Positive electrode and secondary battery

Abstract

A positive electrode (10) according to the present disclosure is provided with a positive electrode current collector (11) and a positive electrode active material layer (12) supported on the positive electrode current collector (11). The positive electrode active material layer (12) contains a positive electrode active material and a phosphorus compound. The phosphorus compound includes a P = O bond. The positive electrode active material layer (12) is divided into a first region (12a) and a second region (12b) in the plane direction, the mass ratio (P1 / A1) of the phosphorus compound contained in the first region (12a) to the positive electrode active material is 0.2-8 mass%, and the mass ratio (P2 / A2) of the phosphorus compound to the positive electrode active material in the second region (12b) is less than 0.2 mass%.

Description

Technical Field

[0001] The present disclosure relates to a positive electrode and a secondary battery. Background Art

[0002] It is known that conventional secondary batteries may cause side reactions such as reduction and dissolution of transition metals contained in active materials and decomposition reactions of electrolyte solutions caused by these reactions. These side reactions accelerate the deterioration of the secondary battery.

[0003] As a technology for coping with the problem of decomposition reaction of the electrolyte solution, for example, the technology disclosed in Patent Document 1 is known. Patent Document 1 describes a coated positive electrode active material having a coating containing at least one selected from a specific phosphonic acid and a specific triester of phosphite.

[0004] Prior art literature

[0005] Patent Document 1: International Publication No. 2017 / 126276 Summary of the Invention

[0006] Problems to be solved by the invention

[0007] However, if the positive electrode active material is coated as described above, the internal resistance increases significantly. In other words, reducing the increase in internal resistance caused by the structure for suppressing side reactions is also an important issue. The present disclosure provides a positive electrode that can suppress side reactions in a battery positive electrode and reduce the increase in internal resistance.

[0008] Means for solving problems

[0009] The positive electrode disclosed herein comprises a positive electrode current collector and a positive electrode active material layer supported on the positive electrode current collector.

[0010] The positive electrode active material layer comprises a positive electrode active material and a phosphorus compound,

[0011] The phosphorus compound contains a P=O bond,

[0012] The positive electrode active material layer is divided into a first region and a second region in the surface direction.

[0013] The mass ratio P1 / A1 of the phosphorus compound to the positive electrode active material in the first region is 0.2 mass % or more and 8 mass % or less,

[0014] The mass ratio P2 / A2 of the phosphorus compound to the positive electrode active material in the second region is less than 0.2 mass %.

[0015] Effects of the Invention

[0016] The present disclosure provides a positive electrode capable of suppressing side reactions in a positive electrode of a battery and reducing an increase in internal resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a cross-sectional view schematically showing the structure of the positive electrode 10 according to the first embodiment.

[0018] Figure 2 These are a cross-sectional view and a plan view schematically showing a first example of the positive electrode according to the first embodiment.

[0019] Figure 3 These are a cross-sectional view and a plan view schematically showing a second example of the positive electrode according to the first embodiment.

[0020] Figure 4 It is a longitudinal cross-sectional view schematically showing a secondary battery 100 according to the second embodiment. DETAILED DESCRIPTION

[0021] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. The present disclosure is not limited to the following embodiments.

[0022] (Implementation Method 1)

[0023] The positive electrode of Embodiment 1 includes a positive electrode current collector and a positive electrode active material layer supported on the positive electrode current collector. The positive electrode active material layer contains a positive electrode active material and a phosphorus compound, wherein the phosphorus compound contains a P=O bond. The positive electrode active material layer is divided into a first region and a second region in the plane direction. The mass ratio P1 / A1 of the phosphorus compound to the positive electrode active material in the first region is 0.2% by mass or more and 8% by mass or less, and the mass ratio P2 / A2 of the phosphorus compound to the positive electrode active material in the second region is less than 0.2% by mass.

[0024] Hereinafter, a phosphorus compound containing a P=O bond will also be referred to as a "phosphorus compound." In the positive electrode of Embodiment 1, the positive electrode active material layer is divided into a first region and a second region in the plane direction according to the phosphorus compound content. This can suppress side reactions in the positive electrode of the battery and reduce increases in internal resistance.

[0025] For example, the positive electrode active material layer includes a first layer containing a positive electrode active material and a second layer containing a phosphorus compound, and has a structure in which the second layer covers at least a portion of the surface of the first layer.

[0026] Figure 1This is a cross-sectional view showing the general structure of the positive electrode 10 of Embodiment 1. The positive electrode 10 includes a positive electrode collector 11 and a positive electrode active material layer 12 in this order. The positive electrode active material layer 12 is a layer containing a positive electrode active material and a phosphorus compound, and is supported on the positive electrode collector 11. The positive electrode active material layer 12 includes a first layer 14 containing a positive electrode active material and a second layer 13 containing a phosphorus compound. The second layer 13 covers at least a portion of the surface of the first layer 14. The positive electrode active material layer 12 is divided into a first region 12a and a second region 12b in its surface direction. The ratio of the mass of the phosphorus compound in the first region 12a to the mass of the positive electrode active material in the first region 12a (mass ratio P1 / A1) is 0.2 mass% or more and 8 mass% or less. The ratio of the mass of the phosphorus compound in the second region 12b to the mass of the positive electrode active material in the second region 12b (mass ratio P2 / A2) is less than 0.2 mass%.

[0027] The mass ratio P1 / A1 is calculated by the formula: (mass of the phosphorus compound contained in the first region 12a) ÷ (mass of the positive electrode active material contained in the first region 12a) × 100. The mass ratio P2 / A2 is calculated by the formula: (mass of the phosphorus compound contained in the second region 12b) ÷ (mass of the positive electrode active material contained in the second region 12b) × 100. The mass ratio P1 / A1 and the mass ratio P2 / A2 can be calculated, for example, by measuring the mass ratio of P using high-frequency inductively coupled plasma (ICP) analysis.

