JPWO2013128936A1 - Active material composite and production method thereof, positive electrode active material for non-aqueous electrolyte secondary battery, and non-aqueous electrolyte secondary battery - Google Patents

Abstract

The positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention includes active material particles made of an active material and having an average particle size of 100 nm or less, and conductive particles made of a conductive material and having an average particle size of 100 nm or less. Are bonded to each other, and the specific surface area is 150 m 2 / g or more.

Description

The present invention relates to an active material composite used for an active material for a nonaqueous electrolyte secondary battery and a method for producing the same, a positive electrode active material for a nonaqueous electrolyte secondary battery, and a nonaqueous electrolyte secondary battery.

Among nonaqueous electrolyte secondary batteries, lithium ion secondary batteries are small and have high energy density, and are widely used as power sources for portable electronic devices. In addition, it is considered that a lithium ion secondary battery is used as a vehicle drive source. In recent years, lithium silicate compounds, lithium borate compounds, and lithium phosphate compounds are known as positive electrode active materials for lithium ion secondary batteries.

As described in International Publication No. 2010/089931 and Japanese Patent Application Laid-Open No. 2010-257592, lithium silicate compounds are inexpensive and have a low environmental impact because they are composed of abundant constituent metal elements. The material has a high theoretical charge / discharge capacity and does not release oxygen at a high temperature. Specifically, Li ₂ FeSiO ₄ (theoretical capacity 331.3 mAh / g), Li ₂ MnSiO ₄ (theoretical capacity 333.2 mAh). Lithium silicate compounds such as / g) have been developed.

As described in International Publication No. 2010/104137, lithium borate compounds are also inexpensive, have a large amount of resources, have a low environmental burden, have a high theoretical charge / discharge capacity, and do not release oxygen at high temperatures. It is attracting attention as a material. As a lithium borate compound, for example, LiFeBO ₃ (theoretical capacity 220 mAh / g), LiMnBO ₃ (theoretical capacity 222 mAh / g), and the like are known. The lithium borate material is a material that can be expected to improve the energy density by using boron (B), which is the lightest element in the polyanion unit, and the true density (3.46 g / cm ^{3) of the} borate material. ) Is smaller than the true density (3.60 g / cm ³ ) of the olivine iron phosphate material, and weight reduction can also be expected.

The lithium phosphate compound is represented by LiMPO ₄ (M is a metal such as Mn, Fe, Co), and a hetero element PO ₄ ^3- polyanion having a large electronegativity is arranged around the central metal M. For this reason, it is said that the thermal stability is higher than that of layered LiCoO ₂ or the like in which oxygen atoms are directly coordinated to the transition metal.

However, these materials have low conductivity and are almost at the insulator level. For this reason, the original capacity cannot be taken out from these materials, and it is necessary to improve the charge / discharge characteristics. Therefore, in order to increase the charge / discharge capacity of the various positive electrode active materials, each compound is also subjected to a carbon coating treatment. In WO 2010/089931 and WO 2010/104137, in order to further increase the charge / discharge capacity of a non-aqueous electrolyte secondary battery using a lithium silicate compound as a positive electrode active material, carbon is further added to the lithium silicate compound. It is also disclosed that the coating process is performed.

International Publication No. 2010/089931 JP 2010-257592 A International Publication No. 2010/104137

However, in order to drive a vehicle with a lithium ion secondary battery, a battery with a high charge / discharge capacity is required. In order to meet this demand, further improvement of the positive electrode active material is desired.

The present invention has been made in view of such circumstances, and an active material composite capable of increasing the charge / discharge capacity of a battery, a method for producing the same, a positive electrode active material for a non-aqueous electrolyte secondary battery, and a non-aqueous electrolyte two. It is an object to provide a secondary battery.

(1) In the active material composite of the present invention, active material particles made of an active material and having an average particle size of 100 nm or less are bonded to conductive particles made of a conductive material and having an average particle size of 100 nm or less. And the specific surface area is 150 m ² / g or more.

(2) The method for producing an active material composite according to the present invention is a method for producing the active material composite as described above, and includes an energy application step for applying mechanical energy to the active material and the conductive material. It is characterized by that.

(3) The positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention is characterized by comprising the active material composite described above or the active material composite manufactured by the manufacturing method described above.

(4) The positive electrode for nonaqueous electrolyte secondary batteries of the present invention is characterized by having the positive electrode active material for nonaqueous electrolyte secondary batteries described above.

(5) The nonaqueous electrolyte secondary battery of the present invention is characterized by comprising the positive electrode for a nonaqueous electrolyte secondary battery described above, a negative electrode, and an electrolyte.

In the active material composite of the present invention, fine active material particles and fine conductive particles are bonded to each other, so that the charge / discharge capacity of the battery can be increased. Since the positive electrode active material for a nonaqueous electrolyte secondary battery, the positive electrode for a nonaqueous electrolyte secondary battery, and the nonaqueous electrolyte secondary battery of the present invention use the active material composite, the charge / discharge capacity can be increased. it can.

The upper diagram of FIG. 1 is an SEM cross-sectional photograph of sample 1 (one scale of 1 μm), and the lower diagram of FIG. It is an enlarged photograph of. 2 is a SEM cross-sectional photograph of sample 1 (one scale 0.1 μm). It is a figure which shows the element mapping using the energy dispersive X-ray-analysis apparatus (EDX) of the surface vicinity of the secondary particle of the sample 1. FIG. It is a figure which shows the elemental mapping by the transmission electron microscope (TEM) photograph of the surface vicinity of the secondary particle of the sample 1, the figure which shows an electron beam diffraction, and an electron energy loss analysis method (EELS). 2 is a SEM photograph (one scale 0.1 μm) of the surface of secondary particles of sample 1. 2 is a cross-sectional explanatory view of an active material composite of Sample 1. FIG. 2 is a SEM cross-sectional photograph of sample 2 (one scale 0.2 μm). 3 is a SEM cross-sectional photograph (one scale 0.5 μm) of Sample 3. 4 is a SEM cross-sectional photograph of sample 3 (one scale 0.1 μm). 4 is an SEM photograph (one scale 0.1 μm) of the particle surface of sample 3. FIG. 4 is an SEM photograph (one scale 0.1 μm) of the particle surface of sample 5. FIG. 4 is a diagram showing a charge / discharge curve of a battery produced using Sample 1. FIG. 3 is a diagram showing a charge / discharge curve of a battery produced using Sample 2. FIG. 3 is a diagram showing a charge / discharge curve of a battery manufactured using Sample 3. FIG. FIG. 6 is a diagram showing a charge / discharge curve of a battery manufactured using Sample 4. FIG. 4 is a diagram showing a cycle test result of a battery manufactured using Sample 1. It is a figure which shows the rate test result of the battery produced using the sample 1. FIG. It is a figure which shows the alternating current impedance plot after the charge of the battery produced using the samples 1 and 3. FIG. It is a figure which shows the alternating current impedance plot after the discharge of the battery produced using the samples 1 and 3. FIG. FIG. 20 is an SEM photograph of Li ₂ MnSiO ₄ immediately after synthesis, and the upper diagram in FIG. 20 is a high-magnification SEM photograph, and the lower diagram in FIG. 20 is a low-magnification SEM photograph. FIG. 21 is an SEM photograph of Sample 6, the upper drawing of FIG. 21 is a low magnification SEM photograph, and the lower drawing of FIG. 21 is a high magnification SEM photograph. 3 is a SEM photograph of Sample 8. Immediately after synthesis _Li 2 MnSiO _4, and shows the XRD pattern of the sample 6-8. The charging / discharging curve of the battery using the sample 6 is shown. The charging / discharging curve of the battery using the sample 7 is shown. The charging / discharging curve of the battery using the sample 8 is shown.

