JP2017182949A - Method for manufacturing positive electrode substance material for all-solid battery, and positive electrode active substance material for all-solid battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To use a compound including, as a transition metal M, one of Co and Ni, or both of them, and expressed by LiMPOas a positive electrode active material of an all-solid battery, which is manufactured by a green sheet method.SOLUTION: A method for manufacturing a positive electrode active substance material for an all-solid battery comprises: a mixing step (s1, s2) for weighing and mixing a raw material of a positive electrode active substance consisting of a compound expressed by the chemical formula, LiMPOwhere M includes one of Co and Ni or both of them; a primary baking step (s3) for preliminarily baking a mixture obtained by the mixing step in an ambient atmosphere; a secondary baking step (s5) for baking powder of the mixture after the primary baking step at a temperature higher than that in the primary baking step in an ambient atmosphere; and a pulverizing step (s6) for pulverizing a sintered compact obtained by the secondary baking step. In the secondary baking step, the powder is baked at a temperature of 650-680°C for 20 to 30 hours.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for producing a positive electrode active material used for an all-solid battery and a positive electrode active material produced by the method.

High capacity secondary batteries are used in electric vehicles, portable information terminals, stationary power storage facilities, etc., and the current mainstream of secondary batteries is lithium secondary batteries. As positive electrode active materials for lithium secondary batteries, LiCoO ₂ , LiMn ₂ O _{4 and the} like are known. However, since these positive electrode active materials involve only one Li for one transition metal, they are more expensive. In order to achieve a lithium secondary battery having a capacity, it is necessary to develop a positive electrode layer material including a positive electrode active material exhibiting a so-called “multi-electron reaction” in which a plurality of Lis are involved with one transition metal. Become. And in the positive electrode active material which shows a multi-electron reaction, since several Li contributes to a redox reaction, it operate | moves at a higher potential and high energy density is also obtained with high capacity | capacitance. However, since lithium secondary batteries that are widely used use a flammable organic electrolyte as an electrolyte, safety measures against leakage, short circuit, overcharge, and the like are required more strictly than other batteries. And since the positive electrode active material which shows a multi-electron reaction operate | moves with a high electric potential, it is difficult to use it for the conventional lithium secondary battery using an organic electrolyte solution.

  In recent years, therefore, research and development have been actively conducted on all-solid-state batteries using oxide-based or sulfide-based solid electrolytes as electrolytes. Solid electrolytes are mainly composed of ionic conductors that can conduct ions in solids, and in principle, various problems caused by flammable organic electrolytes occur like conventional lithium secondary batteries. do not do. An all-solid battery is an integrated sintered body (hereinafter referred to as a laminated electrode body) in which a layered solid electrolyte (electrolyte layer) is sandwiched between a layered positive electrode (positive electrode layer) and a layered negative electrode (negative electrode layer). Also has a structure in which a current collector is formed.

Examples of the positive electrode active material for an all solid state battery that can be expected to have the above-mentioned “multi-electron reaction” include, for example, a compound represented by the chemical formula of Li ₂ MP ₂ O ₇ (M is a transition metal). 1 and 2 describe characteristics of Li ₂ FeP ₂ O ₇ (lithium iron pyrophosphate) in which M is Fe. In the above Li ₂ MP ₂ O ₇ , in the compound containing one or both of Co and Ni as the transition metal M, two Li can contribute to the redox reaction for one M on the chemical formula. It is expected as a positive electrode active material having extremely high capacity and energy density.

  In addition, as a manufacturing method of the said laminated electrode body used as the main body of an all-solid-state battery, there exists the method using a known green sheet. Schematically, a slurry-like positive electrode layer material containing a positive electrode active material and a solid electrolyte, a slurry-like negative electrode layer material containing a negative electrode active material and a solid electrolyte, and a slurry-like solid electrolyte layer material containing a solid electrolyte are each sheeted. It is produced by forming a green body (green sheet) and firing a laminated body in which a solid electrolyte layer material green sheet is sandwiched between a positive electrode layer material and a negative electrode layer material green sheet to form a sintered body. In addition, as a method of producing the green sheet of each layer, there is a known doctor blade method. In the doctor blade method, a binder (polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polyvinylidene fluoride (PVDF), acrylic, ethylmethylcellulose, etc.) and a solvent (anhydrous alcohol, etc.) are mixed with ceramic powder such as inorganic oxide. The slurry obtained in this manner is formed into a thin plate by a coating process or a printing process to produce a green sheet. Then, each powder of the positive electrode active material, the solid electrolyte, and the negative electrode active material is used as the ceramic powder to be included in the slurry.

