JP5686378B2 - Hydrogen-containing lithium silicate compound and method for producing the same, and positive electrode active material for non-aqueous electrolyte secondary battery, positive electrode for non-aqueous electrolyte secondary battery, non-aqueous electrolyte secondary battery, and vehicle - Google Patents

Description

  The present invention relates to a lithium silicate compound used for a positive electrode active material for a nonaqueous electrolyte secondary battery and a method for producing the same.

  Non-aqueous electrolyte secondary batteries are small and have high energy density, and are widely used as power sources for portable electronic devices. In recent years, lithium secondary batteries have been studied to be mounted on vehicles.

In recent years, as described in Patent Documents 1 and ₂ , Li ₂ FeSiO ₄ (theoretical capacity 331.3 mAh / g), Li ₂ MnSiO ₄ (theoretical capacity 333.) as the positive electrode active material of the nonaqueous electrolyte secondary battery. Lithium silicate compounds that can occlude and release lithium ions, such as 2 mAh / g), have been developed. Lithium silicate compounds are inexpensive, have abundant resources, have a low environmental impact, have a high theoretical charge / discharge capacity of lithium ions, and do not release oxygen at high temperatures. It has attracted attention as a positive electrode material for next-generation non-aqueous electrolyte secondary batteries.

As a method for improving the positive electrode active material, it is known that the metal oxide is subjected to acid treatment or alkali treatment, although it is not a lithium silicate compound. For example, in Patent Document 3, by treating a compound represented by the chemical formula LiMO ₂ (M is a metal selected from Co, Ni and Mn) with an acid, a proton-containing positive electrode active material is obtained to obtain a crystal structure. It is disclosed that it contributes to stabilization and suppresses abnormal heat generation of the battery.

Patent Documents 4 and 5 disclose that charge / discharge capacity is increased by acid treatment of lithium titanate. In Patent Document 6, by synthesizing a positive electrode active material made of Li _x FeP _y O _z in an acidic solution, the average valence of Fe in Li _x FeP _y O _z approaches 2.0, and It discloses that the Li ions to be inserted are reduced or eliminated to facilitate handling.

  In Patent Document 7, a precursor such as Fe and Mn, a precursor of Li, and a precursor of Si are added to water to prepare an alkaline precursor solution, which is heated at atmospheric pressure to obtain a lithium silicate compound. It is disclosed to generate.

  By performing acid treatment on the positive electrode active material, various effects may be obtained as shown in the above-mentioned patent document. However, the effect varies depending on the type of material of the positive electrode active material, and in some cases, the characteristics may not change before and after the treatment. For this reason, those skilled in the art cannot estimate what effect can be obtained by performing acid treatment on the lithium silicate compound.

  The inventors diligently sought to develop a positive electrode active material having improved charge and discharge characteristics by improving the lithium silicate compound.

International Publication No. 2010/089931 JP 2010-257592 A JP 2007-053116 A International Publication No. 1999/003784 International Publication No. 1999/004442 JP 2011-014369 A Special table 2010-517913

  The present invention has been made in view of such circumstances, and a lithium silicate compound capable of constituting a battery having excellent charge / discharge characteristics, a method for producing the same, a positive electrode active material for a nonaqueous electrolyte secondary battery, a nonaqueous electrolyte two, and the like. A secondary battery positive electrode, a nonaqueous electrolyte secondary battery, and a vehicle are provided.

  The inventor of the present application has intensively studied to achieve the above-described object. As a result, it has been found that by including protons in the lithium silicate compound, charge / discharge characteristics are improved when a battery is constructed.

  (1) The hydrogen-containing lithium silicate compound of the present invention is characterized in that hydrogen is contained in a lithium silicate compound containing lithium, at least one of iron and manganese, and silicon.

(2) the hydrogen-containing lithium silicate-based compound has the formula _{Li 2 + a-b-z} H z A b M 1-x M 'x SiO 4 + δ ( wherein, A is selected Na, K, Rb, from the group of Cs M is at least one element selected from the group consisting of Fe and Mn, and M ′ is Mg, Ca, Co, Al, Ni, Nb, Ti, Cr, Cu, Zn And at least one element selected from the group consisting of Zr, V, Mo and W. The subscripts are as follows: 0 ≦ a <1, 0 ≦ b <0.2, 0 <z, 0 ≦ x ≦ 0.5, δ ≧ 0) is preferable.

  (3) The range of z in the composition formula is preferably 0 <z ≦ 1.0.

  (4) The method for producing a hydrogen-containing lithium silicate compound of the present invention is characterized in that an acid treatment is performed on a lithium silicate compound containing lithium, at least one of iron and manganese, and silicon.

(5) The lithium silicate compound has a composition formula Li _{2 + ab Ab} M _1-x M ′ _x SiO _{4 + δ} (wherein A is at least one element selected from the group consisting of Na, K, Rb, and Cs) M is at least one element selected from the group consisting of Fe and Mn, and M ′ is Mg, Ca, Co, Al, Ni, Nb, Ti, Cr, Cu, Zn, Zr, V, and Mo. And at least one element selected from the group consisting of W. The subscripts are as follows: 0 ≦ a <1, 0 ≦ b <0.2, 0 ≦ x ≦ 0.5, δ ≧ 0. ) Is preferable.

  (6) The positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention is characterized by comprising the hydrogen-containing lithium silicate compound according to any one of (1) to (3) above.

  (7) The positive electrode active material for a nonaqueous electrolyte secondary battery of the present invention is characterized by comprising a hydrogen-containing lithium silicate compound produced by the production method described in (4) or (5) above.

