JP6777181B2 - Lithium ion secondary battery - Google Patents

Description

The present invention relates to a lithium ion secondary battery.

In recent years, the development of electronics technology has been remarkable, and portable electronic devices have been made smaller and lighter, thinner, and more multifunctional. Along with this, there is a strong demand for batteries that are power sources for electronic devices to be smaller and lighter, thinner, and more reliable, and all-solid-state lithium-ion secondary batteries made of solid electrolytes are attracting attention.

Generally, all-solid-state lithium-ion secondary batteries are classified into two types, a thin film type and a bulk type. The thin film type is produced by thin film technology such as PVD method and sol-gel method, and the bulk type is produced by powder molding of an active material or a sulfide-based solid electrolyte having low grain boundary resistance. However, the thin film type has a problem that the capacity is small and the manufacturing cost is high because it is difficult to make the active material layer thick and to make it highly laminated. On the other hand, a sulfide-based solid electrolyte is used for the bulk type, and hydrogen sulfide is generated when this reacts with water. Therefore, it is necessary to manufacture the battery in a glove box with a controlled dew point. In addition, since it is difficult to form a sheet, thinning of the solid electrolyte layer and high stacking of batteries have become issues.

In view of such a problem, in Patent Document 1, using an oxide-based solid electrolyte stable in the air, each member is made into a sheet, laminated, and then fired at the same time, which can be mass-produced industrially. An all-solid-state battery manufactured by a manufacturing method has been proposed. However, since different materials are fired at the same time, it is difficult to firmly bond the positive electrode layer, the negative electrode layer, and the solid electrolyte layer.

Therefore, in Patent Document 2, a multilayer all-solid-state lithium ion secondary battery composed of a laminate in which a positive electrode layer containing a positive electrode active material and a negative electrode layer containing a negative electrode active material are laminated via an electrolyte layer containing a solid electrolyte. In the above, an intermediate layer made of a substance that functions as an active material or an electrolyte is provided at the interface between the positive electrode layer and / or the negative electrode layer and the electrolyte layer, and the intermediate layer is a positive electrode active material and / or a negative electrode active material and a solid electrolyte. A lithium ion secondary battery has been proposed, characterized in that is a layer formed by reaction and / or diffusion. However, if the intermediate layer is formed on the solid electrolyte side, there is a high possibility that a short circuit will occur, which poses a problem from the viewpoint of reliability.

Special Reissue 07-135790 Japanese Patent No. 4797105

The present invention has been made to solve the above-mentioned conventional problems, and an object of the present invention is to provide a highly reliable lithium ion secondary battery having low internal resistance.

In order to solve the above problems, the lithium ion secondary battery according to the present invention is a lithium ion secondary battery having a solid electrolyte layer between a pair of electrodes, wherein the solid electrolyte layer contains titanium aluminum lithium phosphate, and the pair. At least one of the electrodes of the above electrode contains lithium vanadium phosphate, and at least one of the pair of electrodes contains one or both components of titanium and aluminum. The component is characterized in that it is present in a smaller amount on the opposite side of the solid electrolyte layer side than on the opposite side.

According to such a configuration, titanium or aluminum is optimally arranged in the positive electrode active material layer or the negative electrode active material layer, and the components are distributed in different shades, and are farther from the solid electrolyte layer than the side closer to the solid electrolyte layer. Since the component is less present on the side, not only the internal resistance is reduced, but also a highly reliable lithium ion secondary battery can be provided.

The lithium ion secondary battery according to the present invention is a lithium ion secondary battery having a solid electrolyte layer between a positive electrode layer and a negative electrode layer, wherein the positive electrode layer is composed of a positive electrode current collector layer and a positive electrode active material layer. The negative electrode layer is composed of a negative electrode current collector layer and a negative electrode active material layer, and the solid electrolyte layer provided between the positive electrode active material layer and the negative electrode active material layer contains titanium aluminum lithium phosphate and the positive electrode active material. One or both of the layer and the negative electrode active material layer contains lithium vanadium phosphate, and one or both of titanium and aluminum are contained, and titanium or aluminum contained in the positive electrode active material layer or the negative electrode active material layer. Is more abundant on the current collector side than on the solid electrolyte layer side.

According to such a configuration, titanium or aluminum is optimally arranged in the positive electrode active material layer or the negative electrode active material layer, and the components are distributed with shades, and the positive electrode current collector layer side or the negative electrode current collector layer side is more than the solid electrolyte layer side. Since the component is less present on the negative electrode current collector layer side, it is possible to provide a highly reliable lithium ion secondary battery as well as a decrease in internal resistance.

In the above invention, it is preferable that the titanium aluminum lithium phosphate is Li _{1 + x} Al _x Ti _2-x (PO ₄ ) ₃ (0 ≦ x ≦ 0.6).

According to such a configuration, a short circuit of the lithium ion secondary battery can be suppressed, and the reliability is further improved.

Further, in the above invention, it is preferable that lithium vanadium phosphate is one or both of LiVOPO ₄ and Li ₃ V ₂ (PO ₄ ) ₃ .

According to such a configuration, a short circuit of the lithium ion secondary battery can be suppressed, and the reliability is further improved.

Further, in the above invention, it is preferable that the positive electrode current collector layer and the negative electrode current collector layer contain Cu.

According to the present invention, since the materials constituting the positive electrode current collector layer and the negative electrode current collector layer do not react with titanium aluminum lithium phosphate, it is further effective in reducing the internal resistance of the lithium ion secondary battery. ..

According to the lithium ion secondary battery according to the present invention, a solid electrolyte layer is provided between the positive electrode layer and the negative electrode layer, the positive electrode layer is composed of a positive electrode current collector layer and a positive electrode active material layer, and the negative electrode layer is The solid electrolyte layer composed of a negative electrode current collector layer and a negative electrode active material layer and provided between the positive electrode active material layer and the negative electrode active material layer contains titanium aluminum lithium phosphate, and the positive electrode active material layer and the above. One or both of the negative electrode active material layers contain lithium vanadium phosphate, and one or both of titanium and aluminum are diffused into the lithium vanadium phosphate.