[0028] The positive electrode active material layer 12 contains a phosphorus compound, thereby suppressing side reactions. Examples of suppressed side reactions include decomposition of the electrolyte, gas generation caused thereby, and dissolution of metal elements from the positive electrode active material. In addition, in the positive electrode 10 of embodiment 1, the positive electrode active material layer 12 is divided into a first region 12a and a second region 12b in its surface direction according to the content of the phosphorus compound. According to the above structure, side reactions can be suppressed and the increase in the internal resistance of the battery can be reduced. Furthermore, according to the above structure, compared with a structure in which an equal amount of phosphorus compound uniformly covers the entire surface of the positive electrode active material layer, side reactions can be suppressed, and in particular, side reactions when the battery is charged for a long time can be suppressed.

[0029] For a positive electrode coated with a phosphorus compound solution on the entire surface of the positive electrode active material layer, the relationship between the amount of phosphorus compound and the charge and discharge efficiency, etc. was verified. Tris(trimethylsilyl) phosphate (TMSP) was used as the phosphorus compound. When the amount of phosphorus compound relative to the positive electrode active material was set to 3.5% by mass, the charge and discharge efficiency of the trickle test was improved compared to the case where no phosphorus compound was added, and the amount of gas generated was reduced. Furthermore, when the amount of phosphorus compound was set to 6.8% by mass, the charge and discharge efficiency of the trickle test was improved compared to the case of 3.5% by mass, and the amount of gas generated was reduced. Therefore, the more the amount of phosphorus compound increases, the more the degradation inhibition effect of the battery can be seen. When the amount of phosphorus compound is set to 10.9% by mass, there is no difference in the charge and discharge efficiency and gas generation of the trickle test compared to the case of 6.8% by mass. Therefore, it is speculated that when the amount of phosphorus compound is between 6.8% and 10.9% by mass, the improvement effect of the charge and discharge efficiency and gas generation of the trickle test is saturated. Based on the above, it is estimated that the positive electrode of the present disclosure, in which the mass ratio of the phosphorus compound in the first region 12a to the positive electrode active material is 8 mass % or less, can more effectively suppress deterioration associated with gas generation in the positive electrode of the battery.

[0030] The mass ratio P1 / A1 may be 6.8% by mass or less. The mass ratio P1 / A1 may be 0.5% by mass or more and 8% by mass or less, or 0.5% by mass or more and 6.8% by mass or less. The mass ratio P1 / A1 may be 0.5% by mass or more and 1.6% by mass or less.

[0031] The mass ratio P2 / A2 may be less than 50% of the mass ratio P1 / A1. For example, the mass ratio P2 / A2 may be 0.15 mass % or less, or 0.1 mass % or less.

[0032] The second region 12b may also include a portion that does not contain a phosphorus compound. Figure 1 As shown, the second region 12b may include a portion where the second layer 13 is not provided. The second region 12b may be composed of a region that does not contain a phosphorus compound. The mass ratio P2 / A2 may be 0 mass %.

[0033] The area ratio of the first region 12a on the surface of the positive electrode active material layer 12 may be 5% to 70%, 60% or 50% or less.

[0034] When the area of the first region 12a is 10% to 30% of the total area, the mass ratio P1 / A1 can be 0.5% to 1% by mass, with a more preferred range of 0.5% to 0.9% by mass. When the area of the first region 12a is 30% to 50% of the total area, the mass ratio P1 / A1 can be 0.8% to 1.6% by mass, with a more preferred range of 0.9% to 1.3% by mass. In the positive electrode active material layer 12, phosphorus compounds are also a resistive component. Therefore, when phosphorus compounds are locally contained in the positive electrode active material layer 12 (the area of the first region 12a is 10% to 30% of the total area), it is undesirable for the resistance increase due to the phosphorus compounds in the first region 12a to be excessively greater than that in the second region. In contrast, if the area of the first region 12a is 30% to 50%, the first region 12a occupies a relatively large proportion of the positive electrode active material layer 12, thereby mitigating the localized resistance increase caused by the phosphorus compound. Therefore, when the area of the first region 12a is 10% to 30% or less, the mass ratio P1 / A1 is preferably lower than when the area of the first region 12a is 30% to 50% or less. This configuration further suppresses side reactions.

[0035] Figure 1 The positive electrode 10 shown is an example, and the form of the positive electrode of the first embodiment is not limited thereto. For example, the positive electrode active material layer 12 may not include the first layer 14 and the second layer 13. In the positive electrode active material layer 12, the positive electrode active material and the phosphorus compound may be mixed. Figure 1 In the illustrated positive electrode 10, particles 1 of a positive electrode active material, a phosphorus compound 2, a binder 3, and a conductive additive 4 are mixed in a first region 12a, and the surfaces of the positive electrode active material particles 1 are covered with a phosphorus compound coating 5. The phosphorus compound coating 5 is a coating formed of the phosphorus compound 2. In a second region 12b, particles 1 of a positive electrode active material, a binder 3, and a conductive additive 4 are mixed.

[0036] For example, in the first region 12 a , near the interface between the first region 12 a and the second region 12 b , the positive electrode active material particles 1 covered with the phosphorus compound coating 5 and the positive electrode active material particles 1 not covered are mixed.

[0037] exist Figure 1 In the positive electrode 10 shown, the second region 12b does not contain the phosphorus compound 2. However, as long as the mass ratio P2 / A2 of the second region 12b is less than 0.2 mass%, it may contain the phosphorus compound 2. For example, the second region 12b may contain particles 1 of the positive electrode active material coated with the phosphorus compound film 5 near the interface between the first region 12a and the second region 12b.

[0038] Figure 2 These are a cross-sectional view and a plan view schematically showing a first example of the positive electrode according to the first embodiment. Figure 2 (a) is a cross-sectional view of the positive electrode 20A. Figure 2 (b) is a plan view of the positive electrode 20A as viewed from the lower side in the z-axis direction. Figure 2 (a) indicates Figure 2 (b) is a cross section at the position shown by line II-II. In this specification and the accompanying drawings, the x-axis, y-axis, and z-axis represent the three axes of a three-dimensional rectangular coordinate system. In each embodiment, the z-axis direction is used as the thickness direction of the positive electrode. In addition, in this specification, unless otherwise specified, the "thickness direction" refers to the direction perpendicular to the surface of the stacked layers in the positive electrode.

[0039] exist Figure 2 In the illustrated positive electrode 20A, the second layer 13 of the positive electrode active material layer 12 covers the central portion of the surface of the first layer 14. The first region 12a is located in the center of the plane of the positive electrode active material layer 12 and is single. The second region 12b is located around the first region 12a and is also single. The first region 12a or the second region 12b being single means that the first region 12a or the second region 12b is not separated in the plane of the positive electrode active material layer 12.

