JP2014096289A - Electric power storage device - Google Patents

Abstract

An electric storage device capable of stable output in a high voltage state without causing a sudden voltage change during discharge is provided.
The invention relates to a storage device composed of at least the positive electrode and the negative electrode, positive electrode, the general formula _{LiMn 1-xy Fe x M y} PO 4 (0 <x <1,0 ≦ y <1, M is Nb, And at least one selected from Mg, Al, Ti, Zr, V, Cr, Cu, Co, and Ni), and the negative electrode contains at least Sn and P and / or B. It is set as the electrical storage device characterized by including the negative electrode active material containing the oxide material made into a structural element.
[Selection] Figure 1

Description

  The present invention relates to a power storage device such as a lithium ion secondary battery used for portable electronic devices and electric vehicles, for example.

  In recent years, with the spread of portable electronic devices, there is an increasing demand for higher energy density in power storage devices such as lithium ion secondary batteries. Furthermore, in-vehicle power storage devices such as electric vehicles including a hybrid type are desired to have excellent rapid charge / discharge characteristics and stable cycle characteristics in a low temperature or high temperature environment.

  Generally, a lithium-transition metal composite oxide crystal is used as a positive electrode material for a lithium ion secondary battery, and a carbon material is used as a negative electrode material. These materials function as an electrode active material that reversibly occludes and releases lithium ions by charging and discharging, and a so-called rocking chair type secondary battery that is electrochemically connected by a non-aqueous electrolyte or a solid electrolyte. Configure. These electrode active materials are made into a slurry by adding, for example, a binder or a conductive auxiliary agent, and are used as electrodes by applying the slurry to the surface of a metal foil or the like that serves as a current collector. .

As lithium-transition metal complex oxide crystals used for the positive electrode active material, 4V class LiCoO ₂ , LiNiO ₂ , LiCo _1-x Ni _x O ₂ (0 <x <1), etc. are widely used. Here, the lithium-transition metal complex oxide crystal containing Co is expensive and has a limitation in terms of resources. Moreover, although the lithium-transition metal complex oxide crystal containing Ni is excellent in terms of capacity, it is difficult to ensure sufficient safety because it is thermally unstable. On the other hand, in recent years, since it is advantageous in terms of cost and resources, the olivine type crystal represented by the general formula LiFePO ₄ has attracted attention, and various researches and developments have been advanced (for example, Patent Document 1). reference).

However, LiFePO ₄ has a problem that the potential with respect to metallic lithium is low and is about 3.4V. Therefore, olivine-type crystal represented by the general formula LiMn _1-x Fe x PO ₄ obtained by substituting the Fe site of LiFePO ₄ crystal Mn is the potential for the lithium metal has been proposed as a 4V class cathode material (Patent Documents 2).

JP-A-9-134725 JP 2002-151072 A

However, as shown in FIG. 3A, the positive electrode using the positive electrode active material containing the LiMn _1-x Fe _x PO ₄ crystal has two stages of potentials of 4.0 V and 3.5 V with respect to metallic lithium. Here, a capacity corresponding to discharge at a potential of 3.6 V or higher with respect to metallic lithium is referred to as “high potential discharge capacity”, and a capacity corresponding to discharge at less than 3.6 V is referred to as “low potential discharge capacity”. Further, as shown in FIG. 3B, a negative electrode using a negative electrode active material such as a carbon material or lithium titanate that has been used conventionally has an extremely small irreversible capacity. A cathode active material including LiMn _1-x Fe _x PO ₄ crystal, the case of manufacturing the conventional electricity storage device by combining the negative electrode active material, as shown in FIG. 3 (c), the power storage device is positive in the low potential discharge Since charging / discharging is performed in a form including a capacity, the voltage rapidly decreases during the discharging of the electricity storage device. In addition, as shown in FIG. 3D, the voltage rapidly decreases during the discharge of the power storage device in the second and subsequent cycles as well. As a result, there is a problem that the operation of the apparatus using the electricity storage device is hindered.

  This invention is made | formed in view of the above situations, and it aims at providing the electrical storage device which can obtain a stable and high voltage at the time of discharge.

The electric storage device according to the present invention is an electric storage device comprising at least a positive electrode and the negative electrode, positive electrode, the general formula _{LiMn 1-xy Fe x M y} PO 4 (0 <x <1,0 ≦ y <1, M is Nb , Mg, Al, Ti, Zr, V, Cr, Cu, Co, and Ni), and the negative electrode includes Sn, P, and / or B. A negative electrode active material containing an oxide material containing

As shown in FIG. 1 (a), in the present invention, the positive electrode using the positive electrode active material containing a crystal represented by the general formula _{LiMn 1-xy Fe x M y} PO 4, as described above, "high-potential Discharge capacity ”and“ low potential discharge capacity ”. Further, as shown in FIG. 1B, the negative electrode using the negative electrode active material containing an oxide material containing Sn and P and / or B has a discharge capacity (initial charge / discharge) with respect to the initial charge capacity. Capacity) is low and has an “irreversible capacity” which is the difference between the initial charge capacity and the initial discharge capacity. As shown in FIG. 1 (c), the electricity storage device of the present invention produced so that the initial charge capacity of the positive electrode and the negative electrode is equal, the irreversible capacity of the negative electrode is equal to or higher than the low potential discharge capacity of the positive electrode, That is, the initial charge / discharge efficiency (= “initial discharge capacity” / “initial charge capacity”) of the negative electrode active material is equal to the high potential discharge capacity ratio (= “high potential discharge capacity” / (“high potential discharge capacity”) of the positive electrode active material. + "Low potential discharge capacity"))) or equal to low, the low potential discharge of the positive electrode can be canceled out. Therefore, in the electricity storage device, only the region corresponding to the high potential discharge capacity of the positive electrode can be reversibly charged and discharged, and a stable and high voltage can be obtained during discharge. Moreover, as shown in FIG.1 (d), the electrical storage device of this invention can obtain a stable and high voltage also at the time of the discharge after the 2nd cycle.

