JP6973062B2 - Positive electrode plate of lithium ion secondary battery - Google Patents

Description

The present invention relates to a positive electrode plate of a lithium ion secondary battery in which an active material layer containing positive electrode active material particles made of lithium oxide is formed on a current collector foil.

As a positive electrode plate used for a lithium ion secondary battery (hereinafter, also simply referred to as “battery”), a positive electrode plate in which an active material layer containing positive electrode active material particles made of lithium oxide is formed on a current collecting foil is known. ing. Further, as positive electrode active material particles made of lithium oxide, lithium nickel cobalt aluminum composite oxide particles, lithium nickel cobalt manganese composite oxide particles, olivine type iron phosphate lithium particles, spinel type lithium manganese oxide particles and the like are known. Has been done. For example, Patent Document 1 discloses lithium nickel-cobalt-aluminum composite oxide particles as positive electrode active material particles (see the scope of claims of Patent Document 1).

Japanese Unexamined Patent Publication No. 2016-88876

However, when the positive electrode active material particles made of lithium oxide come into contact with water in the atmosphere, _{they react with water (H 2} O) on the surface of the particles 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 ) (2 LiOH + 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. Further, when the positive electrode active material particles react with water and lithium ions are removed from the positive electrode active material particles, the crystal structure of the positive electrode active material particles changes, and it becomes difficult for the lithium ions to be inserted and removed from the positive electrode active material particles. Therefore, in a battery using this positive electrode plate, the reaction resistance becomes high.

The present invention has been made in view of the present situation, and is a lithium ion capable of suppressing an increase in the reaction resistance of a battery when the battery is formed due to contact with moisture and carbon dioxide in the atmosphere. It is an object of the present invention to provide a positive electrode plate of a secondary battery.

One aspect of the present invention for solving the above problems is a collector foil, a first active material layer formed on the current collector foil and containing first positive electrode active material particles made of lithium oxide, and the first active material layer. A positive electrode plate of a lithium ion secondary battery formed on one active material layer and comprising a second active material layer containing the second positive positive active material particles, wherein the first positive positive active material particles are 1 g of the above. The second positive electrode active material particle has a characteristic that the pH of the dispersion liquid in which the first positive electrode active material particle is dispersed in 50 g of water is pH = 11.3 or more, and the second positive electrode active material particle is 1 g of the second positive electrode active material particle. The second active material layer has a characteristic that the pH of the dispersion liquid in which 50 g of water is dispersed is pH = 11.0 or less, and the second active material layer is a positive electrode plate of a lithium ion secondary battery containing a depolarizer particle.

As the first positive electrode active material particles to be included in the first active material layer, there are cases where it is desired to use positive electrode active material particles having a characteristic that the pH of the dispersion liquid is pH = 11.3 or more. However, since such positive electrode active material particles are particularly likely to react with water and carbon dioxide to generate lithium hydroxide and lithium carbonate, the reaction resistance becomes high in a battery using this positive electrode plate as described above. ..
On the other hand, in the above-mentioned positive electrode plate, since the second active material layer is provided on the first active material layer, the first positive electrode active material particles in the first active material layer are used when handling the positive electrode plate or the like. , Moisture in the atmosphere and carbon dioxide are less likely to come into contact. Therefore, due to the contact with water and carbon dioxide, lithium hydroxide and further lithium carbonate are generated on the particle surface of the first positive electrode active material particles in the first active material layer, and crystals are formed on the particle surface. It is possible to suppress the change of the structure.
On the other hand, the second positive electrode active material particles contained in the second active material layer have a characteristic that the pH of the dispersion liquid is pH = 11.0 or less. That is, the second positive electrode active material particles have a milder reaction with water and carbon dioxide than the first positive electrode active material particles. Therefore, when looking at the entire active material layer including the first active material layer and the second active material layer, the water content and carbon dioxide are higher than when the entire active material layer is composed of only the first active material layer. It is possible to suppress the formation of lithium hydroxide and further lithium carbonate on the particle surface of the positive electrode active material particles due to the contact with the positive particle, and the change in the crystal structure on the particle surface.

