JP7179409B2 - Method for manufacturing all-solid-state battery and all-solid-state battery - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing an all-solid-state battery in which all of a positive electrode material, a negative electrode material, and a solid electrolyte material are solid or powder, and to an all-solid-state battery. More specifically, the present invention relates to a method for manufacturing an all-solid-state battery that constitutes a bulk-type battery by sintering, and the all-solid-state battery.

In conventional bulk-type all-solid-state batteries, the cathode material, the anode material, and the electrolyte material interposed between them are all composed of solids and powders. I am trying to make it function as At the time of sintering, the electrode material has sintering conditions of temperature and pressure inherent to the electrode material that does not lose its function as an electrode material and tends to become dense. However, if the pressure and heat exceed these conditions, the powder particles will melt and will no longer function as an electrode material. , will not function as a battery. Therefore, conventional all-solid-state batteries use an electrode material such as NVP (Na ₃ V ₂ (PO ₄ ) ₃ ) that functions as both a positive electrode and a negative electrode, thereby adjusting the sintering conditions for the positive electrode material and the negative electrode material. I am trying to make it compatible. For example, it is composed of a positive electrode and a negative electrode made of NVP (Na ₃ V ₂ (PO ₄ ) ₃ ) and a solid electrolyte of NZSP (Na ₃ Zr ₂ (SiO ₄ ) ₂ PO ₄ ), which is hot-press sintered or spark plasma sintered. Pressure molding is performed while being heated at 900° C. by a sintering plasma method (SPS: Spark Plasma Sintering) (Non-Patent Document 1).

F. Lalere, J.B. Leriche, M. Courty, S. Boulineau, V. Viallet, C. Masquelier, V. Seznec, J. Power Sources, 247, 975-980, 2014.

However, the all-solid-state battery using the same electrode material for the positive electrode and the negative electrode has a problem that the energy density cannot be increased, resulting in a low energy density (see FIG. 8). A higher energy density is desired in order to enable long-term use with a single charge. Therefore, in order to improve the performance of the battery, it is desirable to combine different materials for the positive electrode and the negative electrode. Alternatively, the powder particles may not be densely packed and the battery may fail to function, making it difficult to combine different types of electrode materials.

The present invention is intended to meet such a demand, and an object of the present invention is to provide a method for manufacturing an all-solid-state battery and an all-solid-state battery that enable the combination of different electrode materials for the positive electrode and the negative electrode.

A method for manufacturing an all-solid-state battery for achieving such an object consists of a positive electrode side composite electrode material composed of a positive electrode active material, a solid electrolyte, and a conductive aid, an inorganic solid electrolyte, and a negative electrode active material, a solid electrolyte, and a conductive aid. A step of separately sintering the negative electrode side composite electrode material and the inorganic solid electrolyte under sintering conditions suitable for each to form positive electrode side pellets and negative electrode side pellets, and the inorganic solid electrolyte of the positive electrode side pellets and the negative electrode side pellets. An inorganic adhesive is sandwiched between the inorganic solid electrolyte and the electrode active material having a melting temperature higher than the melting temperature of the inorganic adhesive under pressure and a temperature lower than the temperature at which the electrode active material having a lower melting temperature melts under the applied pressure. and a step of joining and integrating the positive electrode side pellet and the negative electrode side pellet by heating at a temperature.

Here, it is preferable that the positive electrode active material and the negative electrode active material are different materials.

Also, the inorganic adhesive is preferably boric acid, metaboric acid or boron oxide.

Furthermore, a positive electrode side composite electrode material containing NCPP as a positive electrode active material, NZSP as a solid electrolyte, and C as a conductive aid and NZSP as an inorganic solid electrolyte are sintered at 500 ° C. and 255 MPa to form a positive electrode side pellet, A negative electrode side composite electrode material containing NVP as a negative electrode active material, NZSP as a solid electrolyte, and C as a conductive aid and NZSP as an inorganic solid electrolyte are sintered at 900 ° C. and 100 MPa to form a negative electrode pellet, and the positive electrode side. Either boric acid, metaboric acid, or boron oxide is interposed as an inorganic adhesive between the inorganic solid electrolyte surface of the pellet and the inorganic solid electrolyte surface of the negative electrode pellet, and heated at 500° C. and 50 MPa under pressure. Therefore, it is preferable to bond the inorganic solid electrolytes by melting the inorganic adhesive.

Furthermore, in the manufacturing method of the all-solid-state battery of the present invention, it is preferable that the inorganic adhesive is injected as an aqueous solution of boric acid between the inorganic solid electrolyte of the positive electrode pellets and the inorganic solid electrolyte of the negative electrode pellets.

Further, in the all-solid-state battery according to the present invention, a cathode-side composite electrode material composed of a cathode active material, a solid electrolyte, and a conductive aid, and an inorganic solid electrolyte are sintered under sintering conditions suitable for the cathode active material. side pellets, a negative electrode side composite electrode material composed of a negative electrode active material, a solid electrolyte, and a conductive aid, and an inorganic solid electrolyte are sintered under sintering conditions suitable for the negative electrode active material. A negative electrode side pellet, boric acid, metaborate An inorganic adhesive that is any of acid, boron oxide, borax decahydrate, or boron trifluoride is interposed between the inorganic solid electrolyte of the positive electrode pellet and the inorganic solid electrolyte of the negative electrode pellet. It is characterized in that the inorganic solid electrolytes are joined together by being melted under pressure at a temperature lower than the melting point of the electrode material .