[0040] When the electrode is a long strip, such as a strip, the center of the positive electrode active material layer 12 in the plane direction is the center in the width direction. The first region 12a can be located in the center in the width direction of the positive electrode active material layer 12. The positive electrode active material layer 12 can include a strip-shaped second layer 13 that covers the center in the width direction of the surface of the first layer 14.

[0041] Figure 3 These are a cross-sectional view and a plan view schematically showing a second example of the positive electrode according to the first embodiment. Figure 3 (a) is a cross-sectional view of the positive electrode 20B. Figure 3 (b) is a plan view of the positive electrode 20B as viewed from the lower side in the z-axis direction. Figure 3 (a) indicates Figure 3 (b) The cross section at the position indicated by line III-III.

[0042] exist Figure 3 In the illustrated positive electrode 20B, the second layer 13 covers the area along the periphery of the surface of the first layer 14. The second region 12b is located in the center of the surface of the positive electrode active material layer 12 and is a single region. The first region 12a is located around the second region 12b and is a single region. In this specification, the area along the periphery is also referred to as the peripheral region. The periphery refers to the edge that forms the periphery of the surface. In the positive electrode 20B, the first region 12a is provided along the side of the positive electrode active material layer 12.

[0043] The number, shape, and area ratio of the first region 12 a and the second region 12 b in the positive electrode of the first embodiment are not limited to the above-described examples.

[0044] The region containing 0.2% by mass or more of the phosphorus compound relative to the positive electrode active material may be concentrated only in a specific region of the positive electrode active material layer 12. For example, the first region 12a is single. In the positive electrode active material layer 12, the phosphorus compound may be concentrated in a specific region. The second region 12b may be single or may exist in multiple regions. Figure 2 and Figure 3 As shown, the first region 12a and the second region 12b may each be single.

[0045] When the positive electrode active material layer 12 is viewed from at least one of the longitudinal and width directions, a first region 12a and a second region 12b may be present. The longitudinal direction refers to the long side of the elongated strip, and the width direction refers to the short side. The first region 12a and the second region 12b may divide the positive electrode active material layer 12 in the width direction or in the longitudinal direction. A single first region 12a may be located between two second regions 12b in the width direction of the positive electrode active material layer 12, or between two second regions 12b in the longitudinal direction.

[0046] The positive electrode active material layer 12 contains a phosphorus compound containing a P=O bond. Examples of the phosphorus compound include phosphoric acid, phosphonic acid, phosphinic acid, pyrophosphoric acid, phosphate esters, phosphonic acid esters, phosphinic acid esters, derivatives thereof, and condensates thereof. The phosphorus compound may be an organophosphorus compound. In this specification, an organophosphorus compound refers to a compound containing carbon and phosphorus. The phosphorus compound may be an organophosphorus compound having a carbon-phosphorus bond. The phosphorus compound may contain a P-O-P bond. The phosphorus compound may be polyphosphoric acid, polyphosphate esters, and derivatives thereof.

[0047] When the positive electrode active material layer 12 includes the first layer 14 and the second layer 13, the second layer 13 may be substantially composed of a phosphorus compound. "The second layer 13 is substantially composed of a phosphorus compound" means that the mass proportion of the phosphorus compound in the second layer 13 is 97% by mass or greater. The mass proportion of the phosphorus compound in the second layer 13 may be 98% by mass or greater, or 99% by mass or greater. The second layer 13 may also be composed solely of a phosphorus compound.

[0048] The phosphorus compound may contain a structure represented by Chemical Formula (1).

[0049]

[0050] In the chemical formula (1), n1 and n2 are each independently an integer greater than or equal to 0. 1 、R2 、R 4 and R 5 Independently represents -OR or -(CH2) m1 X1. R 3 and R independently represent a direct bond with the positive electrode active material, a hydrogen atom, -(CH2) m2 X2, trimethylsilyl or triethylsilyl. m1 is an integer from 0 to 15. m2 is a natural number from 1 to 3. X1 and X2 are independently hydrogen, hydroxy, amino, carboxyl, cyano or fluorine atoms. 2 In the case of multiple R 2 Independent of each other. 4 In the case of multiple R 4 Independent of each other.

[0051] The phosphorus compound has such a structure and is relatively stable even in high-voltage environments. Therefore, even when the upper limit voltage of the secondary battery is high, for example, exceeding 4.3 V, side reactions such as oxidative decomposition of the electrolyte can be fully suppressed. In addition, the effect of suppressing side reactions can last longer.

[0052] In the chemical formula (1), n1 and n2 may be independently 1 or greater. At least one selected from n1 and n2 is 1 or greater. n1 and n2 may be independently 500 or less. X1 may be a hydrogen atom. X2 may be a hydrogen atom.

[0053] In the chemical formula (1), m1 may be an integer of 0 to 11, or an integer of 0 to 6. When m1 is an integer of 0 to 6, side reactions can be further suppressed.

[0054] In the chemical formula (1), m2 may be 1 or 2. 3 It may be a direct bond with the positive electrode active material.

[0055] Phosphorus compounds include, for example, silyl phosphite, phosphonic acid, phosphoric acid, pyrophosphoric acid, and condensates thereof. The phosphorus compound may be silyl phosphite, tris(trimethylsilyl) phosphate (TMSP), or a compound derived from TMSP such as a condensate of TMSP. In the chemical formula (1), R 1 、R 2 、R 4 and R 5 Can express -OR, R independently of each other 3 and R may independently represent a direct bond with the positive electrode active material, a hydrogen atom, or a trimethylsilyl group.

[0056] The phosphorus compound may be phosphoric acid or a condensate of phosphoric acid. 1 、R 2 、R 4 and R 5 Independently represent -OR, R 3 R and R independently represent a direct bond with the positive electrode active material, or may be a hydrogen atom.

[0057] The positive electrode active material layer 12 may contain one or two or more phosphorus compounds.

