JP7079716B2 - Positive positive active material particles for lithium ion secondary batteries and lithium ion secondary batteries equipped with them - Google Patents

Description

The present invention relates to positive electrode active material particles for a lithium ion secondary battery and a lithium ion secondary battery including the same.

Conventionally, a lithium ion secondary battery has been widely used as a highly convenient secondary battery that can be repeatedly charged and discharged. Lithium-ion secondary batteries have high voltage, capacity, and energy density, and are therefore used especially in the fields of mobile phones, storage batteries for power generation equipment such as wind power and solar power, electric vehicles, and smart grids.

The lithium ion secondary battery includes a positive electrode containing a positive electrode active material, a negative electrode, an electrolyte, and the like. As the positive electrode active material, a lithium nickel cobalt manganese composite oxide (ternary positive electrode active material) having a layered rock salt structure is used. However, it is known that in this ternary positive electrode active material, the positive electrode active material and the electrolyte deteriorate over time when charging and discharging are repeated, resulting in an increase in the electric resistance of the lithium ion secondary battery and a decrease in the discharge capacity. ..

Therefore, as a method of suppressing an increase in electrical resistance, for example, Patent Document 1 describes a method of using a positive electrode active material coated with a coat layer containing a carbonaceous substance and an ionic conductive oxide. As a result, it is said that the formation of a high resistance layer formed at the interface between the positive electrode active material and the electrolyte can be suppressed, and good electron conductivity can be maintained.

International Publication No. 2013/099878

However, the method described in Patent Document 1 could suppress the formation of a high resistance layer formed at the interface between the positive electrode active material and the electrolyte, but could not suppress the deterioration of the positive electrode active material over time.

The present invention has been made in view of the above, and is a positive electrode active material for a lithium ion secondary battery that can suppress deterioration of the positive electrode active material and can suppress an increase in electrical resistance and a decrease in capacity of the lithium ion secondary battery over time. It is an object of the present invention to provide particles and a lithium ion secondary battery containing the particles.

In order to achieve the above object, the present invention is a positive electrode active material particle for a lithium ion secondary battery having a layered rock salt structure of a space group R-3 m in a rhombic crystal system, and the surface portion is stable as compared with the central portion. Provided are positive electrode active material particles for a lithium ion secondary battery formed by a chemical composition having a high property and a low capacity.

The chemical composition may change discretely.

The chemical composition may change continuously.

The positive electrode active material particles for a lithium ion secondary battery are represented by the following general formula (1), and the chemical composition of the surface portion has a higher molar ratio of Mn and Co than the chemical composition of the central portion, while Ni The molar ratio may be low.
[Chemical 1]
LiNi _x Mn _{y Coz} O ₂ ... (1)
[In the general formula (1), x + y + z = 1. ]

The positive electrode active material particles for a lithium ion secondary battery preferably include core particles and a coat layer formed on the surface of the core particles.

The positive electrode active material particles for a lithium ion secondary battery include core particles and a coat layer formed on the surface of the core particles, and the core particles are represented by the following general formula (2). The coat layer is represented by the following general formula (1), and the chemical composition of the surface portion of the coat layer has a higher molar ratio of Mn and Co than the chemical composition of the interface between the core particles and the coat layer. The molar ratio of Ni may be low.
[Chemical 1]
LiNi _x Mn _{y Coz} O ₂ ... (1)
[In the general formula (1), x + y + z = 1. ]
[Chemical 2]
LiNi _{x Coy Al z O 2} ... (2)
[In the general formula (2), x + y + z = 1. ]

The mass of the coat layer is preferably 0.1% by mass to 50% by mass with respect to the total mass of the core particles and the coat layer.

The mass of the coat layer is preferably 0.1% by mass to 20% by mass with respect to the total mass of the core particles and the coat layer.

The coverage of the coat layer on the core particles is preferably 1% to 75% with respect to the surface area of the core particles.

The coverage of the coat layer on the core particles is preferably 1% to 50% with respect to the surface area of the core particles.

