JP6448432B2 - Positive electrode active material for lithium ion battery, positive electrode for lithium ion battery and lithium ion battery - Google Patents

Description

  The present invention relates to a positive electrode active material for a lithium ion battery, a positive electrode for a lithium ion battery, and a lithium ion battery, and more particularly to a surface-modified positive electrode active material for a lithium ion battery, a positive electrode for a lithium ion battery, and a lithium ion battery.

Lithium-containing transition metal oxides are generally used as positive electrode active materials for lithium ion batteries. Specifically, lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), lithium manganate (LiMn ₂ O ₄ ), etc., improved characteristics (higher capacity, cycle characteristics, storage characteristics, reduced internal resistance) In order to improve the rate characteristics and safety, it is underway to combine them. Lithium ion batteries for large-scale applications such as in-vehicle use and load leveling are required to have different characteristics from those of conventional mobile phones and personal computers.

  One of the techniques used for the positive electrode active material for lithium ion batteries is surface modification (Patent Documents 1 to 4). This is mainly based on the following three technologies (a) to (c).

(A) is a technique for suppressing as much as possible a side reaction in which the electrolytic solution decomposes on the surface of the active material. In the past, oxides of single elements such as Al ₂ O ₃ and ZrO ₂ were mainly used, but if the entire surface of the active material is modified with this, Li ions cannot be inserted or desorbed. Is mainly based on the technique of partially modifying the surface or modifying the surface with a Li ion conductor or an active material.

  (B) is a technique for preventing transition metals (particularly Mn) from being eluted from the active material by hydrogen fluoride impurities in the electrolytic solution. In this case as well, the entire surface of the active material cannot be modified in the same manner as in (a), so there is currently a technology for suppressing Mn elution by reacting hydrogen fluoride impurities in the electrolytic solution by blending with a Ni-based active material. It is the subject. The reason why Mn is particularly targeted for elution suppression is that it easily reacts with carbon of the negative electrode, and when the positive electrode is a Mn-based active material and the negative electrode is a graphite-based active material, charging and discharging are repeated. Depending on the design, the discharge capacity becomes 1/10 of the initial one in 10 cycles.

  (C) is a technique related to the coating of a material having a high electron conductivity on an active material having a low electron conductivity. This technology has been established as a technology for coating carbon materials on phosphate-based, silicate-based, and lithium-titanium-based active materials, and is easy to manufacture. Has been.

JP 2011-082133 A JP 2013-175512 A JP 2009-054583 A JP 2014-197540 A

  When considering the techniques (a) to (c), it can be said that a function for improving battery characteristics is also required in the surface modification technique. Here, when manufacturing a positive electrode active material by baking now, when the primary particle diameter is enlarged too much, it turns out that the cycling characteristics of the produced | generated positive electrode active material may deteriorate. As a means to prevent this, the primary particle size of the fired product is suppressed by adjusting the firing pattern, but since the total calorific value is reduced compared to the existing firing pattern, the generation of unreacted raw materials This is a trade-off, and a problem arises in terms of improving battery characteristics.

  Therefore, an object of the present invention is to provide a surface-modified positive electrode active material for a lithium ion battery having good battery characteristics.

  As a result of various studies to solve such problems, the present inventor has included a sulfate group-containing compound or the like in the raw material in the production of an active material whose surface is coated with a sulfate group, In order to suppress the particle growth of the primary particles by precipitating on the surface of the primary particles, and to control the peak of S2p bond when the XPS of the cross section SIM of the active material is measured in order to improve the battery characteristics Has been found effective. In general, when a positive electrode active material for a lithium ion battery whose surface is modified by coating another material on the surface of the active material, a bond is formed chemically on the surface of the active material or is fired for a very short time. The coating material is fixed to the active material surface. In the present invention, the peak of S2p bond is controlled within a predetermined range with the aim of retaining a predetermined amount on the surface of the sulfate radical coated on the surface without dissolving in the active material.

