JP2018073753A - Fluoride ion battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fluoride ion battery which enables the achievement of a higher discharge potential as compared to a conventional fluoride ion battery in which elemental Cu is used for a positive electrode active material.SOLUTION: Provided is a fluoride ion battery comprising at least a positive electrode active material layer, and a solid electrolyte layer. The positive electrode active material layer comprises positive electrode active material particles primarily containing Cu and Sn; and the solid electrolyte layer comprises a solid electrolyte containing Pb, Sn and F.SELECTED DRAWING: Figure 8

Description

  The present invention relates to a fluoride ion battery.

  As a battery having a high voltage and a high energy density, for example, a Li ion battery is known. The Li ion battery is a cation-based battery that utilizes a reaction between Li ions and a positive electrode active material and a reaction between Li ions and a negative electrode active material. On the other hand, a fluoride ion battery using a reaction of fluoride ions (fluoride anions) is known as an anion-based battery.

For example, Patent Document 1 discloses that Cu is used as a positive electrode active material of a fluoride ion battery. As disclosed in Patent Document 1, it is known to exhibit a function as an active material of a fluoride ion battery by a fluorination / defluorination reaction (MeF _x + xe ⁻ → Me + xF ⁻ ) of a metal (M) such as Cu. ing. Patent Document 2 discloses a fluoride ion battery using PbSnF ₄ as a solid electrolyte.

JP 2006-062821 A Japanese Patent Laid-Open No. 05-325973

  Although it is known that the capacity of the fluoride ion battery can be increased by using Cu as the positive electrode active material of the fluoride ion battery as in Patent Document 1, the discharge potential is low and the energy by charging is fully utilized. Is difficult.

  This invention is made | formed in view of the said subject, and it aims at providing the fluoride ion battery which can make discharge electric potential higher than the fluoride ion battery which used the conventional Cu simple substance for the positive electrode active material.

  In order to solve the above problems, in the present invention, at least a positive electrode active material layer and a solid electrolyte layer are included, and the positive electrode active material layer includes positive electrode active material particles mainly composed of Cu and Sn. The solid electrolyte layer provides a fluoride ion battery including a solid electrolyte containing Pb, Sn, and F.

  According to the present invention, by including the positive electrode active material particles containing Cu and Sn, the discharge potential during discharge can be increased.

  The fluoride ion battery of the present invention can be a fluoride ion battery that can have a higher discharge potential than a fluoride ion battery using conventional Cu alone as a positive electrode active material.

It is a schematic sectional drawing which shows an example of the fluoride ion battery of this invention. It is a schematic sectional drawing which shows the other example of the fluoride ion battery of this invention. It is a schematic diagram of the experimental apparatus used in Examples 1-3 and a comparative example. 2 is an XRD measurement result of positive electrode active material particles used in Example 1. FIG. It is a XRD measurement result of the positive electrode active material particle used in Example 2. It is a XRD measurement result of the positive electrode active material particles used in Example 3. It is a XRD measurement result of the positive electrode active material particle used by the comparative example. It is a discharge curve when performing a charging / discharging test using the secondary battery of Examples 1-3 and a comparative example.

  Hereinafter, details of the fluoride ion battery in the embodiment of the present invention will be described.

  The fluoride ion battery in an embodiment of the present invention has at least a positive electrode active material layer and a solid electrolyte layer, and the positive electrode active material layer includes positive electrode active material particles mainly composed of Cu and Sn, and the solid The electrolyte layer includes a solid electrolyte containing Pb, Sn, and F.

  In the present invention, the “positive electrode active material particles mainly composed of Cu and Sn” means the number of moles of all metal elements constituting the positive electrode active material particles, in which the positive electrode active material particles have at least Cu and Sn. (A + B) / X is 0.5 or more, where X is X, the number of moles of Cu element constituting the positive electrode active material particles is A, and the number of moles of Sn element constituting the positive electrode active material particles is B. Means.

FIG. 1 is a schematic cross-sectional view showing an example of a fluoride ion battery of the present invention. As shown in FIG. 1, a fluoride ion battery 10 of the present invention has at least a positive electrode active material layer 1 and a solid electrolyte layer 2, and the solid electrolyte layer 2 contains a solid electrolyte containing Pb, Sn, and F. 2a, the positive electrode active material layer 1 contains at least Cu and Sn, and contains positive electrode active material particles mainly composed of Cu and Sn. Thus, in the configuration of the fluoride ion battery that does not have the negative electrode active material layer, the negative electrode current collector 5 is disposed on the surface of the solid electrolyte layer 2, and the surface of the positive electrode active material layer 1 opposite to the solid electrolyte layer 2. The positive electrode current collector 4 is disposed on the surface.