According to the lithium ion secondary battery according to the present invention, one or both components of titanium and aluminum are diffused and bonded to lithium vanadium phosphate, so that the positive electrode active material layer and the negative electrode active material containing lithium vanadium phosphate are bonded. The bond at the interface between the layer and the solid electrolyte layer is strengthened. At the same time, the interfacial resistance is reduced, and the internal resistance of the lithium ion secondary battery can be reduced. Further, since lithium vanadium phosphate does not diffuse into the solid electrolyte layer, a short circuit of the lithium ion secondary battery can be suppressed and reliability is improved.

According to the present invention, it is possible to provide a lithium ion secondary battery having low internal resistance and high reliability.

FIG. 1 is a cross-sectional view showing a conceptual structure of a laminated body portion of a lithium ion secondary battery. FIG. 2 is an EPMA-WDS element mapping of the cross section of the laminate of Example 1-2. FIG. 3 is a secondary electron image of the cross section of the laminated body of Example 1-2.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. The present invention is not limited to the following embodiments. In addition, the components described below include those that can be easily assumed by those skilled in the art and those that are substantially the same. Further, the components described below can be combined as appropriate.

(Structure of lithium ion secondary battery)
FIG. 1 is a cross-sectional view showing a conceptual structure of the lithium ion secondary battery 10 according to an example of the present embodiment. In the lithium ion secondary battery 10 of the present embodiment, a positive electrode layer 1 and a negative electrode layer 2 are laminated as a pair of electrodes via a solid electrolyte layer 3, and the positive electrode layer 1 is a positive electrode current collector layer 4 and a positive electrode. It is composed of an active material layer 5, and the negative electrode layer 2 is composed of a negative electrode current collector layer 6 and a negative electrode active material layer 7.

Further, the solid electrolyte layer 3 contains titanium aluminum lithium 8 phosphate, and one or both of the positive electrode active material layer 5 and the negative electrode active material layer 7 contains vanadium lithium phosphate 9. In FIG. 1, both the positive electrode active material layer 5 and the negative electrode active material layer 7 contain vanadium lithium phosphate 9, but it may be contained in either one. Further, in FIG. 1, an example in which the same number is assigned and the same material is used is shown. Of course, not limited to this, it is not necessary to use exactly the same material.
In addition, as a description in the following specification, either one or both of the positive electrode active material and the negative electrode active material are collectively referred to as an active material, and either or both of the positive electrode active material layer 5 and the negative electrode active material layer 7 are collectively referred to. The active material layer is generically referred to, and either or both of the positive electrode and the negative electrode may be generically referred to as an electrode.

Prior to sintering, one or both components of titanium and aluminum constituting the titanium-aluminum-lithium 8 phosphate are not diffused into the vanadium-lithium phosphate 9. Therefore, the bonding strength is weak and the contact area is also small. On the other hand, after sintering, one or both components of titanium and aluminum constituting the titanium aluminum lithium phosphate 8 are diffused and bonded to the vanadium lithium phosphate 9 contained in the positive electrode active material layer 5 and the negative electrode active material layer 7. Therefore, a strong bond is formed. At the same time, the contact area between the positive electrode active material layer 5 and the negative electrode active material layer 7 and the solid electrolyte layer 3 is increased, and the internal resistance of the lithium ion secondary battery 10 is reduced. Further, since vanadium of lithium vanadium phosphate 9 does not diffuse into lithium titanium-aluminum phosphate 8, short-circuiting of the lithium ion secondary battery 10 can be suppressed, and reliability is improved.

According to the present embodiment, since the vanadium of the vanadium lithium phosphate 9 does not diffuse into the titanium aluminum lithium phosphate 8, one or both components of titanium and aluminum of the titanium aluminum lithium phosphate 8 are positively phosphorus. A strong bond can be formed by being diffused in the vanadium lithium acid 9.

Whether or not the diffusion of titanium and aluminum present in one or both of the positive electrode active material layer 5 and the negative electrode active material layer 7 is the titanium and aluminum contained in the solid electrolyte layer 3 is determined by the lithium ion secondary battery 10. The cross section can be elementally mapped by the energy dispersive X-ray spectroscope EDS or the wavelength dispersive X-ray spectroscope WDS, and can be determined from the concentration gradients of titanium and aluminum. That is, as shown in the present embodiment, titanium or aluminum, which is neither a constituent element of the positive electrode active material nor a constituent element of the negative electrode active material, is present in the positive electrode active material layer 5 or the negative electrode active material layer 7 and shows a concentration gradient. It can be determined by confirming the state of distribution.

In this embodiment, the reduction of internal resistance by diffusion of titanium or aluminum has been described as described above, but the same phosphate-based material is used for the solid electrolyte layer 3 and the active material layer, and the valence is further applied to the active material layer. It is also important to use a material system that contains elements that change significantly. That is, by joining materials having a common skeleton in a crystal lattice called phosphoric acid and using a material called vanadium lithium 9 in which vanadium can be changed to trivalent, tetravalent or pentavalent, titanium or aluminum. Increased mobility, thereby placing titanium or aluminum in a more optimal position in the active material layer, not only reducing internal resistance, but also unprecedentedly reliable lithium in acceleration tests. It is considered that the ion secondary battery 10 could be provided.

