Positive electrode active material, battery, and method for producing positive electrode active material

Abstract

To provide a positive electrode active material capable of suppressing an increase in battery resistance.SOLUTION: There is provided a positive electrode active material having an O3 structure, the positive electrode active material containing Li2SO4, and the Li2SO4 being present inside the surface of the positive electrode active material.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a positive electrode active material, a battery, and a method for manufacturing a positive electrode active material.

Background Art

[0002] Information-related devices and communication devices such as personal computers, video cameras, and mobile phones have become widespread. Also, from the viewpoint of reducing the environmental load, automobiles using motors such as electric vehicles have become widespread. Along with this, various studies have been conducted on batteries used as their power sources.

[0003] For example, Patent Document 1 discloses a lithium-ion battery including a positive electrode including a conductive material, a layered niobium-containing oxide coating the surface of the conductive material, and a lithium-containing oxide active material having an upper limit potential with respect to the oxidation-reduction potential of metallic lithium of 4.5 V (vs. Li / Li + ).

[0004] Also, Patent Document 2 discloses an all-solid-state lithium secondary battery including a positive electrode layer containing a Li-containing sulfate-coated oxide-based positive electrode active material in which a Li-containing sulfate is formed on the surface of an oxide-based positive electrode active material and a sulfide-based solid electrolyte material.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] As will be described in detail later, the resistance of a battery may increase during charge and discharge. On the other hand, from the perspective of improving the performance of the battery, it is preferable to suppress the increase in resistance. The present disclosure has been made in view of the above circumstances, and the main object thereof is to provide a positive electrode active material capable of suppressing an increase in the resistance of a battery.

Means for Solving the Problems

[0007] [1] A positive electrode active material having an O3 structure, wherein the positive electrode active material contains Li 2 SO 4 and the Li 2 SO 4 is present inside the positive electrode active material rather than on the surface thereof.

[0008] [2] In the positive electrode active material, the proportion of the Li 2 SO 4 is 1.0 wt% or more and 3.0 wt% or less, the positive electrode active material according to [1].

[0009] [3] The positive electrode active material having the O3 structure contains a Li element, a transition metal element containing at least a Ni element, and an O element, and the proportion of the Ni element in the transition metal element is 30 atm% or more, the positive electrode active material according to [1] or [2].

[0010] [4] The Li 2 SO 4 is present on the surface and inside of the positive electrode active material, the positive electrode active material according to any one of [1] to [3].

[0011] [5] A battery having a positive electrode active material layer, a negative electrode active material layer, and an electrolyte layer disposed between the positive electrode active material layer and the negative electrode active material layer, wherein the positive electrode active material layer contains the positive electrode active material according to any one of [1] to [4].

[0012] [6] A method for producing a positive electrode active material according to any one of [1] to [4], comprising: NaOH and NiSO 4 obtaining precursor particles by a coprecipitation method using; a first step; firing the precursor particles together with lithium hydroxide to obtain the positive electrode active material; a second step; A method for producing a positive electrode active material having [Effect of the Invention]

[0013] In the present disclosure, there is an effect that an increase in battery resistance can be suppressed. [Brief Description of the Drawings]

[0014]

Figure 1

Figure 2

Figure 3

Figure 4

[0015] Hereinafter, the positive electrode active material, the battery, and the method for producing the positive electrode active material in the present disclosure will be described in detail.

[0016] A. Positive Electrode Active Material The positive electrode active material in the present disclosure has an O3 structure. Further, the positive electrode active material in the present disclosure contains Li 2 SO 4 and the above Li 2 SO 4 is present inside the positive electrode active material rather than on the surface of the positive electrode active material. In the present specification, "inside the positive electrode active material" may be expressed as "inside the positive electrode active material" and "inside the positive electrode active material".

[0017] According to the present disclosure, Li is present inside the surface of the positive electrode active material, so that when used in a battery, an increase in battery resistance can be suppressed. 2 SO 4 Since it exists, when used in a battery, an increase in battery resistance can be suppressed.