According to the method for manufacturing an all-solid-state battery of the present invention, the sintered body (positive electrode pellet/positive electrode layer) of the positive electrode side composite electrode material and the inorganic solid electrolyte, and the sintering of the negative electrode side composite electrode material and the inorganic solid electrolyte. When the aggregate (negative electrode pellet/negative electrode layer) is sintered separately, it is formed into a desired dense shape, and then joined together with an inorganic adhesive to form a dense sintered body. By combining electrode materials with different sintering conditions, an all-solid-state battery can be manufactured by sintering.

1 is a flow chart showing an embodiment of a method for manufacturing an all-solid-state battery of the present invention; FIG. It is an X-ray diffraction pattern for each heating condition of the positive electrode side composite electrode material (NCPP+NZSP+C), NCPP and NZSP. 2 is a charge/discharge curve at 200° C. and C/10 of an all-solid-state battery manufactured by the method for manufacturing an all-solid-state battery of the present invention; (A) shows the discharge capacity (mAh g ^-1 ) under various voltage ranges and C-rates of the same all-solid-state battery, (B) shows the relative discharge capacity (%) of the rate and cycle characteristics. It is a diagram. 4 is an X-ray diffraction pattern of a composite electrode material on the positive electrode side in an all-solid-state battery after a charge-discharge test. Fig. 3 is a graph showing the thermal stability of electrodes under spark plasma sintering; It is an X-ray diffraction pattern when changing the pressurization conditions of the positive electrode side composite electrode material (NCPP + NZSP + C). 1 is a diagram of capacity/voltage charge/discharge curves, rate characteristics, and cycle characteristics showing the performance of an all-solid-state battery in which the positive electrode material and the negative electrode material are made of the same electrode material, manufactured by a conventional all-solid-state battery manufacturing method. (A) is a flowchart for manufacturing an all-solid-state battery in which the positive electrode material and the negative electrode material are composed of different electrode materials by a conventional all-solid-state battery manufacturing method, and (B) is an all-solid-state battery manufactured by the same manufacturing method. (C) is a diagram showing the negative electrode side of an all-solid-state battery manufactured by the same manufacturing method. 10 is a capacity-voltage charge/discharge curve diagram showing the charge/discharge performance of an all-solid-state battery in which a positive electrode material and a negative electrode material are made of different electrode materials, manufactured by the manufacturing method of FIG. 9. FIG.

Hereinafter, the configuration of the present invention will be described in detail based on the embodiments shown in the drawings.

FIG. 1 shows an embodiment of a method for manufacturing an all-solid-state battery according to the present invention. The manufacturing method of this all-solid-state battery consists of separately molding a negative electrode-side pellet 3 composed of a negative electrode material 1 and a solid electrolyte 2 and a positive electrode-side pellet 5 composed of a positive electrode material 4 and a solid electrolyte 2, and firing them appropriately. The inorganic adhesive 6 is sandwiched between the solid electrolyte 2 of the negative electrode pellet 3 and the solid electrolyte 2 of the positive electrode pellet 5, and the inorganic adhesive 6 is applied under pressure. Heating at a temperature above the melting temperature and below the temperature at which the electrode active material with the lower melting temperature melts under applied pressure to melt the inorganic adhesive 6 and join the solid electrolytes 2, 2 together. and a step of joining and integrating the negative electrode side pellet 3 and the positive electrode side pellet 5 by.

The negative electrode material 1 is configured as, for example, a negative electrode side composite electrode material composed of a negative electrode active material, a solid electrolyte, and a conductive aid. Then, the layer of the negative electrode material (hereinafter referred to as the negative electrode side composite electrode layer 1) and the layer of the solid electrolyte 2 are laminated to form a two-layer green compact, which is then sintered to form the negative electrode pellet 3. are integrated. Moreover, the positive electrode material 4 is configured as a positive electrode composite electrode material including, for example, a positive electrode active material, a solid electrolyte, and a conductive aid. Then, the layer of the positive electrode material (hereinafter referred to as the positive electrode side composite electrode layer 4) and the layer of the solid electrolyte 2 are laminated and formed into a two-layer green compact, which is then sintered to form a positive electrode side pellet 5. are integrated.

The solid electrolyte is contained not only in the solid electrolyte layer 2 but also in the electrode layers (composite electrode layers) 1 and 4, and is interposed between the particles of the electrode active material while covering the particle surfaces of the electrode active material. The solid electrolyte expresses ionic conductivity by being crystallized by firing. In the all-solid-state battery of the present embodiment, the positive electrode-side composite electrode material and the negative electrode-side composite electrode material each contain carbon as a solid electrolyte and a conductive aid. Thus, when the positive electrode and the negative electrode contain a solid electrolyte and carbon, high output and long life can be achieved. The formation of a three-dimensional network by the solid electrolyte between the active material particles that make up the positive and negative electrodes dramatically increases the area of the interfaces that serve as contact points between the positive and negative electrode active materials and the solid electrolyte. It is presumed that this is because it becomes possible to expand to , and as a result, a large reduction in interfacial charge transfer resistance can be realized.

The negative electrode-side pellet 3 and the positive electrode-side pellet 5 are separately sintered at a temperature and pressure suitable for densification specific to each electrode material. It is possible to densify the positive electrode material and the negative electrode side material by sintering them at a specific temperature and pressure at which they are easily densified. Then, an inorganic adhesive 6 is sandwiched between the negative electrode pellet 3 and the positive electrode pellet 5, and the inorganic adhesive is melted by heating while pressurizing, and the solid electrolytes of both pellets are bonded to each other. To obtain a structure that ensures conductivity and functions as a battery.