In addition, since the second active material layer contains the hygroscopic agent particles, even if the positive electrode plate comes into contact with the moisture in the atmosphere, the moisture is absorbed by the hygroscopic agent particles in the second active material layer, so that the moisture is second. It is possible to suppress the reaction with the second positive electrode active material particles in the two active material layers. In addition, it is possible to more effectively suppress the water from reaching the first active material layer below the second active material layer.
As a result, in a battery using this positive electrode plate, a positive electrode plate having suppressed reaction resistance of the battery can be obtained as compared with a battery using a positive electrode plate having no second active material layer on the first active material layer. can.
Further, since the second active material layer contains the positive electrode active material particles (second positive electrode active material particles), the positive electrode plate is compared with the case where the second active material layer is simply a protective layer containing no positive electrode active material particles. The total amount of positive electrode active material particles contained in the above can be increased to increase the battery capacity.

Examples of the "moisture absorbent particles" include silica gel, gypsum, zeolites such as Molecular Sieve (registered trademark) (MS), and particles such as aluminum oxide, boehmite, calcium oxide, calcium chloride, and diphosphorus pentoxide. ..

Further, it is preferable that the positive electrode plate of the lithium ion secondary battery is the positive electrode plate of the lithium ion secondary battery, which is at least one of aluminum oxide particles and boehmite particles, as the hygroscopic agent particles.

Aluminum oxide (Al ₂ O ₃ ) particles and boehmite (AlCOOH) particles are inexpensive and easy to handle, so that they are particularly preferably used as the absorbent particles in the above-mentioned positive electrode plate.

Further, it is preferable to use the positive electrode plate of the lithium ion secondary battery as described above, wherein the average particle size of the aluminum oxide particles and the boehmite particles is 2.0 μm or less.

The smaller the average particle size of the aluminum oxide particles and the boehmite particles, the larger the specific surface area of these particles, so that water is more easily adsorbed by the aluminum oxide particles and the boehmite particles (the moisture absorption effect becomes larger). In particular, since the moisture absorption effect is increased by setting the average particle size of the aluminum oxide particles and the boehmite particles to 2.0 μm or less, it is effective that the moisture comes into contact with the first positive electrode active material particles and the second positive electrode active material particles. Can be suppressed.
The average particle size of the aluminum oxide particles and the boehmite particles is preferably 0.2 μm or more from the viewpoint of manufacturing and cost of these particles.

Further, another aspect is a lithium ion secondary battery, which is a lithium ion secondary battery including an electrode body including the positive electrode plate and the negative electrode plate according to any one of the above.

The positive electrode plate used in the above-mentioned lithium ion secondary battery has a second active material layer on the first active material layer. Therefore, in this battery, the reaction resistance of the battery can be suppressed as described above, as compared with the battery using the positive electrode plate which does not have the second active material layer on the first active material layer.

It is a perspective view of the battery which concerns on embodiment. It is sectional drawing of the battery which concerns on embodiment. It is a perspective view of the positive electrode plate which concerns on embodiment. It is sectional drawing of the positive electrode plate which concerns on embodiment. It is a flowchart of the manufacturing method of the battery which concerns on embodiment. It is a graph which shows the relationship between the addition amount of a hygroscopic agent particle, and the reaction resistivity ratio of a battery. It is a graph which shows the relationship between the layer thickness of the 2nd active material layer, and the reaction resistivity ratio of a battery. It is a graph which shows the relationship between the average particle diameter of a hygroscopic agent particle, and the reaction resistivity ratio of a battery.

Hereinafter, embodiments of the present invention will be described 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 the present embodiment. Further, FIGS. 3 and 4 show a perspective view and a cross-sectional view of the positive electrode plate 31 of the battery 1. In the following, the battery vertical direction BH, the battery horizontal direction CH, and the battery thickness direction DH of the battery 1 will be described as the directions shown in FIGS. 1 and 2. Further, the longitudinal direction EH, the width direction FH, and the thickness direction GH of the positive electrode plate 31 will be described as the directions shown in FIGS. 3 and 4.

The battery 1 is a square and sealed lithium ion secondary battery mounted on a vehicle such as a hybrid car, a plug-in hybrid car, or an electric vehicle. The battery 1 is composed of a battery case 10, an electrode body 20 housed therein, a positive electrode terminal member 70 supported by the battery case 10, a negative electrode terminal member 80, and the like. Further, the electrolytic solution 17 is housed in the battery case 10, and a part of the electrolytic solution 17 is impregnated in the electrode body 20. The electrolytic solution 17 contains lithium hexafluorophosphate (LiPF ₆ ) as a solute.

