CN111129481B - Method for preparing positive electrode active material for lithium ion battery - Google Patents

Method for preparing positive electrode active material for lithium ion battery Download PDF

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CN111129481B
CN111129481B CN201811653531.5A CN201811653531A CN111129481B CN 111129481 B CN111129481 B CN 111129481B CN 201811653531 A CN201811653531 A CN 201811653531A CN 111129481 B CN111129481 B CN 111129481B
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oxide
aqueous solution
positive electrode
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CN111129481A (en
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曾海生
苏迎春
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Tianjin Guoan MGL New Materials Technology Co Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

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  • Chemical Kinetics & Catalysis (AREA)
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  • Manufacturing & Machinery (AREA)
  • Battery Electrode And Active Subsutance (AREA)

Abstract

The invention discloses a preparation method of a positive active material for a lithium ion battery, wherein the positive active material comprises Li in a formula (I)xNiaMnbMecO4‑yAzIn the formula (I), x is more than or equal to 0.9 and less than or equal to 1.1, y is more than or equal to 0 and less than or equal to 0.3, z is more than or equal to 0 and less than or equal to 0.3, a is more than or equal to 0.35 and less than or equal to 0.5, b is more than or equal to 1.3 and less than or equal to 1.6, c is more than or equal to 0 and less than or equal to 0.3, Me is selected from at least one of metal elements, and A is selected from at least one of non-metal elements. According to the invention, Ni and Mn in the NiMn spinel oxide are replaced by other elements to obtain a crystal structure containing space group Fd-3m and not containing space group P4332, the dissolution of manganese ions in the electrolyte of the positive electrode active material containing the oxide (1) is reduced. A lithium ion secondary battery containing the positive electrode active material has a high discharge voltage and good cycle characteristics.

Description

Method for preparing positive electrode active material for lithium ion battery
Technical Field
The invention belongs to the field of electrochemical energy storage devices and new energy materials, and particularly relates to a positive electrode active substance for a lithium ion battery, a positive electrode containing the positive electrode active substance for the lithium ion battery, and the lithium ion battery containing the positive electrode.
Background
LiNi0.5Mn1.5O4Spinel type oxides (hereinafter also referred to as NiMn spinel oxides) have received great attention as positive electrode active materials for lithium ion batteries, and the use of NiMn spinel oxides increases the average discharge voltage of lithium ion batteries to more than 4.5V, thereby increasing the energy density of lithium ion batteries and contributing to the improvement of the specific capacity thereof.
However, in the electrolyte solution used in the lithium ion battery, since manganese ions of the NiMn spinel oxide are easily dissolved and precipitated, the cycle characteristics of the lithium ion battery using the NiMn spinel oxide as the positive electrode active material are gradually degraded.
Some patents have described modification measures of NiMn spinel oxide, but the cycle characteristics of the lithium ion battery are still insufficient and need to be improved.
Disclosure of Invention
In order to overcome the above problems, the present inventors have conducted intensive studies and, as a result, found that: replacing Ni, Mn or oxygen in the NiMn spinel oxide with other elements to obtain the NiMn spinel oxide which has a crystal structure of a space group Fd-3m and does not contain the space group P4332, and the dissolution of manganese ions in the electrolyte of the positive electrode active material containing the oxide is reduced, and the lithium ion secondary battery containing the positive electrode active material has a high discharge voltage and good cycle characteristics, thereby completing the present invention.
An object of the present invention is to provide a positive electrode active material for a lithium ion battery, which is composed of an oxide (1) represented by the formula (I),
LixNiaMnbMecO4-yAz (I)，
in the formula (I), x is more than or equal to 0.9 and less than or equal to 1.1, y is more than or equal to 0 and less than or equal to 0.3, z is more than or equal to 0 and less than or equal to 0.3, a is more than or equal to 0.35 and less than or equal to 0.5, b is more than or equal to 1.3 and less than or equal to 1.6, c is more than or equal to 0 and less than or equal to 0.3,
me is selected from at least one of metal elements, and A is selected from at least one of non-metal elements.
In the formula (I), a + b + c is 2,
me is at least one element selected from Mg, Ti, Al, Fe, Co, Zr, Zn and Cr,
a is at least one element selected from F, P, S and Cl.
Wherein the oxide (1) represented by the formula (I) has a crystal structure of a space group Fd-3m and does not have a space group P4332.
D of the oxide (1)501 to 30 μm; the specific surface area of the oxide (1) is 0.1-5 m2/g。
The positive electrode active material further includes a compound (2) on the surface of the oxide (1),
the compound (2) contains one or more compounds of metallic and/or non-metallic elements, preferably at least one element selected from Al, Si, Ti, Zr, Mg, Ca, B, Sb, Bi, Na and Li, more preferably at least one or more metal elements selected from Al, Ti and Zr,
the compound (2) contains one or more of metal and/or nonmetal elements, preferably at least one element of Al, Si, Ti, Zr, Mg, Ca, B, Sb, Bi, Na and Li,
the compound (2) is selected from one or more of oxides, sulfates, phosphates, carbonates containing metallic elements and/or non-metallic elements, preferably an oxide.