  In the electricity storage device of the present invention, the positive electrode active material is preferably made of crystallized glass. Since crystallized glass is excellent in homogeneity, almost no magnetic impurities are generated in the active material particles, and hardly deteriorates even after repeated charge and discharge at a high temperature of 60 ° C. or higher.

Furthermore, in the electricity storage device of the present invention, the crystallized glass is in mol%, Li ₂ O 20-50%, MnO ₂ 20-55%, Fe ₂ O ₃ 1-20% and P ₂ O ₅ 20-50%. It is preferable to contain. According to this configuration, the crystals easily precipitate represented by the general formula _{LiMn 1-xy Fe x M y} PO 4.

Furthermore, in the electricity storage device of the present invention, the crystallized glass is Nb ₂ O ₅ + MgO + Al ₂ O ₃ + TiO ₂ + ZrO ₂ + V ₂ O ₅ + Cr ₂ O ₃ + CuO + CoO + NiO 0.1 to 25% in mol% in addition to the above components. It is preferable to contain. According to this configuration, the lithium ion conductivity of the crystallized glass is likely to increase containing crystals represented by the general formula _{LiMn 1-xy Fe x M y} PO 4.

  In the electricity storage device of the present invention, the positive electrode active material preferably contains an amorphous phase. By containing an amorphous phase, the high-speed charge / discharge performance is easily improved, and the discharge capacity is less likely to be reduced during repeated charge / discharge at a high temperature of 60 ° C. or higher.

In the electricity storage device of the present invention, the oxide material contained in the negative electrode active material preferably contains SnO 45 to 95% and P ₂ O _{5 5 to} 55% in mol%. According to this configuration, since the irreversible capacity of the negative electrode active material becomes an appropriate amount, the low potential discharge capacity of the positive electrode can be canceled out.

  Furthermore, in the electricity storage device of the present invention, the negative electrode active material preferably contains an amorphous phase. According to the said structure, it becomes possible to suppress more effectively precipitation of the transition metal in the negative electrode active material surface.

  Furthermore, in the electricity storage device of the present invention, the negative electrode active material preferably contains an inorganic material including at least one metal selected from Si, Sn, and Al, or an alloy made of these metals. By containing this inorganic material, the discharge capacity per weight of the negative electrode active material can be increased.

  The electricity storage device of the present invention can obtain a stable output in a high voltage state without a sudden voltage change during discharge.

(A) is a conceptual diagram showing a charge-discharge curve of the general formula LiMn _1-xy Fe _x M _y positive electrode using the positive electrode active material containing a crystal represented by PO _4. (B) It is a conceptual diagram which shows the charging / discharging curve of the negative electrode using the negative electrode active material containing the oxide material containing Sn and P and / or B. (C) It is a conceptual diagram which shows the charging / discharging curve of the electrical storage device which combined the positive electrode of (a), and the negative electrode of (b). (D) It is a conceptual diagram which shows the charging / discharging curve after the 2nd cycle of the electrical storage device which combined the positive electrode of (a), and the negative electrode of (b). It is a schematic explanatory drawing of one Embodiment of the electrical storage device of this invention. (A) is a conceptual diagram showing a charge-discharge curve of the general formula LiMn _1-xy Fe _x M _y positive electrode using the positive electrode active material containing a crystal represented by PO _4. (B) It is a conceptual diagram which shows the charging / discharging curve of the negative electrode using the negative electrode active material without an irreversible capacity | capacitance. (C) It is a conceptual diagram which shows the charging / discharging curve of the electrical storage device which combined the positive electrode of (a), and the negative electrode of (b). (D) It is a conceptual diagram which shows the charging / discharging curve after the 2nd cycle of the electrical storage device which combined the positive electrode of (a), and the negative electrode of (b).

  FIG. 2 is a schematic explanatory view of the electricity storage device of the present invention. The electricity storage device 1 includes a positive electrode 2 and a negative electrode 3 that are electrically connected to each other, and a nonaqueous electrolyte 4. In the nonaqueous electrolyte 4, a separator 5 is formed between the positive electrode 2 and the negative electrode 3. The separator 5 has a property of allowing ions such as lithium ions to pass therethrough.

  Hereinafter, each constituent member will be described in detail.

1) Positive electrode The positive electrode includes a positive electrode current collector and a positive electrode active material-containing layer formed on one or both surfaces of the positive electrode current collector. A positive electrode active material content layer contains a positive electrode active material, a conductive support agent, and a binder.

The positive electrode active material, the general formula _{LiMn 1-xy Fe x M y} PO 4 (0 <x <1,0 ≦ y <1, M is Nb, Mg, Al, Ti, Zr, V, Cr, Cu, Co and A crystal represented by at least one selected from Ni).

  The positive electrode active material is preferably made of crystallized glass. Since crystallized glass is excellent in homogeneity, it is difficult for magnetic impurities to be generated in the active material particles, and it is difficult to deteriorate even when repeated charge and discharge at a high temperature of 60 ° C. or higher.

The crystallized glass preferably contains, in mol%, Li ₂ O 20 to 50%, MnO ₂ 20 to 55%, Fe ₂ O ₃ 1 to 20% and P ₂ O ₅ 20 to 50%. The reason for limiting the glass composition as described above will be described below.

Li ₂ O is a main component of _{LiMn 1-xy Fe x M y} PO 4 crystal. The content of Li ₂ O is 20 to 50%, preferably 25 to 45%. Li ₂ O content is too small, or too _{large, LiMn 1-xy Fe x M} y PO 4 crystal is less likely to precipitate.