FIG. 2 shows an example in which the fluoride ion battery 10 further includes the negative electrode active material layer 3 and the solid electrolyte layer 2 is formed between the positive electrode active material layer 1 and the negative electrode active material layer 3. The fluoride ion battery 10 normally further includes a positive electrode current collector 4 that collects current from the positive electrode active material layer 1 and a negative electrode current collector 5 that collects current from the negative electrode active material layer 3.

In the fluoride ion battery 10 having no negative electrode active material layer at the time of battery production as shown in FIG. 1, the solid electrolyte 2 a is removed at the interface between the solid electrolyte layer 2 and the negative electrode current collector 5 during the initial charge. A reaction occurs in which a negative electrode active material is produced by fluorination, and the negative electrode active material layer 3 is self-formed as shown in FIG.

One of the reasons why the discharge potential is low when Cu simple particles are used as the positive electrode active material particles as in the past is considered as follows. At the time of charging, it is presumed that the solid electrolyte is oxidized and decomposed on the surface where the positive electrode active material particles, which are electronic conductors, and the solid electrolyte are in contact with each other, thereby producing an oxidized decomposition product. Since the oxidative decomposition product does not have fluoride ion conductivity, it is presumed that the conduction of fluoride ions is hindered and the resistance becomes high, so that the overvoltage increases and the discharge potential decreases.

  On the other hand, in the present invention, although not bound by a specific theory, the presence of Sn together with Cu in the positive electrode active material particles suppresses oxidation of the solid electrolyte between the solid electrolyte and Cu. It is considered that the increase in resistance due to the oxidative decomposition product can be suppressed. In addition, it is considered that the fluoride ion conductivity in the positive electrode active material particles is improved by alloying or solidifying Cu and Sn. For the above reasons, it is presumed that the discharge potential can be improved when the positive electrode active material particles mainly contain Cu and Sn.

  Hereinafter, the detail of each structure in embodiment of the fluoride ion battery of this invention is demonstrated.

1. Positive electrode active material layer The positive electrode active material layer in the present invention is a layer containing at least positive electrode active material particles. The positive electrode active material layer may further include a solid electrolyte, a conductive material, and a binder in addition to the positive electrode active material particles. Especially, in this invention, it is preferable that the material of the solid electrolyte mentioned later is further included as a solid electrolyte.

  The positive electrode active material particles in the present invention contain at least Cu and Sn, and mainly contain Cu and Sn. Since Cu can take up to two valences, in the electrode reaction, two electrons can be reacted with one Cu (moving two electrons), so that the battery has a high capacity. I can expect that. Furthermore, Cu has the advantages that it is relatively safe, stable and inexpensive, and has high electron conductivity.

  The positive electrode active material particles in the embodiment of the present invention may further contain other metal elements in addition to the above-described Cu and Sn. Examples of other metals include alkali metals, alkaline earth metals, lanthanoid metals, and the like. Specific examples of the active material include Ag, Co, Mn, Cu, W, and V alone, and alloys of these metals.

  The number of moles of all metal elements constituting the positive electrode active material particles is X, the number of moles of Cu element constituting the positive electrode active material particles is A, and the number of moles of Sn element constituting the positive electrode active material particles is B. (A + B) / X may be greater than 0.5, 0.7 or greater, or 0.9 or greater. Further, the positive electrode active material particles may be composed only of Cu and Sn. Note that the total content ratio of the Cu element and the Sn element with respect to all the metal elements constituting the positive electrode active material particles can be determined by, for example, Raman spectroscopy, NMR, XPS, or the like.

Examples of the shape of the positive electrode active material particles include a true sphere and an elliptic sphere. The average particle diameter (D ₅₀ ) of the positive electrode active material particles is preferably in the range of 10 nm to 100 nm, and particularly preferably in the range of 20 nm to ₆₀ nm. The average particle diameter can be measured, for example, by observation with a scanning electron microscope (SEM) (for example, n ≧ 20). It can also be calculated from the measured value of the BET specific surface area.

The form containing Cu and Sn in the positive electrode active material particles is not particularly limited, but the form in which a compound containing Sn is coated on Cu particles, the form in which an alloy of Cu and Sn is used as the positive electrode active material particles, etc. Is mentioned.

Although it does not specifically limit as a form which coat | covers the compound containing Sn to Cu particle | grains, From a viewpoint that fluoride ion conductivity is high, it is preferable to coat | cover the fluoride containing Sn. Specifically, SnF ₂ is preferable. In addition to the fluoride containing Sn, La fluoride, Ce fluoride, Ca fluoride and the like having high fluoride ion conductivity may be contained. _{Specifically, LaF 3, CeF 3, CaF} 3 , and the like.

