Positive electrode active material layer, lithium ion battery, and method for manufacturing positive electrode active material layer

Abstract

Provided are a positive electrode active material layer capable of improving battery capacity, a lithium ion battery having such a positive electrode active material layer, and a method for producing such a positive electrode active material layer. A positive electrode active material layer (20) comprises a positive electrode active material (21a) and a lithium alloy (22a) of lithium and a metal element. The positive electrode active material is covered with a carbon material, the alloying potential of the metal element with lithium is 0.5 V (vs. Li / Li +) or more, and the lithium alloy is disposed on the surface of the positive electrode active material layer on the side of the positive electrode current collector (10) and / or the surface of the positive electrode active material layer on the side of the separator (30). A lithium ion battery (1) according to the present invention has a positive electrode current collector (10), a separator (30), and a positive electrode active material layer (20) according to the present invention interposed between the positive electrode current collector (10) and the separator (30).

Description

Technical Field

[0001] The invention relates to a positive electrode active material layer, a lithium ion battery and a method for manufacturing the positive electrode active material layer. Background Art

[0002] A portion of the lithium ions supplied by the positive electrode active material of the lithium ion battery is consumed by reacting with the electrolyte on the surface of the negative electrode active material layer to form a solid electrolyte interface (SEI). As a result, the problem of reduced battery capacity arises. Therefore, in order to maximize the use of the positive electrode active material, it is necessary to supplement the lithium ions consumed by the formation of SEI in the negative electrode active material layer, and a technology for achieving this purpose has been developed.

[0003] For example, Patent Document 1 discloses a positive electrode for a secondary battery including a positive electrode mixture layer (positive electrode active material layer) in which a positive electrode active material and a lithium-based alloy are mixed.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application No. 2021-520614 Summary of the invention

[0007] In a battery having a positive electrode active material layer containing a positive electrode active material and a lithium alloy, a desired battery capacity may not be obtained, and thus there is still room for improvement in battery capacity.

[0008] An object of the present invention is to provide a positive electrode active material layer capable of improving battery capacity, a lithium ion battery having such a positive electrode active material layer, and a method for producing such a positive electrode active material layer.

[0009] The inventors of the present application have found that the above-mentioned problems can be solved by the following means.

[0010] <Method 1>

[0011] A positive electrode active material layer is disposed between the positive electrode current collector and the separator.

[0012] A lithium alloy having a positive electrode active material and lithium and a metal element,

[0013] The positive electrode active material is coated with a carbon material.

[0014] The alloying potential of the above metal elements with lithium is 0.5V (vs. Li / Li + ) or more, and

[0015] The lithium alloy is disposed on a surface of the positive electrode active material layer on the positive electrode current collector side and / or a surface of the positive electrode active material layer on the separator side.

[0016] <Method 2>

[0017] The positive electrode active material layer according to aspect 1, wherein the lithium alloy forms a lithium alloy layer.

[0018] <Method 3>

[0019] The positive electrode active material layer according to aspect 2, wherein the lithium alloy layer has a thickness of 1 μm to 20 μm.

[0020] <Method 4>

[0021] The positive electrode active material layer according to any one of aspects 1 to 3, wherein the positive electrode active material is an olivine-type positive electrode active material.

[0022] <Method 5>

[0023] The positive electrode active material layer according to embodiment 4, wherein the olivine-type positive electrode active material is at least one selected from the group consisting of lithium iron phosphate, lithium manganese iron phosphate, lithium manganese phosphate and lithium cobalt phosphate.

[0024] <Method 6>

[0025] The positive electrode active material layer according to any one of aspects 1 to 5, wherein the metal element is at least one selected from bismuth, antimony, and tin.

[0026] <Method 7>

[0027] The positive electrode active material layer according to any one of aspects 1 to 6, wherein a ratio of the mass of the positive electrode active material to the mass of the lithium alloy is 3.0 to 15.0.

[0028] <Method 8>

[0029] The positive electrode active material layer according to any one of aspects 1 to 7, wherein a thickness of a layer obtained by excluding the lithium alloy from the positive electrode active material layer is 20 μm to 300 μm.

[0030] <Method 9>

[0031] A lithium ion battery comprises the positive electrode current collector, the separator, and the positive electrode active material layer according to any one of aspects 1 to 8 interposed between the positive electrode current collector and the separator.

[0032] <Method 10>

[0033] A lithium ion battery comprises a positive electrode current collector, a separator, and a positive electrode active material layer interposed between the positive electrode current collector and the separator.

[0034] The positive electrode active material layer contains a positive electrode active material and a metal element.

[0035] The positive electrode active material is coated with a carbon material.