Shin-ichi Nishimura, Megumi Nakamura, Ryuichi Natsui, and Atsuo Yamada, `` New Lithium Iron Pyrophosphate as 3.5V Class Cathode Material for Lithium Ion Battery '', J. Am. Chem. Soc., 2010, 132 (39), pp 13596-13597 Hui Zhou, Shailesh Upreti, Natasha A. Chernova, Geoffroy Hautier, Gerbrand Ceder, and M. Stanley Whittingham, "Iron and Manganese Pyrophosphates as Cathodes for Lithium-Ion Batteries", Chem. Mater., 2011, 23 (2), pp293 -300

As described above, the main method of manufacturing the all-solid-state battery is to sinter a laminated body made of a green sheet to produce a laminated electrode body, which is represented by the above chemical formula Li ₂ MP ₂ O ₇ and is a transition metal. A compound containing one or both of Co and Ni as M is theoretically promising as a positive electrode active material capable of obtaining a high capacity and high energy density, but at present, the compound is an all solid produced by a green sheet method. There has been little study for practical use as a positive electrode active material for batteries. That is, in the process of producing an all-solid-state battery by the green sheet method, a study for pulverizing a sintered body made of a positive electrode active material into a ceramic powder state, a positive electrode active material made of the ceramic powder (hereinafter, No study has been made to reliably sinter green containing a positive electrode active material) and a powdered solid electrolyte as a positive electrode layer in a laminated electrode body by firing.

Therefore, the present invention actually uses a compound represented by Li ₂ MP ₂ O ₇ containing one or both of Co and Ni as the transition metal M as a positive electrode active material of an all-solid battery manufactured by the green sheet method. It aims at providing the manufacturing method of the positive electrode active material material for all-solid-state batteries for enabling it. Another object of the present invention is to provide a positive electrode active material produced by the manufacturing method.

The present invention for achieving the above object is a method for producing a positive electrode active material for an all solid state battery,
A mixing step of weighing and mixing the raw material of the positive electrode active material represented by the chemical formula Li ₂ MP ₂ O ₇ , wherein M in the chemical formula is a compound containing one or both of Co and Ni;
A primary firing step in which the mixture obtained by the mixing step is temporarily fired in an air atmosphere;
A secondary firing step of sintering the powder of the mixture after the primary firing step in an air atmosphere at a temperature higher than the primary firing step;
A pulverizing step of pulverizing the sintered body obtained by the secondary firing step;
Including
In the secondary firing step, firing at a temperature of 650 ° C. to 680 ° C. for a time of 20 hours to 30 hours,
This is a method for producing a positive electrode active material for an all solid state battery.

Further, a positive electrode active material having an average particle diameter of 1 μm or more and 7 μm or less is obtained by executing the pulverization step or the step of pulverizing the pulverized material obtained by the pulverization step. A method for producing a positive electrode active material is preferable. Furthermore, the present invention extends to a positive electrode active material for all solid state batteries produced by the above production method. The positive electrode active material for all solid state batteries is represented by Li ₂ MP ₂ O ₇ and has the chemical formula It is characterized in that a sintered body of the compound having a crystal structure in which M in the inside contains a compound containing one or both of Co and Ni and does not contain a different phase is pulverized into a powder form.

According to the method for producing a positive electrode active material for an all solid state battery of the present invention, a compound represented by Li ₂ MP ₂ O ₇ (M is a transition metal containing one or both of Co and Ni) is used as the positive electrode active material of the all solid state battery. It can be put into practical use as a substance. The positive electrode active material produced by the production method is a ceramic powder containing a positive electrode active material exhibiting a multi-electron reaction, and an all solid state battery including a positive electrode layer containing a positive electrode active material is obtained by a green sheet method. Can be produced. Therefore, an all-solid battery having a large capacity and a high energy density can be provided at low cost.

It is a figure which shows the flow of the manufacturing method of the positive electrode active material material for all-solid-state batteries which concerns on the Example of this invention. It is a figure which shows the relationship between the temperature of the said positive electrode active material material, and a thermal contraction rate.