[0058] The positive electrode active material layer 12 contains a phosphorus compound. For example, in the positive electrode active material layer 12, the second layer 13 covers at least a portion of the surface of the first layer 14. This structure can prevent direct contact between the positive electrode active material and the electrolyte, thereby suppressing side reactions such as decomposition of the electrolyte. Figure 2 and Figure 3 As shown, the positive electrode active material layer 12 can be divided into a first region 12a and a second region 12b by the second layer 13 covering a portion of the first layer 14. The second layer 13 may cover the center of the surface of the first layer 14, while the outer peripheral region of the surface of the first layer 14 is not covered by the second layer 13. Alternatively, the second layer 13 may cover the outer peripheral region of the surface of the positive electrode active material layer 12, while the center of the surface of the positive electrode active material layer 12 is not covered by the second layer 13. The second layer 13 may cover a portion of the surface of the elongated first layer 14 in the width direction. The second layer 13 may also cover a portion of the surface of the elongated first layer 14 in the length direction. The phosphorus compound may be localized in a specific region of the positive electrode active material layer 12, for example, in a specific region. The second layer 13 may cover a portion of the surface of the first layer 14 and be single. The second layer 13 being single means that the second layer 13 is not separated in the surface direction of the positive electrode active material layer 12.

[0059] The second layer 13 may cover the entire surface of the first layer 14. In this case, the positive electrode active material layer 12 can be divided into the first region 12a and the second region 12b by adjusting the concentration of the phosphorus compound in the second layer 13 in the surface direction of the second layer 13.

[0060] As described above, the positive electrode of Embodiment 1 partially includes a region with a low phosphorus compound concentration or a region not covered with a phosphorus compound in the positive electrode active material layer, and thus can reduce an increase in the internal resistance of the battery.

[0061] The first region 12a contains a relatively large amount of phosphorus compounds, so the resistance increases compared to the second region 12b. Therefore, the potential during charging is relatively high in the first region 12a and relatively low in the second region 12b. On the other hand, the first region 12a contains a sufficient amount of phosphorus compounds, so the withstand voltage performance is improved. Since side reactions such as the decomposition of the electrolyte during charging are accelerated in areas with high potentials than in areas with low potentials, they are more likely to occur in the first region 12a and less likely to occur in the second region 12b. However, since the withstand voltage performance of the first region 12a is improved, side reactions can be suppressed. As described above, the positive electrode of embodiment 1 has areas where side reactions are less likely to occur and areas where side reactions can be suppressed, so side reactions as a whole can be suppressed. Therefore, for example, by designing the amount and area of the phosphorus compound of the second layer 13 that covers the surface of the first layer 14, the increase in internal resistance can be reduced and side reactions can be suppressed compared to a positive electrode in which the same amount of phosphorus compound uniformly covers the entire surface of the positive electrode active material layer.

[0062] The thickness of the second layer 13 in the first region 12 a may be 0.05 μm or more and 2 μm or less.

[0063] The second layer 13 may be in contact with the first layer 14 .

[0064] The phosphorus compound may or may not form a chemical bond with the positive electrode active material, and may be physically attached to the positive electrode active material.

[0065] The positive electrode active material layer 12 contains a positive electrode active material. There is no particular limitation on the positive electrode active material. As the positive electrode active material, lithium-containing transition metal oxides, lithium-containing transition metal phosphates, transition metal fluorides, polyanion materials, fluorinated polyanion materials, transition metal sulfides, transition metal oxysulfides, transition metal oxynitrides, etc. can be used. In particular, when lithium-containing transition metal oxides or lithium-containing transition metal phosphates are used as the positive electrode active material, the manufacturing cost of the battery can be reduced and the average discharge voltage can be increased. Examples of lithium-containing transition metal oxides include lithium cobaltate, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese oxide, and lithium nickel manganese oxide. Examples of lithium-containing transition metal phosphates include lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, and lithium nickel phosphate.

[0066] The positive electrode active material may include lithium nickel oxide having a layered rock salt crystal structure. Among the metal elements other than Li contained in the lithium nickel oxide, the proportion of Ni may be 50 atomic % or more. The lithium nickel oxide may also contain other transition metals. Lithium nickel oxide can be used to achieve a high operating voltage. According to the structure of the positive electrode of embodiment 1, the dissolution of metal ions from the positive electrode active material can be suppressed. Since nickel is easily dissolved from the positive electrode active material, the dissolution suppression effect brought about by the technology disclosed in this disclosure is particularly expected.

[0067] Lithium nickel oxide can be represented by the following composition formula (I). Element M1 is at least one selected from V, Co, and Mn. Element M2 is at least one selected from Mg, Al, Ca, Ti, Cu, Zn, and Nb. Composition formula (I) satisfies 0.9 ≤ α ≤ 1.10, −0.05 ≤ β ≤ 0.05, 0.5 ≤ x1 < 1, 0 ≤ x2 ≤ 0.5, and 0 < 1 − x1 − x2 ≤ 0.5.

[0068] Li α Ni x1 M1 x2 M2 (1-x1-x2) O 2+β ···(I)

[0069] The positive electrode active material layer 12 may contain other materials such as a binder, an ion conductor, and a conductive additive. When the positive electrode active material layer 12 includes a first layer 14 and a second layer 13, the first layer 14 may contain other materials such as a binder, an ion conductor, and a conductive additive in addition to the positive electrode active material.

[0070] For example, metal foil can be used as the positive electrode current collector 11. Examples of the metal constituting the positive electrode current collector 11 include aluminum, titanium, alloys containing these metal elements, and stainless steel.

[0071] The positive electrode of the first embodiment can be produced, for example, by the following method.

[0072] A positive electrode slurry containing a positive electrode active material is prepared. For example, the positive electrode active material, a binder, and a conductive additive are dispersed in a dispersion medium to prepare the positive electrode slurry.

[0073] A positive electrode slurry is applied to the positive electrode current collector 11 to form the positive electrode active material layer 12. Specifically, the positive electrode slurry is applied to the positive electrode current collector 11 to form a coating. The first layer 14 is obtained by removing the dispersion medium from the coating. As a method for removing the dispersion medium, a method of heating the coating can be cited. As the dispersion medium, for example, N-methyl-2-pyrrolidone (NMP) can be used.

[0074] Next, a solution containing a phosphorus compound and a solvent is prepared.

