JP6102615B2 - Negative electrode active material and secondary battery using the same - Google Patents

Description

  The present invention relates to a negative electrode active material and a secondary battery using the same.

  Increased power storage demand, such as higher performance of portable devices and increased power consumption, power sources for ships and railways, development and diffusion of electric vehicles and hybrid vehicles, and smart grid applications, etc. High performance is required. An example of such a secondary battery is a lithium secondary battery.

Lithium secondary batteries include, for example, a positive electrode using a lithium transition metal oxide (for example, LiCoO ₂ ) as an electrode active material, a negative electrode using a carbon material or the like as an electrode active material, and organically using a lithium salt as a supporting salt. And a non-aqueous electrolyte solution dissolved in a solvent. In such a lithium secondary battery, lithium ions desorbed from the positive electrode are stored in the negative electrode during charging, and conversely, lithium ions desorbed from the negative electrode are stored in the positive electrode during discharging. That is, the lithium secondary battery is a rocking chair type secondary battery using lithium ions as a carrier.

  As an electrode active material (that is, a negative electrode active material) used for the negative electrode, graphite as a carbon material is known. However, when graphite is used as the negative electrode active material, the voltage when lithium ions are occluded in the graphite is about 0.09 V to 0.2 V with respect to metallic lithium. Therefore, decomposition of the non-aqueous electrolyte proceeds due to such a low voltage, and the cycle characteristics of the lithium secondary battery may be deteriorated.

In order to solve such a problem, a negative electrode using lithium titanate is known. Specifically, Patent Document 1 discloses an exterior material, a positive electrode accommodated in the exterior material, and accommodated in the exterior material, spatially separated from the positive electrode, a crystallite diameter of 690 mm or less, and X When the main peak intensity of spinel type lithium titanate by line diffraction method is 100, a lithium titanium composite oxide in which the main peak intensity of rutile type TiO ₂ , anatase type TiO ₂ and Li ₂ TiO ₃ are all 7 or less A non-aqueous electrolyte battery comprising a negative electrode including a non-aqueous electrolyte filled in an exterior material is described.

JP 2006-318797 A

  However, when the lithium titanate described in Patent Document 1 is used as a negative electrode, the voltage of the negative electrode tends to increase. Therefore, the potential difference between the positive electrode and the negative electrode is reduced, and the energy density of the secondary battery is likely to decrease. Furthermore, the cycle characteristics are likely to be lowered as the energy density is lowered.

  The problem to be solved by the present invention is to provide a negative electrode active material capable of constituting a secondary battery having good energy density and cycle characteristics, and a secondary battery using the same.

The present invention comprises a vanadium, saw including a glass including oxides and Li down, and wherein the glass transition point of the glass is 340 ° C. or higher, using the negative electrode active material and it two Next battery.

  ADVANTAGE OF THE INVENTION According to this invention, the negative electrode active material which can comprise the secondary battery which has a favorable energy density and cycling characteristics, and a secondary battery using the same can be provided.

It is a schematic diagram of the lithium secondary battery of this embodiment. It is a plot in which the horizontal axis represents the transition metal content and the vertical axis represents the discharge voltage. 10 is a charging curve of a lithium secondary battery using the negative electrode active material of Reference Example 9. 10 is a charge curve of a lithium secondary battery using the negative electrode active material of Reference Example 10. It is the graph obtained by the thermogravimetry about glass. 6 is a charge curve of a lithium secondary battery using the negative electrode active material of Example 27. FIG. It is a plot which makes a horizontal axis a glass transition point and makes a vertical axis | shaft discharge voltage.

  Hereinafter, a form (this embodiment) for carrying out the present invention will be described.

[1. Negative electrode active material]
[Physical properties]
The negative electrode active material of this embodiment is selected from the group consisting of at least one transition metal element selected from the group consisting of vanadium, manganese, iron, cobalt, nickel and copper, and phosphorus, barium, germanium, lead and silicon. An oxide containing at least one element, and containing an amorphous phase of the transition metal element. Amorphous means a purely stable state that is less ordered than a crystal and is thermodynamically non-equilibrium. Hereinafter, the term “transition metal element” simply means “at least one transition metal element selected from the group consisting of vanadium, manganese, iron, cobalt, nickel, and copper”. Further, “at least one element selected from the group consisting of phosphorus, barium, germanium, lead, and silicon” is appropriately referred to as “additional element” for convenience of explanation.

Vanadium, manganese, iron, cobalt, nickel, and copper (transition metal element) perform charge compensation when lithium ions are inserted (occluded) into the negative electrode active material. Of these, vanadium is preferred. This is because since vanadium is a pentavalent metal, the amount of charge compensation that accompanies insertion of lithium ions increases, and the energy density can be further improved. In addition, vanadium is more easily amorphized by an additional element described later in detail. Further, when vanadium glass as an amorphous phase, which will be described later in detail, is contained, vanadium glass exhibits electronic conductivity by hopping conduction, and thus can function more effectively as a negative electrode active material.
In addition, the transition metal element contained in a negative electrode active material may be 1 type, and 2 or more types may be contained by arbitrary ratios and combinations.

