JP7226513B2 - Method for manufacturing positive electrode active material particles, method for manufacturing positive electrode paste, method for manufacturing positive electrode plate, and method for manufacturing lithium ion secondary battery - Google Patents

Description

The present invention provides a method for producing positive electrode active material particles capable of inserting and extracting lithium ions, a method for producing a positive electrode paste containing the positive electrode active material particles, a method for producing a positive electrode plate containing the positive electrode active material particles in an active material layer, and a method for manufacturing a lithium-ion secondary battery including this positive electrode plate.

A lithium ion secondary battery (hereinafter also simply referred to as a “battery”) uses positive electrode active material particles into which lithium ions can be inserted and extracted. Known positive electrode active material particles include, for example, lithium-nickel-cobalt-aluminum composite oxide particles, lithium-nickel-cobalt-manganese composite oxide particles, olivine-type lithium iron phosphate particles, and spinel-type lithium manganese oxide particles. . In addition, patent document 1 is mentioned as a related prior art.

JP 2013-175325 A

By the way, when positive electrode active material particles capable of intercalating and deintercalating lithium ions come into contact with moisture in the atmosphere, the particle surfaces react with water (H ₂ O) to generate lithium hydroxide (LiOH) (Li ₂ O+H ₂ O→2LiOH). Furthermore, this lithium hydroxide reacts with carbon dioxide (CO ₂ ) in the atmosphere to produce lithium carbonate (Li ₂ CO ₃ ) (2LiOH+CO ₂ →Li ₂ CO ₃ +H ₂ O). Lithium carbonate generated on the particle surface of the positive electrode active material particles is a resistor. In addition, when the positive electrode active material particles react with water and lithium ions are released from the positive electrode active material particles, the crystal structure of the positive electrode active material particles changes, making it difficult for lithium ions to be inserted into and removed from the positive electrode active material particles. Therefore, in a battery manufactured using such positive electrode active material particles, the IV resistance of the battery is high.

The present invention has been made in view of such circumstances, and a positive electrode that can suppress an increase in the IV resistance of the battery when the battery is manufactured due to contact with moisture and carbon dioxide in the atmosphere. An object of the present invention is to provide a method for manufacturing active material particles, a method for manufacturing a positive electrode paste, a method for manufacturing a positive electrode plate, and a method for manufacturing a lithium ion secondary battery.

One aspect of the present invention for solving the above problems is a method for producing positive electrode active material particles capable of intercalating and deintercalating lithium ions, comprising inorganic phosphoric acid (H ₃ PO ₄ ), inorganic phosphoric acid salt, organic phosphoric acid, a contacting step of contacting the positive electrode active material particles before treatment with a phosphoric acid compound solution obtained by dissolving a phosphoric acid compound, which is at least one of an acid and a salt of an organic phosphoric acid, in a first dispersion medium; a particle drying step of drying the pre-dried positive electrode active material particles wetted with the phosphoric acid compound solution to obtain the positive electrode active material particles having a coating containing phosphorus on the particle surface, wherein the phosphoric acid compound is an inorganic phosphoric acid and a salt of an inorganic phosphoric acid, the first dispersion medium is water, and the pH of the phosphoric acid compound solution before contact with the positive electrode active material particles before treatment is pH=4. This is a method for producing positive electrode active material particles having a ratio of 0 to 5.2.

In the above-described method for producing positive electrode active material particles, the resistor (lithium carbonate, etc.) already formed on the particle surface of the untreated positive electrode active material particles can be removed by performing the above-described contact step and particle drying step. In addition, it is possible to obtain positive electrode active material particles having the above-described coating containing phosphorus (hereinafter also referred to as “phosphorus-containing coating”) on the particle surface. Such positive electrode active material particles are less likely to react with moisture and carbon dioxide in the atmosphere than positive electrode active material particles that do not have a phosphorus-containing coating on the particle surface. Lithium carbonate (Li ₂ CO ₃ ) is difficult to form. In addition, since the positive electrode active material particles are less likely to react with water than the positive electrode active material particles that do not have a phosphorus-containing coating on the particle surface, lithium ions are released from the positive electrode active material particles by the reaction with water, resulting in positive electrode active material particles. It is possible to suppress changes in the crystal structure of the substance particles. Therefore, in the lithium ion secondary battery using the positive electrode active material particles, the IV resistance of the battery can be suppressed as compared with the lithium ion secondary battery using the positive electrode active material particles that do not have a phosphorus-containing coating on the particle surface. .
When inorganic phosphoric acid and a salt of inorganic phosphoric acid are used as the phosphoric acid compound, and water is used as the first dispersion medium, the lower the pH of the phosphoric acid compound solution before contact with the positive electrode active material particles before treatment, the higher the contact. It was found that the positive electrode active material particles were greatly damaged by the acid in the process and after that, specifically, lithium ions were eluted from the positive electrode active material particles and the crystal structure of the positive electrode active material particles was irreversibly changed. It's here. On the other hand, if the pH of the phosphoric acid compound solution before contact with the untreated positive electrode active material particles is too high, the salt of inorganic phosphoric acid precipitates in the phosphoric acid compound solution in granular form.
On the other hand, in the manufacturing method described above, the pH of the phosphoric acid compound solution before being brought into contact with the untreated positive electrode active material particles is set to pH=4.0 to 5.2. By setting the pH of the phosphoric acid compound solution to 4.0 or more, it is possible to suppress the positive electrode active material particles from being greatly damaged by the acid in the contact step and thereafter, compared to the case where the pH is less than 4.0. . On the other hand, by adjusting the pH of the phosphoric acid compound solution to 5.2 or less, it is possible to prevent the salt of inorganic phosphoric acid from precipitating in the phosphoric acid compound solution in granular form.