An active material composite according to an embodiment of the present invention and a manufacturing method thereof, a positive electrode active material for a nonaqueous electrolyte secondary battery, a nonaqueous electrolyte secondary battery, and a vehicle will be described in detail.

(1) Active material composite The active material composite according to the present invention includes active material particles made of an active material having an average particle diameter of 100 nm or less, and conductive particles made of a conductive material having an average particle diameter of 100 nm or less. It consists of a composite formed by bonding. By mixing and joining the active material particles and the conductive particles in a very small nano-level fine particle state of 100 nm or less, the charge / discharge capacity of the battery can be increased as shown in Examples described later. The reason is that the active material particles and the conductive particles are joined to each other in a fine particle state at the nano level, thereby increasing the number of conductive paths composed of the conductive particles in the active material complex, This is presumed to be due to the increase in the utilization rate of the active material due to the active movement of electrons.

The specific surface area of the active material composite is 150 m ² / g or more, preferably 170 m ² / g or more. Thus, when the specific surface area of an active material composite is large, a contact area with electrolyte solution becomes large, it becomes easy to occlude and discharge | release lithium ion, and can improve the charge / discharge capacity of a battery.

Here, the average particle diameter of the active material particles is 100 nm or less, and the average particle diameter of the conductive particles is 100 nm or less. The average particle diameter of each particle is the maximum diameter of a plurality of particles obtained by analyzing an image of the active material complex using a transmission electron microscope (TEM) or the like (the distance between two parallel lines sandwiching the particles). (Maximum value) is a value calculated by actual measurement.

When the average particle diameter of the active material particles exceeds 100 nm, or when the average particle diameter of the conductive particles exceeds 100 nm, the effect of increasing the charge / discharge capacity of the battery may be reduced. Preferably, the average particle diameter of the active material particles is 10 nm or more and 90 nm or less, and the average particle diameter of the conductive particles is 2 nm or more and 50 nm or less. In this case, the charge / discharge capacity of the battery is further increased. More preferably, the average particle size of the active material particles is 10 nm to 50 nm, and the average particle size of the conductive particles is 2 nm to 10 nm.

The active material particles and the conductive particles are mixed and bonded as primary particles to each other in a nano-level fine particle state to form a composite that is a secondary particle.

The average particle size of the active material complex is preferably 0.7 μm or more and 20 μm or less, and more preferably 1 μm or more and 10 μm or less. When the average particle diameter of the active material composite is too small, granulation of the active material composite is not yet developed, and the composite of the active material particles and the conductive particles is insufficient. When the average particle size of the active material complex is excessive, the rate at which the active material complex occludes / releases lithium ions may decrease.

The specific surface area of the active material composite is 150 m ² / g or more, preferably 170 m ² / g or more. The specific surface area refers to the BET specific surface area. The upper limit of the specific surface area of the active material composite is preferably 300 m ² / g, and more preferably 250 m ² / g. When the specific surface area of the active material composite is too small, the charge / discharge capacity of the battery may be reduced. When the specific surface area of the active material composite is excessive, the active material composite is too small, and there is a possibility that the composite of the conductive particles and the active material particles is insufficient.

In the entire active material composite, the active material particles and the conductive particles may be uniformly finely mixed and bonded to each other. Moreover, the active material complex is preferably composed of a core part and a surface layer covering the core part. The surface layer may contain more carbon than the core portion. The thickness of the surface layer is preferably 500 nm or more and 2 μm or less. When the active material composite has the surface layer, the conductive network between the composites increases.

Fine surface particles are preferably adhered to the surface of the active material composite. The average particle size of the surface particles is preferably 20 nm or more and 100 nm or less, more preferably 30 nm or more and 90 nm or less, and preferably 35 nm or more and 75 nm or less. Examples of surface particles include:
A part of the raw material of the active material particles may be included. When the active material composite has the surface particles, the reaction in which the active material particles occlude / release lithium ions is promoted.

The active material constituting the active material particles may be made of a material that can occlude and release lithium ions. In this case, the active material for nonaqueous electrolyte secondary batteries can be used for the electrode of a lithium ion secondary battery.

The active material is preferably composed of one or more members selected from the group consisting of a lithium silicate compound, a lithium phosphate compound, and a lithium borate compound. According to the active material composite including the active material particles made of such an active material, it constitutes an active material for a non-aqueous electrolyte secondary battery, and further an active material for a lithium ion secondary battery or a lithium secondary battery. can do. The lithium silicate-based compound may be, for example, at least one selected from the group consisting of lithium iron silicate (Li ₂ FeSiO ₄ ) and lithium manganese silicate (Li ₂ MnSiO ₄ ). The lithium iron silicate is represented by, for example, Li ₂ FeSiO ₄ . The lithium manganese silicate is represented by, for example, Li ₂ MnSiO ₄ .

As the conductive material constituting the conductive particles, a material having higher conductivity than the active material is used. For example, a carbon material is preferably used as the conductive material. As the carbon material, acetylene black (AB), ketjen black (KB), carbon black, carbon nanotube, graphene, carbon fiber, graphite, or the like can be used. Among these, acetylene black (AB), ketjen black (KB), and carbon black are preferable.