The ratio of the lattice constant of the coat layer to the lattice constant of the core particles is preferably 1 to 2.

The present invention also provides a positive electrode for a lithium ion secondary battery containing the positive electrode active material particles for the lithium ion secondary battery.

The present invention also provides a lithium ion secondary battery including the positive electrode for a lithium ion secondary battery, a negative electrode, and an electrolyte.

According to the present invention, the deterioration of the positive electrode active material can be suppressed, and the positive electrode active material particles for the lithium ion secondary battery capable of suppressing the increase in the electric resistance and the decrease in the capacity of the lithium ion secondary battery with time and the lithium ion provided therein. A secondary battery can be provided.

It is sectional drawing of the positive electrode active material particle which concerns on one Embodiment of this invention. It is a figure which shows the relationship between the performance maintenance rate of the battery obtained in Example 1, Example 2, and Comparative Example 1, and the core particle diameter. It is a figure which shows the relationship between the performance maintenance rate of the battery obtained in Example 3, Example 4, and Comparative Example 1, and the core particle diameter. It is a figure which shows the relationship between the total resistance ratio of the battery obtained in Example 1, Example 2, and Comparative Example 1, and the core particle diameter. It is a figure which shows the relationship between the total resistance ratio of the battery obtained in Example 3, Example 4, and Comparative Example 1 and the core particle diameter. It is a figure which shows the relationship between the performance maintenance rate and the number of cycles of the battery obtained in Example 5 and Comparative Example 2. FIG. It is a figure which shows the relationship between the total resistance ratio of the battery obtained in Example 5 and Comparative Example 2 and the number of cycles.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following embodiments.

[Positive electrode active material particles for lithium-ion secondary batteries]
The positive electrode active material particles for a lithium ion secondary battery according to the present embodiment (hereinafter referred to as “positive positive active material particles”) are lithium transition metal composite oxides having a layered rock salt structure of a space group R-3 m in a rhombic crystal system. Is formed by.

The positive electrode active material particles according to the present embodiment are formed by a chemical composition in which the surface portion has higher stability but lower volume than the central portion.

The chemical composition of the positive electrode active material particles may change from the central portion to the surface portion so that the interfaces are clearly separated, but the chemical composition is not limited to this, and continuously changes so as to be integrated as a crystal structure. You may.

The chemical composition of the positive electrode active material particles according to this embodiment is represented by the following general formula (1).
[Chemical 1]
LiNi _x Mn _{y Coz} O ₂ ... (1)
[In the general formula (1), x + y + z = 1. ]

The positive electrode active material particles according to the present embodiment have a high molar ratio of Mn and Co and a low molar ratio of Ni as compared with the chemical composition of the central portion in the chemical composition of the surface portion. When the molar ratio of Mn and Co is high, the stability of the positive electrode active material is improved, but the capacity is reduced. On the other hand, as the molar ratio of Ni increases, the stability decreases but the capacity increases. Therefore, the positive electrode active material particles according to the present embodiment have higher stability from the central portion toward the surface portion, and conversely, have a higher capacity from the surface portion toward the central portion.

The molar ratio of Mn, Co, and Ni may be changed so that the interface is clearly separated from the central portion to the surface portion of the positive electrode active material particles, but is not limited to this, and is integrated as a crystal structure. May change continuously.

Here, it is known that the crystal structure of conventional general ternary positive electrode active material particles having a layered rock salt structure changes with time from a layered rock salt structure to a spinel structure by charge and discharge. The phase transition from the layered rock salt structure to the spinel structure reduces the area where lithium can be occluded. Therefore, the capacity of the lithium ion secondary battery is reduced. In addition, the phase transition to the spinel structure also increases the electrical resistance.

It is considered that the above-mentioned change in the crystal structure proceeds particularly from the vicinity of the surface of the positive electrode active material particles in contact with the electrolyte.