[0036] The alloying potential of the above metal elements with lithium is 0.5V (vs. Li / Li + ) or more, and

[0037] The metal element is disposed on a surface of the positive electrode active material layer on the positive electrode current collector side and / or a surface of the positive electrode active material layer on the separator side.

[0038] <Method 11>

[0039] A method for producing a positive electrode active material layer according to any one of aspects 1 to 8 comprises the following steps:

[0040] (a) applying a first slurry containing the lithium alloy and a first dispersion medium onto a substrate,

[0041] (b) applying a second slurry containing the positive electrode active material and a second dispersion medium after the step (a);

[0042] (c) drying and removing the first and second dispersion media to obtain a laminated body, and

[0043] (d) Pressurizing the stacked body.

[0044] <Method 12>

[0045] The method according to embodiment 11, wherein the substrate is a positive electrode current collector.

[0046] <Method 13>

[0047] The method according to embodiment 11 or 12, further comprising the step of drying and removing the first dispersion medium to obtain an initial lithium alloy layer before the step (b).

[0048] <Method 14>

[0049] The method according to embodiment 13, further comprising the step of pressurizing the initial lithium alloy layer to obtain the lithium alloy layer.

[0050] <Method 15>

[0051] The method according to any one of aspects 11 to 14, wherein the first and second dispersion media are the same dispersion medium.

[0052] According to the present invention, it is possible to provide a positive electrode active material layer capable of improving battery capacity, a lithium ion battery having such a positive electrode active material layer, and a method for producing such a positive electrode active material layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 It is a schematic cross-sectional view showing an example of the positive electrode active material layer of the present invention.

[0054] Figure 2 It is a schematic cross-sectional view showing an example of the positive electrode active material layer of the present invention.

[0055] Figure 3 It is a schematic cross-sectional view of a positive electrode active material layer of a comparative example.

[0056] Figure 4 It is a schematic cross-sectional view showing an example of the battery of the present invention.

[0057] Explanation of symbols

[0058] 1 Lithium-ion battery

[0059] 10Positive electrode collector

[0060] 20Positive electrode active material layer

[0061] 21 Layer containing positive electrode active material

[0062] 21a Positive electrode active material

[0063] 22 Lithium alloy layer

[0064] 22a Lithium Alloy

[0065] 30 Isolators

[0066] 40 Negative electrode active material layer

[0067] 50 Negative electrode collector DETAILED DESCRIPTION

[0068] Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and various modifications can be made within the scope of the gist of the invention.

[0069] 《Positive electrode active material layer》

[0070] The positive electrode active material layer of the present invention is between the positive electrode collector and the separator, and has a positive electrode active material and a lithium alloy of lithium and a metal element. The positive electrode active material is coated with a carbon material, and the alloying potential of the metal element with lithium is 0.5V (vs. Li / Li + ) or more, and the lithium alloy is arranged on the surface of the positive electrode collector side of the positive electrode active material layer and / or the surface of the separator side of the positive electrode active material layer. It should be noted that in the present invention, "the lithium alloy is arranged on the surface of the positive electrode collector side of the positive electrode active material layer and / or the surface of the separator side of the positive electrode active material layer" means that the lithium alloy is arranged on the surface of the positive electrode collector side or the surface of the separator side at a higher density than other parts, and in particular, it means that the lithium alloy is arranged only on the surface of the positive electrode collector side and / or the surface of the separator side.

[0071] The inventors of the present application believe that one of the reasons why the desired battery capacity cannot be obtained in a battery having a positive electrode active material layer containing a positive electrode active material and a lithium alloy is that the carbon material coated with the positive electrode active material reacts with the lithium alloy. Specifically, the reason is not intended to be limited to any theory, but it is speculated as follows. That is, since the redox potential of the lithium alloy is low, it is believed that the lithium alloy will react with the carbon material coated with the positive electrode active material during the first charge and damage the coating of the carbon material. As a result, it is believed that the adhesion of the positive electrode active material to the carbon material is reduced, and the resistance is increased, so that the desired battery capacity cannot be obtained.

[0072] In this regard, the inventors of the present application have found that the battery capacity is improved by configuring the lithium alloy on the surface of the positive electrode collector side of the positive electrode active material layer and / or the surface of the separator side of the positive electrode active material layer in the positive electrode active material layer containing a positive electrode active material coated with a carbon material and a lithium alloy of lithium and a specified metal element. The reason for this is not intended to be limited to any theory, but it is speculated as follows. That is, it is believed that the contact area between the carbon material coating the positive electrode active material and the lithium alloy can be reduced compared to the state in which the positive electrode active material and the lithium alloy are mutually dispersed in the positive electrode active material layer.

[0073] Hereinafter, the positive electrode active material layer of the present invention will be described with reference to the drawings as appropriate. It should be noted that the dimensional relationship in each drawing does not reflect the actual dimensional relationship.