  It has been found that such a configuration allows surface modification that does not inhibit lithium ion conduction and suppresses electrolyte decomposition, and further improves battery characteristics.

In one aspect, the present invention completed based on the above knowledge has a composition formula: Li _a Ni _b Co _c Mn _{d Me} O ₂
(In the above formula, 1.0 ≦ a ≦ 1.05, 0.5 ≦ b ≦ 0.9, 0.1 ≦ c ≦ 0.3, 0.1 ≦ d ≦ 0.3, 0 ≦ e ≦ 0 .005, b + c + d + e = 1, and M is at least one selected from the group consisting of Mg, Al, and Zr.)
The sulfur-containing compound or the sulfur-containing ion is attached to the surface of the primary particle, and S / (Ni + Co + Mn + M) of the whole particle is 0.001 to 0.005 in molar ratio, and the cross-section SIM of the active material When XPS is measured, the peak of the S2p bond is a positive electrode active material for a lithium ion battery present at 165 to 175 eV.

  In another aspect, the present invention is a positive electrode for a lithium ion battery using the positive electrode active material for a lithium ion battery of the present invention.

  In still another aspect, the present invention is a lithium ion battery using the positive electrode for a lithium ion battery of the present invention.

  ADVANTAGE OF THE INVENTION According to this invention, the positive electrode active material for lithium ion batteries by which the battery characteristic was favorable can be provided.

(Configuration of positive electrode active material for lithium ion battery)
The positive electrode active material for a lithium ion battery of the present invention is
Composition formula: Li _a Ni _b Co _c Mn _{d Me} O ₂
(In the above formula, 1.0 ≦ a ≦ 1.05, 0.5 ≦ b ≦ 0.9, 0.1 ≦ c ≦ 0.3, 0.1 ≦ d ≦ 0.3, 0 ≦ e ≦ 0 .005, b + c + d + e = 1, and M is at least one selected from the group consisting of Mg, Al, and Zr.)
It is represented by
The ratio of lithium to the total metal in the positive electrode active material for a lithium ion battery is 1.0 to 1.05. When the ratio is less than 1.0, it is difficult to maintain a stable crystal structure. This is because the high capacity cannot be secured.
In addition, since the composition of nickel in the positive electrode active material for lithium ion batteries is 0.5 to 0.9, the capacity, output, and safety of the lithium ion battery using the positive electrode active material for lithium ion batteries are balanced. Improve well. The composition of nickel in the positive electrode active material for lithium ion batteries is preferably 0.7 to 0.9, more preferably 0.8 to 0.9.

In the positive electrode active material for a lithium ion battery of the present invention, a sulfur-containing compound or a sulfur-containing ion is attached to the surface of the primary particles. The sulfur-containing compound adhering to the surface of the primary particles may be, for example, lithium sulfate, nickel sulfate, cobalt sulfate, manganese sulfate or the like. Further, the sulfur-containing ions attached to the surface of the primary particles may be, for example, SO ₄ ^2- etc. By including the sulfur-containing ions before firing and having the above-described configuration when the positive electrode active material is obtained, the primary particle size does not develop much during firing, resulting in the primary particle size of the positive electrode active material. Becomes smaller, and the cycle characteristics of the battery are improved.

  As for the positive electrode active material for lithium ion batteries of this invention, S / (Ni + Co + Mn + M) of the whole particle | grains is 0.001-0.005 by molar ratio. When S / (Ni + Co + Mn + M) of the whole particle is less than 0.001 in terms of molar ratio, the primary particle diameter is not so small, and there is a problem that cycle characteristics are not improved. Moreover, when S / (Ni + Co + Mn + M) of the whole particle exceeds 0.005 by molar ratio, the problem that the capacity | capacitance when it is set as a battery will arise.