On the other hand, the positive electrode active material particles according to the present embodiment have a concentration gradient formed so that the stability is high and the volume is low from the central portion to the surface portion. Since the outermost surface in contact with the electrolyte has the highest stability, it is possible to suppress the phase transition of the positive electrode active material particles. Further, since the capacity increases toward the central portion, the positive electrode active material particles have a high discharge capacity as a whole. This makes it possible to suppress an increase in electrical resistance and maintain a high capacity.

The positive electrode active material particles according to the present embodiment preferably have a particle diameter D _sem of 1 to 7 μm based on electron microscope observation. Thereby, the above-mentioned effect can be more reliably exerted.

Further, the positive electrode active material particles according to the present embodiment preferably include core particles and a coat layer formed on the surface of the core particles. The preferable structure of the positive electrode active material particles will be described in detail with reference to FIG.
FIG. 1 is a cross-sectional view of positive electrode active material particles according to this embodiment. As shown in FIG. 1, the positive electrode active material particles 1 are composed of granular core particles 2 and coat layers 3 and 4 coated on the core particles 2. The number of coat layers according to the present embodiment is two, but the number of coat layers is not particularly limited, and may be one layer or three or more layers.

In the positive electrode active material particles 1, the core particles 2 have the highest capacity and the lowest stability, and the coat layer 4 has the highest stability and the lowest capacity. As an example of the chemical composition that realizes this structure, the core particle 2 is LiNi _8/10 Mn _1/10 Co _1/10 O ₂ , the coat layer 3 is LiNi _3/5 Mn _1/5 Co _1/5 O ₂ , and the coat is coated. Examples thereof include a chemical composition in which the layer 4 is LiNi _1/3 Mn _1/3 Co _1/3 O ₂ . In this chemical composition, the molar ratio of Mn and Co of the core particles 2, the coat layers 3 and 4 is the lowest in the core particles 2 and the highest in the coat layer 4. On the other hand, the molar ratio of Ni is highest in the core particles 2 and lowest in the coat layer 4.

In the positive electrode active material particles 1, the core particles 2, the coat layers 3 and 4, are formed of lithium nickel-cobalt-manganese composite oxide, and the core particles 2 are made of lithium nickel-cobalt aluminum represented by the following general formula (2). It may be positive electrode active material particles to be formed.
[Chemical 2]
LiNi _{x Coy Al z O 2} ... (2)
[In the general formula (2), x + y + z = 1. ]

The ratio of the coat layer coated on the core particles of the positive electrode active material particles is preferably 0.1% by mass to 50% by mass with respect to the total of the mass of the core particles and the mass of the coat layer. It is more preferably 0.1% by mass to 20% by mass, still more preferably 0.1% by mass to 10% by mass, still more preferably 0.1% by mass to 1% by mass. When the surface of the core particles is uniformly coated, the stability of the positive electrode active material particles can be sufficiently improved if the coat layer is 0.1% by mass or more. Further, if the coat layer exceeds 50% by mass, low resistance and high capacity may not be maintained.

The coverage of the core particles by the coat layer is preferably 1% to 75%, more preferably 1% to 60%, and 1% with respect to the surface area of the core particles of 100%. It is more preferably to 50%. When the coverage is 1% or more, the stability of the positive electrode active material particles can be sufficiently improved. If the coverage exceeds 75%, it may not be possible to maintain low resistance. Further, if the coverage exceeds 75%, the coat layer may be peeled off from the core particles.

The ratio of the lattice constant of the core particles to the lattice constant of the coat layer is preferably 1 to 2. By reducing the difference in crystal structure between the core particles and the coat layer, it is possible to prevent peeling between the core particles and the coat layers and between the coats.

[Manufacturing method of positive electrode active material particles for lithium ion secondary battery]
A method for producing positive electrode active material particles according to this embodiment will be described. The manufacturing method according to the present embodiment includes a core particle manufacturing step and a coating step.