Of these, the battery case 10 has a rectangular parallelepiped shape and is made of metal (aluminum in this embodiment). The battery case 10 is composed of a bottomed square cylindrical case body member 11 having an opening only on the upper side, and a rectangular plate-shaped case lid member 13 welded in a form of closing the opening of the case body member 11. NS. A positive electrode terminal member 70 made of aluminum is fixed to the case lid member 13 in a state of being insulated from the case lid member 13. The positive electrode terminal member 70 is connected to and conducts with the positive electrode exposed portion 31 m of the positive electrode plate 31 of the electrode body 20 inside the battery case 10, while penetrating the case lid member 13 and extending to the outside of the battery. Further, a negative electrode terminal member 80 made of copper is fixed to the case lid member 13 in a state of being insulated from the case lid member 13. The negative electrode terminal member 80 is connected to and conducts with the negative electrode exposed portion 51m of the negative electrode plate 51 of the electrode body 20 inside the battery case 10, while penetrating the case lid member 13 and extending to the outside of the battery.

The electrode body 20 has a flat shape and is housed in the battery case 10 in a state of being laid on its side. A bag-shaped insulating film enclosing body 19 made of an insulating film is arranged between the electrode body 20 and the battery case 10. In the electrode body 20, a band-shaped positive electrode plate 31 and a band-shaped negative electrode plate 51 are superposed on each other via a pair of separators 61 and 61 made of a band-shaped and resin porous film, and are wound flat around an axis. It becomes.

The positive electrode plate 31 (see also FIGS. 3 and 4) has a positive electrode current collector foil 32 made of strip-shaped aluminum foil. On one main surface 32a of the positive electrode current collector foil 32, a first active material layer 33 having a layer thickness t1 = 140 μm is formed on a region of the positive electrode plate 31 that is a part of the width direction FH and extends in the longitudinal direction EH. It is formed in a band shape. Further, on the other main surface 32b of the positive electrode current collector foil 32, which is a part of the FH in the width direction of the positive electrode plate 31 and extends in the EH in the longitudinal direction, the first active material having a layer thickness t1 = 140 μm is also similarly formed. The layer 34 is formed in a band shape.

These first active material layers 33 and 34 include first positive electrode active material particles 41 made of lithium oxide, a conductive material 42, and a binder 43. In the present embodiment, as the first positive electrode active material particles 41 consisting of lithium oxide, lithium-nickel-cobalt-aluminum composite oxide having a layered rock salt structure, specifically, the average particle size is 10μm LiNi _x Co _y Al _{1- Particles of xy} O ₂ (NCA) are used. In addition, x = 0.75 to 0.95, y = 0.05 to 0.25, 1-xy = 0.01 to 0.1. The first positive electrode active material particles 41 have a characteristic that the pH of a dispersion liquid in which 1 g of the first positive electrode active material particles 41 is dispersed in 50 g of water has a pH of 11.3 or more.
Further, in the present embodiment, acetylene black (AB) is used as the conductive material 42, and polyvinylidene fluoride (PVDF) is used as the binder 43. The weight blending ratio of the first positive electrode active material particles 41, the conductive material 42, and the binder 43 is 93: 6: 1.

Further, on one of the first active material layers 33, a second active material layer having a layer thickness t2 = 10 μm (t2 <t1) thinner than the layer thickness t1 = 140 μm of the first active material layer 33 over the entire surface thereof. 35 is formed. Further, on the other first active material layer 34, the second active material layer having a layer thickness t2 = 10 μm (t2 <t1) thinner than the layer thickness t1 = 140 μm of the first active material layer 34 over the entire surface thereof. 36 is formed. These second active material layers 35 and 36 include the second positive electrode active material particles 49, the conductive material 45, the binder 46 and the hygroscopic agent particles 47.