The ratio of the sum of the molar amounts of the metal element and/or the nonmetal element in the compound (2) to the molar amount of the oxide (1) is (0.005-0.05): 1.
Another aspect of the present invention provides a method for preparing the positive electrode active material of the first aspect, including the steps of:
step 1, preparing a precursor containing Ni, Mn and Me;
step 2, mixing the precursor in the step 1 with a lithium-containing compound, and carrying out heat treatment;
optionally, further comprising step 3: and (3) coating the product obtained in the step (2) by using a compound (2).
Wherein, in the step 2, the heat treatment temperature is 600-1100 ℃, and the heat treatment time is 10-40 h.
In the step 3, heat treatment is carried out during coating, wherein the heat treatment temperature is 200-600 ℃, and the heat treatment time is 3-15 h.
A third aspect of the invention provides a positive electrode comprising the positive electrode active material according to the first aspect of the invention.
A fourth aspect of the invention provides a lithium ion battery comprising the positive electrode according to the third aspect of the invention.
The invention has the following beneficial effects:
(1) the invention adopts other metal elements to replace Ni and Mn in the NiMn spinel oxide and carries out heat treatment at a certain temperature, and the obtained NiMn spinel oxide has the crystal structure of a space group Fd-3m and does not have the space group P4332, which has an XRD pattern having characteristic peaks at around 18.8 °, 36.4 ° and 44.3 ° 2 θ and no characteristic peak at around 15.3 ° 2 θ, and a lithium ion secondary battery prepared from the oxide as a positive electrode active material has good cycle characteristics, and has a low dissolution ratio of Ni and Mn, for example, a cycle retention ratio of 50 cycles of the lithium secondary battery at 25 ℃, 3.0 to 4.9V is higher than 97%, even higher than 97.8, and can reach 99.1%, and the dissolution ratios of Mn and Ni are respectively lower than 1.2% and 1.1%, for example, 1.16% and 1.04%, respectively;
(2) the present invention is a crystal structure containing space group Fd-3m, and does not contain space group P4332, the dissolution ratios of Ni and Mn are reduced during charge and discharge cycles of the lithium ion secondary battery, for example, the dissolution ratios of Mn and Ni are respectively lower than 1.2% and 1.1%, even respectively lower than 1.16% and 1.04%, and can be respectively as low as 0.78% and 0.65%, and the cycle characteristics of the lithium ion secondary battery are good;
(3) the positive electrode active material for the lithium ion battery is applied to the lithium ion secondary battery, and the obtained lithium ion secondary battery has the advantages of high discharge voltage (for example, the discharge voltage is more than 4.5V and even reaches 4.7V) and good cycle characteristic;
(4) the preparation method of the anode active substance has simple process and easily obtained raw materials, and is suitable for industrial large-scale production.
Drawings
FIG. 1 shows XRD patterns of positive electrode active materials prepared in examples 1 to 4 of the present invention and comparative examples 1 to 2;
fig. 2 shows an XRD pattern of the positive electrode active material prepared in example 5 of the present invention;
fig. 3 shows an XRD pattern of the positive electrode active material prepared in example 6 of the present invention;
fig. 4 shows an XRD pattern of the positive electrode active material prepared in example 7 of the present invention;
fig. 5 shows an XRD pattern of the positive electrode active material prepared in example 8 of the present invention;
fig. 6 shows an XRD pattern of the positive electrode active material prepared in example 9 of the present invention;
fig. 7 shows an XRD pattern of the positive electrode active material prepared in example 10 of the present invention;
fig. 8 shows an XRD pattern of the positive electrode active material prepared in example 11 of the present invention;
FIG. 9 shows LiNi having a space group Fd-3m crystal structure0.5Mn1.5O4The XRD standard curve of (1);
FIG. 10 shows a space group P43LiNi of 32 crystal structure0.5Mn1.5O4The XRD standard curve of (1);
fig. 11 shows an SEM image of the positive electrode active material prepared in example 1;
fig. 12 shows an SEM image of the positive electrode active material prepared in example 2;
FIG. 13 is a graph showing the first discharge capacity of lithium ion secondary batteries produced from the positive electrode active materials obtained in examples 1 to 4 of the present invention and comparative examples 1 to 2, and a partial enlarged view thereof.
Detailed Description
The invention is explained in more detail below with reference to the drawings and preferred embodiments. The features and advantages of the present invention will become more apparent from the description.
According to one aspect of the present invention, there is provided a positive electrode active material for a lithium ion battery, comprising an oxide (1) represented by formula (I),
LixNiaMnbMecO4-yAz (I)，
according to the present invention, in formula (I), 0.9. ltoreq. x.ltoreq.1.1, where x is in this range, the discharge capacity and cycle characteristics of a lithium ion battery produced from the positive electrode active material are high, preferably, 0.93. ltoreq. x.ltoreq.1.07, more preferably, 0.95. ltoreq. x.ltoreq.1.05.
According to the present invention, in formula (I), y is 0. ltoreq. y.ltoreq.0.3, and y is in this range, the energy density of the lithium ion battery produced from the positive electrode active material is high, and preferably, y is 0. ltoreq. y.ltoreq.0.2.
