JP5561547B2 - Nonaqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte secondary battery and a method for producing an electrode active material used for the non-aqueous electrolyte secondary battery.

  So-called secondary batteries that can be charged and discharged have become increasingly important in recent years as power sources for vehicles or as power sources for personal computers and portable terminals. In particular, a lithium secondary battery (typically a lithium ion battery) that is lightweight and obtains a high energy density is expected to be preferably used as a large-scale power supply for vehicles. One typical configuration of this type of lithium secondary battery includes an electrode having a configuration in which an electrode active material capable of reversibly inserting and extracting Li ions is formed on an electrode current collector. Currently, as an electrode active material for a positive electrode, a compound (lithium transition metal compound) containing lithium and one or more transition metal elements as constituent metal elements is widely used. However, since lithium has a limited reserve as a resource, there is a concern about a shortage of supply to cope with an increase in demand for large power sources.

In recent years, therefore, non-aqueous electrolyte secondary batteries using sodium instead of lithium, which has limited resources, have been studied. Sodium has abundant resources and is inexpensive, so by putting it into practical use, it is possible to meet demands for mass supply and cost reduction. As an electrode active material contained in an electrode of such a nonaqueous electrolyte secondary battery using sodium, Patent Document 1 discloses an electrode active material composed of a sodium compound represented by the general formula Na _{1 + y} MPO ₄ F _{1 + y.} Have been described.

JP 2004-533706 A

In Patent Document 1, a sodium compound such as Na _{1 + y} MPO ₄ F _{1 + y} is synthesized by a solid phase method. However, the sodium compound synthesized by the solid phase method has a problem that the diffusion resistance of Na ions in the particles is large and it becomes a material that is difficult to apply to a secondary battery. Therefore, an object of the present invention is to provide a non-aqueous electrolyte secondary battery that includes an electrode active material containing Na _{1 + x} MnPO ₄ F _x and can be charged and discharged.

According to the present invention, there is provided a method for producing an electrode active material comprising a metal compound represented by the composition formula Na _{1 + x} MnPO ₄ F _x (where x is 0 <x ≦ 1). This manufacturing method comprises a step of preparing a raw material mixture by mixing starting raw materials including a sodium source, a manganese source, a phosphoric acid source and a fluorine source in a solvent containing a metal chelate-forming functional group; It includes a step of heating the liquid to obtain a precursor and a step of firing the precursor at a predetermined temperature.

In general, Na _{1 + x} MnPO ₄ F _x has a symmetry of the space group P21 / n, and there is a Na ion diffusion path only in the b-axis direction because of the structure. In order to increase the diameter, the diffusion path in the b-axis direction is long. For this reason, the diffusion resistance of Na ions in the particles was very large and could not be charged / discharged.

On the other hand, according to the method of the present invention, the particle shape of Na _{1 + x} MnPO ₄ F _x is conventionally obtained by reacting a starting material of Na _{1 + x} MnPO ₄ F _{x in} a solvent containing a metal chelate-forming functional group. It is controlled to a plate-like form that is not present. For this reason, the Na ion diffusion path only in the b-axis direction is shortened, and the Na ions diffuse efficiently in the particles. Such Na _{1 + x} MnPO ₄ F _x powder is a chargeable / dischargeable material that promotes Na ion diffusibility and reversibly absorbs and releases Na ions, and is an active material for a non-aqueous electrolyte secondary battery (for example, a positive electrode). It can be suitably used as an active material.

In a preferred embodiment of the production method disclosed herein, the metal chelate-forming functional group is at least one functional group selected from the group consisting of an alcohol group, a carbonyl group, and an ether group. Since the solvent molecules having these functional groups have high coordination ability and can form a chelate with a transition metal (especially Mn), the solvent molecules coordinate to the particle surface to grow particles (especially in the b-axis direction). ) Is appropriately suppressed. Therefore, Na _{1 + x} MnPO ₄ F _x can be easily controlled in a plate shape. In addition, the coordination of the solvent molecules ensures that fluorine is taken into the precursor (phosphate). Therefore, fluorine is prevented from decomposing and deviating in the subsequent firing step, and the target compound can be obtained stably.

  In a preferred embodiment of the production method disclosed herein, the solvent is a polyol solvent. Since the polyol solvent has an alcohol (OH) group capable of chelating with a transition metal (particularly Mn), it can be suitably used as a solvent suitable for the purpose of the present invention.

  In a preferred embodiment of the production method disclosed herein, the firing temperature of the precursor is 500 ° C to 800 ° C. In order to allow the reaction to proceed sufficiently, the firing temperature needs to be 500 ° C. or higher. On the other hand, if the firing temperature exceeds 800 ° C., fluorine decomposes and deviates during firing, so that by-products May lower the purity of the target compound. The baking temperature is usually suitably 500 to 800 ° C, preferably 550 to 700 ° C, more preferably 550 to 650 ° C.