  In the compound containing Sn of the embodiment of the present invention, the coverage of the compound containing Sn with respect to the surface of the Cu particles is, for example, preferably 20% or more, more preferably 50% or more, and 70 % Or more is more preferable, and may be 100%. Examples of the method for measuring the coverage of the compound containing Sn include a transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS).

  The average thickness of the compound containing Sn is, for example, preferably 0.5 nm or more, preferably 1 nm or more, and preferably 10 nm or more. Moreover, the thickness of the compound containing Sn is, for example, preferably 30 nm or less, preferably 20 nm or less, and preferably 15 nm or less. Moreover, as a measuring method of the average thickness of the compound containing Sn, a transmission electron microscope (TEM) etc. can be mentioned, for example. Moreover, it can also obtain | require from the average particle diameter of positive electrode active material particle, and the weight ratio of a raw material.

The form of using an alloy of Cu and Sn as the positive electrode active material particles is the ratio of the number of moles of Cu element (A) to the total number of moles of Cu element (A) and the number of moles of Sn element (B) (A / The value of A + B) is not particularly limited, but is preferably 0.5 or more, preferably 0.7 or more, and preferably 0.9 or more. The value of A / A + B is smaller than 1. This is because the discharge potential due to Sn can be improved while taking advantage of the high capacity due to Cu.

  Further, the content of the positive electrode active material particles in the positive electrode active material layer is preferably larger from the viewpoint of capacity, for example, 20% by weight or more, preferably 50% by weight or more, and 70% by weight or more. More preferably.

  The conductive material is not particularly limited as long as it has desired electronic conductivity, and examples thereof include a carbon material. Examples of the carbon material include carbon black such as acetylene black, furnace black, and thermal black, graphene, fullerene, and carbon nanotube.

  As content of the solid electrolyte in a positive electrode active material layer, it is preferable to exist in the range of 10 weight%-80 weight%, for example. Further, the thickness of the positive electrode active material layer varies greatly depending on the configuration of the battery, and is not particularly limited.

2. Solid Electrolyte Layer The solid electrolyte layer of the present invention includes a solid electrolyte containing Pb, Sn, and F.

The solid electrolyte in the embodiment of the present invention only needs to contain at least Pb, Sn, and F, may contain only the above three elements, and may further contain other elements. good. Examples of other elements include Sm. When other elements are contained, other elements may be doped based on a solid electrolyte containing Pb, Sn, and F. F in a solid electrolyte usually functions as a fluoride ion (F ⁻ ) that is a carrier.

  The ratio of the total of Pb element, Sn element and F element to the total of all elements in the solid electrolyte in the embodiment of the present invention is, for example, preferably 70 mol% or more, and more preferably 80 mol% or more. Preferably, it is 90 mol% or more, and may be 100 mol%. The total ratio of the Pb element, Sn element, and F element can be determined by, for example, Raman spectroscopy, NMR, XPS, or the like.

The solid electrolyte in the embodiment of the present invention preferably has, for example, a composition represented by the general formula Pb _1-x Sn _x F ₂ (0 <x <1). The value of x in the above general formula is larger than 0, preferably 0.2 or more, and more preferably 0.4 or more. Moreover, the value of x in the above general formula is preferably smaller than 1 and 0.6 or less. More specific examples of the solid electrolyte include Pb _0.4 Sn _0.6 F ₂ (x = 0.6), Pb _0.6 Sn _0.4 F ₂ (x = 0.4), and the like. . In the present invention, Pb _0.6 Sn _0.4 F ₂ (x = 0.4) is particularly preferable. The composition of the solid electrolyte in the present invention can be confirmed, for example, by performing high frequency inductively coupled plasma (ICP) emission spectroscopic analysis.

For example, the reduction potential of the solid electrolyte in the embodiment of the present invention is preferably 0.2 V (vs. Pb / PbF ₂ ) or more, and more preferably 0.3 V (vs. Pb / PbF ₂ ) or more. preferable. Further, the oxidation potential of the solid electrolyte, for example, preferably 1.4V (vs.Pb / PbF ₂₎ or less, and more preferably 1.3V (vs.Pb / PbF ₂₎ or less. The reduction potential and oxidation potential of the solid electrolyte can be determined by, for example, cyclic voltammetry (CV).