According to the present invention, in formula (I), z is 0. ltoreq. z.ltoreq.0.3, and z is in the range, the cycle characteristics of the lithium ion battery produced from the positive electrode active material are high, preferably, 0. ltoreq. z.ltoreq.0.2,
according to the present invention, in formula (I), 0.35. ltoreq. a.ltoreq.0.5, and a is in this range, the energy density of the lithium ion battery is high, preferably 0.45. ltoreq. a.ltoreq.0.5, more preferably 0.475. ltoreq. a.ltoreq.0.5.
According to the invention, in the formula (I), b is more than or equal to 1.3 and less than or equal to 1.6, and if b is in the range, the cycle characteristic of the lithium ion battery is high. Preferably, 1.45. ltoreq. b.ltoreq.1.55, more preferably, 1.455. ltoreq. b.ltoreq.1.498.
According to the invention, in formula (I), c is greater than or equal to 0 and less than or equal to 0.3. When c is within this range, the cycle characteristics of the lithium ion battery are high. Preferably 0 < c.ltoreq.0.3, more preferably 0.005. ltoreq.c.ltoreq.0.05, still more preferably 0.01. ltoreq.c.ltoreq.0.03.
According to the invention, in formula (I), a + b + c is 2.
In the present invention, as can be seen from formula (I), in the oxide (1), a part of Ni and Mn is substituted by Me.
According to the present invention, in formula (I), Me is selected from at least one of metal elements, preferably, Me is selected from at least 1 or more of Mg, Ti, Al, Fe, Co, Zr, Zn and Cr, and part of Ni and Mn in oxide (1) is replaced by Me, so that the crystal structure of oxide (1) is stabilized, dissolution of manganese ions in oxide (1) is suppressed, and Me is preferably selected from at least 1 or more of Mg, Ti, Al, Fe and Zr for further improving the stability of the crystal structure of oxide (1). For example, Me may be a combination of Mg and Ti, or a combination of Fe and Ti, or Fe alone, or Zr alone, or Al alone, or Ti alone. More preferably, Me is a combination of Mg and Ti, or a combination of Fe and Ti.
In the present invention, as can be seen from the formula (I), in the oxide (1), a part of oxygen is replaced with A.
According to the invention, in formula (I), A is chosen from at least one of the non-metallic elements, preferably at least 1 element chosen from F, P, S and Cl.
In the present invention, in the oxide (1), impurity elements (e.g., metal elements such as Zn, Fe, Ca, K, Na, etc. or some non-metal elements, etc. in the order of ppm or ppb) which are inevitably mixed in the production may be present in the oxide (1) within a range not to impair the effects of the present invention.
According to the present invention, the oxide (1) represented by the formula (I) has a crystal structure containing a space group Fd-3m and does not contain a space group P4332.
In the spinel crystal structure, Ni and Mn are regularly arranged as a space group P4332 crystal structure, Ni and Mn are randomly arranged to form a space group Fd-3m crystal structure. An oxide (I) represented by the formula (I), which has a crystal structure of a space group Fd-3m and does not contain a space group P43The crystal structure of 32 results in less dissolution and precipitation of manganese ions in the oxide (1). Thus, the lithium ion battery containing the oxide (1) has good cycle characteristics.
In the present invention, the crystal structure of the space group Fd-3m of the oxide (1) was confirmed by XRD pattern to have peaks at around 2 θ of 18.8 °, 36.4 ° and 44.3 °, and no peak at around 2 θ of 15.3 °. Among them, peaks near 18.8 °, 36.4 ° and 44.3 ° are characteristic peaks of the spinel-type crystal structure of the NiMn spinel oxide.
Space group P43The crystal structure of 32 appears in the XRD pattern as: there are peaks near 18.8 °, 36.4 ° and 44.3 ° for 2 θ, and peaks near 15.3 ° for 2 θ.
In the present invention, the primary particles are particles considered to be elementary particles (ultraparticles) as judged from the apparent geometric shape. The secondary particles are formed by aggregating a plurality of primary particles. The shape of the primary particles and the secondary particles is not particularly limited, and is spherical, acicular, plate-like, or the like.
According to the present invention, the oxide (1) is preferably a secondary particle sphere in which a plurality of primary particles are agglomerated as shown in SEM fig. 11 and 12. Secondary particle balls D of oxide (1)501 to 30 μm, D of secondary particle spheres of oxide (1)50Within this range, the packing density of the positive electrode active material in the lithium ion battery is high, preferably, D 503 to 20 μm, more preferably, D 505 to 10 μm.
In the present invention, D50The median diameter refers to a particle diameter corresponding to 50% of the total of fine particles in a volume-based particle size distribution measured by a particle size distribution measurement by a general laser diffraction-light scattering method, and is also referred to as an average particle diameter.
According to the invention, the specific surface area of the oxide (1) is 0.1 to 5m2/g。
The inventors have found that the specific surface area of the oxide (1) is less than 0.1m2(g) the lithium ion battery containing the oxide (1) has a low discharge capacity and a specific surface area of more than 0.1m2(iv) a high discharge capacity; if the specific surface area of the oxide is greater than 5m2(g), the lithium ion battery containing the oxide (1) has low cycle characteristics, and conversely, the specific surface area is less than 5m2(g), high cycle performance.