MnO ₂ is also a major component of _{LiMn 1-xy Fe x M y} PO 4 crystal. The content of MnO ₂ is preferably 20 to 55%, 25 to 54%, 30 to 52%, particularly 35 to 50%. When the content of MnO ₂ is too _{small, LiMn 1-xy Fe x M} y PO 4 crystal is less likely to precipitate. When the content of MnO ₂ is too large, with _{LiMn 1-xy Fe x M y} PO 4 crystal is less likely to precipitate, MnO ₂ crystals are likely to precipitate unwanted.

Fe ₂ O ₃ is also a major component of _{LiMn 1-xy Fe x M y} PO 4 crystal. The content of Fe ₂ O ₃ is preferably 1 to 20%, 2 to 15%, particularly 3 to 10%. When Fe ₂ content of O ₃ is too _{small, LiMn 1-xy Fe x M} y PO 4 crystal is less likely to precipitate. When Fe ₂ O content of ₃ is too large, with _{LiMn 1-xy Fe x M y} PO 4 crystal is less likely to precipitate, Fe ₂ O ₃ crystals are likely to precipitate unwanted.

P ₂ O ₅ is also a major component of _{LiMn 1-xy Fe x M y} PO 4 crystal. The content of P ₂ O ₅ is 20 to 50%, preferably 25 to 45%. P ₂ content of O ₅ is too small, or too _{large, LiMn 1-xy Fe x M} y PO 4 crystal is less likely to precipitate.

Further in addition to the above _{components, LiMn 1-xy Fe x M} y PO 4 as a component of the crystal, for example, _{Nb 2 O 5, MgO, Al} 2 O 3, TiO 2, ZrO 2, V 2 O 5, Cr 2 O 3 At least one oxide selected from CuO, CoO and NiO may be added. The total content of these oxides is preferably 0.1 to 25%, particularly preferably 0.2 to 10%. According to this configuration, the lithium ion conductivity of the crystallized glass is likely to increase containing crystals represented by the general formula _{LiMn 1-xy Fe x M y} PO 4. When there is too little content of the said component, it will become difficult to acquire said effect. On the other hand, the content of the component is too large, crystallinity of the _{LiMn 1-xy Fe x M y} PO 4 crystals in the crystallized glass may be reduced.

Among these, Nb ₂ O ₅ is an effective component for obtaining a homogeneous glass, and easily forms an amorphous phase in the crystallized glass. The content of Nb ₂ O ₅ is preferably 0.1 to 20%, 0.2 to 10%, and particularly preferably 0.3 to 5%. If the content of Nb ₂ O ₅ is too small, it is difficult to obtain the above effect. On the other hand, when the content of Nb ₂ O ₅ is too large, different crystals such as iron niobate precipitate during crystallization, and the charge / discharge characteristics of the battery tend to deteriorate.

In addition to the above components, as a component for improving glass forming ability, for example, at least one oxidation selected from SiO ₂ , B ₂ O ₃ , GeO ₂ , Ga ₂ O ₃ , Sb ₂ O ₃ and Bi ₂ O _3, for example. Things may be added. The total content of these oxides is preferably 0.1 to 25%, particularly preferably 0.2 to 10%. When there is too little content of the said component, vitrification will become difficult easily. On the other hand, the content of the component is too large, crystallinity of the _{LiMn 1-xy Fe x M y} PO 4 crystals in the crystallized glass may be reduced.

  The high potential discharge capacity ratio of the positive electrode active material is preferably 50% or more, 55% or more, and particularly preferably 60% or more. If the high potential discharge capacity rate is too low, the discharge capacity of the electricity storage device tends to decrease. The high potential discharge capacity rate is the ratio of the high potential discharge capacity to the discharge capacity of the positive electrode active material. The high potential discharge capacity is a discharge capacity when a voltage of 3.6 V or higher is exhibited.

In the crystallized _{glass, LiMn 1-xy Fe x M} y PO 4 crystallinity of the crystal 70 mass% or more, 80 wt% or more, and especially preferably 90 mass% or more. When crystallinity of the _{LiMn 1-xy Fe x M y} PO 4 crystal is too small, the discharge capacity tends to decrease. In addition, although it does not specifically limit about an upper limit, In reality, it is 99 mass% or less, Furthermore, it is 97 mass% or less.

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

    Xc = [Ic / (Ic + Ia)] × 100 (%)

  The positive electrode active material preferably contains an amorphous phase. By containing an amorphous phase on the surface of the active material particles, the diffusion resistance of lithium ions at the interface of the active material particles is reduced, and high-speed charge / discharge characteristics are improved.

  The average particle size of the positive electrode active material is preferably 0.01 to 30 μm, 0.05 to 20 μm, and 0.1 to 10 μm. If the average particle size of the positive electrode active material is too large, lithium ions present in the active material cannot be effectively occluded and released when charged and discharged, and the discharge capacity tends to decrease. On the other hand, if the average particle size of the positive electrode active material is too small, it tends to be difficult to produce a uniform electrode. In addition, since the specific surface area becomes too large and the positive electrode active material powder is difficult to disperse when producing a paste for forming an electrode, a large amount of binder and solvent are required. Furthermore, it is inferior to the applicability of the electrode forming paste, and it becomes difficult to form a positive electrode having a uniform thickness.

  In addition, in this invention, an average particle diameter points out the value computed from the observation image of the electron microscope of a positive electrode. Specifically, 20 positive electrode active material particles are randomly selected from an electron microscope image and calculated from an average value of their particle diameters. In addition, about flat particle | grains, let the average value of a long diameter and a short diameter be a particle diameter.

  Next, the manufacturing method of crystallized glass is demonstrated.

