WO2013187160A1 - ナトリウム電池用正極材料及びその製造方法 - Google Patents
ナトリウム電池用正極材料及びその製造方法 Download PDFInfo
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- H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
- H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
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- H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
- H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
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- H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
- H01M4/5805—Phosphides
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- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
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- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
- H01M2004/028—Positive electrodes
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- H01M2220/00—Batteries for particular applications
- H01M2220/30—Batteries in portable systems, e.g. mobile phone, laptop
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
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- Y02E60/10—Energy storage using batteries
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- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
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Definitions
- the present invention relates to a positive electrode material for a sodium battery and a method for producing the same.
- a lithium metal composite oxide having a layered structure such as lithium nickelate or lithium cobaltate is generally used as a positive electrode active material, and lithium ion insertion / extraction is performed as a negative electrode active material.
- Possible carbon materials, lithium metals, lithium alloys and the like are used.
- an electrolyte solution in which a lithium salt is dissolved, a solid electrolyte containing lithium, or the like is used.
- Lithium batteries are excellent in energy density and output as described above. On the other hand, the price of lithium has increased along with the expansion of demand for lithium batteries, and the amount of lithium reserves has been limited. It has become a bottleneck in the process.
- Patent Document 1 describes Ma x Mb y P 2 O 7 (Ma represents Na, Li, Ca, or Mg, Mb represents a transition metal that is tetravalent or more and stably exists, and 0 ⁇ x ⁇ 4. , 0.5 ⁇ y ⁇ 3 and 6 ⁇ z ⁇ 14).
- the positive electrode active material for a non-aqueous electrolyte secondary battery is disclosed.
- it is MoP 2 O 7 that is actually manufactured and evaluated in the examples.
- Patent Document 1 since MoP 2 O 7 actually produced and evaluated in Patent Document 1 does not contain Na, when used as a positive electrode active material of a sodium battery, the operation of the sodium battery is caused by insertion of Na ions (discharge). Reaction). Therefore, it is necessary to use an active material containing Na in advance as the negative electrode active material to be combined.
- a Na-containing negative electrode active material that operates in a low potential region and can secure a sufficient electromotive force has not been reported at present, and there is a problem that it is difficult to put into practical use.
- the active material is required to have good electronic conductivity.
- the present invention has been accomplished in view of the above circumstances, and an object of the present invention is a positive electrode material for sodium batteries, which has a high operating potential, can be charged / discharged at a high potential, and has good electronic conductivity. And a method of manufacturing the same.
- the positive electrode material for sodium batteries of the present invention comprises positive electrode active material particles represented by the following general formula (1) and a conductive carbon material that covers at least a part of the surface of the positive electrode active material particles.
- M is at least one selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn, and A is Al, Si, P, S, It is at least one selected from the group consisting of Ti, V and W, x satisfies 4 ⁇ x ⁇ 2, y satisfies 4 ⁇ y ⁇ 1, z satisfies 4 ⁇ z ⁇ 0, and w is 1 ⁇ w ⁇ 0 is satisfied, and at least one of z and w is 1 or more).
- the positive electrode material for sodium batteries of the present invention has a high operating potential and good electronic conductivity. Therefore, according to the present invention, it is possible to increase the energy density of the sodium battery, and further improve the initial discharge capacity, the initial charge / discharge efficiency, and the discharge capacity after the charge / discharge cycle.
- the M is preferably divalent before charging. It is because it becomes possible to operate at a high potential by being in a highly oxidized state of 3 or more during charging.
- the positive electrode active material preferably has a crystal structure belonging to the space group Pn2 1 a.
- the space group Pn2 1 a When having a crystal structure belonging to the space group Pn2 1 a, all of the Na ions in the crystal structure are arranged in any one of the a-axis, b-axis, and c-axis, which is very advantageous for Na ion conduction. This is because.
- the M is at least one selected from the group consisting of Mn, Co, and Ni, and a part thereof , Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn, which may be substituted with at least one selected from the group consisting of M and the like.
- the positive electrode active material for a sodium battery in such a form easily takes a crystal structure belonging to the space group Pn2 1 a and is excellent in Na ion conductivity.
- M is Mn, and a part of Mn is Ti, V, Cr, Fe, Co, Ni, Cu and Zn. The thing which may be substituted by at least 1 sort (s) chosen from the group which consists of is mentioned.
- A is P, and a part of P is selected from the group consisting of Al, Si, S, Ti, V, and W.
- the thing which may be substituted by at least 1 sort (s) chosen is mentioned.
- the positive electrode active material having such a form easily takes a crystal structure belonging to the space group Pn2 1 a and is excellent in Na ion conductivity.
- positive electrode active material used in the present invention include those represented by the general formula Na 4 Mn 3 (PO 4 ) 2 (P 2 O 7 ).
- the manufacturing method of the positive electrode material for sodium batteries of this invention contains the positive electrode active material particle represented by following General formula (1), and the electroconductive carbon material which coat
- a method for producing a positive electrode material for a sodium battery comprising: A composite including the positive electrode active material particles and the conductive carbon material pressure-bonded to the surfaces of the positive electrode active material particles by press-bonding the conductive carbon material to the surfaces of the positive electrode active material particles by a mechanochemical treatment. A preparation process to prepare; and And heat-treating the composite in an inert atmosphere or a reducing atmosphere.
- M is at least one selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn, and A is Al, Si, P, S, It is at least one selected from the group consisting of Ti, V and W, x satisfies 4 ⁇ x ⁇ 2, y satisfies 4 ⁇ y ⁇ 1, z satisfies 4 ⁇ z ⁇ 0, and w is 1 ⁇ w ⁇ 0 is satisfied, and at least one of z and w is 1 or more.
- the production method of the present invention it is possible to produce a positive electrode material for a sodium battery having a high operating potential and good electronic conductivity, and increasing the energy density of the sodium battery, further, the initial discharge capacity, It is possible to improve the initial charge / discharge efficiency and the discharge capacity after the charge / discharge cycle.
- the M is preferably divalent before charging.
- the positive electrode active material used in the production method of the present invention preferably has a crystal structure belonging to the space group Pn2 1 a.
- M is at least one selected from the group consisting of Mn, Co, and Ni, and a part thereof is Ti, V, The thing which may be substituted by at least 1 sort (s) different from this M chosen from the group which consists of Cr, Mn, Fe, Co, Ni, Cu, and Zn is mentioned.
- M is Mn, and a part of Mn is Ti, V, Cr, Fe, Co, Ni, Cu and Zn. The thing which may be substituted by at least 1 sort (s) chosen from the group which consists of is mentioned.
- A is P, and a part of P is selected from the group consisting of Al, Si, S, Ti, V, and W.
- the thing which may be substituted by at least 1 sort (s) chosen is mentioned.
- the positive electrode active material having such a form easily takes a crystal structure belonging to the space group Pn2 1 a and is excellent in Na ion conductivity.
- positive electrode active material examples include those represented by the general formula Na 4 Mn 3 (PO 4 ) 2 (P 2 O 7 ).
- the present invention it is possible to provide a positive electrode material for a sodium battery having a high operating potential and good electronic conductivity, and a method for producing the same.
- positive electrode material for sodium batteries of the present invention
- positive electrode material the positive electrode material for sodium batteries of the present invention
- the positive electrode material for sodium batteries of the present invention comprises positive electrode active material particles represented by the following general formula (1) and a conductive carbon material that covers at least a part of the surface of the positive electrode active material particles. It is what.
- M is at least one selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn, and A is Al, Si, P, S, It is at least one selected from the group consisting of Ti, V and W, x satisfies 4 ⁇ x ⁇ 2, y satisfies 4 ⁇ y ⁇ 1, z satisfies 4 ⁇ z ⁇ 0, and w is 1 ⁇ w ⁇ 0 is satisfied, and at least one of z and w is 1 or more.
- the conventional positive electrode active material for a general sodium battery has a low operating potential of about 3.5 V or less. Moreover, when Li of the lithium battery active material is replaced with Na, the operating potential tends to decrease greatly. Furthermore, conventionally, since Na ions have a larger ion radius than Li ions, it has been considered that Na ions are difficult to move when Li in the Li-containing active material is replaced with Na. For these reasons, it was a general finding that in a lithium battery active material, simply replacing lithium with sodium did not yield a useful high-potential-operated sodium battery active material. .
- the present inventors the above general formula (1) Na x M y ( AO 4) z (P 2 O 7) compounds represented by where w is usable as a positive electrode active material of sodium battery, furthermore, 3 It has been found that it operates in a high potential region such as 0.0 to 5.0V.
- the positive electrode active material can exhibit high potential operability in a relatively low temperature range of 25 ° C.
- the general formula (1) Na x M y ( AO 4) z (P 2 O 7) compounds represented by w is, as a positive electrode active material of sodium battery, why it is possible to operate at high potential zone as follows Can be considered. That is, in the general formula (1), M is an electrochemically active bivalent or higher transition metal. Moreover, M has Mn (refer an Example) by which high potential operability was confirmed, or has an ion radius close
- the tetrahedral structure is a structure in which one A covalently bonded to these four oxygen atoms is contained in a tetrahedral void having four oxygen atoms as apexes.
- (AO 4 ) and (P 2 O 7 ) that are polyanion parts at least one of z representing the composition ratio of (AO 4 ) in the positive electrode active material and w representing the composition ratio of (P 2 O 7 ) Is 1 or more, it is considered that the positive electrode active material obtained operates in a high potential region due to the inductive effect on the MO bond by at least one of (AO 4 ) and (P 2 O 7 ).
