JP7067858B2 - Lithium-ion secondary battery and positive electrode active material for the lithium-ion secondary battery - Google Patents

Description

The present invention relates to a lithium ion secondary battery and a positive electrode active material used for the positive electrode thereof.

In recent years, secondary batteries such as lithium ion secondary batteries and nickel-metal hydride batteries have been preferably used as so-called portable power sources for personal computers and mobile terminals and power sources for driving vehicles. In particular, lithium-ion secondary batteries, which are lightweight and have high energy density, are high-output power supplies used in vehicles such as electric vehicles and hybrid vehicles (for example, power supplies that drive motors connected to the drive wheels of vehicles). ) Is becoming more important.

The positive electrode of such a lithium ion secondary battery is formed by coating the surface of a positive electrode current collector, which is a foil body having conductivity, with a positive electrode active material layer containing granular positive electrode active materials. The positive electrode active material for a lithium ion secondary battery (hereinafter, also simply referred to as “positive electrode active material”) is a material capable of storing and releasing lithium ions, and is a lithium element and one or more kinds of transition metal elements. Lithium-containing compounds containing and (eg, lithium transition metal composite oxides) are used. Examples of the lithium transition metal composite oxide include a lithium nickel composite oxide (for example, LiNiO ₂ ), a lithium cobalt composite oxide (for example, LiCoO ₂ ), a lithium manganese composite oxide (for example, LiMn ₂ O ₄ ), or lithium nickel. Examples thereof include a ternary lithium-containing composite oxide such as a cobalt-manganese composite oxide (for example, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ).

Further, in order to improve various battery performances, yttrium (Y), zirconium (Zr) and the like are added to the positive electrode active material in addition to the above-mentioned main metal elements.

For example, Non-Patent Document 1 describes a technique in which Y is added to a positive electrode active material to allow Y to exist in the crystal lattice of a lithium transition metal composite oxide in order to reduce battery resistance and improve cycle durability. It has been disclosed. Further, Patent Document 1 discloses a technique for containing Zr in a lithium nickel composite oxide in order to improve cycle durability.

Further, in Patent Document 2, in order to achieve both thermal stability in a charged state and high discharge capacity, Nisite, which is a lithium nickel composite oxide, is a trivalent element and has a strong binding force with oxygen (Al). ), And a technique for substituting one or more elements selected from Zr and Y at a constant ratio is disclosed.

Further, Patent Documents 3 and 4 disclose a technique for forming a compound containing Y on the surface of a lithium transition metal composite oxide. Specifically, Patent Document 3 discloses a technique of using a lithium cobalt composite oxide whose surface is covered with Y ₂ O ₃ or Li ₂ YO ₃ as a positive electrode active material, and Patent Document 4 discloses lithium. A technique for fixing a hydroxide or oxyhydroxide of a rare earth element such as Y to the surface of a transition metal composite oxide is disclosed. In addition, Patent Document 4 discloses a positive electrode active material in which a hydroxide or oxide of Zr is fixed to the surface of a lithium transition metal composite oxide as an unfavorable example of deteriorating battery performance.

Patent No. 5714899 Japanese Unexamined Patent Publication No. 2000-340230 Japanese Unexamined Patent Publication No. 5-6780 Japanese Unexamined Patent Publication No. 2011-141989

Meng Wang, Yunbo Chen, Feng Wu, Yuefeng Su, Lin Chen, Dongling Wang, "Characterization of yttrium sub-stituted LiNi0.33Mn0.33Co0.33O2cathode"

However, when Y or Zr is present in the crystal lattice of the lithium transition metal composite oxide, Y or Zr is present in an unstable state in the crystal lattice, so that it is eluted from the crystal lattice or has a crystal structure. May promote the collapse of. Therefore, the above-mentioned effects such as reduction of resistance and improvement of cycle durability cannot be continuously exerted, and sufficient effects cannot be obtained.
In particular, when Y or Zr elutes, the eluted Y or Zr migrates to the negative electrode side and reduces and precipitates on the surface of the negative electrode, thereby forming a SEI (Solid Electrolyte Interphase) layer having high resistance. In some cases. This inhibits the occlusion and release of lithium ions in the negative electrode, and there is a risk that metallic lithium will precipitate during charging.

The present invention has been made in view of this point, and a main object thereof is a positive electrode for a lithium ion secondary battery capable of improving the battery performance of a lithium ion secondary battery by containing Y and Zr. It is an object of the present invention to provide a lithium ion secondary battery using an active material and the positive electrode active material.

In order to realize the above object, the present invention provides a positive electrode active material having the following constitution.

The positive electrode active material disclosed here is a positive electrode active material used in a lithium ion secondary battery, and is provided with a lithium transition metal composite oxide having a layered crystal structure containing at least lithium and nickel as core particles. There is.
In the positive electrode active material disclosed here, a coating layer composed of a composite oxide containing lithium, yttrium, and zirconium is formed on at least a part of the surface of the core particles.