Preferably, the specific surface area of the oxide (1) is 0.2 to 2m2A more preferable range is 0.5 to 2 m/g2/g。
In the present invention, the oxide (1) itself or the oxide (1) having the compound (2) present on the surface thereof can be used as the positive electrode active material.
The present inventors have found that when a positive electrode active material obtained from an oxide (1) having a compound (2) present on the surface thereof is applied to a lithium ion battery, dissolution and precipitation of manganese ions in the oxide (1) can be suppressed, and the cycle characteristics of the lithium ion battery can be improved.
According to the present invention, the positive electrode active material further includes a compound (2) on the surface of the oxide (1).
According to the present invention, the compound (2) is coated on the surface of the oxide (1) to form a positive electrode active material.
According to the invention, the compound (2) comprises at least one of metallic and/or non-metallic elements, preferably at least one or more of Al, Si, Ti, Zr, Mg, Ca, B, Sb, Bi, Na and Li.
According to the present invention, the compound (2) is at least one selected from the group consisting of oxides, hydroxides, sulfates, phosphates, carbonates, and nitrates containing a metal element and/or a non-metal element, preferably an oxide, and more preferably an oxide containing a metal element.
According to the invention, the compound 2 is chosen from the group comprising aluminium oxide, lithium aluminate (LiAlO)2) At least one of silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, bismuth oxide, sodium sulfate, calcium sulfate, magnesium sulfate, aluminum phosphate, lithium phosphate, calcium carbonate, and magnesium carbonate.
According to a preferred embodiment of the present invention, the compound (2) contains at least 1 or more metal elements selected from Al, Ti and Zr.
The present inventors have found that the presence of the compound (2) containing at least 1 or more metal elements of Al, Ti and Zr causes the compound (2) to coat the oxide (1), and thus dissolution and precipitation of manganese ions in the oxide (1) in the electrolyte solution are further reduced, and the cycle characteristics of a lithium ion battery containing the positive electrode active material are further improved.
According to a particularly preferred embodiment of the invention, compound (2) is an Al-containing compound, preferably an aluminum-containing oxide, more preferably one or a mixture of two of alumina and lithium aluminate, for example compound (2) is a mixture of alumina and lithium aluminate.
(method for producing Positive electrode active Material)
Another aspect of the present invention provides a method for preparing the positive electrode active material according to the first aspect of the present invention, the method comprising the steps of:
step 1, preparing a precursor containing Ni and Mn, preferably Me and/or A elements;
according to the invention, in step 1, a precursor containing Ni, Mn, preferably also containing, preferably also Me and/or a elements, can be prepared by process (a) or process (B):
(A) the method comprises the following steps Preparing a Ni and Mn coprecipitation product by a coprecipitation method, and doping Me and/or A elements in the coprecipitation product to obtain a precursor containing Ni, Mn and Me, Ni, Mn and A or Ni, Mn, Me and A elements.
(B) The method comprises the following steps The precursor of the coprecipitation product containing Ni, Mn and Me, Ni, Mn and A or Ni, Mn, Me and A is directly prepared by a coprecipitation method.
The invention adopts a coprecipitation method, preferably an alkaline coprecipitation method or a carbonate coprecipitation method, more preferably an alkaline coprecipitation method to prepare a coprecipitation product, and the obtained lithium ion battery has good cycle characteristics.
In the present invention, the basic coprecipitation method is a method in which an aqueous solution containing metal salts of Ni and Mn and a pH adjuster containing strong basicity are continuously added to a reaction vessel and mixed, the pH in the reaction solution is kept constant, and a coprecipitation product containing Ni and Mn is precipitated.
According to the present invention, the mixing of the aqueous solution of a metal salt containing Ni and Mn with the pH adjuster is carried out in a nitrogen atmosphere or an argon atmosphere in order to suppress oxidation of a coprecipitation product; in order to reduce the cost, it is preferable to carry out the reaction under a nitrogen atmosphere.
According to the invention, in the alkaline coprecipitation method, the metal salt containing Ni and Mn can be nitrate, acetate, halide salt or sulfate of Ni or Mn. In view of the low material cost, it is preferable to use a sulfate of Ni or Mn.
According to the invention, the sulfate of Ni can be used in various aqueous compounds of nickel (II) sulfate; as the sulfate of Mn, various aqueous compounds of manganese (II) sulfate can be used.
According to the invention, in the alkaline coprecipitation method, the pH of the reaction solution is 10-12.
According to the invention, the pH regulator is an aqueous solution of at least 1 selected from the group consisting of sodium hydroxide, potassium hydroxide and lithium hydroxide, preferably an aqueous sodium hydroxide solution.
According to the present invention, an aqueous ammonia solution or an aqueous ammonium sulfate solution may be added to the reaction solution in the basic coprecipitation method to adjust the solubility of Ni and Mn.
In the present invention, the carbonate coprecipitation method is a method in which an aqueous solution containing a metal salt of Ni and Mn and an aqueous solution of a carbonate containing a basic metal are continuously added to a reaction vessel and mixed, and a coprecipitation product containing Ni and Mn is precipitated in the reaction solution.