  (8) A positive electrode for a non-aqueous electrolyte secondary battery according to the present invention includes the positive electrode active material for a non-aqueous electrolyte secondary battery according to (6) or (7).

  (9) A nonaqueous electrolyte secondary battery according to the present invention includes the positive electrode for a nonaqueous electrolyte secondary battery described in (8) above.

  (10) A vehicle according to the present invention includes the positive electrode for a nonaqueous electrolyte secondary battery according to (9) above.

  ADVANTAGE OF THE INVENTION According to this invention, the lithium silicate type compound which can comprise the battery excellent in charging / discharging characteristics, its manufacturing method, the positive electrode active material for nonaqueous electrolyte secondary batteries, the positive electrode for nonaqueous electrolyte secondary batteries, a nonaqueous electrolyte A secondary battery and a vehicle can be provided.

The XRD pattern about the powder of Example 1 and Comparative Examples 1 and 2 is shown. The SEM photograph of the powder of Example 1 is shown. The SEM photograph of the powder of the comparative example 2 is shown. The charging / discharging curve of the battery produced using the powder of Example 1 is shown. The charging / discharging curve of the battery produced using the powder of the comparative example 1 is shown. The charging / discharging curve of the battery produced using the powder of the comparative example 2 is shown. The cycle characteristic of the battery produced using the powder of Example 1 is shown. The cycle characteristic of the battery produced using the powder of the comparative example 2 is shown. The discharge rate characteristic of the battery produced using the powder of Example 1 is shown. The discharge rate characteristic of the battery produced using the powder of the comparative example 2 is shown. The XRD pattern of the powder at the time of changing the time of acid treatment is shown. The charging / discharging curve of the battery produced using the powder obtained by acid-processing for 30 minutes is shown. The cycle characteristic of the battery produced using the powder obtained by acid-processing for 30 minutes is shown.

  The hydrogen-containing lithium silicate compound of the present invention and the production method thereof, the positive electrode active material for nonaqueous electrolyte secondary battery, the positive electrode for nonaqueous electrolyte secondary battery, and the nonaqueous electrolyte secondary battery will be described in detail.

(1) Hydrogen-containing lithium silicate compound The hydrogen-containing lithium silicate compound is obtained by adding hydrogen (proton) to a lithium silicate compound containing lithium, at least one of iron and manganese, and silicon. In order to contain hydrogen in the lithium silicate compound, for example, the lithium silicate compound may be subjected to an acid treatment. When the lithium silicate compound is subjected to an acid treatment, protons enter the lithium silicate compound. Proton enters the lithium site of the lithium silicate compound, and lithium ions and protons exchange ions.

  The lithium silicate compound is in the form of particles, and an inactive film is formed in the air on the particle surface. This film provides resistance to lithium ion diffusion. For this reason, it is considered that when the lithium silicate compound is used as it is as an active material of a battery, the voltage and capacity are lowered. Therefore, as in the present invention, the lithium silicate compound is subjected to acid treatment and protons are introduced to remove the film on the particle surface, and this is used as a positive electrode active material to constitute a nonaqueous electrolyte secondary battery. Therefore, it is considered that the discharge voltage and capacity of the battery are increased, and the charge / discharge characteristics are improved.

Hydrogen-containing lithium silicate-based compound, composition formula _{Li 2 + a-b-z} H z A b M
_1-x M ′ _x SiO _{4 + δ} (wherein A is at least one element selected from the group consisting of Na (sodium), K (potassium), Rb (rubidium), and Cs (cesium)), and M is Fe ( Iron) and at least one element selected from the group consisting of Mn (manganese), and M ′ is Mg (magnesium), Ca (calcium), Co (cobalt), Al (aluminum), Ni (nickel), Nb. (Niobium), Ti (titanium), Cr (chromium), Cu (copper), Zn (zinc), Zr (zirconium), V (vanadium), Mo (molybdenum) and W (tungsten) Each subscript is as follows: 0 ≦ a <1, 0 ≦ b <0.2, 0 <z, 0 ≦ x ≦ 0.5, δ ≧ 0) A compound.

  The range of a in the above formula is 0 ≦ a <1. When a is 0, the lithium content in the lithium silicate compound is stoichiometric, and when a is greater than 0, the lithium content exceeds the stoichiometric amount. Become. When a is less than 1, the cycle characteristics are good and the capacity is high.

  The range of b in the above formula is 0 ≦ b <0.2. When b is zero, the hydrogen-containing lithium silicate compound does not contain at least one element A selected from the group of Na, K, Rb, and Cs. When b is larger than zero, the element A is included. The element A is an alkali metal. For example, when a lithium silicate compound is produced by a molten salt method, an alkali metal contained in the molten salt is introduced. When lithium is used as the alkali metal contained in the molten salt, the element A is often not contained, and instead, Li is easily introduced in excess of the stoichiometric amount. When b is less than 0.2, the Li content can be maintained and the capacity can be maintained high.

  The range of z in the above formula is z> 0. When z exceeds zero, H (proton) is included in the lithium silicate compound. The range of z in the above formula is preferably 0 <z ≦ 1.0. When z is 1.0 or less, the content of Li can be maintained and the capacity can be maintained high. Furthermore, it is preferable that 0 <z ≦ 0.8.

  The range of x in the above formula is 0 ≦ x ≦ 0.5. When x is 0.5 or less, at least one of Fe and Mn is sufficiently contained in the lithium silicate compound, so that the capacity can be kept high.

  The range of δ in the above formula is δ ≧ 0. Preferably, 0 ≦ δ <2. When δ is less than 2, the stability of the crystal structure of the lithium silicate compound is enhanced.