First, the raw material powder is prepared so as to have a glass composition containing Li ₂ O 20 to 50%, MnO ₂ 20 to 55%, Fe ₂ O ₃ 1 to 20% and P ₂ O ₅ 20 to 50% in mol%. Precursor glass, which is a precursor, is obtained from the raw material powder prepared and obtained by a chemical quenching process such as a melt quenching process, a sol-gel process, spraying a solution mist into a flame, or a mechanochemical process. . According to these processes, vitrification is easily promoted, and as a result, generation of unreacted raw materials and magnetic impurities hardly occurs.

Crystallized glass is obtained by heat-treating the obtained precursor glass. The heat treatment of the precursor glass is performed, for example, in an electric furnace capable of controlling the temperature and the atmosphere.
The heat treatment temperature is not particularly limited because it varies depending on the composition of the precursor glass and the desired crystal content, but at least the glass transition temperature, more than the crystallization temperature, specifically, 500 ° C. or more, It is preferable to perform the heat treatment at 550 ° C. or higher. If the heat treatment temperature is lower than the glass transition temperature, the crystal precipitation is insufficient and the discharge capacity may be reduced. On the other hand, the upper limit of the heat treatment temperature is preferably 900 ° C., particularly preferably 850 ° C. If the heat treatment temperature is too high, different crystals are likely to precipitate, and the discharge capacity may be reduced.

  The heat treatment time is appropriately adjusted so that the crystallization of the precursor glass proceeds sufficiently. Specifically, it is preferably 10 to 180 minutes, particularly 20 to 120 minutes.

During the heat treatment, it is preferable to add conductive carbon such as carbon black or an organic compound such as a surfactant to the precursor glass and perform firing in an inert or reducing atmosphere. According to this method, a positive electrode active material having an electron-conductive amorphous coating layer formed on the crystallized glass surface is obtained, so that the electron conductivity on the surface of the positive electrode active material is improved, and good rapidity can be achieved in an electricity storage device. Charge / discharge characteristics can be obtained. The amorphous coating layer also plays a role of suppressing elution of transition metal ions. Since the conductive carbon or organic compounds show a reducing action by baking, the valence of iron in the glass is liable to change into divalent upon _{crystallization, LiMn 1-xy Fe x M} y PO 4 crystal Can be selectively obtained at a high rate.

  As addition amount of electroconductive carbon or an organic compound, it is preferable that it is 0.1-50 mass parts, 1-30 mass parts, especially 1.5-20 mass parts with respect to 100 mass parts of precursor glass. If the amount of conductive carbon or organic compound added is too small, the above effect is difficult to obtain. On the other hand, if the amount of conductive carbon or organic compound added is too large, the potential difference between the positive electrode and the negative electrode in the electricity storage device becomes small, and a desired electromotive force may not be obtained.

  The positive electrode, for example, is obtained by adding a conductive additive and a binder to the positive electrode active material, suspending them in a solvent such as water or N-methylpyrrolidone, and making this slurry into a current collector such as an aluminum foil. It is produced by applying, drying and pressing to form a strip.

  A conductive support agent is a component added in order to achieve rapid charging / discharging. Specific examples include highly conductive carbon black such as acetylene black and ketjen black, graphite, coke and the like. Among them, it is preferable to use highly conductive carbon black that exhibits excellent conductivity when added in a very small amount.

  Examples of the binder include thermoplastic linear polymers such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), fluorine-based rubber, and styrene-butanediene rubber (SBR); thermosetting polyimide, polyamide Thermosetting resins such as imide, polyamide, phenolic resin, epoxy resin, urea resin, melamine resin, unsaturated polyester resin, polyurethane; carboxymethylcellulose (including carboxymethylcellulose salts such as carboxymethylcellulose sodium; the same shall apply hereinafter), hydroxypropylmethylcellulose , Cellulose derivatives such as hydroxypropylcellulose, hydroxyethylcellulose, ethylcellulose and hydroxymethylcellulose, polyvinyl alcohol, polyacrylamide, polyvinylpyrrolidone And water-soluble polymers such as copolymers thereof. Only one kind of these binders may be used, or two or more kinds may be mixed and used.

  The compounding ratio of the positive electrode active material, the conductive auxiliary agent and the binder is preferably in the range of 70 to 95% by mass of the positive electrode active material, 3 to 20% by mass of the conductive auxiliary agent, and 2 to 10% by mass of the binder.

  As the positive electrode current collector, for example, an aluminum foil or an aluminum alloy foil can be used. Examples of the aluminum alloy include alloys containing aluminum and elements such as magnesium, zinc, and silicon.

2) Negative electrode The negative electrode includes a negative electrode current collector and a negative electrode active material-containing layer carried on one or both surfaces of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material and a binder. The negative electrode active material layer may further contain a conductive additive as necessary.

The negative electrode active material includes an oxide material containing Sn and P and / or B. Specifically, the negative electrode active material preferably contains P ₂ O ₅ and / or B ₂ O ₃ in addition to SnO.

  When a negative electrode active material containing SnO is used, it is known that the following reaction occurs in the negative electrode during charge and discharge.

SnO + 2Li ⁺ + 2e ⁻ → Sn + Li ₂ O (1)
Sn + yLi ⁺ + ye ⁻ ← → Li _y Sn (2)

First, during the first charge, a reaction in which SnO accepts electrons and metal Sn is generated occurs irreversibly (formula (1)). Subsequently, the produced metal Sn combines with lithium ions that have moved from the positive electrode through the nonaqueous electrolyte and electrons supplied from the circuit to form a Li _y Sn alloy (formula (2)). As Li _y Sn alloys, Li _2.6 Sn, Li _3.5 Sn, Li _4.4 Sn and the like are known. The reaction occurs as a reversible reaction that proceeds rightward during charging and proceeds leftward during discharging. Thereafter, the charge / discharge reaction of the formula (2) is repeatedly performed.