Phosphorus, barium, germanium, lead, and silicon (additive elements) are those that make the transition metal element amorphous. Of these, phosphorus is preferable from the viewpoint of making the transition metal element more amorphous. Phosphorus has a particularly large effect of raising the glass transition point when the transition metal element is made amorphous. Therefore, the glass transition point can be further increased by containing phosphorus, and the voltage of the negative electrode using the negative electrode active material can be further decreased. Incidentally, when phosphorus is contained, phosphorus is usually contained in an amorphous phase described later.
In addition, the additional element contained in a negative electrode active material may be 1 type, and 2 or more types may be contained by arbitrary ratios and combinations.

  Moreover, the negative electrode active material of this embodiment is an oxide containing a transition metal element and an additional element. In this oxide (negative electrode active material), the transition metal element is made amorphous, and the transition metal element is contained as an amorphous phase. When the negative electrode active material includes an amorphous phase of a transition metal element, the oxidation-reduction potential when lithium ions are inserted can be sufficiently reduced. Thereby, the characteristic as a negative electrode active material can fully be drawn out. In addition, by including an amorphous phase, volume expansion of the negative electrode active material when lithium ions are inserted can be suppressed. Thereby, the fall of negative electrode performance can be suppressed. Furthermore, by including an amorphous phase, the voltage at the time of occlusion of lithium ions can be made higher than that of graphite or the like as a negative electrode active material that has been conventionally used, thereby achieving good cycle characteristics. Can do.

  The amorphous phase is preferably a glass having a glass transition point. Since the amorphous phase is glass, there is an advantage that the physical properties of the amorphous phase can be easily controlled. Although details will be described later, the negative electrode active material used in the secondary battery of this embodiment can satisfactorily reduce the voltage of the negative electrode by adjusting the glass transition point, for example, and can achieve a good energy density.

Moreover, it is preferable that content of the amorphous phase contained in a negative electrode active material is 90 volume% or more with respect to the whole negative electrode active material. The reason for this will be described below.

  Conventionally, transition metal elements such as vanadium have often been included in the positive electrode active material. This is because the voltage (charge / discharge voltage) when lithium ions are inserted into the positive electrode active material containing a transition metal element or when lithium ions are desorbed (released) from the positive electrode active material is high. Thereby, the electric potential difference between a positive electrode and a negative electrode can be enlarged, and it can be set as a favorable energy density.

式（１）中、ΔＵは格子エネルギ（化合物を構成イオン（原子）の状態に解離するのに必要なエネルギ）を表し、Ｉ_Ｍ ^ａ＋は遷移金属Ｍ^ａ＋のイオン化ポテンシャルを表し、Ｉ_Ｌｉ ^＋は遷移金属Ｍ^ａ＋のイオン化ポテンシャルを表し、ΔＨｓｕｂ（Ｌｉ）はリチウムイオンの溶媒和エネルギを表す。リチウムイオンのイオン化ポテンシャルＩ_Ｌｉ ^＋及びΔＨｓｕｂ（Ｌｉ）は定数である。 Here, when the counter electrode is lithium and the lithium ion is inserted into the transition metal M ^{a +} (where a is a valence), the voltage that can be taken out is described using the Born-Habercycle, and the following formula (1) become that way.

In the formula (1), ΔU represents lattice energy (energy required to dissociate a compound into a constituent ion (atom) state), I _M ^{a +} represents an ionization potential of the transition metal M ^{a +} , and I _Li ⁺ represents This represents the ionization potential of the transition metal M ^{a +} , and ΔHsub (Li) represents the solvation energy of lithium ions. The ionization potentials I _Li ⁺ and ΔHsub (Li) of lithium ions are constants.

In the above formula (1), in a crystal containing a transition metal such as vanadium, manganese, iron, cobalt, nickel, copper, etc., the lattice energy change (ΔU (compound after Li insertion) −ΔU (compound before Li insertion)) Since the ionization potential I _M ^{a +} of the transition metal is large and the voltage E is high. Therefore, as described above, an active material containing these metals is often used as a positive electrode active material.

  However, it has been found that when these transition metals (“transition metal element” in the present embodiment) are changed to an amorphous phase (preferably glass), the lattice energy change and the ionization potential are reduced. For this reason, the lattice energy can be considered as the cohesive energy of atoms. Therefore, it is considered that the agglomeration energy can be reduced and the lattice energy can be reduced by making the material amorphous. The same applies to the ionization potential, and it is considered that the amorphous transition metal element easily becomes an ion by making it amorphous, and the ionization potential can be reduced.

  For the reasons described above, the transition metal element used as the positive electrode active material can be applied as the negative electrode active material by amorphization. In addition, as described above, the voltage can be sufficiently lowered by amorphization, and a good energy density can be obtained.