[0075] As described above, the phosphorus compound includes the structure represented by Chemical Formula (1). The phosphorus compound at the raw material stage is in a state before it can condense with each other and / or combine with the positive electrode active material, and can be distinguished from the phosphorus compound contained in the positive electrode active material layer 12. The phosphorus compound at the raw material stage includes, for example, the structure represented by Chemical Formula (2).

[0076]

[0077] In chemical formula (2), R 7 Represents a hydrogen atom, -(CH2) k1 Y1, trimethylsilyl or triethylsilyl. 6 and R 8 Independently represents -OR or -(CH2) k2 Y2. R represents a hydrogen atom, -(CH2) k3 Y3, trimethylsilyl or triethylsilyl. k1 and k3 are each independently a natural number of 1 to 3. k2 is an integer of 0 to 15. Y1, Y2 and Y3 are each independently a hydrogen atom, a hydroxyl group, an amino group, a carboxyl group, a cyano group or a fluorine atom.

[0078] The phosphorus compound in the raw material stage may contain at least one selected from silyl phosphite and phosphoric acid. The silyl phosphite may be TMSP.

[0079] As the solvent, cyclic carbonates, chain carbonates, cyclic carboxylic acid esters, etc. can be used. As cyclic carbonates, for example, propylene carbonate (PC) can be mentioned. As chain carbonates, diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC) etc. can be mentioned. As cyclic carboxylic acid esters, gamma-butyrolactone (GBL), gamma-valerolactone (GVL) etc. can be mentioned. One solvent can be used alone, or two or more can be used in combination.

[0080] The prepared solution is applied on the first layer 14 to form the second layer 13. For example, a coating film is formed by selectively applying the solution to a target position on the first layer 14. The solution can be applied to the target position using a pipette, or the solution can be applied after masking a portion of the surface of the first layer 14. The second layer 13 is obtained by removing the solvent from the coating film. As a method for removing the solvent, a method of heating the coating film can be cited. The heating temperature is, for example, 20°C or higher and 60°C or lower. The heating time is, for example, 15 minutes or higher and 120 minutes or lower. In this way, a positive electrode divided into the first region 12a and the second region 12b is obtained.

[0081] (Implementation Method 2)

[0082] The secondary battery of the second embodiment includes the positive electrode, the negative electrode, and the electrolyte of the first embodiment. By using the positive electrode of the first embodiment, the characteristics of the secondary battery can be improved.

[0083] Figure 4 This is a schematic longitudinal cross-sectional view of a secondary battery 100 according to Embodiment 2. The secondary battery 100 is a cylindrical battery comprising a cylindrical battery case, a wound electrode group 24, and an electrolyte (not shown). The electrode group 24 is housed in the battery case and in contact with the electrolyte.

[0084] The battery case consists of a case body 25, a bottomed cylindrical metal container, and a sealing member 26 that seals the opening of the case body 25. A gasket 37 is disposed between the case body 25 and the sealing member 26. The gasket 37 ensures the airtightness of the battery case. Insulating plates 27 and 28 are disposed within the case body 25 at both ends of the electrode group 24 in the winding axis direction.

[0085] The housing body 25 has, for example, a stepped portion 31. The stepped portion 31 can be formed by partially punching the side wall of the housing body 25 from the outside. The stepped portion 31 can be formed in an annular shape on the side wall of the housing body 25 along the circumference of an imaginary circle defined by the housing body 25. In this case, the sealing member 26 is supported by, for example, the surface of the stepped portion 31 on the opening side.

[0086] The sealing body 26 includes a filter 32, a lower valve body 33, an insulating member 34, an upper valve body 35, and a lid 36. These components are stacked in this order in the sealing body 26. The sealing body 26 is attached to the opening of the housing body 25 so that the lid 36 is located outside the housing body 25 and the filter 32 is located inside the housing body 25.

[0087] Each of the aforementioned members constituting the sealing member 26 is, for example, in the form of a disk or a ring. Except for the insulating member 34 , each of the aforementioned members is electrically connected to one another.

[0088] The electrode assembly 24 includes a positive electrode 21, a negative electrode 22, and a separator 23. The positive electrode 21, negative electrode 22, and separator 23 are all in a strip shape. The width direction of the strip-shaped positive electrode 21 and negative electrode 22 is, for example, parallel to the winding axis of the electrode assembly 24. The separator 23 is provided between the positive electrode 21 and the negative electrode 22. The positive electrode 21 and the negative electrode 22 are wound in a spiral shape with the separator 23 interposed between these electrodes.

[0089] When viewing a cross section of the secondary battery 100 perpendicular to the winding axis of the electrode group 24 , the positive electrodes 21 and the negative electrodes 22 are alternately stacked in the radial direction of the imaginary circle defined by the case body 25 with the separator 23 interposed therebetween.

[0090] The positive electrode 21 is electrically connected to the cap 36, which also serves as a positive electrode terminal, via a positive electrode lead 29. One end of the positive electrode lead 29 is connected, for example, to a position near the center of the positive electrode 21 in the longitudinal direction of the positive electrode 21. The positive electrode lead 29 extends from the positive electrode 21 to the filter 32 through a through-hole formed in the insulating plate 27. The other end of the positive electrode lead 29 is welded, for example, to the surface of the filter 32 on the electrode group 24 side.

[0091] The negative electrode 22 is electrically connected to the case body 25, which also serves as a negative electrode terminal, via a negative electrode lead 30. One end of the negative electrode lead 30 is connected to, for example, the longitudinal end of the negative electrode 22. The other end of the negative electrode lead 30 is welded to the inner bottom surface of the case body 25, for example.

[0092] Hereinafter, each structure of the secondary battery 100 will be described in detail.

[0093] The positive electrode 21 is the positive electrode of the first embodiment.

[0094] The negative electrode 22 is made of a material that has the property of absorbing and releasing metal ions (such as lithium ions). The negative electrode 22 includes, for example, a negative electrode active material. The negative electrode can include a negative electrode current collector and a negative electrode active material layer supported on the surface of the negative electrode current collector.

[0095] The negative electrode current collector is, for example, a foil made of a metal material such as stainless steel, nickel, a nickel alloy, copper, or a copper alloy.