The all-solid-state battery manufactured by the above-described manufacturing method is a combination of positive electrode material and negative electrode material composed of different electrode materials, and is fired separately under sintering conditions that densify the positive electrode material and the negative electrode material inherently. The bonded negative electrode pellet 3 and the positive electrode pellet 5 are bonded to each other by an inorganic adhesive 6 so as to function as a battery. Therefore, electrode materials (composite electrode materials) are not directly bonded to each other with an inorganic adhesive. Therefore, in the production method of the present invention, the selection and combination of electrode materials are not subject to any restrictions, and the pressure and temperature during sintering have optimum conditions unique to the electrode materials, and selection is possible. Needless to say, it is changed as appropriate depending on the electrode material to be used. In addition, the all-solid-state battery according to the present embodiment is a combination of a positive electrode material and a negative electrode material made of different electrode materials, but is not particularly limited to this, and an electrode active material having the same thermal stability That is, it goes without saying that the production method of the present invention can be applied even when the same electrode material is employed.

In the present embodiment, a method for manufacturing an all-solid-state battery will be described in more detail by taking an example of an all-solid-state sodium battery. In the present embodiment, for example, a spark plasma sintering (SPS) apparatus is used to sinter the negative electrode-side pellets 3 and the positive electrode-side pellets 5 and to bond the negative electrode-side pellets 3 and the positive electrode-side pellets 5 together. The explanation will mainly be given with an example of performing. Spark plasma sintering, like hot press sintering (HP), is a type of solid compression sintering method, in which a powder or solid-filled graphite sintering mold is heated while being pressurized. Rapid heating and cooling are possible, and pressurization and rapid heating are expected to produce a dense sintered body that suppresses grain growth.

Here, the all-solid-state sodium battery includes, for example, Na ₄ Co ₃ (PO ₄ ) ₂ (P ₂ O ₇ ) (hereinafter referred to as NCPP) as a positive electrode active material, and Na ₃ V ₂ (PO ₄ ) as a negative electrode active material. ) ₃ (hereinafter referred to as NVP), and Na ₃ Zr ₂ (SiO ₄ ) ₂ PO ₄ (hereinafter referred to as NZSP) as a solid electrolyte. It is preferable that the positive electrode member and the negative electrode member are composed of a compound/composite material of an electrode active material, a solid electrolyte, and carbon (C) as a conductive agent, that is, a composite electrode member. Specifically, the positive electrode side composite electrode member is, for example, a compound of NCPP, NZSP, and C, and the negative electrode side composite electrode member is, for example, a compound of NVP, NZSP, and C.

In addition, the inorganic solid electrolyte is not limited to a specific crystal structure or material, but is not limited to, for example, a lithium ion-based inorganic solid electrolyte and a sodium ion-based inorganic solid electrolyte, NASICON crystal, garnet type crystal structure, A LISICON type crystal structure is mentioned. Among them, it is preferable to use NASICON crystal, which has excellent sodium ion conductivity. Examples of NASICON crystals include Na ₃ Zr ₂ (SiO ₄ ) ₂ PO ₄ and Na ₁ +xZr ₂ SixP ₃ -xO ₁₂ (where x=0 to 3). _Na2 ( _B12H12 ) _0.5 ( _B10H10 ) _0.5 , _{Na11Sn2PS12 , Na3 + 5xP1 - xS4 (} where x = 0 to 3), but Na ₃ Zr ₂ (SiO ₄ ) ₂ PO ₄ (hereinafter referred to as NZSP) is preferably employed. Of course, the solid electrolyte is not limited to NZSP. Solid electrolytes that react with boron include, for example, garnet-type crystal structures and lysicone-type crystal structures. is considered applicable to all solid electrolytes. The positive electrode material, the negative electrode material, and the solid electrolyte of the present embodiment show a suitable example, and are not particularly limited to these combinations.

The mixing ratio of the electrode active material, the solid electrolyte and the conductive carbon of the negative electrode side composite electrode material 1 and the positive electrode side composite electrode material 4 is not limited to a specific ratio, but for example, the electrode active material: Solid electrolyte: carbon=20-70:75-20:5-15 wt % is preferred. In the field of all-solid-state batteries, this numerical value range is a general numerical value in which the empirically expected performance can be obtained. Even if the content is higher than 70 wt %, it is considered that the performance (capacity in this case) is lower than expected. That is, when the ratio of the electrode active material is less than 20 wt %, the battery characteristics tend to deteriorate in terms of energy density characteristics and output density characteristics per unit mass. Also, the conductive aid should be contained in an amount of 5 to 15 wt%, preferably 15 wt%, of the powder of the composite electrode member. If the content of the conductive aid is too small, it tends to be difficult to achieve high capacity and high rate of the electrode mixture. On the other hand, if the content of the conductive aid is too high, the amount of active material per unit mass of the electrode mixture will decrease, and the charge/discharge capacity will tend to decrease. In addition, the inhibition of sintering tends to cut ion conduction paths, resulting in a decrease in charge/discharge capacity and a decrease in discharge voltage. On the other hand, if the ratio of the active material is higher than 70 wt %, the solid electrolyte network in the electrode layer may be broken. Therefore, the respective composite electrode materials for the positive and negative electrodes are appropriately adjusted within the range of the mixing ratio described above. For example, in this embodiment, the positive electrode side composite electrode material is NCPP:NZSP:C=25:60:15 wt. %, and the negative electrode side composite electrode material is NVP:NZSP:C=25:60:15 wt. % mixed.