[0074] like Figure 1 and 2As shown, the positive electrode active material layer 20 of the present invention has a positive electrode active material 21a and a lithium alloy 22a of lithium and a metal element. The positive electrode active material layer optionally contains a conductive auxiliary agent and a binder. In addition, when the lithium ion battery of the present invention is a solid battery, the positive electrode active material layer optionally contains a solid electrolyte.

[0075] like Figure 1 and 2 As shown, the positive electrode active material layer 20 of the present invention is interposed between the positive electrode collector 10 and the separator 30 .

[0076] like Figure 1 As shown in FIG. 1 , the lithium alloy 22a is disposed on the surface of the positive electrode current collector 10. Although not shown in the figure, the lithium alloy 22a may also be disposed on the surface of the separator 30. It is considered that by forming such a structure, it is possible to Figure 3 In the illustrated state where the positive electrode active material 21 a and the lithium alloy 22 a are mutually dispersed in the positive electrode active material layer 20 , the contact area between the carbon material covering the positive electrode active material 21 a and the lithium alloy 22 a is smaller.

[0077] It should be explained, such as Figure 2 As shown, the lithium alloy 22a may form the lithium alloy layer 22 on the surface of the positive electrode current collector 10. Although not shown, the lithium alloy 22a may form the lithium alloy layer on the surface of the separator 30.

[0078] It is believed that the durability of the battery is improved when the lithium alloy 22a is arranged on the surface on the positive electrode collector 10 side. The reason is not intended to be bound by any theory, but it is speculated as follows. That is, the ions of the metal element generated by releasing lithium ions from the lithium alloy during charging sometimes move toward the negative electrode collector during repeated charging and discharging, and precipitate on the negative electrode collector in the form of a single substance of the metal element. When the precipitate is locally generated, it becomes a dendrite, and when the dendrite grows and reaches the positive electrode collector, a short circuit occurs. By configuring the lithium alloy 22a on the surface on the positive electrode collector 10 side, the distance between the metal element and the negative electrode collector becomes longer than that on the surface on the side of the separator 30, so that local dendrite precipitation is less likely to occur. As a result, it is believed that the possibility of the above-mentioned short circuit can be reduced.

[0079] 〈Positive electrode active material〉

[0080] The positive electrode active material is covered with a carbon material.

[0081] The positive electrode active material may be an olivine-type positive electrode active material.

[0082] The olivine-type positive electrode active material may be at least one selected from lithium iron phosphate, lithium manganese iron phosphate, lithium manganese phosphate and lithium cobalt phosphate.

[0083] Carbon materials can improve the electron conductivity of positive electrode active materials by coating the positive electrode active materials. In particular, olivine-type positive electrode active materials have lower electron conductivity than ternary positive electrode active materials such as nickel-cobalt-manganese (NCM), so coating with carbon materials is effective.

[0084] The method of coating the positive electrode active material with the carbon material is not particularly limited, and an example thereof includes coating the positive electrode active material with a predetermined organic compound and calcining the positive electrode active material coated with the organic compound in an inert atmosphere to carbonize the organic compound.

[0085] In the present invention, a commercially available product can be used as the positive electrode active material covered with a carbon material.

[0086] 〈Lithium Alloy〉

[0087] The lithium alloy can supply lithium ions, thereby preventing the lithium ions of the positive electrode active material from being consumed in the formation of SEI in the negative electrode active material layer. As a result, the positive electrode active material can be used to the maximum extent, and the reversible capacity can be increased.

[0088] The alloying potential of the metal element forming the lithium alloy with lithium is 0.5V (vs. Li / Li + ) or more. Thus, the lithium alloy can be stabilized and made easy to handle. The alloying potential can be 0.6V (vs Li / Li + ) or above, 0.7V(vsLi / Li + ) or above, or 0.8V(vs Li / Li + ) or more, and can also be 1.5V (vs Li / Li + ) or less, 1.4V(vs Li / Li + ) or less, 1.3V(vs Li / Li + ) or less, 1.2V(vs Li / Li + ) or less, 1.1V(vs Li / Li + ) or below, or 1.0V(vsLi / Li + )the following.

[0089] Here, the alloying potential (vs Li / Li + ) is the electrode potential of the electrode reaction of formula (1), expressed based on the electrode potential of lithium of the following formula (2):

[0090] x + +M+xe － ←→Li x M (1)

[0091] Li+ +e － ←→Li (2)

[0092] Alloying potential (vs Li / Li + ) can be measured as the electrode potential obtained when the alloy is immersed in a Li salt solution.

[0093] The metal element may be at least one selected from bismuth, antimony, and tin.