In a preferred embodiment of the production method disclosed herein, a carbon material is mixed and pulverized in the obtained fired product after the firing. By this pulverization treatment, a carbon material is pressure-bonded to the surface of Na _{1 + x} MnPO ₄ F _x , and the particle surface is covered with the carbon material. Conductivity can be imparted by the coating of the carbon material. Further, a mechanochemical reaction occurs due to frictional heat generated in the pulverization process, and the remaining impurity phase (such as unreacted starting materials and reaction byproducts) due to insufficient reaction can be decomposed.

In a preferred embodiment of the production method disclosed herein, after the pulverization, the obtained pulverized product is refired at 500 ° C to 800 ° C. According to this aspect, the impurity phase is decomposed by the above pulverization, and the reactivation is performed after lowering the activation energy for the reaction between the impurity phases, so that homogenization of the target compound further proceeds and the purity of Na _{1 + x} MnPO ₄ F _x Can be further enhanced.

The present invention also provides a nonaqueous electrolyte secondary battery constructed using the electrode active material produced by any of the production methods disclosed herein. This non-aqueous electrolyte secondary battery is a non-aqueous electrolyte secondary battery including an electrode active material capable of reversibly occluding and releasing sodium, and the electrode active material has a plate shape and a composition It is represented by the formula Na _{1 + x} MnPO ₄ F _x (where x is 0 <x ≦ 1). In such a non-aqueous electrolyte secondary battery, the Na _{1 + x} MnPO ₄ F _x particle shape is controlled to an unprecedented plate-like shape (typically a flake shape). It may be good and exhibit better battery performance. Preferably, x in the above formula is 0.5 ≦ x ≦ 1. In this case, the diffusibility of Na ions in the particles is further improved.

It is a figure which shows typically the nonaqueous electrolyte secondary battery which concerns on one Embodiment of this invention. It is a figure which shows typically the wound electrode body which concerns on one Embodiment of this invention. (A) is a diagram showing an X-ray diffraction pattern of the _Na 1 + _x MnPO ₄ F x powder after the sintering, the _Na 1 + _x MnPO ₄ F x powder X-ray diffraction pattern of (b) before firing (precursor) FIG. It is a SEM photograph of _Na 1 + _x MnPO ₄ F x powder after the sintering. (A) is a figure which shows the X-ray-diffraction pattern of the composite material powder after re-baking, (b) is a figure which shows the X-ray-diffraction pattern of the composite material powder after a ball mill process. It is a SEM photograph of the composite material powder after refiring. It is a figure which shows typically the coin cell for a test concerning a present Example. It is a graph which shows the result of the cyclic voltammetry measurement which concerns on a present Example. It is a side view showing typically a vehicle provided with a nonaqueous electrolyte secondary battery concerning one embodiment of the present invention.

  Embodiments according to the present invention will be described below with reference to the drawings. In the following drawings, members / parts having the same action are described with the same reference numerals. In addition, this invention is not limited to the following embodiment.

A nonaqueous electrolyte secondary battery according to an embodiment of the present invention is a nonaqueous electrolyte secondary battery including an electrode active material capable of reversibly inserting and extracting sodium. The electrode active material has a plate shape in particle shape, and has the following composition formula:
Na _{1 + x} MnPO ₄ F _x ;
It is represented by

Here, the possible range of x in the above formula is any real number within the range of 0 <x ≦ 1 as long as the structure can be maintained without destroying the crystal structure of Na _{1 + x} MnPO ₄ F _x. However, the larger the value of x, the better the diffusibility of Na ions in the particles, which is preferable. Preferably 0.3 ≦ x ≦ 1.0, more preferably 0.5 ≦ x ≦ 1.0, still more preferably 0.7 ≦ x ≦ 1.0, and particularly preferably the value of x. Is substantially 1.0.

The Na _{1 + x} MnPO ₄ F _x powder can be manufactured through a raw material mixture preparation step, a heating step, and a firing step. Hereinafter, each process will be described in detail.

<Raw material mixture preparation process>
In the raw material mixture preparation step, starting raw materials including a sodium source, a manganese source, a phosphoric acid source and a fluorine source are mixed in a solvent containing a metal chelate-forming functional group to prepare a raw material mixture. In this embodiment, starting materials including a sodium source, a manganese source, a phosphoric acid source and a fluorine source are weighed so as to have a predetermined mixing ratio, and these are mixed and dissolved in a solvent.