First, in the core particle manufacturing step, a hydroxide, an oxyhydroxide, an oxide, or the like of Li, Ni, Co, and Mn, or Al is precipitated or coprecipitated in an aqueous solution. By firing the obtained precipitate in an atmosphere of 650 ° C to 850 ° C in an atmosphere, core particles of positive electrode active material particles having a designed chemical composition can be obtained. At this time, the precipitate may be simply calcined in a calcining furnace, or the precipitate may be previously dried and calcined with fine particles by using a spray dryer method. The core particles obtained from the above steps are crushed using various crushing devices such as a counter jet mill and a pulperizer, and the crushed core particles are classified using a pulse jet collector or the like.

Next, in the coating step, the surface of the core particles obtained by the core particle manufacturing step is coated with hydroxides, oxyhydroxides, oxides and the like of Li, Ni, Co and Mn. As a coating method, for example, a mechano-fusion system, a nobilta bellcom system, a sputter, or the like that causes a mechanochemical reaction is used to generate positive electrode active material particles having a stable composition on the surface of the core particles so as to have a predetermined surface composition. .. A coat layer is formed so that the stability becomes higher toward the outside from the core particles. The number of coat layers having different chemical compositions is not particularly limited, and may be one or more. By forming coat layers having different chemical compositions, it is possible to form a stable layer. At this time, the core particles and each coat layer are coated so that the difference in lattice constant is small.

Here, a method of covering so that the difference in lattice constant becomes small will be described. First, the core particles are slightly coated with a coat layer. As a result, a coat layer having lattice strain and having a crystal structure intermediate between the core particles and the coat layer is formed. Next, a coat layer having the same chemical composition as the coat layer is coated. As a result, a coat layer having a stable layered rock salt structure is formed on the outermost surface. This step is repeated for coat layers having other chemical compositions. As a result, the difference in the lattice constants of the core particles and each coat layer can be reduced, and a stable coat layer that does not peel off from the core layer can be obtained.

[Positive electrode for lithium-ion secondary battery]
A positive electrode for a lithium ion secondary battery (hereinafter, referred to as “positive electrode”) according to the present embodiment will be described. The positive electrode according to the present embodiment is composed of the above-mentioned positive electrode active material particles, a conductive auxiliary agent, and a binder.
As the conductive auxiliary agent, acetylene black, ketjen black, graphite and the like are used.
As the binder, polytetrafluoroethylene, polyvinylidene fluoride (PVDF), polyethylene, polyacrylic acid salt, styrene-butadiene copolymer, carboxymethyl cellulose and the like are used.

[Lithium-ion secondary battery]
The lithium ion secondary battery according to this embodiment will be described. The lithium ion secondary battery according to the present embodiment includes the above-mentioned positive electrode, an electrolyte, and a negative electrode. Examples of the battery shape include a square type, a paper type, a laminated type, a cylindrical type, and a coin type.

As the electrolyte, a solid electrolyte or a non-aqueous electrolyte solution in which salts are dissolved in an organic solvent is used.

The solid electrolyte is not particularly limited as long as it has lithium ion conductivity, and may be an organic solid electrolyte material or an inorganic solid electrolyte material.

As the organic solid electrolyte material, derivatives, mixtures or complexes of polyethylene oxide, polyphosphazene, polyaziridine, polyethylene sulfide, polyvinyl alcohol and the like are used.

Examples of the inorganic solid electrolyte material include a sulfide solid electrolyte material, an oxide solid electrolyte material, a nitride solid electrolyte material, a halide solid electrolyte material, and the like, and among them, the sulfide solid electrolyte material is preferable. This is because the lithium ion conductivity is higher than that of the oxide solid electrolyte material.

Examples of the sulfide solid electrolyte material include Li ₂ SP ₂ S ₅ and Li ₂ SP ₂ S ₅ -Li I. The above description of "Li ₂ SP _{2 S 5" means a sulfide solid electrolyte material using a raw material composition containing Li 2 S and P 2 S 5 , and} the same applies to other descriptions. be.