[0094] The lithium alloy can be prepared by a conventional method or may be a commercially available product. Examples of the method for preparing the lithium alloy include a method of mixing lithium and a metal element in a mortar in an inert atmosphere, but the method is not limited thereto.

[0095] The ratio of the mass of the positive electrode active material in the positive electrode active material layer of the present invention to the mass of the lithium alloy can be 3.0 to 15.0. The ratio can be 3.5 or more, 4.0 or more, 5.0 or more, or 6.0 or less, 14.0 or less, 13.0 or less, 12.0 or less, or 11.0 or less. Lithium alloys can contribute to the increase of battery capacity even if a small amount is added as in the above range due to the high capacity characteristics of the material itself. It should be noted that the ratio can be appropriately designed according to the type of positive electrode active material and lithium alloy used.

[0096] The ratio of the volume of the positive electrode active material of the present invention to the volume of the lithium alloy can be 5.0 or more, 6.0 or more, 7.0 or more, 8.0 or more, or 8.5 or less, 20.0 or less, 19.0 or less, 18.0 or less, 17.0 or less, or 16.5 or less. It should be noted that the ratio can be appropriately designed according to the type of the positive electrode active material and the lithium alloy used.

[0097] When the lithium alloy forms a lithium alloy layer on the surface of the positive electrode collector and / or the surface of the separator, the thickness of the lithium alloy layer may be 1 μm to 20 μm. The thickness may be 2 μm or more, 3 μm or more, 4 μm or more, or 5 μm or less, 18 μm or less, 16 μm or less, 15 μm or less, 14 μm or less, 12 μm or less, 11 μm or less, or 10 μm or less.

[0098] It should be noted that the thickness of the layer obtained by removing the lithium alloy from the positive electrode active material layer can be 20 μm to 300 μm. The thickness can be 40 μm or more, 60 μm or more, 70 μm or more, 80 μm or more, or 90 μm or more, or 250 μm or less, 200 μm or less, 150 μm or less, 130 μm or less, 120 μm or less, or 110 μm or less. The layer obtained by removing the lithium alloy from the positive electrode active material layer can be a layer obtained by removing the lithium alloy layer from the positive electrode active material layer. It should be noted that, with respect to the present invention, the layer obtained by removing the lithium alloy or the lithium alloy layer from the positive electrode active material layer is sometimes described as a layer containing a positive electrode active material (e.g., LFP).

[0099] The lithium alloy content in the positive electrode active material layer can be adjusted to prevent the lithium alloy from forming a layer or to form a layer. That is, to prevent the lithium alloy from forming a layer, the lithium alloy content can be reduced, and to make the lithium alloy form a layer, the lithium alloy content can be increased.

[0100] 〈Conductive additives〉

[0101] As a conductive aid, a material known as a conductive aid used in a lithium ion battery can be used. Specifically, carbon materials such as Ketjen black (KB), vapor grown carbon fiber (VGCF), acetylene black (AB), carbon nanotubes (CNT), carbon nanofibers (CNF), carbon black, coke, graphite, etc. can be used. Alternatively, a metal material that can withstand the environment when the battery is used can also be used. As a conductive aid, only one can be used alone, or two or more can be used in combination. The shape of the conductive aid can be various shapes such as powdery and fibrous. The amount of the conductive aid contained in the positive electrode active material layer is not particularly limited.

[0102] 〈Binder〉

[0103] As a binder, a material known as a binder used in a lithium ion battery can be used. For example, a styrene-butadiene rubber (SBR) binder, a carboxymethyl cellulose (CMC) binder, an acrylonitrile-butadiene rubber (ABR) binder, a butadiene rubber (BR) binder, a polyvinylidene fluoride (PVDF) binder, a polytetrafluoroethylene (PTFE) binder, etc. can be used. The binder can be used alone or in combination of two or more. The amount of the binder contained in the positive active material layer is not particularly limited.

[0104] 〈Solid Electrolyte〉

[0105] The material of the solid electrolyte is not particularly limited, and a material that can be used as a solid electrolyte for lithium-ion batteries can be used. For example, the solid electrolyte can be a sulfide solid electrolyte, an oxide solid electrolyte, or a polymer electrolyte.

[0106] Examples of sulfide solid electrolytes include, but are not limited to, sulfide amorphous solid electrolytes, sulfide crystalline solid electrolytes, and Argyrodite-type solid electrolytes. Specific examples of sulfide solid electrolytes include Li2S-P2S5 (Li7P3S 11 , Li3PS4, Li8P2S9, etc.), Li2S-SiS2, LiI-Li2S-SiS2, LiI-Li2S-P2S5, LiI-LiBr-Li2S-P2S5, Li2S-P2S5-GeS2 (Li 13 GeP3S 16 , Li 10 GeP2S 12 etc.), LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, Li 7－x PS 6－x Cl x etc.; or combinations thereof, but not limited thereto.