[0018] Generally, a positive electrode active material is used in a positive electrode active material layer of a battery together with electrolytes such as an electrolytic solution and a solid electrolyte. On the other hand, there is a risk that the positive electrode active material reacts with the electrolyte and the battery resistance increases. In particular, when the potential is manipulated to a high potential during charging of the battery, the electrolyte may decompose, and there may be a side reaction in which the decomposition product reacts with the active material, resulting in an increase in resistance and deterioration of capacity. Here, from the viewpoint of suppressing the reaction between the active material and the electrolyte (or the decomposition product of the electrolyte), as in Patent Document 2, providing a coating layer on the surface of the positive electrode active material has been considered. On the other hand, depending on the thickness of the coating layer, new problems such as the movement of carrier ions such as lithium ions in the positive electrode active material may be inhibited have arisen.

[0019] On the other hand, in the positive electrode active material in the present disclosure, since Li is present inside the surface, that is, inside, the electrolyte (or the decomposition product of the electrolyte) that has penetrated into the inside of the active material can be prevented from reacting with and decomposing the positive electrode active material. Further, since Li is present inside, an ion path inside the positive electrode active material can be secured. As a result, an increase in the resistance of the battery can be suppressed. In addition, since side reactions of the positive electrode active material can be suppressed, a decrease in the capacity of the battery can also be suppressed. 2 SO 4 SO 2 SO 4 Since it exists inside, an ion path inside the positive electrode active material can be secured. As a result, an increase in the resistance of the battery can be suppressed. In addition, since side reactions of the positive electrode active material can be suppressed, a decrease in the capacity of the battery can also be suppressed.

[0020] The positive electrode active material in the present disclosure has an O3 structure. The O3-type structure means a structure in which Li occupies an octahedral site in the oxide and there are three types of oxide layers with different oxygen positions in the unit cell.

[0021] The composition of the positive electrode active material in the present disclosure is not particularly limited as long as it has an O3 structure. On the other hand, the positive electrode active material has at least an Li element, a transition metal element containing at least an Ni element, and an O element, and the ratio of the Ni element in the transition metal element is preferably 30 atm% or more. In particular, it is preferable that the ratio of the Ni element in the transition metal element is higher. For example, when manufacturing the positive electrode active material by itself as in the manufacturing method described later, it is because the positive electrode active material having an O3 structure can be manufactured more easily. The ratio of the Ni element may be 50 atm% or more, may be 70 atm% or more, may be 90 atm% or more, and may be 100 atm%. Further, examples of the transition element other than the Ni element include Co, Mn, and Al. That is, the composition of the positive electrode active material is LiNi x Me 1-x O 2 (where x satisfies 0.3 ≦ x ≦ 1 and Me is at least one of Co, Mn, and Al) is preferably represented.

[0022] Specific compositions of the positive electrode active material include, for example, LiNiO 2 , LiNi 0.8 Co 0.2 O 2 , LiNi 0.5 Mn 0.5 O 2 , LiNi 0.33 Co 0.33 Mn 0.33 O 2 and LiNi 0.85 Co 0.15 Al 0.05 O 2 can be mentioned.

[0023] Here, whether the positive electrode active material has an O3 structure can also be confirmed by XRD. For example, when the composition of the positive electrode active material is LiNiO 2When it is the case, characteristic peak positions can include 2θ = 18.7° ± 0.5°, 36.6° ± 0.5°, 38.3° ± 0.5°, 44.4 ± 0.5°, 48.7° ± 0.5°, 58.6° ± 0.5° and 64.6° ± 0.5°.

[0024] Also, the positive electrode active material in the present disclosure may or may not have a coating layer. By not having a coating layer, a good ion conduction path can be maintained. On the other hand, by having a coating layer, it is possible to suppress the decomposition of the electrolyte on the surface of the positive electrode active material. The material of the coating layer is preferably a material having ion conductivity. Examples of the material of the coating layer include LiNbO 3 、Li 3 PO 4 、Li 4 Ti 5 O 12 and the like. As will be described later, Li 2 SO 4 may be present in the coating layer. On the other hand, Li 2 SO 4 may or may not be present in the coating layer. Here, in this specification, the "surface" of the positive electrode active material means the surface of the core particles in the coated positive electrode active material when the positive electrode active material has the above coating layer.