Examples of the oxide solid electrolyte material include NASICON type oxides, garnet type oxides, perovskite type oxides and the like. Examples of the NASION-type oxide include oxides containing Li, Al, Ti, P and O (for example, Li _1.5 Al _0.5 Ti _1.5 (PO ₄ ) ₃ ). Examples of the garnet-type oxide include oxides containing Li, La, Zr and O (for example, Li ₇ La ₃ Zr ₂ O ₁₂ ). Examples of the perovskite-type oxide include oxides containing Li, La, Ti and O (for example, LiLaTIO ₃ ).

Examples of salts contained in the non-aqueous electrolyte solution include LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiB (C ₆ H ₅ ) ₄ , LiSbF ₆ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, LiCl, LiC. ₄ F ₉ SO ₃ , LiN (CF ₃ SO ₂ ) (C ₂ F ₅ SO ₂ ), LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiBr, LiBOB, LiTFSI, LiFSI, Examples thereof include CTFSI and LiPF ₂ O ₂ .

Examples of the solvent for dissolving the electrolyte include propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, fluoroethylene carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran and 2-methyl. Examples thereof include tetrahydrofuran, 1,3-dioxolane, 4-methyl 1,3-dioxolane, diethyl ether, sulfolane, methylsulfolane, acetonitrile, propionitrile, anisole, acetic acid ester, butyric acid ester, propionic acid ester and the like.

The negative electrode is composed of negative electrode active material particles capable of occluding and releasing lithium ions, the conductive auxiliary agent, and the binder.
Examples of the negative electrode active material particles include those containing a lithium element and those not containing a lithium element. Examples of the negative electrode active material particles containing a lithium element include metallic lithium such as lithium aluminum alloy and lithium tin alloy, lithium oxide such as lithium titanate, and lithium nitride such as lithium cobalt nitride. Examples of the negative electrode active material particles containing no lithium element include graphite materials such as mesocarbon microbeads, calcined phenolic resins and pitches, carbon-based materials such as activated carbon and graphite, and SiO, SiO ₂ and the like. Silicon-based materials, tin-based materials such as SnO and SnO ₂ , lead-based materials such as PbO and PbO ₂ , germanium-based materials such as GeO and GeO ₂ , phosphorus-based materials, niobium-based materials, antimony-based materials, and these. Examples include a mixture of materials.

In addition, the lithium ion secondary battery according to the present embodiment includes a separator when a non-aqueous electrolyte solution is used as the electrolyte.

As the separator, a porous polymer, a glass filter or the like is used.

According to the lithium ion secondary battery according to the present embodiment described above, the following effects are obtained.

In the present embodiment, the positive electrode active material particles used in the lithium ion secondary battery have a layered rock salt type structure of a space group R-3 m in a rhombic crystal system, and the surface portion is more stable than the central portion. The positive electrode active material particles formed by the chemical composition having a high capacity but a low capacity were used. Further, the positive electrode active material particles cover the core particles represented by the following general formula (1) at the center of the particles and having a layered rock salt type structure of a space group R-3 m in a rhombic crystal system. It may have a covering layer having a stable layered rock salt type structure.
[Chemical 1]
LiNi _x Mn _{y Coz} O ₂ ... (1)
[In the general formula (1), x + y + z = 1. ]

This makes it possible to suppress changes in the crystal structure of the positive electrode active material and improve the durability of the lithium ion battery.

Further, in the present embodiment, the particle diameter D _sem based on the electron microscope observation of the positive electrode active material particles is set to 1 to 7 μm.
Thereby, the above-mentioned effect can be more reliably exerted.

Further, in the present embodiment, the surface coverage of the particles by the coat layer formed on the outermost periphery is set to 1 to 75%, preferably 1 to 60%, and more preferably 1 to 50%.
As a result, the positive electrode active material can be appropriately coated with the stable coating layer, and high capacity, low resistance value and high durability can be achieved at the same time.

Further, in the present embodiment, the weight ratio of the coating layer to the particles is 2.0% by mass or less, preferably 0.03 to 1.5% by mass, and more preferably 0.03 to 1.0% by mass. ..
As a result, a coating layer having a stable structure can be formed with an appropriate thickness, and both a low resistance value and a high durability can be achieved at the same time.