- the inductive effect means that the A—O bond constituting (AO 4 ) and the P—O bond constituting (P 2 O 7 ) have high covalent bonds, so that the M—O bond electrons are converted into A—O bonds and P— As a result of being pulled to the -O bond side, the covalent bond between M and O is reduced, and the energy gap of the mixed orbitals is reduced. As a result, the redox level of M is lowered and the energy difference from sodium is increased. That is, the redox potential of sodium increases.
- This inventor was able to obtain a certain amount of results in expressing the high potential operability of the sodium battery by using the compound represented by the general formula (1) as the positive electrode active material of the sodium battery.
- the electron conductivity of the positive electrode active material is lowered depending on the type of M. Specifically, when M is Mn, M is compared with the case of other metals. Thus, it has been found that the electron conductivity of the positive electrode active material is extremely low at 1.0 ⁇ 10 ⁇ 12 S / cm or less. Therefore, when M is Mn, the internal resistance at the time of charging / discharging is large, and there arises a problem that a capacity density of only about 18 mAh / g can be obtained.
- the present inventor has applied a conductive carbon material to the surface of the positive electrode active material particles by mechanochemical treatment and heat-treated to coat at least a part of the surface of the positive electrode active material particles with the conductive carbon material. It has been found that by using the positive electrode material for a sodium battery thus obtained for a positive electrode of a sodium battery, the problem of low electron conductivity in a positive electrode active material such as M is M can be solved.
- the conductive carbon material covers at least part of the surface of the positive electrode active material particles means that the crystal phase of the positive electrode active material is amorphous of the conductive carbon material on at least a part of the surface of the positive electrode active material particles. It is in contact with a phase.
- Whether the surface of the positive electrode active material particles is coated with a conductive carbon material can be confirmed by observing the surface of the positive electrode active material particles of the positive electrode material for a sodium battery with a transmission electron microscope (TEM).
- TEM transmission electron microscope
- the positive electrode active material particles that are crystalline can be confirmed as a phase (crystal phase) having a lattice pattern derived from the periodic structure by electron diffraction using TEM.
- the conductive carbon material is amorphous, it is confirmed as a phase that does not have a lattice pattern like the positive electrode active material. Therefore, by TEM observation, the portion where the crystalline phase of the positive electrode active material having a lattice pattern and the amorphous phase of the conductive carbon material not having the lattice pattern are in contact with each other without any gaps. If it can observe, it can be said that the electroconductive carbon material has coat
- the measurement conditions with a transmission electron microscope are not particularly limited as long as an electron diffraction image can be confirmed. For example, the measurement magnification is preferably 200,000 to 500,000. The larger the coverage area of the surface of the positive electrode active material particles with the conductive carbon material, the better. It is preferable that the entire surface of the positive electrode active material is covered.
- the reason why the problem of low electron conductivity of the positive electrode active material can be solved is considered as follows. That is, by covering at least a part of the surface of the positive electrode active material particles with the conductive carbon material at the atomic level as described above, the conductive carbon material can supplement the electronic conductivity of the positive electrode active material. . Since the positive electrode material for sodium batteries of the present invention has good electronic conductivity, it can dramatically improve the initial discharge capacity, the initial charge / discharge efficiency, and the discharge capacity after cycling when used for the positive electrode of a sodium battery. Can be made.
- the M may be at least one metal species selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn.
- the state before charging it is preferably divalent. This is because when M is a metal species that is divalent in a state before charging, it can operate at a high potential by being in a highly oxidized state of trivalent or higher during charging.
- Mn, Co, and Ni are particularly preferable. This is because Mn, Co and Ni are divalent in the state before charging. These Mn, Co, and Ni are partly selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn (ie, Mn, Co, and Ni). It may be substituted with at least one different from at least one selected from Ni).
- the conductive carbon material supplements the electron conductivity of the positive electrode active material, and high electron conductivity can be ensured. Therefore, even when the positive electrode active material itself has a low electron conductivity as in the case where M is Mn, the electron conductivity can be improved and a suitable positive electrode material can be obtained.
- Mn may be substituted with at least one selected from the group consisting of Ti, V, Cr, Fe, Co, Ni, Cu, and Zn.
- the A may be at least one selected from the group consisting of Al, Si, P, S, Ti, V and W, but from Si, P and S It is preferably at least one selected from the group consisting of This is because Si, P, and S are particularly easy to form a tetrahedral structure, and Si and S can form a crystal structure similar to P.
- A is preferably P.
- a part of these Si, P, and S is selected from the group consisting of Al, Si, P, S, Ti, V, and W.
- At least one selected from A (that is, Si, P, and S) It may be substituted with at least one species different from the species.
- x satisfies 4 ⁇ x ⁇ 2
- y satisfies 4 ⁇ y ⁇ 1
- z satisfies 4 ⁇ z ⁇
- w satisfies 1 ⁇ w ⁇ 0, and z and w
- the positive electrode active material include a compound represented by Na 4 Mn 3 (PO 4 ) 2 (P 2 O 7 ).
- Na 4 Mn 3 (PO 4 ) 2 (P 2 O 7 ) contains Mn as a redox element and has (PO 4 ) and (P 2 O 7 ) as a polyanion part. This is because high electrical conductivity is ensured by assisting electronic conductivity by the conductive carbon material, and high potential operability is achieved by a high inductive effect.
- M is Mn, sufficient electron conductivity cannot be ensured as it is, so that it can be said that the effect of improving the electron conductivity by the coating of the conductive carbon material is particularly high.
- Na 4 Mn 3 (PO 4 ) 2 (P 2 O 7 ) has a crystal structure belonging to the space group Pn2 1 a.
- FIGS. 1 to 3 show the crystal structure (Na 4 Mn 3 (PO 4 ) 2 (P 2 O 7 )) belonging to the space group Pn2 1 a as seen from the a-axis direction (FIG. 1), from the b-axis direction.
- the figure (FIG. 2) seen and the figure (FIG. 3) seen from c-axis direction are shown.
- FIGS. 1 to 3 show the crystal structure belonging to the space group Pn2 1 a as seen from the a-axis direction (FIG. 1), from the b-axis direction.
- the figure (FIG. 2) seen and the figure (FIG. 3) seen from c-axis direction are shown.
- the positive electrode active material in the positive electrode material of the present invention preferably has a crystal structure belonging to the space group Pn2 1 a.
- the average particle diameter of the positive electrode active material particles is not particularly limited, but for example, it is preferably in the range of 1 nm to 100 ⁇ m, more preferably in the range of 10 nm to 30 ⁇ m.
- the average particle diameter of the positive electrode active material particles can be measured by, for example, a scanning electron microscope (SEM), a transmission electron microscope (TEM), or the like.
- the method for producing the positive electrode active material particles is not particularly limited. For example, a raw material mixture containing at least a Na-containing compound, an M-containing compound, an A-containing compound, and a P-containing compound is fired at 150 to 500 ° C. in an air atmosphere. And a main firing step in which the obtained calcined product is calcined at 500 to 800 ° C. in an air atmosphere after the calcining.
- the raw material mixture is first temporarily calcined at 150 to 500 ° C., lower than that in the main firing step, and then main calcined at 500 to 800 ° C., whereby the reaction proceeds uniformly and the single-phase positive electrode active material is activated. Substances can be synthesized.
- Na-containing compound, M-containing compound, A-containing compounds, and P-containing compound the positive electrode active material Na x M y (AO 4) z (P 2 O 7) is a raw material of w, respectively, Na source, M source, A source and P source.
- the Na-containing compound, M-containing compound, A-containing compound and P-containing compound are not particularly limited, and can be appropriately selected. Each compound may be used individually by 1 type, or may be used in combination of 2 or more type. One compound may contain two or more of Na, M, A and P. When M and A contain a common atom, the M-containing compound and the A-containing compound may be the same compound, and when A is P, the A-containing compound and the P-containing compound are The same compound may be used.
- Na-containing compound that is the Na source examples include Na 4 P 2 O 7 , Na 2 CO 3 , Na 2 O, Na 2 O 2 , Na 3 PO 4 , and CH 3 COONa.
- M-containing compound as the M source examples include Ti-containing compounds such as TiO 2 and Ti 2 O 3 , V-containing compounds such as V 2 O 3 , V 2 O 5 , and NH 4 VO 3 , Cr
- the containing compound examples include Cr 2 O 3 and Cr (NO 3 ) 3.
- Mn-containing compound examples include MnCO 3 and (CH 3 COO) 2 Mn.
- Fe-containing compound examples include FeO, Fe 2 O 3 , and Fe.
- Co-containing compounds such as CoCO 3 , (CH 3 COO) 2 Co, CoO, and Co 2 O 3 , and the like
- Ni-containing compounds such as (CH 3 COO) 2 Ni, NiCO 3 , and NiO etc.
- Cu-containing compounds include (CH 3 COO) 2 Cu, and CuO or the like, as Zn-containing compound, (CH 3 COO) 2 Zn , and, ZnO and the like
- Examples of the A-containing compound as the A source include Al (NO 3 ) 3 , Al 2 O 3 , and Al (OH) 3 as the Al-containing compound, SiO 2 and SiO, etc. as the Si-containing compound, P Examples of the compound containing NH 4 H 2 PO 4 , (NH 4 ) 2 HPO 4 , H 3 PO 4 , Na 2 P 2 O 7, and Na 3 PO 4, such as S-containing compounds (NH 4 ) 2 SO 4 , Na 2 SO 4 and H 2 SO 4, etc. Ti-containing compounds such as TiO 2 and Ti 2 O 3 , V-containing compounds such as V 2 O 3 , V 2 O 5 , NH 4 VO 3, etc. W containing Examples of the compound include WO 3 and Na 2 WO 4 .