According to the present invention, in the carbonate coprecipitation method, a nitrate, an acetate, a halide salt or a sulfate of Ni or Mn may be used as the metal salt containing Ni and Mn. In view of the low material cost, it is preferable to use a sulfate of Ni or Mn. More preferably, the sulfate of Ni may employ various aqueous compounds of nickel (II) sulfate; as the sulfate of Mn, various aqueous compounds of manganese (II) sulfate can be used.
According to the invention, in the carbonate coprecipitation method, the pH of the reaction solution is 7-9.
According to the present invention, the aqueous carbonate solution is selected from an aqueous solution of at least one of sodium carbonate, sodium bicarbonate, potassium carbonate, and potassium bicarbonate.
In the reaction solution in the carbonate coprecipitation method, an aqueous ammonia solution or an aqueous ammonium sulfate solution may be added to adjust the solubility of Ni and Mn.
And filtering or centrifugally separating the reaction solution containing the coprecipitation product, and recovering the coprecipitation product. Wherein the filtration is pressure filtration, reduced pressure filtration or press filtration, and the centrifugation is preferably centrifugal dehydration.
According to the present invention, the obtained coprecipitation product can be washed to remove impurity ions (or impurity ions). The washing method may employ repeated pressure filtration and dissolution of distilled water for washing.
According to the invention, the conductivity of the supernatant clear liquid or filtrate obtained by dispersing the coprecipitation product in distilled water during the washing operation is 50mS/m or less, preferably 20mS/m or less.
According to the present invention, the coprecipitation product is washed and then dried.
The inventor finds that the drying temperature is less than 60 ℃, the drying time is longer, the drying temperature is more than or equal to 60 ℃, and the drying time can be shortened; the drying temperature is higher than 200 ℃, the coprecipitation generating substance can be subjected to oxidation reaction, and the drying temperature is lower than 200 ℃, so that the oxidation reaction of the coprecipitation generating substance can be inhibited. The drying time is appropriately set according to the amount of the coprecipitation product.
According to the invention, the drying temperature is 60-200 ℃, preferably, the drying temperature is 80-130 ℃; and/or the drying time is 1-300 h, preferably 5-120 h.
According to the invention, D of the substance formed is coprecipitated501 to 30 μm, and coprecipitating D50Within this range, D of the oxide (1) obtained by coprecipitation of the product substance50More suitably, and preferably, D of the co-precipitated product species50Is 3 to 20 μm, and more preferably 5 to 10 μm.
According to the invention, the specific surface area of the coprecipitation product is 10-100 m2The range of/g is more suitable. When the specific surface area of the coprecipitation product is within this range, the specific surface area of the oxide (1) obtained by coprecipitation of the product can be controlled within a suitable range. Preferably, the specific surface area of the coprecipitation product is 20-60 m2/g。
In the method (a), the method of doping Me and/or a element in the coprecipitation product to obtain the precursor is to mix the coprecipitation product with an aqueous solution containing Me or a doping element in a contact manner, and then dry the mixture.
According to the present invention, Me is selected from at least one of Mg, Ti, Al, Fe, Co, Zr, Zn and Cr, preferably from at least one of Mg, Ti, Al, Fe and Zr, and the aqueous solution for doping with Mg may be an aqueous solution of a Mg salt (e.g., an aqueous magnesium nitrate compound); the aqueous solution containing Ti doping may be an aqueous solution of a water-soluble titanium compound (titanate, etc.); as the aqueous solution containing Al, an aqueous solution of an Al salt (e.g., aluminum lactate); the aqueous solution for doping with Fe may be an aqueous solution of Fe salt (e.g., an aqueous compound of iron (III) nitrate); as the aqueous solution for doping Zr, an aqueous solution of a Zr salt (e.g., ammonium zirconium carbonate) can be used.
According to the present invention, when A is at least one element selected from the group consisting of F, P, S and Cl, preferably at least one element selected from the group consisting of F and P, the aqueous solution containing F for doping may be an aqueous solution of ammonium fluoride salt; the aqueous solution for doping P may be an aqueous solution of phosphoric acid or ammonium phosphate; as the aqueous solution for S doping, an aqueous solution of sulfuric acid or an ammonium sulfate salt can be used.
According to the present invention, the contact mixing method of the aqueous solution for doping with Me or a element and the coprecipitation product may be a method of spraying the aqueous solution for doping with Me or a element onto the coprecipitation product, a method of impregnating the coprecipitation product into the aqueous solution for doping with Me or a element, or the like.
According to the invention, in the method (A), when drying is carried out, the drying temperature is lower than 50 ℃, the drying time is longer, the drying temperature is more than or equal to 50 ℃, and the drying time can be shortened; the drying temperature is higher than 200 ℃, the precursor can be subjected to oxidation reaction, and the drying temperature is lower than 200 ℃, so that the oxidation reaction of the precursor can be inhibited. The drying time is appropriately set according to the amount of the coprecipitation product.
According to the invention, the drying temperature is 50-200 ℃, preferably 60-150 ℃, and more preferably 70-90 ℃; and/or the drying time is 2-10 h, preferably 3-6 ℃.
In the invention, the precursor containing Ni, Mn and Me, Ni, Mn and A or Ni, Mn, Me and A is obtained in step 1.
And 2, mixing the precursor in the step 1 with a lithium-containing compound, and carrying out heat treatment.