As the starting material, one or more compounds including at least a sodium source, a manganese source, a phosphoric acid source, and a fluorine source can be appropriately selected and used. The sodium source, manganese source, phosphoric acid source, and fluorine source are not particularly limited as long as the target compound can be formed by final firing. For example, simple metals, oxides, halides (for example, fluorides), and various compounds (for example, acetates, oxalates, carbonates, etc.) can be used. These may be used alone or in combination of two or more. Particularly preferred examples include sodium fluoride (NaF) as a sodium source and fluorine source, ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ) as a phosphate source, and manganese acetate ((CH ₃ COO) as a manganese source. ₂ Mn).

  The solvent can be used without any particular limitation as long as it contains a functional group having a metal chelate-forming ability and has a relatively high boiling point. Examples of the functional group having a metal chelate forming ability include an alcohol group, a carbonyl group, and an ether group. Preferable examples of the solvent having an alcohol group include diethylene glycol (245 ° C.), ethylene glycol (196 ° C.), 1,2-propanediol (187 ° C.), 1,3-propanediol (214 ° C.), 1,4- A polyol solvent such as propanediol (230 ° C.) is exemplified. Preferable examples of the solvent having a carbonyl group include N, N-dimethylformaldehyde (153 ° C.). One or more of these solvents can be used. Of these solvents, it is preferable to use a polyol solvent, particularly diethylene glycol. In addition, the numerical value in the said parenthesis has shown the boiling point of each solvent.

Since solvent molecules having these functional groups have high coordination ability and can form a chelate with a transition metal (especially Mn), the solvent molecules having the functional groups coordinate to the particle surface to grow particles (especially b). Axial growth) is appropriately suppressed. Therefore, Na _{1 + x} MnPO ₄ F _x can be easily controlled in a plate shape. In addition, the coordination of the solvent molecules ensures that fluorine is taken into the precursor (phosphate). Therefore, fluorine is prevented from decomposing and deviating in the subsequent firing step, and the target compound can be obtained stably.

The amount of the solvent to be used is not particularly limited as long as it is the stoichiometric amount or more necessary for chelate formation, but usually 20 times mole or more relative to Na _{1 + x} MnPO ₄ F _x is appropriate, for example, 20 to 100 It is preferable to use a double mole, particularly 40 to 60 moles.

  When the above starting materials are dissolved in a solvent, stirring may be performed as necessary. The operation of stirring the starting material in a solvent can be performed using an appropriate stirring means such as a magnetic stirrer. By this stirring, mixing can be performed in a short time.

<Heating process>
In the heating step, the prepared raw material mixture is heated to obtain a precursor. The means for heating the raw material mixture is not particularly limited, and any means such as a hot plate can be employed. Although the heating temperature varies depending on the composition of the starting material, for example, when using manganese acetate as a manganese source, it is necessary to heat at a temperature at which volatilization of acetic acid proceeds sufficiently, and is usually 120 ° C. or higher (eg, 120 to 180 ° C) is preferable. The upper limit of the heating temperature may be a temperature lower than the boiling point of the solvent used. The heating time may be a time until the starting material reacts and the precursor sufficiently reacts, and is usually about 8 to 24 hours, preferably about 10 to 15 hours.

  When the raw material mixture is heated to volatilize the solvent, a precipitate is generated and a precursor is generated. At that time, the growth of particles (particularly, growth in the b-axis direction) is appropriately suppressed by coordinating solvent molecules having a metal chelate-forming functional group to the particle surface.

<Baking process>
In the firing step, the obtained precursor is fired at 500 ° C to 800 ° C. By this firing, the precursor becomes Na _{1 + x} MnPO ₄ F _x . The firing temperature is not particularly limited as long as it is a temperature capable of synthesizing the target compound. However, in order to allow the reaction to proceed sufficiently, the firing temperature needs to be 500 ° C. or higher. When the temperature exceeds 800 ° C., fluorine decomposes and deviates during firing, and the by-product may lower the purity of the target compound. The baking temperature is usually suitably 500 to 800 ° C, preferably 550 to 700 ° C, more preferably 550 to 650 ° C. The firing time may be a time until each component of the precursor sufficiently (uniformly) reacts, and is usually 1 to 10 hours, preferably 3 to 6 hours, and particularly preferably 4 to 5 hours. It's time. The firing means is not particularly limited, and any means such as an electric heating furnace can be adopted. The firing atmosphere is not particularly limited. For example, the firing atmosphere may be fired in an air atmosphere or, if necessary, in an inert gas atmosphere such as Ar gas. From the viewpoint of preventing more reliably, firing in an inert gas atmosphere such as Ar gas is preferable.