- P-containing compounds that are P sources include Na 4 P 2 O 7 , NH 4 H 2 PO 4 , (NH 4 ) 2 HPO 4 , H 3 PO 4 , Na 2 P 2 O 7, and Na 3 PO 4. It is done.
- Raw material mixture, the Na-containing compound, M-containing compound, the mixing ratio of the A-containing compounds and P-containing compounds, synthesized Na x M y (AO 4) z (P 2 O 7) x in w, y, z, And w may be set as appropriate.
- the preparation method of a raw material mixture is not specifically limited, Arbitrary mixing methods, stirring methods, etc. are employable.
- the size of the particles of each compound is not particularly limited, but in order to make the reaction proceed uniformly, it is preferable that the contact area between the particles is large. It is preferable to keep it. That is, it is preferable to provide a pulverization step for pulverizing the Na-containing compound, the M-containing compound, the A-containing compound, and the P-containing compound in the raw material mixture before temporary firing.
- the compound may be pulverized simultaneously for a plurality of compounds or for each compound.
- the pulverization method is not particularly limited, and any method can be adopted, and a method combining mixing, stirring and pulverization of the raw material mixture can also be adopted.
- a ball mill, a bead mill, and the like can be mixed and stirred while pulverizing the raw material mixture.
- the calcination temperature is lower than that in the main calcination step and may be in the range of 150 to 500 ° C., but is preferably 180 to 450 ° C., more preferably 250 to 350 ° C.
- the calcination time is not particularly limited and may be set as appropriate. For example, it may be about 1 to 5 hours.
- the air atmosphere that is the atmosphere of the pre-baking step means an oxygen-containing gas atmosphere.
- the temporarily fired product obtained in the temporary firing step is fired at 500 to 800 ° C. in an air atmosphere.
- the firing temperature in the main firing step is preferably 550 to 750 ° C.
- the main baking time is not particularly limited and may be set as appropriate. For example, it may be about 1 to 30 hours.
- the air atmosphere that is the atmosphere of the main baking step is the same as the air atmosphere of the temporary baking step.
- the manufacturing method of positive electrode active material particle is not limited to the said method.
- it can be manufactured by the following method. That is, first, an Na-containing compound as a Na source, an M-containing compound as an M source, an A-containing compound as an A source, and a P-containing compound as a P source are dissolved in an acidic solution together with a gelling agent. Heat to prepare gel. Next, the obtained gel is baked in an air atmosphere.
- any compound that can be dissolved in an acidic solution may be used.
- Each compound may be used individually by 1 type, or may be used in combination of 2 or more type.
- One compound may contain two or more of Na, M, A and P.
- M and A contain a common atom
- the M-containing compound and the A-containing compound may be the same compound
- a is P the A-containing compound and the P-containing compound are The same compound may be used.
- examples of the Na-containing compound include Na 4 P 2 O 7 , Na 2 CO 3 , Na 2 O, Na 2 O 2 , and CH 3 COONa.
- M-containing compounds examples include Cr-containing compounds such as Ti-containing compounds such as TiO 2 , Ti 2 O 3 , and Ti (NO 3 ) 4 , and V-containing compounds such as V 2 O 3 and V 2 O 5 .
- Mn-containing compounds such as Cr (NO 3 ) 3 , MnCO 3 , MnO, MnO 2 , and (CH 3 COO) 2 Mn etc.
- Fe-containing compounds Fe (NO 3 ) 3 , FeC 2 O 4 , And (CH 3 COO) 3 Fe, etc., Co-containing compounds such as CoCO 3 , (CH 3 COO) 2 Co, and Co 2 O 3, etc., Ni-containing compounds such as (CH 3 COO) 2 Ni, etc., Cu-containing compounds (CH 3 COO) 2 Cu and the like, and as the Zn-containing compound, (CH 3 COO) 2 Zn and the like can be mentioned.
- Examples of the A-containing compound include Al (NO 3 ) 3 as the Al-containing compound, (CH 3 CH 2 O) 4 Si, etc. as the Si-containing compound, NH 4 H 2 PO 4 , ( NH 4 ) 2 HPO 4 , H 3 PO 4, etc., as S-containing compounds, Na 2 SO 4 , H 2 SO 4 etc., Ti-containing compounds, such as TiO 2 , Ti 2 O 3 , and Ti (NO 3 ) 4 , V 2 -containing compounds such as V 2 O 3 and V 2 O 5 , and W-containing compounds include WO 3 and Na 2 WO 4 .
- Examples of the P-containing compound include NH 4 H 2 PO 4 , (NH 4 ) 2 HPO 4 , and H 3 PO 4 .
- Raw material mixture, the Na-containing compound, M-containing compound, the mixing ratio of the A-containing compounds and P-containing compounds, like pre-baking step, Na x M y (AO 4 ) to synthesize z (P 2 O 7) x in w , Y, z, and w may be set as appropriate.
- gelling agent examples include glycolic acid.
- an acidic solution examples include nitric acid aqueous solution etc. are mentioned, for example.
- the heating temperature at the time of gel preparation is not particularly limited as long as the above-mentioned compounds can be dissolved in an acidic solution to prepare a gel, and can be set to 60 to 120 ° C., for example.
- the firing temperature of the gel can be, for example, 500 to 800 ° C., and preferably 600 to 750 ° C.
- the air atmosphere at the time of gel baking is the same as the air atmosphere in the preliminary baking step.
- the conductive carbon material is not particularly limited as long as it can supplement the electron conductivity of the positive electrode active material, and examples thereof include acetylene black, graphite, and ketjen black.
- the content of the conductive carbon material in the positive electrode material is not particularly limited, but is preferably 1% by weight or more, particularly preferably 5% by weight or more from the viewpoint of obtaining the electronic conductivity auxiliary effect, and securing the positive electrode active material amount. In view of the above, it is preferably 35% by weight or less.
- the thickness of the conductive carbon material covering the surface of the positive electrode active material particles is not particularly limited, but is preferably 1 to 30 nm.
- the positive electrode active material particles are Li, Mg, Al, Ca, Sr, Y, Zr, Nb, etc. for the purpose of improving cycle characteristics, improving oxidation breakdown voltage characteristics, improving high rate discharge characteristics / storage characteristics, and the like.
- the positive electrode active material particles are Li, Na, Mg, Al, Si, Ca, Ti, V, etc.
- cycle characteristics for the purpose of improving cycle characteristics, improving oxidation breakdown voltage characteristics, improving high rate discharge characteristics / storage characteristics, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sr, Y, Zr, Nb, Mo, Pd, Ag, In, Sn, Sb, Ba, Hf, Ta, W, Ir, Bi, lanthanoid (La, Such as Ce, Pr, Nd, Sm, Eu, Gd, Dy, Er, Yb, etc.), and oxides, fluorides, oxyfluorides, phosphides, nitrides, sulfides, carbides, borides of these metals.
- All or part of the surface thereof may be coated with at least one selected from chloride, bromide, iodide, phosphate, carbonate, sulfate, silicate, and titanate.
- the thickness of the covering portion is not particularly limited, but is preferably in the range of 1 nm to 200 nm.
- the positive electrode active material particles having such a covering portion may be coated with a conductive carbon material, or the region not covered with the covering portion may be covered with a conductive carbon material. Also good.
- a method for synthesizing a positive electrode active material containing the above element for example, a raw material (such as a compound containing the above element) that becomes the element source at the time of synthesizing the positive electrode active material is mixed with other positive electrode active material materials, Examples of the method include synthesis by baking, a sol-gel method, a hydrothermal method, a coprecipitation method, and the like, and further heating in some cases.
- a gas phase method for example, sputtering method, vapor deposition method, atomic layer deposition method (ALD method), etc.
- the liquid phase method for example, sol-gel method, hydrothermal method, coprecipitation method, etc.
- spin coating method for example, spraying by spraying, etc.
- the positive electrode active material surface is coated with the constituent material of the coating part, In some cases, a method of further heating may be mentioned.
- the above synthesis methods are not limited to these, and known synthesis processes can be widely used.
- Method for producing positive electrode material Although the method for manufacturing the positive electrode material of the present invention is not particularly limited, a preferable method includes a manufacturing method described below.
- the method for producing the positive electrode material for sodium batteries of the present invention comprises A conductive carbon material is pressure-bonded to the surface of the positive electrode active material particles by mechanochemical treatment, and a composite including the positive electrode active material particles and the conductive carbon material pressure-bonded to the surface of the positive electrode active material particles is prepared. A preparation process; And heat-treating the composite in an inert atmosphere or a reducing atmosphere.
- preparation process In the preparation step, a composite containing a positive electrode active material particle and a conductive carbon material pressure-bonded to the surface of the positive electrode active material particle is bonded to the surface of the positive electrode active material particle by mechanochemical treatment. It is a process to prepare.
- the mechanochemical treatment mechanical energy is applied to the positive electrode active material particles and the conductive carbon material, the conductive carbon material is pressure-bonded to the surface of the positive electrode active material particles, and the positive electrode active material particles and the surface of the positive electrode active material particles
- bonded to For example, processes, such as a planetary ball mill, a bead mill, and a stone mill, are mentioned.
- the rotational speed when the planetary ball mill is used is not particularly limited, but may be, for example, 80 to 450 rpm.
