Secondary battery

Abstract

To improve characteristics such as charge / discharge speed or charge / discharge capacity in a power storage device.SOLUTION: By making a particle diameter of positive electrode active material particles nano-sized, a surface area of an active material per unit mass is increased. Particularly, the particle diameter is 10nm or more and 100nm or less, preferably 20 nm or more and 60 nm or less. Alternatively, a surface area per unit mass is 10 m2 / g or more, preferably 20 m2 / g or more. A XRD half-width is specified as 0.12 degree or more and less than 0.17, preferably 0.13 degrees or more and less than 0.16 degrees, whereby crystallinity of the active material is improved.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The technical field relates to a power storage device and a manufacturing method thereof. [Background technology]

[0002] As interest in environmental issues grows, the secondary batteries and electric power sources used in hybrid vehicles are becoming increasingly The development of energy storage devices such as double layer capacitors is thriving. High-performance lithium-ion batteries and lithium-ion capacitors are attracting attention. Batteries are small but can store a large amount of electricity, so they are already used in mobile phones and laptops. They are installed in portable information terminals such as computers, and play a role in making products smaller.

[0003] Secondary batteries and electric double layer capacitors have a structure in which an electrolyte is interposed between a positive electrode and a negative electrode. The positive electrode and the negative electrode each have a current collector and an active material provided on the current collector. For example, a lithium-ion battery has a structure in which lithium ions are inserted and extracted. The electrode is constructed by using a material that can be used as an active material and interposing an electrolyte therebetween.

[0004] Lithium oxides and the like are known as active materials for the positive electrodes of lithium ion batteries (particularly (See Patent Document 1 and Patent Document 2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-257894 [Patent Document 2] International Publication No. 2006 / 049001 Summary of the Invention [Problem to be solved by the invention]

[0006] The lithium oxide disclosed in Patent Document 1 is capable of inserting and extracting lithium ions. This makes it difficult for the crystal structure to change due to the insertion and desorption of lithium ions, making it suitable for use as a positive electrode. However, lithium oxide has low conductivity and its properties are unclear. The current situation is that no improvement has been achieved.

[0007] In view of the above problems, an object of one embodiment of the present invention is to improve the characteristics of a power storage device. do. [Means for solving the problem]

[0008] In the disclosed invention, the particle size of the active material in the positive electrode of the power storage device is reduced to nano-size. This increases the diffusion paths for reactants (such as lithium ions).

[0009] Alternatively, by making the surface area per unit mass of the active material as large as possible, the reactants (e.g. The surface area per unit mass of the active material is The aggregation of small particles increases the surface roughness of the active material, and the size becomes larger.

[0010] In addition, in the disclosed invention, lithium oxide is used as an active material for a positive electrode of a power storage device.

[0011] The lithium oxide has the general formula Li (2-x) It is expressed as MSiO4 and is as follows: Use materials that satisfy (I) and (II). (I) x is a value that changes with the insertion and desorption of lithium ions during charging and discharging, and 0≦x≦2. satisfy. (II) M is iron (Fe), nickel (Ni), manganese (Mn), or cobalt ( Co).

[0012] The above general formula Li (2-x) The material represented by MSiO4 is composed of lithium atoms and other The ratio of metal atoms (M atoms) is a maximum of 2:1 (molar ratio). It is possible to insert and extract up to two lithium ions (reactants) at the same time. By using this material as the active material for the positive electrode, it is possible to increase the capacity and improve the characteristics of the energy storage device. It can be raised.

[0013] In addition, the disclosed invention uses an active material supported by a carbon material (also called a carbon coating). Used in the positive electrode. The high conductivity of carbon materials reduces the internal resistance of the energy storage device. do.

[0014] In one aspect of the present invention, the particle size is 10 nm or more and 100 nm or less, and the surface area is 10 m 2 / g or more, and the XRD half width is 0.12 degrees or more and less than 0.17 degrees. It is an active material.

[0015] Another aspect of the present invention is a method for manufacturing a 10 m2 granular sieve having a surface area of ​​10 m2. 2 / g or more, and XRD half width The positive electrode active material for an electricity storage device has a viscosity of 0.12 degrees or more and less than 0.17 degrees.

[0016] In another aspect of the present invention, the particle size is 10 nm or more and 100 nm or less, and XR The positive electrode active material for a power storage device has a D half width of 0.12 degrees or more and less than 0.17 degrees.

[0017] Another embodiment of the present invention is a positive electrode for a power storage device having a particle size of 10 nm to 100 nm. It is an active material.

[0018] Another aspect of the present invention is a method for manufacturing a 10 m2 granular sieve having a surface area of ​​10 m2. 2 / g or more of the positive electrode active material for an electricity storage device is.

[0019] Another aspect of the present invention is a battery comprising a positive electrode, a negative electrode, and a capacitor provided between the positive electrode and the negative electrode. and an electrolyte, wherein the active material provided in the positive electrode has a particle size of 10 nm or more and 100 nm or less. and the surface area is 10 m 2 / g or more, and the XRD half width is 0.12 degrees or more It is a storage device that is less than 0.17 degrees above sea level.

[0020] In addition, the active material is Li (2-x) It is represented by MSiO4, and the following (I) and (II) It is preferable that the following is satisfied. (I) x is a value that changes with the insertion and desorption of lithium ions during charging and discharging, and 0≦x≦2. satisfy. (II) M is one or more of iron, nickel, manganese, and cobalt. It is a transition metal element.

[0021] The active material satisfies at least one of the following (III) to (VI): It is preferable to do so. (III) It has a crystal structure belonging to the space group P1211. (IV) It has a crystal structure belonging to the space group Pmn21. (V) It has a crystal structure belonging to the space group P121 / n1. (VI) It has a crystal structure belonging to the space group Pbn21.

[0022] In addition, the active material is Li (2-x) Fe s Ni u SiO4, and the following (I) and It is preferable that the conditions (VIII) and (VIII) are satisfied. (I) x is a value that changes due to the insertion and desorption of lithium ions during charging and discharging. However, 0≦ x≦2. (VIII) s+u=1, 0≦s≦1, and 0≦u≦1.

[0023] In addition, the active material is Li (2-x) Fe s Mn t Ni u SiO4, and the following ( It is preferable that conditions I) and (IX) are satisfied. (I) x is a value that changes with the insertion and desorption of lithium ions during charging and discharging, and 0≦x≦2. satisfy. (IX) s+t+u=1, 0≦s≦1, 0≦t≦1, and 0≦u≦1.

[0024] The surface of the active material may be supported by a carbon material.

[0025] In another aspect of the present invention, raw materials for an active material are mixed to prepare a mixture, and the mixture is The mixture is subjected to a first grinding, the mixture is subjected to a first firing, and the mixture is subjected to a second grinding. By adding sugar to the mixture, a carbon material is supported on the surface of the mixture, and the mixture is a step of subjecting the product to a second firing at a temperature higher than that of the first firing to form a positive electrode; and forming a negative electrode facing the positive electrode via an electrolyte, wherein the particle size of the active material is 10n m or more and 100 nm or less, and the surface area is 10 m 2 / g or more, and XRD characteristics The manufacturing method of a power storage device in which the value range is 0.12 degrees or more and less than 0.17 degrees is provided.

[0026] Another embodiment of the present invention is an electric propulsion vehicle equipped with the above-described power storage device. [Effects of the Invention]

[0027] By making the positive electrode active material into fine particles, it is possible to increase the diffusion paths of the reactants. Therefore, the diffusion rate of the reactants can be increased, and the charge / discharge rate of the electricity storage device can be increased. That is, the characteristics of the power storage device can be improved.

[0028] In addition, the above general formula Li (2-x) The material represented by MSiO4 is composed of lithium atoms and The ratio of metal atoms (M atoms) other than the hydroxyl group is 2:1 (molar ratio) at most. Up to two lithium ions (reactants) can be inserted and removed per By using such a material as the active material for the positive electrode, it is possible to increase the capacity, and the characteristics of the power storage device can be improved. It can improve the performance.

[0029] By supporting a highly conductive carbon material on the surface of the active material, the internal resistance of the energy storage device is reduced. Therefore, the voltage obtained is higher and the discharge capacity can be increased. That is, the characteristics of the power storage device can be improved.

[0030] Furthermore, fine particles, general formula Li (2-x) Application of materials represented by MSiO4, carbon materials By combining multiple methods of support, the characteristics of the electricity storage device can be significantly improved. Cut. [Brief explanation of the drawings]

[0031] [Figure 1] FIG. 10 shows an example of an active material. [Figure 2] FIG. 10 is a graph showing an example of characteristics of a power storage device. [Figure 3] FIG. 10 is a graph showing an example of characteristics of a power storage device. [Figure 4] FIG. 10 is a graph showing an example of characteristics of a power storage device. [Figure 5] FIG. 10 is a diagram showing an example of the effect of carbon coating. [Figure 6] FIG. 10 is a graph showing an example of characteristics of a power storage device. [Figure 7] FIG. 10 shows an example of an active material. [Figure 8] FIG. 10 is a graph showing an example of characteristics of a power storage device. [Figure 9] FIG. 10 is a graph showing an example of characteristics of a power storage device. [Figure 10] A diagram showing an example of the crystal structure of the space group to which Li(2-x)MSiO4 belongs (P1211). [Figure 11] A diagram showing an example of the crystal structure of the space group to which Li(2-x)MSiO4 belongs (Pmn21). [Figure 12] A diagram showing an example of the crystal structure of the space group to which Li(2-x)MSiO4 belongs (P121 / n1). [Figure 13] A diagram showing an example of the crystal structure of the space group to which Li(2-x)MSiO4 belongs (Pbn21). [Figure 14] FIG. 1 illustrates an example of a structure of a power storage device. [Figure 15] 3A to 3C illustrate an example of a method for manufacturing a negative electrode. [Figure 16] 3A to 3C illustrate an example of a method for manufacturing a negative electrode. [Figure 17] FIG. 2 is a diagram illustrating an example of an active material layer of a negative electrode. [Figure 18] 3A to 3C illustrate an example of a method for manufacturing a negative electrode. [Figure 19] 3A to 3C illustrate an example of a method for manufacturing a negative electrode. [Figure 20] 1A to 1C are diagrams illustrating examples of electronic devices. [Figure 21] FIG. 1 is a diagram showing an example of an electric propulsion vehicle. [Figure 22] FIG. 1 shows the results of X-ray diffraction measurements. DETAILED DESCRIPTION OF THE INVENTION

[0032] The following describes the embodiments in detail with reference to the drawings. The present invention can be implemented in many different ways without departing from the spirit and scope thereof. It will be readily understood by those skilled in the art that various modifications can be made to the modes and details. Therefore, the present invention should not be construed as being limited to the description of the following embodiments. In all drawings for explaining the form, the same parts or parts having similar functions are denoted by the same reference numerals. The following numbers are used and their repeated explanations will be omitted.

[0033] (Embodiment 1) In this embodiment, a positive electrode active material for a power storage device will be described.