In the present embodiment, as the second positive electrode active material particles 49, a lithium nickel cobalt manganese composite oxide having a layered rock salt structure, specifically, Li _1.02 (Ni _0.33 Co _0.33 Mn _0.33 ) O _{2 having an average particle size of 10 μm.} Particles are used. The second positive electrode active material particles 49 have a characteristic that the pH of the dispersion liquid in which 1 g of the second positive electrode active material particles 49 is dispersed in 50 g of water is pH = 11.0 or less. Further, aluminum oxide particles having an average particle size of 0.5 μm are used as the hygroscopic agent particles 47. Further, AB is used as the conductive material 45 like the conductive material 42 of the first active material layers 33 and 34, and PVDF is used as the binder 46 like the binder 43 of the first active material layers 33 and 34. The weight blending ratio of the second positive electrode active material particles 49, the conductive material 45, the binder 46, and the hygroscopic agent particles 47 is 91: 8: 1: 1.5.
In this embodiment, the ratio of the conductive material 45 in the second active material layers 35 and 36 (7.9 wt%) is higher than the ratio of the conductive material 42 in the first active material layers 33 and 34 (6.0 wt%). There are also many. Therefore, even if the second active material layers 35 and 36 become thick and the positive electrode plate 31 becomes thick, the continuity in the positive electrode plate 31 can be kept high.

At one end of the positive electrode plate 31 in the width direction FH, the first active material layers 33, 34 and the second active material layers 35, 36 do not exist in the thickness direction GH, and the positive electrode current collector foil 32 has a thickness. The positive electrode exposed portion 31 m exposed in the direction GH. The above-mentioned positive electrode terminal member 70 is welded to the positive electrode exposed portion 31m.

The negative electrode plate 51 has a negative electrode current collector foil 52 made of a strip-shaped copper foil. A negative electrode active material layer (not shown) is formed in a band shape on a region of one main surface of the negative electrode current collector foil 52, which is a part of the negative electrode plate 51 in the width direction and extends in the longitudinal direction. Further, a negative electrode active material layer (not shown) is formed in a band shape on a region of the other main surface of the negative electrode current collector foil 52, which is a part of the negative electrode plate 51 in the width direction 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 this embodiment, 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.

As described above, the first positive electrode active material particles 41 are positive electrode active material particles having a characteristic that the pH of the above-mentioned dispersion liquid is pH = 11.3 or more, and in particular, they react with water and carbon dioxide. Prone to generate lithium hydroxide and lithium carbonate. Therefore, the reaction resistance of the battery 1 tends to increase. On the other hand, in the positive electrode plate 31 of the present embodiment, since the second active material layers 35 and 36 are provided on the first active material layers 33 and 34, the first active material is used when the positive electrode plate 31 is handled. Moisture and carbon dioxide in the atmosphere are less likely to come into contact with the first positive electrode active material particles 41 in the layers 33 and 34. Therefore, due to the contact with water and carbon dioxide, lithium hydroxide and further lithium carbonate are generated on the particle surface of the first positive electrode active material particles 41 in the first active material layers 33 and 34, and It is possible to suppress changes in the crystal structure on the particle surface.

On the other hand, the second positive electrode active material particles 49 contained in the second active material layers 35 and 36 have a characteristic that the pH of the above-mentioned dispersion liquid is pH = 11.0 or less. That is, the second positive electrode active material particles 49 have a milder reaction with water and carbon dioxide than the first positive electrode active material particles 41. Therefore, when the entire active material layer including the first active material layers 33 and 34 and the second active material layers 35 and 36 is viewed, the entire active material layer is composed of only the first active material layers 33 and 34. Compared to the above, due to the contact with water and carbon dioxide, lithium hydroxide and further lithium carbonate are applied to the particle surface of the positive electrode active material particles (first positive positive active material particles 41 and second positive positive active material particles 49). It is possible to suppress the occurrence and change of the crystal structure on the particle surface.

In addition, since the second active material layers 35 and 36 contain the hygroscopic agent particles 47, even if the positive electrode plate 31 comes into contact with the moisture in the atmosphere, the moisture remains in the hygroscopic agent particles 47 in the second active material layers 35 and 36. Therefore, it is possible to suppress the reaction of water with the second positive electrode active material particles 49 in the second active material layers 35 and 36. In addition, it is possible to more effectively suppress the water from reaching the first active material layers 33, 34 below the second active material layers 35, 36.
As a result, in the battery 1 using the positive electrode plate 31, the reaction resistance of the battery 1 is compared with the battery using the positive electrode plate having no second active material layers 35, 36 on the first active material layers 33, 34. The positive electrode plate 31 can be obtained.