  The amorphous phase contained is preferably as much as possible. Here, the charge / discharge curve of the negative electrode active material in which amorphous and crystal are mixed is a combination of these two characteristics. Then, when lithium ions are inserted into the negative electrode active material, it is preferable to reduce the amount of crystals as much as possible, since the reaction takes place first from the high-voltage crystal portion. Specifically, the crystal content is preferably 10% by volume or less. In other words, the content of the amorphous phase is 90% by volume or more with respect to the whole of the negative electrode active material. preferable. Thereby, the electric potential difference between a positive electrode and a negative electrode can be expanded more reliably, and the energy density as a secondary battery can be achieved more reliably.

  Whether or not the transition metal element contained in the negative electrode active material is in an amorphous phase can be confirmed using a powder X-ray diffraction measurement apparatus using CuKα rays. As a specific measuring apparatus, for example, the measuring apparatus used in the examples described later can be cited.

  The content of the transition metal element contained in the negative electrode active material is preferably 60 mol% or less, preferably 30 mol% or less, and preferably 20 mol% in terms of oxide with respect to the whole negative electrode active material. The following is more preferable. By setting the content in this range, the charge / discharge voltage lowering effect (that is, the negative electrode voltage lowering effect) obtained by making the transition metal element amorphous can be further exhibited.

Moreover, when the negative electrode active material of this embodiment contains vanadium and the said amorphous phase is glass, it is preferable that the glass transition point of a negative electrode active material is 340 degreeC or more. Furthermore, it is preferable that the oxygen ion molar volume of the negative electrode active material is 13 cm ³ / mol or more regardless of whether the amorphous phase is glass or not. Here, “oxygen ion molar volume” means a volume occupied by 1 mol of oxygen, and the smaller this value, the denser the skeleton as amorphous (preferably glass). By controlling the glass transition point and the oxygen ion molar volume within this range, the negative electrode voltage can be more reliably lowered, and a favorable function as the negative electrode can be more reliably achieved.

  According to a study by the present inventors, it is considered that there is a correlation between the glass transition point, the oxygen ion molar volume, and the negative electrode voltage. Specifically, the oxygen ion molar volume is correlated with ΔU (compound after Li insertion) in the formula (1), and the glass transition point is correlated with ΔU (compound before Li insertion) in the formula (1). It is thought that there is. For example, when the oxygen ion molar volume is increased, ΔU (compound after Li insertion) is decreased, which is considered to decrease the voltage. On the other hand, if the glass transition point becomes high, ΔU (compound before Li insertion) becomes large, which is considered to decrease the voltage.

  Therefore, in consideration of these points, the glass transition point of the negative electrode active material is preferably as high as possible, and specifically, is preferably in the above range. Similarly, the oxygen ion molar volume of the negative electrode active material is preferably as large as possible, and specifically, is preferably in the above range.

  The negative electrode active material preferably contains at least one element selected from the group consisting of lithium, sodium and magnesium in addition to the above-described components. These elements are ions that can serve as carriers in the secondary battery, and the irreversible capacity during charge and discharge can be reduced by preliminarily containing them in the negative electrode active material.

  Furthermore, the negative electrode active material preferably contains at least one element selected from the group consisting of tungsten and antimony. By containing these elements, the softening point of the glass as an amorphous phase can be raised, and the durability of the secondary battery can be improved.

  The negative electrode active material preferably contains iron. By containing iron, a conversion reaction occurs, and the battery capacity of the secondary battery can be greatly improved.

  Furthermore, the negative electrode active material is preferably coated with a carbon material such as graphite. Thereby, electrical conductivity can be improved. The particle size of the negative electrode active material is preferably 5 μm or less, more preferably 3 μm or less. As a result, the absolute content of the amorphous phase that tends to increase the electrical resistance can be reduced, and the electrical conductivity can be improved.

〔Production method〕
The negative electrode active material of this embodiment can be manufactured by arbitrary methods. Hereinafter, an example of the method for producing the negative electrode active material of the present embodiment will be described.

  First, the transition metal element and the additional element, which are raw materials, are prepared. These may be simple substances or compounds, but oxides are preferably used from the viewpoint of ease of preparation. Specifically, vanadium pentoxide can be used when vanadium is used as the transition metal element, and diphosphorus pentoxide or the like can be used when phosphorus is used as the additional element.

  And the usage-amount of these is determined so that a negative electrode active material may become a desired composition, and after mixing, it puts into a platinum crucible and heats with an electric furnace. Thereby, the lump of the negative electrode active material which has a desired composition can be obtained. Although it does not restrict | limit especially as heating conditions, For example, it is set as the temperature increase rate of about 5 degreeC-10 degreeC per minute, for example, after raising temperature to 900 degreeC or more and 1100 degrees C or less, Preferably it is 950 degrees C or less, It can be held for several hours (for example, about 2 hours). During holding in the electric furnace, stirring is preferably performed so that the amorphous phase is uniformly contained.