Here, the charge / discharge reaction of Formula (2) is accompanied by a volume change, but when the negative electrode active material includes an oxide material containing Sn and P and / or B, Sn ^{x +} ions in the oxide material are phosphorous. Since the acid network and / or the boric acid network are included, the volume change of Sn accompanying charge / discharge can be mitigated by the phosphoric acid network and / or the boric acid network. Therefore, it is possible to suppress a decrease in cycle characteristics.

Oxide materials, in mol%, containing SnO 45 to 95% and P ₂ O ₅ 5~55% (Composition A) that, or, in _{mol%, SnO 10~85%, B 2} O 3 3~ 90% and P ₂ O ₅ 0-55% (however, B ₂ O ₃ + P ₂ O ₅ 15% or more) is preferably contained (Composition B). The reason why each composition is limited in this way will be described below.

(Composition A)
SnO is an active material component that serves as a site for occluding and releasing lithium ions. The SnO content is preferably 45 to 95%, 50 to 90%, 55 to 87%, 60 to 85%, 68 to 83%, particularly 71 to 82%. If the SnO content is too small, the discharge capacity per unit mass of the negative electrode active material tends to be small. On the other hand, when the content of SnO is too large, the amorphous component in the negative electrode active material is relatively reduced, so that the volume change associated with insertion and extraction of lithium ions during charge and discharge cannot be reduced, and the discharge capacity May decrease rapidly. In the present invention, the content of SnO is oxidized tin component other than SnO (SnO _2, etc.) also refers to that summed in terms of SnO.

P ₂ O ₅ is a network-forming oxide and includes lithium ion storage and release sites in SnO, and functions as a solid electrolyte to which lithium ions can move. The content of P ₂ O ₅ is preferably ₅ to 55%, 10 to 50%, 12 to 45%, 13 to 40%, 14 to 32, particularly 15 to 29%. If the content of P ₂ O ₅ is too small, the volume change of SnO that accompanies occlusion and release of lithium ions during charge / discharge cannot be alleviated, resulting in structural deterioration, and the discharge capacity tends to decrease during repeated charge / discharge. On the other hand, when the content of P ₂ O ₅ is too large, the water resistance tends to lower. In addition, when a water-based electrode paste is produced, a large amount of heterogeneous crystals (for example, SnHPO ₄ ) that do not contribute to the charge / discharge reaction are formed, and the discharge capacity tends to decrease when the charge / discharge is repeated. Furthermore, it is easy to form a stable crystal (for example, SnP ₂ O ₇ ) together with the Sn atom, and the influence of the coordination bond to the Sn atom by the lone pair of electrons in the chain P ₂ O ₅ becomes stronger. . As a result, since many electrons are required to reduce SnO in the above formula (1), the initial charge / discharge efficiency tends to decrease.

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

(Composition B)
SnO is an active material component that serves as a site for occluding and releasing lithium ions. The SnO content is preferably 10 to 85%, 30 to 83%, 40 to 80%, and particularly preferably 50 to 75%. If the SnO content is too small, the discharge capacity per unit mass of the negative electrode active material tends to be small. On the other hand, when the content of SnO is too large, the amorphous component in the negative electrode active material is relatively reduced, so that the volume change associated with insertion and extraction of lithium ions during charge and discharge cannot be reduced, and the discharge capacity May decrease rapidly.

B ₂ O ₃ is a network-forming oxide that covers the storage and release sites of SnO lithium ions, mitigates volume changes associated with storage and release of lithium ions during charge and discharge, and maintains the structure of the negative electrode active material To play a role. The content of B ₂ O ₃ is preferably ₃ to 90%, 5 to 70%, 7 to 60%, particularly 9 to 55%. If the content of B ₂ O ₃ is too small, the volume change of SnO associated with insertion and extraction of lithium ions during charge / discharge cannot be relaxed, causing structural deterioration, and the cycle characteristics are likely to deteriorate. On the other hand, when the content of B ₂ O ₃ is too large, the influence of the coordinate bond to the Sn atom by the lone electron pair of the oxygen atom present in the boric acid network becomes stronger. As a result, since many electrons are required to reduce SnO during the initial charge, the initial charge / discharge efficiency tends to decrease. In addition, the SnO content is relatively low, and the discharge capacity per unit mass of the negative electrode active material tends to be small.

P ₂ O ₅ is a network-forming oxide, and has a function of comprehensively occluding and releasing SnO lithium ions by forming a composite network by three-dimensionally entwining with a boric acid network. Thereby, it plays the role which relieves the volume change accompanying the occlusion and discharge | release of lithium ion accompanying charging / discharging, and maintains the structure of a negative electrode active material. The content of P ₂ O ₅ is preferably 0 to 55%, 5 to 50%, particularly preferably 10 to 45%. When the content of P ₂ O ₅ is too large, the water resistance tends to lower. In addition, when a water-based electrode paste is produced, a large amount of heterogeneous crystals (for example, SnHPO ₄ ) that do not contribute to the charge / discharge reaction are formed, and the discharge capacity tends to decrease when the charge / discharge is repeated. Moreover, the influence of the coordinate bond to Sn atom by the lone electron pair which the oxygen atom which exists in a phosphate network and a boric acid network has will be in a stronger state. As a result, since many electrons are required to reduce SnO during the initial charge, the initial charge / discharge efficiency tends to decrease. Furthermore, the content of SnO is relatively reduced, and the discharge capacity per unit mass of the negative electrode active material tends to be reduced.