The "pre-treated positive electrode active material particles" are positive electrode active material particles containing lithium before the phosphorus-containing coating is formed. For example, lithium nickel cobalt aluminum composite oxide particles, lithium nickel cobalt manganese composite oxide particles, olivine-type lithium iron phosphate particles, spinel-type lithium manganese oxide particles, and the like. In addition, the “post-contact and pre-drying positive electrode active material particles” refer to positive electrode active material particles before being dried after contact with the phosphoric acid compound solution.
Examples of "salts of inorganic phosphoric acid _{( H3PO4} )" include lithium phosphate ( _Li3PO4 ), sodium _phosphate ( _Na3PO4 ) _, potassium phosphate ( _K3PO4 ), and the like _. be done. In a lithium ion secondary battery, lithium phosphate is particularly preferable as the salt of inorganic phosphoric acid because lithium ions contribute to the battery reaction.

"Organic phosphoric acid" includes, for example, phenylphosphonic acid, methylphosphonic acid and the like.
Examples of "salts of organic phosphoric acid" include lithium salts, sodium salts and potassium salts of organic phosphoric acids, such as lithium salts of phenylphosphonic acid and methylphosphonic acid. In a lithium-ion secondary battery, lithium ions contribute to the battery reaction, so the organic phosphoric acid salt is particularly preferably a lithium salt of an organic phosphoric acid.

As the "first dispersion medium", a dispersion medium in which the phosphoric acid compound can be dissolved may be selected according to the phosphoric acid compound to be used. For example, water, N-methyl-2-pyrrolidone (NMP), benzene, An organic solvent etc. are mentioned.
The composition of the “film containing phosphorus (phosphorus-containing film)” on the surface of the positive electrode active material particles varies depending on the phosphoric acid compound used. For example, when inorganic phosphoric acid or a salt of inorganic phosphoric acid is used as the phosphoric acid compound, it is considered that a film made of lithium phosphate (Li ₃ PO ₄ ) is formed. Further, when phenylphosphonic acid or a salt thereof is used as the phosphoric acid compound, it is considered that a film made of lithium phenylphosphonate is formed.

Examples of the "alkaline aqueous solution" include aqueous solutions of lithium hydroxide (LiOH), sodium hydroxide (NaOH), potassium hydroxide (KOH), and the like. In a lithium ion secondary battery, since lithium ions contribute to the battery reaction, the alkaline aqueous solution is particularly preferably a lithium hydroxide aqueous solution.

Further, in the method for producing the positive electrode active material particles described above, the positive electrode active material particles before treatment are obtained by dispersing 1 g of the positive electrode active material particles before treatment in 50 g of water. A method for producing positive electrode active material particles having characteristics of .3 or more is preferable.

In the manufacturing method described above, as the positive electrode active material particles before treatment, those having a characteristic that the pH of the dispersion liquid becomes pH=11.3 or higher are used. Such positive electrode active material particles before treatment are particularly likely to react with water and carbon dioxide to produce lithium hydroxide and even lithium carbonate, and a battery using these positive electrode active material particles as they are has a high IV resistance. easy to become For this reason, as described above, it is particularly preferable to perform the contacting step and the particle drying step to provide a phosphorus-containing coating on the particle surface of the positive electrode active material particles to suppress the reaction with water and carbon dioxide.

Another aspect is a method for producing a positive electrode paste containing positive electrode active material particles capable of inserting and extracting lithium ions and a second dispersion medium, wherein the positive electrode active material particles according to any one of the above are produced. Manufacture of a positive electrode paste comprising: a particle manufacturing step of manufacturing the positive electrode active material particles by a method; and a mixed paste forming step of mixing the positive electrode active material particles and the second dispersion medium to form the positive electrode paste. The method.

In the positive electrode paste manufacturing method described above, the positive electrode active material particles having the phosphorus-containing coating on the particle surface are manufactured in the particle manufacturing step, and the positive electrode active material particles are used in the mixed paste forming step to manufacture the positive electrode paste. Therefore, if a positive electrode plate is formed using this positive electrode paste and a battery is manufactured using this positive electrode plate, the battery performance will be lower than that of a battery using positive electrode active material particles that do not have a phosphorus-containing coating on the particle surface. IV resistance can be suppressed.

Another aspect is a method for producing a positive electrode plate comprising a current collector foil and an active material layer formed on the current collector foil and containing positive electrode active material particles capable of inserting and extracting lithium ions, A paste manufacturing step of manufacturing the positive electrode paste by the above positive electrode paste manufacturing method, a coating step of coating the positive electrode paste on the current collector foil to form an undried active material layer, and the current collector. a layer drying step of drying the undried active material layer on the foil to form the active material layer.

In the method for producing a positive electrode plate described above, a positive electrode paste containing positive electrode active material particles having a phosphorus-containing coating on the particle surface is produced in the paste production process, and the positive electrode plate is produced using this positive electrode paste. Therefore, in a battery using this positive electrode plate, the IV resistance of the battery can be suppressed as compared with a battery using positive electrode active material particles that do not have a phosphorus-containing coating on the particle surface.

Another aspect is a lithium ion secondary battery comprising a positive electrode plate having a current collector foil and an active material layer formed on the current collector foil and containing positive electrode active material particles capable of inserting and extracting lithium ions. A lithium ion manufacturing method, comprising: a positive electrode plate manufacturing step of manufacturing the positive electrode plate by the positive electrode plate manufacturing method; and a battery assembling step of assembling the lithium ion secondary battery using the positive electrode plate. A method for manufacturing a secondary battery.

In the above-described battery manufacturing method, a positive electrode plate containing positive electrode active material particles having a phosphorus-containing coating on the particle surface is manufactured in the positive electrode plate manufacturing process, and a battery is assembled using this positive electrode plate in the battery assembling process. Therefore, in this battery, the IV resistance of the battery can be suppressed as compared with a battery using positive electrode active material particles that do not have a phosphorus-containing coating on the particle surface.