The composite oxide containing Li, Y, and Zr (hereinafter, also referred to as “Li—Y—Zr—O-based compound”) constituting the coating layer is a chemically stable compound. Therefore, unlike the positive electrode active material in which Y or Zr is present in the crystal lattice, in the positive electrode active material provided with the Li—Y—Zr—O-based compound as the coating layer, the elution of Y or Zr causes the negative electrode surface. Does not cause Li precipitation.
Further, in the positive electrode active material disclosed here, since the surface of the core particles is covered with a chemically stable coating layer, the crystal lattice of the core particles which is a lithium transition metal composite oxide as in the conventional technique. Even when Y or Zr is present inside, it is possible to suppress the elution of Y or Zr from the core particles and prevent the occurrence of Li precipitation on the surface of the negative electrode.

Further, in one preferred embodiment of the positive electrode active material disclosed herein, the weight ratio of the coating layer is 0.005 wt% to 0.1 wt% when the core particles are 100 wt%.
According to this aspect, the coating layer is formed to the extent that the surface of the core particles can be appropriately covered, and the core particles are formed to the extent that sufficient charge / discharge can be performed, so that the battery performance is further improved. It can be improved appropriately.

Further, in another preferred embodiment of the positive electrode active material disclosed herein, the positive electrode active material contains lithium, nickel, cobalt, manganese or aluminum, and also contains both yttrium and zirconium. hand,
Here, the contents of yttrium and zirconium, respectively, when the total number of moles of nickel, cobalt, and manganese or aluminum is 100 mol%, are determined.
Yttrium: 0.25 to 1 mol%
Zirconium: 0.25 to 1 mol%.
According to this aspect, since a sufficient and not excessive amount of the coating layer is formed, the above-mentioned improvements in various battery performances can be more appropriately exhibited.

Further, as another aspect of the present invention, a lithium ion secondary battery including the positive electrode active material is provided. In such a lithium ion secondary battery, the elution of Y or Zr from the positive electrode active material is suppressed, and the generation of Li precipitation on the surface of the negative electrode is prevented, so that the battery performance is improved as compared with the conventional case. ..

It is a perspective view which shows typically the outer shape of the lithium ion secondary battery which concerns on one Embodiment of this invention. It is a perspective view which shows typically the electrode body of the lithium ion secondary battery which concerns on one Embodiment of this invention.

As used herein, the term "lithium ion secondary battery" refers to a secondary battery that uses lithium ions as electrolyte ions and is charged and discharged by the transfer of electric charges associated with the lithium ions between the positive and negative electrodes. Further, in the present specification, the “active substance” refers to a substance (compound) involved in electricity storage on the positive electrode side or the negative electrode side, and stores and releases lithium ion, which is a charge carrier, during charging and discharging of a lithium ion secondary battery. A substance involved in.

1. 1. Positive Electrode Active Material for Lithium Ion Secondary Battery The positive electrode active material disclosed here includes core particles made of a lithium transition metal composite oxide and a coating layer formed on the surface of the core particles.

The positive electrode active material disclosed here can be represented by the following formula (1) as a suitable form. It should be noted that this formula (1) is a general formula showing the elemental composition of the entire positive electrode active material including both the core particles and the coating layer.
Li _{1 + m} Ni _p Co _q M _s Y _α Zr _β O _{2 + δ} (1)
M in the above formula (1) is composed of Al, Mn, W, Cr, Fe, V, Mg, Si, Ti, Mo, Cu, Zn, Ga, In, Sn, La, Ce, Ca and Na. One or more elements selected from the group.
Further, m, p, q, and s in the above equation (1) are 0 ≦ m ≦ 0.5, 0 <p <1, 0 ≦ q ≦ 0.6, 0 ≦ s ≦ 0.6, respectively. 0.9 ≦ p + q + s ≦ 1, and δ is a value determined so as to satisfy the charge neutrality condition. And α and β are 0 <α ≦ 0.1 and 0 <β ≦ 0.1, respectively.

Hereinafter, each of the core particles and the coating layer constituting the positive electrode active material disclosed here will be specifically described.

(1) Core Particles The positive electrode active material disclosed here is a lithium transition metal composite oxide having a layered crystal structure (typically, a layered rock salt type structure belonging to a hexagonal system) containing at least Li and Ni. Is provided as a core particle.
Further, the lithium transition metal composite oxide constituting the core particles may contain at least Li and Ni as described above, and further, a transition metal element other than Ni (that is, Co and the above formula (1)). (Metal element represented by M) may be contained alone or in combination of two or more. Examples of the lithium transition metal composite oxide include a lithium nickel composite oxide, a lithium nickel cobalt composite oxide, and a ternary lithium-containing composite oxide such as a lithium nickel cobalt manganese composite oxide.