Therefore, the characteristic configuration of the present embodiment is that one or both components of titanium and aluminum may be distributed in the positive electrode active material layer 5 or the negative electrode active material layer 7 in different shades, and the side closer to the solid electrolyte layer 3 It suffices that the side farther from the solid electrolyte layer 3 (that is, the side closer to the positive electrode current collector layer 4 or the negative electrode current collector layer 6) exists in a state where the element concentration of the component is lower. Normally, the characteristics do not diffuse to the vicinity of the interface between the active material layer and the current collector layer, so that the characteristics may not be maintained when an acceleration test is performed. However, in the present embodiment, the positive electrode active material layer 5 and the positive electrode current collector are used. By diffusing to the vicinity of the interface between the layer 4 or the negative electrode active material layer 7 and the negative electrode current collector layer 6, that is, over the entire area of the positive electrode active material layer 5 or the negative electrode active material layer 7, not only the internal resistance is reduced but also the internal resistance is reduced. It is possible to provide the lithium ion secondary battery 10 having unprecedented high reliability even in the acceleration test.

In the present embodiment, the thickness of the positive electrode active material layer 5 and the negative electrode active material layer 7 is 10 μm or less in order to diffuse titanium or aluminum more uniformly over the entire area of the positive electrode active material layer 5 and the negative electrode active material layer 7. Is desirable, and more preferably 5 μm or less.

Further, it is preferable that one or both components of titanium and aluminum in the present embodiment are distributed in the active material layer so as to cover the particle surface of the active material.

Further, the titanium or aluminum preferably exists even inside the particles of the active material, and is more preferably distributed from the surface of the particles to the inside of the particles with a concentration gradient.

The materials constituting the solid electrolyte layer 3, the positive electrode active material layer 5 and the negative electrode active material layer 7 of the lithium ion secondary battery 10 of the present embodiment can be identified by X-ray diffraction measurement. The distribution of titanium and aluminum can be analyzed by EPMA-WDS element mapping and the like.

Note that FIG. 1 shows a cross-sectional view of a lithium ion secondary battery 10 composed of a set of a positive electrode layer 1 and a negative electrode layer 2. However, the technique relating to the lithium ion secondary battery 10 of the present embodiment is not limited to FIG. 1, and can be applied to the lithium ion secondary battery 10 in which any plurality of layers are laminated, and the required capacity of the lithium ion secondary battery 10 can be applied. It is possible to change it widely according to the current specifications.

(Solid electrolyte)
The solid electrolyte layer 3 of the lithium ion secondary battery 10 of the present embodiment contains titanium aluminum phosphate lithium 8. The titanium aluminum lithium lithium 8 is preferably Li _{1 + x} Al _x Ti _2-x (PO ₄ ) ₃ (0 ≦ x ≦ 0.6). Further, the solid electrolyte layer 3 may contain a solid electrolyte material other than titanium-aluminum-lithium phosphate 8. For example, Li _{3 + x1} Si _x1 P _1-x1 O ₄ (0.4 ≤ x 1 ≤ 0.6), Li _3.4 V _0.4 Ge _0.6 O ₄ , Lithium germanium phosphate (LiGe ₂ (PO ₄ )). ₃ ), Li ₂ O-V ₂ O ₅ -SiO ₂ , Li ₂ O-P ₂ O _5- B ₂ O ₃ , Li ₃ PO ₄ , Li _0.5 La _0.5 TiO ₃ , Li ₁₄ Zn (GeO) ₄ ) It is preferable to include at least one selected from the group consisting of ₄ , Li ₇ La ₃ Zr ₂ O ₁₂ .

(Positive electrode active material and negative electrode active material)
As described above, one or both of the positive electrode active material layer 5 and the negative electrode active material layer 7 of the lithium ion secondary battery 10 of the present embodiment contains vanadium lithium phosphate 9. Lithium vanadium phosphate 9 includes LiVOPO ₄ , Li ₃ V ₂ (PO ₄ ) ₃ , Li ₂ VOP ₂ O ₇ , Li ₂ VP ₂ O ₇ , Li ₄ (VO) (PO ₄ ) ₂ , and Li ₉ V ₃ (P ₂ O ₇ ) ₃ (PO ₄ ) ₂ is preferably one or more, and in particular, one or both of LiVOPO ₄ and Li ₃ V ₂ (PO ₄ ) ₃ is preferable. Furthermore, LiVOPO ₄ and Li ₃ V ₂ (PO ₄ ) ₃ preferably have a lithium deficiency, such as Li _x VOPO ₄ (0.94 ≤ x ≤ 0.98) and Li _x V ₂ (PO ₄ ) _3. It is more preferable if (2.8 ≦ x ≦ 2.95).

Further, it is preferable that the materials in the positive electrode active material layer 5 and the negative electrode active material layer 7 are exactly the same material, and according to such a configuration, a non-polar lithium ion secondary battery 10 is formed. Therefore, when the material is attached to the circuit board, It is also advantageous in that it is not necessary to specify the direction and the mounting speed can be significantly improved.

The particle size of the vanadium lithium phosphate 9 is preferably in the range of 0.4 μm to 4 μm.

Further, it is preferable that the surface of the above vanadium lithium phosphate 9 is coated with one or both components of titanium and aluminum coated with 9 particles of vanadium lithium phosphate. At this time, the thickness of the coating layer covering the 9 particles of vanadium lithium phosphate is preferably 0.1 μm to 1 μm.

Further, the titanium or aluminum preferably exists even inside the particles of the active material, and is more preferably distributed from the surface of the particles to the inside of the particles with a concentration gradient.