1 is a perspective view of a battery according to Embodiment 1 and a reference embodiment; FIG. 1 is a vertical cross-sectional view of a battery according to Embodiment 1 and a reference embodiment; FIG. 1 is a perspective view of a positive electrode plate according to Embodiment 1 and a reference embodiment; FIG . 1 is a cross-sectional view of positive electrode active material particles according to Embodiment 1 and a reference embodiment; FIG . 1 is a flow chart of a method for manufacturing a battery according to Embodiment 1 and Reference Embodiment . 4 is a flowchart of a positive electrode plate manufacturing process subroutine according to Embodiment 1 and Reference Embodiment . 4 is a flow chart of a particle manufacturing process subroutine according to Embodiment 1 and Reference Mode . 4 is a graph showing the IV resistance ratio of each battery according to Example 1, Reference Example , and Comparative Examples 1 and 2. FIG.

(Embodiment 1)
A first embodiment of the present invention will be described below with reference to the drawings. 1 and 2 show a perspective view and a cross-sectional view of a lithium ion secondary battery (hereinafter also simply referred to as "battery") 1 according to Embodiment 1. FIG. 3 shows a perspective view of the positive electrode plate 31 that constitutes the battery 1. As shown in FIG. In the following description, the battery vertical direction BH, the battery horizontal direction CH, and the battery thickness direction DH of the battery 1 are defined as the directions shown in FIGS. 1 and 2 . Further, the longitudinal direction EH, width direction FH, and thickness direction GH of the positive electrode plate 31 are defined as the directions shown in FIG.

The battery 1 is a prismatic sealed lithium-ion secondary battery mounted in a vehicle such as a hybrid car, a plug-in hybrid car, an electric car, or the like. The battery 1 comprises a battery case 10, an electrode body 20 housed therein, a positive terminal member 70 and a negative terminal member 80 supported by the battery case 10, and the like. The battery case 10 contains an electrolytic solution 15 , part of which is impregnated in the electrode assembly 20 . This electrolytic solution 15 contains lithium hexafluorophosphate (LiPF ₆ ) as a solute.

Among them, the battery case 10 has a rectangular parallelepiped box shape and is made of metal (aluminum in the first embodiment). The battery case 10 is composed of a case main body member 11 in the shape of a bottomed square cylinder with an opening only on the upper side, and a case cover member 13 in the shape of a rectangular plate welded so as to close the opening of the case main body member 11 . be. A positive electrode terminal member 70 made of aluminum is fixed to the case lid member 13 while being insulated from the case lid member 13 . The positive electrode terminal member 70 is connected to the positive electrode exposed portion 31m of the positive electrode plate 31 of the electrode body 20 in the battery case 10 to be electrically connected, and extends through the case lid member 13 to the outside of the battery. A negative electrode terminal member 80 made of copper is fixed to the case lid member 13 while being insulated from the case lid member 13 . The negative electrode terminal member 80 is connected to the negative electrode exposed portion 51m of the negative electrode plate 51 of the electrode body 20 in the battery case 10 and is electrically connected, and extends through the case lid member 13 to the outside of the battery.

The electrode body 20 has a flat shape and is accommodated in the battery case 10 in a laid down state. Between the electrode body 20 and the battery case 10, a bag-shaped insulating film enclosure 19 made of an insulating film is arranged. The electrode body 20 is formed by stacking a strip-shaped positive electrode plate 31 and a strip-shaped negative electrode plate 51 on each other with a pair of strip-shaped porous resin membrane separators 61 interposed therebetween, and then flatly wound around the axis. It becomes

The positive electrode plate 31 (see also FIG. 3) has a positive collector foil 32 made of strip-shaped aluminum foil. A positive electrode active material layer 33 is formed in a strip shape on one main surface 32a of the positive electrode current collector foil 32 on a region that is part of the positive electrode plate 31 in the width direction FH and extends in the longitudinal direction EH. A positive electrode active material layer 34 is also formed in a strip shape on a region of the other main surface 32b of the positive electrode current collector foil 32 that is part of the positive electrode plate 31 in the width direction FH and extends in the longitudinal direction EH. .

These positive electrode active material layers 33 and 34 contain positive electrode active material particles 41 made of lithium oxide capable of intercalating and deintercalating lithium ions, a conductive material 42 and a binder 43 . In Embodiment 1, lithium-nickel-cobalt-aluminum composite oxide particles having a layered rock salt structure, specifically Li _1.02 (Ni _0.82 Co _0.14 Al _0.04 )O ₂ particles, are used as the positive electrode active material particles 41 . Phosphorus-containing coatings 41y, which are coatings containing phosphorus, are formed on the particle surfaces 41a of the positive electrode active material particles 41 (see FIG. 4). Further, in Embodiment 1, acetylene black (AB) is used as the conductive material 42 and polyvinylidene fluoride (PVDF) is used as the binder 43 .
At one end of the positive electrode plate 31 in the width direction FH, the positive electrode active material layers 33 and 34 do not exist in the thickness direction GH, and the positive electrode collector foil 32 is exposed in the thickness direction GH. It's becoming The aforementioned positive electrode terminal member 70 is welded to the positive electrode exposed portion 31m.