[0096] The negative electrode active material layer contains a negative electrode active material. The negative electrode active material can be a material that has the ability to absorb and release lithium ions. Examples of negative electrode active materials include lithium titanate, graphite, silicon, silicon compounds, and NiBi alloys.

[0097] The negative electrode active material layer may contain other materials such as a conductive additive, an ion conductor, and a binder.

[0098] The electrolyte solution may contain a non-aqueous solvent and a lithium salt dissolved in the non-aqueous solvent. The concentration of the lithium salt in the electrolyte solution may be, for example, 0.5 mol / L or higher and 2 mol / L or lower. By controlling the lithium salt concentration within this range, an electrolyte solution with excellent ion conductivity and moderate viscosity can be obtained. However, the lithium salt concentration is not limited to the above range.

[0099] As the non-aqueous solvent, cyclic carbonates, chain carbonates, cyclic ethers, chain ethers, nitriles, amides, etc. may be used. One type selected from these solvents may be used alone, or two or more types may be used in combination.

[0100] As lithium salts, lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(perfluoroethylsulfonyl)imide (LiN(SO2C2F5)2), LiAsF6, LiCF3SO3, lithium difluoro(oxalato)borate, etc. can be used. One selected from these electrolyte salts can be used, or two or more can be used in combination.

[0101] Typically, a separator is preferably sandwiched between the positive electrode and the negative electrode. The separator 23 has high ion permeability and possesses appropriate mechanical strength and insulating properties. Microporous films, woven fabrics, and non-woven fabrics can be used as separator 23. For example, polymers can be used as materials for separator 23. Examples of polymers include polyolefins such as polypropylene and polyethylene.

[0102] In the secondary battery of the present disclosure, the electrolyte solution may be impregnated in a polymer provided as a separator, for example. That is, the secondary battery of the present disclosure may have a structure using both the electrolyte solution and the polymer.

[0103] The secondary battery of the present disclosure may also include a solid electrolyte as an electrolyte. That is, the secondary battery of the present disclosure may have a hybrid structure in which an electrolyte solution and a solid electrolyte are used together. Examples of solid electrolyte materials include halide solid electrolytes, sulfide solid electrolytes, oxide solid electrolytes, or organic polymer solid electrolytes. In the present disclosure, "halide solid electrolyte" refers to a solid electrolyte containing a halogen element as the main component of anions. "Sulfide solid electrolyte" refers to a solid electrolyte containing sulfur as the main component of anions. "Oxide solid electrolyte" refers to a solid electrolyte containing oxygen as the main component of anions. The main component of anions refers to the anion with the largest mass among all anions constituting the solid electrolyte. The coating material in the secondary battery of the present disclosure may include a halide solid electrolyte.

[0104] In this disclosure, as an example of the structure of the secondary battery of Embodiment 2, Figure 4 The structural example shown is a secondary battery in which a stacked electrode group and an electrolyte are housed in an outer body, wherein the stacked electrode group is formed by stacking a positive electrode and a negative electrode with a separator therebetween. However, the secondary battery disclosed herein is not limited to this structural example. The secondary battery disclosed herein may be in any form, for example, cylindrical, square, coin-shaped, button-shaped, laminated, or the like. In addition, as the electrode group in the secondary battery disclosed herein, an electrode group in another form, such as an electrode group in which a positive electrode and a negative electrode are wound with a separator therebetween, may be applied instead of the stacked electrode group.

[0105] The positive electrode of the first embodiment is not limited to the secondary battery 100. In addition to lithium secondary batteries, the positive electrode of the first embodiment can be applied to various secondary batteries such as sodium secondary batteries and magnesium secondary batteries. These secondary batteries can use electrolyte solutions or solid batteries.

[0106] (Other embodiments)

[0107] (Note)

[0108] Based on the description of the above embodiments, the following technical solutions are disclosed.

[0109] (Technical Solution 1)

[0110] A positive electrode comprises a positive electrode current collector and a positive electrode active material layer supported on the positive electrode current collector.

[0111] The positive electrode active material layer comprises a positive electrode active material and a phosphorus compound,

[0112] The phosphorus compound contains a P=O bond,

[0113] The positive electrode active material layer is divided into a first region and a second region in the surface direction.

[0114] The mass ratio P1 / A1 of the phosphorus compound to the positive electrode active material in the first region is 0.2 mass % or more and 8 mass % or less,

[0115] The mass ratio P2 / A2 of the phosphorus compound to the positive electrode active material in the second region is less than 0.2 mass %.

[0116] This technical configuration can suppress side reactions in the positive electrode of the battery and reduce an increase in internal resistance.

[0117] (Technical Solution 2)

[0118] According to the positive electrode of claim 1, the mass ratio P2 / A2 is less than 50% of the mass ratio P1 / A1. With such a technical configuration, the increase in internal resistance can be further reduced.

[0119] (Technical Solution 3)

[0120] In the positive electrode according to claim 1 or 2, the second region includes a portion that does not contain the phosphorus compound. This technical configuration can further reduce the increase in internal resistance.

[0121] (Technical Solution 4)

[0122] In the positive electrode according to any one of claims 1 to 3, the area ratio of the first region on the surface of the positive electrode active material layer is 5% to 70%. This technical configuration can suppress side reactions in the positive electrode of the battery and reduce the increase in internal resistance.

[0123] (Technical Solution 5)

[0124] In the positive electrode according to any one of claims 1 to 4, when the area ratio of the first region is 10% to 30%, the mass ratio P1 / A1 is 0.5% to 1% by mass. This technical configuration further suppresses side reactions in the positive electrode of the battery.

[0125] (Technical Solution 6)

[0126] In the positive electrode according to any one of claims 1 to 5, when the area ratio of the first region is greater than 30% and less than 50%, the mass ratio P1 / A1 is greater than 0.8% by mass and less than 1.6% by mass. This technical configuration further suppresses side reactions in the positive electrode of the battery.

[0127] (Technical Solution 7)

[0128] In the positive electrode according to any one of claims 1 to 6, the first region is located at the center of the surface of the positive electrode active material layer. This technical configuration can further suppress side reactions in the positive electrode of the battery and further reduce the increase in internal resistance.

[0129] (Technical Solution 8)

[0130] The positive electrode according to any one of claims 1 to 7, wherein the phosphorus compound contains a POP bond. With such a technical configuration, side reactions in the positive electrode of the battery can be further suppressed.