In the active material composite, the mass ratio of the conductive particles when the active material particles are 100 parts by mass is preferably 2 parts by mass or more and 60 parts by mass or less, and more preferably 5 parts by mass or more and 30 parts by mass. It may be the following. In this case, the active material particles and the conductive particles are uniformly dispersed, and the electric capacity can be greatly extracted.

(2) Method for Producing Active Material Complex A method for producing the above active material complex, characterized in that it has an energy imparting step for imparting mechanical energy to the active material and the conductive material.

The active material used in the energy application step may be, for example, any one of a lithium silicate compound, a lithium phosphate compound, and a lithium borate compound.

The lithium silicate compound is, for example, a lithium silicate compound having a composition formula of Li ₂ M ¹ SiO ₄ (M ¹ is Fe, Mn, Co), or a composition formula of 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, and M is at least one element selected from the group consisting of Fe, Mn and Co) , M ′ is at least one element selected from the group consisting of Mg, Ca, Al, Ni, Nb, Ti, Cr, Cu, Zn, Zr, V, Mo, and W. The subscripts are as follows. Preferably, it is made of a compound represented by 0 ≦ a <1, 0 ≦ b <0.2, 0 ≦ x ≦ 0.5, δ ≧ 0).

Specifically, for _{example, Li 2 FeSiO 4, Li 2} MnSiO 4, Li 2 CoSiO 4 can be cited.

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, the above-described carbonate mixture, lithium silicate compound, and a substance containing a metal element (corresponding to M ¹ in the composition formula; the same shall apply hereinafter) are mixed to form a ball mill. Or the like, and then 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 molten salt raw material is in the range of 20 to 300 parts by mass with respect to 100 parts by mass of the total amount of the carbonate mixture. The amount is more preferably in the range of ˜80 parts by mass.

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 0.5 mol per mol of carbon dioxide, and preferably 0.03 to 0.4 mol. . 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 mass 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.

Examples of the lithium borate compound include LiM ² BO ₃ (M ² is composed of at least one selected from the group consisting of Mn, Fe, and Co). Among them, composition formula: Li _{1 + ab Ab} M ² _1-x M ′ _x BO _{3 + c} (wherein A is at least one element selected from the group consisting of Na, K, Rb and Cs) M ² is at least one element selected from the group consisting of Fe, Mn, and Co, and M ′ is a group consisting of Mg, Ca, Al, Ni, Nb, Mo, W, Ti, and Zr. Each subscript is as follows: 0 ≦ x ≦ 0.5, 0 <a <1, 0 ≦ b <0.2, 0 <c <0.3 And a> b) is preferred. This compound is, for example, in a reducing atmosphere in a molten salt of a carbonate mixture comprising at least one alkali metal carbonate and lithium carbonate selected from the group consisting of potassium carbonate, sodium carbonate, rubidium carbonate and cesium carbonate. Manufactured by reacting a divalent metal compound containing at least one compound selected from the group consisting of a divalent iron compound and a divalent manganese compound, boric acid, and lithium hydroxide at 400 to 650 ° C. can do. In this way, using a metal compound containing an iron compound or a manganese compound, boric acid, and lithium hydroxide as raw materials, in a molten salt of a mixture of lithium carbonate and other alkali metal carbonate, in a reducing atmosphere, According to the method of reacting the raw materials, a lithium borate compound containing iron or manganese can be obtained under relatively mild conditions. The obtained lithium borate compound is a borate compound that is fine, has a small impurity phase, contains excessive lithium atoms, and has good cycle characteristics when used as a positive electrode active material of a lithium ion secondary battery. It becomes a material having a capacity.

Examples of the lithium phosphate compound include LiM ³ PO ₄ (M ³ is at least one selected from the group consisting of Mn, Fe, and Co), Li ₃ M ₂ (PO ₄ ) ₃ (M = Fe, V). , Li ₂ FeP ₂ O ₇ , Li ₂ MnP ₂ O ₇ , Li ₂ MPO ₄ F (M = Fe, Mn, Co, Ni) and the like. Among these, LiMnPO ₄ , LiFePO ₄ , and LiCoPO ₄ are preferable.

The conductive material used in the energy application step is made of, for example, a carbon material. As the carbon material, acetylene black (AB), ketjen black (KB), carbon black, carbon nanotube, graphene, carbon fiber, graphite and the like can be used. Among them, acetylene black (AB) is preferred because of its high specific surface area. Ketjen black (KB) and carbon black are preferred.

The average particle diameter of the active material used in the energy application step is preferably 200 nm to 5 μm, and the average particle diameter of the conductive material is preferably 100 nm to 5 μm. In this case, active material particles having an average particle size of 100 nm or less and conductive particles having an average particle size of 100 nm or less by applying mechanical energy to the active material and the conductive material in the energy application step. Can be easily obtained.

The energy application step may be a step of applying mechanical energy by milling. Thereby, mechanical energy can be uniformly given to the active material and the conductive material. Although there is no particular limitation on the milling method, ball milling in which mechanical energy is introduced by moving the container by an external force in a state where a hard ball is accommodated in the container together with the sample is preferable. As the ball milling device, any of a planetary type that gives energy to the sample by rotation and revolution and a vibration type that gives energy to the sample by vibration in the horizontal direction or the vertical direction can be adopted.

In the energy application step, the active material and the conductive material may be rotated by a ball mill at a relatively high speed. When a mechanical milling device (Fritch Japan Co., Ltd., planetary ball mill P-7 series) is used, the rotational speed of the ball mill is preferably greater than 700 rpm and not greater than 1100 rpm. In this case, both the active material particles and the conductive particles can be uniformly dispersed and mixed with an average particle size of 100 nm or less to be amorphized and combined. When it is less than 700 rpm, the average particle diameter of the active material particles and the conductive particles may be larger than 100 nm. If it exceeds 1100 rpm, there is a risk of increased contamination of impurities.

Furthermore, it is preferable that the rotation speed of a ball mill is 750 rpm or more and less than 1000 rpm. In this case, the active material particles and the conductive particles can be more uniformly dispersed and mixed.

If the milling conditions are daringly specified, in the X-ray diffraction measurement using CuKα rays as a light source, a diffraction peak derived from the (111) plane (2θ) for a sample containing a lithium silicate compound precursor having crystallinity before milling. (Detected at 23 ° to 26 °) is B (111) crystal and the half width of the same peak of the sample after milling is B (111) mill, B (111) crystal / B (111) mill The ratio is preferably in the range of 0.7 to 1.1, more preferably 0.8 to 1.0.