[0034] First, the energy storage device is made of a material that can insert and remove reactive substances (such as lithium ions). By using the material as an active material, charging and discharging can be performed.

[0035] The first requirement for an excellent power storage device is that it must be able to charge and discharge at a high rate. do.

[0036] In one aspect of the present invention, the particle size of the positive electrode active material is narrowed to increase the charge / discharge rate. Alternatively, the surface area per unit mass of the positive electrode active material is increased. It is something.

[0037] FIG. 1 shows an example of an active material 101 per unit mass and particles 103 in the active material 101. FIG. 1(A) shows the case where the particle diameter of the particle 103 is large, and FIG. 1(B) shows the case where the particle diameter of the particle 103 is small. This shows the case where

[0038] In FIG. 1(B), the particle diameter of the particles 103 is smaller than that in FIG. 1(A), and the active material per unit mass is The number of particles 103 in the substance 101 is large. By increasing the number of particles 103, the living matter The diffusion paths of reactants (such as lithium ions) in the matrix are increased. This increases the speed at which the electricity storage device is charged and discharged, thereby increasing the speed at which the electricity storage device is charged and discharged. The diameter is 10 nm or more and 100 nm or less, preferably 20 nm or more and 60 nm or less.

[0039] In addition, in FIG. 1B, the active material 101 has more irregularities than in FIG. 1A, and the active material 101 has more irregularities per unit mass. The surface area of ​​the active material 101 is large. By increasing the surface area, the reaction in the active material The diffusion path of the substance increases, so the diffusion rate of the reactant can be increased, and the accumulation In particular, the surface area per unit mass is 10 m 2 / g or more, preferably 20m 2 / g or more. This increases the surface area of ​​the active material 101 per unit mass.

[0040] The particle size indicates the length of the particle 103 in the major axis direction, and is the active material per unit mass. The surface area is measured by the BET method. It is important to note that reducing the particle size of the active material or the amount of the active material per unit mass is Increasing the surface area of ​​a particle is also called microparticulation.

[0041] Figure 2 shows the active material per unit mass when lithium oxide is used as the positive electrode active material. The horizontal axis shows the relationship between the surface area of ​​the active material and the rate characteristics. m 2 / g), and the vertical axis represents the rate characteristics.

[0042] Here, we will explain the rate characteristics on the vertical axis. 1C means one discharge per hour. nC means that n discharges are made in one hour, in other words, 1 In other words, in Figure 2, the vertical axis shows the 10C / 2C capacity. The larger the value, the faster the charge / discharge rate can be. 2C capacity is the ratio of the discharge capacity when the discharge rate is 2C to the discharge capacity when the discharge rate is 10C. The vertical axis indicates the percentage of discharge capacity.

[0043] As shown in Figure 2, increasing the surface area can improve the rate characteristics. The rate characteristic then changes linearly. This is because the surface area increases and the lithium This is because the diffusion paths of ions increase. 2 / g or more The rate characteristic can be increased to 80% or more. 2 / g or more By doing so, the rate characteristic can be increased to 85% or more. At least 10m 2 / g or more 40m 2 / g or less, typically 24m 2 / g or more27. 5m 2 / g or less, the rate characteristics are good. If it is above this, it can be said to be good.

[0044] Alternatively, since the larger the surface area, the smaller the particle size, the smaller the particle size. The particle size is 10 nm or more and 100 nm or less (preferably It is preferable that the thickness is 20 nm or more and 60 nm or less.

[0045] As described above, by microparticulating the active material, it is possible to increase the diffusion paths of the reactants. This makes it possible to obtain a power storage device with a high charge / discharge rate.

[0046] A second requirement for an excellent electricity storage device is that it has a large discharge capacity.

[0047] One aspect of the present invention is to increase the crystallinity of the active material (high This is also called crystallization.

[0048] FIG. 3 shows the relationship between the crystallinity of the active material and the discharge capacity when lithium oxide is used as the positive electrode active material. The horizontal axis shows the XRD half-width (degrees) of the active material, and the vertical axis shows the discharge capacity (mAh The smaller the XRD half-width (half-width of the X-ray diffraction peak), the higher the crystallinity. This indicates that the angle is good. The unit "degree" indicates the angle (°).

[0049] As shown in Figure 3, the smaller the XRD half-width, the larger the discharge capacity. That is, the higher the crystallinity, the larger the discharge capacity. In particular, by setting the XRD half-width to less than 0.2°, the discharge capacity In Figure 3, the XRD half-width is at least 0.12° or more. If the angle is within the range of 0.2° or less, the discharge capacity will be large.

[0050] In this way, by increasing the crystallinity of the active material, it is possible to obtain a power storage device with a large discharge capacity. can be done.

[0051] Thirdly, the conditions for excellent battery characteristics are a fast charge / discharge rate and a long discharge capacity. One of the advantages is that it is possible to achieve both high quality and large quantities.

[0052] In one embodiment of the present invention, as a means for achieving both of these, the active material is made into fine particles and the crystallinity is improved. It is something that can be done.

[0053] Figure 4 shows the relationship between the crystallinity of the active material and the rate characteristics. The horizontal axis is the XRD half-width. The vertical axis represents the rate characteristics described above.

[0054] As shown in Figure 4, the rate characteristics can be improved by reducing the XRD half-width. However, the maximum value of the rate characteristic appears at the XRD half-width of 0.15°. That is, this means that there is a maximum value in the crystallinity with respect to the rate characteristics.

[0055] If the crystallinity is too low, carrier ions are trapped in the grain boundaries between the particles. This slows down the mobility of carrier ions, resulting in a decrease in rate characteristics. On the other hand, if the crystallinity is too high, it takes time for the carrier ions in one particle to come out. This results in a decrease in rate characteristics.

[0056] As shown in Figure 4, by setting the XRD half-width to 0.12° or more and less than 0.17°, the charge / discharge rate can be increased. It can achieve high speed (rate characteristics of 80% or more). Furthermore, it can achieve a rotation angle of 0.13° or more and less than 0.16°. This makes it possible to increase the charge / discharge rate (rate characteristics of 85% or more).

[0057] Therefore, from Figures 2 to 4, when the surface area of ​​the active material is 10 m 2 / g or more, and X By setting the RD half width to 0.12° or more and less than 0.17°, the charge / discharge speed is fast (rate characteristics Furthermore, it is possible to obtain a power storage device with a large discharge capacity. is 20m 2 / g or more and 0.13° or more and less than 0.16°, It is possible to obtain an electricity storage device with high speed (rate characteristics of 85% or more) and large discharge capacity.

[0058] In this way, by making the active material finer and increasing the crystallinity, the charge / discharge speed can be improved. The discharge capacity can be increased quickly.

[0059] As an example of the method for achieving the above-mentioned fine particle size or high crystallinity, (1) a method for mixing materials is as follows: (2) the method of baking the material, and (3) the carbon coating of the material. In the following, lithium iron phosphate with an olivine structure will be used as an example of the active material. The case of producing a lithium ion battery (LiFePO4) will be described.

[0060] The first method is to achieve fine particle size or high crystallinity by mixing the materials (raw materials). do.

[0061] First, as raw materials for lithium iron phosphate, lithium carbonate (Li2CO3), iron oxalate ( Mix FeC2O4 and ammonium dihydrogen phosphate (NH4H2PO4).

[0062] Lithium carbonate is a raw material for introducing lithium, and iron oxalate is a raw material for introducing iron. Ammonium dihydrogen phosphate is a raw material for introducing phosphate. The raw materials are not limited to these, as long as they can be introduced. This is carried out by ball milling (first ball milling).

[0063] The ball mill treatment may be carried out, for example, by adding a solvent and rotating the mixture at a speed of 50 rpm to 500 rpm. The rotation time is between 30 minutes and 5 hours, and the ball diameter is between φ1 mm and φ10 mm.

[0064] As a mixing method, the raw materials can be finely divided by ball milling. The lithium iron phosphate particles can be made finer after production. This allows the raw materials to be mixed uniformly, improving the crystallinity of the lithium iron phosphate particles after production. It is possible.

[0065] The second method is to achieve fine particle size or high crystallinity by the firing method of the material.

[0066] This method involves performing two stages of calcination on a mixture of raw materials to crystallize the mixture. For example, in the first method, the mixture after the first ball mill treatment is .

[0067] Specifically, the mixture is heated in a nitrogen atmosphere at 250°C to 450°C for 1 hour or more. The first firing is carried out for 20 hours or less.

[0068] After the first firing, the mixture is pulverized in a mortar or the like.

[0069] The pulverized mixture is then subjected to a ball mill treatment (second ball mill treatment). The ball mill treatment is carried out by adding a solvent, rotating at a speed of 50 rpm or more and 500 rpm or less, and for a rotation time of 100 rpm or more. The test should be carried out for 30 minutes or more and 5 hours or less, with a ball diameter of φ1mm or more and 10mm or less.

[0070] After the second ball mill treatment, the mixture is heated to 300°C or more and 700°C or less in a nitrogen atmosphere. The second firing is carried out for 1 hour to 20 hours. Therefore, it is preferable to increase the temperature.

[0071] After the second firing, the mixture is pulverized in a mortar or the like.

[0072] The pulverized mixture is then subjected to a ball mill treatment (third ball mill treatment). The ball mill treatment is carried out by adding a solvent, rotating at a speed of 50 rpm or more and 500 rpm or less, and for a rotation time of 100 rpm or more. The test should be carried out for 30 minutes or more and 5 hours or less, with a ball diameter of φ1mm or more and 10mm or less.

[0073] As described above, by performing two-stage firing, crystal nuclei are formed in the first firing. Therefore, the second firing can be performed in a short time. Therefore, crystal growth is suppressed and the grain size is reduced. In other words, by making the lithium iron phosphate particles finer, Furthermore, the formation of crystal nuclei makes it possible to increase the crystallinity even with short firing times. do.

[0074] It is also possible to perform the firing in one step instead of two steps. However, in order to suppress crystal growth, Therefore, it is necessary to perform firing at a low temperature for a long time, for example, for several days. Therefore, as in the second method, the first firing is performed at a low temperature, and the second firing is performed at a higher temperature than the first firing. It is preferable to carry out the second firing.

[0075] FIG. 5 shows the relationship between the second baking time and the surface of lithium iron phosphate when two-stage baking is performed. The relationship between the second baking time and the crystallinity of lithium iron phosphate is shown in Fig. 1. The horizontal axis is the firing time (hours), and the vertical axis is the unit mass on the left. Surface area per unit volume (m 2 / g), and the right side is the XRD half-width indicating crystallinity. The three conditions were 3 hours, 5 hours, and 10 hours, and the conditions other than the firing time were the same.

[0076] As shown in Figure 5, by performing two-stage firing and shortening the second firing time, the surface area can be increased. In addition, high crystallinity can be obtained even if the firing time is shortened (solid line 501). This can be done (dashed line 503).