The positive electrode active material layer 5 and the negative electrode active material layer 7 may contain a positive electrode active material and a negative electrode active material other than lithium vanadium phosphate 9. For example, it preferably contains a transition metal oxide and a transition metal composite oxide. Specifically, lithium manganese composite oxide Li ₂ Mn _x3 Ma _1-x3 O ₃ (0.8 ≦ x3 ≦ 1, Ma = Co, Ni), lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂₎ ), Lithium manganese spinel (LiMn ₂ O ₄ ), and general formula: LiNi _{x4 Coy4} Mn _z4 O ₂ (x4 + y4 + z4 = 1, 0 ≦ x4 ≦ 1, 0 ≦ y4 ≦ 1, 0 ≦ z4 ≦ 1) Composite metal oxide, lithium vanadium compound (LiV ₂ O ₅ ), olivine type LiMbPO ₄ (however, Mb is one or more selected from Co, Ni, Mn, Fe, Mg, Nb, Ti, Al, Zr. Li ₂ MnO _3- LiMcO ₂ (Mc = Mn, Co, Ni), lithium titanate (Li ₄ Ti ₅ O ₁₂ ), Li _a Ni _x5 Co _y5 Al _z5 O ₂ (0) It is preferably any of the composite metal oxides represented by 9.9 <a <1.3, 0.9 <x5 + y5 + z5 <1.1). The content of these materials is
In the same active material layer, the amount of vanadium lithium phosphate 9 is preferably in the range of 1 part by mass to 20 parts by mass with respect to 100 parts by mass.

Here, there is no clear distinction between the active materials constituting the positive electrode active material layer 5 or the negative electrode active material layer 7, and there are two types of compounds, the compound in the positive electrode active material layer 5 and the compound in the negative electrode active material layer 7. By comparing the potentials, a compound showing a more noble potential can be used as the positive electrode active material, and a compound showing a lower potential can be used as the negative electrode active material. Further, the same compound may be used for the positive electrode active material layer 5 and the negative electrode active material layer 7 as long as the compound has both lithium ion releasing ability and lithium ion storing ability at the same time.

(Positive current collector and negative electrode current collector)
As the material constituting the positive electrode current collector layer 4 and the negative electrode current collector layer 6 of the lithium ion secondary battery 10 of the present embodiment, it is preferable to use a material having a high conductivity, for example, silver, palladium, gold, platinum. , Aluminum, copper, nickel and the like are preferably used. In particular, copper is preferable because it does not easily react with titanium-aluminum-lithium 8 and is effective in reducing the internal resistance of the lithium ion secondary battery 10. The materials constituting the positive electrode current collector layer 4 and the negative electrode current collector layer 6 may be the same for the positive electrode and the negative electrode, or may be different.

Further, it is preferable that the positive electrode current collector layer 4 and the negative electrode current collector layer 6 of the lithium ion secondary battery 10 in the present embodiment contain a positive electrode active material and a negative electrode active material, respectively.

Since the positive electrode current collector layer 4 and the negative electrode current collector layer 6 contain the positive electrode active material and the negative electrode active material, respectively, the positive electrode current collector layer 4, the positive electrode active material layer 5, the negative electrode current collector layer 6 and the negative electrode active material are contained. This is desirable because the adhesion with the layer 7 is improved.

The ratio of the positive electrode active material and the negative electrode active material in the positive electrode current collector layer 4 and the negative electrode current collector layer 6 in the present embodiment is not particularly limited as long as it functions as a current collector, but the positive electrode current collector and the positive electrode active material are not particularly limited. Alternatively, it is preferable that the negative electrode current collector and the negative electrode active material are in the range of 90/10 to 70/30 in volume ratio.

(Manufacturing method of lithium ion secondary battery)
In the lithium ion secondary battery 10 of the present embodiment, the materials of the positive electrode current collector layer 4, the positive electrode active material layer 5, the solid electrolyte layer 3, the negative electrode active material layer 7, and the negative electrode current collector layer 6 are made into a paste. , Coating and drying to prepare a green sheet, laminating the green sheet, and simultaneously firing the prepared laminate to produce the product.

The method of making a paste is not particularly limited, and for example, a paste can be obtained by mixing powders of the above materials with a vehicle. Here, vehicle is a general term for a medium in a liquid phase. The vehicle contains a solvent and a binder. According to the method, a paste for the positive electrode current collector layer 4, a paste for the positive electrode active material layer 5, a paste for the solid electrolyte layer 3, a paste for the negative electrode active material layer 7, and a paste for the negative electrode current collector layer 6. Make a paste.

The prepared paste is applied on a base material such as PET (polyethylene terephthalate) in a desired order, dried if necessary, and then the base material is peeled off to prepare a green sheet. The method of applying the paste is not particularly limited, and known methods such as screen printing, coating, transfer, and doctor blade can be adopted.

The produced green sheets are stacked in a desired order and the number of layers, and if necessary, alignment, cutting, etc. are performed to produce a laminated block. When producing a parallel type or a series-parallel type battery, it is preferable to perform alignment and stack the batteries so that the end faces of the positive electrode layer 1 and the end faces of the negative electrode layer 2 do not match.

When producing the laminated block, the active material unit described below may be prepared to produce the laminated block.

The method is as follows: First, a paste for the solid electrolyte layer 3 is formed on a PET film in the form of a sheet by the doctor blade method, a sheet for the solid electrolyte layer 3 is obtained, and then screen printing is performed on the sheet for the solid electrolyte layer 3. The paste for the positive electrode active material layer 5 is printed and dried. Next, the paste for the positive electrode current collector layer 4 is printed on it by screen printing and dried. Further, the paste for the positive electrode active material layer 5 is printed again by screen printing, dried, and then the PET film is peeled off to obtain a positive electrode active material layer unit. In this way, the positive electrode active material layer unit in which the paste for the positive electrode active material layer 5, the paste for the positive electrode current collector layer 4, and the paste for the positive electrode active material layer 5 are formed in this order on the sheet for the solid electrolyte layer 3. obtain. A negative electrode active material layer unit is also produced by the same procedure, and the negative electrode active material layer 7 paste, the negative electrode current collector layer 6 paste, and the negative electrode active material layer 7 paste are placed in this order on the solid electrolyte layer 3 sheet. The formed negative electrode active material layer unit is obtained.