  When the XPS of the cross-section SIM of the active material of the positive electrode active material for a lithium ion battery of the present invention is measured, the peak of S2p bond exists at 165 to 175 eV. With such a configuration, the primary particle diameter does not develop so much and therefore the cycle characteristics are good. Moreover, since it is not necessary to suppress the primary particle size, it is not necessary to adjust the firing pattern as a result, and the problem of generation of unreacted raw materials is solved. Moreover, it turns out that the sulfur containing compound or the sulfur containing ion has adhered to the surface of a primary particle as the peak of S2p coupling | bonding which is an XPS spectrum of sulfur is 165-175 eV. When the peak range exceeds 175 eV, for example, 180 eV or more, the sulfur-containing compound or the sulfur-containing ion is not “attached” to the surface of the primary particle, and the sulfur-containing compound or the sulfur-containing ion is “ "Solution". When the sulfur-containing compound or the sulfur-containing ion is “solid-solved” in the primary particles as described above, lattice irregularities occur in the vicinity of the surface of the primary particles, resulting in poor cycle characteristics. Further, when the peak is lower than 165 eV, for example, 150 eV or less, the degree of “adhesion” of the sulfur-containing compound or the sulfur-containing ions on the surface of the primary particles becomes weak, and the contribution to the improvement of the cycle characteristics is lost.

  In addition, when the peak position of the S2p bond is less than 165 eV, the coating of the active material is easily peeled off, and the cycle characteristics of the battery are deteriorated. On the other hand, when the peak position of the S2p bond exceeds 175 eV, the coating of the active material is broken, and sulfate radicals enter the active material, thereby degrading the cycle characteristics of the battery.

(Configuration of positive electrode for lithium ion battery and lithium ion battery using the same)
The positive electrode for a lithium ion battery according to an embodiment of the present invention includes, for example, a positive electrode mixture prepared by mixing a positive electrode active material for a lithium ion battery having the above-described configuration, a conductive additive, and a binder from an aluminum foil or the like. The current collector has a structure provided on one side or both sides. Moreover, the lithium ion battery which concerns on embodiment of this invention is equipped with the positive electrode for lithium ion batteries of such a structure.

(Method for producing positive electrode active material for lithium ion battery)
Next, the manufacturing method of the positive electrode active material for lithium ion batteries which concerns on embodiment of this invention is demonstrated in detail. First, an aqueous solution containing nickel sulfate, cobalt sulfate, and manganese sulfate in a molar ratio of a predetermined metal is prepared.
Next, ammonia water and caustic soda water are added to the nickel, cobalt, and manganese sulfate aqueous solution, and the pH of these solutions is adjusted to 11 to 12 to prepare seed crystals. Next, particles are grown at a pH of 10 to 11 to produce a coprecipitation intermediate.
Next, filtration is performed to obtain a precursor. At this time, washing was performed so that S / (Ni + Co + Mn + M) of the entire particle was 0.001 to 0.005 in molar ratio.
Next, a precursor in which S / (Ni + Co + Mn + M) of the whole particle is 0.001 to 0.005 in molar ratio is baked at 700 ° C. for 1 hour in an O ₂ flow rotary furnace, and then Li / (Ni + Co + Mn + M) is mixing the inter Li ₂ CO ₃ and coprecipitation body so as to be 1.01 to 1.05 in molar ratio, calcining. As the firing, (1) firing at 660 to 680 ° C. for 2 to 4 hours, and (2) firing at 720 to 750 ° C. for 5 to 7 hours. Alternatively, (1 ′) baking at 690 to 710 ° C. for 2 to 4 hours, and (2 ′) baking at 720 to 900 ° C. for 3 to 5 hours.

  Thereafter, if necessary, the fired body is pulverized using, for example, a pulverizer to obtain a powder of the positive electrode active material.

  Examples for better understanding of the present invention and its advantages are provided below, but the present invention is not limited to these examples.

