JP6369126B2 - Positive electrode active material powder for non-aqueous electrolyte secondary battery, method for producing the same, and non-aqueous electrolyte secondary battery - Google Patents

Description

  The present invention provides a positive electrode active material particle powder for a non-aqueous electrolyte secondary battery having a layered rock salt structure exhibiting high capacity and high cycle characteristics while using an inexpensive raw material, and a method for producing the same.

  In recent years, electronic devices such as AV devices and personal computers are rapidly becoming portable and cordless, and there is an increasing demand for secondary batteries having a small size, light weight, and high energy density as power sources for driving these devices. Under such circumstances, a lithium ion secondary battery having advantages such as a high charge / discharge voltage and a large charge / discharge capacity has attracted attention.

Conventionally, as a positive electrode active material useful for a high energy type lithium ion secondary battery having a voltage of 4 V class, spinel type structure LiMn ₂ O ₄ , rock salt type structure LiMnO ₂ , LiCoO ₂ , LiCo _1-X Ni _X O ₂ , LiNiO _2, etc. are generally known. Among them, LiCoO ₂ is excellent in that it has a high voltage and a high capacity, but there is a problem of high manufacturing cost due to a small supply amount of cobalt raw material. It includes environmental safety issues of waste batteries. Therefore, a ternary positive electrode active material particle powder having a layered rock salt structure that is a solid solution of Ni, Co, and Mn having a layered rock salt structure that can be used with excellent versatility (basic composition: Li (Ni _x Co _y Mn _z ) Research on O _2- and so on is the same.

  As is well known, the ternary positive electrode active material particle powder having a layered rock salt structure is prepared by mixing a Ni compound, a Co compound, a Mn compound, and a lithium compound in a predetermined ratio and firing at a temperature range of 700 to 1000 ° C. Can be obtained.

However, in this material, when lithium is extracted, Ni ²⁺ becomes Ni ^{3+ and} yarn teller distortion occurs, and when Li is extracted 0.45, from hexagonal to monoclinic, when further extracted, monoclinic to hexagonal And the crystal structure changes. Therefore, repeated charge / discharge reactions cause the crystal structure to become unstable, resulting in poor cycle characteristics, and reactions with the electrolyte solution due to oxygen release, etc., resulting in poor initial charge / discharge efficiency and storage characteristics of the battery. There is. The cause of this is that the crystal lattice expands and contracts due to the desorption / insertion behavior of lithium ions in the crystal structure with repeated charge and discharge, and the crystal structure becomes unstable.

  In a lithium ion secondary battery using ternary positive electrode active material particle powder, it is possible to suppress deterioration of charge / discharge capacity due to repeated charge / discharge, and to reduce or eliminate the amount of Co, but at a low cost. There is currently a strong demand for materials with high capacity and high stability.

  In order to achieve high capacity while being low cost, the amount of Co in the ternary positive electrode active material particle powder is reduced, the filling property is excellent, it has an appropriate size, and the crystal structure It has been considered important to suppress destabilization. As the means, a method of controlling the composition balance, particle diameter and particle size distribution of Ni, Co, and Mn compounds used in the ternary positive electrode active material particle powder, a method of obtaining a high crystal powder by controlling the firing temperature, A method for strengthening the bonding force of crystals by adding an element, a method for achieving the target by surface treatment, and the like are performed.

  Up to now, a ternary positive electrode active material particle powder having a small amount of Co and a material having Mg / Ca> 0.5 and a Ca amount of 150 ppm or less is known (Patent Document 1). Further, a material capable of increasing the capacity while being Co-less is known (Patent Document 2).

JP 2003-068306 A JP 2003-086183 A

  Currently, there is a demand for a low-cost and high-capacity material as a positive electrode active material for a non-aqueous electrolyte secondary battery. However, a material that satisfies the necessary and sufficient requirements and a method for manufacturing the same are still available. It is not done.

  In other words, Patent Document 1 only focuses on the added amounts of Mg and Ca, and the battery capacity is still insufficient when considered practically. Further, in Patent Document 2, although the Me element is composed of only Ni and Mn and is a Co-less material, there is a problem in the manufacturing method, the battery capacity is low, the stability is low, and high temperature cycle characteristics are also described. It was not practically enough.

