain size of crystal grains in charge / discharge phase after heat treatment About the negative electrode active material after heat treatment, the thickness is increased by gallium (Ga) ions accelerated using a FIB (focused ion beam) apparatus. A foil piece of 200 nm or less was prepared, and a wide-angle annular dark field image was photographed with a transmission electron microscope (TITA80-300 manufactured by FEI) to observe the charge / discharge phase. The shape of the observed charge / discharge phase was a round shape with an aspect ratio of less than 1.5. The vertical and horizontal lengths of the phases observed on the photograph were measured, and the average value was taken as the crystal grain size. The target phase was observed with n = 4, and the average value of the obtained particle sizes was defined as the average crystal particle size. The results are shown in Table 1.

(6) Production of negative electrode 5 parts by mass of styrene butadiene rubber (SBR) (binder), 5 parts by mass of carboxymethyl cellulose (CMC) (binder), with respect to 75 parts by mass of the produced negative electrode active material (powder), 15 parts by mass of acetylene black powder (conductive powder) was mixed to prepare a mixture. Further, distilled water was added to the mixture and kneaded to prepare a negative electrode mixture slurry.

The negative electrode mixture slurry was thinly applied onto an electrolytic copper foil having a thickness of 30 μm using a doctor blade (150 μm) and dried to form a coating film. This coating film was punched out using a punch having a diameter of 13 mm to produce a negative electrode. The coating amount of the negative electrode mixture slurry on the copper foil was ² to 3 mg / cm ² .

(7) Manufacture of coin-type battery A coin-type battery (2016 type) using Li metal foil for the counter electrode (positive electrode) was manufactured. Specifically, a separator having a diameter of 19 mm was disposed on the negative electrode. Further, a metal Li foil having a diameter of 15 mm was disposed on the separator to form a laminate. The laminate was placed in the case. The outer periphery of the case containing the laminate was pressed with a dedicated caulking machine to produce a coin-type battery (2016 type). The supporting electrolyte was LiPF ₆ and LiPF ₆ : ethylene carbonate (EC): ethyl methyl carbonate (EMC): dimethyl carbonate (DMC): vinylene carbonate (VC): fluoroethylene carbonate (FEC) = 16: 48: 23: 16: A mixed solvent at 1: 8 (mass ratio) was used as the electrolytic solution.

<Evaluation of battery characteristics>
(1) Measurement of initial discharge capacity and average charge / discharge efficiency In the manufactured coin-type battery, first, it was doped with a constant current at a current value of 0.15 mA / cm ² until the potential difference became 5.0 mV with respect to the counter electrode. (Equivalent to insertion of lithium ions into the electrode and charging of the lithium ion secondary battery). Thereafter, while maintaining 5.0 mV, the counter electrode was continuously doped at a constant voltage until 10 μA / cm ² , and the doping capacity was measured. Next, dedoping (corresponding to detachment of lithium ions from the electrode and discharging of the lithium ion secondary battery) is performed at a constant current of 0.15 mA / cm ² until the potential difference becomes 1.2 V, and the dedoping capacity is measured. did. The doping capacity and the dedoping capacity at this time correspond to the charging capacity and discharging capacity when this electrode is used as the negative electrode of the lithium ion secondary battery, respectively. Therefore, the measured doping capacity was taken as the charge capacity, and the measured dedoping capacity was taken as the discharge capacity. A cycle consisting of dope and dedope was repeated 40 times under the same conditions (40 cycles).

  From the charge capacity and discharge capacity measured as described above, the charge capacity and discharge capacity per volume of the anode active material material alone were calculated in consideration of the capacity of acetylene black and the capacity of the binder. Since the ratio of dedoping capacity / doping capacity corresponds to the ratio of discharge capacity / charge capacity of the lithium ion secondary battery, this ratio was defined as charge / discharge efficiency. The average value of the charge / discharge efficiency of the second cycle to the 40th cycle was defined as the average charge / discharge efficiency. The results are shown in Table 1. If average charging / discharging efficiency was 95.0% or more, it evaluated that average charging / discharging efficiency was favorable as a practical battery.

(2) Measurement of capacity retention after 40 cycles 40 cycles of the dope and dedope cycles were repeated under the same conditions as described above, and the "discharge capacity at the first cycle of undoping" The ratio of “discharge capacity” was determined. The obtained ratio was defined as the capacity retention rate after 40 cycles, which was used as an index of cycle characteristics. The results are shown in Table 1. If the capacity retention rate after 40 cycles was 60.0% or more, it was evaluated that the cycle characteristics were good as a practical battery.