Further, since the second active material layers 35 and 36 contain the positive electrode active material particles (second positive electrode active material particles 49), the second active material layers 35 and 36 are merely protective layers that do not contain the positive electrode active material particles. Compared with the case, the total amount of the positive electrode active material particles (first positive electrode active material particles 41 and the second positive electrode active material particles 49) contained in the positive electrode plate 31 can be increased to increase the battery capacity.

Further, in the present embodiment, aluminum oxide particles are used as the hygroscopic agent particles 47. Since the aluminum oxide particles are inexpensive and easy to handle, it is particularly preferable to use the aluminum oxide particles as the hygroscopic agent particles 47 in the positive electrode plate 31.
Further, the average particle size of this aluminum oxide is set to 2.0 μm or less (0.5 μm in this embodiment). The smaller the average particle size, the larger the specific surface area, so that water is more easily adsorbed by the aluminum oxide particles (the hygroscopic effect becomes larger). In particular, since the hygroscopic effect is increased by setting the average particle size to 2.0 μm or less, it is possible to effectively suppress the contact of water with the first positive electrode active material particles 41 and the second positive electrode active material particles 49. On the other hand, from the viewpoint of manufacturing and cost of aluminum oxide particles, it is preferable that the average particle size of the aluminum oxide particles is 0.2 μm or more (0.5 μm in this embodiment).

Further, the positive electrode plate 31 used for the battery 1 of the present embodiment is provided with the second active material layers 35 and 36 on the first active material layers 33 and 34. Therefore, in this battery 1, the reaction resistance of the battery 1 is suppressed as described above, as compared with the battery using the positive electrode plate which does not have the second active material layers 35 and 36 on the first active material layers 33 and 34. is made of.

Next, a method of manufacturing the battery 1 including a method of manufacturing the positive electrode plate 31 will be described (see FIG. 5). In this embodiment, each process from the "positive electrode plate manufacturing process S1" and the "negative electrode plate manufacturing process S2" to the "battery assembly process S4" is performed in an environment of 25 ° C., a humidity of 60%, and a dew point temperature of 16 ° C. DP. went.
First, the "positive electrode plate manufacturing step S1" is performed to manufacture the positive electrode plate 31. A first paste used for forming the first active material layers 33 and 34 and a second paste used for forming the second active material layers 35 and 36 are prepared in advance.

Specifically, the first positive electrode active material particles 41 made of lithium oxide (lithium nickel cobalt aluminum composite oxide particles in this embodiment), the conductive material 42 (AB in this embodiment), and the binder 43 (this embodiment). In the embodiment, PVDF) is kneaded with a dispersion medium (N-methyl-2-pyrrolidone (NMP) in this embodiment) to obtain a first paste. The mixing ratio of the first positive electrode active material particles 41, the conductive material 42, and the binder 43 was 93: 6: 1 by weight. Further, the solid content ratio of the first paste was set to 75 wt% (the ratio of NMP was 25 wt%).

Further, the second positive electrode active material particles 49 (lithium nickel cobalt manganese composite oxide in this embodiment), the conductive material 45 (AB in this embodiment), the binder 46 (PVDF in this embodiment), and the hygroscopic agent particles 47. (Aluminum oxide particles in this embodiment) are kneaded together with a dispersion medium (NMP in this embodiment) to obtain a second paste. The mixing ratio of the second positive electrode active material particles 49, the conductive material 45, the binder 46, and the hygroscopic agent particles 47 was 91: 8: 1: 1.5 by weight. The solid content of the second paste was 65 wt% (NMP ratio was 35 wt%).

Then, the first paste is applied on one main surface 32a of the positive electrode current collector foil 32 by die coating to form an undried first active material layer (not shown), and subsequently, by gravure coating. A second paste is applied to form an undried second active material layer (not shown). Then, they are heated and dried to form the first active material layer 33 and the second active material layer 35 at the same time.
Similarly, the first paste is applied to the other main surface 32a of the positive electrode current collector foil 32 to form an undried first active material layer (not shown), and then the second paste is not applied. A dry second active material layer (not shown) is formed. Then, they are heated and dried to form the first active material layer 34 and the second active material layer 36.
After that, the positive electrode plate is pressed to increase the densities of the first active material layers 33 and 34 and the second active material layers 35 and 36, respectively. Thus, the positive electrode plate 31 is manufactured.