[0077] Before the first or second firing, the material may be subjected to a pressure treatment. The material can be made into pellets by molding it into pellets. Density By improving the solubility, the number of lithium iron phosphate particles per unit mass after production increases. In other words, the particles can be made into fine particles. By carrying out a pressure treatment before firing, the effect of microparticulation can be enhanced.

[0078] The third method is to support a carbon material on the surface of the material (also called carbon coating), It is made into fine particles.

[0079] This method involves crushing a mixture of raw materials and then supporting a carbon material on the surface of the crushed material. For example, in the second method, the mixture pulverized after the first firing is subjected to carbonization. Add a material that generates carbon.

[0080] Specifically, the pulverized mixture is added with a substance capable of generating conductive carbon by thermal decomposition (hereinafter referred to as " The conductive carbon precursor is, for example, a glucose sol. Addition of a conductive carbon precursor increases the surface area of ​​the mixture. The surface is supported with a carbon material, i.e., the mixture is carbon-coated.

[0081] When sugar is added as a conductive carbon precursor, the many hydroxyl groups in the sugar and the surface of the mixture This strongly interacts with the surface, suppressing the crystal growth of the lithium iron phosphate particles. By suppressing the crystal growth of lithium iron phosphate particles, it is possible to prevent the particle size from increasing. Cut.

[0082] The amount of sugar added is preferably 1 wt% or more and 20 wt% or less.

[0083] Figure 6 shows the relationship between the presence or absence of a carbon material and the surface area of ​​lithium iron phosphate. The axis indicates whether or not carbon material is supported, and the vertical axis indicates the surface area (m 2 / g) of carbon materials. The conditions other than the presence or absence of support were the same.

[0084] As shown in FIG. 6, the carbon material-supported sample (vertical bar A) shows a larger increase in the carbon content compared to the sample without the carbon material. In the case of vertical bar B, the surface area can be increased by more than two times.

[0085] By supporting a carbon material on the surface of the crushed material in this way, the lithium iron phosphate particles This suppresses crystal growth and allows the lithium iron phosphate particles to be finer after production.

[0086] The carbon material used here was also supported on the surface of the lithium iron phosphate particles after production. By supporting highly conductive carbon materials, the internal resistance of the energy storage device is reduced, and the charging capacity is increased. Increasing the discharge capacity also increases the amount of the active material. The output per unit mass can be increased. The output is 10 W / g or more, preferably can be 20 W / g or more.

[0087] That is, the lithium iron phosphate particles carrying the carbon material improve the characteristics of the electricity storage device. Therefore, supporting a carbon material on a material is not just an effect of the manufacturing method. There is no limitation, and the produced lithium iron phosphate particles themselves also have an effect.

[0088] By carrying out any one of the first to third methods, lithium iron phosphate particles In particular, the first to third methods can be carried out as a series of steps. However, these methods are just examples. It is not limited to:

[0089] In this embodiment, lithium iron phosphate (LiFePO4) having an olivine structure is produced. Although the above description is directed to the case where the active material is produced, the first to fourth methods can also be used to produce other active materials. By carrying out the third method, it is possible to make the active material into fine particles.

[0090] For example, the active material may be a compound represented by the general formula A x M y PO z (x≧0, y>0, z>0) materials can be used, where A is, for example, lithium, sodium or potassium. Alkali metals such as iron, or beryllium, magnesium, calcium, strontium or an alkaline earth metal such as barium. M is, for example, iron, nickel, manganese, or the like. The general formula A is a transition metal element such as tungsten or cobalt. x M y PO z (x≧0, y>0 , z>0), such as lithium iron phosphate and sodium iron phosphate. The material represented by A and the material represented by M may be any one or more of the above. You just need to select a number.

[0091] Alternatively, the active material may be a compound represented by the general formula A x M y O z Material expressed as (x≧0, y>0, z>0) Examples of materials that can be used include lithium manganese oxide and lithium cobalt oxide. A and M may be selected from one or more of the above.

[0092] Alternatively, the active material may be a compound represented by the general formula A x M y SiO z (x≧0, y>0, z>0) In other words, materials containing silicate can be used. Examples include lithium iron silicate and lithium iron manganese silicate. In addition, the range of x in the above general formula (x≧0) In this case, x=0 means that all reactants (lithium ions, etc.) are released.

[0093] As an example of M being a plurality of transition metal elements, M may be a mixture of two elements, manganese and iron (M y Mn s Fe t Then, s+t=1, 0≦s≦1, 0≦t≦1), two types of iron and nickel (M y Fe t Ni u Then, t+u=1, 0≦t≦1, 0≦u≦1), or manganese and iron and nickel (M y Mn s Fe t Ni u Then, s+t+u=1, 0≦s≦1 , 0≦t≦1, 0≦u≦1), where s+t=1, t+u=1, and s+ t+u=1 is the time when s+t≒1, t+u≒1, and s+t+u≒1 are respectively due to defects etc. Inclusive range.

[0094] In particular, M is the combination of manganese and iron (Mn s Fe t Then, s+t=1, 0≦s≦1, 0≦t≦1), and by using iron and manganese, which has a higher redox potential than iron, The original reaction is promoted, and the charge / discharge characteristics and the like can be improved.

[0095] The active material may also be a solid solution containing the above-mentioned plurality of transition metal elements.

[0096] This embodiment mode can be implemented in appropriate combination with other embodiment modes or examples. .

[0097] (Embodiment 2) In this embodiment, a positive electrode active material for a power storage device will be described.

[0098] First, the energy storage device is made of a material that can insert and remove reactive substances (such as lithium ions). By using the material as an active material, charging and discharging can be performed.

[0099] A requirement for an excellent power storage device is that it has a large charge capacity or discharge capacity. do.

[0100] One aspect of the present invention is to provide a method for increasing the charge / discharge capacity by using a carbon material supported on a substrate (carbon core). The positive electrode uses a carbon-based active material that is highly conductive, which reduces the internal resistance of the power storage device. can be reduced.

[0101] FIG. 7 shows an example of an active material on which a carbon material is supported. In FIG. 7(A), the particles of the active material The surface of the element 103 is partially or entirely covered with a carbon material 105. In the particle group 107 formed by gathering a plurality of particles 103, 7(C) shows a state in which a plurality of particles are coated with a carbon material 105. In the layer formed by 103 (also called particle layer 109), one part of the surface of the particle layer 109 A part or the whole of the surface is covered with a carbon material 105 .

[0102] Figure 8 shows the structure of a lithium iron phosphate (LiFePO4) with an olivine structure as the active material. 8A shows the charge and discharge characteristics of the power storage device, and FIG. 8B shows the discharge characteristics. In both cases, the horizontal axis represents capacity (mAh / g) and the vertical axis represents voltage (V). .

[0103] FIG. 8(A) shows the results for the case where a carbon material is supported (solid line 201) and the case where a carbon material is not supported. 2 shows the charging characteristics when the battery is charged (dashed line 203).

[0104] FIG. 8(B) shows the results for the case where a carbon material is supported (solid line 205) and the case where a carbon material is not supported. 2 shows the discharge characteristics when there is no charge (dashed line 207).

[0105] As shown in Figure 8, the charge and discharge capacities when the carbon material was supported were 160 mAh / g, and the charge and discharge capacities without supporting carbon material are 120-140mAh / g.

[0106] The theoretical capacity when using lithium iron phosphate is 170 mAh / g. In particular, in a power storage device using lithium iron phosphate supported on a carbon material as a positive electrode active material, The diffusion of lithium ions accounts for 94% of the total lithium iron phosphate ((160mAh / g) / (170 This shows that the energy density reaches 100% (mAh / g) × 100(%).

[0107] In this way, by supporting a highly conductive carbon material on lithium iron phosphate, The internal resistance can be reduced, and the charge capacity and discharge capacity can be increased.

[0108] Next, a method for supporting a carbon material on an active material will be described below. The case of producing lithium iron phosphate as the starting material will be described.

[0109] First, as raw materials for lithium iron phosphate, lithium carbonate (Li2CO3), iron oxalate ( Mix FeC2O4 and ammonium dihydrogen phosphate (NH4H2PO4).

[0110] Lithium carbonate is a raw material for introducing lithium, and iron oxalate is a raw material for introducing iron. Ammonium dihydrogen phosphate is a raw material for introducing phosphate. The raw materials are not limited to these, as long as they can be introduced.

[0111] Next, the mixture is pulverized in a mortar or the like.

[0112] Then, a substance capable of generating conductive carbon by thermal decomposition (hereinafter referred to as "conductive carbon") was added to the pulverized mixture. The conductive carbon precursor may be, for example, glucose, Adding sugar such as sucrose. Adding a conductive carbon precursor creates carbon on the surface of the mixture. The base material is supported, i.e., the mixture is carbon coated.

[0113] The amount of sugar added is preferably 1 wt% or more and 20 wt% or less. The thickness of the carbon material supported in the lithium iron phosphate layer is greater than 0 nm and less than 100 nm. It is preferable that the particle size is less than 100 μm. The output per unit mass of the active material is set to 10 W / g or more, preferably 20 W / g or more. This can be done.

[0114] By carrying out the above steps, lithium iron phosphate supported on a carbon material can be produced. By using this lithium iron phosphate as an active material to fabricate an electricity storage device, The internal resistance of the battery can be reduced, and the charge and discharge capacities can be increased. In a later step, lithium iron phosphate particles are mixed with a conductive additive to improve conductivity. The conductive additive is carbon black such as acetylene black. In addition, if conductivity can be ensured by carbon coating, a conductive additive can be used. It doesn't have to be there.

[0115] In addition, by supporting a carbon material, lithium iron phosphate can be made into fine particles. This increases the diffusion paths of lithium ions and can also speed up the charge and discharge speed of the energy storage device. do.

[0116] In this embodiment, lithium iron phosphate (LiFePO4) having an olivine structure is produced. However, when producing other active materials, the same method can be used with a carbon material. This makes it possible to increase the charge capacity and discharge capacity of the power storage device.

[0117] For example, the active material may be a compound represented by the general formula A x M y PO z (x≧0, y>0, z>0) materials can be used, where A is, for example, lithium, sodium or potassium. Alkali metals such as iron, or beryllium, magnesium, calcium, strontium or an alkaline earth metal such as barium. M is, for example, iron, nickel, manganese, or the like. The general formula A is a transition metal element such as tungsten or cobalt. x M y PO z (x≧0, y>0 , z>0), such as lithium iron phosphate and sodium iron phosphate. The material represented by A and the material represented by M may be any one or more of the above. You just need to select a number.

[0118] Alternatively, the active material may be a compound represented by the general formula A x M y O z Material expressed as (x≧0, y>0, z>0) Examples of materials that can be used include lithium manganese oxide and lithium cobalt oxide. A and M may be selected from one or more of the above.

[0119] Alternatively, the active material may be a compound represented by the general formula A x M y SiO z (x≧0, y>0, z>0) In other words, materials containing silicate can be used. Examples include lithium iron silicate and lithium iron manganese silicate. In addition, the range of x in the above general formula (x≧0) In this case, x=0 means that all reactants (lithium ions, etc.) are released.