Then, each composite electrode material and solid electrolyte are sintered at a temperature and pressure suitable for obtaining a dense sintered body peculiar to each electrode material, and dense electrode material pellets 3 and 5 are obtained. For example, in the case of the positive electrode-side pellets 3 of the composite electrode material using NCPP as the positive electrode active material, the sintering is performed at 500° C. and 255 MPa, and in the case of the negative electrode-side pellets 5 of the composite electrode material using NVP as the negative electrode active material, the sintering is performed at 900° C. ℃, sintering at 100 MPa. In this embodiment, the pressure (255 MPa) applied when sintering the positive electrode is the maximum pressure of the pressurizing capability of the device used, and is not necessarily limited to this. Instead, a higher pressure may be applied, or a lower pressure may be applied depending on the case. The sintering conditions described above are merely examples, and are not particularly limited. For example, the conditions for sintering the NCPP composite electrode material (positive electrode) and the inorganic solid electrolyte are that the upper limit of the heating temperature at 255 MPa is 500 ° C., and a sintered body can be obtained even at less than 500 ° C. . For example, in an experiment using Na ₄ Co ₃ P ₄ O ₁₅ as the positive electrode material, the positive electrode was stable even after discharge plasma sintering at 4 kN and 450° C. (see FIG. 6). On the other hand, as a result of conducting an experiment to confirm the change in the XRD pattern by switching the pressure while fixing the temperature in the discharge plasma sintering at 500 ° C., the X-ray diffraction peak was not obtained until the apparatus limit pressure of 20 kN (255 MPa) used. did not disappear and was stable (see FIG. 7). In other words, when the positive electrode was produced, it was not enough to increase the pressure, and it was not possible to make the positive electrode dense unless the temperature was set to the highest possible temperature, such as 500° C., in a range that does not cause melting. 500° C. is one of the preferable upper limit values for forming a positive electrode. However, it is not particularly limited to this, and can be carried out at temperatures up to 500°C. This also applies to the negative electrode.

As described above, sintering at a suitable temperature and pressure specific to the electrode material makes it possible to obtain a denser sintered body than sintering under pressureless conditions. Therefore, the interface between the solid electrolyte and the electrode active material is formed in a good state, and the inorganic solid electrolyte layer is formed between the solid electrolytes in the composite electrode material or between the solid electrolyte in the composite electrode material and the composite electrode material. It is possible to form an all-solid-state battery with a lower internal resistance because the particles between the particles are more dense.

Next, an inorganic adhesive 6 is sandwiched between the solid electrolyte 2 of the negative electrode pellet 3 and the solid electrolyte 2 of the positive electrode pellet 5, which are separately sintered under optimum conditions, and the inorganic adhesive 6 is pressed under pressure. They are integrated by heating and joining at a temperature above the melting point of the electrode material containing the electrode active material with the lower melting temperature, for example, at a temperature below the melting point of the positive electrode material.

Here, as the inorganic adhesive ₆ , an electrode material having a lower melting point, such as a positive electrode material _, can be melted at a temperature lower than that of the positive electrode material to bond the solid electrolytes together. (OH ₃ )), metaboric acid (HBO ₂ ), boron oxide (B ₂ O ₃ ), sodium tetraborate + hydrate (also called decahydrate borax. Na ₂ B ₄ O ₇ -10H ₂ O) , boron trifluoride (BF ₃ ) and the like can be used. Among others, the inorganic adhesive 6 is preferably used in the form of boric acid, metaboric acid or boron oxide, and more preferably as an aqueous solution of boric acid. At the time of the experiment, an attempt was made to use B ₂ O ₃ as the inorganic adhesive. However, as a result of taking out the powder from the reagent bottle and performing X-ray diffraction measurement, it was found that it was not B ₂ O ₃ but a mixture of α and β phases of HBO ₂ as the main component, and a small amount of B(OH ) ₃ was in it. This is presumably because it reacted with water in the air during storage and did not remain as B ₂ O ₃ . In other words, boron oxide (B ₂ O ₃ ) dissolves in water and easily changes to metaboric acid and boric acid. It changes from HBO ₂ (melting point 300° C.) to B ₂ O ₃ (melting point 480° C.). Therefore, whether used in the form of boric acid, metaboric acid or boric oxide _, it is speculated that the chemical form of boron when reacting with the solid electrolyte would probably be _B2O3 .

Although the inorganic adhesive 6 may be used as a powder, it is preferable to dissolve it in water and handle it in the same way as an organic adhesive if it is a material that is easily soluble in water. For example, when boric acid, metaboric acid, or boric oxide is used as the inorganic adhesive, it can be dissolved in water to form an aqueous boric acid solution, which can be applied to the surface of each solid electrolyte. or by injecting it between the solid electrolytes of the negative electrode-side pellet 3 and the positive electrode-side pellet 5, it is possible to disperse and disperse it uniformly in the same manner as an organic solvent. Then, by drying at 100° C. to evaporate water, a thin and uniform boric acid powder film can be easily formed. That is, by pouring the inorganic adhesive dissolved in water or applying it to the surface of each solid electrolyte, it is possible to uniformly disperse the adhesive.

The amount of the inorganic adhesive required for bonding the solid electrolytes of the positive and negative electrodes is desired to be an appropriate amount necessary and sufficient for bonding the two pellets. For example, the amount is such that it is thinly and uniformly dispersed over substantially the entire surface of the solid electrolyte, and is preferably 1.27 mg/cm ² to 12.74 mg/cm ² (in other words, 1 to 10 mg/layer).