One positive electrode active material layer unit and one negative electrode active material layer unit are combined with a positive electrode active material layer 5 paste, a positive electrode current collector layer 4 paste, a positive electrode active material layer 5 paste, a solid electrolyte layer 3 sheet, and a negative electrode. The paste for the active material layer 7, the paste for the negative electrode current collector layer 6, the paste for the negative electrode active material layer 7, and the sheet for the solid electrolyte layer 3 are stacked in this order. At this time, the paste for the positive electrode current collector layer 4 of the first positive electrode active material layer unit extends only to one end face, and the paste for the negative electrode current collector layer 6 of the second negative electrode active material layer unit is the other. Each unit is staggered and stacked so that it extends only to the surface of. Sheets for the solid electrolyte layer 3 having a predetermined thickness are further stacked on both sides of the stacked units to prepare a laminated block.

The produced laminated blocks are collectively crimped. The crimping is performed while heating, and the heating temperature is, for example, 40 to 95 ° C.

The crimped laminated block is heated to, for example, 600 ° C. to 1000 ° C. in a nitrogen atmosphere and fired. The firing time is, for example, 0.1 to 3 hours. The laminate is completed by this firing.

(Example 1-1)
Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited to these Examples. Unless otherwise specified, the part display is a mass part.

(Preparation of positive electrode active material and negative electrode active material)
As the positive electrode active material and the negative electrode active material, Li ₃ V ₂ (PO ₄ ) ₃ prepared by the following method was used. As a method for producing the same, Li ₂ CO ₃ and V ₂ O ₅ and NH ₄ H ₂ PO ₄ are used as starting materials, wet-mixed with a ball mill for 16 hours, dehydrated and dried, and then the obtained powder is prepared at 850 ° C. It was calcined in a nitrogen-hydrogen mixed gas for 2 hours. The calcined product was wet-pulverized with a ball mill and then dehydrated and dried to obtain a positive electrode active material powder and a negative electrode active material powder. It was confirmed by using an X-ray diffractometer that the composition of the prepared powder was Li ₃ V ₂ (PO ₄ ) ₃ .

(Preparation of paste for positive electrode active material layer and paste for negative electrode active material layer)
The positive electrode active material layer paste and the negative electrode active material layer paste are both mixed by adding 15 parts of ethyl cellulose as a binder and 65 parts of dihydroterpineol as a solvent to 100 parts of Li ₃ V ₂ (PO ₄ ) ₃ powder. -Dispersed to prepare a paste for the positive electrode active material layer and a paste for the negative electrode active material layer.

(Preparation of paste for solid electrolyte layer)
As the solid electrolyte, Li _1.3 Al _0.3 Ti _1.7 (PO ₄ ) ₃ prepared by the following method was used. The production method was as follows: Li ₂ CO ₃ , Al ₂ O ₃ , TIO ₂ and NH ₄ H ₂ PO ₄ were used as starting materials, wet-mixed with a ball mill for 16 hours, and then dehydrated and dried. The obtained powder was calcined in air at 800 ° C. for 2 hours. The calcined product was wet-pulverized with a ball mill for 16 hours and then dehydrated and dried to obtain a solid electrolyte powder. It was confirmed by using an X-ray diffractometer that the composition of the prepared powder was Li _1.3 Al _0.3 Ti _1.7 (PO ₄ ) ₃ .

Next, 100 parts of ethanol and 200 parts of toluene were added to this powder as a solvent by a ball mill and wet-mixed. After that, 16 parts of a polyvinyl butyral binder and 4.8 parts of benzylbutyl phthalate were further added and mixed to prepare a paste for a solid electrolyte layer.

(Preparation of sheet for solid electrolyte layer)
This paste for a solid electrolyte layer was sheet-molded using a PET film as a base material by a doctor blade method to obtain a sheet for a solid electrolyte layer having a thickness of 15 μm.

(Preparation of paste for positive electrode current collector layer and paste for negative electrode current collector layer)
Cu used as the positive electrode current collector and the negative electrode current collector and Li ₃ V ₂ (PO ₄ ) ₃ are mixed so as to have a volume ratio of 80/20, and then 10 parts of ethyl cellulose as a binder and dihydroterpineol as a solvent. 50 parts were added and mixed / dispersed to prepare a paste for the positive electrode current collector layer and a paste for the negative electrode current collector layer. The average particle size of Cu was 0.9 μm.

(Preparation of terminal electrode paste)
A thermosetting terminal electrode paste was prepared by mixing and dispersing silver powder, epoxy resin, and solvent.

Using these pastes, a lithium ion secondary battery was prepared as follows.

(Preparation of positive electrode active material layer unit)
A paste for the positive electrode active material layer having a thickness of 5 μm was printed on the above-mentioned solid electrolyte layer sheet by screen printing, and dried at 80 ° C. for 10 minutes. Next, a paste for the positive electrode current collector layer was printed on it to a thickness of 5 μm by screen printing, and dried at 80 ° C. for 10 minutes. Further, the paste for the positive electrode active material layer was reprinted on it by screen printing to a thickness of 5 μm, dried at 80 ° C. for 10 minutes, and then the PET film was peeled off. In this way, the sheet of the positive electrode active material layer unit in which the paste for the positive electrode active material layer, the paste for the positive electrode current collector layer, and the paste for the positive electrode active material layer are printed and dried in this order on the solid electrolyte layer sheet is formed. Obtained.