  Therefore, in the present invention, the positive electrode active material particle powder for a non-aqueous electrolyte secondary battery that exhibits low cost, high capacity, high cycle characteristics, particularly high cycle characteristics even at high temperatures, a method for producing the same, and a non-aqueous electrolyte Providing a secondary battery is a technical issue.

  The technical problem can be achieved by the present invention as follows.

  That is, the present invention is a positive electrode active material particle powder having a layered rock salt structure and comprising a composite oxide containing at least Li, Ni, and Mn, and using the positive electrode active material particle powder for one electrode, A coin cell having a counter electrode of Li was assembled, and initial charge was performed up to 4.6 V in a 60 ° C. environment. The horizontal axis represents voltage, and the vertical axis represents dQ / dV which is a value obtained by differentiating the initial charge capacity with voltage. It is a positive electrode active material particle powder for nonaqueous electrolyte secondary batteries characterized by having a peak between 4.25 and 4.45 V when a graph (dQ / dV curve) is prepared (Invention 1).

  In the graph (dQ / dV curve) showing the dQ / dV which is a value obtained by differentiating the voltage on the horizontal axis and the initial charge capacity on the vertical axis, the present invention is 3.65 to 3.85V. The positive electrode active material particle powder for a non-aqueous electrolyte secondary battery according to the present invention 1, wherein the intensity ratio of the peak maximum value appearing between 4.25 and 4.45 V with respect to the peak maximum value appearing in (Invention 2).

  Further, the present invention is a composite oxidation containing at least Li, Ni, and Mn by mixing a hydroxide containing at least Ni and Mn and lithium carbonate and firing at 700 to 1000 ° C. in the atmosphere. This is a method for producing a positive electrode active material particle powder for a non-aqueous electrolyte secondary battery according to the present invention 1 (Invention 3).

  Moreover, this invention is a nonaqueous electrolyte secondary battery using the positive electrode active material particle powder for nonaqueous electrolyte secondary batteries of this invention 1 (this invention 4).

  The positive electrode active material particle powder for a nonaqueous electrolyte secondary battery according to the present invention is suitable as a positive electrode active material for a nonaqueous electrolyte secondary battery because it exhibits high capacity and high cycle characteristics.

  In addition, the method for producing a positive electrode active material particle powder for a non-aqueous electrolyte secondary battery according to the present invention can reduce the content of Co, and can use lithium carbonate, which is an inexpensive lithium raw material, thereby reducing raw material costs. Thus, it is possible to provide a positive electrode active material for a non-aqueous electrolyte secondary battery that exhibits excellent characteristics at a low cost.

It is the graph (dQ / dV curve) which showed dQ / dV which is the value which differentiated the voltage on the horizontal axis and the initial charge capacity by the voltage on the vertical axis.

  The configuration of the present invention will be described in more detail as follows.

  First, the positive electrode active material particle powder for a non-aqueous electrolyte secondary battery according to the present invention will be described.

  The positive electrode active material particle powder according to the present invention has a layered rock salt structure and is composed of a composite oxide containing at least Li, Ni, and Mn.

  The Li content of the positive electrode active material particle powder according to the present invention is preferably such that Li / (Ni + Co + Mn) is 0.98 to 1.07 in molar ratio. If the Li content is too small, cation mixing is likely to occur, and the characteristics deteriorate. Moreover, when there is too much Li content, a residual lithium content will increase and there exists a possibility of gelatinizing in the case of coating-izing. The Li content is more preferably Li / (Ni + Co + Mn) in a molar ratio of 1.00 to 1.04.

  The range of Ni content of the positive electrode active material particle powder according to the present invention is preferably such that Ni / (Ni + Co + Mn) is 0.2 to 0.8 in terms of molar ratio, and 0.3 to 0.7. More preferred.

  As for the range of the Mn content of the positive electrode active material particle powder according to the present invention, Mn / (Ni + Co + Mn) is preferably 0.1 to 0.4 in terms of molar ratio, and preferably 0.2 to 0.4. More preferred.