  If necessary, the firing can be performed in a plurality of times. That is, in performing the above-mentioned firing, first, it is temporarily fired in a relatively low temperature range (for example, 300 ° C. to 400 ° C.), and after temporarily crushing the temporarily fired product, a higher temperature range (for example, 500 ° C. to The main baking is performed at 800 ° C.). In this way, when the precursor is fired in a higher temperature range (for example, 500 ° C. to 800 ° C.) from the beginning by first performing preliminary firing in a lower temperature range and then performing main firing in a higher temperature range. In comparison, the homogeneity of the finally obtained compound can be increased. The operation of crushing the calcined product and firing it again may be repeated before the main firing.

Na _{1 + x} MnPO ₄ F _x can also be produced by a conventionally known solid phase method. However, particles obtained by the conventional solid phase method (typically in a spherical form) have a long diffusion path in the b-axis direction of the crystal because they are enlarged by sintering. Therefore, the diffusion resistance of Na ions in the particles is large, and charging / discharging cannot be performed.

On the other hand, according to the manufacturing method according to the present embodiment, Na _{1 + x} MnPO ₄ F _x starting material is reacted in a solvent containing a metal chelate-forming functional group to grow particles (particularly in the b-axis direction). Growth) is appropriately suppressed, and the particle shape of Na _{1 + x} MnPO ₄ F _x is controlled to an unprecedented plate shape. For this reason, the Na ion diffusion path only in the b-axis direction is shortened, and the Na ions diffuse efficiently in the particles. Such Na _{1 + x} MnPO ₄ F _x powder is a chargeable / dischargeable material that promotes Na ion diffusibility and reversibly absorbs and releases Na ions, and is an active material for a non-aqueous electrolyte secondary battery (for example, a positive electrode). It can be suitably used as an active material.

The Na _{1 + x} MnPO ₄ F _x powder thus obtained may be used as a positive electrode active material as it is, but may be formed into a composite with a carbon material in order to supplement electronic conductivity. Examples of the carbon material include carbon black (acetylene black (AB) and the like), carbon fiber, and the like. Although it is not particularly limited, the preferred amount of the carbon material is about 1 to 30% by mass with respect to the total mass of Na _{1 + x} MnPO ₄ F _x , and is usually preferably 5 to 25% by mass. . Formation of the composite can be performed by mixing the obtained fired product (Na _{1 + x} MnPO ₄ F _x ) and a carbon material and pulverizing them using an appropriate pulverizing apparatus (for example, a ball mill apparatus) after the above calcination. it can. By this pulverization treatment, a carbon material is pressed onto the surface of Na _{1 + x} MnPO ₄ F _x , and the particle surface is covered with the carbon material. Conductivity can be imparted by the coating of the carbon material. In addition, there is a merit that a mechanochemical reaction occurs due to frictional heat generated in the pulverization process, and an impurity phase remaining due to insufficient reaction (for example, unreacted starting materials and reaction byproducts) can be decomposed. Although it does not specifically limit as grinding | pulverization time, From the viewpoint of decomposing | disassembling an impurity phase reliably, it is appropriate to set it as about 10 hours or more normally, and it is usually preferable to set it as about 15-25 hours.

Preferably, after the pulverization, the obtained pulverized body (electrode active material-carbon material composite material powder) is refired at 500 ° C to 800 ° C. According to this aspect, the impurity phase is decomposed by the above pulverization, and the reactivation is performed after lowering the activation energy for the reaction between the impurity phases, so that homogenization of the target compound further proceeds and the purity of Na _{1 + x} MnPO ₄ F _x Can be further enhanced. The re-baking temperature may be the same as the main baking temperature described above, and is usually 500 to 800 ° C, preferably 550 to 700 ° C, more preferably 550 to 650 ° C. The refiring time may be a time for sufficiently homogenizing the target compound, and is usually 1 to 10 hours, preferably about 3 to 6 hours, and particularly preferably about 4 to 5 hours.

As described above, the Na _{1 + x} MnPO ₄ F _x obtained by the manufacturing method of the present embodiment is controlled to have a plate shape that is not conventional as described above, and reversibly occludes and releases Na ions. Therefore, it can be preferably used as a component of a nonaqueous electrolyte secondary battery of various forms or a component of a electrode (positive electrode active material) incorporated in the nonaqueous electrolyte secondary battery. Except for using Na _{1 + x} MnPO ₄ F _x disclosed herein as the positive electrode active material, a non-aqueous electrolyte secondary battery can be constructed by adopting the same process as the conventional one.