(Manufacturing of negative electrode active material layer unit)
A paste for the negative electrode active material layer having a thickness of 5 μm was printed on the above-mentioned solid electrolyte layer sheet by screen printing, and dried at 80 ° C. for 10 minutes. Next, a paste for the negative electrode current collector layer was printed on it to a thickness of 5 μm by screen printing, and dried at 80 ° C. for 10 minutes. Further, the paste for the negative electrode active material layer was reprinted on it by screen printing to a thickness of 5 μm, dried at 80 ° C. for 10 minutes, and then the PET film was peeled off. In this way, the negative electrode active material layer unit sheet on which the negative electrode active material layer paste, the negative electrode current collector layer paste, and the negative electrode active material layer paste are printed and dried in this order on the solid electrolyte layer sheet. Obtained.

(Preparation of laminate)
Positive electrode active material layer unit and negative electrode active material layer unit, positive electrode active material layer paste, positive electrode current collector layer paste, positive electrode active material layer paste, solid electrolyte layer sheet, negative electrode active material layer paste, negative electrode collection The paste for the electric body layer, the paste for the negative electrode active material layer, and the sheet for the solid electrolyte layer were stacked in this order. At this time, the paste for the positive electrode current collector layer of the positive electrode active material layer unit extends only to one end surface, and the paste for the negative electrode current collector layer of the negative electrode active material layer unit extends only to the other surface. Each unit was staggered and stacked. Sheets for the solid electrolyte layer were stacked on both sides of the stacked units so as to have a thickness of 500 μm, and then this was formed by thermocompression bonding and then cut to prepare a laminated block. Then, the laminated blocks were simultaneously fired to obtain a laminated body. In the simultaneous firing, the temperature was raised to a firing temperature of 750 ° C. in nitrogen at a heating rate of 200 ° C./hour, kept at that temperature for 2 hours, and naturally cooled after firing.

(Terminal electrode forming process)
The terminal electrode paste was applied to the end faces of the laminated blocks and thermoset at 150 ° C. for 30 minutes to form a pair of terminal electrodes to obtain a lithium ion secondary battery.

(Example 1-2)
A lithium ion secondary battery was produced in the same manner as in Example 1-1 except that the firing temperature was set to 800 ° C. in the simultaneous firing of the laminated blocks.

(Comparative Example 1-1)
In the simultaneous firing of the laminate, a lithium ion secondary battery was produced in the same manner as in Example 1-1 except that the firing temperature was set to 700 ° C.

(Example 2-1)
As the positive electrode active material and the negative electrode active material, LiVOPO ₄ produced by the following method was used. Using Li ₂ CO ₃ , V ₂ O ₅ and NH ₄ H ₂ PO ₄ as starting materials, wet mixing was carried out in a ball mill for 16 hours, and then dehydration and drying were performed. The obtained powder was calcined at 650 ° C. for 2 hours in a nitrogen-hydrogen mixed gas. The calcined product was wet-pulverized with a ball mill for 16 hours and then dehydrated and dried to obtain a positive electrode active material powder and a negative electrode active material powder. It was confirmed by using an X-ray diffractometer that the composition of the prepared powder was LiVOPO ₄ .

A lithium ion secondary battery was produced in the same manner as in Example 1-1 except that LiVOPO ₄ was used as the positive electrode active material and the negative electrode active material.

(Example 2-2)
In the simultaneous firing of the laminated blocks, a lithium ion secondary battery was produced in the same manner as in Example 2-1 except that the firing temperature was set to 800 ° C.

(Comparative Example 2-1)
A lithium ion secondary battery was produced in the same manner as in Example 2-1 except that the firing temperature was set to 700 ° C. in the simultaneous firing of the laminated blocks.

(Example 3-1)
A lithium ion secondary battery was produced in the same manner as in Example 1-1 except that LiVOPO ₄ was used as the paste for the negative electrode active material layer.

(Example 3-2)
A lithium ion secondary battery was produced in the same manner as in Example 3-1 except that the firing temperature was set to 800 ° C. in the simultaneous firing of the laminated blocks.

(Comparative Example 3-1)
A lithium ion secondary battery was produced in the same manner as in Example 3-1 except that the firing temperature was set to 700 ° C. in the simultaneous firing of the laminated blocks.

(Comparative Example 4-1)
A lithium ion secondary battery was produced in the same manner as in Comparative Example 3-1 except that LiFePO ₄ was used as the paste for the positive electrode active material layer and Li ₄ Ti ₅ O ₁₂ was used as the paste for the negative electrode active material layer.

(Comparative Example 4-2)
A lithium ion secondary battery was produced in the same manner as in Comparative Example 4-1 except that the firing temperature was set to 750 ° C. in the simultaneous firing of the laminated blocks.

(Comparative Example 4-3)
A lithium ion secondary battery was produced in the same manner as in Comparative Example 4-1 except that the firing temperature was set to 800 ° C. in the simultaneous firing of the laminated blocks.

(Example 5-1)
A lithium ion secondary battery was produced in the same manner as in Example 1-2 except that Li _2.95 V ₂ (PO ₄ ) ₃ was used as the positive electrode active material and the negative electrode active material.

(Example 5-2)
A lithium ion secondary battery was produced in the same manner as in Example 1-2 except that Li _2.9 V ₂ (PO ₄ ) ₃ was used as the positive electrode active material and the negative electrode active material.

(Example 5-3)
A lithium ion secondary battery was produced in the same manner as in Example 1-2 except that Li _2.8 V ₂ (PO ₄ ) ₃ was used as the positive electrode active material and the negative electrode active material.

(Example 5-4)
A lithium ion secondary battery was produced in the same manner as in Example 1-2 except that Li _2.7 V ₂ (PO ₄ ) ₃ was used as the positive electrode active material and the negative electrode active material.

(Example 5-5)
A lithium ion secondary battery was produced in the same manner as in Example 1-2 except that Li _2.6 V ₂ (PO ₄ ) ₃ was used as the positive electrode active material and the negative electrode active material.

(Example 6-1)
Thereby producing a lithium ion secondary battery of Li _0.98 V O PO ₄ except for using as the positive electrode active material and the negative electrode active material in the same manner as in Example 1-2.