The negative electrode plate 51 has a negative current collecting foil 52 made of strip-shaped copper foil (see FIG. 2). A strip-shaped negative electrode active material layer (not shown) is formed on one main surface of the negative electrode current collector foil 52 on a region that is part of the width direction of the negative electrode plate 51 and extends in the longitudinal direction. A negative electrode active material layer (not shown) is also formed in a belt shape on a region of the other main surface of the negative electrode current collector foil 52 that is part of the width direction of the negative electrode plate 51 and extends in the longitudinal direction. . These negative electrode active material layers are composed of negative electrode active material particles, a binder and a thickener. In Embodiment 1, graphite particles are used as the negative electrode active material particles, styrene-butadiene rubber (SBR) is used as the binder, and carboxymethyl cellulose (CMC) is used as the thickener.
At one end of the negative electrode plate 51 in the width direction, there is no negative electrode active material layer in the thickness direction, and the negative electrode collector foil 52 is exposed in the thickness direction to form a negative electrode exposed portion 51m. The aforementioned negative electrode terminal member 80 is welded to the negative electrode exposed portion 51m.

Next, a method for manufacturing the battery 1 will be described (see FIGS. 5 to 7). First, the positive electrode active material particles 41 are manufactured in the particle manufacturing step S110 (see FIG. 7) in the paste manufacturing step S11 (see FIG. 6) of the positive electrode plate manufacturing step S1 (see FIG. 5).
That is, first, in the "dissolving step S111" of the "particle manufacturing step S110", the phosphoric acid compound is dissolved in the first dispersion medium to prepare a phosphoric acid compound solution. In Embodiment 1, inorganic phosphoric acid (H ₃ PO ₄ ) and lithium phosphate (Li ₃ PO ₄ ), which is a salt of inorganic phosphoric acid, are used as the phosphoric acid compound, and water is used as the first dispersion medium. Specifically, 10 g of inorganic phosphoric acid and 90 g of lithium phosphate are dissolved in 100 g of water, and the pH is 4.0 to 5.2 (pH = 5.0 in the first embodiment). An acid compound solution was prepared.

Next, in the “particle mixing step (corresponding to the contact step described above) S112”, the above-mentioned phosphate compound solution is brought into contact with the pre-treated positive electrode active material particles 41x (see FIG. 4) (the phosphate compound solution is the positive electrode active material particles 41x are mixed). In Embodiment 1, lithium-nickel-cobalt-aluminum composite oxide particles having a layered rock salt structure, specifically, Li _1.02 (Ni _0.82 Co _0.14 Al _0.04 ) having an average particle size of 11 μm, are used as the untreated positive electrode active material particles 41x. _O2 particles were used. The positive electrode active material particles 41x before treatment have a pH of 11.3 or higher (pH=11.6 in Embodiment 1) of a dispersion obtained by dispersing 1 g of positive electrode active material particles 41x before treatment in 50 g of water. It has the characteristics of

Specifically, at an ambient temperature of 25° C., 120 g of the positive electrode active material particles 41x before treatment were added to 100 g of the phosphoric acid compound solution, and stirred and mixed for 1 hour. As a result, the resistor (such as lithium carbonate) already formed on the particle surface 41xa of the positive electrode active material particles 41x before treatment is removed, and the coating containing phosphorus is formed on the particle surfaces 41xa of the positive electrode active material particles 41x before treatment. is formed. Further, the phosphorus-containing coating 41y of Embodiment 1 is considered to be a coating made of lithium phosphate (Li ₃ PO ₄ ). In Embodiment 1, the positive electrode active material particles contained in the phosphoric acid compound solution after the particle mixing step S112 correspond to the above-mentioned "post-contact and pre-drying positive electrode active material particles 41z".

Next, in the “particle drying step S113”, the positive electrode active material particles 41z before drying after contact that have been wetted with the phosphoric acid compound solution are dried to obtain positive electrode active material particles in which the phosphorus-containing coating 41y is formed on the particle surface 41a. get 41. Specifically, the mixed solution obtained in the particle mixing step S112 was filtered to recover the positive electrode active material particles 41z after contact and before drying. After that, the post-contact and pre-drying positive electrode active material particles 41z were dried by heating with hot air at 150° C. or less (130° C. in the first embodiment) to obtain the positive electrode active material particles 41 .
After that, the positive electrode active material particles 41 were sieved to obtain the positive electrode active material particles 41 having a predetermined particle size or less. Thus, the positive electrode active material particles 41 having the phosphorus-containing coating 41y on the particle surface 41a were produced.

Next, in the “mixed paste forming step S120” of the paste manufacturing step S11 (see FIG. 6), the positive electrode active material particles 41 manufactured in the particle manufacturing step S110 and the second dispersion medium are mixed, A positive electrode paste 45 is formed. In Embodiment 1, N-methyl-2-pyrrolidone (NMP) is used as the second dispersion medium. The positive electrode paste 45 also includes a conductive material 42 (AB in the first embodiment) and a binder 43 (PVDF in the first embodiment). Specifically, the weight mixing ratio of the positive electrode active material particles 41, the conductive material 42, and the binder 43 is set to 93:6:1, and the solid content rate NV of the positive electrode paste 45 is 70 wt% (NMP rate is 30 wt%). %), the positive electrode active material particles 41, the conductive material 42 and the binder 43 were kneaded with MP. Thus, the positive electrode paste 45 was produced.

Next, in the "first coating step S12" (see FIG. 6), the positive electrode paste 45 produced in the paste producing step S11 is die-coated on one main surface 32a of the separately prepared positive electrode current collector foil 32. is applied by a process to form an undried active material layer 33x.
Next, in the "first layer drying step S13", the undried active material layer 33x on the positive electrode current collector foil 32 is dried to form the positive electrode active material layer 33. As shown in FIG. Specifically, the positive electrode current collector foil 32 on which the undried active material layer 33x is formed is conveyed into a heating and drying furnace, and hot air is applied to the undried active material layer 33x to heat and dry the undried active material layer 33x. Then, the positive electrode active material layer 33 was formed.