Next, examples of the present invention will be described, but the present invention is not limited to these examples.

[Manufacturing method of lithium ion secondary battery]
<Example 1>
(Preparation of positive electrode active material particles)
By the above-mentioned production method, the chemical composition of the core particles is LiNi _2/3 Co _1/6 Al _1/6 O ₂ and the chemical composition of the coat layer is LiNi _1/2 Co _1/5 Mn _3/10 O ₂ . Certain positive electrode active material particles were prepared. The surface coverage of the coat layer on the core particles was set to 50%. Further, the core particle diameter D _sem based on the electron microscope observation of the positive electrode active material particles was set to 1 μm to 10 μm.

(Preparation of positive electrode)
The positive electrode active material particles, acetylene black, and PVDF were dispersed in N-methyl-2-pyrrolidone (NMP) to prepare a positive electrode mixture. The obtained positive electrode mixture was applied to an aluminum foil as a current collector, dried, compression-molded by a roll press, and then cut into a predetermined size to prepare a positive electrode.

(Manufacturing of negative electrode)
Negative electrode active material particles and PVDF were dispersed in NMP to prepare a negative electrode mixture. The obtained negative electrode mixture was applied to a copper foil as a current collector, dried, compression-molded by a roll press, and then cut into a predetermined size to prepare a negative electrode.

(Manufacturing of lithium-ion secondary battery for evaluation)
After attaching the lead electrodes to the current collectors of the positive electrode and the negative electrode, separators were arranged between the positive electrode and the negative electrode, and they were stored in a bag-shaped laminate pack. Then, this was vacuum dried to remove the moisture adsorbed on each member. Then, the electrolytic solution was injected into the laminate pack under an argon atmosphere and sealed. The lithium ion secondary battery thus obtained was placed in a constant temperature bath and aged with a weak current. As the electrolytic solution, ethylene carbonate (EC) and methyl ethyl carbonate (MEC) are mixed at a volume ratio of 3: 7, and lithium hexafluorophosphate (LiPF ₆ ) is dissolved so as to have a concentration of 1 mol / l. Was used.

<Example 2>
In Example 2, the same method as in Example 1 was used except that the surface coverage on the core particles by the coat layer having a chemical composition of LiNi _1/2 Co _1/5 Mn _3/10 O ₂ was set to 25%. A lithium ion secondary battery was manufactured.

<Comparative Example 1>
In Comparative Example 1, a lithium ion secondary battery was produced in the same manner as in Example 1 except that the core particles were not coated with the coat layer.

<Example 3>
In Example 3, a coat having a chemical composition of LiNi _1/3 Co _1/3 Mn _1/3 O ₂ is further coated on a coat layer having a chemical composition of LiNi _1/2 Co _1/5 Mn _3/10 O ₂ . A lithium ion secondary battery was produced in the same manner as in Example 1 except that the layers were coated and the surface coverage on the core particles by these coated layers was 50%.

<Example 4>
In Example 4, a coat having a chemical composition of LiNi _1/3 Co _1/3 Mn _1/3 O ₂ is further coated on a coat layer having a chemical composition of LiNi _1/2 Co _1/5 Mn _3/10 O ₂ . A lithium ion secondary battery was produced by the same method as in Example 1 except that the layers were coated and the surface coverage on the core particles by these coated layers was 25%.

<Example 5>
In Example 5, a coat layer having a chemical composition of LiNi _1/3 Co _1/3 Mn _1/3 O ₂ is placed on core particles having a chemical composition of LiNi _8/10 Co _1/10 Mn _1/10 O ₂ . A lithium ion secondary battery was produced in the same manner as in Example 1 except that the surface coverage was 50%.

<Comparative Example 2>
In Comparative Example 2, a lithium ion secondary battery was produced in the same manner as in Example 5 except that the core particles were not coated with the coat layer.