[0120] As an example of M being a plurality of transition metal elements, M may be a mixture of two elements, manganese and iron (M y Mn s Fe t Then, s+t=1, 0≦s≦1, 0≦t≦1), two types of iron and nickel (M y Fe t Ni u Then, t+u=1, 0≦t≦1, 0≦u≦1), or manganese and iron and nickel (M y Mn s Fe t Ni uThen, s+t+u=1, 0≦s≦1 , 0≦t≦1, 0≦u≦1), where s+t=1, t+u=1, and s+ t+u=1 is the time when s+t≒1, t+u≒1, and s+t+u≒1 are respectively due to defects etc. Inclusive range.

[0121] In particular, M is the combination of manganese and iron (Mn s Fe t Then, s+t=1, 0≦s≦1, 0≦t≦1), and by using iron and manganese, which has a higher redox potential than iron, The original reaction is promoted, and the charge / discharge characteristics and the like can be improved.

[0122] The active material may also be a solid solution containing the above-mentioned plurality of transition metal elements.

[0123] This embodiment mode can be implemented by appropriately combining with other embodiments or examples. .

[0124] (Embodiment 3) In this embodiment, a material suitable for a positive electrode active material according to one embodiment of the present invention will be described. do.

[0125] As the active material for the positive electrode according to one embodiment of the present invention, lithium oxide is used. In this embodiment, an example will be described in which a silicate-based lithium is used as the lithium oxide. Reveal.

[0126] The positive electrode active material according to the present embodiment is represented by the general formula Li (2-x) It is expressed as MSiO4 and and satisfy the following conditions (I) and (II). (I) x is a value that changes due to the insertion and desorption of lithium ions during charging and discharging. However, 0≦ x≦2. (II) M is iron (Fe), nickel (Ni), manganese (Mn), or cobalt ( Co).

[0127] General formula Li (2-x) The material represented by MSiO4 (lithium silicate) is a lithium atom. The ratio of the metal atoms to other metal atoms (M atoms) is a maximum of 2:1 (molar ratio). Therefore, if all the lithium atoms contained in the material can be used in the reaction, Up to two lithium ions (reactants) can be inserted and extracted per molecule. By using such a material as the active material for the positive electrode, it is possible to increase the capacity, and The characteristics can be improved.

[0128] General formula Li (2-x) The material represented by MSiO4 is composed of lithium atoms and other metals. The crystal structure belongs to a space group in which the ratio of M atoms to M atoms is at most 2:1 (molar ratio). It is possible.

[0129] For example, Li2FeSiO4, where M = iron and x = 0, is a crystal that belongs to the space group P1211. M=manganese, x = 0, Li2MnSiO4 has a crystal structure that belongs to the space group Pmn21, or the space group P1 It can have a crystal structure belonging to the 21 / n1 group. Li2 where M = cobalt and x = 0 CoSiO4 can have a crystal structure belonging to the space group Pbn21.

[0130] Figure 10 shows an example of the crystal structure of Li2FeSiO4, which belongs to the space group P1211. Li2FeSiO4, which belongs to the space group P1211, has eight lithium atoms (1001) and one iron atom (1001). The crystal has four atoms 1003, four silicon atoms 1005, and 16 oxygen atoms 1007. As shown in Figure 10, Li2FeSiO4, which belongs to the space group P1211, The ratio of lithium atoms (1001) to other metal atoms (iron atoms (1003)) is 2:1. This allows the ratio of lithium atoms to other metal atoms, such as LiCoO2, to be 1: This shows that theoretically the capacity can be increased compared to materials with a capacity of 1.

[0131] Figure 11 shows an example of the crystal structure of Li2FeSiO4, which belongs to the space group Pmn21. Li2FeSiO4, which belongs to the space group Pmn21, has four lithium atoms (1101) and one iron atom (1102). The minimum number of atoms in the crystal is two nuclei 1103, two silicon atoms 1105, and eight oxygen atoms 1107. As shown in Figure 11, Li2FeSiO4, which belongs to the space group Pmn21, The ratio of lithium atoms 1101 to other metal atoms (iron atoms 1103) is 2:1. This allows the ratio of lithium atoms to other metal atoms, such as LiCoO2, to be 1:1. This shows that the capacity can theoretically be increased compared to materials with a

[0132] Li2MnSiO4, which belongs to the space group Pmn21, also has the crystal structure shown in Figure 11. In this case, the iron atom 1103 in Figure 11 is replaced by a manganese atom. Li2MnSiO4, which belongs to the space group Pmn21, has lithium atoms and manganese atoms. The ratio of lithium atoms in LiCoO2 and other metals is 2:1. Theoretically, this material can have a larger capacity than a material with a 1:1 atomic ratio.

[0133] Figure 12 shows an example of the crystal structure of Li2MnSiO4, which belongs to the space group P121 / n1. Li2MnSiO4, which belongs to the space group P121 / n1, has 8 lithium atoms (1201). 1203, 4 manganese atoms 1203, 4 silicon atoms 1205, 1 oxygen atom 1207 Six of these molecules make up the smallest unit of a crystal. As shown in Figure 12, they belong to the space group P121 / n1. Li2MnSiO4 consists of 1201 lithium atoms and 12 other metal atoms (manganese atoms). 03) is 2:1. This allows the lithium atoms in LiCoO2 and other It has been found that theoretically, the capacity can be increased compared to materials with a 1:1 ratio of other metal atoms. do.

[0134] Figure 13 shows an example of the crystal structure of Li2CoSiO4, which belongs to the space group Pbn21. Li2CoSiO4, which belongs to the space group Pbn21, has eight lithium atoms (1301) and It is composed of four silicon atoms 1303, four silicon atoms 1305, and 16 oxygen atoms 1307. As shown in Figure 13, Li2CoS belongs to the space group Pbn21. iO4 is the ratio of lithium atoms 1301 to other metal atoms (cobalt atoms 1303). The ratio is 2:1. This allows the lithium atoms in LiCoO2 and other metal atoms to This shows that theoretically the capacity can be increased compared to a material with a 1:1 ratio.

[0135] General formula Li (2-x) The material represented by MSiO4 is determined by the type of metal M atom and the manufacturing method (e.g. By controlling the temperature, for example, the firing temperature, it is possible to create different space groups of crystal structures. Examples include the following (III) to (VI). (III) It has a crystal structure belonging to the space group P1211. (IV) It has a crystal structure belonging to the space group Pmn21. (V) It has a crystal structure belonging to the space group P121 / n1. (VI) It has a crystal structure belonging to the space group Pbn21.

[0136] General formula Li (2-x) The material represented by MSiO4 belongs to any of the above space groups. Even in a crystalline structure, the ratio of lithium atoms to other metal atoms is 2:1. Therefore, it is theoretically possible to increase the capacity. If used as such, it is possible to improve the characteristics of the electricity storage device, such as increasing the capacity.

[0137] 10 to 13 show examples in which one type of element is introduced as the metal M atom. However, one embodiment of the present invention is not limited thereto.

[0138] For example, the active material for the positive electrode is a compound of the general formula Li (2-x) Fe s Mn t It is represented by SiO4 and satisfying the following conditions (I) and (VII): (I) x is a value that changes due to the insertion and desorption of lithium ions during charging and discharging. However, 0≦ x≦2. (VII) s+t=1, 0≦s≦1, and 0≦t≦1.

[0139] The above materials (general formula Li (2-x) Fe s Mn t SiO4) has the general formula Li (2-x) Iron and manganese are used as the metal M in materials expressed as MSiO4. M may be nickel or cobalt.

[0140] In addition, s+t=1 in the above (VII) includes the range of s+t≒1 due to defects, etc. .

[0141] Also, the general formula Li (2-x) Fe s Ni u SiO4 and the following (I) and ( VIII). (I) x is a value that changes due to the insertion and desorption of lithium ions during charging and discharging. However, 0≦ x≦2. (VIII) s+u=1, 0≦s≦1, and 0≦u≦1.

[0142] The above materials (general formula Li (2-x) Fe s Ni u SiO4) has the general formula Li (2-x) Iron and nickel are used as the metal M in materials represented by MSiO4. M may be manganese or cobalt.

[0143] In addition, s+u=1 in the above (VIII) includes the range of s+u≒1 due to defects, etc. nothing.

[0144] In addition, the active material for the positive electrode is a compound of the general formula Li (2-x) Fe s Mn t Ni u Expressed as SiO4 Examples of such materials include those that satisfy the following conditions (I) and (IX). (I) x is a value that changes due to the insertion and desorption of lithium ions during charging and discharging. However, 0≦ x≦2. (IX) s+t+u=1, 0≦s≦1, 0≦t≦1, and 0≦u≦1.

[0145] The above materials (general formula Li (2-x) Fe s Mn t Ni u SiO4) has the general formula Li (2 -x) As the metal M of the material represented by MSiO4, iron, manganese, and nickel are used. Also, cobalt may be used as the metal M.

[0146] Note that s + t + u = 1 in the above (IX) includes the range where s + t + u ≒ 1 due to defects or the like. including.

[0147] As described above, even in a material using two types of elements or three or more types of elements as metal M atoms, the ratio of lithium atoms to other metal atoms is at most 2:1. By using such a material as the active material for the positive electrode, it is possible to increase the capacity and improve the characteristics of the power storage device. This embodiment can be appropriately combined with the configurations of other embodiments and examples. This embodiment can be appropriately combined with the configurations of other embodiments and examples. This embodiment can be appropriately combined with the configurations of other embodiments and examples.

[0148] This embodiment can be appropriately combined with the configurations of other embodiments and examples.

[0149] (Embodiment 4) In this embodiment, an example of a method for producing lithium silicate will be described.

[0150] <Method for Producing Li2FeSiO4> An example of a production method when the metal M atom is iron will be described.

[0151] Li2FeSiO4 can be produced using a raw material for introducing lithium, a raw material for introducing iron, and a raw material for introducing silicate (silicate). For example, lithium carbonate (Li2CO3) can be used as the raw material for introducing lithium, iron oxalate (FeC2O4) can be used as the raw material for introducing iron, and silicon oxide (SiO2) can be used as the raw material for introducing silicate (silicate). It can also be produced using lithium silicate (Li2SiO3) as the raw material for introducing lithium and silicate. Note that lithium, iron, and silicon using. using lithium carbonate (Li2CO3) as the raw material for introducing lithium, iron oxalate (FeC2O4) as the raw material for introducing iron, and silicon oxide (SiO2) as the raw material for introducing silicate (silicate). using. using. using lithium silicate (Li2SiO3) as the raw material for introducing lithium and silicate. Note that lithium, iron, and silicon The raw materials are not limited to these, as long as they can introduce the carboxylate.

[0152] Li2FeSiO4 is made by mixing the materials (raw materials) and then firing them. It is possible.