  When the platinum crucible is removed from the electric furnace after heating, in order to prevent moisture adsorption to the amorphous phase, it is poured onto a graphite mold or stainless steel plate heated to about 100 ° C. to 150 ° C. in that state. It is preferable to cool. And after cooling and solidifying, it may be pulverized to a desired particle size. As the degree of pulverization, for example, pulverization can be performed until the particle diameter is as described above. For example, a stamp mill or a jet mill can be used as the pulverizing means.

  After that, it is preferable to coat the surface of the negative electrode active material with a carbon material using a ball mill or the like. Thereby, the electrical conductivity of a negative electrode active material can be improved.

  The negative electrode active material of this embodiment is obtained by the above method.

[2. Secondary battery]
Next, a secondary battery including a negative electrode including the negative electrode active material of the present embodiment (hereinafter referred to as “secondary battery of the present embodiment”) will be described. Although various structures and types are conceivable as the secondary battery, in the following description, the secondary battery of this embodiment will be described by taking a cylindrical lithium secondary battery as an example. In addition, the following description is an example to the last, and a secondary battery provided with the negative electrode containing the negative electrode active material of this embodiment is not limited to the following content and the example of illustration.

  FIG. 1 is a schematic diagram of a secondary battery (lithium secondary battery) 100 of the present embodiment. In FIG. 1, some members are omitted for simplification of illustration. A lithium secondary battery is an electrochemical device in which lithium ions in a non-aqueous electrolyte are responsible for electrical conduction, and electrical energy can be stored and used by occlusion and release of lithium ions to and from electrodes.

  The secondary battery 100 includes a positive external terminal 10d and a negative external terminal 20d, and power storage and discharge are performed through these terminals. Sheet-like positive plates 10a and 10b (10) accommodated in the battery container 40 are connected to the positive external terminal 10d via a positive lead wire 10c. The negative electrode external terminal 20d is connected to sheet-like negative electrode plates 20a and 20b (20) accommodated in the battery container 40 via a negative electrode lead wire 20c. The positive plates 10 a and 10 b (10) and the negative plates 20 a and 20 b (20) are alternately stacked via the separators 30. The separator 30 is also provided between the positive electrode plate 10 a and the battery container 40, and between the negative electrode plate 20 b and the battery container 40, so that a short circuit with the battery container 40 is prevented.

  An insulating seal member 70 is provided between the positive external terminal 10 d and the battery cover 60 and between the negative external terminal 20 d and the battery cover 60. As a result, a short circuit between the positive external terminal 10d and the negative external terminal 20d is prevented.

  The battery container 40 that accommodates the positive plates 10 a and 10 b (10), the negative plates 20 a and 20 b (20), the separator 30 (hereinafter collectively referred to as “electrode group”), and the like includes a liquid injection port 50. The battery lid 60 keeps it sealed. That is, after the electrode group is stored in the battery container 40, the battery cover 60 is covered with the battery container 40, and the outer periphery of the battery cover 60 is welded, caulked, bonded, or the like, so that the battery cover 60 is fixed to the battery container 40. . Thereafter, the inside of the battery container 40 is maintained in a sealed state by injecting a non-aqueous electrolyte (described later) into the inside through the liquid inlet 50 provided in the battery lid 60 and then sealing the liquid inlet 50. It has become so. The injected electrolyte is held on the surface of the electrode group and inside the pores.

  Although not shown, a current interruption mechanism using a positive temperature coefficient (PTC) resistance element is provided in the middle of the positive lead wire 10c and the negative lead wire 20c. Thereby, when the internal temperature of the secondary battery 100 becomes high, charging / discharging can be stopped and the secondary battery 100 can be protected.

The positive electrode plates 10a and 10b (10) are made of, for example, a positive electrode mixture containing a positive electrode active material, a conductive agent, a binder, a solvent, etc., and a current collector made of a thin film or mesh of, for example, copper, nickel, aluminum, etc. It can be prepared by applying to both sides. Examples of the positive electrode active material include LiCoO ₂ , LiFePO ₄ , Li ₃ V ₂ (PO ₄ ) _{3, and the} like. Examples of the conductive agent include carbon materials. Examples of the binder include polyvinylidene fluoride and fluororubber. Examples of the solvent include organic solvents such as N-methyl-2-pyrrolidone.

  In addition to the negative electrode active material of this embodiment, the negative electrode plates 20a and 20b (20) include, for example, a negative electrode mixture containing a binder, a solvent, and the like on both surfaces of a current collector made of copper foil, aluminum foil, or mesh. It can be prepared by drying and pressing. As the binder and the solvent, those similar to those used for the production of the positive plates 10a and 10b (10) can be applied.

  As the separator 30, for example, a microporous film or a nonwoven fabric made of a polyolefin such as polyethylene or polypropylene can be used.