(Example 6-2)
Thereby producing a lithium ion secondary battery of Li _0.96 V O PO ₄ except for using as the positive electrode active material and the negative electrode active material in the same manner as in Example 1-2.

(Example 6-3)
Thereby producing a lithium ion secondary battery of Li _0.94 V O PO ₄ except for using as the positive electrode active material and the negative electrode active material in the same manner as in Example 1-2.

(Example 6-4)
Thereby producing a lithium ion secondary battery of Li _0.92 V O PO ₄ except for using as the positive electrode active material and the negative electrode active material in the same manner as in Example 1-2.

(Example 6-5)
A lithium ion secondary battery was produced in the same manner as in Example 1-2 except that Li _0.90 V O PO ₄ was used as the positive electrode active material and the negative electrode active material.

(Battery evaluation)
Lead wires were attached to the terminal electrodes of each lithium-ion secondary battery, and charge / discharge tests were repeated. The measurement conditions were 2.0 μA for the current during charging and discharging, and 4.0V and 0V for the cutoff voltage during charging and discharging, respectively. Table 1 shows the internal resistance calculated from the discharge capacity at the 5th cycle and the voltage drop at the start of discharge as the internal resistance before the acceleration test.
Further, in order to evaluate the reliability, the internal resistance measured after the acceleration test at a temperature of 60 ° C. and a humidity of 90% for 200 hours is also shown in Table 1 as the internal resistance after the acceleration test.

(Battery cross-section observation)
Table 1 also shows the presence or absence of one or both components of titanium and aluminum in the active material layer obtained from the EPMA-WDS element mapping for the cross section of the prepared lithium ion secondary battery of Example 1-2. It is also shown. Here, a sample for observing the cross section of the lithium ion secondary battery was prepared by embedding each lithium ion secondary battery in a resin and then mechanically polishing the sample.

From Table 1, one or both components of titanium and aluminum were diffused into lithium vanadium phosphate, Example 1-1, Example 1-2, Example 2-1 and Example 2-2, Example 3-1. And Example 3-2 have a large decrease in internal resistance and an increase in discharge capacity as compared with Comparative Example 1-1, Comparative Example 2-1 and Comparative Example 3-1 in which both aluminum and titanium were not diffused. It was seen.

Further, the change in internal resistance before and after the acceleration test was observed in Example 1-1, Example 1-2, Example 2-1 and Example 2 in which one or both components of titanium and aluminum were diffused into lithium vanadium phosphate. -2, Example 3-1 and Example 3-2 showed a slight increase but hardly changed, whereas both titanium and aluminum did not diffuse in Comparative Examples 1-1 and 3-2. In 2-1 and Comparative Example 3-1 a large increase in internal resistance was observed.

On the other hand, in the positive electrode active material layer containing LiFePO ₄ as the positive electrode active material, neither titanium nor aluminum could be confirmed after firing, and in Comparative Example 4-1 and Comparative Example 4-2 and Comparative Example 4-3, the firing temperature was set. Even if it is changed, the discharge capacity does not increase and the internal resistance does not decrease significantly. In addition, the internal resistance after the accelerated test showed a large increase compared to before the accelerated test.

The EPMA-WDS element mapping and the secondary electron image of the interface between the positive electrode active material layer and the solid electrolyte layer of the lithium ion secondary battery after firing in Example 1-2 are shown in FIGS. 2 and 3, respectively. From FIG. 2, the titanium and aluminum constituting the solid electrolyte layer Li _1.3 Al _0.3 Ti _1.7 (PO ₄ ) ₃ were not present in the positive electrode active material layer before sintering. However, after firing, titanium and aluminum are on the opposite side of the solid electrolyte layer side (that is, the positive electrode) over the entire _three layers of Li ₃ V ₂ (PO ₄ ) constituting the positive electrode active material layer having a thickness of about 2.5 μm. On the collector layer side), it was observed that the distribution was less and had a concentration gradient. Focusing on each particle, it was found that titanium and aluminum are distributed from the surface of the Li ₃ V ₂ (PO ₄ ) ₃ particle to the inside of the particle with a concentration gradient.

The distribution of titanium and aluminum at the interface between the negative electrode active material layer and the solid electrolyte layer was also the same as that at the interface between the positive electrode active material layer and the solid electrolyte layer. That is, it can be seen that titanium and aluminum are distributed on the negative electrode current collector layer side with a smaller concentration gradient than on the solid electrolyte side. Focusing on each particle, titanium and aluminum are Li. _It was observed that the ₃ V ₂ (PO ₄ ) ₃ particles were distributed from the surface of the particles to the inside of the particles with a concentration gradient.

Furthermore, as a result of measuring the diffusion ratio of aluminum and titanium into Li ₃ V ₂ (PO ₄ ) ₃ constituting the positive electrode active material layer, the diffusion ratio of aluminum and titanium in the solid electrolyte layer (aluminum element concentration / titanium). When (element concentration) is 1, the positive electrode active material layer near the interface with the solid electrolyte layer is 1.28, the central part of the positive electrode active material layer in the thickness direction is 1.38, and the vicinity of the interface with the positive electrode current collector. It was 1.83 in the positive electrode active material layer, and it was found that aluminum was more diffused than titanium. This is because the ionic radius of Al ³⁺ is smaller than the ionic radius of 68 pm of Ti ⁴⁺ , so it diffuses farther and plays a role of forming a strong bond, and also creates a path of ion conduction and internal resistance. It is presumed that it was effective in reducing the amount of water.

On the other hand, vanadium constituting Li ₃ V ₂ (PO ₄ ) ₃ of the positive electrode active material layer is distributed in Li _1.3 Al _0.3 Ti _1.7 (PO ₄ ) ₃ of the solid electrolyte layer. It was not seen.