(2) Coating layer In the positive electrode active material disclosed here, at least a part of the surface of the core particles described above is made of a composite oxide (Li-Y-Zr-O-based compound) containing Li, Y, and Zr. The configured covering layer is formed. As this Li-Y-Zr-O-based compound, Li _1-a Y _1-b Zr _b O _{2 + δ} (where 0 ≦ a <1, 0 <b <0.5, δ satisfy the charge neutrality condition). Examples of the compound represented by (), for example, Li _0.9 Y _0.9 Zr _0.1 O ₂ and the like can be mentioned. The compound forming the coating layer may contain a trace amount of other metal elements derived from the core particles.

Since this Li-Y-Zr-O-based compound is a chemically stable compound, it is Y or Zr that exists in the crystal lattice of the lithium transition metal composite oxide during charging and discharging. Alternatively, Zr does not elute from the coating layer and precipitate on the surface of the negative electrode. Therefore, according to the positive electrode active material disclosed here, it is possible to sufficiently suppress the precipitation of metallic Li at the negative electrode.

Further, the positive electrode active material disclosed here also has a function of significantly improving the cycle durability of the lithium ion secondary battery as compared with the conventional technique.
Specifically, since the particle surface is stabilized by the coating layer formed on the surface of the core particles, the side reaction between the active material and the electrolytic solution is suppressed. Furthermore, this coating layer can also function as a buffer layer that relieves stress due to expansion and contraction of the particles at the grain boundaries of the active material particles, and at the same time, improves the mechanical strength of the active material particles to crack the particles. It is also possible to suppress the occurrence. The positive electrode active material disclosed here can significantly improve the cycle durability as compared with the conventional technique by these functions.

Furthermore, as a result of conducting various experiments on the lithium ion secondary battery using the positive electrode active material disclosed here, the present inventor has reduced the resistance value in charge and discharge as compared with the conventional case, and has increased the output. I found that. This effect is due to the fact that Li is contained in the crystal lattice of the coating layer of the Li-Y-Zr-O-based compound, and when Li is deficient on the surface of the core particles during charging and discharging, the coating layer containing Li becomes Li. It is presumed that this is to alleviate the deficiency state and promote the deinsertion reaction of Li ions.

In the case of the positive electrode active material containing Li, Ni, Co, Mn or Al, and Y and Zr as the whole positive electrode active material, Ni and Co, which are metal elements other than Li, and Co. And the respective contents of Y and Zr when the total number of moles of Mn or Al is 100 mol%.
Yttrium: 0.25 to 1 mol%
Zirconium: preferably 0.25 to 1 mol%.
Since the positive electrode active material containing Zr and Y in such a ratio can form a sufficient and sufficient amount of coating layer on the surface of the core particles, the above-mentioned effects of improving various battery performances are sufficient. Can be demonstrated in

The weight ratio of the coating layer when the core particles are 100 wt% is preferably 0.005 wt% to 0.1 wt%, more preferably 0.01 wt% to 0.05 wt%. As a result, a coating layer that can appropriately cover the surface of the core particles is formed, and the core particles that can be sufficiently charged and discharged are formed, so that the battery performance is improved more appropriately. Can be made to. The weight ratio of the coating layer to the core particles can be calculated by performing powder X-ray diffraction on the powder of the positive electrode active material and then performing Liberty analysis on the result of the powder X-ray diffraction.

Y and / or Zr may be present in the crystal lattice of the lithium transition metal composite oxide constituting the core particles. As described above, by allowing Y or Zr to exist in the crystal lattice of the core particles, it is possible to exert the effects of reducing the battery resistance and improving the cycle durability as in the prior art.
In the positive electrode active material disclosed here, Y or Zr is present in the crystal lattice because the coating layer of the chemically stable Li—Y—Zr—O compound covers the surface of the core particles. Despite the use of the lithium transition metal composite oxide, it is possible to prevent Y or Zr from elution and causing metal Li precipitation.
Further, since the elution of Y or Zr is prevented, the effects of reducing the resistance of the battery and improving the cycle durability can be maintained for a long period of time.

2. 2. Method for Producing Positive Electrode Active Material for Lithium Ion Secondary Battery Next, a method for producing the positive electrode active material disclosed herein will be described.

(1) Preparation of core particles Core particles are produced through the same steps as a general positive electrode active material for a lithium ion secondary battery. Specifically, an aqueous solution is prepared by weighing a source (raw material) of a metal element other than Li so as to have a desired composition ratio and mixing it with an aqueous solvent. As a source of the metal element other than Li, at least a nickel supply source (a compound containing nickel such as nickel sulfate (NiSO ₄ )) is used, and further, a source of other metal elements (for example, depending on the desired composition) is used. , Cobalt source such as cobalt sulfate, manganese source such as manganese sulfate) and the like can be used.