Next, in the “second coating step S14”, the positive electrode paste 45 described above is applied onto the other main surface 32b of the positive electrode current collector foil 32 to form the undried active material layer 34x.
Next, in the “second layer drying step S15”, the undried active material layer 34x on the main surface 32b of the positive electrode current collector foil 32 is dried to form the positive electrode active material layer 34. FIG. Specifically, the positive electrode current collector foil 32 having the undried active material layer 34x formed on the main surface 32b is conveyed into a heating and drying furnace, and hot air is applied to the undried active material layer 34x to dry the undried active material. Layer 34x was dried by heating to form cathode active material layer 34 .
Next, in "pressing step S16", the positive electrode plate is pressed by a roll press (not shown) to increase the density of the positive electrode active material layers 33 and 34, respectively. Thus, the positive electrode plate 31 was manufactured.

Separately, in the "negative plate manufacturing step S2" (see FIG. 5), the negative electrode plate 51 is manufactured. Specifically, negative electrode active material particles (graphite particles in the first embodiment), a binder (SBR in the first embodiment) and a thickener (CMC in the first embodiment) are added to a dispersion medium (the 1 was kneaded with water) to produce a negative electrode paste. This negative electrode paste is applied on one main surface of the negative electrode current collector foil 52 by die coating to form an undried active material layer (not shown), and then this undried active material layer is heated with hot air. It is dried to form a negative electrode active material layer (not shown). Similarly, the negative electrode paste is also applied to the other main surface of the negative electrode current collector foil 52 to form an undried active material layer (not shown), and then the undried active material layer is dried by heating, A negative electrode active material layer (not shown) is formed. Thereafter, this negative electrode plate is pressed with a roll press (not shown) to increase the density of the negative electrode active material layer. Thus, the negative electrode plate 51 was manufactured.

Next, in the "electrode body forming step S3", the electrode body 20 is formed. Specifically, the positive electrode plate 31 and the negative electrode plate 51 were stacked with two separators 61, 61 interposed therebetween, and wound around the axis using a winding core. Thereafter, this was compressed into a flat shape to form a flat wound electrode body 20 (see FIG. 2).

Next, in "battery assembly step S4", the battery 1 is assembled. Specifically, the case lid member 13 is prepared, and the positive electrode terminal member 70 and the negative electrode terminal member 80 are fixed thereto (see FIGS. 1 and 2). After that, the positive electrode terminal member 70 and the negative electrode terminal member 80 were welded to the positive electrode exposed portion 31m of the positive electrode plate 31 and the negative electrode exposed portion 51m of the negative electrode plate 51 of the electrode assembly 20, respectively. Next, the electrode body 20 is covered with the insulating film surrounding body 19 and inserted into the case body member 11 , and the opening of the case body member 11 is closed with the case lid member 13 . Then, the battery case 10 was formed by welding the case body member 11 and the case lid member 13 together.

Next, in the “injection step S5”, the electrolytic solution 15 is injected into the battery case 10 through the injection hole 13h to impregnate the electrode assembly 20 with the electrolyte solution 15 . After that, the sealing member 17 seals the injection hole 13h.
Next, in the "initial charging step S6", the battery 1 is initially charged. After that, the battery 1 is subjected to various tests. Thus, the battery 1 is completed.

As described above, in Embodiment 1, by performing the particle mixing step S112 and the particle drying step S113, the resistor (carbonic acid) already formed on the particle surface 41xa of the untreated positive electrode active material particle 41x Lithium, etc.) can be removed. Moreover, positive electrode active material particles 41 having phosphorus-containing coatings 41y on particle surfaces 41a can be obtained. The positive electrode active material particles 41 are less likely to react with moisture and carbon dioxide in the atmosphere than the positive electrode active material particles that do not have the phosphorus-containing coating 41y on the particle surface. Lithium carbonate (Li ₂ CO ₃ ), which serves as a resistor, is difficult to form. In addition, since the positive electrode active material particles 41 are less likely to react with water than the positive electrode active material particles that do not have the phosphorus-containing coating 41y on the particle surface, lithium ions are released from the positive electrode active material particles 41 by the reaction with water. Therefore, it is possible to suppress the change in the crystal structure of the positive electrode active material particles 41 . Therefore, if the positive electrode paste 45 is prepared using the positive electrode active material particles 41, the positive electrode plate 31 is formed using the positive electrode paste 45, and the battery 1 is manufactured using the positive electrode plate 31, phosphorus-containing The IV resistance of the battery can be suppressed as compared with a battery using positive electrode active material particles that do not have the coating 41y on the particle surface.

Further, in Embodiment 1, the phosphoric acid compound is at least inorganic phosphoric acid (inorganic phosphoric acid and lithium phosphate in Embodiment 1) among inorganic phosphoric acid and inorganic phosphoric acid salts, and the first dispersion medium is water. In this case, the lower the pH of the phosphoric acid compound solution before contact with the untreated positive electrode active material particles 41x, the more the positive electrode active material particles 41 are damaged by the acid in the particle mixing step S112 and thereafter. Specifically, it has been found that lithium ions are eluted from the positive electrode active material particles 41 and the crystal structure of the positive electrode active material particles 41 is irreversibly changed. On the other hand, if the pH of the phosphate compound solution before contact with the unprocessed positive electrode active material particles 41x is too high, the salt of inorganic phosphoric acid (lithium phosphate in the first embodiment) becomes granular in the phosphate compound solution. Precipitate.

On the other hand, in Embodiment 1, the pH of the phosphate compound solution before contact with the untreated positive electrode active material particles 41x is set to pH=4.0 to 5.2 (pH=5.0 in Embodiment 1). ). By setting the pH of the phosphoric acid compound solution to be 4.0 or higher, the positive electrode active material particles 41 are less damaged by the acid in the particle mixing step S112 and thereafter than when the pH is lower than 4.0. can be suppressed. On the other hand, by adjusting the pH of the phosphate compound solution to 5.2 or less, it is possible to prevent the salt of inorganic phosphoric acid (lithium phosphate) from depositing in the phosphate compound solution in granular form.