The hydrogen-containing lithium silicate compound has a composition formula Li _{2 + ab Ab} M _1-x M ′ _x SiO _{4 + δ} (wherein A is at least one element selected from the group of Na, K, Rb, and Cs) , M is at least one element selected from the group consisting of Fe and Mn, and M ′ is Mg, Ca, Co, Al, Ni, Nb, Ti, Cr, Cu, Zn, Zr, V, Mo, and W. And at least one element selected from the group consisting of the following: 0 ≦ a <1, 0 ≦ b <0.2, 0 ≦ x ≦ 0.5, δ ≧ 0) It is obtained by subjecting the lithium silicate compound represented to the acid treatment.

  The lithium silicate compound may contain inevitable impurities. Inevitable impurities may be mixed in, for example, raw materials or manufacturing processes. The obtained lithium silicate-based compound as a whole may be based on the composition shown in the general formula, and may slightly deviate from the above general formula due to the unavoidable loss of metal elements or oxygen.

  The hydrogen-containing lithium silicate compound obtained by the above-described method is particularly preferably one having an average particle diameter in the range of 50 nm to 1 μm. In the present specification, the average particle diameter is a value determined by a laser diffraction particle size distribution measuring apparatus (SALD7100 manufactured by Shimadzu).

(2) Method for producing hydrogen-containing lithium silicate compound In order to produce a hydrogen-containing lithium silicate compound, an acid treatment is performed on a lithium silicate compound containing lithium, at least one of iron and manganese, and silicon. What is generally known as an acid can be used for the acid treatment performed on the lithium silicate compound. For example, hydrochloric acid, sulfuric acid, oxalic acid, acetic acid, boric acid, phosphoric acid, nitric acid, tartaric acid, ascorbic acid and the like can be mentioned. The temperature of the acid treatment can be, for example, from room temperature to 100 ° C. The acid treatment time depends on the acid to be used and the treatment temperature, but may be any time when the acid is introduced into the lithium silicate compound. When the type of acid is hydrochloric acid, it is preferably 40 minutes or longer and 2 hours or shorter, and more preferably 40 minutes or longer and 1.5 hours or shorter. When the time is less than 40 minutes, almost no proton is introduced, and when the time exceeds 2 hours, there is a risk that the amount of Li ions is excessively dropped and the battery capacity is reduced.

The lithium silicate compound subjected to the acid treatment contains lithium, at least one of iron and manganese, and silicon. The lithium silicate compound has a composition formula Li _{2 + ab Ab} M _1-x M ′ _x SiO _{4 + δ} (wherein A is at least one element selected from the group of Na, K, Rb, and Cs, and M Is at least one element selected from the group consisting of Fe and Mn, and M ′ is composed of Mg, Ca, Co, Al, Ni, Nb, Ti, Cr, Cu, Zn, Zr, V, Mo and W. At least one element selected from the group, each subscript being as follows: 0 ≦ a <1, 0 ≦ b <0.2, 0 ≦ x ≦ 0.5, δ ≧ 0) It may be a compound.

  The lithium silicate compound can be produced, for example, by a molten salt method, a solid phase method, a hydrothermal method, or the like. Especially, it is good to manufacture by the molten salt method.

  The molten salt method is a method of synthesizing a lithium silicate compound in a molten salt containing an alkali metal salt. Examples of the alkali metal salt used in the molten salt method include at least one selected from the group consisting of a lithium salt, a potassium salt, a sodium salt, a rubium salt, and a cesium salt. Of these, lithium salts are desirable. When a molten salt containing a lithium salt is used, the formation of an impurity phase is small, and a lithium silicate compound containing excessive lithium atoms is likely to be formed. The lithium silicate compound thus obtained is a positive electrode material for lithium ion batteries having good cycle characteristics and high capacity.

Moreover, it is desirable that the alkali metal salt used in the molten salt method contains at least one of alkali metal chloride, alkali metal carbonate, alkali metal nitrate, and alkali metal hydroxide. Specifically, lithium chloride (LiCl), potassium chloride (KCl), rubidium chloride (RbCl), cesium chloride (CsCl), lithium carbonate (Li ₂ CO ₃ ), potassium carbonate (K ₂ CO ₃ ), sodium carbonate ( Na ₂ CO ₃ ), rubidium carbonate (Rb ₂ CO ₃ ), cesium carbonate (Cs ₂ CO ₃ ), lithium nitrate (LiNO ₃ ), potassium nitrate (KNO ₃ ), sodium nitrate (NaNO ₃ ), rubidium nitrate (RbNO ₃ ) , Cesium nitrate (CsNO ₃ ), lithium hydroxide (LiOH), potassium hydroxide (KOH), sodium hydroxide (NaOH), rubidium hydroxide (RbOH) and cesium hydroxide (CsOH), of which One kind may be used alone, or two or more kinds may be mixed and used.

  Among them, the alkali metal carbonate is preferably an alkali metal carbonate, and further preferably contains lithium carbonate. Desirably, a carbonate mixture comprising at least one alkali metal carbonate selected from the group consisting of potassium carbonate, sodium carbonate, rubidium carbonate and cesium carbonate and lithium carbonate is preferable. By mixing two or more carbonates, the melting temperature of the molten salt can be lowered, and the synthesis reaction can be performed at a low temperature of 400 to 650 ° C.

  In addition, by performing the reaction at a relatively low temperature of 400 to 650 ° C. in the molten salt of the mixture, the growth of crystal grains is suppressed, and the average particle diameter becomes fine particles of 50 nm to 10 μm. The amount is greatly reduced. As a result, when used as a positive electrode active material for a non-aqueous electrolyte secondary battery, the material has good cycle characteristics and high capacity.