3. Negative electrode active material layer The negative electrode active material layer in the embodiment of the present invention is a layer containing at least a negative electrode active material. The negative electrode active material layer may further contain a conductive material and a binder in addition to the negative electrode active material. In the present invention, the negative electrode active material layer may be derived from the solid electrolyte in the solid electrolyte layer. Specifically, it may be obtained by precipitating a metal element or the like contained in the solid electrolyte at the time of charging (at the time of initial charging).

  The negative electrode active material is not particularly limited as long as it is an active material having a lower potential than the positive electrode active material particles described above, and examples thereof include Pb.

  As the conductive material and the binder, the same materials as those described in “1. Positive electrode active material layer” can be used. Further, the content of the negative electrode active material in the negative electrode active material layer is preferably higher from the viewpoint of capacity, for example, 30% by weight or more, preferably 50% by weight or more, and 70% by weight or more. It is more preferable. In addition, the thickness of the negative electrode active material layer varies greatly depending on the configuration of the battery, and is not particularly limited.

4). Fluoride ion battery The fluoride ion battery of the present invention includes at least the positive electrode active material layer and the solid electrolyte layer described above, and may include a negative electrode active material layer. Furthermore, it usually has a positive electrode current collector for collecting current of the positive electrode active material layer and a negative electrode current collector for collecting current of the negative electrode active material layer. Examples of the positive electrode current collector and the negative electrode current collector include SUS, Cu, Ni, Al, Fe, Pt, and Pb. Examples of the shape of the current collector include a foil shape, a mesh shape, and a porous shape.

  The fluoride ion battery in the embodiment of the present invention is usually a solid battery. Further, the fluoride ion battery of the present invention may be a primary battery or a secondary battery, but among them, a secondary battery is preferable. This is because it can be repeatedly charged and discharged and is useful, for example, as an in-vehicle battery. Note that the primary battery includes primary battery use (use for the purpose of discharging only once after charging).

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and those having substantially the same configuration as the technical idea described in the claims of the present invention and having the same operational effects are within the technical scope of the present invention. Is included.

  Hereinafter, the present invention will be described in more detail with reference to examples.

[Example 1]
(Synthesis of positive electrode active material particles)
As positive electrode active material particles, Cu particles coated with SnF ₂ were synthesized using a thermal plasma method. As raw materials, 100 g of Cu and 10 g of SnF ₂ were used. At this time, the particle diameter of the Cu particles was 30 nm, and the thickness of the SnF ₂ coat was about 0.7 nm.

(Preparation of positive electrode mixture)
Pb _0.6 Sn _0.4 F ₂ was produced as a solid electrolyte in a glove box under an Ar atmosphere. Specifically, PbF ₂ and SnF ₂ were used as raw materials, and weighed so that the molar ratio was PbF ₂ : SnF ₂ = 3: 2. The obtained raw material was mechanically milled and then heat treated at 400 ° C. to obtain Pb _0.6 Sn _0.4 F ₂ . Moreover, acetylene black was prepared as a conductive material. The positive electrode active material: solid electrolyte: conductive material = 25: 70: 5 was mixed in a weight ratio to obtain a positive electrode mixture.

(Production of secondary battery)
Pb foils were prepared as a positive electrode current collector and a negative electrode current collector, respectively. 250 mg of the above solid electrolyte was weighed into a 1 cm ² ceramic mold and pressed at 1 ton / cm ² (10 ³ kg / cm ² ) to produce a solid electrolyte layer. A positive electrode active material layer was prepared by putting 10 mg of the positive electrode mixture on one side of the obtained solid electrolyte layer and pressing it at ¹ ton / cm ² . Pb foil was disposed on the surfaces of the positive electrode active material layer and the solid electrolyte layer. Thereafter, the whole was pressed at 4 ton / cm ² . Thus, a secondary battery as shown in FIG. 3 in a 1 cm ² pellet shape was obtained. The secondary battery has a configuration in which a positive electrode current collector, a positive electrode active material layer, a solid electrolyte layer, and a negative electrode current collector are stacked in this order. Note that the negative electrode active material layer is self-formed at the interface between the solid electrolyte and the negative electrode current collector.

[Example 2]
A secondary battery was fabricated in the same manner as in Example 1 except that an alloy represented by 41Cu-11Sn was used as the positive electrode active material particles. Here, 41Cu-11Sn indicates an alloy in which the molar ratio of Cu and Sn is Cu: Sn = 41: 11.

[Example 3]
A secondary battery was fabricated in the same manner as in Example 1 except that an alloy represented by 6Cu-5Sn was used as the positive electrode active material particles. Here, 6Cu-5Sn indicates an alloy in which the molar ratio of Cu and Sn is Cu: Sn = 6: 5.