[0153] The raw materials can be mixed, for example, by a ball mill treatment. By doing so, the raw materials can be mixed and simultaneously atomized, and the L It is possible to achieve fine particle formation of i2FeSiO4. This allows the raw materials to be mixed uniformly, improving the crystallinity of the Li2FeSiO4 after production. This can be done.

[0154] When mixing raw materials by ball milling, the raw materials, solvent, and balls are mixed in a device ( Mix in a ball mill pot. The solvent is acetone, ethanol, etc. The balls can be made of metal or ceramic. The milling process requires a rotation speed of 50 rpm to 500 rpm, and a rotation time of 30 minutes to 5 hours. Hereinafter, this can be done with a ball diameter of φ1 mm or more and 10 mm or less.

[0155] For example, the raw materials are lithium carbonate, iron oxalate dihydrate, and silicon oxide, and the solvent is Acetone and zirconia (Zr) balls with a diameter of φ3 mm were used as the ball mill pot. The mixture is placed in a container, rotated at 400 rpm for 2 hours, and mixed with the raw materials. can be done.

[0156] The raw material mixture is fired at a firing temperature of 700°C to 1100°C for 1 hour. It can be done for more than 24 hours.

[0157] The raw material mixture is fired in two stages: the first firing (pre-firing) and the second firing (main firing). The second baking may be carried out in stages. The second baking is preferably carried out at a higher temperature than the first baking. By performing two-stage firing, the Li2FeSiO4 particles are made finer after production, or the crystallinity is improved. can be increased.

[0158] The first firing is performed, for example, in a nitrogen atmosphere at a firing temperature of 250° C. or higher and 450° C. or lower. The second baking can be performed for 1 hour to 20 hours. The firing temperature is between 300°C and 700°C, and the firing time is between 1 hour and 20 hours. It is possible.

[0159] Before the first firing or the second firing, the mixture of raw materials may be subjected to a pressure treatment. For example, the raw material mixture can be formed into pellets and then fired. When pelletizing the mixture and performing two-stage firing, the pelletized mixture is fired in the first stage. The fired material is sintered in a mortar, etc., and then mixed by a ball mill, etc., and then mixed again. The mixture can be formed into pellets and then subjected to a second firing.

[0160] For example, the raw materials (lithium carbonate, iron oxalate dihydrate) mixed by the first ball mill treatment The mixture of silicon dioxide and silicon hydrate was heated to 50°C to evaporate the solvent (acetone). Then, apply pressure of 150 kgf for 5 minutes in a pellet press to form pellets. The pelletized mixture was baked in a nitrogen atmosphere at 350°C for 10 hours. The first firing (pre-firing) is carried out.

[0161] After lightly pulverizing the fired product (pre-fired product), the fired product (pre-fired product), the solvent (acetone), and Put zirconia (Zr) balls with a ball diameter of φ3 mm into a pot for a ball mill, and the rotation speed Perform the second ball mill treatment under the conditions of 400 rpm and a rotation time of 2 hours.

[0162] The fired product (pre-fired product) mixed by the second ball mill treatment is heated to 50 °C to evaporate the solvent ( acetone), and then pressured at 150 kgf for 5 minutes with a pellet press and molded into pellets. The fired product (pre-fired product) molded into pellets is placed in a nitrogen atmosphere, [[ID=1I4]]Perform the second firing (main firing) at a firing temperature of 700 °C or 800 °C and a firing time of 10 hours. In this example, by setting the firing temperature of the second firing to 700 °C, Li2FeSiO4 having a crystal structure belonging to the space group P1211 can be produced. Also, by setting the firing temperature of the second firing to 800 °C, Li2FeSiO 4 having a crystal structure belonging to the space group Pmn21 can be produced. 4 can be produced.

[0163] The Li2FeSiO4 obtained as described above can have a maximum insertion and desorption amount of lithium ions per composition of 2. Using such a material as the active material for the positive electrode makes it possible to increase the capacity and contribute to improving the characteristics of the power storage device. When the metal M atom is manganese, instead of the raw material for introducing iron in the production method of the above Li2FeSiO4, a raw material for introducing manganese is used. For example, it can be produced using lithium silicate (Li2

[0164] <Production method of Li2MnSiO4> SiO3) and manganese oxalate (MnC2O4) as raw materials. SiO3) and manganese oxalate (MnC2O4) as raw materials. Li2MnSiO4 can be produced by mixing the materials (raw materials) and then firing them. It is possible.

[0165] The Li2MnSiO4 obtained in this way has a lithium ion intercalation rate per composition of 1. The amount of charge and charge released can be increased to a maximum of 2. By using such a material as the active material for the positive electrode, This enables a higher capacity to be achieved, which can contribute to improving the characteristics of the power storage device.

[0166] In this embodiment, the metal M atom is iron or manganese. By appropriately selecting the raw material for introduction, the desired Li (2-x) Material represented as MSiO4 It is possible to prepare the following.

[0167] This embodiment mode can be combined with the configurations of other embodiments and examples.

[0168] (Embodiment 5) In this embodiment, an example of a power storage device using the positive electrode active material described in the above embodiment will be described. We will explain about this.

[0169] FIG. 14A shows part of the structure of a power storage device 2200. The power storage device 2200 has a positive electrode 2 201, and a negative electrode 2211 provided opposite to the positive electrode 2201 with the electrolyte 2207 interposed therebetween. It has the following features.

[0170] The positive electrode 2201 includes a current collector 2203 and a positive electrode active material layer 22 provided on the current collector 2203. It consists of 05 and.

[0171] The active material for the positive electrode 2201 (positive electrode active material layer 2205) is the same as that described in the above embodiment. The material and manufacturing method of the positive electrode active material layer 2205 are the same as those in the above embodiment modes. The material of the current collector 2203 may be, for example, a conductive material such as platinum, copper, or titanium. A non-reactive material can be used.

[0172] The negative electrode 2211 includes a current collector 2213 and a negative electrode active material layer 22 The material of the current collector 2213 is a conductive material such as platinum, copper, or titanium. The material of the negative electrode active material layer 2215 can be a carbon material such as graphite, Examples of materials that can be used include lithium metal and silicon.

[0173] The electrolyte 2207 has the function of conducting reactants (lithium ions, etc.). The material of 207 can be solid or liquid.

[0174] If the electrolyte 2207 material is solid, for example, Li3PO4, Li3PO4 mixed with nitrogen, Zeta Li x PO y N z (x, y, z are positive real numbers), Li2S-SiS2, Li2S-P2 S5, Li2S-B2S3, etc. can be used. In addition, these can be doped with LiI, etc. The above can be used.

[0175] When the material of the electrolyte 2207 is liquid, it contains a solvent and a solute (salt) that is dissolved in the solvent. Examples of the solvent include propylene carbonate and ethylene carbonate. or chain carbonates such as dimethyl carbonate or diethyl carbonate. Carbonates can be used. Examples of solutes (salts) include LiPF6, LiB F4, or LiTFSA, etc., containing one or more light metal salts (lithium salts, etc.) can be used.

[0176] If the electrolyte 2207 is a liquid, a separator 2209 is provided. 09 prevents contact between the positive electrode 2201 and the negative electrode 2211 and also prevents contact between the positive electrode 2201 and the negative electrode 2211 and the reactant (lithium The separator 2209 has a function of passing ions, etc. The material of the separator 2209 is, for example, paper. , nonwoven fabric, glass fiber, or nylon (polyamide), vinylon (polyvinyl alcohol) Coal fiber, also known as Vinalon), polypropylene, polyester, acrylic, Synthetic fibers such as polyolefin and polyurethane can also be used. It is necessary to select a material that does not dissolve in the electrolyte 2207. Also, a solid electrolyte should be used for the electrolyte 2207. Even when using a separator 2209, it is possible to provide the separator 2209.

[0177] Next, an example of charging and discharging when a lithium ion secondary battery is used as the power storage device will be described. .

[0178] As shown in FIG. 14(B), charging is performed by connecting a power source 222 between a positive electrode 2201 and a negative electrode 2211. When a voltage is applied from the power supply 2221, the positive electrode 2201 The lithium ions are ionized and released from the positive electrode 2201 as lithium ions 2217. Electrons 2219 are generated. Lithium ions 2217 are transported to the negative electrode via the electrolyte 2207. 2211. Electrons 2219 move to the negative electrode 2211 via the power source 2221. Then, the lithium ion 2217 receives the electron 2219 at the negative electrode 2211, and inserted into the negative electrode 2211 as a cathode.

[0179] On the other hand, as shown in FIG. 14(C), the discharge is performed by connecting a load 2201 between the positive electrode 2201 and the negative electrode 2211. This is done by connecting the negative electrode 2211 to the negative electrode 223. The lithium in the negative electrode 2211 is ionized, and the lithium ions Lithium is released from the negative electrode 2211 as lithium ions 2217, and electrons 2219 are generated. The ion 2217 moves to the positive electrode 2201 through the electrolyte 2207. moves to the positive electrode 2201 through the load 2223. Then, the lithium ions 2217 , receives electrons 2219 at the positive electrode 2201 and is inserted into the positive electrode 2201 as lithium.

[0180] In this way, lithium ions move between the positive electrode 2201 and the negative electrode 2211, and charging In the positive electrode 2201 of the power storage device 2200, the positive electrode active material layer 2205 is By applying the materials shown in the above embodiments, it is possible to increase the charge / discharge rate or increase the capacity. This makes it possible to improve the characteristics of the electricity storage device.

[0181] This embodiment mode can be implemented in appropriate combination with other embodiment modes and examples. .

[0182] (Embodiment 6) In this embodiment, a power storage device having a different structure from that of the above embodiment will be described.

[0183] Carbon materials such as graphite have been put to practical use as the active material for the negative electrode. The theoretical capacity of the raw materials is limited, and it is difficult to increase the capacity beyond that currently in practical use. In this embodiment, a silicon material is used as an active material for a negative electrode, We aim to improve the characteristics of the product.

[0184] As the active material for the positive electrode according to this embodiment, the material shown in the above embodiment is used. This makes it possible to improve the characteristics of the electricity storage device.

[0185] Furthermore, in this embodiment, a silicon material is used as the active material for the negative electrode. In addition to the improvement of the characteristics of the power storage device by the positive electrode active material shown in the above embodiment, Furthermore, the characteristics of the power storage device can be improved.

[0186] In this embodiment, in order to effectively improve the characteristics of the power storage device, crystalline silicon One of the features of the present invention is that the active material is used as a negative electrode active material. The crystalline silicon crystallized by the above method is used as the active material for the negative electrode. The diffusion rate of reactants (lithium ions, etc.) is faster than that of amorphous silicon, and the characteristics of the energy storage device This can lead to further improvements in

[0187] Crystalline silicon can be obtained by heat treating amorphous silicon to crystallize it. In this case, if crystallization is performed using a catalyst element, the process temperature for crystallization can be lowered and This is preferable because it can shorten the process time.