Furthermore, in a molten salt of a carbonate mixture consisting of at least one alkali metal carbonate and lithium carbonate selected from the group consisting of potassium carbonate, sodium carbonate, rubidium carbonate and cesium carbonate, it is represented by Li ₂ SiO _3. The lithium silicate compound and a substance containing at least one metal element selected from the group consisting of iron and manganese may be reacted at 400 to 650 ° C.

  The specific reaction method is not particularly limited. For example, a substance containing the above-described carbonate mixture, lithium silicate compound, and metal element (corresponding to M and M ′ in the composition formula; the same applies hereinafter) is mixed. After mixing uniformly using a ball mill or the like, the carbonate mixture may be melted by heating. Thereby, in molten carbonate, reaction with a lithium silicate compound and the said metal element advances, and a lithium silicate type compound can be obtained.

  At this time, the mixing ratio of the raw material composed of the lithium silicate compound and the metal element-containing material and the carbonate mixture is not particularly limited, and the amount of the raw material can be uniformly dispersed in the molten salt of the carbonate mixture. For example, it is preferable that the total amount of the substance containing the lithium silicate compound and the metal element is in the range of 100 to 300 parts by weight with respect to 100 parts by weight of the total amount of the carbonate mixture. The amount is more preferably in the range of ˜250 parts by weight.

  The above-described reaction is performed in a mixed gas atmosphere containing carbon dioxide and a reducing gas because the metal element stably exists as a divalent ion during the reaction. Under this atmosphere, the metal element can be stably maintained in a divalent state. Regarding the ratio of carbon dioxide and reducing gas, for example, the reducing gas may be 0.01 to 0.2 mol, preferably 0.03 to 0.1 mol, per 1 mol of carbon dioxide. . As the reducing gas, for example, hydrogen, carbon monoxide and the like can be used, and hydrogen is particularly preferable.

  There is no particular limitation on the pressure of the mixed gas of carbon dioxide and reducing gas, and it may be usually atmospheric pressure, but it may be under pressure or under reduced pressure.

  The reaction time between the lithium silicate compound and the substance containing the metal element is usually 0.1 to 30 hours, preferably 5 to 25 hours.

  After the above reaction is performed, the target lithium silicate compound can be obtained by removing the alkali metal carbonate used as the flux.

  As a method for removing the alkali metal carbonate, the alkali metal carbonate may be dissolved and removed by washing the product using a solvent capable of dissolving the alkali metal carbonate. For example, although water can be used as the solvent, it is preferable to use a nonaqueous solvent such as alcohol or acetone in order to prevent oxidation of the transition metal contained in the lithium silicate compound. In particular, it is preferable to use acetic anhydride and acetic acid in a weight ratio of 2: 1 to 1: 1. In addition to being excellent in the action of dissolving and removing the alkali metal carbonate, this mixed solvent, when acetic acid reacts with the alkali metal carbonate to produce water, acetic anhydride takes in the water and produces acetic acid. Therefore, it is possible to suppress the separation of water. When acetic anhydride and acetic acid are used, first, acetic anhydride is mixed with the product, ground with a mortar or the like to make particles fine, and then acetic anhydride is added in a state where acetic anhydride is intimately mixed with the particles. It is preferable. According to this method, since the water produced by the reaction of acetic acid and alkali metal carbonate reacts quickly with acetic anhydride, the chance of the product and water coming into contact with each other can be reduced. Can be suppressed.

<Carbon treatment>
The lithium silicate compound obtained by the above-described method may be further subjected to carbon treatment with carbon to improve conductivity.

The specific method of the carbon treatment is not particularly limited. In addition to a vapor phase method in which heat treatment is performed in an atmosphere containing a carbon-containing gas such as methane gas, ethane gas, butane gas, etc., an organic substance that is a carbon source and a lithium silicate system A thermal decomposition method in which an organic substance is carbonized by heat treatment after the compound is uniformly mixed is also applicable. In particular, it is preferable to apply a ball milling method in which a carbon material and Li ₂ CO ₃ are added to the lithium silicate-based compound, and uniformly mixed until the lithium silicate-based compound becomes amorphous by a ball mill, followed by heat treatment. According to this method, the lithium silicate compound that is the positive electrode active material is amorphized by ball milling, and is uniformly mixed with carbon to increase adhesion. Further, by heat treatment, the lithium silicate compound is recrystallized. At the same time, carbon can be uniformly deposited around the lithium silicate compound, and the lithium silicate compound can be combined with carbon. At this time, the presence of Li ₂ CO ₃ does not cause the lithium-excess lithium silicate compound to be deficient in lithium, and exhibits a high charge / discharge capacity.

Regarding the degree of amorphization, in the X-ray diffraction measurement using CuKα rays as a light source, a diffraction peak derived from the (011) plane corresponding to a peak at 2θ = 24 to 25 degrees for a sample having crystallinity before ball milling. the half-value width _{B (011) crystal,} when the half-width of B _{(011) mill} of the same peaks of the sample obtained by ball milling _{of, B (011) crystal / B} (011) ratio of the _mill is 0. It may be in the range of about 1 to 0.5.

  In this method, acetylene black (AB), ketjen black (KB), graphite or the like can be used as the carbon material.

Regarding the mixing ratio of the lithium silicate compound, the carbon material, and Li ₂ CO ₃ , the carbon material is 20 to 40 parts by mass and Li ₂ CO ₃ is 20 to 40 parts by mass with respect to 100 parts by mass of the lithium silicate compound. do it.