[Comparative example]
A secondary battery was fabricated in the same manner as in Example 1 except that Cu single particles (no Sn) were used as the positive electrode active material particles.

[Evaluation]
(XRD measurement)
X-ray diffraction measurement (using CuKα rays) was performed using the positive electrode active material particles obtained in Examples 1 to 3 and Comparative Example. The results are shown in FIGS. In FIG. 4, the positive electrode active material particles obtained in Example 1 are 2θ = 25.4 ± 0.5, 43.3 ± 0.5, 50.5 ± 0.5 attributed to Cu and SnF ₂ . A peak of 74.0 ± 0.5 was confirmed, and the positive electrode active material particles obtained in Example 1 were confirmed to have SnF ₂ and Cu. In FIG. 5, the positive electrode active material particles obtained in Example 2 are 2θ = 25.8 ± 0.5, 42.6 ± 0.5, 62.0 ± 0.5, 78 attributed to 41Cu-11Sn. A peak of 2 ± 0.5 was confirmed, and the positive electrode active material particles obtained in Example 2 were confirmed to have 41Cu-11Sn. In FIG. 6, the positive electrode active material particles obtained in Example 3 are 2θ = 30.0 ± 0.5, 35.0 ± 0.5, 43.0 ± 0.5, 53 attributed to 6Cu-5Sn. A peak of 0.0 ± 0.5 was confirmed, and the positive electrode active material particles obtained in Example 3 were confirmed to have 6Cu-5Sn. In FIG. 7, the positive electrode active material particles obtained in the comparative example have peaks of 2θ = 43.3 ± 0.5, 50.5 ± 0.5, 74.1 ± 0.5 attributed to Cu. It was confirmed that the positive electrode active material particles obtained in the comparative example were Cu.

(Charge / discharge test)
The following charging / discharging test was done about the secondary battery produced in Examples 1-3 and the comparative example. The process in which the positive electrode is fluorinated and the negative electrode is defluorinated is referred to as “charging”, and the process in which the positive electrode is defluorinated and the negative electrode is fluorinated is referred to as “discharge”. The battery was placed in a desiccator and evaluated while evacuating. Measurement conditions were as follows: charge 40 μA, discharge −20 μA, 1.3 V (vs. Pb / PbF ₂ ) to 0.3 V (vs. Pb / PbF ₂ ), and a temperature in the desiccator at 140 ° C. for one cycle. The result of the capacity retention rate is shown in FIG.

In FIG. 8, the vertical axis represents the discharge potential (vs. Pb / PbF ₂ ), and the horizontal axis represents the capacity (mAh). The discharge potentials of the positive electrode active material particles of Examples 1 to 3 were 0.72 V (vs. Pb / PbF ₂ ), 0.72 V (vs. Pb / PbF ₂ ), and 0.72 V (vs. Pb / PbF ₂ ), respectively. The discharge potential of the positive electrode active material particles using the single Cu particles of Comparative Example 1 was 0.68 V (vs. Pb / PbF ₂ ). That is, the positive electrode active material particles of Examples 1 to 3 having Sn had a discharge potential higher by about 0.04 V (vs. Pb / PbF ₂ ) than the positive electrode active material particles of the comparative example.

In the comparative example, it is presumed that the solid electrolyte in the positive electrode active material layer is oxidatively decomposed at the interface with the Cu single particles by charging, and an oxidative decomposition product is generated. And it is estimated that an oxidative decomposition product inhibits conduction of fluoride ion, and resistance becomes high. On the other hand, in the positive electrode active material particles of Example 1, Cu and Sn are solid-solved in the vicinity of the interface between Cu and SnF _2, and in the positive electrode active material particles of Examples 2 to 3, Cu and Sn are alloyed. Thus, it is presumed that the oxidative decomposition of the solid electrolyte at the interface between the Cu particles and the solid electrolyte was suppressed. Moreover, it is estimated that fluoride ion conductivity was improved by solid solution and alloying of Cu and Sn. From the above, it is presumed that the discharge potential is increased by containing Cu and Sn in the positive electrode active material particles.

DESCRIPTION OF SYMBOLS 10 ... Fluoride ion battery 1 ... Positive electrode active material layer 2 ... Solid electrolyte layer 2a ... Solid electrolyte 3 ... Negative electrode active material layer 4 ... Positive electrode collector 5 ... Negative electrode collector

Claims (1)

Having at least a positive electrode active material layer and a solid electrolyte layer;
The positive electrode active material layer includes positive electrode active material particles mainly composed of Cu and Sn,
The solid electrolyte layer includes a solid electrolyte containing Pb, Sn, and F.
Fluoride ion battery.

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