Also, from the secondary electron image of FIG. _{3, Li 3 V 2 (PO} 4) positive electrode active material layer and _{Li 1.3 Al 0.3 Ti 1.7 (PO} 4) solid electrolyte layer consisting of ₃ of ₃ It was observed that the electrons were firmly joined. On the other hand, although not shown, in Comparative Example 1-1, Comparative Example 2-1 and Comparative Example 3-1 the positive electrode active material layer and the solid electrolyte layer or the negative electrode active material layer and the solid electrolyte layer were separated from each other. There was a place where it was.

These results, one or both of aluminum and titanium constituting the _{Li 1.3 Al 0.3 Ti 1.7 (PO} 4) 3 of the solid electrolyte layer is _{Li 3 V 2 (PO 4)} 3 in the solid electrolyte layer It is less on the opposite side than the side, diffuses with a concentration gradient, and finally titanium and aluminum take the optimum distribution state at the optimum position to form a strong bond, and at the same time, the positive electrode active material layer. It is considered that the internal resistance of the lithium ion secondary battery is reduced because the contact area between the surface and the solid electrolyte layer is increased.

Further, in Example 1-1, Example 1-2, Example 2-1 and Example 2-2, Example 3-1 and Example 3-2, no short circuit was observed. This is because vanadium, which is a component of Li ₃ V ₂ (PO ₄ ) ₃ , did not diffuse into Li _1.3 Al _0.3 Ti _1.7 (PO ₄ ) ₃ , resulting in a short circuit in the lithium ion secondary battery. It is thought that this was because it was suppressed.

Next, from the comparison of Example 1-1, Example 5-1 and Example 5-2, Example 5-3, Example 5-4, and Example 5-5 in Table 1, there is no Li deficiency. _{Li 3 V 2 (PO 4)} 3 and as compared with examples 1-1 was used as the positive electrode active material and the negative electrode active _{material, Li 3 V 2 (PO 4} ) with a lack of Li ₃ a positive electrode active material and the anode active material Examples 5-1 and 5-2, 5-3, 5-4, and 5-5 used in the above have lower internal resistance and higher discharge capacity before the acceleration test. In addition, the increase in internal resistance after the accelerated test is small compared to the internal resistance before the accelerated test.

Similarly, from the comparison of Example 1-1, Example 6-1 and Example 6-2, Example 6-3, Example 6-4, and Example 6-5 in Table 1, Li deficiency free LiVOPO ₄ as compared with examples 1-1 was used as the positive electrode active material and the negative electrode active material, examples 6-1 using a LiVOPO ₄ with Li-deficient cathode active material and the negative electrode active material, example 6 2. Examples 6-3, 6-4, and 6-5 have lower internal resistance and higher discharge capacity before the acceleration test. In addition, the increase in internal resistance after the accelerated test is small compared to the internal resistance before the accelerated test.

The above results show that the presence of Li in the positive electrode active material and the negative electrode active material promotes the diffusion of titanium and aluminum during firing, and as a result, the optimum arrangement of titanium and aluminum is further promoted, and the lithium ion secondary It is probable that the internal resistance of the battery was low and the discharge capacity was high.

1 Positive electrode layer 2 Negative electrode layer 3 Solid electrolyte layer 4 Positive electrode current collector layer 5 Positive electrode active material layer 6 Negative electrode current collector layer 7 Negative electrode active material layer 8 Titanium aluminum lithium phosphate 9 Vanadium lithium phosphate 10 Lithium ion secondary battery

Claims (6)

In a lithium ion secondary battery including a laminate having a solid electrolyte layer between a positive electrode layer and a negative electrode layer.
The positive electrode layer is composed of a positive electrode current collector layer and a positive electrode active material layer.
The negative electrode layer is composed of a negative electrode current collector layer and a negative electrode active material layer.
The solid electrolyte layer provided between the positive electrode active material layer and the negative electrode active material layer contains titanium aluminum lithium phosphate.
One or both of the positive electrode active material layer and the negative electrode active material layer contains lithium vanadium phosphate and contains one or both components of titanium and aluminum.
The component exists even inside the particles of lithium vanadium phosphate, and is distributed from the surface of the particles to the inside of the particles with a concentration gradient.
The laminated body is a sintered body, which is a lithium ion secondary battery. In a lithium ion secondary battery including a laminate having a solid electrolyte layer between a positive electrode layer and a negative electrode layer.
The positive electrode layer is composed of a positive electrode current collector layer and a positive electrode active material layer.
The negative electrode layer is composed of a negative electrode current collector layer and a negative electrode active material layer.
The solid electrolyte layer provided between the positive electrode active material layer and the negative electrode active material layer contains titanium aluminum lithium phosphate.
One or both of the positive electrode active material layer and the negative electrode active material layer contains lithium vanadium phosphate and contains one or both components of titanium and aluminum.
The component forms a coating layer that covers the surface of the lithium vanadium phosphate particles.
The component exists even inside the particles and is distributed from the surface of the particles to the inside of the particles with a concentration gradient.
The laminated body is a sintered body, which is a lithium ion secondary battery. The lithium ion secondary battery according to claim 2, wherein the thickness of the coating layer is 0.1 μm to 1 μm. The lithium ion secondary battery according to any one of claims 1 to 3 , wherein the component is present in a smaller amount on the current collector side than on the solid electrolyte layer side. The lithium vanadium phosphate is one or both of Li _y VOPO ₄ (0.94 ≦ y ≦ 0.98) and Li _z V ₂ (PO ₄ ) ₃ (2.8 ≦ z ≦ 2.95). The lithium ion secondary battery according to any one of claims 1 to 4 . Any one of claims 1 to 5 , wherein the component is diffused and bonded to the titanium aluminum lithium phosphate in one or both of the positive electrode active material layer and the negative electrode active material layer. The lithium ion secondary battery described in.

Images