[0025] Examples of the shape of the positive electrode active material in the present disclosure include particulate form. The positive electrode active material may be primary particles or secondary particles formed by aggregation of primary particles. Here, in this specification, "inside" (inside the positive electrode active material) compared to the surface of the positive electrode active material means inside (inside the primary particles) of the primary particles of the positive electrode active material.

[0026] The average particle diameter (D 50 ) of the positive electrode active material (core particles) is not particularly limited, but for example, it is 0.01 μm or more and 100 μm or less. Note that the average particle diameter (D 50 ) refers to the cumulative 50% particle diameter in the volume-based particle diameter distribution measured by a laser diffraction particle size distribution measuring device.

[0027] The cathode active material in the present disclosure contains Li 2 SO 4 and the above Li 2 SO 4 is present inside rather than on the surface of the cathode active material. The "surface" and "inside" of the cathode active material are as described above.

[0028] Li 2 SO 4 The presence of Li

[0029] inside the cathode active material can be confirmed, for example, by elemental mapping using SEM-EDX. 2 SO 4 in the cathode active material may be present only inside rather than on the surface of the cathode active material. On the other hand, Li 2 SO 4 may also be present outside rather than on the surface of the cathode active material. That is, Li 2 SO 4 may be present in the above-described coating layer. If Li 2 SO 4 is present on the surface of the cathode active material, the reaction with the electrolyte on the surface of the cathode active material can be suppressed, so that the increase in the resistance of the battery can be further suppressed.

[0030] The proportion of Li 2 SO 4 in the cathode active material is, for example, 0.5% by weight or more, and may be 1.0% by weight or more, 1.3% by weight or more, 1.6% by weight or more, or 1.9% by weight or more. On the other hand, the proportion of Li 2 SO 4 in the cathode active material is, for example, 4.0% by weight or less, and may be 3.5% by weight or less, 3.0% by weight or less, or 2.7% by weight or less. The proportion of Li 2 SO 4 can be determined, for example, as in the examples described below. Here, the proportion of Li 2 SO 4When the proportion is 0.03% by weight or less, Li 2 SO 4 is considered to be substantially absent on the "inside" of the positive electrode active material (and on the surface of the positive electrode active material).

[0031] The capacity of the positive electrode active material is not particularly limited, but a higher capacity is preferred. The capacity of the positive electrode active material is, for example, 200 mAh / g or more, and may be 220 mAh / g or more, 240 mAh / g or more, or 260 mAh / g or more.

[0032] The positive electrode active material in the present disclosure can be produced, for example, by the method described below.

[0033] B. Battery The positive electrode active material in the present disclosure is usually used in a battery. FIG. 1 is a schematic cross-sectional view illustrating a battery in the present disclosure. The battery 10 shown in FIG. 1 includes a positive electrode active material layer 1, a negative electrode active material layer 2, and an electrolyte layer 3 disposed between the positive electrode active material layer 1 and the negative electrode active material layer 2. The positive electrode active material layer 1 contains the positive electrode active material layer in the present disclosure described above.

[0034] 1. Positive electrode active material layer The positive electrode active material layer contains the positive electrode active material described above. The positive electrode active material is the same as the content described in "A. Positive electrode active material". Further, the positive electrode active material layer may contain at least one of a conductive material, a binder, and an electrolyte as necessary.

[0035] Examples of the conductive material include carbon materials, metal particles, and conductive polymers. Examples of the carbon material include particulate carbon materials such as acetylene black (AB) and ketjen black (KB), and fibrous carbon materials such as carbon fiber, carbon nanotube (CNT), and carbon nanofiber (CNF). Examples of the binder include fluorine-containing binders such as polyvinylidene fluoride (PVDF), rubber-based binders such as butadiene rubber, and acrylic binders.