[0107] As an example of oxide solid electrolyte, Li7La3Zr2O 12 , Li 7－x Ln3Z 1－x Nb x O 12 , Li 7－ 3x La3Zr2Al x O 12 , Li 3x La 2 / 3－x TiO3、Li 1+x Al x Ti 2－x (PO4)3、Li 1+x Al x Ge 2－x (PO4)3, Li3PO4, or Li 3+ x PO 4－x N x (LiPON), etc., but not limited to these.

[0108] The sulfide solid electrolyte and the oxide solid electrolyte may be glass or crystallized glass (glass ceramic).

[0109] Examples of the polymer electrolyte include polyethylene oxide (PEO), polypropylene oxide (PPO), and copolymers thereof, but the polymer electrolyte is not limited thereto.

[0110] 《Method for producing positive electrode active material layer》

[0111] The method of the present invention for manufacturing a positive electrode active material layer includes the following steps: (a) applying a first slurry containing a lithium alloy and a first dispersion medium to a substrate, (b) applying a second slurry containing a positive electrode active material and a second dispersion medium after step (a), (c) drying and removing the first and second dispersion media to obtain a stack, and (d) pressurizing the stack.

[0112] <First slurry coating step>

[0113] The method of the present invention comprises: (a) applying a first slurry containing a lithium alloy and a first dispersion medium to a substrate.

[0114] Regarding the lithium alloy, reference may be made to the above description related to the positive electrode active material layer of the present invention.

[0115] The first dispersion medium is not particularly limited as long as it is a dispersion medium that can disperse the lithium alloy and does not deteriorate the lithium alloy. As the first dispersion medium, alcohols, glycols, cellosolves, amines, ketones, carboxamides, phosphoramides, sulfoxides, carboxylates, phosphates, ethers, and nitriles can be cited. Specifically, ethanol, 2-propanol, methyl ethyl ketone, and N-methyl-2-pyrrolidone can be cited.

[0116] The substrate may be a positive electrode current collector. When the substrate is a positive electrode current collector, the lithium alloy layer can be directly formed on the positive electrode current collector.

[0117] The substrate may also be a separator. When the substrate is a separator, the lithium alloy layer can be directly formed on the separator.

[0118] Examples of the coating method include a metal mask printing method, an electrostatic coating method, a dip coating method, a spray coating method, a roll coating method, a doctor blade method, a gravure coating method, and a screen coating method.

[0119] <Second slurry coating step>

[0120] The method of the present invention includes applying a second slurry containing a positive electrode active material and a second dispersion medium after the step (a).

[0121] For the positive electrode active material, reference may be made to the above description related to the positive electrode active material of the present invention.

[0122] The second dispersion medium is not particularly limited as long as it is a dispersion medium that can disperse the positive electrode active material and does not deteriorate the positive electrode active material. As the second dispersion medium, alcohol, glycol, cellosolve, amine, ketone, carboxamide, phosphoramide, sulfoxide, carboxylic acid ester, phosphate ester, ether and nitrile can be cited. Specifically, ethanol, 2-propanol, methyl ethyl ketone and N-methyl-2-pyrrolidone can be cited.

[0123] The first and second dispersion media in the method of the present invention can be the same dispersion medium. By adopting such a method, even in the case where the second slurry is directly coated on the first slurry, it is possible to form each slurry layer without being affected by the different surface tensions of the dispersion media, that is, without excessively mixing the components in the first and second slurries.

[0124] Furthermore, the first and second slurries may contain a binder, and by using the same binder in each slurry, the same effect as when the dispersion medium is the same can be achieved.

[0125] Furthermore, for example, even when the first slurry has a high viscosity by increasing the solid content concentration of the first slurry and applying the second slurry directly on the first slurry, mixing of the components in the first and second slurries can be effectively suppressed.

[0126] 〈Drying process〉

[0127] The method of the present invention comprises: (c) removing the first and second dispersion media by drying to obtain a laminated body.

[0128] The drying temperature, drying time and the like can be appropriately designed according to the content and boiling point of the dispersion medium and the like.

[0129] The method of the present invention may further include: drying and removing the first dispersion medium to obtain an initial lithium alloy layer before step (b). By adopting such a method, the dispersion medium and the binder of the first and second slurries can be selected without particular limitation.

[0130] <Pressing process>

[0131] The method of the present invention comprises: (d) pressing the laminate. According to this method, the number of times of pressing can be reduced to one, so the production cost is low. As a method of pressing, a method such as roller pressing can be exemplified.