[0131] (Technical Solution 9)

[0132] According to any one of technical solutions 1 to 8, the positive electrode, the phosphorus compound includes a structure represented by chemical formula (1).

[0133]

[0134] n1 and n2 are independently integers greater than 0,

[0135] R 1 、R 2 、R 4 and R 5 Independently represents -OR or -(CH2) m1 X1,

[0136] R 3 and R independently represent a direct bond with the positive electrode active material, a hydrogen atom, -(CH2) m2 X2, trimethylsilyl or triethylsilyl,

[0137] m1 is an integer from 0 to 15,

[0138] m2 is a natural number from 1 to 3,

[0139] X1 and X2 independently represent a hydrogen atom, a hydroxyl group, an amino group, a carboxyl group, a cyano group or a fluorine atom,

[0140] In the case of multiple R 2 In the case of multiple R2 Independent of each other,

[0141] In the case of multiple R 4 In the case of multiple R 4 Independent of each other.

[0142] The phosphorus compound has such a structure, which makes it relatively stable even in high-voltage environments. Therefore, even when the upper voltage limit of the battery is high, it can fully suppress side reactions such as oxidative decomposition of the electrolyte. In addition, the effect of suppressing side reactions can last longer.

[0143] (Technical Solution 10)

[0144] According to the positive electrode described in technical solution 9, in the chemical formula (1), R 1 、R 2 、R 4 and R 5 Independently represent -OR, R 3 R and R independently represent a direct bond to the positive electrode active material, a hydrogen atom, or a trimethylsilyl group. This technical configuration can further suppress side reactions in the positive electrode of the battery and further reduce the increase in internal resistance.

[0145] (Technical Solution 11)

[0146] According to any one of claims 1 to 10, the positive electrode active material layer includes a first layer containing the positive electrode active material and a second layer containing the phosphorus compound, and the second layer covers at least a portion of the surface of the first layer.

[0147] (Technical Solution 12)

[0148] A secondary battery comprises the positive electrode according to any one of claims 1 to 11, a negative electrode, and an electrolyte.

[0149] This technical configuration can improve the characteristics of the secondary battery, such as the charge and discharge efficiency.

[0150] Example

[0151] The present disclosure is described in more detail below using examples. The following examples are merely examples and are not intended to limit the present disclosure.

[0152] (Example 1)

[0153] Will have LiNi 0.5 Co 0.2 Mn 0.3A positive electrode active material composed of O2 (NCM523), acetylene black (AB), and polyvinylidene fluoride (PVDF) was added to N-methyl-2-pyrrolidone (NMP) and stirred to prepare a positive electrode slurry. The mass ratio of these materials in the positive electrode active material layer was NCM523:AB:PVDF = 92:5:3.

[0154] The positive electrode slurry was applied to the surface of an aluminum foil (1.5 cm x 1.5 cm), and after drying, the coating was rolled to form a positive electrode mixture layer containing a positive electrode active material. The positive electrode mixture layer was formed on one surface of the aluminum foil.

[0155] Tris(trimethylsilyl) phosphate (TMSP) was added to dimethyl carbonate (DMC) to obtain a TMSP solution. The TMSP concentration in the TMSP solution was adjusted to 2% by mass.

[0156] On the positive electrode mixture layer obtained above, a TMSP solution is applied using a pipette to form a coating. At this time, the TMSP solution is applied to the center of the surface of the positive electrode mixture layer in such a way that the area of the coating becomes 50% of the surface area of the positive electrode mixture layer. At this time, the mass ratio of TMSP to the positive electrode active material is 0.5 mass %. That is, the mass ratio of TMSP to the positive electrode active material in the area coated with the TMSP solution is set to 1 mass %. The coating is dried to form a phosphorus-containing layer. Thus, the positive electrode of Example 1 having a positive electrode collector and a positive electrode active material layer is obtained. In the positive electrode of Example 1, the mass ratio P1 / A1 is 1 mass %, and the mass ratio P2 / A2 is 0 mass %. The positive electrode mixture layer and the phosphorus-containing layer correspond to the first layer 14 and the second layer 13 of the present disclosure, respectively.

[0157] Evaluation cells for Example 1 were fabricated using the positive electrode of Example 1, a Li metal foil serving as a counter electrode, a separator, and an electrolyte. A PP / PE / PP three-layer separator was used. The LiPF6 concentration in the electrolyte was 13 mol / L. The electrolyte solvent contained ethylene carbonate (EC) and DMC in a volume ratio of EC:DMC = 25:75.

[0158] (Example 2)

[0159] A positive electrode of Example 2 was produced in the same manner as in Example 1, except that the TMSP solution was applied to the outer peripheral region of the surface of the positive electrode mixture layer so that the area of the coating film was 50% of the surface area of the positive electrode mixture layer during the formation of the phosphorus-containing layer. In the positive electrode of Example 2, the mass ratio P1 / A1 was 1% by mass, and the mass ratio P2 / A2 was 0% by mass. Using the positive electrode of Example 2, an evaluation cell of Example 2 was produced in the same manner as in Example 1.

[0160] (Example 3)

[0161] In the same manner as in Example 1, a positive electrode mixture layer was formed on the positive electrode current collector.

[0162] Phosphoric acid (H3PO4) was added to a solvent containing DMC and γ-butyrolactone (GBL) at a volume ratio of DMC:GBL = 90:10 to obtain a phosphoric acid solution. The concentration of phosphoric acid in the phosphoric acid solution was adjusted to 0.2% by mass.

[0163] A phosphoric acid solution is applied to the positive electrode mixture layer using a pipette to form a coating. At this time, as in Example 1, the phosphoric acid solution is applied to the center of the surface of the positive electrode mixture layer in such a manner that the area of the coating becomes 50% of the surface area of the positive electrode mixture layer. At this time, the mass ratio of phosphoric acid to the positive electrode active material is 0.2%. That is, the mass ratio of phosphoric acid to the positive electrode active material in the area coated with the phosphoric acid solution is set to 0.4% by mass. The coating is dried to form a phosphorus-containing layer. Thus, the positive electrode of Example 3 having a positive electrode collector and a positive electrode active material layer is obtained. In the positive electrode of Example 3, the mass ratio P1 / A1 is 0.4% by mass, and the mass ratio P2 / A2 is 0% by mass.