Further, in Embodiment 1, the positive electrode having the characteristic that the pH of the dispersion liquid obtained by dispersing 1 g of the untreated positive electrode active material particles 41x in 50 g of water becomes pH=11.3 or higher as the untreated positive electrode active material particles 41x. Active material particles are used. Such positive electrode active material particles 41x before treatment are particularly likely to react with water and carbon dioxide to produce lithium hydroxide and further lithium carbonate. tends to be high. Therefore, as described above, it is particularly preferable to provide the phosphorus-containing coating 41y on the particle surface 41a of the positive electrode active material particle 41 to suppress the reaction with water and carbon dioxide.

( Reference form )
Next, a reference form will be described. In Embodiment 1, inorganic phosphoric acid and a salt of inorganic phosphoric acid (lithium phosphate) were used as the phosphoric acid compound. In contrast, in the present embodiment , only inorganic phosphoric acid is used as the phosphoric acid compound.
Further, in Embodiment 1, the particle drying step S113 was performed following the particle mixing step S112 to manufacture the positive electrode active material particles 41 . On the other hand, in the particle manufacturing step S710 of this reference embodiment , as indicated by the dashed line in FIG. ) is different in that S715 is executed.

Specifically, in the present embodiment , in the particle manufacturing step S710 (see FIG. 7) of the paste manufacturing step S71 (see FIG. 6) of the positive electrode plate manufacturing step S7 (see FIG. 5), the positive electrode active material particles 141 are manufacture. That is, first, in the “dissolving step S111”, only inorganic phosphoric acid (H ₃ PO ₄ ) is used as the phosphoric acid compound, and 100 g of inorganic phosphoric acid is dissolved in 100 g of the first dispersion medium (also water in this embodiment ). to prepare a phosphate compound solution. The pH of this phosphate compound solution is pH=3.0.

Next, in the “particle mixing step (contact step) S112”, the same untreated positive electrode active material particles 41x (see FIG. 4) as in Embodiment 1 are added to the phosphoric acid compound solution described above, and Mix. As a result, the resistor (such as lithium carbonate) already formed on the particle surface 41xa of the positive electrode active material particles 41x before treatment is removed, and the coating containing phosphorus is formed on the particle surfaces 41xa of the positive electrode active material particles 41x before treatment. is formed. Further, the phosphorus-containing coating 141y of this reference embodiment is also considered to be a coating made of lithium phosphate (Li ₃ PO ₄ ).

After that, in the present reference embodiment , in the "alkali mixing step S715", an alkaline aqueous solution is added to the phosphoric acid compound solution to adjust the pH to 5.2 or higher. Specifically, an alkaline aqueous solution obtained by dissolving lithium hydroxide (LiOH) in water is prepared as the alkaline aqueous solution, and this alkaline aqueous solution is added to and mixed with the phosphoric acid compound solution to which the untreated positive electrode active material particles 41x are added. Therefore, the pH was set to 5.2 or more (pH=11.5 in the present embodiment ). In this reference embodiment , the positive electrode active material particles contained in the phosphoric acid compound solution after the alkali mixing step S715 correspond to the above-mentioned "post-contact and pre-drying positive electrode active material particles 141z".

Next, in the “particle drying step S113”, in the same manner as in Embodiment 1, the post-contact and pre-drying positive electrode active material particles 141z wet with the phosphoric acid compound solution are dried, and the phosphorus-containing coatings 141y are formed on the particle surfaces 141a. to obtain positive electrode active material particles 141 formed with Thus, positive electrode active material particles 141 were manufactured.

Thereafter, in the same manner as in Embodiment 1, the positive electrode active material particles 141 are used to produce the positive electrode paste 145, the positive electrode paste 145 is used to produce the positive electrode plate 131, and the positive electrode plate 131 is used to produce the battery. 100 are manufactured. That is, in the mixed paste forming step S120 (see FIG. 6), the positive electrode active material particles 141 and the second dispersion medium (also NMP in this embodiment ) are mixed to form the positive electrode paste 145 . Thereafter, in the "first coating step S12", the positive electrode paste 145 is used to form an undried active material layer 133x on one main surface 32a of the positive electrode current collector foil 32, followed by the "first layer drying step S13. , the undried active material layer 133 x is dried to form the positive electrode active material layer 133 .

Thereafter, in the "second coating step S14", the positive electrode paste 145 is used to form the undried active material layer 134x also on the other main surface 32b of the positive electrode current collector foil 32, followed by the "second layer drying step S15. ”, the undried active material layer 134 x is dried to form the positive electrode active material layer 134 . Thereafter, in a pressing step S16, this positive electrode plate is pressed to increase the density of the positive electrode active material layers 133 and 134, respectively. Thus, the positive electrode plate 131 was manufactured.

Separately, in the "negative electrode plate manufacturing step S2" (see FIG. 5), the negative electrode plate 51 is manufactured in the same manner as in the first embodiment. Next, in the "electrode assembly step S3", the electrode assembly 20 is formed using the positive electrode plate 131, the negative electrode plate 51, and the two separators 61, 61 described above. After that, the “battery assembly step S4”, the “injection step S5”, and the “initial charging step S6” are performed in the same manner as in the first embodiment to manufacture the battery 100. FIG.