[0188] By using silicon as the active material for the negative electrode, the capacity can be increased compared to using carbon materials. Furthermore, among silicon, crystalline silicon can be used. This makes it possible to improve the diffusion rate of carrier ions compared to the application of amorphous silicon. Then, a method using a catalytic element is applied as a method for producing crystalline silicon. This makes it possible to lower the process temperature for crystallization and shorten the process time. In other words, by applying a silicon layer crystallized using a catalytic element to the negative electrode active material layer, The manufacturing method is aimed at reducing manufacturing costs and improving productivity, and the characteristics of the power storage device are improved. can be done.

[0189] The structure and manufacturing method of the negative electrode will be described with reference to FIG. The above-mentioned FIG. 14 can be applied, and corresponds to the negative electrode 2211 in FIG.

[0190] An amorphous silicon layer 413 is formed over a negative electrode current collector 411 (see FIG. 15A).

[0191] The negative electrode current collector 411 is made of a conductive material such as titanium, nickel, copper, indium, tin, or silver. For example, in this embodiment, titanium is used as the negative electrode current collector 411. There are.

[0192] The amorphous silicon layer 413 is formed by plasma CVD, low pressure CVD, sputtering, or vacuum deposition. A thickness of 100 nm to 5 μm, preferably 1 μm to 3 μm, is obtained by using a deposition method or the like. If the thickness of the amorphous silicon layer 413 is less than 100 nm, the amorphous silicon layer 413 is formed in a range of 100 nm after crystallization. In this case, the thickness of the negative electrode active material layer 417 obtained may be too thin to allow charging and discharging. If the thickness of the silicon layer 413 is greater than 5 μm, the amorphous silicon layer 413 cannot be completely crystallized. Alternatively, if the thickness of the amorphous silicon layer 413 is greater than 5 μm, the thickness of the amorphous silicon layer 413 may be increased after crystallization. There is a risk that the negative electrode active material layer 417 obtained in this way may peel off due to stress changes during charge and discharge. Therefore, it is preferable that the thickness of the amorphous silicon layer 413 be within the above range. It's nice.

[0193] For example, in this embodiment, a 3 μm thick amorphous silicon layer is formed by plasma CVD. Form 413.

[0194] A catalyst element 415 is added to the amorphous silicon layer 413 to promote crystallization (FIG. 1 5(B)).

[0195] The catalytic element 415 may be an element that promotes the crystallization of amorphous silicon. Specifically, a metal element can be used as the catalyst element 415, for example, nickel. (Ni), copper (Cu), indium (In), tin (Sn), or silver (Ag) One or more of the elements can be used. The catalytic element can be converted into a non-metallic compound by a subsequent heat treatment. It reacts with the silicon in the amorphous silicon to form silicide. The silicide acts as a crystalline nucleus. , which contributes to the subsequent crystal growth.

[0196] The catalyst element 415 is added by coating the surface of the amorphous silicon layer 413 or by sputtering. A method of directly attaching the amorphous silicon layer 413 to the surface of the amorphous silicon layer 413 using a deposition method or a vacuum deposition method. Which one should I use?

[0197] By adding the catalytic element 415 to the amorphous silicon layer 413, the amorphous silicon layer 4 It is possible to lower the crystallization temperature of 13 by about 50 to 100°C. The time required for crystallization of the porous silicon layer 413 can be reduced to about 1 / 5 to 1 / 10. It is possible.

[0198] Nickel is an excellent catalyst element 415 in terms of its effectiveness and reproducibility. Nickel forms nickel silicide when amorphous silicon is crystallized, In this embodiment, the catalyst element 415 functions as a crystal nucleus when the silicon is crystallized. A specific method for adding nickel as a ferrite is described with reference to FIG.

[0199] As shown in FIG. 16(A), a catalyst element 415 is formed on the surface of an amorphous silicon layer 413. For example, when nickel is used as the catalytic element 415, the solution 416 is added. 6 is a nickel acetate solution, a nickel hydrochloride solution, a nickel nitrate solution, or a nickel sulfate solution. In this embodiment, a nickel acetate solution is used as the solution 416. There are.

[0200] As shown in FIG. 16(B), spin drying is performed using a spinner 421. By carrying out the above process, a solution containing the catalytic element 415 is uniformly formed on the surface of the amorphous silicon layer 413. The liquid 416 can be retained.

[0201] Before adding the solution 416, a thin oxide layer was formed on the surface of the amorphous silicon layer 413. This is because the surface of the amorphous silicon layer 413 is hydrophobic, so that the solution If 416 is a solution containing water, the solution 416 is repelled by the surface of the amorphous silicon layer 413 and contacts the surface. This is because there is a risk that the catalyst element 415 may not be added to the entire surface of the amorphous silicon layer 413 . By forming a thin oxide layer on the surface of the amorphous silicon layer 413, the wettability to the solution 416 is improved. The oxide layer can be formed by using amorphous silicon. The surface of the amorphous silicon layer 413 is irradiated with UV light, or the surface of the amorphous silicon layer 413 is irradiated with ammonia hydrogen peroxide. Alternatively, a method of treating with ozone water or the like can be used. The oxide layer formed by such a method is so thin that the catalytic element 415 reaches the amorphous silicon layer 413 through the oxide layer. It is possible.

[0202] Alternatively, organic octylic acid solution or toluene solution can be used as the solution 416. The organic solution contains carbon, which is an element of the same group as silicon, and forms an amorphous silicon layer 4. 13It is suitable because it has high wettability with the surface.

[0203] The amorphous silicon layer 413 is subjected to heat treatment (see FIG. 15C). The crystalline silicon layer 413 is then crystallized to obtain a crystalline silicon layer. The conductive silicon layer can be used as the negative electrode active material layer 417. 11, a negative electrode 419 having a negative electrode active material layer 417 formed thereon can be obtained (FIG. 15(D)). reference).

[0204] The heat treatment for crystallizing the amorphous silicon layer 413 can be carried out in, for example, a heating furnace. It can also be performed by irradiating light such as a laser beam.

[0205] When heat treatment is carried out in a heating furnace, the temperature is 450°C or higher and 750°C or lower, preferably 550°C or lower. The heat treatment can be carried out at a temperature in the range of 1 hour to 240°C. For example, the reaction can be carried out for 55 hours or less, preferably for 4 hours or more and 10 hours or less. Heat treatment is carried out at 0°C for 4 hours.

[0206] Also, as shown in FIG. 15(C), when performing heat treatment by irradiating a laser beam, for example, If the energy density is 100 mJ / cm 2 More than 400mJ / cm 2 Below 200, preferably mJ / cm 2 More than 400mJ / cm 2 The range below, typically 250 mJ / cm 2 as For example, a laser beam from a KrF excimer laser (wavelength 248 nm, power Heat treatment is performed using a pulse width of 20 nsec.

[0207] The catalytic element 415 moves in the amorphous silicon layer 413 by heat treatment and functions as a crystal nucleus. For example, when the catalytic element 415 is nickel, the Nickel reacts with the silicon in the amorphous silicon to form nickel silicide, The silicide acts as a crystal nucleus and contributes to subsequent crystal growth. This promotes crystallization. This allows the process temperature for crystallization to be lowered and the process time to be shortened, This can contribute to reducing manufacturing costs and improving productivity.

[0208] The catalytic element 415 remaining in the crystalline silicon layer that becomes the negative electrode active material layer 417 is particularly There is no need to remove the catalyst element 415 because it is a metal element and has electrical conductivity. be.

[0209] Here, when the amorphous silicon layer 413 is crystallized using the catalytic element 415, the heat treatment means Depending on the conditions, etc., after crystallization, the outermost surface of the crystalline silicon layer (negative electrode active material layer 417) In this case, the catalytic element segregates in the depth direction (film thickness direction) of the crystalline silicon layer. In this case, the closer to the surface, the higher the concentration of the catalytic element 415. The catalytic element 415 is oxidized by heat treatment and becomes a conductive oxide. When nickel is used as the material, nickel oxide segregates on the outermost surface of the crystalline silicon layer.

[0210] 17(A) and (B), a conductive layer is formed on the outermost surface of the negative electrode active material layer 417 (crystalline silicon layer). FIG. 17(A) shows the state in which the conductive oxide 418 is segregated. 17(B) shows the state where the particles are segregated on the outermost surface of the negative electrode active material layer 417 in the shape of 1 shows a state in which a conductive oxide 418 is segregated in a layer on the outermost surface of the negative electrode active material layer 417. There are.

[0211] The conductive oxide 418 is conductive. Therefore, the conductive oxide 418 segregates on the outermost surface of the negative electrode active material layer 417. Therefore, the use of a catalytic element is advantageous in the process. In addition, a crystalline silicon layer is applied to the negative electrode active material layer 417. It can be effective.

[0212] When copper, indium, tin, or silver is used as the catalyst element 415, The oxides are oxidized and copper oxide, indium oxide, tin oxide, or silver oxide segregate. Since the material is a conductive oxide like nickel oxide, it can exert the above-mentioned effect. can.

[0213] In this manner, the negative electrode 419 can be formed. A crystalline silicon layer is used as the active material for the negative electrode. Therefore, the characteristics of the power storage device can be improved. The application of a crystalline silicon layer that has been thinned contributes to reducing manufacturing costs and improving productivity. In addition, in the positive electrode, the material shown in the above embodiment can be used as a positive electrode active material. Therefore, the characteristics of the electricity storage device can be improved from both the negative electrode side and the positive electrode side.

[0214] This embodiment mode can be combined as appropriate with the structures of other embodiment modes and examples.

[0215] (Embodiment 7) In this embodiment, a power storage device having a different structure from that of the above embodiment will be described.

[0216] In the sixth embodiment, an amorphous silicon layer 413 is formed on the negative electrode current collector 411. After adding the catalytic element 415 to the porous silicon layer 413, the layer is crystallized by heat treatment. An example of obtaining a crystalline silicon layer to be the negative electrode active material layer 417 is shown. The current collector itself is used as a catalytic element to form a crystalline silicon layer that will become the negative electrode active material layer. An example will be explained.

[0217] An amorphous silicon layer 453 is formed over a negative electrode current collector 451 (see FIG. 18A).

[0218] The negative electrode current collector 451 contains a catalytic element that promotes the crystallization of amorphous silicon and is conductive. The catalyst element is made of a material having the same properties as the catalyst element 415 described above. Nickel (Ni), copper (Cu), indium (In), tin (Sn) The negative electrode current collector 451 may be made of any of the above-mentioned catalytic elements. The negative electrode current collector 451 contains one or more elements. Alternatively, an alloy of the catalytic element and other materials may be used. When alloying 1, it is preferable to select a material that does not form an alloy with lithium. However, if a material that forms an alloy with lithium is used, the stability of the negative electrode current collector 451 itself may decrease. This is because there is a

[0219] The amorphous silicon layer 453 is formed in the same manner as the amorphous silicon layer 413 described above.

[0220] Next, the amorphous silicon layer 453 is subjected to a heat treatment. The negative electrode current collector 45 is crystallized to obtain a crystalline silicon layer that becomes the negative electrode active material layer 457. The negative electrode 459 is formed by stacking the negative electrode active material layer 1 and the negative electrode active material layer 457 (see FIG. 18B).