[0036] Examples of the electrolyte include, for example, liquid electrolytes (electrolyte solutions) and solid electrolytes. Examples of the electrolyte solution include conventionally known electrolyte solutions used in lithium ion batteries. Specifically, electrolytes containing lithium salts such as LiPF 6 and non-aqueous solvents such as ethylene carbonate can be mentioned. Examples of the solid electrolyte include inorganic solid electrolytes such as sulfide solid electrolytes, oxide solid electrolytes, and halide solid electrolytes.

[0037] The thickness of the positive electrode active material layer is not particularly limited, but is, for example, 0.5 μm or more and 1000 μm or less.

[0038] 2. Negative electrode active material layer and electrolyte layer The negative electrode active material layer contains at least a negative electrode active material, and may contain at least one of a conductive material, a binder, and an electrolyte as necessary. Examples of the negative electrode active material include metal active materials such as Li and Si, carbon active materials such as graphite, and Li 4 Ti 5 O 12 and other oxide active materials. The shape of the negative electrode active material is, for example, particulate or foil-like.

[0039] Regarding the conductive material, the binder, and the electrolyte, they are the same as the contents described in "1. Positive electrode active material layer". The thickness of the negative electrode active material layer is not particularly limited, but is, for example, 0.5 μm or more and 1000 μm or less.

[0040] The electrolyte layer contains at least an electrolyte. The electrolyte is the same as the content described in "1. Positive electrode active material layer". Note that the electrolyte layer in the present disclosure may be a layer in which an electrolyte solution has infiltrated into the separator. The separator can be a conventionally known member.

[0041] In the present disclosure, an electrolyte layer containing a solid electrolyte may be referred to as a solid electrolyte layer, and a battery having a solid electrolyte layer may be referred to as an all-solid-state battery. Further, the electrolyte layer may contain a binder as necessary. The binder is the same as that described in "1. Positive electrode active material layer". The thickness of the electrolyte layer is, for example, 1 μm or more and 500 μm or less.

[0042] As shown in FIG. 1, the battery in the present disclosure usually has a positive electrode current collector 4 that collects electrons from the positive electrode active material layer 1 and a negative electrode current collector 5 that collects electrons from the negative electrode active material layer 2. Examples of the material of the positive electrode current collector include SUS, aluminum, nickel, iron, titanium, and carbon. Examples of the material of the negative electrode current collector include SUS, copper, nickel, and carbon. Further, the battery in the present disclosure may have an exterior body that houses an electrode body including a positive electrode active material layer, an electrolyte layer, and a negative electrode active material layer. Examples of the exterior body include a case-type exterior body and a laminate-type exterior body.

[0043] The battery in the present disclosure is typically a lithium-ion secondary battery. Further, the battery in the present disclosure may be a liquid-based battery containing an electrolytic solution as an electrolyte, or may be an all-solid-state battery containing a solid electrolyte as an electrolyte. Examples of the use of the battery include power sources for vehicles such as hybrid vehicles (HEV), plug-in hybrid vehicles (PHEV), battery electric vehicles (BEV), gasoline vehicles, and diesel vehicles. Further, the battery in the present disclosure may be used as a power source for moving bodies other than vehicles (for example, railways, ships, airplanes), and may also be used as a power source for electrical products such as information processing devices.

[0044] C. Method for manufacturing positive electrode active material FIG. 2 is a flowchart illustrating a method for manufacturing a positive electrode active material in the present disclosure. In the method for manufacturing the active material shown in FIG. 2, first, precursor particles are obtained by a coprecipitation method using NaOH and NiSO 4 (first step). Next, the obtained precursor particles are fired together with lithium hydroxide to obtain the positive electrode active material (second step).

[0045] According to the present disclosure, precursor particles having sulfide ions inside can be obtained by a coprecipitation method using NiSO 4 . Then, by firing such precursor particles together with LiOH, a positive electrode active material in which Li 2 SO 4 is present can be produced.

[0046] 1. First Step The first step is a step of obtaining precursor particles by a coprecipitation method using NaOH and NiSO 4 . In the coprecipitation method, salts of transition elements other than Ni such as Co, Mn, and Al may be used. The coprecipitation method can be a conventionally known method.