The solid electrolyte layer of the positive electrode-side pellet and the solid electrolyte layer of the negative electrode-side pellet can be separated by simply applying pressure while heating to the extent that the electrode material with the lower melting point, such as the positive electrode material, does not melt or lose battery performance. not joined to each other. In other words, the positive electrode pellet and the negative electrode pellet after sintering cannot be joined together without the presence of the inorganic adhesive. Even if an inorganic adhesive was sandwiched between the solid electrolyte layer of the positive electrode-side pellet and the solid electrolyte layer of the negative electrode-side pellet and the solid electrolyte layer was heated to melt the inorganic adhesive, the solid electrolyte layer could not be joined. It is necessary to heat and melt the inorganic adhesive at a temperature lower than that of the electrode material having a lower melting point, such as the positive electrode material, and apply pressure. For example, when boric acid, metaboric acid or boron oxide is used as the inorganic adhesive, it is preferable to apply a pressure of 50 MPa while heating to 500°C. In this case, the inorganic solid electrolytes of the negative electrode-side pellet and the positive electrode-side pellet could be bonded together via the molten boron oxide.

As is clear from FIG. 2, which shows the X-ray diffraction of the positive electrode material, when heating is performed without applying pressure (under atmospheric pressure), the positive electrode material (NCPP) and the solid electrolyte ( NZSP) and diffraction peaks derived from both compositions appear clearly, and it is recognized that the composition is stable. However, it was confirmed that when pressure is applied, even at about 50 MPa, heating at 600° C. causes the peaks derived from the composition of the positive electrode material to disappear, leaving only the diffraction peaks derived from the composition of the solid electrolyte. In other words, it is suggested that the positive electrode material melts and disappears and does not function as an electrode. On the other hand, it was confirmed that diffraction peaks derived from the compositions of both the positive electrode material and the solid electrolyte clearly appeared at 500° C. even under a pressure of 50 MPa. That is, under conditions of 500° C. and 50 MPa, the compositions of both the positive electrode material and the solid electrolyte are stable. From this, it was found that the bonding of the solid electrolytes of the positive electrode pellet and the negative electrode pellet with the inorganic adhesive can be carried out by applying pressure within a temperature range in which the positive electrode material does not melt.

Here, the upper limit of heating in the above-described embodiment is less than the temperature at which the positive electrode side composite electrode material melts under pressurized conditions, for example, 500°C. The positive electrode material was stable up to 500°C under pressurized conditions, but from 550°C the structure of the electrode material began to break down and melted at 600°C. Therefore, under pressure conditions, temperatures up to 500°C are suitable conditions for bonding. However, the temperature is not limited to 500°C, and the melting point of boron oxide is 480°C, and the temperature is further lowered by pressurization. It should be understood that it is possible.

According to experiments by the present inventors, even if boric acid is used as the inorganic adhesive 6 and heated at 200° C. or 300° C., which is higher than the melting point of boric acid, a good bonding state cannot be obtained. Moreover, when heated at 200° C. to 300° C., there is concern that HBO ₂ or boron oxide remains in the form and returns to boron hydroxide to separate the positive electrode pellet and the negative electrode pellet. On the other hand, if pressure is applied while heating to a temperature higher than the melting point of boron oxide, at which the positive electrode member does not melt, and as high as possible, for example, up to 500° C., it reacts with the solid electrolyte and functions irreversibly as an adhesive. I found out. Specifically, the inventors have found that by applying pressure while heating at 500° C. and 50 MPa, the solid electrolytes of the positive electrode-side pellet and the negative electrode-side pellet having the composition described above can be bonded together to function as a battery. In the XRD pattern at this time, it was confirmed that the diffraction peak of B ₂ O ₃ did not exist and disappeared (in other words, boron oxide reacted with the solid electrolyte, and in the form of B ₂ O ₃ I don't think there are any left). From this, it is considered that the situation is such that B ₂ O ₃ cannot exist under the same conditions. There are two possibilities for the disappearance of the diffraction line of B ₂ O ₃ : reaction with the solid electrolyte, or B ₂ O ₃ becoming amorphous. In neither case is the diffraction line of B ₂ O ₃ visible. It is known that NZSP having a Nasicon-type crystal structure, and other solid electrolytes having a garnet-type crystal structure or a lysicone-type crystal structure react with boron oxide (B ₂ O ₃ ). It is believed that when the solid electrolyte and boron oxide (boron oxide) react with each other, boron enters the crystal structure of the solid electrolyte and replaces any element, or changes to a crystal structure different from the parent structure. On the other hand, when B ₂ O ₃ is amorphized, it is amorphized regardless of the solid electrolyte, so it is considered applicable to all solid electrolytes. In any case, the change in the chemical form of the inorganic adhesive (dissolution/solidification reaction or chemical reaction with the solid electrolyte) is used to bond the positive electrode layer and the negative electrode layer, and to function as a battery. was confirmed.

As described above, since the positive electrode material and the negative electrode material are separately sintered at temperatures and pressures suitable for each, it is possible to obtain a dense sintered body. Therefore, the interface between the solid electrolyte and the electrode active material is formed in a good state, and the inorganic solid electrolyte layer is formed between the solid electrolytes in the composite electrode material or between the solid electrolyte in the composite electrode material and the composite electrode material. It is possible to form an all-solid-state battery with a lower internal resistance because the particles between the particles are more dense.

Moreover, the bonding of the positive electrode pellet and the negative electrode pellet with the inorganic adhesive enables the use of the all-solid-state battery in a relatively high temperature environment, for example, about 200° C. (see FIG. 3). Using an all-solid-state battery in a relatively high-temperature environment reduces the resistance of the all-solid-state battery and enables smooth charging and discharging. Of course, the all-solid-state battery of the present embodiment can be charged and discharged at temperatures below the above temperature. For example, according to experiments conducted by the present inventor, it was possible to charge and discharge even at 70°C.