[0164] Using the positive electrode of Example 3, a cell for evaluation of Example 3 was produced in the same manner as in Example 1.

[0165] (Comparative Example 1)

[0166] In forming the phosphorus-containing layer, the same amount of TMSP solution as that in Example 1 was applied to the entire surface of the positive electrode mixture layer formed on the positive electrode current collector.

[0167] Using the positive electrode of Comparative Example 1, a cell for evaluation of Comparative Example 1 was produced in the same manner as in Example 1.

[0168] (Reference Example 1)

[0169] A positive electrode of Reference Example 1 was obtained in the same manner as in Example 1 except that the phosphorus-containing layer was not formed.

[0170] Using the positive electrode of Reference Example 1, a cell for evaluation of Reference Example 1 was produced in the same manner as in Example 1.

[0171] [Battery evaluation]

[0172] For the evaluation cells of the Examples, Comparative Examples, and Reference Examples, constant current charging at a current value of 0.1C until the voltage reached 4.6V, and constant current discharging at a current value of 0.1C until the voltage reached 2.5V were repeated twice at an ambient temperature of 25°C. A trickle current test was then performed according to the following procedure. Constant current charging at a current value of 0.2C until the voltage reached 4.6V, followed by trickle charging at an ambient temperature of 55°C, maintaining the voltage at 4.6V for three days. Discharging at an ambient temperature of 25°C was then performed at a current value of 0.1C.

[0173] The evaluation results are shown in Table 1. Internal resistance is a relative value, calculated from the discharge curve during the initial charge and discharge, with the internal resistance of Reference Example 1 set to 100%. Charge and discharge efficiency is the charge and discharge efficiency of the trickle test and is calculated as 100 × (discharge capacity during the trickle test) / (total charge capacity during the trickle test). Gas generation is the amount of gas generated within the battery during the trickle test and is calculated as {(battery volume after the trickle test) - (battery volume before the trickle test)} / (mass of the positive electrode active material).

[0174] In Table 1, "position" refers to the position of the phosphorus-containing layer on the surface of the positive electrode mixture layer. "Area ratio" refers to the ratio of the surface area of the phosphorus-containing layer to the surface area of the positive electrode mixture layer facing the phosphorus-containing layer. "Phosphorus compound amount" refers to the ratio of the mass of the phosphorus compound used to the mass of the positive electrode active material in the entire positive electrode active material layer. "Coating mass ratio" refers to the ratio of the mass of the phosphorus compound contained in the positive electrode active material layer in the area covered by the phosphorus-containing layer to the mass of the positive electrode active material.

[0175] Table 1

[0176]

[0177] As shown in Table 1, the batteries of Examples 1-3 were able to reduce the increase in internal resistance, suppress gas generation, and improve charge-discharge efficiency compared to the battery of Comparative Example 1. It can be seen that the batteries of Examples 1-3 were able to significantly suppress gas generation and improve charge-discharge efficiency without significantly increasing internal resistance compared to the battery of Reference Example 1. Based on this, it is speculated that the positive electrode of the present disclosure not only reduces the increase in internal resistance but also further suppresses side reactions such as electrolyte decomposition.

[0178] Industrial availability

[0179] The technology disclosed herein can be applied to secondary batteries used as power sources for mobile communication devices, portable electronic devices, electric vehicles, and the like.

Claims

1. A positive electrode comprising a positive electrode current collector and a positive electrode active material layer supported on the positive electrode current collector, The positive electrode active material layer comprises a positive electrode active material and a phosphorus compound, The phosphorus compound contains a P=O bond, The positive electrode active material layer is divided into a first region and a second region in the surface direction. The mass ratio P1 / A1 of the phosphorus compound to the positive electrode active material in the first region is 0.2 mass % or more and 8 mass % or less, The mass ratio P2 / A2 of the phosphorus compound to the positive electrode active material in the second region is less than 0.2 mass %.

2. The positive electrode according to claim 1, The mass ratio P2 / A2 is less than 50% of the mass ratio P1 / A1.

3. The positive electrode according to claim 1, The second region includes a portion that does not contain the phosphorus compound.

4. The positive electrode according to claim 1, The ratio of the area of the first region to the surface of the positive electrode active material layer is 5% or more and 70% or less.

5. The positive electrode according to claim 1, When the area ratio of the first region is 10% or more and 30% or less, the mass ratio P1 / A1 is 0.5% by mass or more and 1% by mass or less.

6. The positive electrode according to claim 1, When the area ratio of the first region is greater than 30% and less than 50%, the mass ratio P1 / A1 is greater than or equal to 0.8% by mass and less than or equal to 1.6% by mass.

7. The positive electrode according to claim 1, The first region is located at the center of the positive electrode active material layer in a plane direction.

8. The positive electrode according to claim 1, The phosphorus compound contains a POP bond.

9. The positive electrode according to claim 8, The phosphorus compound comprises a structure represented by chemical formula (1), n1 and n2 are independently integers greater than 0, R 1 、R 2 、R 4 and R 5 Independently represents -OR or -(CH2) m1 X1, R 3 and R independently represent a direct bond with the positive electrode active material, a hydrogen atom, -(CH2) m2 X2, trimethylsilyl or triethylsilyl, m1 is an integer from 0 to 15, m2 is a natural number from 1 to 3, X1 and X2 independently represent a hydrogen atom, a hydroxyl group, an amino group, a carboxyl group, a cyano group or a fluorine atom, In the case of multiple R 2 In the case of multiple R 2 Independent of each other, In the case of multiple R 4 In the case of multiple R 4 Independent of each other.

10. The positive electrode according to claim 9, In the chemical formula (1), R 1 、R 2 、R 4 and R 5 Independently of each other, R 3 and R independently represent a direct bond with the positive electrode active material, a hydrogen atom, or a trimethylsilyl group.

11. The positive electrode according to claim 1, The positive electrode active material layer includes a first layer containing the positive electrode active material and a second layer containing the phosphorus compound. The second layer covers at least a portion of the surface of the first layer. 12 . A secondary battery comprising the positive electrode according to claim 1 , a negative electrode, and an electrolyte.

Images