  Ball milling is performed until the lithium silicate compound becomes amorphous, and then heat treatment is performed. The heat treatment is preferably performed in a reducing atmosphere in order to keep the transition metal ions contained in the lithium silicate compound divalent. As the reducing atmosphere in this case, in order to suppress the reduction of the divalent transition metal ion to the metal state, as in the synthesis reaction of the lithium silicate compound in the molten salt, the reducing atmosphere is reduced with carbon dioxide. A gas mixed gas atmosphere is preferred. The mixing ratio of carbon dioxide and reducing gas may be the same as in the synthesis reaction of the lithium silicate compound.

  The heat treatment temperature is preferably 500 to 800 ° C. If the heat treatment temperature is too low, it is difficult to deposit carbon uniformly around the lithium silicate compound, while if the heat treatment temperature is too high, decomposition of the lithium silicate compound or lithium deficiency may occur. This is not preferable because the charge / discharge capacity decreases. Moreover, what is necessary is just to make heat processing time into 1 to 10 hours normally.

As another carbon treatment method, a carbon material and LiF are added to the lithium silicate compound, and the mixture is uniformly mixed by a ball mill until the lithium silicate compound is amorphized in the same manner as described above, followed by heat treatment. You may go. In this case, as in the case described above, carbon is uniformly deposited around the lithium silicate compound simultaneously with recrystallization of the lithium silicate compound, and the conductivity is improved. Further, the lithium silicate compound is further improved. A part of the oxygen atoms is substituted with fluorine atoms to form a fluorine-containing lithium silicate-based composite represented by the following composition formula. The lithium silicate compound is represented by the composition formula: Li _{2 + ab Ab} M _1-x M ′ _x SiO _{4 + δ} (A, M, M ′ and subscripts a, b, x, and δ are the same as above). In this case, the composition formula of the lithium silicate-based composite obtained by the carbon treatment using the carbon material and LiF is Li _{2 + ab Ab} M _1-x M ′ _x SiO _{4 + δ} F _2z (A in the formula, M, M ′, and subscripts a, b, x, and δ are the same as described above, and can be represented by 0 <z <1).

  When the composite lithium silicate compound is used as a positive electrode due to the addition of F, the average voltage increases, and a positive electrode material having better performance is obtained. At this time, the presence of LiF does not cause the lithium-excess lithium silicate compound to be deficient in lithium, and exhibits a high charge / discharge capacity.

In this method, the mixing ratio of the lithium silicate compound, the carbon material, and LiF may be 20 to 40 parts by mass of the carbon material and 10 to 40 parts by mass of LiF with respect to 100 parts by mass of the lithium silicate compound. . Furthermore, Li ₂ CO ₃ may be included as necessary. The conditions for ball milling and heat treatment may be the same as described above.

(3) Positive electrode active material for non-aqueous electrolyte secondary battery An active material for a lithium secondary battery positive electrode is the above-described hydrogen-containing lithium silicate compound, or a hydrogen-containing lithium silicate compound obtained by subjecting a lithium silicate compound to acid treatment Consists of. According to such an active material for a positive electrode of a lithium secondary battery, a battery having excellent charge / discharge characteristics can be configured.

(4) Positive electrode for non-aqueous electrolyte secondary battery The positive electrode for non-aqueous electrolyte secondary battery has a positive electrode active material composed of the hydrogen-containing lithium silicate compound, A similar structure can be used.

  For example, the above-mentioned hydrogen-containing lithium silicate-based compound may be added to acetylene black (AB), ketjen black (KB), vapor grown carbon fiber (VGCF) or other conductive additive, polyvinylidene fluoride (PVdF). Add a binder such as polytetrafluoroethylene (PTFE) or styrene-butadiene rubber (SBR), or a solvent such as N-methyl-2-pyrrolidone (NMP) to apply as a paste to the current collector Can produce a positive electrode. The amount of the conductive auxiliary agent used is not particularly limited, but for example, it can be 5 to 20 parts by weight with respect to 100 parts by weight of the hydrogen-containing lithium silicate compound. Further, the amount of the binder used is not particularly limited, but may be 5 to 20 parts by weight with respect to 100 parts by weight of the hydrogen-containing lithium silicate compound, for example. As another method, a mixture of a hydrogen-containing lithium silicate compound, the above-described conductive additive and binder is kneaded using a mortar or a press to form a film, which is then pressed into a current collector. The positive electrode can also be produced by a method of pressure bonding with.

  The current collector is not particularly limited, and materials conventionally used as positive electrodes for nonaqueous electrolyte secondary batteries, such as aluminum foil, aluminum mesh, and stainless steel mesh, can be used. Furthermore, a carbon nonwoven fabric, a carbon woven fabric, etc. can be used as a collector.

  The shape and thickness of the positive electrode for a nonaqueous electrolyte secondary battery are not particularly limited. For example, the positive electrode for a nonaqueous electrolyte secondary battery is filled with an active material and then compressed to have a thickness of 10 to 200 μm, more preferably 20 It is preferable to set it to -100 micrometers. Therefore, the filling amount of the active material may be appropriately determined so as to have the above-described thickness after compression according to the type and structure of the current collector to be used.

(5) Nonaqueous electrolyte secondary battery The nonaqueous electrolyte secondary battery includes the above-described positive electrode for a nonaqueous electrolyte secondary battery. The nonaqueous electrolyte secondary battery can be manufactured by a known method. The positive electrode described above is used as the positive electrode material. As the negative electrode material, for example, when using a known metal lithium, carbon-based material such as graphite, silicon-based material such as silicon thin film, alloy-based material such as copper-tin and cobalt-tin, and oxide material such as lithium titanate Good. As an electrolytic solution, a lithium salt such as lithium perchlorate, LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ or the like is added to a known non-aqueous solvent such as ethylene carbonate, dimethyl carbonate, propylene carbonate, dimethyl carbonate to 0.5 mol / L to 1 A solution dissolved at a concentration of 7 mol / L may be used, and other known battery components may be used.