=== The process of conceiving the present invention ===
As is well known, the sintered body is a polycrystalline material, and the positive electrode active material and the negative electrode active material in the state of ceramic powder in the positive electrode layer and the negative electrode layer (hereinafter also collectively referred to as electrode layer) of the all-solid-state battery. In materials (hereinafter collectively referred to as electrode active material), individual particles constituting the powder are crystallized. When crystallized, it is necessary that the individual particles have the same crystal phase. That is, when a laminate composed of a green sheet of an electrode active material in which different phases are mixed and a green sheet of a solid electrolyte layer is fired and sintered as a laminated electrode body, there is a heterophase interface in the electrode layer of the laminated electrode body. Will exist. And distortion and a defect are easy to generate | occur | produce in a heterophase interface, and sintering property deteriorates. Therefore, the present inventor includes the above-described compound represented by Li ₂ MP ₂ O ₇ (M includes at least one of Co and Ni) in the green sheet in order to use it as the positive electrode active material of the all-solid battery. A study was conducted to make individual particles of the positive electrode active material in a ceramic powder state in phase. In addition, studies were also conducted to further increase the capacity of the all-solid-state battery using the positive electrode active material. And this invention is made | formed as a result of repeating earnest research based on these examination matters.

=== Method for Producing Positive Electrode Active Material ===
As a method for producing a positive electrode active material for an all solid state battery according to an embodiment of the present invention, a procedure for producing a positive electrode active material using lithium cobalt pyrophosphate (Li ₂ CoP ₂ O ₇ , hereinafter also referred to as LCPO) as a positive electrode active material Give up. FIG. 1 shows the flow of the manufacturing procedure. First, (NH ₄ ) ₂ HPO ₄ , Li ₂ CO ₃ , CoC ₂ O ₄ .2H ₂ O are used as raw materials for LCPO, these are weighed in a stoichiometric ratio (s1), and the raw materials are mixed in a magnetic mortar. (S2). The mixture of these raw materials was placed in an alumina crucible, and pre-baked (hereinafter also referred to as primary firing) by heating at a predetermined temperature for 2 hours in the atmosphere (s3). Next, the mixture after primary firing is pulverized in an agate mortar to obtain a calcined powder (s4), and the calcined powder is placed in an alumina crucible and subjected to main firing in an air atmosphere (hereinafter also referred to as secondary firing). Thus, a sintered body was obtained (s5). And the ceramic powder which consists of LCPO obtained by grind | pulverizing the sintered compact with an agate mortar is made into a positive electrode active material material (s6).

  Thus, the manufacturing procedure of the positive electrode active material is substantially the same as that of other positive electrode active materials except that the raw materials are different. However, in the manufacturing method of this example, the temperature and time in the secondary firing step are optimized to control all the particles in the produced positive electrode active material material to have the same crystal phase. Moreover, in view of manufacturing costs, the secondary firing is performed in an air atmosphere instead of a nitrogen atmosphere or the like. That is, there is no need to exhaust the firing furnace or introduce an inert gas into the furnace during the secondary firing. Alternatively, it is possible to use an inexpensive firing furnace that does not have an incidental device necessary for introducing exhaust gas or inert gas. As is well known, the primary firing step (s3) in the above production procedure is performed by firing the raw material at a temperature lower than that of the secondary firing step (s5), thereby removing carbonic acid and nitric acid contained in the raw material, It is to oxidize. That is, the primary firing is premised on the atmosphere. Therefore, according to the manufacturing method of the present embodiment, both primary firing and secondary firing can be performed in an air atmosphere.

<Optimization of secondary firing conditions>
As described above, in the manufacturing method of the present embodiment, the secondary firing step is performed in the air atmosphere, and all the particles in the positive electrode active material are obtained by optimizing the temperature and time in the secondary firing step. It is controlled so as to have the same crystal phase. Therefore, in order to optimize the conditions (temperature, time) in the secondary firing step, the secondary firing step was performed under various conditions in which the temperature and time were changed in the manufacturing procedure shown in FIG. And the crystal structure analysis which used the X ray diffraction method was performed with respect to the sintered compact after the secondary baking.

  Table 1 below shows the relationship between the conditions of the secondary firing step and the results of the crystal structure analysis.

表１に示した結果から、６５０℃以上６８０℃以下の温度で２０時間以上３０時間以下の時間で焼成することで結晶構造に異相がない焼結体が得られることがわかった。したがって本発明の実施例では、この二次焼成条件によって得られた焼結体を粉砕したものを正極活物質材料とすることになる。なお６５０℃未満の温度でも焼成時間を３０時間よりも長くすることで同相の結晶構造が得られる可能性もあるが、闇雲に焼成時間を長くしても製造コストを増大させるだけである。もちろん焼成時間が長ければ焼成後に炉内を冷却させる時間も長くなり製造高ストがさらに嵩むことになる。そこで本発明の実施例では、３０時間以下の時間で二次焼成した際に異相がない結晶構造が得られることを条件として規定した。