Separately, the "negative electrode plate manufacturing process S2" is performed to manufacture the negative electrode plate 51. Negative electrode of negative electrode active material particles (graphite particles in this embodiment), binder (SBR in this embodiment) and thickener (CMC in this embodiment) kneaded together with a dispersion medium (water in this embodiment) in advance. Have the paste ready. Then, 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 negative electrode active material layer (not shown), and then this is heated and dried to form a negative electrode active material. Form a layer (not shown). Similarly, a negative electrode paste is applied to the other main surface of the negative electrode current collector foil 52 to form an undried negative electrode active material layer (not shown), and then this is heated and dried to form a negative electrode active material layer (non-dried). (Illustrated) is formed. Then, the negative electrode plate is pressed to increase the density of each of the negative electrode active material layers. Thus, the negative electrode plate 51 is manufactured.

Next, in the "electrode body forming step S3", the electrode body 20 is formed. Specifically, the strip-shaped positive electrode plate 31 and the strip-shaped negative electrode plate 51 are overlapped with each other via the two strip-shaped separators 61 and 61, and wound around the axis using a winding core. Further, this is compressed into a flat shape to form a flat winding type electrode body 20 (see FIG. 2).

Next, in the "battery assembly step S4", the battery 1 is assembled. That is, the case lid member 13 is prepared, and the positive electrode terminal member 70 and the negative electrode terminal member 80 are fixedly attached to the case lid member 13 (see FIGS. 1 and 2). After that, the positive electrode terminal member 70 and the negative electrode terminal member 80 are welded to the positive electrode exposed portion 31 m of the positive electrode plate 31 of the electrode body 20 and the negative electrode exposed portion 51 m of the negative electrode plate 51, respectively. Next, the electrode body 20 is covered with the insulating film enclosing body 19, and these are inserted into the case main body member 11, and the opening of the case main body member 11 is closed with the case lid member 13. Then, the case body member 11 and the case lid member 13 are welded to form the battery case 10.

Next, in the "liquid injection step S5", the electrolytic solution 17 is injected into the battery case 10 from the liquid injection hole 13h and impregnated into the electrode body 20. After that, the liquid injection hole 13h is sealed with the sealing member 15. Note that this liquid injection step S5 is performed in a dry environment at 25 ° C. and a dew point temperature of −30 ° C. DP or less, unlike each step of the positive electrode plate manufacturing step S1 to the battery assembly step S4 described above.
Next, in the "first charging step S6", the battery 1 is first charged. This initial charging step S6 is performed in an environment of 25 ° C., a humidity of 60%, and a dew point temperature of 16 ° C. DP, as in each step of the positive electrode plate manufacturing step S1 to the battery assembly step S4. After that, various inspections are performed on the battery 1. Thus, the battery 1 is completed.

(Test results)
Next, the results of the tests conducted to verify the effect of the present invention will be described (see FIGS. 6 to 8). First, the relationship between the amount of the absorbent particles 47 added to the second active material layers 35 and 36 and the reaction resistance R of the battery was investigated. As shown in Table 1, aluminum oxide particles (average particle size 1.0 μm) and boehmite particles (average particle size 2.0 μm) are prepared as the hygroscopic agent particles 47 to be included in the second active material layers 35 and 36, and moisture absorption is performed. The addition amount of the agent particles 47 was changed to 0 to 2.5 wt%, and the positive electrode plate 31 was manufactured in the same manner as in the other embodiments, and the battery 1 was further manufactured. The amount of the hygroscopic agent particles 47 added (wt%) is the amount added based on the total amount of the second positive electrode active material particles 49, the conductive material 45, and the binder 46 (= 100 wt%). ..

Then, for each battery, the reaction resistance R of the battery was measured. Specifically, the initial IV resistance was calculated from the discharges at 0.3C, 1C, 3C, and 5C at an environmental temperature of 25 ° C. for each battery adjusted to SOC 60%. Further, the reaction resistivity ratios of the other batteries were determined with the reaction resistivity R of each battery as a reference (= 100%) when the addition amount of the hygroscopic agent particles 47 was 0 wt%. The results are shown in Table 1 and FIG.