  In particular, the positive electrode active material particle powder according to the present invention is characterized by not containing Co or having a low Co content. The Co content is preferably a molar amount, and 0 ≦ Co / (Ni + Mn) ≦ 0.22. The present invention can reduce the amount of excess Li necessary to satisfy the electrical neutral condition of the compound by controlling the blending state of Ni and Mn while reducing the amount of Co. Believes that can be achieved. The Co content is more preferably 0.02 ≦ Co / (Ni + Mn) ≦ 0.20, and further preferably 0.05 ≦ Co / (Ni + Mn) ≦ 0.18. By containing a small amount of Co in the positive electrode active material particle powder, conductivity as particles can be improved. Therefore, characteristics such as rate characteristics and direct current resistance of a battery using the positive electrode active material particle powder of the present invention can be improved.

  Further, the positive electrode active material particle powder in the present invention contains metal elements such as Mg, Al, Ti, V, Fe, Ga, Sr, Y, Zr, Nb, Mo, Ru, In, Sn, Ta, W, and Bi. You may contain. By incorporating these metal elements into the positive electrode active material particle powder, the cycle characteristics and rate characteristics of the battery can be improved.

  Using the positive electrode active material particle powder of the present invention as one electrode and assembling a coin cell with Li as the counter electrode, initial charge is performed up to 4.6 V in a 60 ° C. environment, voltage is plotted on the horizontal axis, and initial charge is plotted on the vertical axis. When a graph (dQ / dV curve) showing dQ / dV, which is a value obtained by differentiating the capacity with voltage, is created, this graph means that the battery capacity appears in the voltage width where the peak exists. Therefore, in the dQ / dV curve of the above coin cell, the presence of a peak between 4.25 and 4.45V means that the positive electrode active material used is charged with the upper limit voltage of the battery up to 4.45V. This suggests that the material can have a higher capacity.

  In general, when the counter electrode is set to Li, a battery capacity with a cut-off voltage of 3.0 to 4.3 V is used, but by using the positive electrode active material in the present invention, the upper limit voltage is 4.45 V. It is conceivable that a battery using a next-generation positive electrode active material having a high capacity and excellent stability can be provided. It is considered that by increasing the upper limit voltage, the amount of positive electrode active material used for the battery can be reduced, and the cost of the battery can be reduced.

  In the dQ / dV curve in the present invention, no peak is observed between 4.25 and 4.45 V in the positive electrode active material particle powder having a general layered rock salt structure. Through various investigations, the present inventors have found a positive electrode active material particle powder material having a peak at 4.25 to 4.45 V, and not only reduced costs but also increased capacity.

  In the dQ / dV curve in the present invention, the intensity ratio of the peak maximum value appearing between 4.25 and 4.45 V to the peak maximum value appearing at 3.65 to 3.85 V is preferably 0.10 or more, More preferably, it is 0.15 or more, More preferably, it is 0.20 or more.

  Next, the manufacturing method of the secondary battery positive electrode active material particle powder for nonaqueous electrolyte which concerns on this invention is described.

  The secondary battery positive electrode active material particle powder for non-aqueous electrolyte according to the present invention uses a hydroxide containing at least Ni and Mn as a precursor, and the precursor and lithium carbonate are added in a predetermined ratio and mixed uniformly. And it can obtain by passing through 700 degreeC-1000 degreeC baking in air | atmosphere.

  The hydroxide containing at least Ni and Mn in the present invention can be obtained by a conventional method such as coprecipitation by a wet reaction.

  Further, by adding Co in the course of the wet reaction, a hydroxide of Ni, Co, and Mn can be obtained. As described above, the amount of Co at that time is preferably about 0 ≦ Co / (Ni + Mn) ≦ 0.22.

  In addition, other metal elements can be added in the course of the wet reaction. The added metal element may be present in the hydroxide particles or may be present at the outer edge of the hydroxide particles. Examples of the metal element that can be added include Mg, Al, Ti, V, Fe, Ga, Sr, Y, Zr, Nb, Mo, Ru, In, Sn, Ta, W, and Bi.