Next, a basic aqueous solution (sodium hydroxide aqueous solution or the like) is added to the prepared aqueous solution and stirred to precipitate the above-mentioned metal hydroxide to obtain a raw material hydroxide (precursor).
Then, a predetermined amount of a lithium supply source (lithium carbonate, lithium hydroxide, lithium nitrate, etc.) is mixed with the obtained precursor, and then the temperature is 700 ° C. to 1000 ° C. (for example, 800 ° C.) for 5 hours under an oxidizing atmosphere. The firing process is performed for 20 hours (for example, 10 hours). By crushing the fired body thus obtained, core particles made of a lithium transition metal composite oxide having a layered crystal structure can be obtained.

(2) Preparation of Coating Layer Next, a coating layer composed of a Li—Y—Zr—O-based compound is formed on at least a part of the surface of the core particles obtained as described above. Hereinafter, an example of a method for forming a covering layer will be described.

(A) Preparation of mixed solution First, the core particles obtained in the above step are added to an aqueous solution in which a zirconium salt and a yttrium salt are mixed at a ratio of 1: 1 to prepare a mixed solution. At this time, the amounts of the zirconium salt, the yttrium salt, and the core particles are adjusted so that the ratio of each of Zr and Y to the metal element other than Li is 0.25 mol% to 1.0 mol%.

(B) Preparation of precursor Next, the prepared mixed solution is heated and evaporated to prepare a precursor containing Y and Zr on the surface of the core particles. The heating temperature at this time is set to, for example, 60 ° C.

(C) Firing treatment Next, the core particles having the precursor formed on the surface are calcined. Specifically, the powder obtained with the above configuration is fired at a temperature condition of 400 ° C. to 600 ° C. (for example, 500 ° C.) for 3 hours to 10 hours (for example, 5 hours). As a result, Li on the surface of the core particles reacts with Y and Zr in the precursor to form a coating layer of the Li—Y—Zr—O-based compound on the surface of the core particles.
Further, at this time, a part of Y and / or Zr contained in the precursor is dissolved in the core particles to obtain core particles in which Y and / or Zr are present in the crystal lattice of the lithium transition metal composite oxide. May be

Whether or not the positive electrode active material obtained through the above steps satisfies the above formula (1) is determined by performing powder X-ray diffraction on the powder of the positive electrode active material and qualitatively determining the obtained peak. It can be confirmed by analysis.

Further, in order to confirm the composition of the compound formed as the coating layer, the obtained positive electrode active material powder is embedded in a resin (for example, an epoxy resin) and then subjected to focused ion beam (FIB) processing. After preparing a sample for STEM observation of the particle cross section, the sample is observed with a scanning transmission electron microscope (STEM). Then, it can be confirmed by performing a spot quantitative analysis using STEM-EDX analysis on the coating layer formed on the surface of the core particles.

Further, if it is only necessary to confirm whether or not Y and Zr are contained in the produced positive electrode active material, it is said that elemental analysis is performed using the ICP (Inductively Coupled Plasma) method after dissolving the positive electrode active material with an acid or the like. A simple analysis can also be performed.

In the above method, a positive electrode active material having a coating layer is produced by using a so-called coating method in which a precursor containing Y and Zr is formed on the surface of the core particles prepared in advance and the precursor is fired. However, the method for producing the positive electrode active material disclosed here is not limited to the above method.

3. 3. Lithium-ion secondary battery Next, as a preferred embodiment of the present invention, a lithium-ion secondary battery in which the above-mentioned positive electrode active material is used for the positive electrode will be described. In the following, a lithium ion secondary battery provided with a wound electrode body will be described as an example, but it is not intended to limit the usage mode of the present invention. For example, the positive electrode active material of the present invention can also be used for a laminated electrode body in which a plurality of positive electrodes and negative electrodes are laminated.

FIG. 1 is a perspective view schematically showing the outer shape of the lithium ion secondary battery according to the present embodiment. As shown in FIG. 1, the lithium ion secondary battery 100 is configured by accommodating an electrode body (not shown) inside a square case 50.

(1) Case The case 50 is composed of a flat case body 52 having an open upper end and a lid 54 that closes the upper end thereof. The lid 54 is provided with a positive electrode terminal 70 and a negative electrode terminal 72. Although not shown, the positive electrode terminal 70 is electrically connected to the positive electrode of the electrode body in the case 50, and the negative electrode terminal 72 is electrically connected to the negative electrode.

(2) Electrode body Next, the structure of the electrode body housed inside the case 50 described above will be described. FIG. 2 is a perspective view schematically showing an electrode body of the lithium ion secondary battery according to the present embodiment.
As shown in FIG. 2, the electrode body in the present embodiment has a flat-shaped winding formed by laminating and winding a long sheet-shaped positive electrode 10 and a negative electrode 20 together with a long sheet-shaped separator 40. The electrode body 80.