As is clear from Table 1 and FIG. 6, when the hygroscopic agent particles 47 are included in the second active material layers 35 and 36, the second active is regardless of whether aluminum oxide particles or boehmite particles are used as the hygroscopic agent particles 47. It can be seen that the reaction resistance ratio of the battery is lower (reaction resistance R is lower) than when the material layers 35 and 36 do not include the hygroscopic agent particles 47 (addition amount of the hygroscopic agent particles 47 = 0 wt%). In particular, when aluminum oxide particles were used as the hygroscopic agent particles 47, the reaction resistivity of the battery was particularly low when the addition amount was 1.0 to 2.0 wt%. Further, when the boehmite particles were used as the hygroscopic agent particles 47, the reaction resistivity of the battery was particularly low when the addition amount was 1.5 to 2.5 wt%. The reason for this result is considered to be as follows.

That is, when the first positive electrode active material particles 41 and the second positive electrode active material particles 49 come into contact with water in the atmosphere, they react with water on the particle surface to generate lithium hydroxide (Li ₂ O + H ₂ O → 2 LiOH). Furthermore, this lithium hydroxide _{reacts with carbon dioxide (CO 2} ) in the atmosphere to produce lithium carbonate (2LiOH + CO ₂ → Li ₂ CO ₃ + H ₂ O). Lithium carbonate produced on the surface of the particles is a resistor. Further, when the first positive electrode active material particles 41 and the second positive electrode active material particles 49 react with water and lithium ions are released from the first positive electrode active material particles 41 and the second positive electrode active material particles 49, the first positive electrode active material The crystal structures of the particles 41 and the second positive electrode active material particles 49 are changed, and it becomes difficult for the lithium ions to be inserted and removed from the first positive electrode active material particles 41 and the second positive electrode active material particles 49. Therefore, in the battery using this positive electrode plate, the reaction resistivity ratio is high (the reaction resistivity R is high).

On the other hand, when the hygroscopic agent particles 47 are included in the second active material layers 35 and 36, even if the positive electrode plate 31 comes into contact with the moisture in the atmosphere, the moisture is the hygroscopic agent particles in the second active material layers 35 and 36. Moisture is absorbed by 47. Therefore, it is possible to suppress the reaction of water with the second positive electrode active material particles 49 in the second active material layers 35 and 36. In addition, it is possible to prevent water from reaching the first active material layers 33, 34 below the second active material layers 35, 36. As a result, it is considered that when the hygroscopic agent particles 47 were included in the second active material layers 35 and 36, the reaction resistivity ratio of the battery was low (reaction resistivity R was low).

It is considered that the reason why the reaction resistivity ratio of the battery was rather high (92%) when the addition amount was increased to 2.5 wt% by using aluminum oxide particles as the hygroscopic agent particles 47 is as follows. Since the hygroscopic agent particles 47 such as aluminum oxide particles are originally unnecessary materials for the battery reaction, if the addition amount of the hygroscopic agent particles 47 is increased too much, the conductive path in the second active material layers 35 and 36 is obstructed. It is considered that the reaction resistance R of the battery becomes high.

Next, the relationship between the layer thickness t2 of the second active material layers 35 and 36 and the reaction resistance R of the battery was investigated. As shown in Table 2, aluminum oxide particles (average particle size 1.0 μm) and boehmite particles (average particle size 2.0 μm) were prepared as the absorbent particles 47 to be included in the second active material layers 35 and 36. The positive electrode plate 31 was manufactured by changing the layer thickness t2 of the two active material layers 35 and 36 to 5 to 30 μm, and the battery 1 was further manufactured. Then, the reaction resistivity R of each battery is measured as described above, and the reaction resistivity R of each battery when the addition amount of the hygroscopic agent particles 47 in Table 1 is 0 wt% is used as a reference (= 100%). The reaction resistivity of each battery was determined. The results are shown in Table 2 and FIG.