  In the present invention, it is important to use lithium carbonate as the Li source and perform the firing in the air. In general, the ternary particle powder having a high Ni content uses lithium hydroxide as the Li source and needs to be fired in a region where the oxygen concentration exceeds 80%. Since cheaper lithium carbonate can be used as the Li source and it is not necessary to use high-concentration oxygen during firing, the cost can be further reduced.

  Next, the positive electrode using the positive electrode active material which consists of the positive electrode active material particle powder for nonaqueous electrolyte secondary batteries which concerns on this invention is described.

  When manufacturing the positive electrode containing the positive electrode active material particle powder according to the present invention, a conductive agent and a binder are added and mixed according to a conventional method. As the conductive agent, acetylene black, carbon black, graphite and the like are preferable, and as the binder, polytetrafluoroethylene, polyvinylidene fluoride and the like are preferable.

  The secondary battery manufactured using the positive electrode containing the positive electrode active material particle powder which concerns on this invention is comprised from the said positive electrode, a negative electrode, and electrolyte.

  In the present invention, as the negative electrode active material, lithium metal, lithium / aluminum alloy, lithium / tin alloy, graphite, graphite or the like can be used.

  In addition to the combination of ethylene carbonate and diethyl carbonate, an organic solvent containing at least one of carbonates such as propylene carbonate and dimethyl carbonate and ethers such as dimethoxyethane can be used as the solvent for the electrolytic solution.

  Further, as the electrolyte, in addition to lithium hexafluorophosphate, at least one lithium salt such as lithium perchlorate and lithium tetrafluoroborate can be dissolved in the above solvent and used.

  The nonaqueous electrolyte secondary battery manufactured using the positive electrode containing the positive electrode active material particle powder according to the present invention has an initial discharge capacity of 170 mAh / g or more by an evaluation method described later.

  When the positive electrode active material particle powder according to the present invention is used, a high capacity can be expected because the Ni content is generally large. However, the positive electrode active material particle powder is reduced in the Co amount as in the present invention, and It is important that high capacity can be achieved even by using the manufacturing method according to the present invention.

  A typical embodiment of the present invention is as follows.

  The composition of the positive electrode active material particle powder was as follows. 0.2 g of a sample was heated and dissolved in 25 ml of a 20% hydrochloric acid solution, and after cooling, pure water was added to a 100 ml volumetric flask to prepare an adjustment solution. For measurement, ICAP [SPS- 4000 Seiko Denshi Kogyo Co., Ltd.] was used to quantitatively determine each element.

  The identification of the compound phase of the positive electrode active material particle powder is performed using an X-ray diffractometer [SmartLab Co., Ltd., manufactured by Rigaku Corporation] in the range of 2θ of 10 to 90 degrees and 0.8 degrees / min in increments of 0.02 degrees. Performed by step scan.

  About the positive electrode active material particle powder which concerns on this invention, battery evaluation was performed using the 2032 type | mold coin cell.

For coin cells for battery evaluation, 90% by weight of composite oxide as positive electrode active material powder, 3% by weight of acetylene black as a conductive material, 3% by weight of graphite, and polyvinylidene fluoride dissolved in N-methylpyrrolidone as a binder After mixing 4% by weight, it was applied to an Al metal foil and dried at 120 ° C. This sheet was punched out to 14 mmΦ, and then pressure-bonded at 1.5 t / cm ² was used as the positive electrode. A 2032 type coin cell was manufactured using a solution in which EC and DMC mixed with 1 mol / L LiPF ₆ dissolved in a volume ratio of 1: 2 were used as the negative electrode made of metallic lithium having a thickness of 500 μm punched to 16 mmΦ.

  The graph (dQ / dV curve) showing dQ / dV which is a value obtained by differentiating the voltage on the horizontal axis and the initial charge capacity on the vertical axis is 4 at 0.2 C in an environment of 60 ° C. The initial charge is performed at a charge density of 16 mA / g up to .6V, the voltage at that time is plotted on the horizontal axis, and dQ / dV, which is a value obtained by differentiating the initial charge capacity with the voltage, is plotted on the vertical axis. A graph in the range of 4.6V was created. FIG. 1 shows dQ / dV curves of Examples and Comparative Examples.