The total amount of B ₂ O ₃ and P ₂ O ₅ is preferably 15% or more, 20% or more, and particularly preferably 30% or more. If the total amount of B ₂ O ₃ and P ₂ O ₅ is too small, the change in volume of SnO that accompanies occlusion and release of lithium ions during charge / discharge cannot be alleviated, resulting in structural deterioration, and cycle characteristics are likely to deteriorate. .

_{Incidentally, SnO / (P 2 O 5} + B 2 O 3) ( molar ratio), 0.8～19,1～18, particularly preferably from 1.2 to 17. If SnO / (P ₂ O ₅ + B ₂ O ₃ ) is too small, Sn atoms in SnO are likely to be affected by the coordination of P ₂ O ₅ and B ₂ O ₃ , and the initial charge / discharge efficiency tends to decrease. is there. On the other hand, if SnO / (P ₂ O ₅ + B ₂ O ₃ ) is too large, the discharge capacity tends to decrease when repeated charge / discharge is performed. This is not sufficiently comprehensive and SnO is less P ₂ O ₅ and B ₂ O ₃ is coordinated to SnO in the oxide, as a result, reduce the volume change SnO accompanying occlusion of lithium ions and releasing This is considered to be because it becomes impossible to cause structural deterioration.

In composition A or composition B, various components can be further added in addition to the above components. For example, MnO, CuO, ZnO, MgO, CaO, Al ₂ O ₃ , SiO ₂ , R ₂ O (R represents at least one selected from Li, Na, K, and Cs) in a total amount of 0 to 50% 0 to 40%, 0 to 20%, 0 to 10%, particularly 0.1 to 7%. When the total amount of these components is too large, it becomes easy to become amorphous, but on the other hand, there is a problem that the phosphate network is easily cleaved. As a result, the volume change of the negative electrode active material accompanying charge / discharge cannot be relaxed, and the cycle characteristics may be deteriorated.

  The negative electrode active material preferably contains an amorphous phase. The presence of the amorphous phase is advantageous from the viewpoint of suppressing the decrease in discharge capacity because the volume change during repeated charge / discharge can be alleviated.

  The degree of crystallinity of the negative electrode active material is preferably 95% or less, 80% or less, 70% or less, 50% or less, 40% or less, particularly 10% or less before charge / discharge reaction. The negative electrode active material may be substantially amorphous. Here, “consisting essentially of amorphous” means that the crystallinity is substantially 0% (specifically, less than 0.1%), and will be described later by powder X-ray diffraction measurement. In which no crystalline diffraction line is detected. In particular, when the negative electrode active material contains SnO in a high proportion, the smaller the crystallinity (the larger the proportion of the amorphous phase), the smaller the volume change during repeated charging / discharging, and the viewpoint of suppressing the decrease in discharge capacity. Is advantageous. The crystallinity is obtained by the same method as that for the positive electrode active material.

  The average particle diameter of the negative electrode active material is preferably 0.01 to 30 μm, 0.05 to 20 μm, and 0.1 to 10 μm. If the average particle size of the negative electrode active material is too large, the negative electrode material can be easily peeled off from the current collector without relaxing the volume change of the negative electrode active material due to insertion and extraction of lithium ions during charge and discharge. There is a tendency for the properties to decrease significantly. On the other hand, if the average particle size of the negative electrode active material is too small, it tends to be difficult to produce a uniform electrode. In addition, since the specific surface area becomes too large and the negative electrode active material powder is difficult to disperse when producing a paste for forming an electrode, a large amount of binder and solvent are required. Furthermore, it is inferior to the applicability of the electrode forming paste, and it becomes difficult to form a negative electrode having a uniform thickness. In addition, an average particle diameter is calculated | required by the method similar to the case of a positive electrode active material.

  Moreover, it is preferable that a negative electrode active material contains the inorganic material containing the alloy which consists of at least 1 sort (s) of metal chosen from Si, Sn, and Al, or those metals. In particular, the inclusion of Si is preferable because the discharge capacity increases.

The initial charge / discharge efficiency of the negative electrode active material is preferably 40 to 90%, 45 to 85%, particularly 50 to 80%. If the initial charge / discharge efficiency is too low, the discharge capacity of the electricity storage device tends to be low. On the other hand, when the initial charge and discharge efficiency is too high, the low-potential discharge capacity tends to remain in the positive electrode active material containing _{LiMn 1-xy Fe x M y} PO 4 crystal.

  For example, the negative electrode is prepared by adding a conductive additive and a binder to a powdered negative electrode active material, and suspending the suspension in, for example, water or an organic solvent such as N-methylpyrrolidone. It is produced by applying to a negative electrode current collector of a metal foil made of a copper alloy, drying and pressing to form a strip.

  As the conductive auxiliary agent, the same material as the positive electrode conductive auxiliary agent can be used.

  The binder is a component that is added to bind materials constituting the negative electrode and prevent the negative electrode active material from being detached from the negative electrode due to a volume change associated with charge and discharge. Can be used. Among these, a thermosetting resin or a water-soluble polymer is preferable from the viewpoint of excellent binding properties, and thermosetting polyimide or carboxymethyl cellulose that is widely used industrially is more preferable. In particular, carboxymethyl cellulose, which is inexpensive and has a low environmental load and does not require an organic solvent when preparing an electrode forming paste, is most preferable. Only one kind of these binders may be used, or two or more kinds may be mixed and used.

  It is preferable that content of each component in a negative electrode is the mass%, and is 55-90% of negative electrode active materials, 2-30% of binders, and 3-20% of conductive support agents. When each component satisfies the range, a negative electrode having a high capacity and excellent cycle characteristics is easily obtained.