<Charge / discharge cycle test>
The evaluation batteries obtained in the above Examples and Comparative Examples were subjected to charge / discharge cycle tests as follows to evaluate durability (performance resistivity), total resistivity, and film resistivity. The total resistance ratio here is the resistance ratio of electrons (e- ⁾ as a battery, and the coating resistance ratio is a resistance component in a reaction (such as the ingress and egress of Li ions) accompanied by a change in the valence of the active material (oxidation-reduction). The ratio. In the charge / discharge cycle test, the battery is charged to a charge upper limit voltage of 4.2 V with a constant current of current density of 2.0 mA / cm ² under a temperature condition of 60 ° C., and then a discharge lower limit voltage is charged with a constant current of current density of 20 mA / cm ² . One cycle was charged and discharged to discharge up to 2.7V. Then, the discharge capacity and the coating resistance were measured for each cycle. The performance maintenance rate was calculated using the following formula.
Performance maintenance rate = (discharge capacity of each cycle / discharge capacity of the first cycle) x 100

In FIGS. 2 and 3, the vertical axis shows the performance maintenance rate after 1000 cycles, and the horizontal axis shows the core particle diameter of the positive electrode active material particles. From this result, it was confirmed that in Examples 1 to 4 and Comparative Example 1, the performance maintenance rate increased as the core particle diameter increased. Further, Examples 1 to 4 having the outermost surface covered had a higher performance retention rate than Comparative Example 1 having no coat layer, and the performance retention rate improved as the surface coverage rate increased. Further, when Example 1 and Example 3 or Example 2 and Example 4 are compared, it is better to use positive electrode active material particles having a plurality of kinds of coat layers having different chemical compositions even if the surface coverage is the same. It was confirmed that the performance maintenance rate was higher than that of the lithium ion secondary battery using the positive electrode active material particles coated with one kind of coat layer.

In FIGS. 4 and 5, the vertical axis indicates the total resistivity, and the horizontal axis indicates the core particle diameter of the positive electrode active material particles. From this result, it was confirmed that in Examples 1 to 4 and Comparative Example 1, as the core particle size increased, the total resistance ratio also increased. Further, it was confirmed that Examples 1 to 4 having the outermost surface covered had a higher total resistance ratio than Comparative Example 1 having no coat layer.

In FIG. 6, the vertical axis shows the performance maintenance rate at each cycle, and the horizontal axis shows the number of cycles. In Comparative Example 2 without a coat layer, the reduction rate of the discharge capacity is high, and the performance maintenance rate decreases to 0.6 or less after 1000 cycles, but in Example 5 using the positive electrode active material particles having a coat layer. It was confirmed that the performance maintenance rate was around 0.9 even when 2000 cycles were carried out, and that a high discharge capacity was maintained.

In FIG. 7, the vertical axis shows the film resistivity at each cycle, and the horizontal axis shows the number of cycles. In Comparative Example 2 without a coat layer, the film resistivity at the time of initial discharge is low, but increases with repeated charging and discharging, and when it exceeds 1000 cycles, the film resistivity exceeds 30. On the other hand, in Example 5, the film resistivity at the time of initial discharge was higher than that of Comparative Example 2, but no significant increase was observed even at the time of 2000 cycles, and it was confirmed that a low film resistivity was maintained. ..

1 Positive electrode active material particles 2 Core particles 3 Coat layer 4 Coat layer

Claims (12)