  With respect to the initial discharge capacity, the coin cell was charged under a CC-CV condition at a C rate of 0.2 C up to 4.3 V under an environment of 25 ° C. under a CC-CV condition, and rested for 5 minutes, and then at a C rate of 0.1 C. The discharge capacity of the first cycle discharged to 0V was used. Table 2 shows the initial discharge capacities of the examples and comparative examples.

  Regarding the 60 ° C. cycle characteristics, first, the above-mentioned coin cell was charged in an environment of 60 ° C. under a C rate condition of 0.2 C to 4.3 V (CC-CV condition), and after 5 minutes of rest, the discharge was reduced to 0. 0. It carried out to 3.0V on the C rate conditions of 2C. Under this condition, after 2 cycles of charge / discharge, charge was charged to 4.3V under 0.5C C rate condition (CC-CV condition), and after 5 minutes rest, the discharge was discharged at 1C C rate condition To 3.0V. Under these conditions, 70 cycles of charge / discharge were performed, and when the discharge capacity at the 70th cycle relative to the discharge capacity x at the 3rd cycle was y, the 60 ° C. cycle characteristics were (y / x) × 100%. Table 2 shows the 60 ° C. cycle characteristics of Examples and Comparative Examples.

Example 1 <Li _1.02 (Ni _0.6 Co _0.1 Mn _0.3 ) O ₂ Particle Powder>
Nickel sulfate, cobalt sulfate, and manganese sulfate were weighed so that each element had a molar ratio of Ni: Co: Mn = 6: 1: 3 and coprecipitated by a wet reaction. By washing with water and drying, (Ni _0.6 Co _0.1 Mn _0.3 ) (OH) ₂ particle powder (precursor) was obtained. The precursor and lithium carbonate were mixed in a mortar for 1 hour so that the molar ratio of Li / (Ni + Co + Mn) was 1.02, and a uniform mixture was obtained. Positive electrode active material particle powder in which 50 g of the obtained mixture is put in an alumina crucible and becomes Li _1.02 (Ni _0.6 Co _0.1 Mn _0.3 ) O ₂ by holding at 900 ° C. for 5 hours in an air atmosphere. Got.

  A coin-type battery was fabricated using the positive electrode active material particle powder obtained here. This coin-type battery had a peak in the range of 4.25 to 4.45 V in the dQ / dV curve described above. The intensity ratio of the maximum value of the peak appearing between 4.25 and 4.45 V to the maximum value of the peak appearing at 3.65 to 3.85 V was 0.29.

Reference Example 1 <Li _1.02 (Ni _0.67 Mn _0.33 ) O ₂ Particle Powder>
A hydroxide precursor was obtained in the same manner as in Example 1 except that nickel sulfate and manganese sulfate were changed to Ni: Mn67: 33 in the molar ratio of Ni element and Mn element. The precursor and lithium carbonate were mixed in a mortar for 1 hour so that the Li / (Ni + Mn) molar ratio was 1.02, and a uniform mixture was obtained. 50 g of the obtained mixture was put in an alumina crucible and held at 900 ° C. for 5 hours in an air atmosphere to obtain positive electrode active material particle powder that became Li _1.02 (Ni _0.67 Mn _0.33 ) O ₂ . Table 1 shows various characteristics of the obtained positive electrode active material particle powder.

Comparative Example 1 <Li _1.04 (Ni _0.5 Co _0.2 Mn _0.3 ) O ₂ Particle Powder>
A hydroxide precursor was obtained in the same manner as in Example 1 except that nickel sulfate, cobalt sulfate, and manganese sulfate were used at a molar ratio of each element of Ni: Co: Mn = 5: 2: 3. The precursor and lithium carbonate were mixed for 1 hour in a mortar so that the molar ratio of Li / (Ni + Co + Mn) was 1.04 to obtain a uniform mixture. Positive electrode active material particle powder that is put into Li _1.04 (Ni _0.5 Co _0.2 Mn _0.3 ) O ₂ by putting 50 g of the obtained mixture in an alumina crucible and holding at 920 ° C. for 5 hours in an air atmosphere. Got. Various characteristics of the obtained positive electrode active material particle powder are shown in Tables 1 and 2.