Also in this reference embodiment , by performing the particle mixing step (contact step) S112 and the particle drying step S113, the resistor (such as lithium carbonate) already formed on the particle surface 41xa of the positive electrode active material particle 41x before treatment can be removed. . In addition, positive electrode active material particles 141 having phosphorus-containing coatings 141y on particle surfaces 141a can be obtained. The positive electrode active material particles 141 are also less likely to react with water than the positive electrode active material particles that do not have the phosphorus-containing coating 141y on the particle surface. A change in the crystal structure of the active material particles 141 can be suppressed. Therefore, if the positive electrode paste 145 is prepared using the positive electrode active material particles 141, the positive electrode plate 131 is formed using the positive electrode paste 145, and the battery 100 is manufactured using the positive electrode plate 131, phosphorus-containing The IV resistance of the battery can be suppressed as compared with a battery using positive electrode active material particles that do not have the coating 141y on the particle surface.

Furthermore, in this reference embodiment , inorganic phosphoric acid is used as the phosphoric acid compound, and water is used as the first dispersion medium. Therefore, the pH of the phosphate compound solution before contact with the untreated positive electrode active material particles 41x is low. As described above, the lower the pH of the phosphate compound solution, the more the positive electrode active material particles 141 are damaged by the acid in the particle mixing step S112 and thereafter (lithium ions are eluted and the crystal structure is irreversibly changed. ). In contrast, in the present embodiment , after the particle mixing step S112 and before the particle drying step S113, in the alkali mixing step (alkali adding step) S715, an alkaline aqueous solution is added to set the pH to 5.2 or higher. Compared to the case where the mixing step S715 is not performed, it is possible to prevent the positive electrode active material particles 141 from being greatly damaged by the acid after the particle mixing step S112. In addition, the parts similar to those of the first embodiment have the same effects as those of the first embodiment.

(Examples , reference examples and comparative examples)
Next, the results of tests conducted to verify the effects of the present invention will be described. The battery 1 of Embodiment 1 was prepared as Example 1, and the battery 100 of the reference form was prepared as a reference example .
On the other hand, as Comparative Example 1, the positive electrode active material particles without the phosphorus-containing coatings 41y and 141y, that is, the untreated positive electrode active material particles 41x of Embodiment 1 and the reference form are used as they are, and the paste manufacturing step S11 is performed to perform the positive electrode. A paste was made. Other than that, the battery was manufactured in the same manner as in the first embodiment.

Further, as Comparative Example 2, in the paste manufacturing step S11, the positive electrode active material particles without the phosphorus-containing coatings 41y and 141y (positive electrode active material particles 41x before treatment) were used as they were, and the positive electrode active material particles were added to the positive electrode paste. A positive electrode paste was produced by mixing 1 g of lithium phosphate (Li ₃ PO ₄ ) with 100 g of (untreated positive electrode active material particles 41x). A battery was manufactured using this positive electrode paste. That is, in Embodiment 1, lithium phosphate (Li ₃ PO ₄ ) was used in the process of manufacturing the positive electrode active material particles 41 (particle manufacturing step S110), whereas in Comparative Example 2, the process of mixing the positive electrode paste was The difference is that lithium phosphate is used in (mixed paste forming step S120).

Next, the IV resistance R was measured for 10 batteries each of Example 1, Reference Example , and Comparative Examples 1 and 2. Specifically, each battery adjusted to SOC 50% is discharged for 5 seconds at a discharge current value I = 5C at an ambient temperature of 25 ° C., and the battery voltage V1 at the start of this discharge and the battery voltage V2 after 5 seconds was measured, and the IV resistance R of each battery was calculated from R=(V1-V2)/I. Furthermore, with the IV resistance value (average value) of the battery according to Comparative Example 1 as a reference (=100%), the IV resistance ratio (average value) of the batteries according to Example 1, Reference Example , and Comparative Example 2 was obtained. . The results are shown in FIG.

Compared with the batteries of Comparative Examples 1 and 2, the IV resistance ratios of the batteries 1 and 100 of Example 1 and Reference Example were lower (93.0% in Example 1 and 94.7% in Reference Example ). The reason for such results is considered as follows. That is, in Comparative Example 1, since the particle mixing step (contact step) S112 and the particle drying step S113 were not performed, the particle surfaces 41xa of the positive electrode active material particles (pre-treated positive electrode active material particles 41x) were coated with lithium carbonate or the like. Resistors remain, and phosphorus-containing films 41y and 141y are not formed.

Also in Comparative Example 2, since the particle mixing step S112 and the particle drying step S113 were not performed, a resistor such as lithium carbonate remained on the particle surface 41xa of the positive electrode active material particles (untreated positive electrode active material particles 41x). Moreover, the phosphorus-containing films 41y and 141y are not formed. In Comparative Example 2, lithium phosphate is added to the positive electrode paste in the positive electrode paste mixing process (mixed paste forming step S120). However, the phosphorus-containing coatings 41y and 141y are not formed on the particle surfaces 41xa of the positive electrode active material particles (untreated positive electrode active material particles 41x) only by adding lithium phosphate to the positive electrode paste.

Therefore, in Comparative Examples 1 and 2, in the process of manufacturing the battery, the positive electrode active material particles (untreated positive electrode active material particles 41x) come into contact with moisture in the atmosphere, react with water on the particle surfaces 41xa, and undergo hydroxylation. Lithium is produced (Li ₂ O+H ₂ O→2LiOH). Furthermore, this lithium hydroxide reacts with carbon dioxide in the atmosphere to produce lithium carbonate (2LiOH+CO ₂ →Li ₂ CO ₃ +H ₂ O). Lithium carbonate generated on the particle surface 41xa of the positive electrode active material particles (untreated positive electrode active material particles 41x) is a resistor. Further, when the positive electrode active material particles (pre-treated positive electrode active material particles 41x) react with water and lithium ions are released from the positive electrode active material particles (pre-treated positive electrode active material particles 41x), the positive electrode active material particles (pre-treated positive electrode active material particles 41x) The crystal structure of the particles 41x) changes, and insertion and extraction of lithium ions in the positive electrode active material particles (untreated positive electrode active material particles 41x) becomes difficult. For this reason, in the batteries of Comparative Examples 1 and 2, the IV resistance R is considered to be high.