When the active material is a lithium silicate compound, in addition to the lithium silicate compound, in addition to the conductive material, Li ₂ CO ₃ is added to the lithium silicate compound, and the lithium silicate compound is made amorphous by ball milling. Mix evenly until By the presence of Li ₂ CO ₃ , lithium deficiency of the lithium silicate compound is suppressed, and a high charge / discharge capacity is exhibited.

In the energy application step, the active material and the conductive material can be mixed in an inert gas atmosphere (argon gas, nitrogen gas) or in an air atmosphere.

When the active material is a lithium silicate compound, the mixing ratio of the lithium silicate compound and the conductive material may be 5 to 50 parts by mass of the carbon material with respect to 100 parts by mass of the lithium silicate compound. .

After the energy application step, a heat treatment step may be performed in which heat treatment is performed on the mixture of the active material and the conductive material to which mechanical energy is applied. In the heat treatment step, the mixed active material and conductive material are heated at a predetermined temperature. By heat treatment and sintering together with recrystallization of the active material, the particles are brought into close contact with each other to improve conductivity.

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 and 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.

When the active material is a lithium silicate compound, 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.

When the active material is a lithium borate compound, the heat treatment is preferably performed in a mixed atmosphere of carbon dioxide and a reducing gas. The reason is that decomposition of the lithium borate compound is suppressed.

When the active material is a lithium phosphate compound, the heat treatment is preferably performed in a mixed atmosphere of carbon dioxide and a reducing gas or in an inert gas atmosphere. The reason is that decomposition of the lithium phosphate compound can be suppressed.

(3) Positive electrode active material for nonaqueous electrolyte secondary battery A positive electrode active material for a nonaqueous electrolyte secondary battery is composed of the active material composite described above. According to such a non-aqueous electrolyte secondary battery positive electrode active material, a battery having excellent charge / discharge characteristics can be configured.

(4) Positive electrode for nonaqueous electrolyte secondary battery The positive electrode for nonaqueous electrolyte secondary battery comprises the positive electrode active material for nonaqueous electrolyte secondary battery and a current collector. The positive electrode for a nonaqueous electrolyte secondary battery has a positive electrode active material made of the above active material composite, and can have the same structure as a normal positive electrode for a nonaqueous electrolyte secondary battery.

For example, the active material composite may include acetylene black (AB), ketjen black (KB), a conductive additive such as vapor grown carbon fiber (VGCF), polyvinylidene fluoride (PVdF), By adding a binder such as polytetrafluoroethylene (PTFE) and styrene-butadiene rubber (SBR) and a solvent such as N-methyl-2-pyrrolidone (NMP) to form a paste and applying it to the current collector A positive electrode can be produced. The amount of the conductive aid used is not particularly limited, but can be 5 to 20 parts by mass with respect to 100 parts by mass of the active material composite, for example. The amount of the binder used is not particularly limited, but may be 5 to 20 parts by mass with respect to 100 parts by mass of the active material composite, for example. In addition, as another method, a mixture of the active material composite, the conductive aid and the binder described above is kneaded using a mortar or a press to form a film, and this is crimped to the current collector with a press. The positive electrode can be manufactured also by the method to do.

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 be set to ˜100 μm. 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. The negative electrode material is composed of an element compound that can occlude and release lithium ions and can be alloyed with lithium or / and an element compound that can be alloyed with lithium. Elements capable of alloying with lithium are Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Ti, Ag, Zn, Cd, Al, Ga, In, Si, Ge. , Sn, Pb, Sb, Bi may be included. Examples of the negative electrode material include known metal-based materials such as lithium metal and graphite, silicon-based materials such as SiOx (0.5 ≦ x ≦ 1.5), alloy-based materials such as copper-tin and cobalt-tin, An oxide material such as lithium titanate is preferably used.

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.

(6) Vehicle, etc. The nonaqueous electrolyte secondary battery can be mounted on a vehicle. 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.

<Manufacture of Active Material Complex (1)> The active material complexes of Samples 1 to 5 were manufactured by the following method. The active material composites of Samples 1 to 5 are made of Li ₂ FeSiO ₄ and carbon.

A mixture of 0.03 mol of iron (purity 99.9%, manufactured by High Purity Chemical Co., Ltd.) and 0.03 mol of lithium silicate compound Li ₂ SiO ₃ (Kishida Chemical Co., Ltd., purity 99.5%) Acetone (20 ml) was added to the mixture, and mixed with a zirconia ball mill at 500 rpm for 60 minutes and dried. This was mixed with a carbonate mixture (lithium carbonate (manufactured by Kishida Chemical, purity 99.9%), sodium carbonate (manufactured by Kishida Chemical, purity 99.5%), and potassium carbonate (manufactured by Kishida Chemical, purity 99.5%) in a molar ratio of 0. 435: 0.315: 0.25, and the mixing ratio is 100 parts by mass of the total amount of iron and lithium silicate.
It was set as the mass part. Acetone (20 ml) was added thereto, mixed in a zirconia ball mill at 500 rpm for 60 minutes, and dried.

Thereafter, the obtained powder was heated in a gold crucible and heated to 500 ° C. in a mixed gas atmosphere of carbon dioxide (flow rate: 100 ml min-1) and hydrogen (flow rate: 3 ml min-1) to form carbonate. The mixture was allowed to react for 13 hours in the molten state. 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, and dissolved in water to remove salts and the like, and then a filtered powder was obtained. This powder was put into a dryer at 100 ° C. and dried for about 1 hour. Thereafter, as a result of confirming the crystal structure by powder X-ray diffraction (XRD), it was found that substantially single-phase Li ₂ FeSiO ₄ was obtained. The average particle diameter of the active material particles made of Li ₂ FeSiO ₄ was 0.5 μm.

The obtained active material particles and acetylene black (AB, average particle size 0.3 μm) were mixed at a mass ratio of 5: 4, and a mechanical milling device (Fritch Japan Co., Ltd., planetary ball mill P-7) was used. Then, mechanical milling treatment was performed under the following predetermined conditions in an air atmosphere to give mechanical energy to the mixture. This step was performed by putting 50 g of φ4 mm zirconia balls and 300 mg of the mixture in a ball mill grinding container made of zirconia and having a volume of 45 cc.