Example 1
First, an aqueous solution containing nickel sulfate, cobalt sulfate, and manganese sulfate at a molar ratio of Ni: Co: Mn = 8: 1: 1 was prepared, and at the same time, 14 mol / L ammonia water and 18 mol / L caustic soda water were prepared. . These solutions were put into one reaction vessel so that the pH was 11 to 12 to prepare seed crystals, and then particles were grown at pH 10 to 11 to prepare a coprecipitation intermediate. Thereafter, filtration was performed, but the washing amount was adjusted so that S / (Ni + Co + Mn + M) was 0.001 in molar ratio. This was calcined in an O ₂ flow rotary furnace at 700 ° C. for 1 hour, and then Li ₂ CO ₃ and the coprecipitated intermediate were mixed so that Li / (Ni + Co + Mn) was 1.01 in molar ratio. This was placed in a firing furnace in an O ₂ atmosphere, fired at 660 ° C. for 3 hours, and then fired at 750 ° C. for 5 hours to obtain an active material.

(Example 2)
Firing in the firing furnace of the O ₂ atmosphere, after 3 hours baking at 660 ° C., except that was calcined at 750 ° C. 7 hours to prepare an active material in the same manner as in Example 1.

Example 3
Firing in the firing furnace of the O ₂ atmosphere, after 3 hours baking at 700 ° C., except that calcined 5 hours at 750 ° C. to produce the active material in the same manner as in Example 1.

(Examples 4-11, 14-21, 24-31, 34-40)
An active material was produced in the same manner as in Example 1 except that the molar ratio of Ni: Co: Mn in the sulfates of nickel, cobalt and manganese and the molar ratio of S / (Ni + Co + Mn + M) in the filtration step were changed. .
In Examples 8, 18, 28, and 38, Mg, which is an M type metal, was added in the composition of the positive electrode active material by adding nickel, cobalt, and manganese sulfates in the form of magnesium sulfate at the same time.
In Examples 9, 19, 29, and 39, Al, which is an M-type metal, was added in the composition of the positive electrode active material by adding nickel sulfate, cobalt sulfate, and manganese sulfate in the form of aluminum sulfate.
Further, in Examples 10, 20, 30, and 40, Zr, which is an M-type metal, was added in the composition of the positive electrode active material by adding nickel, cobalt, and manganese sulfates in the form of zirconium oxysulfate at the same time. .

(Examples 12, 22, and 32)
An active material was produced in the same manner as in Example 2 except that the molar ratio of Ni: Co: Mn in the sulfates of nickel, cobalt and manganese and the molar ratio of S / (Ni + Co + Mn + M) in the filtration step were changed. .

(Examples 13, 23, 33)
An active material was prepared in the same manner as in Example 3 except that the molar ratio of Ni: Co: Mn in the sulfates of nickel, cobalt and manganese and the molar ratio of S / (Ni + Co + Mn + M) in the filtration step were changed. .

(Comparative Example 1)
Firing in the firing furnace of the O ₂ atmosphere, after 3 hours baking at 690 ° C., except that was calcined at 750 ° C. 7 hours to prepare an active material in the same manner as in Example 1.

(Comparative Example 2)
Firing in the firing furnace of the O ₂ atmosphere, after 3 hours baking at 620 ° C., except that was calcined 1 hour at 750 ° C. to produce the active material in the same manner as in Example 1.

(Comparative Examples 3-6)
An active material was produced in the same manner as in Example 1 except that the molar ratio of Ni: Co: Mn in the sulfates of nickel, cobalt and manganese and the molar ratio of S / (Ni + Co + Mn + M) in the filtration step were changed. .
In Comparative Example 4, Ti, which is an M-type metal, was added in the composition of the positive electrode active material by adding it in the form of titanyl sulfate simultaneously with the sulfates of nickel, cobalt, and manganese.