As is clear from Table 2 and FIG. 7, regardless of whether aluminum oxide particles or boehmite particles are used as the hygroscopic agent particles 47, when the layer thickness t2 of the second active material layers 35 and 36 is increased, the reaction resistivity of the battery is increased. The ratio is low (reaction resistivity R is low). However, it can be seen that if the layer thickness t2 of the second active material layers 35 and 36 is made too thick, the reaction resistivity ratio of the battery becomes rather high (reaction resistance R becomes high). The reason is considered to be as follows.

That is, the thicker the layer thickness t2 of the second active material layers 35 and 36, the more it is possible to prevent water from passing through the second active material layers 35 and 36 and reaching the first active material layers 33 and 34 below the second active material layers 35 and 36. Therefore, it is possible to suppress the reaction of water with the first positive electrode active material particles 41 in the first active material layers 33 and 34. As a result, it is considered that the thicker the layer thickness t2 of the second active material layers 35 and 36, the lower the reaction resistivity ratio of the battery (the lower the reaction resistivity R).

However, if the layer thickness t2 of the second active material layers 35 and 36 is made too thick, cracks may occur between the second active material layers 35 and 36 and the first active material layers 33 and 34 below the second active material layers 35 and 36. Since the second active material layers 35 and 36 became too thick, the permeability of the electrolytic solution 17 decreased, and the battery reaction could not be efficiently performed in the first active material layers 33 and 34, so that the reaction resistance of the battery was reduced. It is considered that the ratio was high (reaction resistivity R was high).

Next, the relationship between the average particle size of the hygroscopic agent particles 47 and the reaction resistance R of the battery was investigated. As shown in Tables 3 and 4, aluminum oxide particles and boehmite particles having different average particle sizes are prepared as the hygroscopic agent particles 47 included in the second active material layers 35 and 36, and the positive electrode plate 31 is manufactured using these particles. Then, the battery 1 was further manufactured. Then, the reaction resistivity R of each battery is measured as described above, and the reaction resistivity R of each battery when the addition amount of the hygroscopic agent particles 47 in Table 1 is 0 wt% is used as a reference (= 100%). The reaction resistivity of each battery was determined. The results are shown in Table 3, Table 4 and FIG.

As is clear from Tables 3, 4 and 8, regardless of whether aluminum oxide particles or boehmite particles are used as the hygroscopic agent particles 47, the smaller the average particle size, the lower the reaction resistivity of the battery (reaction). It can be seen that the resistance R is low). The smaller the average particle size of the hygroscopic agent particles 47, the larger the specific surface area, so that moisture is easily adsorbed by the hygroscopic agent particles 47. Therefore, it is possible to suppress the reaction of water with the first positive electrode active material particles 41 and the second positive electrode active material particles 49. As a result, it is considered that the smaller the average particle size of the hygroscopic agent particles 47, the lower the reaction resistivity ratio (reaction resistance R) of the battery.

Although the present invention has been described above in accordance with the embodiment, it is needless to say that the present invention is not limited to the above-described embodiment and can be appropriately modified and applied without departing from the gist thereof.

1 Lithium-ion secondary battery 17 Electrolyte 20 Electrolyte body 31 Positive plate plate 32 Positive current collector foil 33, 34 First active material layer 35, 36 Second active material layer 41 First positive positive material particle 42 (First active material layer) Conductive material 43 (1st active material layer) Binder 45 (2nd active material layer) Conductive material 46 (2nd active material layer) Binder 47 (2nd active material layer) Moisture absorber Particle 49 Second positive electrode active material particle t1 (of the first active material layer) layer thickness t2 (of the second active material layer) layer thickness

Claims (1)

With the current collector foil,
A first active material layer formed on the current collector foil and containing first positive electrode active material particles made of lithium oxide, and
A positive electrode plate of a lithium ion secondary battery formed on the first active material layer and comprising a second active material layer containing the second positive electrode active material particles.
The first positive electrode active material particles have a characteristic that the pH of a dispersion liquid in which 1 g of the first positive electrode active material particles is dispersed in 50 g of water has a pH of 11.3 or more.
The second positive electrode active material particles have a characteristic that the pH of a dispersion liquid in which 1 g of the second positive electrode active material particles is dispersed in 50 g of water has a pH of 11.0 or less.
The second active material layer is a positive electrode plate of a lithium ion secondary battery containing hygroscopic agent particles.

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