Comparative Example 2 <Li _1.05 (Ni _0.33 Co _0.33 Mn _0.33 ) O ₂ Particle Powder>
A hydroxide precursor was obtained in the same manner as in Example 1 except that nickel sulfate, cobalt sulfate, and manganese sulfate were used at a molar ratio of Ni: Co: Mn = 1: 1: 1. The precursor and lithium carbonate were mixed for 1 hour in a mortar so that the molar ratio of Li / (Ni + Co + Mn) was 1.05 to obtain a uniform mixture. Positive electrode active material particle powder that is put into Li _1.05 (Ni _0.33 Co _0.33 Mn _0.33 ) O ₂ by putting 50 g of the obtained mixture in an alumina crucible and holding at 950 ° C. for 5 hours in an air atmosphere. Got. Table 1 shows various characteristics of the obtained positive electrode active material particle powder.

Comparative Example _{3 <Li 1.00 (Ni 0.6 Co} 0.2 Mn 0.2) O 2 particles>
A hydroxide precursor was obtained in the same manner as in Example 1 except that nickel sulfate, cobalt sulfate, and manganese sulfate were used at a molar ratio of each element of Ni: Co: Mn = 6: 2: 2. The precursor and lithium carbonate were mixed for 1 hour in a mortar so that the molar ratio of Li / (Ni + Co + Mn) was 1.00 to obtain a uniform mixture. The resultant mixture 50g placed in an alumina crucible, 930 ° C. in an air atmosphere, the positive electrode active material particles forming _{Li 1.00 (Ni 0.6 Co 0.2 Mn} 0.2) O 2 by 5 hours Got. Table 1 shows various characteristics of the obtained positive electrode active material particle powder.

  The positive electrode active material particle powder for a non-aqueous electrolyte secondary battery according to the present invention was able to reduce the cost by reducing Co while having a high capacity when used as a battery, so that the positive electrode for a non-aqueous electrolyte secondary battery Suitable as an active material.

Claims (4)

A positive electrode active material particle powder comprising a composite oxide having a layered rock salt structure and containing at least the following molar ratios of Li, Ni, Mn, and Co, the positive electrode active material particle powder being one electrode In this example, a coin cell having a counter electrode of Li is assembled, and an initial charge is performed up to 4.6 V in a 60 ° C. environment. The horizontal axis represents the voltage, and the vertical axis represents the value obtained by differentiating the initial charge capacity by the voltage dQ / dV. A positive electrode active material particle powder for a non-aqueous electrolyte secondary battery, having a peak between 4.25 and 4.45 V when a graph (dQ / dV curve) showing is shown.
Li / (Ni + Co + Mn): 1.00 to 1.04
Ni / (Ni + Co + Mn): 0.3 to 0.7
Mn / (Ni + Co + Mn): 0.2 to 0.4
Co / (Ni + Co + Mn): 0.05 to 0.18 The maximum value of the peak appearing at 3.65 to 3.85 V in the graph (dQ / dV curve) showing dQ / dV which is a value obtained by differentiating the voltage on the horizontal axis and the initial charge capacity on the vertical axis. The positive electrode active material particle powder for nonaqueous electrolyte secondary batteries according to claim 1, wherein the intensity ratio of the maximum value of the peak appearing between 4.25 and 4.45 V relative to is 0.10 or more. It is characterized in that a hydroxide containing at least Ni and Mn and lithium carbonate are mixed and fired at 700 to 1000 ° C. in the atmosphere to obtain a composite oxide containing at least Li, Ni and Mn. The manufacturing method of the positive electrode active material particle powder for nonaqueous electrolyte secondary batteries of Claim 1. The nonaqueous electrolyte secondary battery using the positive electrode active material particle powder for nonaqueous electrolyte secondary batteries of Claim 1.

Images