(Comparative Example 7)
First, Li ₂ CO ₃ , NiO, Co ₃ O ₄ , and MnO ₂ are mixed into one reaction tank so that Ni: Co: Mn = 8: 1: 1 and Li / (Ni + Co + Mn) has a molar ratio of 1.01. To prepare a slurry, which was fired at 900 ° C. for 5 hours.
Next, additional Li ₂ CO ₃ and simple sulfur are added to the mechanochemical apparatus so as to have a molar ratio of (Li ₂ CO ₃ to be additionally added) / S = 2 and S / (Ni + Co + Mn) = 0.001. After mixing, the temperature was raised at a rate of 3 ° C. per minute, held at 700 ° C. for 3 hours, and then slowly cooled to produce an active material.

(Evaluation)
-Evaluation of composition of positive electrode material-
The metal content in each positive electrode material was measured with an inductively coupled plasma optical emission spectrometer (ICP-OES), the composition ratio (molar ratio) of each metal was calculated, and the oxygen content was measured by the LECO method.

-XPS measurement-
XPS measurement of the cross-section SIM of the active material was performed under the following conditions to obtain a peak of S2p bond.
・ X-ray output: 15kV, 25W
・ Measurement area: 100μmφ
・ Extraction angle: 45 °
Bond energy axis correction: 284.6 eV which is a carbonic acid-derived peak on the C1s spectrum

-Evaluation of battery characteristics-
Each positive electrode material, conductive material, and binder are weighed in a ratio of 85: 8: 7, and the positive electrode material and the conductive material are mixed into a slurry in which the binder is dissolved in an organic solvent (N-methylpyrrolidone). And coated on an Al foil, dried and pressed to obtain a positive electrode. Subsequently, a 2032 type coin cell for evaluation with Li as the counter electrode was prepared, and 1M-LiPF ₆ dissolved in EC-DMC (1: 1) was used as the electrolyte, and the current density was 0.2C. The discharge capacity was measured. Moreover, the cycle characteristic when repeating 10 cycles charging / discharging with the thermostat kept in the range of 45-55 degreeC was measured.
These results are shown in Tables 1 and 2. In addition, S / (Ni + Co + Mn + M) in Tables 1 and 2 represents the molar ratio of the whole particles of the active material.

(Evaluation results)
In each of Examples 1 to 40, a sulfur-containing compound or a sulfur-containing ion is attached to the surface of the primary particle, and S / (Ni + Co + Mn + M) of the entire particle is 0.001 to 0.005 in terms of molar ratio. When XPS of the cross section SIM of the material was measured, a peak of S2p bond was present at 165 to 175 eV, and both the discharge capacity and the cycle characteristics were good.
In Comparative Examples 1, 2, and 7, the peak of S2p bond did not exist at 165 to 175 eV, and the cycle characteristics were poor.
In Comparative Example 3, since S / (Ni + Co + Mn + M) of the entire particle exceeded 0.005 in terms of molar ratio, the cycle characteristics were poor.
In Comparative Example 4, since the core contained Ti, the effect of stabilizing the structure was lost, and the cycle characteristics were poor.
In Comparative Example 5, the Ni composition was small, and the discharge capacity and cycle characteristics were poor.
In Comparative Example 6, the battery could not be produced because the positive electrode active material was gelled.

Claims (3)

Composition formula: Li _a Ni _b Co _c Mn _{d Me} O ₂
(In the above formula, 1.0 ≦ a ≦ 1.05, 0.5 ≦ b ≦ 0.9, 0.1 ≦ c ≦ 0.3, 0.1 ≦ d ≦ 0.3, 0 ≦ e ≦ 0 .005, b + c + d + e = 1, and M is at least one selected from the group consisting of Mg, Al, and Zr.)
Represented by
A sulfur-containing compound or a sulfur-containing ion is attached to the surface of the primary particle, and S / (Ni + Co + Mn + M) of the whole particle is 0.001 to 0.005 in molar ratio,
A positive electrode active material for a lithium ion battery having an S2p bond peak at 165 to 175 eV when XPS of a cross section SIM of the active material is measured.   The positive electrode for lithium ion batteries using the positive electrode active material for lithium ion batteries of Claim 1.   The lithium ion battery using the positive electrode for lithium ion batteries of Claim 2.