(3) Evaluation of electrolyte decomposition characteristics (constant potential holding test)
The electrolyte solution was subjected to constant potential electrolysis using the manufactured coin-type battery. The potential difference between the prepared negative electrode and the positive electrode as a counter electrode was kept constant, and the current at each potential difference was measured. The measured potential differences were 2.00V, 1.80V, 1.60V, 1.55V, 1.50V, 1.45V, 1.4V, 1.35V, 1.30V, 1.25V, 1.20V. 1.18V, 1.15V, 1.10V, 1.05V, 1.00V. The current at each potential difference was measured, and the amount of reaction electricity was calculated from the measured current value. The maximum value among the amounts of each reaction electricity was defined as the electrolyte decomposition characteristic (mAh / g). The results are shown in Table 1. When the electrolytic solution decomposition characteristic was 10.0 mAh / g or less, it was evaluated that the electrolytic solution decomposition characteristic was good as a practical battery. In test number 1, when the potential difference was 1.4 V, the amount of reaction electricity was the maximum.

<Evaluation results>
With reference to Table 1, the negative electrode active material of the test numbers 1-12 was in the scope of the present invention. Therefore, it showed excellent average charge / discharge efficiency, capacity retention after 40 cycles, and electrolyte decomposition characteristics. Specifically, the average charge / discharge efficiency was 95.0% or more, the capacity retention rate after 40 cycles was 60.0% or more, and the electrolyte decomposition characteristic was 10.0 mAh / g or less.

  In test numbers 1, 3-6, and 8-12, the ratio RP was within the range of 91.0-99.5%. Therefore, compared with test numbers 2 and 7, the electrolyte decomposition characteristics were low.

  On the other hand, in Test Nos. 13 and 14, no binding portion was formed in the negative electrode active material. Therefore, the electrolytic solution decomposition characteristic exceeded 10.0 mAh / g. This is probably because the contact area between the specific particles and the electrolytic solution is large, and the decomposition of the electrolytic solution could not be suppressed.

  In test number 15, ceramic particles were not contained in the specific particles, and no binding portion was formed. Therefore, the capacity retention rate after 40 cycles was low and less than 60.0%. Furthermore, the electrolytic solution decomposition characteristic exceeded 10.0 mAh / g.

  In Test Nos. 9 and 12, since the heat treatment temperature of the mixed powder was 800 ° C., the binding part became non-graphitic carbon. Therefore, the capacity retention rate after 40 cycles was higher than those of Test Nos. 1-8, 10 and 11. This is probably because the binding part has conductivity.

  The embodiment of the present invention has been described above. However, the above-described embodiment is merely an example for carrying out the present invention. Therefore, the present invention is not limited to the above-described embodiment, and can be implemented by appropriately changing the above-described embodiment without departing from the spirit thereof.

100 Negative electrode active material 110 Specific particle 120 Binding part

Claims (8)

Multiple specific particles,
Containing at least one of non-graphitic carbon and carbon precursor as a main component, and comprising a binding part that binds the specific particles,
The specific particles are:
A plurality of charge and discharge phases comprising at least one selected from the group consisting of Si, Sn and Zn, and having an average crystal grain size of 10 to 200 nm;
One or more elements selected from the group consisting of Group 2 elements, transition elements, Group 12 elements, Group 13 elements and Group 14 elements (however, the charge-discharge element and C are excluded) And a solid solution or an intermetallic compound composed of an element contained in the charge / discharge phase, and a constrained phase in which the charge / discharge phase is dispersed,
Dispersed in the charge / discharge phase, having an average particle diameter of 0.01 to 0.1 μm, containing 1 to 10% by mass of a plurality of ceramic particles with respect to the total mass of the specific particles;
A negative electrode active material in which the half-value width of the peak of the constrained phase is 0.30 to 0.65 ° in X-ray diffraction by CuKα rays. The negative electrode active material according to claim 1,
The negative electrode active material, wherein the binding portion is non-graphitic carbon. The negative electrode active material according to claim 1 or 2, wherein
The negative electrode active material, wherein the ratio of the total mass of the specific particles to the total sum of the total mass of the specific particles and the mass of the binding portion is 91.0% to 99.5%. It is a negative electrode active material of any one of Claims 1-3, Comprising:
The ceramic particles are one or more selected from the group consisting of Al ₂ O ₃ , MgO, ZrO ₂ , Y ₂ O ₃ , TiO ₂ , La ₂ O ₃ and CeO _2. . The negative electrode active material according to any one of claims 1 to 4, wherein
The charge / discharge phase is made of Si,
The constrained phase is a negative electrode active material made of one or more metal silicides. The negative electrode active material according to claim 5,
The metal silicide is a negative electrode active material containing Ni and / or Ti.   The negative electrode containing the negative electrode active material of any one of Claims 1-6.   A battery comprising the negative electrode according to claim 7.

Images