According to the invention, in step 2, the precursor obtained in step 1 is mixed with a lithium-containing compound and heat treated (or sintered) to obtain the oxide (1).
According to the invention, in the step 2, the lithium-containing compound is one or more selected from lithium carbonate, lithium hydroxide, lithium acetate and lithium nitrate, and lithium carbonate is preferred in consideration of the cost and the effect.
According to the invention, in the step 2, the mixing mode is one or more mixing modes commonly used in the field, such as inclined mixing, pear knife mixing and alligator mixing.
In the present invention, in step 2, the mixing ratio of the precursor and the lithium-containing compound in step 1 is appropriately set according to the composition of the oxide (1).
According to the present invention, in step 2, the ratio of the number of moles of lithium element in the lithium-containing compound to the sum of the number of moles of metal in the precursor is 0.45 to 0.55, preferably 0.5.
In the step 2, the precursor and the lithium-containing compound are uniformly mixed and then subjected to heat treatment (or sintering) to obtain the oxide (1) with good crystallinity.
According to the invention, in the step 2, the temperature of the heat treatment is 600-1100 ℃, preferably 700-1000 ℃, and more preferably 800-900 ℃; and/or
The heat treatment time is 10-40 h, preferably 15-25 h.
According to the present invention, an electric furnace, a continuous heating furnace, a continuous rolling heating furnace, or the like can be used as the heat treatment apparatus.
According to the present invention, the precursor is oxidized at the time of heat treatment, and heat treatment is preferably performed in an air atmosphere, and more preferably ventilation air.
The spinel crystal structure contains oxygen defects, and in order to reduce the oxygen defects, the conventional solution is to convert 3-valent manganese ions into 4-valent manganese ions and subject the oxides to a secondary heating treatment.
The present invention is characterized in that the oxide obtained by the primary heat treatment is used as it is without performing a secondary heat treatment (temperature range: 650 to 750 ℃) of the oxide. Thus, a crystal structure containing space group Fd-3m, not containing space group P4, was obtained332 (1) in a crystal structure. The oxide obtained by the secondary heat treatment has space group P4332.
Optionally, further comprising step 3: and (3) coating the product obtained in the step (2).
According to the invention, in the step 3, the method for coating the product obtained in the step 2 comprises the following steps: the aqueous coating solution containing the metal element of the compound (2) is mixed with the oxide (1) in contact therewith, and then subjected to heat treatment.
According to the present invention, the aqueous coating solution contains at least one element selected from the group consisting of Al, Si, Ti, Zr, Mg, Ca, B, Sb, Bi, Na and Li, and preferably contains at least 1 or more metal elements selected from the group consisting of Al, Ti and Zr. For example, the aqueous solution containing Ti to be doped may be an aqueous solution of a water-soluble titanium compound (e.g., titanate, etc.); as the aqueous solution containing Al, an aqueous solution of an Al salt (e.g., aluminum lactate); as the aqueous solution for doping Zr, an aqueous solution of a Zr salt (e.g., ammonium zirconium carbonate) can be used.
According to the invention, in step 3, the pH of the aqueous solution for coating is 3-12. When the pH of the aqueous coating solution is within this range, the surface of the oxide (1) is not corroded and the crystal structure is not destroyed, and the pH of the aqueous coating solution is preferably 5 to 9.
According to the present invention, in step 3, the method of contacting the aqueous coating solution with the oxide (1) may be a method of spraying the aqueous coating solution onto the oxide (1) or a method of impregnating the oxide (1) with the aqueous coating solution.
The inventor finds that in the step 3, the heat treatment temperature is lower than 200 ℃, the heat treatment time is longer, and the heat treatment temperature is higher than 200 ℃, so that the heat treatment time can be shortened; the heat treatment temperature is higher than 600 ℃, the oxide (1) may be oxidized or the crystal structure may be changed, and the heat treatment temperature is lower than 600 ℃, so that the oxidation or the crystal structure change of the oxide (1) can be suppressed. The time of the heat treatment can be appropriately set according to the amount of the oxide (1).
According to the invention, in the step 3, the heat treatment temperature is 200-600 ℃, preferably 350-500 ℃; and/or
The heat treatment time is 3-15 h, preferably 5-10 h.
In the present invention, the product obtained by the production method of the second aspect of the present invention is a positive electrode active material containing the oxide (1) represented by the formula (I), and a positive electrode active material having a good discharge voltage can be obtained from the positive electrode active materialA lithium ion battery wherein the oxide (1) has a crystal structure of a space group Fd-3m and does not contain a space group P4332, the manganese ions are less dissolved and precipitated. Further, the cycle characteristics of a lithium ion battery containing the positive electrode active material are improved.
In order to further improve the cycle characteristics of the lithium ion battery, the compound (2) is coated on the whole or part of the surface of the oxide (1) to obtain a positive electrode active substance, and the dissolution and precipitation of manganese ions in the lithium ion battery electrolyte prepared from the positive electrode active substance are further reduced. Therefore, the cycle characteristics of the lithium ion battery containing the positive electrode active material are further improved, and the cycle characteristics are good.
The present inventors have found that P4 is a space group3The surface of the general type NiMn spinel oxide having a crystal structure of 32 was not improved in the cycle characteristics of the lithium ion battery even when the compound (2) was coated.