  When metal lithium is used as the negative electrode, a lithium secondary battery is obtained, and when a material other than metal lithium is used as the negative electrode, a lithium ion secondary battery is obtained. In general, many secondary batteries that perform a battery reaction with these lithium ions are non-aqueous electrolyte secondary batteries.

  The non-aqueous electrolyte secondary battery can be mounted on a vehicle, for example. The vehicle may be an electric vehicle or a hybrid vehicle. The nonaqueous electrolyte secondary battery is preferably connected to, for example, a traveling motor mounted on a vehicle and used as a drive source. In this case, a high driving torque can be output for a long time. Further, the non-aqueous electrolyte secondary battery can be mounted on devices other than vehicles such as personal computers and portable communication devices.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment. The present invention can be implemented in various forms without departing from the gist of the present invention, with modifications and improvements that can be made by those skilled in the art.

(Example 1)
A hydrogen-containing lithium silicate compound was produced by the following method.

First, a mixture composed of 0.03 mol of iron (purity 99.9%, manufactured by Kojun Chemical Co., Ltd.) and 0.03 mol of lithium silicate Li ₂ SiO ₃ (purity 99.5%, manufactured by Kishida Chemical Co., Ltd.) Acetone (20 ml) was added and mixed with a zirconia ball mill at 500 rpm for 60 minutes and dried. This was mixed with a carbonate mixture (lithium carbonate (Kishida Chemical, purity 99.9%), sodium carbonate (Kishida Chemical, purity 99.5%), and potassium carbonate (Kishida Chemical, purity 99.5%). The ratio was 0.435: 0.315: 0.25, and the mixing ratio was 82 parts by mass of the carbonate mixture with respect to 100 parts by mass of the total amount of iron and lithium silicate. 20 ml was added, mixed in a zirconia ball mill for 60 minutes at 500 rpm, dried, and then the obtained powder was heated in a gold crucible to produce carbon dioxide (flow rate: 100 ml min ⁻¹ ) and hydrogen (flow rate: 3 ml min). ^-1 ) under a mixed gas atmosphere, the mixture was heated to 500 ° C. and reacted for 13 hours in a molten state of the carbonate mixture.

  After the reaction, when the temperature was lowered to 400 ° C., the entire reactor core was taken out from the electric furnace, which was a heater, and rapidly cooled to room temperature through the gas. Next, water (20 ml) was added to the obtained reaction product and ground in a mortar, dissolved in water to remove salts and the like, and then filtered to obtain a powder. This powder was put into a dryer at 100 ° C. and dried for about 1 hour. This obtained the powder which consists of a lithium silicate type compound.

  Thereafter, the powder composed of this lithium silicate compound was added to a previously prepared hydrochloric acid solution (a solution obtained by diluting 2 ml of hydrochloric acid HCl (manufactured by Kishida Chemical Co., Ltd., special grade, concentration 35.0 to 37.0%) in 18 ml of distilled water). It was soaked for about 1 hour and acid-treated. Subsequently, the acid-treated powder was filtered and dried (100 ° C., 2 hours) to obtain a powder (acid-treated product).

(Comparative Example 1)
It is possible to perform alkali treatment by immersing the powder composed of the precursor compound in a potassium hydroxide solution (30% by mass KOH solution (containing 30 g / L LiOH) (manufactured by Kishida Chemical)) prepared in advance for about 1 hour. Otherwise, powder was obtained in the same manner as in Example 1 (alkali-treated product).

(Comparative Example 2)
An untreated powder (untreated product) was obtained without any treatment on the powder composed of the lithium silicate compound prepared in Example 1.

<XRD diffraction>
The powders of Example 1 and Comparative Examples 1 and 2 were subjected to X-ray diffraction measurement using a CuKα ray by a powder X-ray diffractometer. The XRD pattern (X-ray diffraction pattern) is shown in FIG.

As shown in FIG. 1, the peak A having a diffraction angle (2θ) near 25 ° is attributed to Li ₂ FeSiO ₄ , and can be seen in all XRD patterns of Example 1 and Comparative Examples 1 and 2. A peak B having a diffraction angle (2θ) of around 22 ° is observed only in Example 1 subjected to the acid treatment, and the intensity of diffraction is relatively high. The XRD pattern of the alkali-treated product (Comparative Example 1) was not significantly different from the diffraction pattern of the untreated product Li ₂ FeSiO ₄ (Comparative Example 2). However, the XRD pattern of Example 1 is significantly different from the XRD patterns of Comparative Examples 1 and 2, and the XRD pattern of the acid-treated product (Example 1) is different from that of the untreated product (Comparative Example 2). It was shown that a large structural change was caused by the acid treatment. This is considered to be due to the ion exchange between lithium in the untreated product and proton (H) in hydrochloric acid by the acid treatment.