(A) Positive electrode The positive electrode 10 in FIG. 2 is formed by coating both surfaces of a long sheet-shaped positive electrode current collector 12 with a positive electrode active material layer 14 containing a positive electrode active material. A positive electrode active material layer non-forming portion 16 in which the positive electrode active material layer 14 is not coated is formed on one side edge portion in the width direction of the positive electrode 10, and the positive electrode active material layer non-forming portion 16 is formed. Is electrically connected to the positive electrode terminal 70 (see FIG. 1).

Then, in the present embodiment, as the positive electrode active material contained in the positive electrode active material layer 14 described above, a coating layer made of a Li—Y—Zr—O compound is formed on the surface of core particles made of a lithium transition metal composite oxide. The positive electrode active material in which is formed is used.
As a result, as described above, the Li precipitation resistance and cycle durability of the produced lithium ion secondary battery can be improved, and the battery resistance can be reduced.

Further, in addition to the above-mentioned positive electrode active material, the positive electrode active material layer 14 can contain one or more kinds of materials that can be used in a general lithium ion secondary battery, if necessary. An example of such a material is a conductive auxiliary material. As the conductive auxiliary material, a carbon material such as carbon powder or carbon fiber is preferably used, but a conductive metal powder such as nickel powder may be used.
In addition, examples of the material that can be used for the positive electrode active material layer include various polymer materials that can function as a binder (binder). Polymers such as polyvinylidene fluoride (PVDF) and polyvinylidene chloride (PVDC) can be preferably used for this binder. Alternatively, styrene-butadiene rubber (SBR), polytetrafluoroethylene (PTFE), polyethylene (PE), polyacrylic acid (PAA) and the like may be used.

(B) Negative electrode As for the negative electrode 20, similarly to the positive electrode 10, a negative electrode active material layer 24 containing a negative electrode active material as a main component is formed on both sides of a long sheet-shaped negative electrode current collector 22. A negative electrode active material layer non-forming portion 26 is formed on one side edge portion in the width direction of the negative electrode 20, and the negative electrode active material layer non-forming portion 26 is electrically connected to the negative electrode terminal 72 (see FIG. 1). It is connected.

The negative electrode active material is not particularly limited, and one of various materials that can be used as the negative electrode active material of the lithium ion secondary battery may be used alone or in combination of two or more (mixed or combined). Can be used.
Preferable examples include carbon materials such as graphite (graphite), non-graphitized carbon (hard carbon), easily graphitized carbon (soft carbon), carbon nanotubes, or those having a structure combining these. From the viewpoint of energy density, graphite-based materials (natural graphite (stone ink), artificial graphite, etc.) can be preferably used among these.
Further, the negative electrode active material is not limited to the above-mentioned carbon-based material, and for example, a lithium titanium composite oxide such as Li ₄ Ti ₅ O ₁₂ or a lithium transition metal composite oxide such as a lithium transition metal composite nitride should be used. You can also.

Further, the negative electrode active material layer 24 may also contain a binder and various additives, if necessary, as in the positive electrode active material layer 14. For example, the same binder as the positive electrode active material layer 14 described above can be used as the binder. In addition, various additives such as thickeners and dispersants can be appropriately used. For example, carboxymethyl cellulose (CMC) or methyl cellulose (MC) can be preferably used as the thickener.

(C) Separator The separator 40 is arranged so as to be interposed between the positive electrode 10 and the negative electrode 20 described above. As the separator 40, a strip-shaped sheet material having a plurality of minute holes and having a predetermined width is used. For example, a single-layer structure sheet material or a laminated structure sheet material made of a porous polyolefin resin can be used. Further, a layer of insulating particles may be further formed on the surface of the sheet material. Examples of the insulating particles include an insulating inorganic filler (for example, a filler such as a metal oxide and a metal hydroxide), an insulating resin particle (for example, particles such as polyethylene and polypropylene), and the like. Can be mentioned.

(3) Electrolyte The electrolytic solution (non-aqueous electrolytic solution) stored in the case 50 together with the wound electrode body 80 described above is the same as the non-aqueous electrolytic solution conventionally used for lithium ion secondary batteries. Can be used without particular limitation.
Such a non-aqueous electrolyte solution typically has a composition in which a supporting salt is contained in a non-aqueous solvent. The non-aqueous solvent includes, for example, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 1,3-dioxolane and the like. One or more selected from the group can be used. Examples of the supporting salt include LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , and the like. Lithium salts can be used. As an example, a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) (for example, volume ratio 3: 4: 3) containing LiPF ₆ at a concentration of about 1 mol / L is not contained. Examples include water electrolyte.