< Positive electrode for lithium ion Battery >
A third aspect of the present invention provides a positive electrode for a lithium ion battery, which contains the positive electrode active material prepared by the method of the first aspect of the present invention or the second aspect of the present invention, a conductive agent, and a binder, forming a layer on a positive electrode current collector.
According to the present invention, the conductive agent is a carbon material, preferably at least one selected from carbon black, graphite, vapor-grown carbon fiber, and carbon nanotube.
According to the present invention, the binder is at least one selected from the group consisting of fluorine-containing resins, polyolefins, unsaturated hydrocarbon polymers and the like.
According to the present invention, an aluminum foil, a stainless steel foil, or the like can be used as the positive electrode collector.
(method for producing Positive electrode)
The positive electrode for the lithium ion battery can be prepared by the following method:
the positive electrode active material, the conductive agent and the binder are dissolved or dispersed in a solvent to obtain a mixed slurry. The obtained mixed slurry is applied to a positive electrode current collector, and then dried to remove the solvent, thereby forming a positive electrode active material layer. Optionally, after the positive electrode active material layer is formed, rolling may be performed to obtain a positive electrode for a lithium ion battery.
Or mixing the positive electrode active material, the conductive agent, the adhesive and the solvent together to obtain a mixture; the obtained mixture was rolled on a positive electrode current collector to obtain a positive electrode for a lithium ion battery.
The positive electrode contains the positive electrode active material according to the first aspect, and a lithium ion battery having a high discharge voltage and good cycle characteristics can be obtained.
< lithium ion Battery >
The lithium ion battery of the present invention comprises a positive electrode, a negative electrode, and a nonaqueous electrolytic solution.
(Positive electrode)
The positive electrode according to the third aspect of the present invention contains the positive electrode active material according to the first aspect of the present invention.
(cathode)
The negative electrode contains a negative electrode active material, and is formed on a negative electrode current collector by using the negative electrode active material, a conductive agent, and a binder.
(nonaqueous electrolyte solution)
The non-aqueous electrolyte can be a non-aqueous electrolyte prepared by dissolving an organic solvent electrolyte salt; or an inorganic solid electrolyte; or a solid or gel-like polymer electrolyte prepared by mixing or dissolving an electrolyte salt. Such as LiPF6And (3) solution.
The lithium ion battery of the fourth aspect of the present invention has excellent electrochemical properties, a high discharge voltage (e.g., an average discharge voltage higher than 4.5V, even up to 4.70V), and good cycle characteristics. For example, when a lithium ion battery is subjected to a charge-discharge cycle test at 25 ℃ and under a voltage of 3.0-4.9V, after 50 cycles of cycle, the cycle retention rate is higher than 97%, even higher than 97.8, and can reach 99.1%, the dissolution rates of Mn and Ni are respectively lower than 1.2% and 1.1%, even respectively lower than 1.16% and 1.04%, and can be respectively lower than 0.78% and 0.65%.
Examples
Example 1
Step 1:
1086.4g of nickel (II) sulfate hexahydrate, 2989.6g of manganese (II) sulfate pentahydrate and 6814.6g of distilled water are weighed, and the nickel (II) sulfate hexahydrate, the manganese (II) sulfate pentahydrate and the distilled water are mixed and dissolved to be used as a metal salt aqueous solution.
109.4g of ammonium sulfate and 641.6g of distilled water were weighed, and the mixture was dissolved in distilled water to prepare an aqueous ammonium sulfate solution.
158.4g of ammonium sulfate and 3841.6g of distilled water were weighed, and the mixture was dissolved in a distilled water and used as a mother liquor.
800g of sodium hydroxide and 1200g of distilled water are weighed, and the sodium hydroxide and the distilled water are mixed and dissolved to be used as a pH regulator.
The mother liquor was charged into a 4L glass manufacturing reaction tank with a bubbling function, heated to 60 ℃ in a heating mantle, and the pH was controlled to 11.0. The solution in the reaction vessel was kept stirred, and 10.0 g/min of an aqueous metal salt solution and 2.0 g/min of an aqueous ammonium sulfate solution were added to precipitate Ni and Mn containing coprecipitation products. During the addition of the aqueous metal salt solution, a pH adjuster was added to maintain the reaction solution in the reaction tank at pH 11.0. Meanwhile, in order to prevent the precipitated coprecipitation product from being oxidized, a nitrogen gas flow rate of 1.0L/min was introduced into the reaction tank. Meanwhile, in order that the amount of liquid in the reaction tank does not exceed 4L, the reaction solution was continuously withdrawn.
In order to remove impurity ions from the coprecipitation product, repeated pressure filtration and dispersion washing of the obtained cake in distilled water were carried out. The washing process was terminated when the conductivity of the filtrate reached 25. mu.S/cm or less, and then the coprecipitation product was dried at 120 ℃ for 12 hours.
The obtained coprecipitation product D508.2 μm, a specific surface area of 25.7m2(ii) in terms of/g. The composition analysis of the coprecipitation product showed that the molar ratio of Ni to Mn was 0.248:0.752, and the total content of Ni and Mn was 11.576 mol/kg.