- the kneading time when a planetary ball mill is used is not particularly limited, and can be, for example, 1 to 30 hours.
- the material of the ball when the planetary ball mill is used is not particularly limited, and examples thereof include zirconia, and a material having high hardness is preferable.
- the diameter of the ball when the planetary ball mill is used is not particularly limited, but can be set to 1 to 10 mm, for example.
- the heat treatment step is a step of heat-treating the composite obtained in the preparation step in an inert atmosphere or a reducing atmosphere.
- the lower limit of the heat treatment temperature in the heat treatment step is preferably 500 ° C. or higher, more preferably 550 ° C. or higher, and particularly preferably 600 ° C. or higher.
- the upper limit value of the heat treatment temperature in the heat treatment step is preferably 800 ° C. or lower, more preferably 750 ° C. or lower.
- the heat treatment time is not particularly limited and may be set as appropriate. For example, the heat treatment time may be 1 to 24 hours, more preferably about 3 to 10 hours.
- Examples of the inert atmosphere include an argon-containing gas atmosphere and a nitrogen-containing gas atmosphere
- examples of the reducing atmosphere include a hydrogen-containing gas atmosphere.
- the positive electrode material provided by this invention can be used conveniently for the positive electrode of a sodium battery.
- the sodium battery may be a primary battery or a secondary battery.
- a sodium battery using the positive electrode material provided by the present invention will be described by taking a sodium secondary battery as an example.
- FIG. 4 is a schematic cross-sectional view showing one embodiment of a sodium secondary battery.
- the sodium secondary battery 8 usually has a structure in which the electrolyte layer 3 is interposed between the negative electrode 1 and the positive electrode 2.
- the negative electrode 1 includes a negative electrode active material layer 4 containing a negative electrode active material, and a negative electrode current collector 5 that collects current from the negative electrode active material layer 4.
- the positive electrode 2 includes a positive electrode active material layer 6 containing a positive electrode active material and a positive electrode current collector 7 that collects current from the positive electrode active material layer 6.
- Each configuration will be described below.
- the negative electrode contains a negative electrode active material capable of releasing and capturing sodium ions.
- the negative electrode usually has a negative electrode active material layer containing at least a negative electrode active material, and further includes a negative electrode current collector that collects current from the negative electrode active material layer as necessary.
- the negative electrode active material examples include Na metal, titanium oxide (for example, Na 2 Ti 3 O 7 , Na 2 Ti 6 O 13 , TiO 2 , Li 4 Ti 5 O 12, etc.), carbon (for example, hard carbon, Carbon microspheres, carbon nanotubes, etc.), those forming an alloy with Na (for example, Sn, Sb, Pb, Ge, Se, S, Te, Tl, and a metal species containing at least one element selected from Si and Si) Compounds), those that cause a conversion reaction (for example, Co 3 O 4 , Fe 2 O 3 , SnO, MoO 3 , NiCoO 4, etc.), Y 2 Ti 2 O 5 S 2 , and NaTi 2 (PO 4 ) 3
- titanium oxide for example, Na 2 Ti 3 O 7 , Na 2 Ti 6 O 13 , TiO 2 , Li 4 Ti 5 O 12, etc.
- carbon for example, hard carbon, Carbon microspheres, carbon nanotubes, etc.
- those forming an alloy with Na for example, Sn, Sb
- the negative electrode active material layer may contain only the negative electrode active material, but may contain a binder, a conductive material, an electrolyte and the like in addition to the negative electrode active material.
- a negative electrode layer containing only the negative electrode active material can be obtained.
- the negative electrode active material is in a powder form, a negative electrode layer containing a binder in addition to the negative electrode active material can be obtained.
- binder examples include polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), styrene butadiene rubber (SBR), polyimide, polyacrylamide, celluloses (for example, carboxymethyl cellulose (CMC)), polyacrylic, and the like.
- binder examples include, but are not limited to, acid salts (for example, sodium polyacrylate) and known conductive polymers.
- the conductive material include carbon materials such as carbon black, activated carbon, carbon carbon fiber (eg, carbon nanotube, carbon nanofiber, etc.), graphite, and the like.
- the thickness of the negative electrode active material layer varies greatly depending on the intended configuration of the sodium secondary battery, but is preferably in the range of 0.1 ⁇ m to 1000 ⁇ m, for example.
- the positive electrode usually contains a positive electrode active material capable of releasing and incorporating sodium ions.
- the positive electrode includes at least a positive electrode material for a sodium battery including positive electrode active material particles represented by the general formula (1) and a conductive carbon material covering at least a part of the surface of the positive electrode active material particles. And a positive electrode current collector that collects the positive electrode active material layer as necessary.
- the positive electrode active material layer may contain only the positive electrode material, but may contain a conductive material, a binder, an electrolyte, an electrode catalyst and the like in addition to the positive electrode material.
- the positive electrode active material layer is formed of Li, Na, Mg in the positive electrode active material layer and / or on the surface of the positive electrode active material layer for the purpose of improving cycle characteristics, improving oxidation breakdown voltage characteristics, improving high rate discharge characteristics / storage characteristics, etc.
- the content of the metal, metal compound, etc. in the positive electrode active material layer is not particularly limited, but is preferably in the range of 0.1 wt% to 35 wt
- the thickness of the positive electrode active material layer varies greatly depending on the structure of the intended sodium secondary battery, but is preferably in the range of 0.1 ⁇ m to 1000 ⁇ m, and more preferably in the range of 0.1 ⁇ m to 300 ⁇ m.
- the negative electrode active material layer and the positive electrode active material layer can be prepared by, for example, slurry containing each material by any coating method such as a dip coating method, a spray coating method, a roll coating method, a doctor blade method, a gravure coating method, and a screen printing method.
- the electrode active material layer can be formed by coating, drying, and rolling as necessary.
- Examples of the method for producing the positive electrode active material layer containing the metal or the metal compound include the following methods. That is, at the time of forming the positive electrode active material layer, a predetermined amount of the metal or metal compound material powder is mixed with the other positive electrode active material layer material so that the positive electrode active material layer contains the metal or metal compound. Can be made.
- a vapor phase method for example, a sputtering method, a vapor deposition method, an ALD method, etc.
- a liquid phase method for example, sol-gel method, hydrothermal method, etc.
- spin coating method, spray spraying, etc. the metal or metal is heated by heating in some cases.
- a positive electrode active material layer containing a compound or the like on the surface can be formed.
- a vapor phase method for example, a sputtering method, a vapor deposition method, an ALD method, etc.
- a liquid phase method for example, a sol-gel method, a hydrothermal method, etc.
- a spin coating method and a spray spray are previously applied to the surface of the positive electrode current collector.
- the above metal, metal compound, etc. can be obtained by heating in some cases to create a positive electrode active material layer on the surface of the coated surface of the current collector.
- a positive electrode active material layer contained on the surface can be formed.
- the method for forming the positive electrode active material layer containing the metal, the metal compound, or the like is not limited to these.
- the positive electrode current collector and the negative electrode current collector are not particularly limited in material, structure, and shape as long as the materials have desired electronic conductivity and do not cause an alloying reaction with sodium ions in the battery environment.
- the material for the positive electrode current collector include metal materials such as stainless steel, nickel, aluminum, iron, titanium, and copper, carbon materials such as carbon fiber and carbon paper, and high electron conductive ceramic materials such as titanium nitride. It is done.
- the battery case may have a function as a positive electrode current collector.
- Examples of the material for the negative electrode current collector include copper, stainless steel, nickel, and aluminum.
- the battery case may have a function as a negative electrode current collector.
- the shape of the positive electrode current collector and the negative electrode current collector include a plate shape, a foil shape, and a mesh shape, and a mesh shape is preferable.
- the electrolyte layer contains at least an electrolyte that enables conduction of sodium ions between the positive electrode and the negative electrode.
- the electrolyte only needs to have sodium ion conductivity, and examples thereof include an electrolyte, a gel electrolyte obtained by gelling the electrolyte using a polymer, a solid electrolyte, and the like.
- Examples of the electrolytic solution having sodium ion conductivity include an electrolytic solution in which a sodium salt is dissolved in an aqueous solvent or a non-aqueous solvent.
- the non-aqueous solvent is not particularly limited.
- cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), and fluoroethylene carbonate (FEC); cyclic esters such as ⁇ -butyrolactone (GBL); dimethyl carbonate Chain carbonates such as (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC); ester solvents such as methyl acetate, ethyl acetate, methyl difluoroacetate, and ethyl trifluoroacetate; tetraglyme, triglyme, etc.
- PC propylene carbonate
- EC ethylene carbonate
- FEC fluoroethylene carbonate
- GBL ⁇ -butyrolactone
- DMC dimethyl carbonate Chain carbonates
- DEC diethyl carbonate
- EMC ethyl methyl carbonate
- ester solvents such as methyl acetate, ethyl a
- cyclic ether solvents such as furan, 2,5-dimethylfuran, tetrahydropyran, and dioxane.
- an ionic liquid can also be used.
- a quaternary ammonium cation for example, (N, N, N-trimethyl-N-propylammonium bis (trifluoromethanesulfonyl) imide: abbreviation) TMPA TFSI
- piperidinium cations for example, (N-methyl-N-propylpiperidinium bis (trifluoromethanesulfonyl) imide: abbreviation PP13 TFSI), etc.
- pyrrolidinium for example, (N-butyl- N-methylpyrrolidinium bis (trifluoromethanesulfonyl) imide: abbreviation P14 TFSI), etc.