[0047] The average particle diameter (D 50 ) of the precursor particles obtained in the first step is not particularly limited, but for example, it is 5 μm or more, and may be 6 μm or more, or may be 7 μm or more. On the other hand, the average particle diameter (D 50 ) of the precursor particles is, for example, 10 μm or less, 9 μm or less, and salts of transition elements other than Ni may be used.

[0048] 2. Second Step The second step is a step of firing the above precursor particles together with lithium hydroxide to obtain the above positive electrode active material. The ratio of the precursor particles to lithium hydroxide is not particularly limited as long as the positive electrode active material having the above-described O3 structure can be obtained.

[0049] The firing conditions are not particularly limited as long as the positive electrode active material having the above-described O3 structure can be obtained. The firing temperature is, for example, 600 °C or higher and 1000 °C or lower. The firing time is, for example, 1 hour or longer and 30 hours or shorter. Also, the firing atmosphere is, for example, an oxidizing atmosphere such as an oxygen gas atmosphere. Further, the firing may be performed in an air atmosphere or in a reduced pressure atmosphere. Also, the firing may be a one-step firing or a two-step or more firing with changed conditions.

[0050] In addition, in the second step, in order to obtain a positive electrode active material having a desired average particle size, a crushing treatment may be performed after firing.

[0051] The positive electrode active material is the same as the content described in "A. Positive Electrode Active Material".

[0052] Note that the present disclosure is not limited to the above-described embodiments. The above-described embodiments are examples, and any configuration that has substantially the same configuration as the technical idea described in the claims of the present disclosure and exhibits the same operational effects is included in the technical scope of the present disclosure.

Example

[0053] [Example] (Production of positive electrode active material) As follows, a positive electrode active material having an O3 structure and containing Li 2 SO 4 was prepared. First, the temperature of the reaction vessel was set to 30 ° C, and the reaction solution in the reaction vessel was maintained at pH 11.5 with an 8 mol / L aqueous sodium hydroxide solution. An aqueous nickel sulfate solution and a 28 mass% aqueous ammonia solution were dropped into the reaction solution whose pH was maintained, and nickel hydroxide as a precursor was synthesized by a crystallization method. Filtration was performed using suction filtration to separate the filtrate and the precursor, and the recovered precursor was washed with water. After washing with water, the precursor was left standing overnight in a hot air dryer at 120 ° C. As a result, nickel hydroxide was obtained as precursor particles.

[0054] A predetermined amount of the obtained precursor particles and lithium hydroxide (lithium hydroxide monohydrate) were weighed and mixed in a mortar. Using an electric furnace, the mixture was calcined temporarily under an oxygen atmosphere at 485 ° C at a rate of 10 ° C / min for 5 hours, and then calcined at 700 ° C for 20 hours. Thereafter, it was cooled in the furnace to room temperature and subjected to a crushing treatment. As a result, lithium nickel-containing oxide (LiNiO 2 ) was obtained. When SEM-EDX measurement was performed on the obtained lithium nickel-containing oxide, it was confirmed that the S element was present inside and on the surface of the primary particles, and Li was inside the positive electrode active material 2SO 4 was confirmed to be present.

[0055] (Fabrication of Coin Battery) A predetermined amount of the above positive electrode active material, a binder (PVDF), and a conductive assistant (carbon black) were weighed and mixed in a mortar for 5 minutes. Then, they were mixed with a solvent to obtain a positive electrode slurry. The positive electrode slurry was dropped onto an Al foil and coated with a 150-μm doctor blade. After coating, it was dried in an electric furnace at 100 °C for 30 minutes to fabricate a positive electrode having a positive electrode current collector and a positive electrode active material layer.

[0056] The positive electrode was punched out to φ16 and sandwiched between Al foils and pressed. The pressed positive electrode was dried in a vacuum dryer at 120 °C for 8 hours. Also, the Li foil was stretched with a roller in a glove box and punched out to φ19. Then, the Li foil was placed in a 2032k-type negative electrode can, an electrolytic solution was added, a separator punched out to φ19 was placed, and a packing was fitted. One drop of the electrolytic solution was added, the positive electrode was placed, a SUS spacer and a SUS washer were placed in this order, and the positive electrode can was fitted. Then, it was pressed with a coin press for 3 seconds. Thereby, a coin battery (liquid-based battery) was fabricated.