When mixing the obtained powder and AB, the material obtained when the rotation speed of the ball mill was 800 rpm and the rotation time was 5 hours was designated as Sample 1. The material obtained when the rotation speed of the ball mill was 700 rpm and the rotation time was 5 hours was designated as Sample 2. The material obtained when the rotation speed of the ball mill was 450 rpm and the rotation time was 5 hours was designated as Sample 3. The material obtained when the rotation speed of the ball mill was 200 rpm and the rotation time was 5 hours was designated as Sample 4. Sample 5 was obtained by mixing Li ₂ FeSiO ₄ and carbon by hand using a mortar for 30 minutes. Each sample was heat-treated. The heat treatment conditions were 700 ° C., 2 hours, and an atmosphere of CO ₂ / H ₂ = 100/3 ccm (mixed gas of carbon dioxide (flow rate 100 mL / min) and hydrogen (flow rate 3 mL / min)).

(SEM Observation) Samples 1 to 5 were observed with an SEM (scanning electron microscope). SEM photographs of the material of Sample 1 are shown in FIGS. A SEM photograph of the active material composite of Sample 2 is shown in FIG. SEM photographs of the active material composite of Sample 3 are shown in FIGS. An SEM photograph of the active material composite of Sample 5 is shown in FIG. Among these drawings, FIGS. 1, 2, 7, 8, and 9 are SEM cross-sectional photographs of materials taken at various magnifications, and FIGS. 5, 10, and 11 are images of the surface of particles. It is the SEM photograph which was done.

In the sample 1, as shown in FIGS. 1 and 2, relatively large large particles having a major axis of about 20 μm and fine particles having a particle size of about 1 to 4 μm were mixed. As shown in the lower diagram of FIG. 1 and FIG. 2, a large number of fine particles were uniformly dispersed inside the large particles. That is, the large particles are those in which fine primary particles are combined into secondary particles. As a result of measuring the specific surface area using the BET method, the composite showed a high value of 171.7 m ² / g.

The upper left photograph of FIG. 3 shows an annular dark-field scanning transmission electron microscope (ADF-STEM) image of the large secondary particles of Sample 1. In the upper stage, the upper right, the lower left, and the lower stage in order, The mapping of oxygen (O), carbon (C), iron (Fe), and silicon (Si) by an energy dispersive X-ray analyzer (EDX) of secondary particles is shown. In each figure of FIG. 3, the part extending from the center to the left is the site where the secondary particles are present, and the lower right part is the site where the secondary particles are not present. As shown in FIG. 3, O, C, Fe, and Si were uniformly dispersed in the site where the secondary particles were present. From this, it was found that the secondary particles contain O, C, Fe, and Si as constituent elements. C was also present outside the secondary particles.

The photograph located on the upper left side of FIG. 4 is a transmission electron microscope (TEM) photograph of the secondary particles of Sample 1. From this photograph, it can be seen that the inside of the secondary particles is an aggregate of a plurality of primary particles. The photograph located on the lower left side of FIG. 4 is a photograph obtained by photographing electron diffraction on the circular black box portion of the secondary particles in the upper left TEM photograph. From the figure, since the diffraction line has a halo pattern, it can be seen that the secondary particles are composed of a large number of particles and the size of each particle is small. When the result of this electron beam diffraction was analyzed, the structure of Li ₂ FeSiO ₄ was confirmed, and it was found that the secondary particles contained Li ₂ FeSiO ₄ .

In the central part of FIG. 4, element mapping using electron energy loss spectroscopy (EELS) is shown, and mapping of various elements in the horizontally-enclosed square white box attached to the photograph on the left side of FIG. 4 is shown. FIG. 5 is a mapping of carbon (C), oxygen (O), silicon (Si), and iron (Fe) in order from the upper side to the lower side of the central portion of FIG. From the figure, all of C, O, Si, and Fe were uniformly dispersed in the portion where the secondary particles were present. About C, it existed also in the part (the upper right part of each photograph) in which secondary particles do not exist. This result was similar to the element mapping by EDX in FIG.

The right side of FIG. 4 shows a mixed image in which the mapping of each element shown in the central part of FIG. 4 is overlaid. In the figure, the dark color portion indicates carbon (C), and the light color portion indicates Fe, Si, and O. From the electron diffraction results shown in the lower left side of FIG. 4, since it was found that the secondary particles contain Li ₂ FeSiO ₄ , Fe, Si, and O in the light-colored portion are elements constituting Li ₂ FeSiO ₄ It is. From this figure, it was found that in the secondary particles, Li ₂ FeSiO ₄ was uniformly dispersed and compounded in carbon to form an active material complex. When the mixed image diagram on the right side of FIG. 4 is compared with the TEM on the upper left side, the light color portion where Li ₂ FeSiO ₄ exists in the mixed image corresponds to the white or light gray portion of the TEM, and C in the mixed image. The existing dark color portion corresponds to the dark gray or black portion of the TEM.

When the analysis by the EELS method of FIG. 4 was performed not only in the vicinity of the surface of the active material complex (secondary particles) but also in the interior, the abundance ratio of CO in the surface layer of about 1 μm in thickness was It was found to be higher than the abundance ratio of C—O. The reason for this is that Li ₂ FeSiO ₄ and carbon are refined and mixed by applying high energy by high-speed rotation, and then they are granulated and bonded together to form an active material composite. After that, it is considered that further refined carbon entered the surface of the active material composite. The reason why the surface layer is rich in oxygen is considered to be due to milling treatment in an air atmosphere.

FIG. 5 is a photograph of the appearance of the active material composite taken with a scanning electron microscope (SEM). From the figure, many fine particles having an average particle diameter of about 100 nm were attached to the surface of the active material composite.

From the results of FIGS. 1 to 5, it can be considered that the structure of the active material complex is as shown in FIG. 6. As shown in FIG. 6, the active material composite 10 includes a core part 1 and a surface layer 2 covering the surface of the core part 1, and the core part 1 has an average particle size of 10 to 10 composed of Li ₂ FeSiO _4. 30 nm active material particles 11 are uniformly dispersed in a matrix 12 made of carbon. The surface layer 2 has a thickness of about 1 μm and constitutes a C—O rich layer.

For sample 2, as shown in FIG. 7, the active material particles and the conductive particles were gradually aggregated to form aggregates, but a hollow portion remained in the aggregates. There were various sizes. For this reason, it cannot be said that the active material particles and the conductive particles are bonded to each other in a finely dispersed state. As a result of measuring the specific surface area using the BET method, the specific surface area of the aggregate was 130.7 m ² / g.