- Examples include imidazolium as a cation (for example, 1-ethyl-3-methylimidazolium bis (trifluoromethanesulfonyl) imide) and the like.
- the anionic species of these ionic liquids are exemplified by bis (trifluoromethanesulfonyl) imide (TFSI) in the above specific examples, but bis (sulfonyl) imide (abbreviation: FSI), tetra for the cationic species in the above specific examples. It is also possible to combine anionic species such as fluoroborate (BF 4 ⁇ ) and hexafluorophosphate (PF 6 ⁇ ).
- nonaqueous solvents may be used alone or in combination of two or more.
- a nitrile compound for example, adiponitrile, acetonitrile, propionitrile, glutaronitrile, etc.
- a cyclic sulfone eg, sulfolane, 3-methylsulfolane, etc.
- Phosphoric acid esters for example, trimethyl phosphate, triethyl phosphate, etc.
- nitrile compound By adding the nitrile compound to the nonaqueous solvent electrolyte, a stable nonaqueous solvent electrolyte that does not decompose can be obtained even in a high potential region where the positive electrode material for sodium batteries of the present invention operates. .
- the sodium salt is not particularly limited, for example, NaPF 6, NaBF 4, NaClO 4, NaCF 3 SO 3, (CF 3 SO 2) 2 NNa, NaN (FSO 2), NaC (CF 3 SO 2) 3 , etc. Is mentioned. These sodium salts may be used individually by 1 type, and may be used in combination of 2 or more type. NaPF 6 which is stable even in a high potential region is particularly preferable.
- the concentration of the sodium salt for example, in the range of 0.1mol / dm 3 ⁇ 5mol / dm 3, in a range of inter alia 0.5mol / dm 3 ⁇ 1.5mol / dm 3 preferable. If the sodium salt concentration is too high, the viscosity may increase and the capacity may decrease at low temperatures. On the other hand, if the sodium salt concentration is too low, the capacity may decrease at high rates. .
- the non-aqueous electrolyte can be used after adding a polymer to gel.
- the gelation method of the non-aqueous electrolyte include, for example, polymers such as polyethylene oxide (PEO), polyacrylonitrile (PAN), polyvinylidene fluoride (PVdF), and polymethyl methacrylate (PMMA). The method of adding is mentioned.
- the solid electrolyte is not particularly limited as long as it has Na ion conductivity.
- examples of the oxide solid electrolyte include Na 3 Zr 2 Si 2 PO 12 , ⁇ -alumina solid electrolyte (for example, Na 2 O-11Al 2 O 3 ) and the like.
- examples of the sulfide solid electrolyte include Na 2 S—P 2 S 5 .
- Examples of the complex hydride solid electrolyte include Na 2 (BH 4 ) (NH 2 ).
- the average particle diameter (D 50 ) of the solid electrolyte is preferably in the range of 1 nm to 100 ⁇ m, and more preferably in the range of 10 nm to 30 ⁇ m.
- the average particle diameter (D 50 ) of the solid electrolyte can be measured by, for example, a scanning electron microscope (SEM), a transmission electron microscope (TEM), or the like.
- the electrolyte layer varies greatly depending on the intended configuration of the sodium secondary battery, but is preferably in the range of 0.1 ⁇ m to 1000 ⁇ m, particularly preferably in the range of 0.1 ⁇ m to 300 ⁇ m.
- a battery case that accommodates the negative electrode, the electrolyte layer, and the positive electrode for example, a battery case having a general shape such as a coin shape, a flat plate shape, a cylindrical shape, or a laminate shape can be used.
- a separator made of an insulating material between the positive electrode and the negative electrode can be provided. Examples of such a separator include porous membranes such as polyethylene porous membrane and polypropylene porous membrane; and nonwoven fabrics such as resin nonwoven fabric and glass fiber nonwoven fabric.
- the current collector of each electrode can be provided with a terminal serving as a connection portion with the outside.
- the powder of positive electrode active material particles obtained by firing and Ketjen black were mixed at a ratio of 5: 1 (weight ratio), and kneaded for 24 hours at 300 rpm with a planetary ball mill (zirconia ball), on the surface of the positive electrode active material particles.
- a conductive carbon material was pressure-bonded to prepare a composite.
- the prepared composite powder was heat-treated at 700 ° C. for 5 hours in an Ar atmosphere to obtain a positive electrode material for a sodium battery.
- Example 1 As shown in FIG. 5, it was confirmed that in Example 1, the initial discharge capacity (unit: mAh) increased more than twice as compared with Comparative Example 1, and the charge / discharge efficiency increased from 51% to 79%. Further, as shown in FIG. 6, it was confirmed that Example 1 was able to maintain a capacity density (unit: mAh / g) twice or more after 10 cycles as compared with Comparative Example 1.