Although the above embodiment is an example of the preferred embodiment of the present invention, the present invention is not limited to this, and can be modified in various ways without departing from the gist of the present invention. For example, in the above-described embodiment, an example of sintering the negative electrode-side pellet 3 and the positive electrode-side pellet 5 and joining the negative electrode-side pellet 3 and the positive electrode-side pellet 5 using a discharge plasma sintering device is mainly given. Although explained, it is not particularly limited to this, and depending on the case, hot pressing (HP), hot isostatic pressure sintering (HIP), and gas pressure sintering can also be used.

In addition, in the present embodiment, an example in which an all-solid-state sodium battery was implemented was mainly described, but it is not particularly limited to this, and can be applied to other all-solid-state batteries such as all-solid-state lithium batteries. It goes without saying that this is possible. That is, in the production method of the present invention, positive electrode side pellets and negative electrode side pellets made of a powdery composite electrode material and an inorganic solid electrolyte material are separately sintered under the optimum sintering conditions for each to form them. The solid electrolytes of these two pellets are bonded together with an inorganic adhesive to function as a battery, and the electrode materials are not directly bonded together with an inorganic adhesive. Therefore, it goes without saying that the manufacturing method of the present invention is applicable to various combinations of electrode materials regardless of the electrode material. Therefore, since the sintering pressure and temperature conditions for obtaining a dense sintered body are specific to the electrode material, the sintering pressure and temperature given in the embodiments are absolute. No meaning. Also, regarding the pressure and temperature conditions when the solid electrolytes of both pellets are bonded together with the inorganic adhesive, it is desirable that the inorganic adhesive reacts with the solid electrolyte and functions irreversibly as an adhesive. It is preferable to set the temperature as high as possible, but since the temperature must be lower than the melting temperature of the electrode material, it depends on the electrode active material employed. In other words, the numerical values given in this specification are merely examples, and the bonding pressures and temperatures given in the embodiments have no absolute significance.

An all-solid-state battery made by sintering a positive electrode and a negative electrode under specific optimum conditions necessary to obtain a dense sintered body, and then bonding them with an inorganic adhesive, is produced by applying different heat to the positive electrode and the negative electrode. It becomes possible to adopt a stable electrode active material. Of course, the same thermally stable electrode active material, that is, the same electrode material may be employed, but it is possible to combine electrode materials that can further improve the performance as an all-solid-state battery.

On the other hand, in the above-described embodiments, in order to realize an all-solid-state battery exhibiting high chemical and thermal stability, an example in which an oxide solid electrolyte (a NASICON-type oxide crystalline electrolyte) is used is mainly described. However, it is not particularly limited to this, and other oxide solid electrolytes or sulfide glass-based solid electrolytes may be used.

A bulk-type all-solid-state sodium battery was produced by the following method, and the result of verifying the battery performance is shown.
First, a negative electrode material, a positive electrode material, and a solid electrolyte material were synthesized. For example, the negative electrode active material for the negative electrode layer is Na ₃ V ₂ (PO ₄ ) ₃ (so-called NVP), and the positive electrode active material for the positive electrode layer is Na ₄ M ₃ (PO ₄ ) 2P ₂ O ₇ (so-called NCPP). , and Na ₃ Zr ₂ (SiO ₄ ) 2PO ₄ (so-called NZSP) was used as a solid electrolyte material. For example, V ₂ O ₃ and NaH ₂ PO ₄ are mixed at a ratio of 1:3 (molar ratio) and fired at 900° C. for 20 hours in an argon-hydrogen (hydrogen: 5% by volume) atmosphere. was pulverized to obtain a material powder of an electrode active material represented by Na ₃ V ₂ (PO ₄ ) ₃ (hereinafter also simply referred to as “NVP material powder”). In addition, nitric acid M hydrate (M = Co, Ni, Mn, Fe), NaNO3, and _NH4H2PO4 were mixed at a ratio of ₃ : ₄ : ₄ (molar ratio) and heated at 700°C for 24 hours in an air atmosphere. After sintering, the obtained sintered product is pulverized to obtain a material powder of an electrode active material represented by Na ₄ M ₃ (PO ₄ ) 2P ₂ O ₇ (hereinafter also simply referred to as “NCPP material powder”). rice field.
Furthermore, the solid electrolyte obtained a precursor solution by the Sol-Gel method. The resulting precursor solution was hydrolyzed to gel and allowed to stand for one day to age the gel, followed by drying at 120° C. for 24 hours. After that, it was ground and calcined at 750° C. for 5 hours to obtain a precursor powder. The obtained powder was sintered at 1000° C. for 5 hours to obtain a solid electrolyte material powder (hereinafter simply referred to as “NASICON material powder”) whose composition is represented by Na3Zr2(SiO4)2(PO4). The solid electrolyte used in this example did not contain impurities that inhibit ion conduction.