  Examples of the insulating seal member 70 include those that do not react with the non-aqueous electrolyte and have excellent airtightness. Specifically, a fluororesin, a thermosetting resin, a glass hermetic seal, etc. are mentioned, for example.

As the non-aqueous electrolyte, for example, a solution obtained by mixing a lithium salt and a non-aqueous solvent can be used. Examples of the lithium salt include LiPF ₆ , LiBF ₄ , LiClO _{4, and the} like. Examples of the non-aqueous solvent include propylene carbonate, ethylene carbonate, butylene carbonate, vinylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, tetrahydrofuran, 1,2-diethoxyethane, and the like.

  In the above example, the two positive plates 10a and 10b (10) and the two negative plates 20a and 20b (20) are alternately stacked, but each has one or three or more configurations. It is good. Moreover, it is not restricted to the structure by which these are laminated | stacked, It can be set as various shapes, such as what was wound by cylindrical and flat arbitrary shapes. In accordance with these shapes, the shape of the battery container 40 can be appropriately selected, for example, a cylindrical shape, a flat oval shape, a rectangular shape, or the like.

  Further, the positive electrode lead wire 10c and the negative electrode lead 20c can take any shape such as a wire shape or a plate shape. Further, the shape and material of the positive electrode lead wire 10c and the negative electrode lead wire 20c may be made of a material that can reduce ohmic loss when energized and does not react with the non-aqueous electrolyte.

  The secondary battery of this embodiment has been described above with reference to FIG. 1, but the secondary battery of this embodiment is not limited to the lithium secondary battery as described above. That is, the secondary battery of this embodiment may be any secondary battery provided with an electrode capable of inserting and extracting metal ions, for example, a sodium secondary battery in which sodium ions are inserted and released. The present invention is also applicable to a magnesium secondary battery in which magnesium ions are occluded and released. Furthermore, the present invention is not limited to a secondary battery using an electrolysis solution, and can also be applied to an all solid state secondary battery.

  Next, the present embodiment will be described more specifically with reference to examples.

[1. Effect of transition metal element content on discharge voltage]
<Example 1>
(1) Production of negative electrode active material A negative electrode active material was produced in such a manner that vanadium (transition metal element) was contained at a ratio of 65 mol% and phosphorus at 35 mol%. Specifically, first, vanadium pentoxide and diphosphorus pentoxide were prepared so that the content of vanadium and phosphorus in the negative electrode active material was the above content. And these were mixed. 100 g of the obtained mixed powder was put into a platinum crucible, heated to a heating temperature of 900 ° C. to 1100 ° C. at a heating rate of 5 ° C./min to 10 ° C./min using an electric furnace, and held for 2 hours. During holding, stirring was performed to obtain a uniform glass.

  Next, the platinum crucible was taken out from the electric furnace, poured onto a stainless steel plate heated to 100 ° C. in advance, and press-cooled using a stainless steel plate to obtain an oxide glass containing vanadium and phosphorus. The obtained oxide glass was pulverized to about 3 μm using a jet mill to obtain a negative electrode active material. Confirmation that vanadium contained in the obtained negative electrode active material was an amorphous phase was performed using a powder X-ray diffraction measurement apparatus (RINT 2500HL, manufactured by Rigaku Corporation) using CuKα rays. As a result of confirmation, it was confirmed that the contained vanadium was in an amorphous phase.

  Negative electrode active material: Ketjen black (EC600JD manufactured by Lion Corporation, particle size of 34 nm or less) = 1: 0.1. Then, 100 g of agate balls were put in an agate pot, and carbon coating was performed on the surface of the negative electrode active material by mixing for 3 hours at 200 rpm using a planetary ball mill. This negative electrode active material coated with carbon was used for the production of the following negative electrode.

(2) Production of negative electrode 55 parts by mass of carbon-coated negative electrode active material, 35 parts by mass of JSP (manufactured by Nippon Graphite Co., Ltd.) as a conductive agent, and polyvinylidene fluoride (manufactured by Kureha Co., Ltd.) as a binder (binder) # 7305) 10 parts by mass were mixed. Then, N-methyl-2-pyrrolidone was added to the obtained mixture to obtain a negative electrode mixture whose viscosity was adjusted to 15 Pa · s.

  Next, this negative electrode mixture was applied to both sides of a current collector (N5-8X-073 manufactured by Mitsubishi Aluminum Co., Ltd.) made of an aluminum foil having a thickness of 20 μm, and then subjected to pressure molding to obtain a dry thickness. A sheet having a negative electrode mixture layer having a thickness of 50 μm on both sides of the current collector was formed. And this sheet | seat was cut | judged so that the area of the part which has the negative mix layer layer (application part of a negative mix) of this sheet | seat may be 50 mm x 100 mm, and the area of an uncoated part as an extraction electrode may be 15 mm x 15 mm. Thus, a negative electrode plate 20 for a secondary battery 100 described later was produced.