[0132] The method of the present invention may further include: pressurizing the initial lithium alloy layer to obtain the lithium alloy layer. By adopting such a method, the second slurry can be applied to the densified lithium alloy layer to inhibit the penetration of the positive electrode active material into the lithium alloy layer, and as a result, the contact frequency between the lithium alloy and the carbon material covering the positive electrode active material can be reduced.

[0133] It should be noted that the positive electrode active material layer of the present invention can also be manufactured by methods other than those described above. For example, first, by immersing the positive electrode collector in an electrolyte containing a metal element constituting a lithium alloy for electroplating, a lithium alloy layer can be formed on the positive electrode collector. Then, as described above, by undergoing a coating step, a drying step, and a pressurizing step of a slurry containing a positive electrode active material, a layer containing a positive electrode active material can be formed to manufacture the positive electrode active material layer of the present invention.

[0134] Lithium-ion battery

[0135] like Figure 4 As shown, the lithium ion battery 1 of the present invention comprises a positive electrode collector 10, a separator 30, and a positive electrode active material layer 20 of the present invention interposed between the positive electrode collector 10 and the separator 30. That is, the lithium ion battery 1 of the present invention comprises the positive electrode collector 10, the positive electrode active material layer 20 of the present invention, and the separator 30 in sequence. The lithium ion battery 1 of the present invention may comprise the positive electrode collector 10, the positive electrode active material layer 20 of the present invention, the separator 30, the negative electrode active material layer 40, and the negative electrode collector 50 in sequence. It should be noted that in Figure 4 In the figure, although the lithium alloy layer 22 is arranged on the surface of the positive electrode collector side, the lithium ion battery 1 of the present invention is not limited to this mode. That is, the lithium alloy may not form a layer, and the lithium alloy or lithium alloy layer may also be arranged on the surface of the separator side.

[0136] The lithium ion battery of the present invention may be a liquid battery containing an electrolyte as an electrolyte layer, or may be a solid battery having a solid electrolyte layer as an electrolyte layer. The electrolyte layer in the liquid battery may be a layer formed by immersing the separator in the electrolyte. The solid electrolyte layer in the solid battery may have the function of a separator. It should be noted that, with respect to the present invention, "solid battery" refers to a battery that uses at least a solid electrolyte as an electrolyte, so a solid battery may also use a combination of a solid electrolyte and a liquid electrolyte as an electrolyte. In addition, the solid battery of the present invention may also be an all-solid battery, that is, a battery that uses only a solid electrolyte as an electrolyte.

[0137] In addition, in the lithium ion battery of the present invention, lithium ions are released from the lithium alloy by performing initial charge and discharge, and the metal elements constituting the lithium alloy remain.

[0138] Therefore, the lithium ion battery of the present invention after initial charge and discharge can be as follows: a lithium ion battery having a positive electrode collector, a separator, and a positive electrode active material layer between the positive electrode collector and the separator, the positive electrode active material layer having a positive electrode active material and a metal element, the positive electrode active material is coated with a carbon material, and the alloying potential of the metal element with lithium is 0.5V (vs. Li / Li + ) or above, and the metal element is arranged on the surface of the positive electrode active material layer on the positive electrode collector side and / or the surface of the positive electrode active material layer on the separator side.

[0139] 〈Positive electrode collector〉

[0140] As the positive electrode collector, it can be composed of a known metal that can be used as a positive electrode collector of a lithium ion battery. As such a metal, a metal material containing at least one element selected from Cu, Ni, Al, V, Au, Pt, Mg, Fe, Ti, Pb, Co, Cr, Zn, Ge, In, Sn, and Zr can be exemplified. The form of the positive electrode collector is not particularly limited, and it can be various forms such as foil, mesh, and porous. The positive electrode collector can also be formed by evaporating the above-mentioned metal on the surface of the substrate.

[0141] <Positive electrode active material layer>

[0142] For the positive electrode active material layer of the present invention, reference can be made to the above description related to the positive electrode active material layer of the present invention.

[0143] 〈Isolator〉

[0144] As the separator, a material known as a separator used in a lithium-ion battery can be used. For example, the separator can be composed of resins such as polyethylene (PE), polypropylene (PP), polyester and polyamide. The separator can be a single-layer structure or a multi-layer structure. As a multi-layer separator, for example, a multi-layer separator composed of the above-mentioned resins can be used, such as a double-layer separator of PE / PP, or a three-layer separator of PP / PE / PP or PE / PP / PE. The separator can be composed of non-woven fabrics such as cellulose non-woven fabrics, resin non-woven fabrics, and glass fiber non-woven fabrics. The thickness of the separator is not particularly limited, for example, it can be 5μm to 1mm.

[0145] When the lithium ion battery of the present invention is a liquid battery, the separator may be impregnated with an electrolyte solution to form an electrolyte layer.