For example, Na _{1 + x} MnPO ₄ F _x plate powder (powdered positive electrode active material) disclosed herein, carbon black such as acetylene black and ketjen black as a conductive material, and other powdery carbon materials (graphite etc.) Can be mixed. In addition to the positive electrode active material and the conductive material, a binder (binder) such as polyvinylidene fluoride (PVDF), styrene butadiene rubber (SBR), polytetrafluoroethylene (PTFE), or carboxymethyl cellulose (CMC) is added. be able to. By dispersing these in a suitable dispersion medium and kneading, the composition for forming a positive electrode active material layer (hereinafter referred to as “positive electrode active material layer forming paste”) is in the form of a paste (including slurry or ink. The same shall apply hereinafter). Can be prepared.). An appropriate amount of this paste is applied onto a positive electrode current collector preferably made of aluminum or an aluminum-based alloy, and then dried and pressed to produce a positive electrode for a nonaqueous electrolyte secondary battery. it can.

  On the other hand, the negative electrode for a non-aqueous electrolyte secondary battery serving as a counter electrode can be produced by a method similar to the conventional one. For example, the negative electrode active material may be any material that can occlude and release sodium. A typical example is a powdery carbon material made of graphite or the like. As in the case of the positive electrode, the powdery material is dispersed in a suitable dispersion medium together with a suitable binder (binder) and kneaded to obtain a paste-like composition for forming a negative electrode active material layer (hereinafter referred to as “negative electrode active material”). May be referred to as “layer forming paste”). An appropriate amount of this paste is applied onto a negative electrode current collector preferably made of copper, nickel, or an alloy thereof, and further dried and pressed, whereby a negative electrode for a nonaqueous electrolyte secondary battery can be produced.

In the nonaqueous electrolyte secondary battery using the Na _{1 + x} MnPO ₄ F _x powder of the present invention as the positive electrode active material, a separator similar to the conventional one can be used. For example, a porous sheet (porous film) made of a polyolefin resin can be used.

Further, as the electrolyte, a non-aqueous electrolyte (typically, an electrolytic solution) can be used. Typically, the composition includes a supporting salt in a suitable nonaqueous solvent. Examples of the non-aqueous solvent include one or two selected from the group consisting of propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and the like. More than seeds can be used. Examples of the supporting salt include NaPF ₆ , NaBF ₄ , NaClO ₄ , NaAsF ₆ , NaCF ₃ SO ₃ , NaC ₄ F ₉ SO ₃ , NaN (CF ₃ SO ₂ ) ₂ , NaC (CF ₃ SO ₂ ). _{3. One} or two or more sodium compounds (sodium salts) selected from NaI and the like can be used.

Further, as long as the employed the Na 1 _{+ x} MnPO ₄ F _x powder disclosed herein as a positive electrode active material is not particularly limited to the non-aqueous electrolyte secondary battery of the shape (outer shape and size) to be constructed. The outer package may be a thin sheet type constituted by a laminate film or the like, and the battery outer case may be a cylindrical or cuboid battery, or may be a small button shape.

  Hereinafter, although the usage mode of the positive electrode disclosed here will be described by taking a nonaqueous electrolyte secondary battery including a wound electrode body as an example, it is not intended to limit the present invention to such an embodiment.

  As shown in FIG. 1, the nonaqueous electrolyte secondary battery 100 according to this embodiment includes a long positive electrode sheet 10 and a long negative electrode sheet 20 wound flatly via a long separator 40. The electrode body (winding electrode body) 80 in the form of being formed is housed in a container 50 having a shape (flat box shape) capable of housing the winding electrode body 80 together with a non-aqueous electrolyte (not shown). .

  The container 50 includes a flat rectangular parallelepiped container body 52 having an open upper end, and a lid body 54 that closes the opening. As a material constituting the container 50, a metal material such as aluminum or steel is preferably used (in this embodiment, aluminum). Or the container 50 formed by shape | molding resin materials, such as polyphenylene sulfide resin (PPS) and a polyimide resin, may be sufficient. On the upper surface of the container 50 (that is, the lid 54), a positive electrode terminal 70 that is electrically connected to the positive electrode of the wound electrode body 80 and a negative electrode terminal 72 that is electrically connected to the negative electrode 20 of the electrode body 80 are provided. Yes. Inside the container 50, a flat wound electrode body 80 is accommodated together with a non-aqueous electrolyte (not shown).

The material and member itself constituting the wound electrode body 80 having the above-described configuration may be the same as the electrode body of the conventional nonaqueous electrolyte secondary battery, except that Na _{1 + x} MnPO ₄ F _x is used as the positive electrode active material. There is no. As shown in FIG. 2, the wound electrode body 80 according to the present embodiment has a long (strip-shaped) sheet structure in a stage before assembling the wound electrode body 80.