(3) Assembly of Secondary Battery Using the produced negative electrode plate 20, a laminate cell type secondary battery 100 shown in FIG. 1 was assembled. However, the secondary battery 100 manufactured in this example includes 10 positive electrodes 10, 11 negative electrodes 20, and 20 separators 30. As the positive electrode plate 10 of the secondary battery 100, a metal lithium sheet cut to be 60 mm × 110 mm leaving the extraction electrode portion (15 mm × 15 mm) was used. As the separator 30, a porous film made of PP (polypropylene) having a thickness of 30 μm was used.

Further, as the non-aqueous electrolyte injected into the secondary battery 100, a non-aqueous organic solvent solution (1 mol / L) of lithium hexafluorophosphate (LiPF ₆ ) was used. As a non-aqueous organic solvent, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) are mixed so that the volume ratio is EC: EMC: DMC = 1: 2: 2. It was used.

  In this laminate cell type lithium secondary battery 100, the laminate is enclosed in the laminate cell together with the non-aqueous electrolyte. The lead electrode portions of the positive electrode 10 and the negative electrode 20 face the outside of the laminate cell, whereby electrical connection to these lead electrode portions is possible, and charging / discharging with the outside is possible.

(3) Characteristic Evaluation of Secondary Battery The charge / discharge voltage characteristics of the secondary battery 100 were evaluated. The measurement of the discharge capacity and capacity retention rate of the laminate cell type lithium secondary battery 100 was performed using a charge / discharge tester (TOSCAT3100U manufactured by Toyo System Co., Ltd.).

In this measurement, the secondary battery 100 was discharged at a constant current of a current density of 0.3 mA / cm ² up to a final discharge voltage of 0.5 V, and then charged at the same current up to a final charge voltage of 4.2 V. At this time, when the negative electrode voltage at a capacity of 50 Ah / kg is 1.5 V or less, ◎, when 1.5 V is greater than 2 V, ○ when greater than 2 V and less than 3 V, from Δ, 3 V When the value was also large, it was evaluated as x.

<Examples 2 and 3 and Reference Examples 4 to 24 >
Negative electrode active materials (carbon coating) of Examples 2 and 3 and Reference Examples 4 to 24 in the same manner as in Example 1 except that the types and contents of transition metal elements and additional elements were changed as shown in Table 1 below. The secondary battery 100 was manufactured. The produced secondary battery 100 was evaluated in the same manner as in Example 1.

  In addition, manganese dioxide is used as a raw material compound of manganese, ferric oxide is used as a raw material compound of iron, cobalt oxide is used as a raw material compound of cobalt, nickel oxide is used as a raw material compound of nickel, and copper oxide is used as a raw material compound of copper. It was. Further, barium oxide was used as the raw material compound for barium, germanium dioxide was used as the raw material compound for germanium, lead oxide was used as the raw material compound for lead, and silicon dioxide was used as the raw material compound for silicon.

<Comparative Example 1 and Comparative Example 2>
The anode was coated with carbon in the same manner as in Example 1 except that vanadium pentoxide (Comparative Example 1) and manganese dioxide (Comparative Example 2) containing only the crystalline phase but not the amorphous phase were used. A negative electrode active material was prepared, and a secondary battery 100 was produced. The produced secondary battery 100 was evaluated in the same manner as in Example 1.

<Result>
The evaluation results are shown in Table 1. In Table 1, the content of each metal is shown in mol% in terms of oxide. Further, FIG. 2 is a graph in which the horizontal axis represents the transition metal element content (mol%, converted to oxide), and the vertical axis represents the discharge voltage. As an example, FIG. 3 shows a charging curve obtained during the evaluation of the secondary battery 100 using the negative electrode active material of Reference Example 9, and FIG. 4 shows the charge curve of the secondary battery 100 using the negative electrode active material of Reference Example 10. The charge curve obtained at the time of evaluation is shown.
In addition, about each sample of a present Example and the reference example , when the powder X-ray-diffraction measurement was performed using the said powder X-ray-diffraction measuring apparatus, a crystal phase was not recognized by each sample, but an amorphous phase was 100. %.

As shown in Table 1, all of the evaluation results of Examples 1 to 3 and Reference Examples 4 to 24 were Δ or more, which was a good result. On the other hand, the evaluation results of Comparative Example 1 and Comparative Example 2 that contain only crystals and do not contain amorphous are both x, and it has been found that good results cannot be obtained when they are made of only crystalline material. .

  Further, as shown in FIG. 2, it was found that the tendency of the discharge voltage is different at the transition metal element content at 60 mol% in terms of oxide. Specifically, the discharge voltage tends to be relatively low if it is 60 mol% or less, but the discharge voltage tends to be high if it exceeds 60 mol%. Since the potential difference between the positive electrode and the negative electrode can be increased and the energy density is improved when the discharge voltage is lower, it was found that the transition metal element content is preferably 60 mol% or less in terms of oxide. .