In sample 3, as shown in FIGS. 8 to 10, active material particles (gray portion) and conductive particles (black portion) were mixed in a larger size than sample 1. The average particle diameter of the active material particles was 500 nm, and the average particle diameter of the conductive particles was 300 nm. The active material particles and the conductive particles are gradually aggregated to form aggregates. The average particle diameter of the aggregates is about 1000 nm, which is smaller than the secondary particles of the sample 1, and has a hollow portion inside. was there. As shown in FIG. 9, in the secondary particles, the sizes of the active material particles and the conductive particles varied, and the active material particles and the conductive particles were dispersed unevenly. As a result of measuring the specific surface area using the BET method, this composite showed 106 m ² / g.

Sample 4 was not posted with SEM photographs, but was observed with SEM. In sample 4, the active material particles and the conductive particles were mixed by being smaller than the particle size before mixing. The active material particles and the conductive particles were mixed as they were primary particles, and secondary particles were not formed. As a result of measuring the specific surface area using the BET method, the specific surface area of this mixture was 59.3 m ² / g.

In sample 5, as shown in FIG. 11, active material particles having an average particle diameter of 1000 nm (particulate white portions) and conductive particles having an average particle diameter of 100 nm (fluffy light gray portions) were mixed. . Each particle had the same shape and size before mixing and was not agglomerated.

<Charge / Discharge Characteristics> As shown below, a battery was prepared using the materials of Samples 1 to 5 as the positive electrode active material, and a charge / discharge test was performed.

The positive electrode active materials of samples 1 to 5, acetylene black (AB), and polytetrafluoroethylene (PTFE) were mixed at a mass ratio of positive electrode active material: AB: PTFE = 17: 5: 1 to obtain a mixture. After the mixture was kneaded, it was made into a sheet shape, pressed onto an aluminum current collector to produce an electrode, and 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 2400, manufactured by Celgard) as a separator, and lithium as a negative electrode. A coin battery using metal foil was prototyped.

<Charge / Discharge Test> The 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 initial charge was 4.8 V and constant voltage charge for 10 hours). The charge / discharge curves of the batteries prepared using the positive electrode active materials of Samples 1, 2, 3, and 4 are shown in FIGS. 12, 13, 14, and 15. The discharge capacity at the second cycle is shown in Table 1.

As shown in FIGS. 12 to 15 and Table 1, the battery using the sample 1 had a significantly larger discharge capacity at the second cycle than the battery using the samples 2 to 4. The discharge capacity of the sample 1 battery is 1.2 times the discharge capacity of the sample 2 battery, 1.6 times the discharge capacity of the sample 3 battery, and 2 times the discharge capacity of the sample 4 battery. .2 times. From this, it was found that the charge / discharge capacity was improved by increasing the milling speed, and in particular, the charge / discharge capacity was significantly improved by setting the milling speed to 800 rpm as in Sample 1.

<Cycle Characteristics> A cycle test of a battery manufactured using Sample 1 was performed. The cycle test conditions were the same as in the charge / discharge test, with a voltage of 1.5 to 4.5 V at 30 ° C. and 0.05 mA / cm ² (only the initial charge was 4.8 V and 10 hours constant voltage charge) The discharge capacity up to 1 time was measured. The measurement results are shown in FIG.

As shown in FIG. 16, the battery of Sample 1 is 42
No significant reduction in discharge capacity was observed until the cycle. From this, it was found that the battery of Sample 1 was excellent in cycle characteristics.

<Rate Characteristic> A rate characteristic test of the coin battery manufactured using Sample 1 was performed. The test conditions were as follows: the discharge rate was 0.1C at the 1st to 5th cycles, 0.2C at the 6th to 10th cycles, 0.5C at the 11th to 15th cycles, 1C at the 16th to 20th cycles, 21st to 25th cycles 2C for the eyes, 5C for the 26th to 30th cycles, and 0.1C for the 31st to 55th cycles, and the rate during charging was constant at 0.1C. The test was conducted at 30 ° C. The test results are shown in FIG.

As shown in FIG. 17, the discharge capacity at 1C was 200 mAh / g, the discharge capacity at 5C was 170 mAh / g, and excellent rate characteristics were exhibited.

<Reaction Resistance> The reaction resistance of the materials of Samples 1 and 3 was measured. The test of the reaction resistance was performed on each battery after charging and discharging using a measuring device (trade name: SI 1280B, manufactured by Solartron) using an AC impedance method. The amplitude of the alternating current at the time of measurement was set to 10 mV, the maximum value of the frequency was 20 kHz, and the minimum value was 0.1 Hz. The charging condition was a constant voltage charging at 4.8V for 10 hours, and the discharging condition was a constant current discharging at 1.5V.

The measurement results are shown in FIGS. FIG. 18 shows the reaction resistance of each material after charging, and FIG. 19 shows the reaction resistance of each material after discharging. 18 and 19, the horizontal axis indicates the real axis of the impedance resistance, and the vertical axis indicates the imaginary axis of the impedance resistance. In the line portions shown in FIGS. 18 and 19, the width between both ends of the arc-shaped portion indicates the reaction resistance inside the particle and at the particle interface included in each material, and the resistance having a larger real part than the arc-shaped portion. The part shows the diffusion resistance outside the particle.

As shown in FIGS. 18 and 19, the reaction resistance of the material of Sample 1 was about one-fourth that of Sample 3. This is a factor that the initial discharge capacity of the battery manufactured using the material of Sample 1 as the positive electrode active material is larger than that of Sample 3.

When the results of the reaction resistance of each material of Samples 1 and 3 shown in FIGS. 18 and 19 are compared with the particle morphology observed in the photographs of FIGS. 1 to 11, the following is estimated. The reaction resistance (impedance) of each material indicates the resistance inside the particle contained in each material and at the particle interface. In general, the impedance decreases as the particle size of the active material particles decreases, and the reaction resistance tends to decrease as the contact area with the conductive particles at the active material particle interface increases. In Sample 1, the active material particles are as fine as an average particle size of 100 nm or less, and the conductive particles are also as fine as an average particle size of 100 nm or less, and these particles are uniformly dispersed. Further, in the portion where the active material composite is formed, the active material particles and the conductive particles are in close contact with each other, and the contact area is large. For this reason, the reaction resistance of the sample 1 becomes small, and it is estimated that the battery produced using this as a positive electrode active material has a large discharge capacity.

<Manufacture of Active Material Complex (2)> The active material complexes of Samples 6 to 8 were manufactured by the following method. The active material composites of Samples 6 to 8 are composed of Li ₂ MnSiO ₄ and carbon.