  The positive electrode sheet 10 has a structure in which a positive electrode active material layer 14 containing a positive electrode active material is held on both surfaces of a long sheet-like foil-shaped positive electrode current collector (hereinafter referred to as “positive electrode current collector foil”) 12. ing. However, the positive electrode active material layer 14 is not attached to one side edge (lower side edge portion in the figure) of the positive electrode sheet 10 in the width direction, and the positive electrode current collector 12 is exposed with a certain width. An active material layer non-formation part is formed. Similarly to the positive electrode sheet 10, the negative electrode sheet 20 holds a negative electrode active material layer 24 containing a negative electrode active material on both sides of a long sheet-like foil-shaped negative electrode current collector (hereinafter referred to as “negative electrode current collector foil”) 22. Has a structured. However, the negative electrode active material layer 24 is not attached to one side edge (the upper side edge portion in the figure) of the negative electrode sheet 20 in the width direction, and the negative electrode active material 22 in which the negative electrode current collector 22 is exposed with a certain width. A material layer non-formation part is formed.

  In producing the wound electrode body 80, the positive electrode sheet 10 and the negative electrode sheet 20 are laminated via the separator sheet 40. At this time, the positive electrode sheet 10 and the negative electrode sheet 20 are formed such that the positive electrode active material layer non-formed portion of the positive electrode sheet 10 and the negative electrode active material layer non-formed portion of the negative electrode sheet 20 protrude from both sides in the width direction of the separator sheet 40. Are overlapped slightly in the width direction. The laminated body thus stacked is wound, and then the obtained wound body is crushed from the side surface direction and ablated, whereby a flat wound electrode body 80 can be produced.

  A wound core portion 82 (that is, the positive electrode active material layer 14 of the positive electrode sheet 10, the negative electrode active material layer 24 of the negative electrode sheet 20, and the separator sheet 40) is densely arranged in the central portion of the wound electrode body 80 in the winding axis direction. Laminated portions) are formed. In addition, the electrode active material layer non-formed portions of the positive electrode sheet 10 and the negative electrode sheet 20 protrude outward from the wound core portion 82 at both ends in the winding axis direction of the wound electrode body 80. A positive electrode lead terminal 74 and a negative electrode lead terminal 76 are respectively provided on the protruding portion 84 (that is, a portion where the positive electrode active material layer 14 is not formed) 84 and the protruding portion 86 (that is, a portion where the negative electrode active material layer 24 is not formed) 86. Attached and electrically connected to the positive terminal 70 and the negative terminal 72 described above.

  The wound electrode body 80 having such a configuration is accommodated in the container main body 52, and an appropriate nonaqueous electrolytic solution is disposed (injected) into the container main body 52. Then, the construction (assembly) of the nonaqueous electrolyte secondary battery 100 according to the present embodiment is completed by sealing the opening of the container body 52 by welding or the like with the lid 54. In addition, the sealing process of the container main body 52 and the arrangement | positioning (injection) process of electrolyte solution can be performed similarly to the method currently performed by manufacture of the conventional nonaqueous electrolyte secondary battery. Thereafter, the battery is conditioned (initial charge / discharge). You may perform processes, such as degassing and a quality inspection, as needed.

In the following test examples, a nonaqueous electrolyte secondary battery (sample battery) was constructed using the Na ₂ MnPO ₄ F powder disclosed herein as a positive electrode active material, and its performance was evaluated.

<Synthesis of Na ₂ MnPO ₄ F powder>
First, 7.3527 g of manganese acetate tetrahydrate ((CH ₃ COO) ₂ Mn · 4H ₂ O) as a Mn source was dissolved in 20 ml of pure water, and this was mixed with 160 ml of diethylene glycol (polyol solvent) with a suitable stirring device. The mixture was heated to 140 ° C. and stirred for 1 hour. Next, 3.4509 g of ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ) as a P source and 1.2597 g of sodium fluoride (NaF) as a Na source and an F source were dissolved in 30 ml of pure water. It added to the stirring apparatus mentioned above, and it heated at 180 degreeC and stirred for 2 hours. Subsequently, 1.2597 g of sodium fluoride (NaF) as Na source and F source was dissolved in 30 ml of pure water, and this was added to the stirring device described above, heated to 140 ° C. and stirred to give a precursor ( Reaction product) was obtained. The obtained precursor was separated by a centrifuge and dried at 180 ° C.

The X-ray diffraction pattern of the obtained precursor was measured. As a result, as shown in FIG. 3B, a peak attributed to Na ₂ MnPO ₄ F was observed. That is, it was confirmed that by reacting the starting material in a polyol solvent, fluorine was taken into the phosphate without deviating and a precursor of Na ₂ MnPO ₄ F could be formed.