On the other hand, in Example 1 and Reference Example , the particle mixing step (contact step) S112 and the particle drying step S113 were performed to remove the resistor on the particle surface 41xa of the positive electrode active material particle 41x before treatment, and to remove the resistor on the particle surface 41xa. Phosphorus-containing coatings 41y and 141y are formed. Such positive electrode active material particles 41 and 141 are less likely to come into contact with moisture and carbon dioxide in the air. Therefore, in the process of manufacturing the battery, lithium hydroxide and lithium carbonate are generated on the particle surfaces 41a and 141a of the positive electrode active material particles 41 and 141 due to contact with moisture and carbon dioxide in the atmosphere. , and changes in the crystal structure on the particle surfaces 41a and 141a can be suppressed. As a result, the batteries 1 and 100 of Example 1 and Reference Example had lower IV resistance ratios (lower IV resistance R) than the batteries of Comparative Examples 1 and 2.

In the above, the present invention has been described in accordance with the first embodiment, but the present invention is not limited to the above-described first embodiment, and it goes without saying that the present invention can be appropriately modified and applied without departing from the gist thereof. .
For example, in Embodiment 1 , lithium-nickel-cobalt-aluminum composite oxide particles are used as the untreated positive electrode active material particles 41x, but the present invention is not limited to this. For example, lithium-nickel-cobalt-manganese composite oxide particles, olivine-type lithium iron phosphate particles, spinel-type lithium-manganese oxide particles, or the like can be used as the positive electrode active material particles 41x before treatment.

Further, in Embodiment 1 and the like , the case of using inorganic phosphoric acid and a salt of inorganic phosphoric acid (lithium phosphate) as the phosphoric acid compound (Embodiment 1) and the case of using only inorganic phosphoric acid ( reference form ) are illustrated. However, it is not limited to this. For example, as the phosphoric acid compound, an organic phosphoric acid such as phenylphosphonic acid or methylphosphonic acid, or a salt (lithium salt or the like) of phenylphosphonic acid or methylphosphonic acid can be used.

1,100 Lithium ion secondary battery (battery)
20 electrode bodies 31, 131 positive electrode plate 32 positive electrode current collector foils 33, 34, 133, 134 positive electrode active material layers 33x, 34x, 133x, 134x undried active material layers 41, 141 positive electrode active material particles 41a, 141a (positive electrode active material Particle surface 41x of particles Pre-treatment positive electrode active material particles 41z, 141z Post-contact and pre-drying positive electrode active material particles 41xa Particle surfaces 41y, 141y (of positive electrode active material particles before treatment) Phosphorus-containing coatings 45, 145 Positive electrode paste 51 Negative electrode plate S1 , S7 positive electrode plate manufacturing process S4 battery assembly process S11, S71 paste manufacturing process S110, S710 particle manufacturing process S120 mixed paste forming process S12 first coating process S13 first layer drying process S14 second coating process S15 second layer drying Step S111 Dissolution step S112 Particle mixing step (contact step)
S715 Alkali mixing step (alkali addition step)
S113 Particle drying step

Claims (5)

A method for producing positive electrode active material particles capable of inserting and extracting lithium ions,
A phosphoric acid compound solution obtained by dissolving a phosphoric acid compound that is at least one of inorganic phosphoric acid (H ₃ PO ₄ ), a salt of inorganic phosphoric acid, organic phosphoric acid, and a salt of organic phosphoric acid in a first dispersion medium before treatment. A contacting step of contacting the positive electrode active material particles;
After the contacting step, a particle drying step of drying the post-contact and pre-drying positive electrode active material particles wetted with the phosphoric acid compound solution to obtain the positive electrode active material particles having a coating containing phosphorus on the particle surface; with
The phosphoric acid compound is an inorganic phosphoric acid and a salt of an inorganic phosphoric acid,
The first dispersion medium is water,
The method for producing positive electrode active material particles, wherein the pH of the phosphoric acid compound solution before being brought into contact with the untreated positive electrode active material particles is pH=4.0 to 5.2. A method for producing the positive electrode active material particles according to claim 1,
The positive electrode active material particles before treatment are
A method for producing positive electrode active material particles having a characteristic that the pH of a dispersion obtained by dispersing 1 g of the positive electrode active material particles before treatment in 50 g of water is pH=11.3 or higher. A method for producing a positive electrode paste containing positive electrode active material particles capable of inserting and removing lithium ions and a second dispersion medium,
A particle manufacturing step of manufacturing the positive electrode active material particles by the method for manufacturing positive electrode active material particles according to claim 1 or claim 2;
A mixed paste forming step of mixing the positive electrode active material particles and the second dispersion medium to form the positive electrode paste. A method for producing a positive electrode plate comprising a current collector foil and an active material layer formed on the current collector foil and containing positive electrode active material particles capable of inserting and extracting lithium ions,
A paste manufacturing step for manufacturing the positive electrode paste by the positive electrode paste manufacturing method according to claim 3;
a coating step of coating the positive electrode paste on the current collector foil to form an undried active material layer;
a layer drying step of drying the undried active material layer on the current collector foil to form the active material layer. A method for producing a lithium ion secondary battery comprising a positive electrode plate having a current collector foil and an active material layer formed on the current collector foil and containing positive electrode active material particles capable of inserting and extracting lithium ions,
A positive electrode plate manufacturing process for manufacturing the positive electrode plate by the positive electrode plate manufacturing method according to claim 4;
A method for manufacturing a lithium ion secondary battery, comprising: a battery assembling step of assembling the lithium ion secondary battery using the positive electrode plate.

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