(4) Construction of Lithium Ion Secondary Battery When constructing a lithium ion secondary battery using the above-mentioned members, first, the wound electrode body 80 is housed inside the case body 52, and a non-aqueous electrolytic solution is used. Is placed (injected) in the case body 52. After that, the respective electrode terminals 70 and 72 provided on the lid 54 are connected to the positive electrode active material layer non-forming portion 16 and the negative electrode active material layer non-forming portion 26 of the wound electrode body 80, and then by the lid 54. The opening at the upper end of the case body 52 is sealed. As a result, the lithium ion secondary battery 100 is constructed.

In the lithium ion secondary battery constructed in this manner, the positive electrode active material contained in the positive electrode active material layer is a Li—Y—Zr—O-based compound on the surface of core particles made of a lithium transition metal composite oxide. A positive electrode active material on which a coating layer is formed is used.
As described above, the positive electrode active material having such a structure can improve various battery performances such as improvement of Li precipitation resistance, improvement of cycle durability, and reduction of battery resistance, and thus can be improved as compared with the conventional case. A high-performance lithium-ion secondary battery can be constructed.

[Test example]
Hereinafter, test examples relating to the present invention will be described, but the description of the test examples is not intended to limit the present invention.

In this test example, the following tests A and B were performed in order to investigate the effect of the positive electrode active material in which the coating layer of the Li—Y—Zr—O compound is formed on the surface of the core particles on the battery performance. ..

1. 1. Test A
A positive electrode was prepared using different positive electrode active materials in each of Test Example 1 to Test Example 10, and a lithium ion secondary battery for an evaluation test was constructed using the positive electrode.

(1) Preparation of Positive Electrode Active Material (a) Preparation of Positive Electrode Active Material of Test Examples 1 to 7 As shown in Table 1, in Test Example 1, a lithium nickel cobalt manganese composite oxide containing no Zr or Y is used. (NCM active material) was prepared as a positive electrode active material, NCM active materials containing Zr were prepared in Test Examples 2 to 4, and NCM active materials containing Y were prepared in Test Examples 5 to 7.

Specifically, an aqueous solution of nickel sulfate, cobalt sulfate, and manganese sulfate was prepared, and then NaOH was added and stirred while neutralizing to obtain a sol-like precursor. Then, after adding lithium carbonate to this precursor, a calcination treatment was carried out at 900 ° C. for 15 hours in an oxidizing atmosphere. Then, the obtained fired body was pulverized to prepare an NCM active material (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) having an average particle diameter of 10 μm.
In Test Examples 2 to 4, an NCM active material containing Zr was prepared by adding Zr in the amount shown in "Zr addition amount" in Table 1 to an aqueous solution of nickel sulfate, cobalt sulfate, and manganese sulfate. bottom. Further, in Test Examples 5 to 7, an NCM active material containing Y was prepared by adding the amount of Y shown in "Y addition amount" in Table 1. The "Zr addition amount" and "Y addition amount" in Table 1 indicate the molar ratio when the total number of moles of metal elements other than Li contained in the entire positive electrode active material is 100 mol%.

(B) Preparation of Positive Electrode Active Material of Test Examples 8 to 10 In Test Examples 8 to 10, an NCM active material was prepared by the same procedure as in Test Example 1 described above, and the NCM active material was used as a core particle to prepare the core. A positive electrode active material was prepared by forming a coating layer containing Y and Zr on the surface of the particles.

Specifically, first, the NCM active material, which is a core particle, was added to an aqueous solution in which zirconium nitrate and yttrium nitrate were mixed at a ratio of 1: 1 to prepare a mixed solution. At this time, as shown in "Zr addition amount" and "Y addition amount" in Table 1, the addition amounts of zirconium nitrate and yttrium nitrate were different in each of Test Examples 8 to 10.
Next, the prepared mixed solution was heated to 60 ° C. to evaporate, and then fired at 450 ° C. for 5 hours to coat the surface of the NCM active material, which is the core particle, with the Li—Y—Zr—O compound. A positive electrode active material having a layer formed was produced.

(2) Construction of a Lithium Ion Secondary Battery for Evaluation Test A procedure for constructing a lithium ion secondary battery for evaluation test will be specifically described.

(A) Preparation of positive electrode As described above, different positive electrode active material powders are prepared for each of Test Examples 1 to 10, and a dispersion medium (NMP: N-methylpyrrolidone), a binder (PVDF), and a conductive auxiliary agent (acetylene) are prepared. Black) and the dispersant were mixed to prepare a paste for the positive electrode active material layer. At this time, each material was weighed so that the solid content was 50 wt%, and mixed using a planetary mixer. The mass ratio of the positive electrode active material, the conductive auxiliary agent, and the binder contained in this paste was set to 90: 6: 4.