From the results shown in Table 1, it was found that a sintered body having no different phase in the crystal structure can be obtained by firing at a temperature of 650 ° C. to 680 ° C. for 20 hours to 30 hours. Therefore, in the Example of this invention, what grind | pulverized the sintered compact obtained by this secondary baking conditions will be used as a positive electrode active material material. Note that even if the firing time is longer than 30 hours even at a temperature lower than 650 ° C., a crystal structure of the same phase may be obtained, but even if the firing time is increased in the dark clouds, only the production cost is increased. Of course, if the firing time is long, the time for cooling the inside of the furnace after firing becomes long, and the manufacturing height is further increased. Therefore, in the examples of the present invention, it is defined as a condition that a crystal structure having no heterogeneous phase can be obtained when the secondary firing is performed for 30 hours or less.

=== About Shrinkage Ratio of Positive Electrode Active Material Material ===
In order to produce an all-solid battery using the cathode active material produced by the production method according to the embodiment of the present invention, a slurry-like cathode layer containing the cathode active material and a powdered solid electrolyte is used. A green sheet is made using the material. That is, the positive electrode layer in the all-solid battery needs to contain a solid electrolyte that does not contribute to the battery capacity in addition to the positive electrode active material. Therefore, in order to obtain a higher-capacity all-solid battery, the positive electrode layer material needs to contain a solid electrolyte that can ensure ionic conductivity and a larger amount of the positive electrode active material. However, in the conventional all solid state battery, the positive electrode active material and the solid electrolyte are contained in the positive electrode layer material in almost the same ratio by mass ratio. If a binder, a solvent, etc. are included, the positive electrode active material in the positive electrode layer material Is less than 50 wt%.

  Accordingly, the present inventor included more positive electrode active material in the positive electrode layer material in parallel with studying the optimum secondary firing conditions for obtaining a powdered electrode active material made of LCPO. In the examination process, the powdered electrode active material made of LCPO shrinks when the slurry-like positive electrode layer material is sintered as the positive electrode layer, and the shrinkage rate is the electrode active material. It was noticed that it changed according to the particle diameter of the particles. That is, in the above manufacturing process, if a contraction rate larger than that of the positive electrode material after the pulverization process is obtained, it was considered that more positive electrode active material can be included in the positive electrode layer material in anticipation of the contraction. Then, electrode active material materials having different average particle diameters were prepared, and the difference in heat shrinkage ratio when sintered was examined. For electrode active material materials having different average particle diameters, an average particle diameter of 1 μm is obtained by crushing an electrode active material material having an average particle diameter of 7 μm manufactured by the above-described manufacturing process in an alcohol medium using a ball mill for a predetermined time. Electrode active material materials adjusted to 2 μm, 3 μm, and 5 μm were obtained. Therefore, together with the electrode active material having an average particle diameter of 7 μm before crushing, five types of electrode active material having different average particle diameters were obtained.

It shows the relationship between the average particle diameter D ₅₀ between disintegration and the electrode active material in Table 2 below.

表２に示したように、解砕時間が長いほど平均粒子径Ｄ_５０が小さくなる。そして１２時間の解砕時間で平均粒子径１μｍの電極活物質が得られた。もちろん、さらに長い時間を掛けて解砕すれば平均粒子径が１μｍ未満の微粉末からなる電極活物質材料も得られる。しかし解砕に長大な時間を掛ければ製造コストが増大する。また微粉末は僅かな気流によって容易に飛沫するので、取り扱いが難しいという問題もある。

As shown in Table 2, average particle diameter D ₅₀ the longer the inter-disintegration becomes smaller. And the electrode active material with an average particle diameter of 1 micrometer was obtained by the crushing time of 12 hours. Of course, an electrode active material made of fine powder having an average particle diameter of less than 1 μm can also be obtained by crushing for a longer time. However, if a long time is taken for crushing, the manufacturing cost increases. In addition, since the fine powder is easily splashed by a slight air flow, there is a problem that handling is difficult.

Next, ₅₀ mg of each of the five types of positive electrode active material having different average particle diameters D ₅₀ was taken out, and the taken out positive electrode active material was subjected to a predetermined pressure (for example, 6 t / cm ² ) to form a pellet. The average particle diameter D ₅₀ of five different pellets of positive electrode active material as a sample was measured for thermal shrinkage rate at each sample in a firing furnace. Here, the heat shrinkage rate of each sample when the temperature in the furnace is raised from 30 ° C. to 700 ° C. at a rate of 100 ° C./h while introducing air into the firing furnace at a flow rate of 100 ml / min Measurements were made using a mechanical analyzer (TMA). FIG. 2 shows changes in the heat shrinkage rate of each sample. FIG. 2 shows the relationship between the elapsed time (h) starting from the temperature rising start time in the firing furnace, the temperature in the firing furnace (° C.), and the measured value (%) of TMA of each sample. . The TMA measurement value indicates the volume change rate (%) of the sample, and when the volume expands, it becomes a numerical value of plus “+” and indicates the thermal expansion coefficient. In the case of contraction, the value is minus “−”, and the absolute value is the thermal contraction rate. And as illustrated, contracts in accordance with the temperature in the firing furnace is increased in each sample, was also confirmed that the average particle diameter D ₅₀ is greater shrinkage smaller the sample.