It is a positive electrode active material particle for a lithium ion secondary battery having a layered rock salt structure of a space group R-3 m in a rhombic crystal system.
The surface is formed by a chemical composition that is more stable but has a lower volume than the central part.
The positive electrode active material particles for a lithium ion secondary battery include core particles and a coat layer formed on the surface of the core particles.
Positive electrode active material particles for a lithium ion secondary battery in which the coverage of the coat layer on the core particles is 1% to 75% with respect to the surface area of the core particles. It is a positive electrode active material particle for a lithium ion secondary battery having a layered rock salt structure of a space group R-3 m in a rhombic crystal system.
The surface is formed by a chemical composition that is more stable but has a lower volume than the central part.
The positive electrode active material particles for a lithium ion secondary battery include core particles and a coat layer formed on the surface of the core particles.
Positive electrode active material particles for a lithium ion secondary battery in which the coverage of the coat layer on the core particles is 1% to 50% with respect to the surface area of the core particles. Expressed by the following general formula (1)
The positive electrode active material particle for a lithium ion secondary battery according to claim 1 or 2, wherein the chemical composition of the surface portion has a high molar ratio of Mn and Co but a low molar ratio of Ni as compared with the chemical composition of the central portion.
[Chemical 1]
LiNi _x Mn _{y Coz} O ₂ ... (1)
[In the general formula (1), x + y + z = 1. ] It is a positive electrode active material particle for a lithium ion secondary battery having a layered rock salt structure of a space group R-3 m in a rhombic crystal system.
The surface is formed by a chemical composition that is more stable but has a lower volume than the central part.
The positive electrode active material particles for a lithium ion secondary battery include core particles and a coat layer formed on the surface of the core particles.
The core particles are represented by the following general formula (2).
The coat layer is represented by the following general formula (1).
The chemical composition of the surface portion of the coat layer is higher than the chemical composition of the interface between the core particles and the coat layer, while the molar ratio of Mn and Co is high, while the molar ratio of Ni is low.
Positive electrode active material particles for a lithium ion secondary battery in which the coverage of the coat layer on the core particles is 1% to 75% with respect to the surface area of the core particles.
[Chemical 1]
LiNi _x Mn _y Co _z O ₂ ... (1)
[In the general formula (1), x + y + z = 1. ]
[Chemical 2]
LiNi _x Co _y Al _z O ₂ ... (2)
[In the general formula (2), x + y + z = 1. ] It is a positive electrode active material particle for a lithium ion secondary battery having a layered rock salt structure of a space group R-3 m in a rhombic crystal system.
The surface is formed by a chemical composition that is more stable but has a lower volume than the central part.
The positive electrode active material particles for a lithium ion secondary battery include core particles and a coat layer formed on the surface of the core particles.
The core particles are represented by the following general formula (2).
The coat layer is represented by the following general formula (1).
The chemical composition of the surface portion of the coat layer is higher than the chemical composition of the interface between the core particles and the coat layer, while the molar ratio of Mn and Co is high, while the molar ratio of Ni is low.
Positive electrode active material particles for a lithium ion secondary battery in which the coverage of the coat layer on the core particles is 1% to 50% with respect to the surface area of the core particles.
[Chemical 1]
LiNi _x Mn _y Co _z O ₂ ... (1)
[In the general formula (1), x + y + z = 1. ]
[Chemical 2]
LiNi _x Co _y Al _z O ₂ ... (2)
[In the general formula (2), x + y + z = 1. ] The positive electrode active material particle for a lithium ion secondary battery according to any one of claims 1 to 5, wherein the chemical composition changes discretely. The positive electrode active material particle for a lithium ion secondary battery according to any one of claims 1 to 5, wherein the chemical composition continuously changes. The positive electrode for a lithium ion secondary battery according to any one of claims 1 to 7, wherein the mass of the coat layer is 0.1% by mass to 50% by mass with respect to the total mass of the core particles and the coat layer. Active material particles. The positive electrode for a lithium ion secondary battery according to any one of claims 1 to 7, wherein the mass of the coat layer is 0.1% by mass to 20% by mass with respect to the total mass of the core particles and the coat layer. Active material particles. The positive electrode active material particle for a lithium ion secondary battery according to any one of claims 1 to 9 , wherein the ratio of the lattice constant of the coat layer to the lattice constant of the core particles is 1 to 2. The positive electrode for a lithium ion secondary battery containing the positive electrode active material particles for a lithium ion secondary battery according to any one of claims 1 to 10 . The lithium ion secondary battery comprising the positive electrode, the negative electrode, and the electrolyte for the lithium ion secondary battery according to claim 11 .

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