Next, the paste for the positive electrode active material layer is applied to both sides of the sheet-shaped positive electrode current collector (aluminum foil) using a die coater, dried, and then pressed at a predetermined pressure to form a sheet-shaped positive electrode. Made.

(B) Preparation of Negative Electrode In each of Test Examples 1 to 10, a negative electrode was prepared using a natural graphite-based material (graphite) having an average particle diameter of 20 μm as a negative electrode active material. Specifically, a negative electrode active material, a binder (SBR: styrene-butadiene copolymer), and a thickener (CMC) were mixed with a dispersion solvent (water) to prepare a paste for the negative electrode active material. Then, the paste for the negative electrode active material was applied to both sides of the sheet-shaped negative electrode current collector (copper foil), dried, and then pressed to prepare a sheet-shaped negative electrode. The mixing ratio of the negative electrode active material, SBR, and CMC in the above-mentioned paste for the negative electrode active material was adjusted to 98: 1: 1.

(C) Preparation of Battery Next, after laminating the above-mentioned positive electrode and negative electrode via a sheet-shaped separator, the laminated body was wound to prepare a flat wound electrode body. Then, after connecting the manufactured wound electrode body to the external terminal of the case, the lithium ion secondary battery for evaluation test was constructed by accommodating it in the case together with the electrolytic solution and sealing it. As the electrolytic solution, a non-aqueous electrolytic solution containing LiPF ₆ as a supporting salt at a concentration of about 1 mol / liter in a mixed solvent containing EC, DMC and EMC in a volume ratio of 3: 4: 3 was used. bottom.

(3) Evaluation test In this test example, (a) Li precipitation resistance evaluation test, (b) cycle durability evaluation test, and (b) cycle durability evaluation test, (a) Li precipitation resistance evaluation test, (b) cycle durability evaluation test, for the lithium ion secondary batteries for evaluation test of Test Examples 1 to 10. c) Three items of the battery resistance evaluation test were evaluated.
In this test example, the lithium ion secondary battery to be evaluated was activated before each evaluation test was performed. Specifically, after charging to 4.2 V by constant current charging with the current value set to 1 / 3C, constant voltage charging was performed until the current value reached 1 / 50C to bring the product into a fully charged state. Then, a constant current discharge with the current value set to 1 / 3C was performed up to 3V, and the capacity at this time was used as the initial capacity. The temperature in this activation treatment was set to 25 ° C.

(A) Li precipitation resistance evaluation test In this evaluation, the "standardized limit current value" was measured in order to evaluate the Li precipitation resistance of the lithium ion secondary batteries of Test Examples 1 to 10.
Specifically, the lithium ion secondary batteries of each test example are placed under a temperature condition of -10 ° C., constant current charging is performed up to 4.2 V with a current value equivalent to 1 C, and then 3 V with a current value of 1 C. The charge / discharge cycle in which constant current discharge was performed was set to one cycle, and after performing this charge / discharge cycle for 50 cycles, each battery was disassembled and it was examined whether or not metallic Li was deposited on the negative electrode.
When the precipitation of metallic Li was not observed, the current value in the charge / discharge cycle described above was increased in 0.2C increments and the test was repeated, and the current value when the precipitation of metallic Li was confirmed was determined. It was set as "standardized limit current value".
The results are shown in Table 1. The "normalized limit current value" in Table 1 is shown as a logarithm with the measurement result of Test Example 1 as 100.

(B) Cycle durability evaluation test In this evaluation, the "capacity retention rate after the cycle" was measured in order to evaluate the cycle durability of Test Examples 1 to 10.
Specifically, the lithium ion secondary battery of each test example is placed under a temperature condition of 60 ° C., and after constant current charging to 4.2 V at a current value of 2C, it is constant to 3 V at a current value of 2C. The charge / discharge cycle for current discharge was set as one cycle, and this charge / discharge cycle was performed for 500 cycles.
Then, the capacity of each battery was measured, and the ratio of the measurement results when the above-mentioned initial capacity was 100 was defined as the "capacity retention rate after cycle". The results are shown in Table 1.

(C) Battery resistance evaluation test In this evaluation, the "standardized resistance value" was measured in order to evaluate the battery resistance of each test example.
Specifically, first, the open circuit voltage of each evaluation test battery was adjusted to 3.70 V, which corresponds to 56% of SOC (State of Charge). Then, each battery was placed under a temperature condition of 25 ° C., and constant current discharge was performed until the voltage between terminals became 3.00 V. Then, the voltage between terminals and the current value at the time of 5 seconds from the start of discharge were measured, and the resistance value calculated based on the measurement result was defined as the "normalized resistance value".
The calculation results are shown in Table 1. The "normalized resistance value" in Table 1 is shown as a logarithm with the measurement result of Test Example 1 as 100.