Of course, it is necessary to prevent heterogeneous crystals from being mixed in the electrode active material in the positive electrode layer even when the laminated electrode body is sintered. That is, it is necessary to sinter the laminated electrode body within the range of the secondary firing conditions in the manufacturing process. And from the time change of the volume change rate of each sample and the time change of the furnace temperature of each sample containing the electrode active material having different average particle diameters D ₅₀ shown in FIG. 2, each sample has a crystal phase in the same phase of 650 ° C. It can be confirmed that the heat shrinkage occurs within a temperature range of 680 ° C. Thus by adjusting the average particle diameter D ₅₀ of the electrode active material to 1μm than 7μm or less, it can be expected to improve the capacity of the all-solid-state battery by using the electrode active material.

=== Other Embodiments ===
In the method for producing a positive electrode active material for an all solid state battery according to an embodiment of the present invention, a positive electrode active material made of LCPO was produced. However, Co and Ni have similar physical properties, and the chemical formula Li _{In 2} MP ₂ O ₇ , even if it is a compound in which M is Ni or a compound containing both Co and Ni as M, it shows a multi-electron reaction in which three Lis move, so that the compound is used as an electrode active material. May be used.

Although the positive electrode active material itself was in a ceramic powder state, zirconia (ZrO ₂ ), alumina (Al ₂ O ₃ ), titanium was formed on the particle surface of the ceramic powder in order to improve the electronic conductivity of the positive electrode active material. lithium acid _{(Li 4 Ti 5 O 12)} , lithium niobate (LiNbO _3), may be coated with a conductive agent such as carbon (C). In order to coat the conductive material on the positive electrode active material, for example, in the production procedure shown in FIG. 1, the powder of the conductive agent is mixed with the powder obtained by the primary firing step (s3), and the mixture is mixed. Secondary firing may be performed.

Note that Li ₂ MP ₂ O ₇ exhibits a high potential of about 5 V with respect to lithium metal. Therefore, at this potential against lithium metal, many of the organic electrolytes used in current non-aqueous electrolyte batteries are oxidatively decomposed. Therefore, at present, the positive electrode active material produced by the method of the above embodiment cannot be used for a lithium ion secondary battery using an organic electrolyte. However, when an electrolytic solution having oxidation resistance is produced in the future, this material can be used for a battery using an organic electrolytic solution. That is, the application range of the present invention is not limited to all solid state batteries, but extends to lithium secondary batteries using an electrolytic solution.

  s2 mixing step, s3 primary firing step, s5 secondary firing step

Claims (3)

A method for producing a positive electrode active material for an all-solid battery,
A mixing step of weighing and mixing the raw material of the positive electrode active material represented by the chemical formula Li ₂ MP ₂ O ₇ , wherein M in the chemical formula is a compound containing one or both of Co and Ni;
A primary firing step in which the mixture obtained by the mixing step is temporarily fired in an air atmosphere;
A secondary firing step of sintering the powder of the mixture after the primary firing step in an air atmosphere at a temperature higher than the primary firing step;
A pulverizing step of pulverizing the sintered body obtained by the secondary firing step;
Including
In the secondary firing step, firing at a temperature of 650 ° C. to 680 ° C. for a time of 20 hours to 30 hours,
This is a method for producing a positive electrode active material for an all solid state battery.   2. The positive electrode active material having an average particle diameter of 1 μm or more and 7 μm or less is obtained by executing the pulverization step or the step of pulverizing the pulverized material obtained by the pulverization step according to claim 1. A method for producing a positive electrode active material for an all solid state battery. A positive electrode active material for all-solid-state battery manufactured by the manufacturing method according to claim 1 or 2, with represented by Li ₂ MP ₂ O _7, one M in the chemical formula of Co and Ni Alternatively, a positive electrode active material for an all-solid-state battery, wherein a sintered body of the compound having a crystal structure containing a compound containing both and having no heterogeneous phase is pulverized into a powder.

Images