[0146] (Electrolyte)

[0147] The electrolyte contains a lithium salt and a solvent. Examples of lithium salts include lithium hexafluorophosphate (LiPF6), lithium tetrafluorophosphate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium trifluoromethanesulfonate (LiCF3SO3), and lithium bis(trifluoromethanesulfonyl)imide (Li(CF3SO2)2N). Examples of solvents include carbonates, cyclic esters (ethylene carbonate (EC), propylene carbonate (PC), etc.), chain esters (dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), etc.), aliphatic carboxylic acid esters (methyl formate (MF), etc.), γ-lactones (γ-butyrolactone (BL), etc.), chain ethers (1,2-dimethoxyethane (DME), etc.), or solvents composed of some combinations thereof. The solvent may be a non-protonic polar organic solvent, a cyclic carbonate compound (high dielectric constant, high viscosity) such as EC, or a chain carbonate compound such as DEC. Alternatively, the solvent may be an ionic liquid.

[0148] When the lithium ion battery of the present invention is a solid battery, the solid electrolyte layer can function as a separator.

[0149] The solid electrolyte layer contains a solid electrolyte. For the solid electrolyte, reference can be made to the above description related to the positive electrode active material layer of the present invention.

[0150] <Negative electrode active material layer>

[0151] The negative electrode active material layer contains a negative electrode active material and may optionally contain a conductive auxiliary agent and a binder. When the lithium ion battery of the present invention is a solid battery, the negative electrode active material layer may optionally contain a solid electrolyte.

[0152] As the negative electrode active material, any known active material can be used. For example, silicon-based active materials such as silicon, silicon alloys, and silicon oxide; carbon-based active materials such as graphite and hard carbon; various oxide-based active materials such as lithium titanate; metallic lithium, lithium alloys, etc. can be used as negative electrode active materials. The negative electrode active material can be used alone or in combination of two or more. The negative electrode active material can be, for example, in the form of particles, and the size thereof is not particularly limited.

[0153] The conductive auxiliary agent, the binder and the solid electrolyte may refer to the above description related to the positive electrode active material layer of the present invention.

[0154] 〈Negative electrode current collector〉

[0155] For the negative electrode current collector, reference may be made to the above description regarding the positive electrode current collector of the present invention.

[0156] Example

[0157] 《Example 1》

[0158] 〈Manufacturing of evaluation battery cells〉

[0159] (Slurry preparation process)

[0160] A first slurry is prepared by mixing a lithium-bismuth (Li3Bi) alloy as a lithium alloy and a binder in N-methyl-2-pyrrolidone (NMP) as a first dispersion medium. In addition, a second slurry is prepared by mixing lithium iron phosphate (LFP) as an olivine-type positive electrode active material coated with a carbon material, a conductive aid and a binder in NMP as a second dispersion medium.

[0161] (First Slurry Coating Step, Drying Step, and Pressing Step)

[0162] The first slurry is applied onto an aluminum (Al) foil as a positive electrode current collector, and then dried to remove NMP as a first dispersion medium to obtain an initial lithium alloy layer. The obtained initial lithium alloy layer is pressurized to obtain a lithium alloy layer.

[0163] (Second Slurry Coating Step, Drying Step, and Pressing Step)

[0164] The second slurry is applied to the lithium alloy layer, and then the NMP as the second dispersion medium is removed by drying, and the resulting layer is pressed to form a positive electrode active material layer on the positive electrode collector.

[0165] (Battery cell manufacturing process)

[0166] A separator and a negative electrode active material layer containing graphite as a negative electrode active material were stacked on the obtained positive electrode active material layer, vacuum dried and arranged in a laminate film. An electrolyte was then injected into the laminate film and the laminate film was sealed to obtain an evaluation battery cell of Example 1.

[0167] "evaluate"

[0168] 〈Charge and discharge test〉

[0169] Based on the mass of the positive electrode active material contained in the evaluation battery cell, the current value reaching 130 mA / g was defined as 1C rate, and CCCV charging and discharging was performed at a voltage of 2.2 to 4.1 V, with a charge and discharge current value of 0.2C and a termination current value of 0.03C. The obtained CCCV capacity was taken as the capacity of the battery cell.

[0170] 《Example 2》

[0171] A battery cell for evaluation of Example 2 was obtained and evaluated in the same manner as in Example 1 except that a lithium-antimony (Li 3 Sb) alloy was used as the lithium alloy.

[0172] 《Example 3》

[0173] A battery cell for evaluation of Example 3 was obtained and evaluated in the same manner as in Example 1 except that a lithium-tin (LiSn) alloy was used as the lithium alloy.