  Moreover, as shown in Table 1, good results were obtained with any combination of transition metal elements and additional elements. From this result, it was found that the discharge voltage can be lowered regardless of the type of transition metal element or additional element.

[2. Effect of glass transition point on discharge voltage]
< Reference Examples 25 and 26 and Examples 27 to 33>
(1) Preparation of negative electrode active material and production and evaluation of secondary battery 100 Reference Example 25 was performed in the same manner as in Example 1 except that the types and contents of transition metal elements and additional elements were changed to Table 2 described later. And 26 and the negative electrode active materials (carbon-coated) of Examples 27 to 33 were prepared, and the secondary battery 100 was produced. The produced secondary battery 100 was evaluated in the same manner as in Example 1.

  Note that lithium oxide was used as the lithium source compound, antimony oxide was used as the antimony source compound, tungsten oxide was used as the tungsten source compound, sodium oxide was used as the sodium source compound, and magnesium oxide was used as the magnesium source compound.

(2) Evaluation of glass transition point Moreover, about the glass obtained during preparation of a negative electrode active material, a glass transition point (Tg) is obtained by performing a differential thermal analysis (DTA) with the temperature increase rate of 5 degree-C / min. It was measured. Alumina powder was used as a standard sample. FIG. 5 shows the DTA curve of the glass. As shown in FIG. 5, the glass transition point Tg was set to the start temperature of the first endothermic peak.

In addition, this evaluation was performed similarly about the reference example 5 and the reference examples 7-9.

  The evaluation results are shown in Table 2. As an example, FIG. 6 shows a charging curve obtained during evaluation of the secondary battery 100 using the negative electrode active material of Example 27. Further, a graph in which the horizontal axis represents the glass transition point and the vertical axis represents the discharge voltage is shown in FIG.

  As shown in Table 2 and FIG. 7, it was found that good results were obtained when the glass transition point was 340 ° C. or higher. Specifically, as shown in FIG. 7, it was found that when the glass transition point is 340 ° C. or higher, the discharge voltage tends to be low, and the characteristics suitable for the negative electrode are exhibited. More specifically, since the voltage difference with the positive electrode widens as the discharge voltage of the negative electrode decreases, the energy density of the secondary battery 100 can be increased. On the other hand, if the glass transition point is less than 340 ° C., the discharge voltage of the negative electrode tends to increase. Therefore, the voltage difference from the positive electrode is reduced, and the energy density is reduced. Therefore, it was found that a better energy density can be achieved by setting the glass transition point to 340 ° C. or higher.

  Moreover, when two kinds of vanadium (vanadium pentoxide) and iron (iron (III) oxide) were used as the transition metal elements, the discharge voltage was improved when the total amount thereof was 60 mol% or less. . That is, when the content of the transition metal element is one, the content is (see Table 1). When the content of the transition metal elements is two or more, the total content is (see Table 2). ), It was found to be 60 mol% or less in terms of oxide with respect to the whole negative electrode active material.

[3. Evaluation of cycle characteristics]
The positive electrode active material as LiCoO ₂ particles (manufactured by Nippon Chemical Industrial Co., Ltd.), using a negative electrode active material of Example 27 as the negative electrode active material, the secondary battery 100 in the same manner as in Example 1 (secondary battery of Example 1) Was made. For comparison, a secondary battery 100 (secondary battery of Comparative Example 1) was produced in the same manner except that graphite was used as the negative electrode active material.

  Each of the prepared two secondary batteries was charged and discharged once with a constant current of 0.1 C, and then charged and discharged 9 times with a constant current of 1 C. Then, this combination (one charge / discharge at 0.1 C and nine charge / discharge at 1 C) was repeated 500 times (500 cycles) to evaluate the cycle characteristics of the secondary battery.

  In addition, "1C constant current" means a current value that completes 100% charging in one hour or a state in which the secondary battery is fully charged in the case of constant current charging from a fully discharged state to the secondary battery. In the case of constant current discharge, the current value that completes 100% discharge in one hour. In other words, 1C means that the speed of charging or discharging is 100% per hour. Therefore, 0.1 C means that the speed of charging or discharging is 10% per hour.

  As a result of the cycle characteristic evaluation, it was found that the capacity retention rate after 500 cycles in the secondary battery of Example 1 was improved by 5% as compared with the secondary battery of Comparative Example 1. Therefore, according to this embodiment, it turned out that the cycling characteristics of a secondary battery can be improved.

[4. Application to batteries with shapes different from those in FIG.
In the above-described example, the negative electrode active material of the present embodiment is applied to the secondary battery 100 (see FIG. 1) using a non-aqueous electrolyte. However, the negative electrode active material of the present embodiment is an all-solid secondary battery. It is also applicable to. An all solid state secondary battery (lithium secondary battery) uses a solid electrolyte instead of a non-aqueous electrolyte containing an electrolyte.