Lithium silicate compound Li ₂ SiO ₃ (lithium silicate, manufactured by Kishida Chemical Co., Ltd., purity 99.5%) 0.03 mol and manganese oxalate (Kishida Chemical Co., Ltd., purity 99.9%) 0.03 mol 20 ml of acetone was added to the mixture and mixed with a zirconia ball mill at 500 rpm for 60 minutes and dried. This was mixed with the carbonate mixture. The carbonate mixture consists of lithium carbonate (Kishida Chemical Co., Ltd., purity 99.9%), sodium carbonate (Kishida Chemical Co., Ltd., purity 99.5%), and potassium carbonate (Kishida Chemical Co., Ltd., purity 99.5%). ) In a molar ratio of 0.435 mol: 0.315 mol: 0.25 mol. The mixing ratio was 80 parts by mass of the carbonate mixture with respect to 100 parts by mass of the total amount of lithium silicate and manganese oxalate. 20 ml of acetone was added to the above mixture, mixed at 500 rpm for 60 minutes in a zirconia ball mill, and dried.

Thereafter, the obtained powder was heated in a gold crucible and heated to 500 ° C. in an electric furnace in a mixed gas atmosphere of carbon dioxide (flow rate: 100 mL / min) and hydrogen (flow rate: 3 mL / min). The mixture was 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 as a reaction system was taken out from the electric furnace and rapidly cooled to room temperature through a mixed gas.

Next, 20 mL of water was added to the obtained reaction product and ground in a mortar, and washing and filtration were repeated using water to obtain a powder from which salt had been removed. This powder was put into a dryer at 100 ° C. and dried for about 1 hour to obtain a lithium manganese silicate compound.

Then, as a result of confirming the crystal structure by powder X-ray diffraction (XRD), it was found that Li ₂ MnSiO ₄ belonging to orthorhombic crystal and space group Pmn2 ₁ was obtained. FIG. 20 is an SEM photograph of active material particles made of Li ₂ MnSiO ₄ . As shown in FIG. 20, the active material particles immediately after the synthesis are formed into flakes and distributed in a particle size of 0.5 to 3 μm. The average particle size was 0.7 μm. As a result of measuring the specific surface area using the BET method, the specific surface area was 12.5 m ² / g.

The obtained active material particles and acetylene black (AB, average particle size 0.3 μm) were mixed at a mass ratio of 5: 4. The mixture is mechanically milled under the following predetermined conditions in an air atmosphere using a mechanical milling device (French Japan Co., Ltd., planetary ball mill P-7). Energized. This step was performed by putting 50 g of φ4 mm zirconia balls and 300 mg of the mixture in a ball mill grinding container made of zirconia and having a volume of 45 cc.

When the powder and AB were mixed, the material obtained when the rotation speed of the ball mill was 800 rpm and the rotation time was 10 hours was designated as Sample 6. The material obtained when the rotation speed of the ball mill was 800 rpm and the rotation time was 5 hours was designated as Sample 7. The material obtained when the rotation speed of the ball mill was 450 rpm and the rotation time was 5 hours was designated as Sample 8. Each sample was heat-treated. The heat treatment conditions were 700 ° C., 2 hours, and CO ₂ : H ₂ = 100: 3 cm ³ atmosphere.

FIG. 21 is a SEM (Scanning Electron Microscope) photograph of Sample 6. As shown in FIG. 21, comparatively large large particles having a major axis of about 10 μm and fine particles having a particle size of about 0.5 to 5 μm were mixed. Inside these particles, many fine particles were uniformly dispersed. Large particles are secondary particles obtained by compositing fine primary particles. The large particles were Li ₂ MnSiO ₄ / C composites in which Li ₂ MnSiO ₄ having a particle diameter of 10 to 50 nm and carbon having a particle diameter of 10 to 50 nm were joined together to form a composite. As a result of measuring the specific surface area using the BET method, this composite showed a high value of 170.2 m ² / g.

When the SEM photograph of sample 6 shown in FIG. 21 is compared with the SEM photograph of sample 1 shown in FIG. 2, the Li ₂ MnSiO ₄ / C composite of sample 6 is similar to the Li ₂ FeSiO ₄ / C composite of sample 1. It was found to have the organization.

From the mapping of oxygen (O), carbon (C), iron manganese (Mn), and silicon (Si) by the energy dispersive X-ray analyzer (EDX) of the secondary particles of sample 6, O, C, Mn, and Si are , And were uniformly dispersed in the site where the secondary particles were present. From this, it was found that the secondary particles contain O, C, Mn, and Si as constituent elements. C was also present outside the secondary particles.

From the transmission electron microscope (TEM) photograph of the secondary particles of Sample 6, it can be seen that the inside of the secondary particles is an aggregate of a plurality of primary particles. When the result of this electron beam diffraction was analyzed, the structure of Li ₂ MnSiO ₄ was confirmed, and it was found that the secondary particles contained Li ₂ MnSiO ₄ .

Although the SEM photograph is not shown for sample 7, the active material particles and the conductive particles were gradually aggregated to form aggregates, but the hollow portions remained in the aggregates. The size of was varied. For this reason, it cannot be said that the active material particles and the conductive particles are bonded to each other in a finely dispersed state. In the secondary particles, the sizes of the active material particles and the conductive particles varied, and the active material particles and the conductive particles were dispersed unevenly. As a result of measuring the specific surface area using the BET method, this complex showed 115 m ² / g.

In Sample 8, as shown in FIG. 22, the active material particles and the conductive particles were mixed in a size larger than that of Sample 6. The active material particles and the conductive particles are gradually aggregated to form aggregates. The average particle diameter of the aggregates is about 1000 nm, which is smaller than the secondary particles of the sample 6, and has a hollow portion inside. was there. In the secondary particles, the sizes of the active material particles and the conductive particles varied, and the active material particles and the conductive particles were dispersed unevenly. Further, as a result of measuring the specific surface area using the BET method, this complex showed 101 m ² / g.

FIG. 23 shows XRD patterns of Li ₂ MnSiO ₄ immediately after synthesis and samples 6 to 8. As shown in FIG. 23, the intensity of the diffraction peak is lower in Sample 6 than in Samples 7 and 8. This is presumed to be due to a decrease in crystallinity and finer particles.

On the other hand, Sample 7 was a Li ₂ MnSiO ₄ / C composite in which Li ₂ MnSiO ₄ having a particle size of 400 nm and carbon having a particle size of 240 nm were bonded together to form a composite. The specific surface area of Sample 7 was 115 m ² / g.