The precursor thus obtained was pre-fired at 300 ° C. for 3 hours in an Ar atmosphere, and once pulverized, it was further fired at 600 ° C. for 5 hours. This _gave Na 2 MnPO ₄ F powder.

The X-ray diffraction pattern of the obtained Na ₂ MnPO ₄ F powder was measured. As a result, as shown in FIG. 3A, a peak attributed to Na ₂ MnPO ₄ F appeared clearly, and it was confirmed that the target compound with high crystallinity was obtained. On the other hand, a peak attributed to the Mn-containing compound and NaF also appeared, and it was found that a slight impurity phase was included. The obtained Na ₂ MnPO ₄ F had a space group of P21 / n, and lattice constants of a = 13.679 ＝, b = 5.3198Å, and c = 13.710Å. An SEM image of such Na ₂ MnPO ₄ F powder is shown in FIG. As is clear from FIG. 4, the Na ₂ MnPO ₄ F powder obtained in this example had a plate-like form with no particle shape. When the average thickness of the plate-like particles (average length in the thickness direction of the plate-like particles) was measured by SEM observation, it was about 100 nm. The average thickness is preferably about 100 nm or less (for example, 50 to 100 nm), more preferably 90 nm or less (for example, 50 to 90 nm), and particularly preferably 80 nm or less (for example, 50 to 80 nm). The smaller the average thickness of the plate-like particles, the better the diffusibility of Na ions.

<Formation of positive electrode active material-carbon material composite powder>
The obtained Na ₂ MnPO ₄ F (positive electrode active material) powder 0.5 g was pulverized for 1 hour using a general ball mill apparatus. Next, 0.17857 g of carbon black as a carbon material is put into a ball mill apparatus and pulverized for 21 hours, and carbon black is pressure-bonded to the particle surface, whereby Na ₂ MnPO ₄ F as a positive electrode active material and carbon as a carbon material. A composite material powder (positive electrode active material-carbon material composite material powder) containing black was obtained. An X-ray diffraction pattern of the obtained composite material powder is shown in FIG. As shown in FIG. _{5 (b), Na 2 MnPO} 4 peak attributable to F becomes broad, the peak intensity weakened. The reason for this is considered that the crystal structure of Na ₂ MnPO ₄ F was broken by the pulverization treatment, and amorphization progressed.

The obtained composite material powder (Na ₂ MnPO ₄ F powder with carbon black) was refired at 600 ° C. for 5 hours in an Ar atmosphere, and the fired product was pulverized to a suitable particle size by a ball mill. The X-ray diffraction pattern of the composite material powder after such re-firing is shown in FIG. As shown in FIG. 5A, a peak attributed to Na ₂ MnPO ₄ F appears clearly, and a peak attributed to Mn-containing compound and NaF remaining due to insufficient reaction (FIG. 3 ( a) also disappeared. FIG. 6 shows an SEM image of the composite material powder after such refiring. As is clear from FIG. 6, it was confirmed that the composite powder maintained a plate-like form even after re-firing.

<Construction of non-aqueous electrolyte secondary battery (sample battery)>
A specimen of a non-aqueous electrolyte secondary battery was constructed using the composite material powder (Na ₂ MnPO ₄ F powder with carbon black) obtained above. Such a specimen was prepared in order to confirm whether the Na ₂ MnPO ₄ F obtained in this example can reversibly occlude and release Na ions, and may differ from an actual battery configuration. Here, a specimen was produced as follows. First, the composite material powder obtained above and polyvinylidene fluoride (PVdF) as a binder are weighed to a mass ratio of 95: 5 and mixed in N-methylpyrrolidone (NMP). A paste-like composition for positive electrode active material was prepared. The positive electrode sheet in which the positive electrode active material layer is provided on one surface of the positive electrode current collector by applying the paste composition for the positive electrode active material layer in a layer form on one surface of the aluminum foil (positive electrode current collector) and drying it. Got.

The positive electrode sheet was punched into a circle having a diameter of 16 mm to produce a positive electrode. This positive electrode (working electrode), metallic lithium as a negative electrode (counter electrode) (metal Li foil having a diameter of 19 mm and a thickness of 0.02 mm was used), and a separator (PP (polypropylene having a diameter of 22 mm and a thickness of 0.02 mm) ) / PE (polyethylene) / PP (polypropylene) three-layer porous sheet) was incorporated into a stainless steel container together with a non-aqueous electrolyte, and had a diameter of 20 mm and a thickness of 3.2 mm (2032 type). A coin cell 60 (half cell for charge / discharge performance evaluation) shown in FIG. 7 was constructed. In FIG. 7, reference numeral 61 is a positive electrode (working electrode), reference numeral 62 is a negative electrode (counter electrode), reference numeral 63 is a separator impregnated with an electrolyte, reference numeral 64 is a gasket, reference numeral 65 is a container (negative electrode terminal), Reference numeral 66 denotes a lid (positive electrode terminal). In addition, as a nonaqueous electrolyte, about 1 mol of LiPF ₆ as a supporting salt is contained in a mixed solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 3: 3: 4. The one contained at a concentration of 1 / liter was used.