  The potential of the negative electrode active material with respect to metallic lithium is preferably 0.05 to 2 V, particularly preferably 0.1 to 1 V. If the potential of the negative electrode active material with respect to metallic lithium is too low, lithium dendrite is likely to precipitate on the negative electrode surface, which may cause an internal short circuit. On the other hand, if the potential of the negative electrode active material with respect to metallic lithium is too high, the potential difference from the positive electrode active material becomes small, and the operating voltage of the electricity storage device tends to be low.

3) Non-aqueous electrolyte The non-aqueous electrolyte includes a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent.

  The non-aqueous solvent is not particularly limited, but propylene carbonate (PC), ethylene carbonate (EC), 1,2-dimethoxyethane (DME), γ-butyrolactone (GBL), tetrahydrofuran (THF), 2 -Methyltetrahydrofuran (2-MeHF), 1,3-dioxolane, sulfolane, acetonitrile (AN), diethyl carbonate (DEC), dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), dipropyl carbonate (DPC), etc. It is done. These nonaqueous solvents may be used alone or in combination of two or more. Of these, propylene carbonate having excellent low-temperature characteristics is preferable.

Examples of the electrolyte salt include LiPF ₆ , LiBF ₄ , Li (CF ₃ SO ₂ ) ₂ N (bistrifluoromethanesulfonylamide lithium; commonly known as LiTFSI), LiCF ₃ SO ₃ (commonly known as LiTFS), and Li (C ₂ F ₅ SO ₂ ). ₂ N (bis pentafluoroethanesulfonyl amide lithium; called _{LiBETI), LiClO 4, LiAsF 6} , LiSbF 6, bisoxalato Lato lithium borate _{(LiB (C 2 O 4)} 2; commonly called LiBOB), difluoro (trifluoro-2 Examples thereof include lithium salts such as oxide-2-trifluoro-methylpropionate (2-)-0,0) lithium borate (LiBF ₂ OCOOC (CF ₃ ) ₃ , commonly known as LiB (HHIB)). These electrolyte salts may be used alone or in combination of two or more. In particular, inexpensive LiPF ₆ and LiBF ₄ are preferable. In general, the electrolyte salt concentration is appropriately adjusted within a range of 1M or more, particularly 3M or less.

The nonaqueous electrolyte may contain additives such as vinylene carbonate (VC), vinylene acetate (VA), vinylene butyrate, vinylene hexanate, vinylene crotonate, catechol carbonate and the like. These additives have a role of forming a protective film (LiCO _x or the like) on the surface of the negative electrode active material. The concentration of the additive is preferably 0.1 to 3 parts by mass, particularly 0.5 to 1 part by mass with respect to 100 parts by mass of the nonaqueous electrolyte.

4) Separator The separator is made of an insulating material, specifically, a porous film or non-woven fabric obtained from a polymer such as polyolefin, cellulose, polyethylene terephthalate, vinylon, a non-woven glass fabric containing fibrous glass, or a fibrous glass. A knitted glass cloth, a film-like glass or the like can be used.

  Hereinafter, examples of the electricity storage device of the present invention will be described in detail, but the present invention is not limited to these examples.

Example 1
(1) Preparation of positive electrode active material Lithium metaphosphate (LiPO ₃ ), lithium carbonate (Li ₂ CO ₃ ), manganese dioxide (MnO ₂ ), ferric oxide (Fe ₂ O ₃ ) and niobium oxide (Nb ₂ O ₅₎ ) Was used as a raw material, and a raw material powder was prepared so as to have the composition shown in Table 1, and was melted at 1250 ° C. for 1 hour in an air atmosphere. Then, molten glass was poured into a pair of forming rolls, and a precursor glass was produced by forming into a film shape while rapidly cooling. The obtained precursor glass was pulverized to obtain a precursor glass powder having an average particle size of 0.5 μm.

Next, with respect to 100 parts by mass of the precursor glass powder, 25.3 polyethylene oxide nonylphenyl ether (HLB value: 13.3 weight average molecular weight: 660), which is a nonionic surfactant, is used as a conductive carbon raw material. Mass parts (corresponding to 15 parts by mass in terms of graphite) and 60 parts by mass of pure water were added, mixed thoroughly, and dried. Then, it crystallized by heat-processing for 30 minutes at 800 degreeC in nitrogen atmosphere, and obtained the crystallized glass powder (positive electrode active material powder) by which the surface was coat | covered with the conductive carbon. When the obtained cathode active material was confirmed by a powder X-ray diffraction pattern, the diffraction line from olivine _{LiMn 1-xy Fe x M y} PO 4 was confirmed.

(2) Production of positive electrode For the positive electrode active material obtained above, ketjen black as a conductive additive, polyvinylidene fluoride as a binder, positive electrode active material: conductive auxiliary agent: binder = 83: 5 : 12 (mass ratio) was weighed and dispersed in N-methylpyrrolidone, and then sufficiently stirred with a rotation / revolution mixer to form a slurry.

Next, the above slurry was coated on a 20 μm-thick aluminum foil as a positive electrode current collector using a doctor blade, dried at 80 ° C. with a dryer, and passed between a pair of rotating rollers. An electrode sheet was obtained by pressing at / cm ² . The electrode sheet was punched to a diameter of 11 mm with an electrode punching machine and dried at 140 ° C. for 6 hours to obtain a circular positive electrode. The charge capacity of the positive electrode at this time was 1.5 mAh.

(3) Production of negative electrode active material Stannous pyrophosphate (Sn ₂ P ₂ O ₇ ) was used as a main raw material, and various other oxides were further added to add 72 mol% of SnO and P ₂ O ₅ 28. The raw material prepared so as to have a composition of mol% was put into a quartz crucible and melted in a nitrogen atmosphere at 950 ° C. for 40 minutes using an electric furnace to vitrify.