<Elemental analysis>
The powders of Example 1 and Comparative Examples 1 and 2 were subjected to elemental analysis by an inductively coupled plasma (ICP) method. As a result, as shown in Table 1, in Comparative Examples 1 and 2, there was no significant difference in the Li content, which was almost 2 mol, but in Example 1, it was 1.224. Hydrogen is an element that cannot be detected by the ICP method. Since hydrogen (proton) atoms are smaller than Li atoms, they are easily introduced into the Li site. In the elemental analysis results of Example 1, there is no element other than Li whose molar ratio is reduced compared to Comparative Examples 1 and 2. From this, the amount obtained by subtracting the amount of Li in Example 1 of the acid-treated product from the amount of Li in Comparative Example 2 of the untreated product (reduced amount of Li) is replaced with hydrogen, and Example 1 including hydrogen is also included. The composition ratio of this powder is Li _1.224 H _0.636 Na _0.006 K _0.004 Fe _1.012 SiO _5.586 .

<SEM photo>
The surfaces of the powders of Example 1 and Comparative Example 2 were observed with an SEM (scanning electron microscope) and shown in FIGS. The powder of Comparative Example 2 shown in FIG. 3 had a long and thin shape, and the surface was relatively smooth. On the other hand, as for the powder of Example 1 shown in FIG. 2, the unevenness | corrugation was recognized on the surface. In addition, as shown in FIG. 2, the average particle size of the powder of Example 1 was 0.3 μm.

  Further, although no photograph is shown, the powder of Example 1 was amber (grayish greenish brown), and the powders of Comparative Examples 1 and 2 were both gray (gray).

  From this, it can be said that the surface shape of the powder of Example 1 has changed significantly compared to Comparative Examples 1 and 2, and irregularities appeared on the surface. The lithium silicate compound is in the form of particles, and the particle surface is oxidized in air to form an inactive film. It is considered that this film was roughened by acid treatment, and irregularities appeared on the particle surface.

<Carbon treatment>
Each powder of Example 1 and Comparative Examples 1 and 2 and acetylene black were mixed at a mass ratio of 5: 4. Ball milling was used for mixing, and the mixing conditions were 450 rpm and 5 hours. Thereafter, the obtained mixed powder was put into a heat treatment furnace capable of controlling the atmosphere, and heat treatment was performed at 700 ° C. for 2 hours under a gas flow rate of CO ₂ : H ₂ = 100: 3 (cm ³ ). Through the above steps, a lithium iron silicate composite was obtained.

<Battery fabrication>
A mixture of lithium iron silicate composite: acetylene black (AB): polytetrafluoroethylene (PTFE) = 17.1: 4.7: 1 (mass ratio) prepared from the powders of Example 1 and Comparative Examples 1 and 2. After being kneaded, it was formed into a film and pressed onto an aluminum current collector to produce an electrode, which was vacuum-dried at 140 ° C. for 3 hours was used as the positive electrode. Thereafter, a solution of LiPF ₆ dissolved in ethylene carbonate (EC): dimethyl carbonate (DMC) = 3: 7 to 1 mol / L was used as an electrolyte, a polypropylene film (Celgard, Celgard 2400) as a separator, and lithium as a negative electrode. A coin battery using metal foil was prototyped.

<Charge / discharge test>
This coin battery was subjected to a charge / discharge test at 30 ° C. The test conditions were 0.05 mA / cm ^{2 and a} voltage of 1.5 to 4.5 V (only the first charge was charged at a constant voltage of 4.8 V for 10 hours). The charge / discharge curves of the batteries using the powders of Example 1, Comparative Examples 1 and 2 are shown in FIGS.

  As shown in FIGS. 4 to 6, the charge / discharge curve of the battery using the alkali-treated product of Comparative Example 1 showed the same behavior as the charge / discharge curve of the battery using the untreated product of Comparative Example 2. On the other hand, the battery using the acid-treated product of Example 1 had a high discharge voltage and a large battery capacity, and showed a good charge / discharge curve.

  Table 2 shows the average discharge voltage and initial discharge capacity in the initial five cycles of the batteries using the powders of Example 1 and Comparative Examples 1 and 2.

  As shown in Table 2, in Example 1, both the average discharge voltage and the initial discharge capacity in the initial five cycles were higher than those in Comparative Examples 1 and 2.

  7 and 8 show the battery capacities of the batteries using the powders of Example 1 and Comparative Example 2 up to 50 cycles. As shown in FIG. 7 and FIG. 8, the discharge capacity and the charge capacity for each cycle showed the same numerical values. In Example 1, the discharge capacity and the charge capacity were hardly decreased even when the number of cycles was increased. On the other hand, in Comparative Example 2, the discharge capacity and the charge capacity gradually decreased as the number of cycles increased.

<Discharge rate characteristics>
9 and 10 show the discharge rate characteristics of the batteries using the powders of Example 1 and Comparative Example 2. FIG. 9 and FIG. 10, the horizontal axis indicates the discharge capacity, and the vertical axis indicates the cell voltage. The discharge rate was variously changed between 0.1C and 8.24C. The temperature during the discharge rate test was kept constant at 30 ° C. As a result of the test, for example, when discharged at 0.82 C, 121 mAh / g in Example 1, 96 mAh / g in Comparative Example 2, and 98 mAh / g in Example 1 when discharged at 3.3 C, Comparative Example 2 was 78 mAh / g. Thus, the discharge capacity of Example 1 was higher than that of Comparative Example 2 at any rate. This indicates that Example 1 (acid-treated product) can discharge a larger capacity than Comparative Example 2 (untreated product), and it is understood that the discharge rate characteristics are excellent. It was.

<Examination of acid treatment time>
In FIG. 11, X-ray diffraction measurement was performed using a CuKα ray with a powder X-ray diffractometer for the hydrogen-containing lithium silicate compound powder when the acid treatment time was changed.

  The acid treatment time was changed to 12 minutes, 30 minutes, 60 minutes, and 120 minutes. The conditions for the acid treatment and the lithium silicate compound subjected to the acid treatment were the same as in Example 1. For comparison, an XRD diffraction result of a lithium silicate compound not subjected to acid treatment is also shown in FIG. When the acid treatment time is 60 minutes, it is the same as in Example 1, and when not treated, it is the same as in Comparative Example 1.