- the powder of positive electrode active material particles obtained by firing and Ketjen black were mixed at a ratio of 5: 1 (weight ratio), and kneaded for 24 hours at 300 rpm with a planetary ball mill (zirconia ball), on the surface of the positive electrode active material particles.
- a conductive carbon material was pressure-bonded to prepare a composite.
- the prepared composite powder was heat-treated at 700 ° C. for 5 hours in an Ar atmosphere to obtain a positive electrode material for a sodium battery.
- Example 2 the discharge capacity (initial discharge capacity) was 90 mAhg ⁇ 1 as shown in FIG.
- Example 2 as shown in FIG. 7, the discharge capacity (initial discharge capacity) was 98 mAhg ⁇ 1 , and it was confirmed that the discharge capacity was increased as compared with Comparative Example 2.
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Abstract
Description
リチウム電池は、上記したようにエネルギー密度や出力に優れる一方、リチウム電池の需要拡大に伴いリチウムの価格が上昇していることや、リチウムの埋蔵量が限られていること等が、量産や大型化のボトルネックとなっている。
例えば、特許文献1には、MaxMbyP2O7(MaはNa、Li、Ca、又はMgを表わし、Mbは4価以上で安定に存在する遷移金属を表わし、0≦x≦4、0.5≦y≦3、6≦z≦14である)で表わされる非水電解質二次電池用正極活物質が開示されている。特許文献1において、実施例で実際に作製、評価されているのは、MoP2O7である。
一般式(1)
NaxMy(AO4)z(P2O7)w
(式(1)中、Mは、Ti、V、Cr、Mn、Fe、Co、Ni、Cu及びZnよりなる群から選ばれる少なくとも1種であり、Aは、Al、Si、P、S、Ti、V及びWよりなる群から選ばれる少なくとも1種であり、xは4≧x≧2を満たし、yは4≧y≧1を満たし、zは4≧z≧0を満たし、wは1≧w≧0を満たし、z及びwの少なくとも一方は1以上である。)。
前記正極活物質のより好ましい具体的な形態として、前記式(1)中、前記Mが、Mnであり、Mnの一部が、Ti、V、Cr、Fe、Co、Ni、Cu及びZnよりなる群から選ばれる少なくとも1種で置換されていてもよいものが挙げられる。
前記正極活物質粒子の表面に、前記導電性炭素材料をメカノケミカル処理により圧着し、前記正極活物質粒子と該正極活物質粒子の表面に圧着された前記導電性炭素材料とを含む複合体を準備する準備工程と、
前記複合体を、不活性雰囲気下又は還元雰囲気下、熱処理する工程と、を有することを特徴とする。
一般式(1)
NaxMy(AO4)z(P2O7)w
(式(1)中、Mは、Ti、V、Cr、Mn、Fe、Co、Ni、Cu及びZnよりなる群から選ばれる少なくとも1種であり、Aは、Al、Si、P、S、Ti、V及びWよりなる群から選ばれる少なくとも1種であり、xは4≧x≧2を満たし、yは4≧y≧1を満たし、zは4≧z≧0を満たし、wは1≧w≧0を満たし、z及びwの少なくとも一方は1以上である。)
前記正極活物質のより好ましい具体的な形態として、前記式(1)中、前記Mが、Mnであり、Mnの一部が、Ti、V、Cr、Fe、Co、Ni、Cu及びZnよりなる群から選ばれる少なくとも1種で置換されていてもよいものが挙げられる。
本発明のナトリウム電池用正極材料は、下記一般式(1)で表わされる正極活物質粒子と、前記正極活物質粒子の表面の少なくとも一部を被覆する導電性炭素材料と、を含むことを特徴とするものである。
一般式(1)
NaxMy(AO4)z(P2O7)w
(式(1)中、Mは、Ti、V、Cr、Mn、Fe、Co、Ni、Cu及びZnよりなる群から選ばれる少なくとも1種であり、Aは、Al、Si、P、S、Ti、V及びWよりなる群から選ばれる少なくとも1種であり、xは4≧x≧2を満たし、yは4≧y≧1を満たし、zは4≧z≧0を満たし、wは1≧w≧0を満たし、z及びwの少なくとも一方は1以上である。)
また、リチウム電池用活物質のLiをNaに置き換えた場合、その作動電位は大きく低下するという傾向がある。さらに、従来、NaイオンがLiイオンと比較してイオン半径が大きいために、Li含有活物質のLiをNaに置換した場合、Naイオンが動きにくくなると考えられてきた。このような理由から、リチウム電池用の活物質において、単にリチウムをナトリウムに置換しても、有用な高電位作動型のナトリウム電池用活物質は得られないというのが一般的な知見であった。
その上、当該正極活物質は、25℃という比較的低温域において、高電位作動性を発現することができる。
また、一般式(1)において、Aは、高電位作動性が確認されたP(実施例参照)、又は、Pと同様、四面体構造をとりやすいものである。ここで四面体構造とは、4つの酸素原子を頂点とする四面体の空隙に、これら4つの酸素原子と共有結合した1つのAが入った構造である。
また、ポリアニオン部である(AO4)及び(P2O7)については、正極活物質における(AO4)の組成比を表わすz及び(P2O7)の組成比を表わすwの少なくとも一方が1以上であれば、(AO4)及び(P2O7)の少なくとも一方による、M-O結合に対するinductive効果により、得られる正極活物質は高電位域で作動すると考えられる。inductive効果とは、(AO4)を構成するA-O結合及び(P2O7)を構成するP-O結合の高い共有結合性により、M-O結合の電子がA-O結合及びP-O結合側に引っ張られ、M-O間の共有結合性が低下し、混性軌道のエネルギーギャップが小さくなる結果、Mの酸化還元準位が下がり、ナトリウムとのエネルギー差が大きくなって対ナトリウムの酸化還元電位が高くなる、というものである。
しかし、一般式(1)において、Mの種類によっては正極活物質の電子伝導性が低下することが見出され、具体的にはMがMnの場合、Mが他の金属の場合と比較して、正極活物質の電子伝導性が1.0×10-12S/cm以下と極めて低いということが見出された。そのため、MがMnの場合、充放電時の内部抵抗が大きく、容量密度が18mAh/g程度しか得られないという問題が生じる。
正極活物質粒子表面が導電性炭素材料で被覆されているか否かは、ナトリウム電池用正極材料の正極活物質粒子表面を透過型電子顕微鏡(TEM)で観測することで確認することができる。
TEMによる電子回折によって、結晶体である正極活物質粒子は、その周期的構造に由来する格子状のパターンを有する相(結晶相)として確認できる。
一方、導電性炭素材料は、非晶質(アモルファス)であるため、正極活物質のような格子状のパターンを有していない相として、確認される。
従って、TEM観察により、格子状のパターンを有する正極活物質の結晶相と、格子状のパターンを有さない導電性炭素材料のアモルファス相とが隙間なく接触している部分が、正極活物質表面で観察できれば、正極活物質粒子表面の少なくとも一部を導電性炭素材料が被覆しているといえる。
透過型電子顕微鏡での測定条件は、電子回折像が確認できれば、特に限定されないが、例えば、測定倍率は200,000~500,000倍で測定することが好ましい。
導電性炭素材料による正極活物質粒子表面の被覆面積は大きければ大きいほどよく、正極活物質の表面全体が覆われていることが好ましい。
本発明のナトリウム電池用正極材料は、良好な電子伝導性を有するため、ナトリウム電池の正極に用いることにより、ナトリウム電池の初回放電容量、初回充放電効率、サイクル後の放電容量を飛躍的に向上させることができる。
本発明の正極材料における正極活物質において、前記Mは、Ti、V、Cr、Mn、Fe、Co、Ni、Cu及びZnよりなる群から選ばれる少なくとも1種の金属種であればよく、中でも、充電前の状態において、2価であることが好ましい。Mが、充電前の状態において2価である金属種の場合、充電時に3価以上の高酸化状態となることで、高電位で作動可能であるからである。
z及びwが共に1以上の場合、ポリアニオン部が、AO4四面体と、AO4四面体と1つの酸素を共有したP2O7と、を含むため、M-O結合に対するinductive効果が高くなり、その結果、より高電位な正極活物質が得られるため好ましい。
また、Na4Mn3(PO4)2(P2O7)は、空間群Pn21aに帰属する結晶構造を有している。図1~3に空間群Pn21aに帰属する結晶構造(Na4Mn3(PO4)2(P2O7))を、a軸方向から見た図(図1)、b軸方向から見た図(図2)、及びc軸方向から見た図(図3)を示す。
図1~3からわかるように、空間群Pn21aに帰属する結晶構造において、結晶構造中の全てのNaイオンが、a軸、b軸及びc軸のいずれかの方向に配列しており、Naイオンの移動性が非常に高い。すなわち、空間群Pn21aに帰属する結晶構造は、Naイオンの伝導に非常に有利であり、Naイオンの挿入、及び、脱離がスムーズに進行する。
以上のような理由から、本発明の正極材料における正極活物質は、空間群Pn21aに帰属する結晶構造を有することが好ましい。
なお、原料混合物中、各化合物の粒子のサイズは特に限定されないが、反応を均一に進行させるためには、粒子間の接触面積が大きい方が好ましいことから、各化合物を仮焼成前に粉砕しておくことが好ましい。すなわち、仮焼成前に、原料混合物中のNa含有化合物、M含有化合物、A含有化合物及びP含有化合物を粉砕する粉砕工程を設けることが好ましい。粉砕工程において、化合物の粉砕は、複数の化合物を同時に行ってもよいし、化合物ごとに行ってもよい。また、粉砕方法は特に限定されず、任意の方法を採用することができ、原料混合物の混合や攪拌と粉砕とを兼ねる方法を採用することもできる。例えば、ボールミル、ビーズミル等は、原料混合物を粉砕しながら、混合、攪拌することもできる。
仮焼成工程の雰囲気である大気雰囲気とは、酸素含有ガス雰囲気を意味する。
本焼成工程における焼成温度は、好ましくは550~750℃である。
本焼成時間は、特に限定されず、適宜設定すればよいが、例えば、1~30時間程度とすることができる。
本焼成工程の雰囲気である大気雰囲気とは、仮焼成工程の大気雰囲気と同様である。