Sample 8 was a Li ₂ MnSiO ₄ / C composite in which Li ₂ MnSiO ₄ having a particle diameter of 500 nm and carbon having a particle diameter of 300 nm were bonded to each other to form a composite. The specific surface area of Sample 7 was 101 m ² / g.

<Charge / Discharge Characteristics> As shown below, half-cells were prepared using the materials of Samples 6 to 8 as the positive electrode active material, and a charge / discharge test was performed.

The electrode configuration is as follows. Each positive electrode active material (Li ₂ MnSiO ₄ / C composite), acetylene black (AB), and polytetrafluoroethylene (PTFE) of Samples 6 to 8 were mixed in a mass of positive electrode active material: AB: PTFE = 17: 5: 1. The mixture was mixed at a ratio. After the mixture was kneaded, it was made into a sheet and pressed onto an aluminum current collector to produce an electrode. Then, what was vacuum-dried at 140 degreeC for 3 hours was used as a positive electrode.

A solution obtained by dissolving LiPF ₆ in ethylene carbonate (EC): dimethyl carbonate (DMC) = 3: 7 to 1 mol / L was used as an electrolytic solution. A polypropylene membrane (Celgard 2400, manufactured by Celgard) and a glass filter were used as the separator. Lithium metal foil was used as the negative electrode. From these, a coin-type half battery was produced.

<Charge / Discharge Test> This 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 4.5 V for 10 hours). The charge / discharge curves of the batteries prepared using the positive electrode active materials of Samples 6, 7, and 8 are shown in FIG. 24, FIG. 25, and FIG. Table 2 shows the initial charge capacity, initial discharge capacity, initial efficiency, and initial discharge average voltage of each battery. The initial efficiency is a percentage of the initial discharge capacity with respect to the initial charge capacity.

As shown in FIGS. 24 to 26 and Table 2, the battery using the sample 6 has an initial charge capacity, an initial discharge capacity, an initial efficiency, and an initial discharge average voltage, as compared with the battery using the samples 7 and 8. High value was shown. The initial discharge capacity of the sample 6 battery was 2.6 times the initial discharge capacity of the sample 7 battery and 2.7 times the discharge capacity of the sample 8 battery. The initial efficiency of the sample 6 battery was 1.2 times the initial efficiency of the sample 7 battery and 1.4 times the initial efficiency of the sample 8 battery. The initial discharge average voltage of the sample 6 battery was 0.1 V higher than the initial discharge average voltage of the sample 7 battery, and 0.2 V higher than the initial discharge average voltage of the sample 8 battery. From this, it was found that the charge / discharge capacity, the initial efficiency, and the average discharge voltage are improved by increasing the milling speed and milling time.

This factor is estimated to be the same as in the case of the sample 1 of Example 1. That is, in the sample 6, the active material particles are as fine as an average particle size of 100 nm or less, and the conductive particles are as fine as an average particle size of 100 nm or less, and these particles are uniformly dispersed. Further, in the portion where the active material composite is formed, the active material particles and the conductive particles are in close contact with each other, and the contact area is large. For this reason, the reaction resistance of the sample 6 becomes small, and it is estimated that the battery produced using this as a positive electrode active material has a large discharge capacity. Further, since the nanoparticles as described above are uniformly dispersed, a lithium ion conductive path is well formed, so that lithium ions released from the active material at the time of charging easily return at the time of discharging. For this reason, it is estimated that the initial efficiency of the sample 6 has improved. Furthermore, it is presumed that due to the reduced reaction resistance, the charge / discharge curve inherent to the active material was obtained, leading to an improvement in the discharge average voltage.

1: Core part, 10: Active material composite, 11: Active material particles, 12: Matrix, 2: Surface layer.

Claims (17)

Active material particles made of an active material and having an average particle diameter of 100 nm or less and conductive particles made of a conductive material and having an average particle diameter of 100 nm or less are bonded to each other, and the specific surface area is 150 m ² / g or more. An active material complex characterized by the above. The active material composite according to claim 1, which is a secondary particle having an average particle diameter of 0.7 μm or more and 20 μm or less. The core part and the surface layer which coat | covers a core part, Content of the said electroconductive particle contained in the said surface layer is larger than content of the said electroconductive particle contained in the said core part. 2. The active material complex according to 2. The active material composite according to any one of claims 1 to 3, wherein surface particles are attached to a surface of the active material composite. The active material composite according to any one of claims 1 to 4, wherein the active material is made of a material capable of inserting and extracting lithium ions. The active material composite according to claim 5, wherein the active material is made of at least one member selected from the group consisting of a lithium silicate compound, a lithium phosphate compound, and a lithium borate compound. The lithium silicate-based compound has a composition formula Li ₂ M ¹ SiO ₄ (M ¹ is Fe, Mn, Co) or a composition formula Li _{2 + ab Ab} M _1-x M ′ _x SiO _{4 + δ} (where A 1 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, Mn, and Co, and M ′ is Mg, Ca, Al , Ni, Nb, Ti, Cr, Cu, Zn, Zr, V, Mo and W. Each of the subscripts is as follows: 0 ≦ a <1, 0 The active material composite according to claim 6, comprising a compound represented by ≦ b <0.2, 0 ≦ x ≦ 0.5, δ ≧ 0). The active material composite according to claim 6 or 7, wherein the lithium silicate-based compound comprises at least one selected from the group of lithium iron silicate and lithium manganese silicate. The active material composite according to claim 1, wherein the conductive material is made of a carbon material. The active material composite according to claim 9, wherein the carbon material is at least one selected from the group consisting of acetylene black (AB), ketjen black (KB), and graphite. A method for producing an active material composite according to any one of claims 1 to 10, comprising an energy application step for applying mechanical energy to the active material and the conductive material. A method for producing a substance complex. The method for producing an active material composite according to claim 11, wherein the energy applying step is a step of applying mechanical energy by milling. The method for producing an active material composite according to claim 12, wherein an average particle size of the active material used in the energy application step is 200 nm to 5 µm, and an average particle size of the conductive material is 100 nm to 5 µm. . The active material composite according to any one of claims 11 to 13, further comprising a heat treatment step of performing a heat treatment on the active material material to which mechanical energy is applied and the conductive material after the energy application step. Production method. It consists of the active material composite_body | complex of any one of Claims 1-10, or the active material composite manufactured by the manufacturing method of any one of Claims 11-14. Positive electrode active material for water electrolyte secondary battery. 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 15. A nonaqueous electrolyte secondary battery comprising the positive electrode for a nonaqueous electrolyte secondary battery according to claim 16 as a constituent element.

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