[0057] [Comparative Example] A lithium nickel-containing oxide was fabricated in the same manner as in the Example. The lithium nickel-containing oxide was immersed in distilled water for 1 minute and washed with water. The washed lithium nickel-containing oxide was recovered by suction filtration and dried overnight in a vacuum dryer at 120 °C. Using the lithium nickel-containing oxide after washing and drying as a positive electrode active material, a coin battery was fabricated in the same method as in the Example.

[0058] [Evaluation] (Measurement of Li 2 SO 4 Amount) For the positive electrode active materials fabricated in the Example and the Comparative Example, the concentration of S element was measured by ICP measurement, and the obtained concentration of S element was converted into the amount of Li 2 SO 4 This converted the amount of Li inside and on the surface of the positive electrode active material. 2 SO 4The amount was obtained. As a result, the Li content in the example was 2.7% by weight, while the Li content in the comparative example was 0.01% by weight. From this, it was confirmed that in the comparative example, there was substantially no Li present inside and on the surface of the positive electrode active material. 2 SO 4 The amount was 2.7% by weight, and the Li content in the comparative example was 0.01% by weight. From this, it was confirmed that in the comparative example, there was substantially no Li present inside and on the surface of the positive electrode active material. 2 SO 4 The amount was 2.7% by weight, and the Li content in the comparative example was 0.01% by weight. From this, it was confirmed that in the comparative example, there was substantially no Li present inside and on the surface of the positive electrode active material. 2 SO 4 was present.

[0059] (Charge and Discharge Test) A charge and discharge test was performed on the coin cells fabricated in the examples and comparative examples. Specifically, they were charged to 4.4 V at 0.1 C and then discharged to 2.8 V at 0.1 C. The charge resistance at an arbitrary potential was measured. The results are shown in FIGS. 3 and 4. Note that FIGS. 3(b) and 4(b) are enlarged graphs of a part of FIGS. 3(a) and 4(a), respectively.

[0060] As shown in FIGS. 3 and 4, at all potentials, the resistance value of the example was lower than that of the comparative example. In particular, on the high potential side and the low potential side, in the example, the increase in the resistance value was significantly suppressed compared to the comparative example. From this, it was confirmed that the positive electrode active material in the present disclosure can suppress the increase in the resistance of the battery.

Explanation of Reference Numerals

[0061] 1... Positive electrode active material layer 2... Negative electrode active material layer 3... Electrolyte layer 4... Positive electrode current collector 5... Negative electrode current collector 10... Battery

Claims

1. A positive electrode active material having an O3 structure, The positive electrode active material contains Li ２ SO ４ and the Li ２ SO ４ is present inside the positive electrode active material rather than on the surface thereof, and is a positive electrode active material.

2. The Li in the positive electrode active material ２ SO ４ The proportion of is 1.0% by weight or more and 3.0% by weight or less, and the positive electrode active material according to claim 1.

3. The positive electrode active material having the O3 structure has a Li element, a transition metal element containing at least a Ni element, and an O element, The proportion of the Ni element in the transition metal element is 30 atm% or more. The positive electrode active material according to Claim 1.

4. The Li ２ SO ４ is present on the surface and inside of the positive electrode active material, and is the positive electrode active material according to claim 1.

5. A battery having a positive electrode active material layer, a negative electrode active material layer, and an electrolyte layer disposed between the positive electrode active material layer and the negative electrode active material layer, The battery, wherein the positive electrode active material layer contains the positive electrode active material according to any one of Claims 1 to 4.

6. A method for manufacturing a positive electrode active material, which manufactures the positive electrode active material according to any one of Claims 1 to 4, NaOH and NiSO ４ A first step of obtaining precursor particles by a coprecipitation method using The method for manufacturing a positive electrode active material having a second step of firing the precursor particles together with lithium hydroxide to obtain the positive electrode active material.

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