[0221] By the heat treatment of the amorphous silicon layer 453, the catalytic element contained in the negative electrode current collector 451 is converted into a negative The material moves from the electrode current collector 451 into the amorphous silicon layer 453 by thermal diffusion. The crystal growth of the porous silicon layer 453 progresses from the interface with the negative electrode current collector 451 toward the other surface. In the depth direction (film thickness direction) of the amorphous silicon layer 453, the The crystal growth proceeds from the interface with 51 to the other surface. In the silicon layer, the concentration of the catalytic element decreases from bottom to top in the depth direction. In other words, the closer to the surface of the crystalline silicon layer, the lower the concentration of the catalytic element. It has become.

[0222] The heat treatment conditions are the same as those for the heat treatment of the amorphous silicon layer 413 described above with reference to FIG. 15(C). In this embodiment, the negative electrode current collector 451 acts as a catalytic element. Therefore, it is possible to lower the process temperature for crystallization and shorten the process time. This can contribute to reducing manufacturing costs and improving productivity.

[0223] In addition, in this embodiment, the negative electrode current collector 451 itself acts as a catalytic element. This eliminates the need for a process of adding elements, which also contributes to reducing manufacturing costs and improving productivity. It is possible.

[0224] The catalytic element remaining in the crystalline silicon layer that will become the negative electrode active material layer 457 does not need to be particularly removed. This is because the catalyst element is a metal element and has electrical conductivity.

[0225] In this manner, the negative electrode can be fabricated. Therefore, the capacity can be increased, and the power storage device In addition, the negative electrode current collector itself can act as a catalytic element, improving the characteristics of the negative electrode. This method contributes to reducing manufacturing costs and improving productivity by crystallizing the amorphous silicon layer. In addition, in the positive electrode, the material shown in the above embodiment can be used as a positive electrode active material. Therefore, the characteristics of the electricity storage device can be improved from both the negative electrode side and the positive electrode side.

[0226] This embodiment mode can be combined as appropriate with the structures of other embodiment modes and examples.

[0227] (Embodiment 8) In this embodiment, a power storage device having a different structure from that of the above embodiment will be described.

[0228] In this embodiment, a current collector, an active material layer, and a mixed layer of a current collector material and an active material are included. The negative electrode is made up of a metal material for the current collector and a silicon material for the active material for the negative electrode. The mixed layer is a mixed layer of the metal material and the silicon material.

[0229] Silicon materials are used as the active material for the negative electrode. Silicon materials are more economical than carbon materials. Since it is theoretically possible to increase the capacity, it is possible to achieve high capacity and improve the characteristics of the energy storage device. This can be achieved.

[0230] In addition, a mixed layer of the current collector material and the active material is provided between the current collector and the active material layer. Therefore, it is possible to improve the adhesion between the current collector and the active material layer and the ease of electron transfer. Even in this case, the characteristics of the electricity storage device can be improved.

[0231] As the active material for the positive electrode, the material shown in the above embodiment mode is used.

[0232] The structure and manufacturing method of the negative electrode will be described with reference to FIG. The above-mentioned FIG. 14 can be applied, and corresponds to the negative electrode 2211 in FIG.

[0233] An amorphous silicon layer 473 is formed over a negative electrode current collector 471 (see FIG. 19A).

[0234] The negative electrode current collector 471 is made of a conductive material such as titanium, nickel, copper, indium, tin, or silver. Uses sexual materials.

[0235] The amorphous silicon layer 473 may be formed in the same manner as the amorphous silicon layer 413 described above.

[0236] Next, a mixed layer 475 of the current collector material and the active material is formed by heat treatment (see FIG. 19(B)).

[0237] For example, when titanium is used as the negative electrode current collector 471, the mixed layer 475 is made of titanium and silicon. The titanium and silicon mixed layer is a titanium silicide layer. Good too.

[0238] In this heat treatment, the amorphous silicon layer 473 is crystallized to become the negative electrode active material layer 477. A crystalline silicon layer may be formed. The layer 477 and the negative electrode 479 are stacked together (see FIG. 19C).

[0239] 19(B) is performed for the purpose of forming a mixed layer 475. Therefore, if the amorphous silicon layer 473 is not crystallized to the desired crystallinity, the crystallization is continued. In addition, the negative electrode active material layer 477 may be subjected to heat treatment (including laser beam irradiation) for the purpose of improving the thermal conductivity. Alternatively, amorphous silicon or microcrystalline silicon may be used.

[0240] As described above, the negative electrode active material layer 477 is made of amorphous silicon, microcrystalline silicon, or Crystalline silicon can be used. Crystalline silicon is more lithium-ionizable than amorphous silicon. This is preferable because the diffusion rate of the mu ions is fast and this contributes to improving the characteristics of the electricity storage device.

[0241] In this manner, the negative electrode can be fabricated. A mixed layer of the current collector material and the active material is provided between the current collector and the active material layer. The characteristics of the interface between the current collector and the active material layer (adhesion, ease of electron transfer, etc.) have been improved, and the energy storage device In addition, in the positive electrode, the material shown in the above embodiment can be used. As a positive electrode active material, the characteristics of the energy storage device are improved from both the negative and positive electrode sides. It can be done.

[0242] This embodiment mode can be combined as appropriate with the structures of other embodiment modes and examples.

[0243] (Embodiment 9) In this embodiment, an application of a power storage device according to one embodiment of the present invention will be described.

[0244] The power storage device can be installed in a variety of electronic devices, such as digital cameras. Cameras such as video cameras, mobile phones, personal digital assistants, e-book readers, portable games The device can be mounted in a variety of devices, including digital cameras, digital photo frames, and audio playback devices. is an electric vehicle, hybrid vehicle, railroad electric vehicle, work vehicle, cart, wheelchair, or It can be mounted on electric propulsion vehicles such as bicycles.

[0245] A power storage device according to one embodiment of the present invention has improved characteristics, such as a higher capacity and an improved charge / discharge rate. Improving the characteristics of the power storage device will also lead to making the device smaller and lighter. By installing such a power storage device, it is possible to charge electronic devices, electric propulsion vehicles, etc. This allows for shorter operation times, longer usage times, and smaller, lighter designs, improving convenience and design. This can also be achieved.

[0246] 20A shows an example of a mobile phone. The mobile phone 3010 has a housing 301 The housing 3011 further includes an operation button 3013, Operation buttons 3017, external connection port 3014, speaker 3015, and microphone 301 6 and the like. When the power storage device according to one embodiment of the present invention is mounted on such a mobile phone, This improves convenience and design.

[0247] FIG. 20(B) shows an example of an e-book terminal. The e-book terminal 3030 is The device is made up of two housings, a first housing 3031 and a second housing 3033, and the two housings are connected to a shaft portion. The first housing 3031 and the second housing 3033 are integrated by a shaft portion 3032. The first housing 3031 has a first display unit 3032 as an axis. The second housing 3033 has a second display unit 3037 built in. In addition, the second housing 3033 includes an operation button 3039, a power supply 3043, and a speaker. The electronic book terminal is provided with a power storage device according to one embodiment of the present invention. By incorporating this device, convenience and design can be improved.

[0248] FIG. 21A shows an example of an electric vehicle. The electric vehicle 3050 includes a power storage device The power storage device 3051 is equipped with a control circuit 3053. The control circuit 3053 is connected to the computer 305 Controlled by 5.

[0249] The drive unit 3057 is a DC motor or an AC motor alone, or a motor and an internal combustion engine, The computer 3055 controls the operation of the driver of the electric vehicle 3050. Operation information (acceleration, deceleration, stopping, etc.) and driving information (uphill and downhill slopes, etc., information on the driving wheels) Based on input information (load information, etc.), a control signal is output to the control circuit 3053. 3053 is supplied from the power storage device 3051 by a control signal from the computer 3055. It adjusts the electrical energy and controls the output of the drive unit 3057. In this case, an inverter that converts direct current to alternating current is also built in.

[0250] The power storage device 3051 can be charged by external power supply using plug-in technology. By incorporating a power storage device according to one embodiment of the present invention as the power storage device 3051, This can contribute to shortening the charging time and improve convenience. Improving the discharge speed can contribute to improving the acceleration of electric vehicles, and improve the performance of electric vehicles. Furthermore, the improvement in the characteristics of the power storage device 3051 can contribute to the improvement of the performance of the power storage device 3052. If the 051 itself can be made smaller and lighter, it will contribute to reducing the weight of the vehicle, which will also lead to improved fuel efficiency. You can attach it.

[0251] FIG. 21(B) shows an example of an electric wheelchair. The wheelchair 3070 includes a power storage device, The control unit 3073 includes a power control unit, a control means, etc. The power of the power storage device whose power has been adjusted is supplied to the drive unit 3075. is connected to the controller 3077. By operating the controller 3077, The drive unit 3075 can be driven via the drive unit 3073, and the wheelchair 3070 can be driven forward and backward. It is possible to control the speed and movements of the vehicle, such as moving forward and turning.

[0252] The wheelchair 3070's power storage device also uses plug-in technology to supply power from an external source. The power storage device according to one embodiment of the present invention can be mounted as a power storage device. This can contribute to shortening charging time and improving convenience. Furthermore, if the characteristics of the power storage device can be improved to make the device itself smaller and lighter, it will be possible to use a wheelchair 3070 This can improve ease of use for users and caregivers.

[0253] When installing a power storage device on an electric railcar as an electrically propelled vehicle, overhead wires and conductive rails are required. It is also possible to charge the battery using power supplied from the grid.

[0254] This embodiment mode can be combined as appropriate with the structures of other embodiment modes and examples. [Example]

[0255] In this example, a specific example of a power storage device using lithium iron phosphate as a positive electrode active material will be described. A method for producing the same will be described.

[0256] The materials for lithium iron phosphate are lithium carbonate (Li2CO3), iron oxalate (FeC 2O4) and ammonium dihydrogen phosphate (NH4H2PO4) in a first ball mill. Mixed by processing.

[0257] Lithium carbonate is a raw material for lithium incorporation, iron oxalate is a raw material for iron incorporation, and phosphorus Ammonium dihydrogen phosphate is the raw material for introducing phosphate.

[0258] In the first ball mill treatment, acetone was added as a solvent, and the rotation speed was 400 rpm. The test was carried out for 2 hours with a ball diameter of φ3 mm.

[0259] After ball milling, the raw material mixture was mixed to form a 1.47 × 10 2 N (150 kgf) pressure The mixture was then molded into pellets.

[0260] Next, the pelletized mixture was subjected to a first firing. The heating was carried out in a nitrogen atmosphere at 350°C for 10 hours.

[0261] After the first firing, the fired mixture was ground in a mortar.

[0262] Next, glucose was added to the pulverized mixture, and the carbon material was supported on the surface of the mixture. The amount of glucose was varied between 5 wt% and 15 wt%.