  Next, the molten glass was poured out between a pair of molding rollers to form film glass while rapidly cooling. This film-like glass was pulverized using a ball mill to obtain a coarse glass powder having an average particle diameter of 3 to 15 μm. Subsequently, the glass powder with an average particle diameter of 2 μm and a maximum particle diameter of 28 μm was obtained by classifying the glass coarse powder with air.

  When the structure of the obtained glass powder was identified by powder X-ray diffraction measurement, no crystals were detected, and it was found that the glass powder was substantially amorphous.

  Into the glass powder obtained above, Si powder, which is an inorganic material, is mixed at a weight ratio of 1: 1 and charged into a nitrogen-filled container, and the negative electrode active material is mixed by using a ball mill. Obtained.

(4) Production of Negative Electrode For the negative electrode active material obtained above, ketjen black is used as a conductive aid, polyimide is used as a binder, and negative electrode active material: conductive aid: binder = 83: 5: 12 ( (Mass ratio), these were weighed and dispersed in pure water, and then sufficiently stirred with a rotation / revolution mixer to form a slurry.

  Next, using a doctor blade with a gap of 100 to 200 μm, the above slurry was coated on a copper foil with a thickness of 18 μm, which was a negative electrode current collector, dried at 40 to 70 ° C., and then between a pair of rotating rollers. The electrode sheet was obtained by pressing through. The electrode sheet was punched to a diameter of 11 mm with an electrode punching machine and dried at 140 ° C. under reduced pressure for 6 hours to obtain a circular negative electrode. The charging capacity of the negative electrode at this time was 1.5 mAh.

(5) Production of test battery On the lower lid of the coin cell, the positive electrode was placed with the aluminum foil surface facing downward, and a separator made of a glass nonwoven fabric with a diameter of 16 mm, which was dried under reduced pressure at 200 ° C. for 8 hours, Further, the negative electrode was laminated and covered with an upper lid to prepare a CR2032-type test battery. As the electrolytic solution, 1M LiPF ₆ solution / EC: DEC = 1: 1 (EC = ethylene carbonate, DEC = diethyl carbonate) was used. The test battery was assembled in an environment with a dew point temperature of −40 ° C. or lower.

(Example 2)
A test battery was produced in the same manner as in Example 1 except that the positive electrode active material was the material shown in Table 1.

(Example 3)
A test battery was produced in the same manner as in Example 1 except that the positive electrode active material was the material shown in Table 1 and that the negative electrode active material was not mixed with Si powder.

(Comparative Example 1)
A test battery was produced in the same manner as in Example 1 except that the negative electrode active material was graphite.

  The battery obtained above was charged with CC (constant current) from 2 V to 4.5 V (occlusion of lithium ions into the negative electrode active material / release of lithium ions from the positive electrode active material), and in the unit weight of the positive electrode active material The amount of electricity charged (charging capacity) was determined. Next, CC discharge (discharge of lithium ions from the negative electrode active material / occlusion of lithium ions into the positive electrode active material) from 4.5 V to 2 V is performed, and the amount of electricity (discharge capacity) discharged in the unit weight of the positive electrode active material is Asked. Thereafter, charge / discharge was repeated in the same manner, and the charge / discharge capacity was determined. The C rate was 0.1C.

Table 1 shows the positive electrode active material, its high potential discharge capacity ratio, the negative electrode active material, its initial charge / discharge efficiency, and the presence or absence of a rapid voltage change during discharge of the test battery.

As apparent from Table 1, with a negative electrode active material containing an oxide material that cathode active material containing _{LiMn 1-xy Fe x M y} PO 4 crystal, the Sn and P and / or B and constituent element In the batteries of Examples 1 to 3, the initial charge / discharge efficiency of the negative electrode active material was lower than the high-potential discharge capacity rate of the positive electrode active material, so that a sudden voltage change during discharge was not observed and the battery operated stably. Was confirmed.

  On the other hand, in the battery of Comparative Example 1 using the graphite negative electrode active material, the initial charge / discharge efficiency of the negative electrode active material was higher than the high potential discharge capacity ratio of the positive electrode active material, and thus a sudden voltage drop occurred during discharge.

1 Power Storage Device 2 Positive Electrode 3 Negative Electrode 4 Nonaqueous Electrolyte 5 Separator

Claims (8)

A power storage device comprising a positive electrode and a negative electrode, positive electrode, the general formula _{LiMn 1-xy Fe x M y} PO 4 (0 <x <1,0 ≦ y <1, M is Nb, Mg, Al, Ti, Zr , At least one selected from V, Cr, Cu, Co and Ni), and the negative electrode contains an oxide material containing Sn and P and / or B An electricity storage device comprising a negative electrode active material.   The power storage device according to claim 1, wherein the positive electrode active material is made of crystallized glass. The crystallized glass contains, in mol%, Li ₂ O 20-50%, MnO ₂ 20-55%, Fe ₂ O ₃ 1-20% and P ₂ O ₅ 20-50%. Item 3. The electricity storage device according to Item 2. The crystallized glass further contains, in mol%, Nb ₂ O ₅ + MgO + Al ₂ O ₃ + TiO ₂ + ZrO ₂ + V ₂ O ₅ + Cr ₂ O ₃ + CuO + CoO + NiO 0.1 to 25%. Power storage device.   The power storage device according to any one of claims 1 to 4, wherein the positive electrode active material contains an amorphous phase. Oxide material contained in the anode active material, in mole percent, according to any of claims 1 to 5, characterized by containing SnO 45 to 95% and P ₂ O ₅ 5 to 55% Power storage device.   The electricity storage device according to any one of claims 1 to 6, wherein the negative electrode active material contains an amorphous phase.   The negative electrode active material contains at least one kind of metal selected from Si, Sn and Al, or an inorganic material containing an alloy made of these metals. The electricity storage device described.

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