[0174] Comparative Example 1

[0175] Li3Bi alloy, LFP, conductive additive and binder were mixed in NMP as a dispersion medium to prepare slurry. The obtained slurry was applied on Al foil. Then, NMP as a dispersion medium was removed by drying, and the obtained layer was pressed to obtain a battery cell for evaluation of Comparative Example 1 and evaluated. It should be noted that Li3Bi alloy and LFP were dispersed in each other.

[0176] 《Comparative Example 2》

[0177] A battery cell for evaluation of Comparative Example 2 was obtained and evaluated in the same manner as in Comparative Example 1 except that Li3Sb alloy was used as the lithium alloy.

[0178] 《Comparative Example 3》

[0179] A battery cell for evaluation of Comparative Example 3 was obtained and evaluated in the same manner as in Comparative Example 1 except that a LiSn alloy was used as the lithium alloy.

[0180] 《Comparative Example 4》

[0181] A battery cell for evaluation of Comparative Example 4 was obtained and evaluated in the same manner as in Comparative Example 1 except that the lithium alloy was not used.

[0182] It should be noted that the total volume of the positive electrode active material and the lithium alloy contained in the positive electrode active material layer was designed to be the same in all the examples and comparative examples.

[0183] "result"

[0184] Table 1 shows the content and volume of LFP, the thickness of the layer containing LFP, the type and alloying potential of the metal elements constituting the lithium alloy, the content and volume of the lithium alloy, and the thickness of the lithium alloy layer for the above-mentioned Examples and Comparative Examples.

[0185] [Table 1]

[0186]

[0187] As shown in Table 1, in the battery cell of the embodiment in which the lithium alloy is arranged on the surface of the positive electrode collector side of the positive electrode active material layer, the battery capacity is larger than the battery cells of Comparative Examples 1 to 3 in which the lithium alloy and the positive electrode active material are mutually dispersed in the positive electrode active material layer and the battery cell of Comparative Example 4 which does not have a lithium alloy.

Claims

1. A positive electrode active material layer, between the positive electrode collector and the separator, A lithium alloy having a positive electrode active material and lithium and a metal element, The positive electrode active material is covered with a carbon material, The alloying potential of the metal element with lithium relative to Li / Li + The reference electrode is 0.5V or above, and The lithium alloy is disposed on a surface of the positive electrode active material layer on the positive electrode current collector side and / or a surface of the positive electrode active material layer on the separator side.

2. The positive electrode active material layer according to claim 1, wherein The lithium alloy forms a lithium alloy layer.

3. The positive electrode active material layer according to claim 2, wherein The thickness of the lithium alloy layer is 1 μm to 20 μm.

4. The positive electrode active material layer according to claim 1, wherein The positive electrode active material is an olivine type positive electrode active material.

5. The positive electrode active material layer according to claim 4, wherein The olivine-type positive electrode active material is at least one selected from lithium iron phosphate, lithium manganese iron phosphate, lithium manganese phosphate and lithium cobalt phosphate.

6. The positive electrode active material layer according to claim 1, wherein The metal element is at least one selected from bismuth, antimony and tin.

7. The positive electrode active material layer according to claim 1, wherein The ratio of the mass of the positive electrode active material to the mass of the lithium alloy is 3.0 to 15.

0.

8. The positive electrode active material layer according to claim 1, wherein The thickness of the layer obtained by excluding the lithium alloy from the positive electrode active material layer is 20 μm to 300 μm.

9. A lithium ion battery having: Positive electrode collector, Isolators, and The positive electrode active material layer according to any one of claims 1 to 8 interposed between the positive electrode current collector and the separator.

10. A lithium ion battery having: Positive electrode collector, Isolators, and a positive electrode active material layer between the positive electrode collector and the separator; The positive electrode active material layer comprises a positive electrode active material and a metal element. The positive electrode active material is covered with a carbon material, The alloying potential of the metal element with lithium relative to Li / Li + The reference electrode is 0.5V or above, and The metal element is disposed on a surface of the positive electrode active material layer on the positive electrode current collector side and / or a surface of the positive electrode active material layer on the separator side.

11. A method for producing a positive electrode active material layer according to any one of claims 1 to 8, comprising the following steps: (a) applying a first slurry containing the lithium alloy and a first dispersion medium onto a substrate, (b) applying a second slurry containing the positive electrode active material and a second dispersion medium after the step (a); (c) drying and removing the first and second dispersion media to obtain a laminated body, and (d) Pressurizing the stacked body.

12. The method according to claim 11, wherein: The substrate is a positive electrode collector.

13. The method according to claim 11, wherein: The method further comprises the step of drying and removing the first dispersion medium to obtain an initial lithium alloy layer before the step (b).

14. The method according to claim 13, wherein: The method further comprises the step of: pressurizing the initial lithium alloy layer to obtain a lithium alloy layer.

15. The method according to claim 11, wherein: The first and second dispersion media are the same dispersion medium.

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