[0263] The mixture with added glucose was subjected to a second ball milling treatment. The treatment was carried out by adding acetone as a solvent, rotating at 400 rpm for 2 hours, and using a ball diameter of φ The experiment was carried out under the condition of 3 mm.

[0264] After the second ball milling, the mixture was again formed into pellets, and then a second firing was carried out. The second firing was performed by placing the mixture in a nitrogen atmosphere at 400 to 600°C for 3 to 1 hour. Multiple conditions were performed at 0 hours.

[0265] After the second firing, the fired mixture was ground in a mortar.

[0266] The ground mixture was then subjected to a third ball mill treatment. The third ball mill treatment was Acetone was added as a solvent, and the rotation speed was 300 rpm, the rotation time was 3 hours, and the ball diameter was φ3 mm. So I went.

[0267] The lithium iron phosphate particles obtained as described above were mixed with a conductive additive, a binder, and a solvent. The mixture was mixed and dispersed using a homogenizer. The dispersed material was applied to a positive electrode current collector and dried. The positive electrode active material layer was obtained by the above process. Styrene black, polyvinylidene fluoride as binder, N-methyl-2-pyridinium fluoride as solvent rolidone (NMP) was used.

[0268] The dried material was then pressed and shaped to form a positive electrode. m, and the amount of lithium iron phosphate supported was 3 mg / cm 2 In order to make it By pressing and punching into a circle of φ12 mm, the lithium ion secondary battery The positive electrode was obtained.

[0269] In addition, lithium foil was used as the negative electrode and polypropylene (PP) was used as the separator. The electrolyte is made of lithium hexafluorophosphate (LiPF6) as the solute and ethylene as the solvent. Carbonate (EC) and dimethyl carbonate (DC) were used. The plate was impregnated with the resin.

[0270] In this manner, a coin-shaped lithium battery having a positive electrode, a negative electrode, a separator, and an electrolyte solution was produced. The positive electrode, negative electrode, separator, and electrolyte were assembled in an argon atmosphere. The test was carried out in an atmospheric glove box.

[0271] The preparation conditions for the obtained lithium iron phosphate particle samples A to G are as follows: The various measurement results (surface area, rate characteristics, XRD half-width, and discharge capacity) are shown in Figure 9. The rate characteristics are 10C and 2C discharge tests (constant current / constant voltage drive (CCCV drive)). The capacity ratio indicates the charge / discharge rate. The XRD half-width is measured by X-ray diffraction. The surface area was measured by the BET method. The discharge capacity was measured by a discharge test at a discharge rate of 0.2C and CCCV drive.

[0272] In addition, Figure 9(B) shows the relationship between surface area and rate characteristics (plotted with ○ (white circle)), and The relationship between crystallinity and rate characteristics (plotted with black circles) is shown. The horizontal axis shows the surface area. (m 2 / g), the upper side is the XRD half width (°), and the vertical axis is the rate characteristic (%).

[0273] From FIG. 9(B), it was confirmed that the rate characteristics improved with increasing surface area. The rate characteristic changes linearly (solid line 601). m 2 / g or more 27.5m 2 / g or less, the rate characteristics are good. It can be taken.

[0274] In addition, sample A had a large surface area but a low rate characteristic. This is due to the fact that the amount of glucose added is larger than that of the original sample. It is considered that the crystallinity was reduced. It is confirmed that high rate characteristics can be obtained when the amount of addition is between 5 wt% and 10 wt%. I was able to confirm this.

[0275] Furthermore, in Samples F and G, a significant decrease in rate characteristics was observed. Compared to other samples, the firing temperature is low, which reduces the crystallinity. It is believed that this is the result of

[0276] In addition, as shown in Figure 9(B), there is a maximum value in the crystallinity (XRD half-width) for the rate characteristics. It was confirmed that the XRD half-width was at least 0.13° (dashed line 603). It can be seen that the rate characteristics are good if the angle is within the range of 0.17° upward.

[0277] Furthermore, Figure 9(C) shows the relationship between crystallinity and discharge capacity. It was confirmed that the discharge capacity increased as the half-width decreased. The discharge capacity changes linearly (solid line 605). It can be seen that a large discharge capacity is obtained if the angle is between 0.13° and 0.2°.

[0278] As shown in FIG. 9(A), even if the firing time is shortened, the rate characteristics are high and the discharge A large-capacity power storage device was obtained.

[0279] This embodiment can be implemented in appropriate combination with other embodiment modes and embodiments. [Example]

[0280] In this example, lithium iron silicate was prepared as the lithium oxide and X-ray diffraction was measured. The results will be explained below.

[0281] First, the method for producing the lithium iron silicate for measurement will be described.

[0282] As a material for lithium iron silicate, lithium carbonate (Li2CO3), iron oxalate dihydrate The material (FeC2O4·2H2O) and silicon oxide (SiO2) were first ball milled. The mixture was mixed according to the theory.

[0283] In the first ball mill treatment, acetone was added as a solvent, and the rotation speed was 400 rpm. The test was carried out for 2 hours with a ball diameter of φ3 mm.

[0284] After the first ball milling, the raw material mixture was removed from the pot and heated to 50°C to form the acetate. The raw material mixture was then pelletized in a pellet press to produce 1.47 x 10 2 N( The mixture was molded into pellets by applying a pressure of 150 kgf for 5 minutes.

[0285] Next, the mixture formed into pellets was subjected to a first firing (pre-firing). The heating was carried out in a nitrogen atmosphere at 350°C for 10 hours.

[0286] After the first firing, the fired mixture was ground in a mortar.

[0287] The ground mixture and 10 wt% glucose of the mixture were then subjected to a second ball milling process. The mixture was mixed according to the theory.

[0288] The second ball mill treatment was carried out with acetone added as a solvent, at a rotation speed of 400 rpm, and The test was carried out for 2 hours with a ball diameter of φ3 mm.

[0289] After the second ball milling, the raw mixture was removed from the pot and heated to 50°C to form the acetate. The raw material mixture was then pelletized in a pellet press to produce 1.47 x 10 2 N( The mixture was molded into pellets by applying a pressure of 150 kgf for 5 minutes.

[0290] Next, the mixture formed into pellets was subjected to a second firing (also called a main firing). The firing was carried out in a nitrogen atmosphere at 700°C for 10 hours.

[0291] X-ray diffraction (XRD) of the lithium iron silicate prepared above was The XRD measurement results are shown in Figure 22(A). The results show that the lithium iron silicate has a crystal structure belonging to the space group P1211. was confirmed.

[0292] In addition, in the above-mentioned manufacturing method, the iron silicate was manufactured by setting the second baking temperature at 800°C. The results of X-ray diffraction measurement of tungsten are shown in Figure 22(B). From the results of Figure 22(B), It was confirmed that the prepared lithium iron silicate has a crystal structure belonging to the space group Pmn21. The results in Figure 22(B) show a peak that is thought to be due to elemental iron. The peak is presumably due to the iron contained in the raw material.

[0293] From the above, the crystal structure belonging to the space group P1211 or the crystal structure belonging to the space group Pmn21 It was confirmed that lithium iron silicate having the structure can be produced. By changing the synthesis temperature, the crystal structure belonging to the space group P1211 or the space group Pmn21 It was confirmed that it is possible to create crystal structures belonging to the above group.

[0294] This embodiment can be implemented in appropriate combination with other embodiment modes and embodiments. [Explanation of symbols]

[0295] 101 Active material 103 particles 105 Carbon Materials 107 Particle group 109 Particle layer 201, 205, 207, 501, 601, 605 solid line 203, 207, 503, 603 dashed lines 2200 Energy storage device 2201 Positive electrode 2203 Current collector 2205 Cathode active material layer 2207 Electrolyte 2209 Separator 2211 negative electrode 2213 Current collector 2215 Negative active material layer 2217 Lithium-ion 2219 Electronic 2221 Power supply 2223 Load 411 Negative electrode current collector 413 Amorphous silicon layer 415 Catalytic elements 416 Solution 417 Negative electrode active material layer 418 Conductive Oxides 419 Negative electrode 421 Spinner 451 Negative electrode current collector 453 Amorphous silicon layer 457 Negative electrode active material layer 459 Negative electrode 471 Current Collector 471 Negative electrode current collector 473 Amorphous silicon layer 475 Mixed layer 477 Negative electrode active material layer 479 Negative electrode 1001 lithium atoms 1003 iron atoms 1005 silicon atoms 1007 oxygen atoms 1101 Lithium atom 1103 Iron atoms 1105 silicon atoms 1107 Oxygen atom 1201 Lithium atoms 1203 Manganese atoms 1205 silicon atoms 1207 Oxygen Atoms 1301 Lithium atoms 1303 Cobalt atoms 1305 silicon atoms 1307 Oxygen atoms 3010 Mobile Phones 3011 chassis 3012 Display section 3013 Operation button 3014 External connection port 3015 Speaker 3016 Mike 3017 Operation button 3030 E-book terminal 3031 Housing 3032 Shaft 3033 Housing 3035 Display section 3037 Display section 3039 Operation button 3041 Speaker 3043 Power supply 3050 Electric Vehicle 3051 Electricity storage devices 3053 Control circuit 3055 Computer 3057 Drive Unit 3070 Wheelchair 3073 Control Unit 3075 Drive unit 3077 Controller

Claims

1. The battery has a positive electrode, a negative electrode, and an electrolyte solution, the positive electrode includes a particle group having a plurality of positive electrode active materials and a carbon material that coats a part or all of the particle group, the positive electrode active material contains lithium iron phosphate, the carbon material has a film thickness of 100 nm or less; The discharge capacity of a coin-type lithium ion secondary battery having the positive electrode active material is greater than 146.3 mAh / g and less than or equal to 160 mAh / g. Secondary battery.

2. The battery has a positive electrode, a negative electrode, and an electrolyte solution, the positive electrode includes a particle group having a plurality of positive electrode active materials and a carbon material that coats a part or all of the particle group, the positive electrode active material contains lithium iron phosphate, the carbon material has a film thickness of 100 nm or less; A coin-type lithium ion secondary battery having the positive electrode active material is assembled, and the discharge capacity measured by a CCCV test is greater than 146.3 mAh / g and less than 160 mAh / g. Secondary battery.

3. In claim 1 or claim 2, The positive electrode active material has a particle size of 10 nm or more and 100 nm or less. Secondary battery.

4. In any one of claims 1 to 3, The positive electrode active material has a major axis length of 10 nm or more and 100 nm or less. Secondary battery.

5. In any one of claims 1 to 4, The positive electrode active material has a surface area of ​​10 m as measured by the BET method. ２ / g or more, Secondary battery.

6. In any one of claims 1 to 5, the rate characteristic of the coin-type lithium ion secondary battery having the positive electrode active material satisfies 80% or more; The rate characteristics were calculated by dividing the discharge capacity in a discharge test at a rate of 10C by the discharge capacity in a discharge test at a rate of 2C × 100. Secondary battery.

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