In this embodiment, the negative electrode layer and the positive electrode layer are configured as composites of negative electrode active materials, positive electrode active materials, solid electrolytes, and conductive graphite, that is, composite electrode materials. The composition of the composite electrode material and the mixing ratio of the cell structure are as follows.
(Mixing ratio of cell configuration)
a) Negative side composite electrode material (NVP: NZSP: C = 25: 60: 15 wt.%) 40 mg
b) Inorganic solid electrolyte material (NZSP) 150 mg
c) Inorganic adhesive ( _HBO2 ) 1mg
d) Inorganic solid electrolyte material (NZSP) 150 mg
e) Positive side composite electrode material (NCPP: NZSP: C = 25: 60: 15 wt.%) 20 mg
(Sintering device)
Spark plasma sintering device (HP D 10 from FCT Systeme GmbH, Germany)

Procedure 1) After weighing 250 mg of the electrode active material, 600 mg of the inorganic solid electrolyte, and 150 mg of carbon, the three different materials were mixed for 30 minutes using a mortar and pestle to obtain composite electrode materials for the positive and negative electrodes.
Step 2) Using a discharge plasma sintering device, prepare green pellets of the inorganic solid electrolyte for the positive electrode and the inorganic solid electrolyte for the negative electrode. That is, the molding die of the discharge plasma sintering device (
150 mg of inorganic solid electrolyte is put into a container (inner diameter: 10 mm), and a disk-shaped compact (green pellet) is formed. Here, the inner peripheral surface of the molding die is covered with carbon paper so as not to damage the sintering jig during energization and sintering. By the way, step 1
The solid electrolyte in step 2) and the inorganic solid electrolyte in step 2) are the same material, and NZSP, for example, is used for both.
Step 3) Weigh 20 mg of the positive electrode composite electrode material and 40 mg of the negative electrode composite electrode material, put them on the solid electrolyte green pellets in the mold of the discharge plasma sintering equipment, and press again. Press to form pellets.
Step 4) Place carbon paper (a carbon sheet that serves as a current collector) on the composite electrode material of each green pellet of the positive and negative electrodes.
Step 5) Conditions for densification by sintering specific to each active material in the spark plasma sintering device,
By sintering at temperature and pressure, pellets of the composite electrode material on the positive electrode side and the solid electrolyte (hereinafter referred to as positive electrode material pellets) and pellets of the composite electrode material on the negative electrode side and the solid electrolyte (hereinafter referred to as negative electrode material pellets) made. The conditions for discharge plasma sintering are 500°C and 255 MPa for 5 minutes for positive electrode material pellets, and 900°C and 100 MPa for 2 minutes for negative electrode material pellets.
Step 6) Lower the temperature of the positive electrode material pellet and the negative electrode material pellet to room temperature, and attach an appropriate amount of inorganic adhesive to the solid electrolyte side of each pellet. In the case of this embodiment, a diameter of 10 mm
1 mg (1.27 mg/
cm ² ). Specifically, 50 µL of boric acid aqueous solution (1 wt%) was applied to the surface of the solid electrolyte and dried at 100°C to form a thin and uniform boric acid film of about 1 mg on the surface of the solid electrolyte. did.
Step 7) In a state in which the positive electrode material pellet and the negative electrode material pellet are combined so that the solid electrolyte sides face each other (a state in which an inorganic adhesive is interposed between the inorganic solid electrolytes of both pellets), a discharge plasma is generated. With a sintering device, 500 for 2 minutes while applying a pressure of 50 MPa
°C. As a result, the inorganic adhesive between the solid electrolyte of the positive electrode material pellet and the solid electrolyte of the negative electrode material pellet was melted and reacted with the solid electrolyte to join the solid electrolytes together. From the X-ray diffraction measurement after mixing and sintering the dissimilar materials, the dissimilar materials are joined under temperature and pressure conditions that do not generate impurities. However, vitrification of the electrode material occurred when the conditions were not met. On the other hand, the solid electrolyte was stable.
Step 8) After removing the all-solid-state battery from the mold of the discharge plasma sintering equipment, the carbon paper on the side of the battery was removed.

A bulk-type all-solid-state sodium battery with a diameter of 10 mm and a length of 4.2 mm was manufactured according to the above procedures 1) to 8). The breakdown of the thickness of the bulk-type all-solid-state sodium battery is as follows: 1mm carbon sheet as current collector, 400μm negative electrode composite electrode material, NZSP 800μm, NZSP 800μm, positive electrode composite electrode material 200μm, 1mm carbon sheet as current collector. there were.

FIG. 3 shows the charge/discharge cycle of the all-solid-state sodium battery manufactured as described above. As is clear from this figure, as a result of conducting charge-discharge tests under various voltage ranges, the all-solid-state sodium battery of this example was charged and discharged normally, and even after repeated charge-discharge cycles, the capacity remained unchanged. It turned out that there was no abrupt drop. In other words, it is considered that the battery functions as an all-solid-state sodium battery and that the battery performance is stable. Furthermore, compared to the output in the case of a bulk type all-solid-state sodium battery manufactured by the conventional manufacturing method (see FIG. 8), the performance was improved (40 to 50% increase from 1.5 V to over 2 V). It was suggested that improvement is expected.

FIG. 4 shows the results of actual charging and discharging. FIG. 4 shows charge-discharge performance showing the relationship between discharge capacity (mAh g ⁻¹ ) and related discharge capacity (%) for all-solid-state batteries under various voltage ranges and C-rates. By varying the charge/discharge voltage range, we obtained the result that the capacity increased depending on the voltage. The dependence of the C rate (Capacity rate) on how it changes when charging/discharging with a small current or charging/discharging with a large amount of charge was investigated. The performance when charging and discharging for 10 hours was better than that of a conventional all-solid-state battery in which the positive and negative electrodes were integrally sintered at 500°C. In addition, it was found that charging and discharging can be performed in the case of charging and discharging over 3 hours, although the rate is about 20%, which is lower than in the case of the 10 hour rate.