<Cyclic voltammetry measurement>
Cyclic voltammetry measurement was performed on the nonaqueous electrolyte secondary battery (sample battery) obtained as described above. Regarding the measurement conditions, the potential scanning range of the working electrode with respect to the lithium metal plate was 2.5 V to 5 V (vs. Li ⁺ / Li), and the potential scanning speed was 0.5 mV / s. The result is shown in FIG. In the figure, the horizontal axis represents the scanning potential (V), and the vertical axis represents the current (mA).

As is clear from FIG. 8, the oxidation current peak P1 appears on the cyclic voltammogram in the potential range of 2.5V to 5V, and the Na ₂ MnPO ₄ F powder obtained in this example releases (desorbs) Na ions. It was confirmed that the material can be charged with Further, a reduction current peak P2 appears on the cyclic voltammogram in the potential range of _2.5 V to ₅ V, and the Na ₂ MnPO ₄ F powder obtained by this example is accompanied by insertion (insertion) of Na ions (and Li ions). It was confirmed that the material can be discharged.

From the above results, according to the present example, by reacting Na _{1 + x} MnPO ₄ F _x starting material in a polyol solvent, Na ₂ MnPO ₄ F is controlled in a plate-like form, whereby a chargeable / dischargeable material and We were able to. Therefore, according to this configuration, it is possible to realize a nonaqueous electrolyte secondary battery including Na ₂ MnPO ₄ F capable of reversibly occluding and releasing Na ions as an electrode active material. A non-aqueous electrolyte secondary battery including Na ₂ MnPO ₄ F as an electrode active material can be manufactured using abundant Na and Mn as resources, and has high utility value.

  The non-aqueous electrolyte secondary battery according to the present invention can be suitably used as a power source for a motor (electric motor) mounted on a vehicle such as an automobile. Therefore, as schematically shown in FIG. 9, the present invention provides a vehicle (typically an automobile, in particular,) having such a non-aqueous electrolyte secondary battery (typically, a plurality of series-connected batteries) 100 as a power source. A vehicle including an electric motor such as a hybrid vehicle, an electric vehicle, and a fuel cell vehicle) 1 is provided.

DESCRIPTION OF SYMBOLS 10 Positive electrode sheet 12 Positive electrode collector 14 Positive electrode active material layer 20 Negative electrode sheet 22 Negative electrode collector 24 Negative electrode active material layer 40 Separator sheet 50 Container 52 Container body 54 Lid 60 Coin cell 70 Positive electrode terminal 72 Negative electrode terminal 74 Positive electrode lead terminal 76 Negative electrode lead terminal 80 Winding electrode body 82 Winding core portion 100 Nonaqueous electrolyte secondary battery

Claims (8)

A non-aqueous electrolyte secondary battery comprising an electrode active material capable of reversibly occluding and releasing sodium,
The electrode active material has a plate shape in particle shape, and has the following composition formula:
Na _{1 + x} MnPO ₄ F _x (wherein x is 0 <x ≦ 1);
A non-aqueous electrolyte secondary battery represented by   The nonaqueous electrolyte secondary battery according to claim 1, wherein x in the formula is 0.5 ≦ x ≦ 1. A method for producing an electrode active material comprising a metal compound represented by a composition formula Na _{1 + x} MnPO ₄ F _x (where x is 0 <x ≦ 1),
Mixing raw materials including a sodium source, a manganese source, a phosphate source and a fluorine source in a solvent containing a metal chelate-forming functional group to prepare a raw material mixture;
Heating the raw material mixture to obtain a precursor;
A method for producing an electrode active material, comprising a step of firing the precursor at a predetermined temperature.   The method according to claim 3, wherein the metal chelate-forming functional group is at least one functional group selected from the group consisting of an alcohol group, a carbonyl group, and an ether group.   The production method according to claim 3 or 4, wherein the solvent is a polyol solvent.   The manufacturing method according to any one of claims 3 to 5, wherein the firing temperature of the precursor is 500C to 800C.   The manufacturing method according to any one of claims 3 to 6, wherein a carbon material is mixed and pulverized in the obtained fired product after the firing. The manufacturing method according to claim 7, wherein after the pulverization, the obtained pulverized product is refired at 500C to 800C.