ゲルの焼成温度は、例えば、500~800℃とすることができ、好ましくは600~750℃である。ゲル焼成時の大気雰囲気とは、上記仮焼成工程の大気雰囲気と同様である。
正極材料に占める導電性炭素材料の含有量は、特に限定されないが、電子伝導性補助効果を得る観点から、1重量%以上、特に5重量%以上であることが好ましく、正極活物質量の確保の観点から35重量%以下であることが好ましい。
正極活物質粒子表面を被覆している導電性炭素材料の厚さは特に限定されないが、1~30nmであることが好ましい。
また、本発明において、正極活物質粒子は、サイクル特性向上、酸化耐圧特性向上、高率放電特性・保存特性向上等を目的として、Li、Na、Mg、Al、Si、Ca、Ti、V、Cr、Mn、Fe、Co、Ni、Cu、Zn、Sr、Y、Zr、Nb、Mo、Pd、Ag、In、Sn、Sb、Ba、Hf、Ta、W、Ir、Bi、ランタノイド(La、Ce、Pr、Nd、Sm、Eu、Gd、Dy、Er、Yb等)等の金属、並びに、これら金属の酸化物、フッ化物、オキシフッ化物、リン化物、窒化物、硫化物、炭化物、硼化物、塩化物、臭化物、沃化物、燐酸塩、炭酸塩、硫酸塩、珪酸塩、及びチタン酸塩から選ばれる少なくとも1種によって、その表面の全部または一部が被覆されていてもよい。該被覆部の厚みは、特に限定されるものではないが、1nm~200nmの範囲内であることが好ましい。尚、このような被覆部を有する正極活物質粒子は、該被覆部が導電性炭素材料によって被覆されていてもよいし、被覆部に被覆されていない領域が導電性炭素材料によって被覆されていてもよい。
また、上記被覆部を有する正極活物質の合成方法としては、例えば、正極活物質を合成した後に、気相法(例えば、スパッタ法、蒸着法、アトミックレイヤーディポジション法(ALD法)等)、液相法(例えば、ゾルゲル法、水熱法、共沈法等)、スピンコート法、及びスプレーによる吹きつけ等を利用して、該正極活物質表面に上記被覆部の構成材料を被覆し、場合によってさらに加熱する方法が挙げられる。
ただし、以上の合成方法はこれらに限定されるものではなく、公知の合成プロセスが広く利用可能である。
本発明の正極材料を製造する方法は特に限定されないが、好ましい方法として、以下に説明する製造方法が挙げられる。
正極活物質粒子の表面に、導電性炭素材料をメカノケミカル処理により圧着し、前記正極活物質粒子と該正極活物質粒子の表面に圧着された前記導電性炭素材料とを含む複合体を準備する準備工程と、
前記複合体を、不活性雰囲気下又は還元雰囲気下、熱処理する工程と、を有することを特徴とするものである。
(準備工程)
準備工程は、正極活物質粒子の表面に、導電性炭素材料をメカノケミカル処理により圧着し、正極活物質粒子と該正極活物質粒子の表面に圧着された導電性炭素材料とを含む複合体を準備する工程である。
遊星ボールミルを用いた場合の回転速度は、特に限定されないが、例えば、80~450rpmとすることができる。また、遊星ボールミルを用いた場合の混練時間は、特に限定されないが、例えば、1~30時間とすることができる。
遊星ボールミルを用いた場合のボールの材質は、特に限定されないが、例えば、ジルコニア等が挙げられ、硬度の高い材質が好ましい。
遊星ボールミルを用いた場合のボールの直径は、特に限定されないが、例えば、1~10mmとすることができる。
熱処理工程は、準備工程で得られた複合体を、不活性雰囲気下、又は還元雰囲気下、熱処理する工程である。
熱処理工程における熱処理温度の下限値は、好ましくは500℃以上であり、より好ましくは550℃以上であり、特に好ましくは600℃以上である。
熱処理工程における熱処理温度の上限値は、好ましくは800℃以下であり、より好ましくは750℃以下である。
熱処理時間は、特に限定されず、適宜設定すればよいが、例えば、1~24時間、より好ましくは3~10時間程度とすることができる。
不活性雰囲気としては、アルゴン含有ガス雰囲気、窒素含有ガス雰囲気等、還元雰囲気としては、水素含有ガス雰囲気等が挙げられる。不活性雰囲気下又は還元雰囲気下で行うことにより、炭素の燃焼による損耗を防止することができる。
本発明により提供される正極材料は、ナトリウム電池の正極に好適に使用することができる。ナトリウム電池は一次電池でも二次電池でもよい。以下、ナトリウム二次電池を例に、本発明により提供される正極材料を用いたナトリウム電池について説明する。
以下、各構成について説明する。
負極活物質層は、負極活物質のみを含有するものであってもよいが、負極活物質の他に結着剤、導電性材料、電解質等を含有するものであってもよい。例えば、負極活物質が板状、箔状等である場合は、負極活物質のみを含有する負極層とすることができる。一方、負極活物質が粉末状である場合は、負極活物質に加えて結着剤を含有する負極層とすることができる。
結着剤としては、例えば、ポリフッ化ビニリデン(PVdF)、ポリテトラフルオロエチレン(PTFE)、スチレンブタジエンゴム(SBR)、ポリイミド、ポリアクリルアミド、セルロース類(例えば、カルボキシメチルセルロース(CMC)等)、ポリアクリル酸塩(例えば、ポリアクリル酸ナトリウム等)、及び、公知の導電性高分子等が挙げられるが、これらに限定されるものではない。
導電性材料としては、例えば、カーボンブラック、活性炭、カーボン炭素繊維(例えばカーボンナノチューブ、カーボンナノファイバー等)、グラファイト等の炭素材料等を挙げることができる。
負極活物質層の厚さは、目的とするナトリウム二次電池の構成によって大きく異なるものであるが、例えば、0.1μm~1000μmの範囲内であることが好ましい。
正極活物質層は、正極材料のみを含有するものであってもよいが、正極材料の他に導電性材料や、結着剤、電解質、電極触媒等を含有するものであってもよい。正極活物質層における導電性材料、結着剤については、負極活物質層と同様の材料を用いることができるため、ここでの説明は省略する。
正極活物質層における上記金属、金属化合物等の含有量は、特に限定されるものではないが、0.1重量%~35重量%の範囲内であることが好ましい。
すなわち、正極活物質層の形成時に、上記金属や金属化合物の材料の粉末を所定量、その他の正極活物質層材料と混合することで、正極活物質層中に上記金属や金属化合物等を含有させることができる。
また、上記金属や金属化合物の材料以外の材料を用いて正極活物質層を形成した後に、該正極活物質層の表面に、気相法(例えば、スパッタ法、蒸着法、ALD法等)、液相法(例えば、ゾルゲル法、水熱法等)、スピンコート法、及びスプレー噴霧等を利用して、上記金属や金属化合物等を被覆した後に、場合によって加熱することによって、上記金属や金属化合物等を表面に含有する正極活物質層を形成することができる。また、正極集電体表面に、予め、気相法(例えば、スパッタ法、蒸着法、ALD法等)、液相法(例えば、ゾルゲル法、水熱法等)、スピンコート法、及びスプレー噴霧等を利用して、上記金属や金属化合物等を被覆した後に、場合によって加熱し、集電体の該被覆面の表面に、正極活物質層を作成することで、上記金属や金属化合物等を表面に含有する正極活物質層を形成することができる。
ただし、上記金属や金属化合物等を含む正極活物質層の作成方法はこれらに限定されるものではない。
正極集電体の材料としては、例えば、ステンレス、ニッケル、アルミニウム、鉄、チタン、銅等の金属材料、カーボンファイバー、カーボンペーパー等のカーボン材料、窒化チタン等の高電子伝導性セラミックス材料等が挙げられる。電池ケースが正極集電体としての機能を兼ね備えていてもよい。
負極集電体の材料としては、銅、ステンレス、ニッケル、アルミニウム等が挙げられる。電池ケースが負極集電体としての機能を有していてもよい。
正極集電体及び負極集電体の形状としては、例えば、板状、箔状、メッシュ状等が挙げられ、中でもメッシュ状が好ましい。
電解質としては、ナトリウムイオン伝導性を有していればよく、例えば、電解液、電解液をポリマー等を用いてゲル化したゲル状電解質、固体電解質等が挙げられる。
ナトリウムイオン伝導性を有する電解液としては、例えば、ナトリウム塩を、水系溶媒又は非水溶媒に溶解した電解液が挙げられる。
非水溶媒としては、イオン性液体も適用可能であり、例えば、4級アンモニウムをカチオンとしたもの(例えば、(N,N,N-トリメチル-N-プロピルアンモニウム ビス(トリフルオロメタンスルフォニル)イミド:略称TMPA TFSI)等)、ピペリジニウムをカチオンとしたもの(例えば、(N-メチル-N-プロピルピペリジニウム ビス(トリフルオロメタンスルフォニル)イミド:略称PP13 TFSI)等)、ピロリジニウム(例えば、(N-ブチル-N-メチルピロリジニウム ビス(トリフルオロメタンスルフォニル)イミド:略称P14 TFSI)等)、N,N-ジエチル-N-メチル-N-(2-メトキシエチル)アンモニウム ビス(トリフルオロメタンスルフォニル)イミド:略称DEME TFSI、4級ホスホニウムをカチオンとしたもの(例えば、(トリエチルペンチルフォスフォニウム ビス(トリフルオロメタンスルフォニル)イミド:略称P2225 TFSI)、及び、トリエチルオクチルフォスフォニウム ビス(トリフルオロメタンスルフォニル)イミド:略称P2228 TFSI)等)、イミダゾリウムをカチオンとしたもの(例えば、1-エチル-3-メチルイミダゾリウム ビス(トリフルオロメタンスルフォニル)イミド等)等が挙げられる。これらイオン性液体のアニオン種は、上記具体例では、ビス(トリフルオロメタンスルフォニル)イミド(TFSI)を例示したが、上記具体例におけるカチオン種に対し、ビス(スルフォニル)イミド (略称:FSI)、テトラフルオロボレート(BF4 -)、及びヘキサフルオロフォスフェート(PF6 -)等のアニオン種を組み合わせることも可能である。
これら非水溶媒は、1種を単独で用いてもよいし、2種以上を組み合わせて用いてもよい。また、鎖状飽和炭化水素化合物の末端にCN基が結合したニトリル系化合物(例えば、アジポニトリル、アセトニトリル、プロピオニトリル、グルタロニトリル等)、環状スルホン(例えば、スルホラン、3-メチルスルホラン等)、燐酸エステル(例えば、トリメチルフォスフェート、トリエチルフォスフェート等)等を、非水溶媒に混合して用いてもよい。ニトリル系化合物を非水溶媒系電解液に添加することで、本発明のナトリウム電池用正極材料が作動するような高電位領域においても、分解しない安定な非水溶媒系電解液を得ることができる。
非水電解液において、ナトリウム塩の濃度は、例えば、0.1mol/dm3~5mol/dm3の範囲内、中でも0.5mol/dm3~1.5mol/dm3の範囲内であることが好ましい。ナトリウム塩の濃度が高すぎると、粘性が高くなり低温での容量低下が生じる可能性があり、一方、ナトリウム塩の濃度が低すぎると、ハイレート時の容量低下が生じる可能性があるからである。
固体電解質は、非晶質であっても良く、結晶質であっても良い。また、固体電解質の平均粒子径(D50)は、例えば1nm~100μmの範囲内、中でも10nm~30μmの範囲内であることが好ましい。固体電解質の平均粒子径(D50)は、例えば、走査型電子顕微鏡(SEM)、透過型電子顕微鏡(TEM)等により測定することができる。