  As shown in FIG. 11, the XRD pattern changed significantly from the untreated XRD pattern as the acid treatment time increased. In particular, there was a large change in the XRD pattern between the case of 30 minutes and the case of 60 minutes. From this, it can be seen that there is a great change in the crystal structure of the hydrogen-containing lithium silicate compound between 30 minutes and 60 minutes.

  For example, a peak having a diffraction angle (2θ) of around 22 ° is conspicuous in the treatment for 60 minutes or more, and is not noticeable in the treatment for 30 minutes or less. The peak at a diffraction angle of around 43 ° was not noticeable at 60 minutes or more, but was noticeable at 30 minutes or less. Here, as characteristics that are present in the treatment for 60 minutes or more and not in the treatment for 30 minutes or less, in the treatment for 60 minutes or more, the peak intensity P1 when the diffraction angle is around 22 ° and the diffraction angle is around 25 °. It was found that the ratio (P1 / P2) with the peak intensity P2 tends to be 0.98 or more.

  FIG. 12 shows a non-aqueous electrolyte secondary battery using a hydrogen-containing lithium silicate compound produced by acid treatment for 30 minutes as a positive electrode active material, and the charge / discharge characteristics of this non-aqueous electrolyte secondary battery. FIG. 13 shows the discharge capacity and charge capacity of a battery using the hydrogen-containing lithium silicate compound powder up to 50 cycles. The discharge capacity and charge capacity for each cycle showed similar numerical values. When the charge / discharge curve (acid treatment 30 minutes) in FIG. 12 was compared with the charge / discharge curve (acid treatment 60 minutes) in FIG. 4, the charge / discharge capacity was significantly lower in the acid treatment 30 minutes than in 60 minutes. Comparing the cycle characteristics (acid treatment 30 minutes) in FIG. 13 with the cycle characteristics (acid treatment 60 minutes) in FIG. 7, the discharge capacity was much lower in the acid treatment 30 minutes than in the acid treatment 60 minutes.

  Further, the average discharge voltage in the initial 5 cycles of the battery using the hydrogen-containing lithium silicate compound powder in the case of 30-minute acid treatment was 2.59 V, and the initial discharge capacity was 80 mAh / g.

  From these, it can be seen that the acid treatment time is preferably longer than 30 minutes, more preferably 40 minutes or more, 45 minutes or more, and preferably 60 minutes or more. Further, the upper limit of the acid treatment time is preferably set to 2 hours or less because the amount of lithium available for charge / discharge decreases as the substitution amount of protons and lithium increases, leading to a decrease in battery capacity.

  For secondary batteries using lithium manganese silicate compounds containing manganese instead of the above lithium iron silicate compounds, charge / discharge characteristics similar to those of lithium iron silicate compounds due to the substitution effect of lithium ions and protons It is estimated that

Claims (9)

Lithium silicate compound containing lithium, iron and silicon is made to contain hydrogen ,
In the composition formula _{Li 2 + a-b-z} H z A b M 1-x M 'x SiO 4 + δ ( wherein, A is at least one element selected Na, K, Rb, from the group of Cs, M is Fe M ′ is at least one element selected from the group consisting of Mg, Ca, Co, Al, Ni, Nb, Ti, Cr, Cu, Zn, Zr, V, Mo, and W. Each subscript. Is represented as follows: 0 ≦ a <1, 0 ≦ b <0.2, 0 <z, 0 ≦ x ≦ 0.5, δ ≧ 0)
A hydrogen-containing lithium silicate compound characterized by having a diffraction angle (2θ) having a peak in the vicinity of 22 ° in an X-ray diffraction pattern using CuKα rays . 2. The hydrogen-containing lithium silicate compound according to claim 1 , wherein the range of z in the composition formula is 0 <z ≦ 1.0. A step of subjecting a lithium silicate compound containing lithium, iron, and silicon to an acid treatment with hydrochloric acid for 40 minutes to 2 hours ;
Wherein the lithium silicate-based compound has the formula _{Li 2 + a-b A b} M 1-x M 'x SiO 4 + δ ( wherein, A is at least one element selected Na, K, Rb, from the group of Cs, M is an Fe element, and M ′ is at least one element selected from the group consisting of Mg, Ca, Co, Al, Ni, Nb, Ti, Cr, Cu, Zn, Zr, V, Mo, and W. The subscripts are as follows: 0 ≦ a <1, 0 ≦ b <0.2, 0 ≦ x ≦ 0.5, δ ≧ 0) The hydrogen-containing lithium silicate system Compound production method.   A method for producing the hydrogen-containing lithium silicate compound according to claim 1 or 2,
  A method for producing a hydrogen-containing lithium silicate compound, wherein the lithium silicate compound is subjected to an acid treatment with hydrochloric acid for 40 minutes to 2 hours. A positive electrode active material for a nonaqueous electrolyte secondary battery, comprising the hydrogen-containing lithium silicate compound according to claim 1 . A positive electrode active material for a non-aqueous electrolyte secondary battery, comprising a hydrogen-containing lithium silicate compound produced by the production method according to claim 3 or 4 . A positive electrode for a non-aqueous electrolyte secondary battery comprising the positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 5 or 6 . Non-aqueous electrolyte secondary battery characterized by comprising a positive electrode for a nonaqueous electrolyte secondary battery according to claim 7. A vehicle comprising the nonaqueous electrolyte secondary battery according to claim 8 .