FIG. 5 shows the X-ray diffraction pattern of the composite electrode material on the positive electrode side in the all-solid-state battery after the charge-discharge test. As a result, it was found to be stable even when the voltage was raised to a high voltage of 3.9V.

From the above experiments, it was confirmed that the all-solid-state battery in which the NCPP positive electrode pellet and the NVP negative electrode pellet manufactured by the manufacturing method of the present invention are bonded with boron oxide functions as a battery. Specifically, the all-solid-state sodium battery operated at 200°C and showed 70 mAh/g.

(Comparative example 1)
A case where an all-solid-state battery having the following cell configuration, in which different electrode materials are used for the positive electrode and the negative electrode, was manufactured by the conventional manufacturing method shown in FIG. 9 was examined.
a) Negative side composite electrode material (NVP: NZSP: C = 25: 60: 15 wt.%) 40 mg
b) Inorganic solid electrolyte material (NZSP) 150 mg
c) Positive electrode side composite electrode material (NCPP: NZSP: C = 25: 60: 15 wt.%) 20 mg
That is, as shown in FIG. 9, a negative electrode composite 101 containing a negative electrode active material and a solid electrolyte, a positive electrode composite 102 containing a solid electrolyte 103 and a positive electrode active material and a solid electrolyte are laminated in this order and sandwiched. An attempt was made to fabricate an all-solid-state battery by sintering at once at 500° C. and 255 MPa at which the positive electrode active material does not melt. Even if the sandwich structure was sintered under sintering conditions suitable for positive electrode materials, such as 500° C. and 255 MPa, the negative electrode did not solidify densely. Therefore, the positive electrode side composite electrode material 102 adhered to the solid electrolyte 103, but 75 to 80% (30 to 32 mg) of the negative electrode side composite electrode material 101 was peeled off. A battery comprising a sintered body of a portion (8 to 10 mg) of the negative electrode composite electrode material 101, the solid electrolyte 103, and the positive electrode composite electrode material 102 was obtained. This all-solid-state battery did not function stably as a battery, as shown in FIG. The battery was charged more than the theoretical value only once at startup, but could not be charged from the second time.

REFERENCE SIGNS LIST 1 negative electrode side composite electrode material 2 fixed electrolyte 3 negative electrode side pellet 4 positive electrode side composite electrode material 5 positive electrode side pellet 6 inorganic adhesive

Claims (6)

A positive electrode side composite electrode material and an inorganic solid electrolyte consisting of a positive electrode active material, a solid electrolyte and a conductive aid, and a negative electrode side composite electrode material and an inorganic solid electrolyte consisting of a negative electrode active material, a solid electrolyte and a conductive aid are sintered respectively. A step of separately sintering under a binding condition to form a positive electrode side pellet and a negative electrode side pellet;
An inorganic adhesive is sandwiched between the inorganic solid electrolyte of the positive electrode-side pellet and the inorganic solid electrolyte of the negative electrode-side pellet, and the one having a melting temperature higher than the melting temperature of the inorganic adhesive under pressure and a lower melting temperature joining and integrating the positive electrode side pellet and the negative electrode side pellet by heating at a temperature below the temperature at which the electrode active material melts under the applied pressure.
A method for manufacturing an all-solid-state battery, characterized by: 2. The method of manufacturing an all-solid-state battery according to claim 1, wherein the positive electrode active material and the negative electrode active material are different materials. 3. The method for manufacturing an all-solid-state battery according to claim 1, wherein said inorganic adhesive is boric acid, metaboric acid or boron oxide. The positive electrode side composite electrode material containing NCPP as the positive electrode active material, NZSP as the solid electrolyte, and C as the conductive aid, and NZSP as the inorganic solid electrolyte are sintered at 500 ° C. and 255 MPa to form the positive electrode pellet. molding the
The negative electrode side composite electrode material containing NVP as the negative electrode active material, NZSP as the solid electrolyte, and C as the conductive aid, and NZSP as the inorganic solid electrolyte are sintered at 900 ° C. and 100 MPa to form the negative electrode pellet. molding the
Between the inorganic solid electrolyte surface of the positive electrode pellet and the inorganic solid electrolyte surface of the negative electrode pellet, boric acid, metaboric acid, or boron oxide is interposed as the inorganic adhesive, and 2. The method for manufacturing an all-solid-state battery according to claim 1, wherein the inorganic adhesive is melted and the inorganic solid electrolytes are bonded together by heating while applying pressure of 50 MPa. 5. The all-solid-state battery according to claim 4, wherein the inorganic adhesive is injected as an aqueous solution of boric acid between the inorganic solid electrolyte of the positive electrode-side pellet and the inorganic solid electrolyte of the negative electrode-side pellet. Production method. a positive electrode-side pellet obtained by sintering a positive electrode-side composite electrode material composed of a positive electrode active material, a solid electrolyte, and a conductive aid, and an inorganic solid electrolyte under sintering conditions suitable for the positive electrode active material;
a negative electrode-side pellet obtained by sintering a negative electrode-side composite electrode material composed of a negative electrode active material, a solid electrolyte, and a conductive aid, and an inorganic solid electrolyte under sintering conditions suitable for the negative electrode active material;
An inorganic adhesive that is any one of boric acid, metaboric acid, boron oxide, borax decahydrate, or boron trifluoride is the inorganic solid electrolyte of the positive electrode-side pellet and the inorganic solid electrolyte of the negative electrode-side pellet. The inorganic solid electrolytes are joined together by being melted at a temperature below the melting point of the electrode material under pressure between
An all-solid-state battery characterized by:

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