(1) Production of positive electrode LiCoO ₂ powder having an average particle diameter of 5 μm as a positive electrode active material, the glass powder of the above-described Example 26 (used as a binder between the negative electrode active material and the positive electrode and the solid electrolyte), and a solid electrolyte Li _1.5 Al _0.5 Ti _1.5 (PO ₄ ) ₃ powder (hereinafter referred to as “LATP”) having an average particle diameter of 3 μm and needle-like (short axis: 0.13 μm, long) as a conductive agent Axis: 1.68 μm) conductive titanium oxide (a rutile-type titanium oxide base material coated with SnO ₂ conductive layer doped with Sb) so that the volume ratio is 53: 30: 10: 7, respectively. Mixed. Then, an appropriate amount of a resin binder and a solvent was mixed with the mixed powder to produce a positive electrode paste.

  In addition, ethyl cellulose or nitrocellulose was used as the resin binder, and butyl carbitol acetate was used as the solvent. The same applies to the production of the negative electrode and the solid electrolyte layer described later.

  This positive electrode paste was applied to an aluminum foil having a thickness of 20 μm, and after heat treatment for solvent removal and binder removal, the positive electrode paste was baked in the atmosphere at 390 ° C. for 1 hour to obtain a positive electrode sheet having a positive electrode active material layer thickness of 10 μm. This was punched out into a disk shape having a diameter of 14 mm to obtain a positive electrode.

(2) Production of Negative Electrode The negative electrode active material of Example 27, LATP having an average particle size of 3 μm as a solid electrolyte, and needles as a conductive agent (short axis: 0.13 μm, long axis: 1.68 μm) The conductive titanium oxide (which is a rutile titanium oxide base material coated with a SnO ₂ conductive layer doped with Sb) was mixed at a volume ratio of 83: 10: 7. Then, an appropriate amount of a resin binder and a solvent was mixed with this mixed powder to prepare a negative electrode paste.

  This negative electrode paste was applied to an aluminum foil having a thickness of 20 μm, heat-treated for solvent removal and binder removal, and then fired at 360 ° C. for 1 hour in the air to obtain a negative electrode sheet having a negative electrode active material layer thickness of 10 μm. This was punched out into a disk shape having a diameter of 14 mm to obtain a negative electrode.

(3) Production of Solid Electrolyte Layer Each volume of LATP, which is a solid electrolyte, having an average particle diameter of 3 μm and the glass powder of Reference Example 26 (used as a negative electrode active material, a binder between the positive electrode and the solid electrolyte), respectively It mixed so that it might become 70:30 by ratio. An appropriate amount of a resin binder and a solvent was added to the mixed powder to prepare a solid electrolyte paste.

  This solid electrolyte paste was applied to the positive electrode (or negative electrode), heat-treated for solvent removal and binder removal, and then fired in the air at 390 ° C. for 1 hour to form a solid electrolyte layer having a thickness of 15 μm on the positive electrode. This was punched into a disk shape having a diameter of 15 mm.

(4) Production of all-solid battery A negative electrode (or positive electrode) is laminated on the other surface produced in “(3) Production of solid electrolyte layer” to improve the adhesion at the interface between the positive electrode, the solid electrolyte layer and the negative electrode. Therefore, the laminate was fired in the air at 350 ° C. for 1 hour while being pressurized. Then, the side surface of the obtained laminate was masked with an insulator, and this was incorporated into a CR2025 type coin battery to produce an all-solid battery.

(5) Confirmation of operation Since it was confirmed that the produced battery was operated, it was confirmed that the negative electrode active material of the present embodiment was also applicable as a negative electrode active material used for an all solid state battery.

10 Positive electrode 20 Negative electrode 30 Separator 100 Secondary battery

Claims (10)

And vanadium, look including a glass of including oxide and Li down, the,
A negative electrode active material, wherein the glass transition point of the glass is 340 ° C. or higher . The content of the glass relative to the total of the negative electrode active material, characterized in that 90% by volume or more, the negative active material of claim 1. 3. The negative electrode active material according to claim 1, wherein a content of the vanadium is 60 mol% or less in terms of oxide with respect to the whole of the negative electrode active material. Lithium, characterized in that it comprises at least one element selected from the group consisting of sodium and magnesium, the negative electrode active material according to any one of claims 1 to 3. Characterized in that it comprises at least one element selected from the group consisting of tungsten and antimony, a negative electrode active material according to any one of claims 1 to 4. Characterized in that it comprises iron, the negative electrode active material according to any one of claims 1 to 5. Characterized by comprising coated by a carbon material, the negative active material according to any one of claims 1 to 6. And vanadium, saw including a glass including oxides and Li down, and characterized in that it comprises a negative electrode having a negative electrode active material the glass transition point of the glass is 340 ° C. or higher, the secondary battery. The secondary battery according to claim 8 , wherein the glass content is 90% by volume or more based on the whole of the negative electrode active material. 10. The secondary battery according to claim 8 , wherein a content of the vanadium is 60 mol% or less in terms of oxide with respect to the whole of the negative electrode active material.

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