(4) Test results Looking at the results of the Li precipitation resistance evaluation test (standardized limit current values in Table 1), in Test Examples 2 to 7 in which Zr and Y are present in the crystal lattice, Zr and Y are present. The standardized limit current value was lower than that of Test Example 1 in which it was not added, and the precipitation of metallic Li on the surface of the negative electrode was likely to occur. On the other hand, in Test Examples 8 to 10 in which the coating layer containing both Zr and Y was formed, the normalized limit current value was about the same as that in Test Example 1, and despite the addition of Zr and Y. , Precipitation of metallic Li was suppressed.

Next, looking at the results of the cycle durability evaluation test (post-cycle capacity retention rate in Table 1), the cycle durability was improved in all of Test Examples 2 to 10 as compared with Test Example 1. However, among these Test Examples 2 to 10, the cycle durability of Test Examples 8 to 10 in which the coating layer containing Zr and Y was formed was particularly greatly improved.

Looking at the test results of the battery resistance evaluation test (normalized resistance values in Table 1), in Test Examples 2 to 4 to which only Zr was added, the resistance value was higher than that of Test Example 1, and only Y was added. The results were obtained that the resistance value was slightly reduced in the tested Examples 5 to 7. On the other hand, in Test Examples 8 to 10 in which the coating layer containing Zr and Y was formed, the result was obtained that the resistance value was significantly reduced.

From the above results, by using a positive electrode active material in which a coating layer containing Y together with Zr is formed on the surface of core particles which are NCM active materials, in terms of Li precipitation resistance, cycle durability, and battery resistance, It was confirmed that a lithium-ion secondary battery with better battery performance than before can be constructed.

2. 2. Test B
Next, Test B was conducted to investigate whether or not the same effect as that of Test A described above could be obtained even if the lithium transition metal composite oxide used for the core particles was changed.
In Test B, the same conditions as in Test A except that the lithium nickel cobalt aluminum composite oxide (NCA active material) represented by LiNi _1/3 Co _1/3 Al _1/3 O ₂ was used as the core particles. The test was conducted at. The test results are shown in Table 2.

As shown in Table 2, Test Examples 16 to 18 obtained more preferable results than the other Test Examples in any of the items of the normalized limit current value, the post-cycle capacity retention rate, and the normalized resistance value.
From this, even when an NCA active material is used as the core particle, by forming a coating layer containing Y and Zr, Li precipitation resistance is improved, cycle durability is improved, and battery resistance is reduced. It was confirmed that a lithium-ion secondary battery with better battery performance than before can be constructed.

Although the present invention has been described in detail above, the above-described embodiment is merely an example, and the invention disclosed herein includes various modifications and modifications of the above-mentioned specific examples.

The non-aqueous electrolytic solution secondary battery provided by the technique disclosed herein can be used as a non-aqueous electrolytic solution secondary battery for various applications because it exhibits excellent performance as described above. For example, it can be suitably used as a power source for a motor (motor) mounted on a vehicle such as an automobile. Such a non-aqueous electrolyte secondary battery may be used in the form of an assembled battery in which a plurality of them are connected in series and / or in parallel. Therefore, according to the techniques disclosed herein, a vehicle (typically an automobile, particularly a hybrid vehicle, an electric vehicle, a fuel cell) equipped with such a non-aqueous electrolyte secondary battery (which may be in the form of an assembled battery) as a power source. A vehicle equipped with an electric motor such as a vehicle) may be provided.

10 Positive electrode 12 Positive electrode current collector 14 Positive electrode active material layer 16 Positive electrode active material layer Non-formed part 20 Negative electrode 22 Negative electrode current collector 24 Negative electrode active material layer 26 Negative electrode active material layer Non-formed part 40 Separator 50 Case 52 Case body 54 Lid 70 Positive electrode terminal 72 Negative electrode terminal 80 Winding electrode body 100 Lithium ion secondary battery

Claims (4)

A positive electrode active material used in lithium-ion secondary batteries.
It is provided with a lithium transition metal composite oxide having a layered crystal structure containing at least lithium and nickel as core particles.
A positive electrode active material for a lithium ion secondary battery in which a coating layer composed of a composite oxide containing lithium, yttrium, and zirconium is formed on at least a part of the surface of the core particles. The positive electrode active material for a lithium ion secondary battery according to claim 1, wherein the weight ratio of the coating layer is 0.005 wt% to 0.1 wt% when the core particles are 100 wt%. A positive electrode active material containing lithium, nickel, cobalt, manganese or aluminum, and containing both yttrium and zirconium.
Here, the content of each of the yttrium and the zirconium when the total number of moles of the nickel, the cobalt, and the manganese or the aluminum is 100 mol% is determined.
Yttrium: 0.25 to 1 mol%
Zirconium: The positive electrode active material for a lithium ion secondary battery according to claim 1 , which is 0.25 to 1 mol%. A lithium ion secondary battery comprising the positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 3.

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