電解質層の厚さは、目的とするナトリウム二次電池の構成によって大きく異なるが、例えば0.1μm~1000μmの範囲内、中でも0.1μm~300μmの範囲内であることが好ましい。
正極、電解質層、負極の順番で配置されている積層体を、繰り返し何層も重ねる構造を取る電池の場合には、安全性の観点から、正極および負極の間に、絶縁性材料からなるセパレータを備えることができる。このようなセパレータとしては、例えばポリエチレン多孔膜、ポリプロピレン多孔膜等の多孔膜;および樹脂不織布、ガラス繊維不織布等の不織布等を挙げることができる。
また、各電極の集電体には、それぞれ、外部との接続部となる端子を設けることができる。
(ナトリウム電池用正極材料の合成)
Na4P2O7(Na含有化合物)、(CH3COO)2Mn(Mn含有化合物)、及びNH4H2PO4(P含有化合物)を、Na:Mn:P=4:3:4(mol比)となるように混合し、グリコール酸(ゲル化剤)と共に硝酸水溶液中に溶解し、80℃で攪拌した。得られた混合物を、大気雰囲気下、700℃で15時間、焼成を行い、正極活物質粒子を得た。
焼成によって得られた正極活物質粒子の粉末とケッチェンブラックとを5:1(重量比)で混合し、遊星ボールミル(ジルコニアボール)により300rpmで24時間混練し、正極活物質粒子の表面上に導電性炭素材料を圧着し、複合体を準備した。
準備した複合体の粉末をAr雰囲気下、700℃で5時間、熱処理を行い、ナトリウム電池用正極材料を得た。
<正極の作製>
Na4Mn3(PO4)2P2O7(正極材料中の正極活物質粒子):ケッチェンブラック(正極材料中の導電性炭素材料):炭素(導電助剤):PVdF(結着剤)=75:15:5:5(重量比)となるように、上記にて合成した正極材料と炭素とPVdFとを混合し、N-メチル-2-ピロリドン(分散剤)中に分散させてスラリーを調製した。
上記スラリーをアルミニウム箔(集電体)上に塗布し、乾燥及び圧延し、集電体と正極活物質層とが積層した正極を作製した。
まず、箔状のナトリウム金属を打ち抜き、対極を得た。
一方、エチレンカーボネート(EC)とジメチルカーボネート(DMC)とを1:1(体積比)で混合した混合溶媒に、ナトリウム塩(NaPF6)を添加し、ナトリウム塩濃度が1.0mol/dm3の非水溶媒系電解液を得た。
上記にて作製した正極、ポリプロピレン製多孔質膜とポリエチレン製多孔質膜とポリプロピレン製多孔質膜とがこの順序で積層した多孔質膜(セパレータ)、及び対極を、この順序で積層した。このとき、正極活物質層がセパレータ側となるように正極を積層した。
上記積層体のセパレータに上記非水溶媒系電解液を含浸させ、コイン型の評価用セルを作製した。
上記にて作製した評価用セルを用いて、充放電試験を下記条件にて行った。結果を図5及び図6に示す。
・電位範囲:上限4.1V、下限2.5V
・電流密度:8.5mA/g
・温度:25℃
・サイクル数:10
実施例1と同様の方法で正極活物質粒子を得た。正極活物質粒子及び導電性炭素材料の複合体化、及び、熱処理は行わなかった。
Na4Mn3(PO4)2P2O7(正極活物質粒子):炭素(導電助剤):PVdF(結着剤)=75:20:5(重量比)となるように、上記にて合成した正極活物質と炭素とPVdFとを混合した以外は実施例1と同様にして正極評価用セルを作製した。得られた評価用セルを用いて実施例1と同様にして充放電試験を行った。結果を図5及び図6に示す。
(ナトリウム電池用正極材料の合成)
Na4P2O7(Na含有化合物)、(CH3COO)2Co(Co含有化合物)、及びNH4H2PO4(P含有化合物)を、Na:Co:P=4:3:4(mol比)となるように混合し、グリコール酸(ゲル化剤)と共に硝酸水溶液中に溶解し、80℃で攪拌した。得られた混合物を、大気雰囲気下、700℃で15時間、焼成を行い、正極活物質粒子を得た。
焼成によって得られた正極活物質粒子の粉末とケッチェンブラックとを5:1(重量比)で混合し、遊星ボールミル(ジルコニアボール)により300rpmで24時間混練し、正極活物質粒子の表面上に導電性炭素材料を圧着し、複合体を準備した。
準備した複合体の粉末をAr雰囲気下、700℃で5時間、熱処理を行い、ナトリウム電池用正極材料を得た。
<正極の作製>
Na4Co3(PO4)2P2O7(正極材料中の正極活物質粒子):ケッチェンブラック(正極材料中の導電性炭素材料):炭素(導電助剤):PVdF(結着剤)=75:15:5:5(重量比)となるように、上記にて合成した正極材料と炭素とPVdFとを混合し、N-メチル-2-ピロリドン(分散剤)中に分散させてスラリーを調製した。
上記スラリーをアルミニウム箔(集電体)上に塗布し、乾燥及び圧延し、集電体と正極活物質層とが積層した正極を作製した。
実施例1と同様にして、コイン型の評価セルを作製し、充放電試験を下記条件にて行った。結果を図7に示す。
・電位範囲:上限4.7V、下限3.0V
・電流密度:17mA/g
・温度:25℃
実施例2と同様の方法で正極活物質粒子を得た。正極活物質粒子及び導電性炭素材料の複合体化、及び、熱処理は行わなかった。
Na4Co3(PO4)2P2O7(正極活物質粒子):炭素(導電助剤):PVdF(結着剤)=75:20:5(重量比)となるように、上記にて合成した正極活物質と炭素とPVdFとを混合した以外は実施例2と同様にして正極評価用セルを作製した。得られた評価用セルを用いて実施例2と同様にして充放電試験を行った。結果を図8に示す。
2…正極
3…電解質層
4…負極活物質層
5…負極集電体
6…正極活物質層
7…正極集電体
8…ナトリウム二次電池
Claims (14)
- 下記一般式(1)で表わされる正極活物質粒子と、前記正極活物質粒子の表面の少なくとも一部を被覆する導電性炭素材料と、を含むことを特徴とするナトリウム電池用正極材料。
一般式(1)
NaxMy(AO4)z(P2O7)w
(式(1)中、Mは、Ti、V、Cr、Mn、Fe、Co、Ni、Cu及びZnよりなる群から選ばれる少なくとも1種であり、Aは、Al、Si、P、S、Ti、V及びWよりなる群から選ばれる少なくとも1種であり、xは4≧x≧2を満たし、yは4≧y≧1を満たし、zは4≧z≧0を満たし、wは1≧w≧0を満たし、z及びwの少なくとも一方は1以上である。) - 前記式(1)中、前記Mが充電前において2価である、請求項1に記載のナトリウム電池用正極材料。
- 前記正極活物質が、空間群Pn21aに帰属する結晶構造を有する、請求項1又は2に記載のナトリウム電池用正極材料。
- 前記式(1)中、前記Mは、Mn、Co、及びNiより成る群から選ばれる少なくとも1種であり、その一部が、Ti、V、Cr、Mn、Fe、Co、Ni、Cu及びZnよりなる群から選ばれる、該Mと異なる少なくとも1種で置換されていてもよい、請求項1乃至3のいずれか一項に記載のナトリウム電池用正極材料。
- 前記式(1)中、前記Mは、Mnであり、Mnの一部が、Ti、V、Cr、Fe、Co、Ni、Cu及びZnよりなる群から選ばれる少なくとも1種で置換されていてもよい、請求項1乃至4のいずれか一項に記載のナトリウム電池用正極材料。
- 前記式(1)中、前記Aは、Pであり、Pの一部が、Al、Si、S、Ti、V及びWよりなる群から選ばれる少なくとも1種で置換されていてもよい、請求項1乃至5のいずれか一項に記載のナトリウム電池用正極材料。
- 前記正極活物質が、一般式Na4Mn3(PO4)2(P2O7)で表わされる、請求項1乃至6のいずれか一項に記載のナトリウム電池用正極材料。
- 下記一般式(1)で表わされる正極活物質粒子と、前記正極活物質粒子の表面の少なくとも一部を被覆する導電性炭素材料と、を含むナトリウム電池用正極材料の製造方法であって、
前記正極活物質粒子の表面に、前記導電性炭素材料をメカノケミカル処理により圧着し、前記正極活物質粒子と該正極活物質粒子の表面に圧着された前記導電性炭素材料とを含む複合体を準備する準備工程と、
前記複合体を、不活性雰囲気下又は還元雰囲気下、熱処理する工程と、を有することを特徴とする、ナトリウム電池用正極材料の製造方法。
一般式(1)
NaxMy(AO4)z(P2O7)w
(式(1)中、Mは、Ti、V、Cr、Mn、Fe、Co、Ni、Cu及びZnよりなる群から選ばれる少なくとも1種であり、Aは、Al、Si、P、S、Ti、V及びWよりなる群から選ばれる少なくとも1種であり、xは4≧x≧2を満たし、yは4≧y≧1を満たし、zは4≧z≧0を満たし、wは1≧w≧0を満たし、z及びwの少なくとも一方は1以上である。) - 前記式(1)中、前記Mが充電前において2価である、請求項8に記載のナトリウム電池用正極材料の製造方法。
- 前記正極活物質が、空間群Pn21aに帰属する結晶構造を有する、請求項8又は9に記載のナトリウム電池用正極材料の製造方法。
- 前記式(1)中、前記Mは、Mn、Co、及びNiより成る群から選ばれる少なくとも1種であり、その一部が、Ti、V、Cr、Mn、Fe、Co、Ni、Cu及びZnよりなる群から選ばれる、該Mと異なる少なくとも1種で置換されていてもよい、請求項8乃至10のいずれか一項に記載のナトリウム電池用正極材料の製造方法。
- 前記式(1)中、前記Mは、Mnであり、Mnの一部が、Ti、V、Cr、Fe、Co、Ni、Cu及びZnよりなる群から選ばれる少なくとも1種で置換されていてもよい、請求項8乃至11のいずれか一項に記載のナトリウム電池用正極材料の製造方法。
- 前記式(1)中、前記Aは、Pであり、Pの一部が、Al、Si、S、Ti、V及びWよりなる群から選ばれる少なくとも1種で置換されていてもよい、請求項8乃至12のいずれか一項に記載のナトリウム電池用正極材料の製造方法。
- 前記正極活物質が、一般式Na4Mn3(PO4)2(P2O7)で表わされる、請求項8乃至13のいずれか一項に記載のナトリウム電池用正極材料の製造方法。
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CN104364946A (zh) | 2015-02-18 |
US9537146B2 (en) | 2017-01-03 |
EP2860800A4 (en) | 2015-09-09 |
EP2860800B1 (en) | 2018-07-25 |
KR101703405B1 (ko) | 2017-02-06 |
CN104364946B (zh) | 2018-01-05 |
US20150180024A1 (en) | 2015-06-25 |
JP5910742B2 (ja) | 2016-04-27 |
KR20150013251A (ko) | 2015-02-04 |
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EP2860800A1 (en) | 2015-04-15 |
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