34.356g of an aqueous titanate solution (Ti content 8.1 wt%, pH 0.7) was added to 65.644g of distilled water to prepare a Ti-containing aqueous solution having a pH 6.
15.430g of an aqueous magnesium nitrate compound was added to 84.570g of distilled water to prepare an aqueous solution containing Mg.
The coprecipitation product (200 g) was mixed with an aqueous solution containing Ti by spraying 20.0g of the aqueous solution containing Ti in portions to thereby contact the coprecipitation product. Then, in the same manner, 20.0g of an aqueous Mg solution was sprayed to mix and contact the coprecipitation product with the aqueous Mg-containing solution. The resulting mixture was dried at 90 ℃ for 3 hours to obtain a co-precipitated product precursor doped with Ti and Mg.
Step 2:
44.727g of lithium carbonate (Li content: 26.85mol/kg) was mixed with the precursor obtained in step 1. The resulting mixture was heat-treated at 850 ℃ for 24 hours in an atmosphere containing oxygen to obtain oxide (1).
ICP (inductively coupled plasma emission spectrometer) test is carried out on the oxide (1), and the composition Li of the oxide (1) is measured1.000Ni0.495Mn1.485Mg0.010Ti0.010O4。
The particle size of the oxide (1) is tested by a particle size tester (Malvern MS3000) to obtain the D of the oxide (1)50It was 8.50 μm.
The specific surface area of the oxide (1) was 0.74m as measured by the BET test method (Micromeritics TristarII3020)2/g。
The positive electrode active material of example 1 was oxide (1). As shown in fig. 11, the SEM image obtained by scanning electron microscope examination of the positive electrode active material prepared in example 1 shows that the oxide (1) has an appearance of secondary particles in which a plurality of primary particles are aggregated, and the primary particles are uniform and have no abnormally coarse particles.
Example 2
4.760g of an aqueous aluminum lactate solution having an Al content of 4.2 wt% (weight percentage) was added to 25.242g of distilled water to prepare an Al-containing aqueous solution having a pH of 5.5.
50.0g of the oxide (1) of example 1 was taken, 10.0g of an Al-containing aqueous solution was co-sprayed in portions a plurality of times to sufficiently mix and contact the oxide (1) and the Al-containing aqueous solution, and then the resulting mixture was dried at 90 ℃ for 3 hours and then heat-treated at 450 ℃ for 8 hours in an atmosphere containing oxygen, to obtain a positive electrode active material in which an Al compound (2)) was present on the surface of the oxide (1).
The relative ratio of the number of moles of Al contained in the compound (2) to the number of moles of the oxide (1) was 0.01 as obtained by the ICP test; the compound (2) on the surface of the oxide (1) is Al2O3And LiAlO2A mixture of (a).
As shown in fig. 12, the SEM image obtained by the scanning electron microscope test of the positive electrode active material of example 2 shows that the oxide (1) has an appearance of secondary particles in which a plurality of primary particles are aggregated, the primary particles are uniform and have no abnormal coarse particles, and the Al compound does not aggregate on the surface of the oxide (1) and is uniformly present, that is, the Al compound is uniformly coated on the surface of the oxide (1).
Example 3
9.516g of an aqueous aluminum lactate solution having an Al content of 4.2 wt% was added to 20.484g of distilled water to prepare an Al-containing aqueous solution having a pH of 5.5.
50.0g of the oxide (1) of example 1 was taken, 10.0g of an Al-containing aqueous solution was co-sprayed in portions a plurality of times to sufficiently mix and contact the oxide (1) and the Al-containing aqueous solution, and then the resulting mixture was dried at 90 ℃ for 3 hours and then heat-treated at 450 ℃ for 8 hours in an atmosphere containing oxygen, to obtain a positive electrode active material in which an Al compound (2)) was present on the surface of the oxide (1).
The relative ratio of the number of moles of Al contained in the compound (2) to the number of moles of the oxide (1) was 0.02, and the compound (2) was Al, as determined by the ICP test2O3And LiAlO2A mixture of (a).
The positive electrode active material of example 3 was subjected to a scanning electron microscope test, and the results were similar to those of example 2.
Example 4
Using the precursor of the coprecipitation product substance not doped with the metal of example 1 in step 2 of example 1, the oxide was obtained in the same manner as in step 2 of example 1, and the composition of the oxide, represented by Li, was obtained by the ICP test1.000Ni0.500Mn1.500O4。
A positive electrode active material of example 4 was obtained by coating the surface of the oxide with the compound (2) in the same manner as in step 3 of example 2, except that the oxide (1) was replaced with the oxide of example 4 in step 3 of example 2.
By the ICP test, the relative ratio of the number of moles of Al contained in the compound (2) to the number of moles of the oxide was 0.01, and the compound (2) was Al2O3And LiAlO2A mixture of (a).
The positive electrode active material of example 4 was subjected to a scanning electron microscope test, and the results showed that no coarse particles were present on the surface of the oxide, indicating that the Al compound was present uniformly on the surface of the oxide and uniformly coated on the surface of the oxide.
Example 5
Step 1:
24.310g of iron (III) nitrate nonahydrate was added to 75.690g of distilled water to prepare an Fe-containing aqueous solution.
The coprecipitation product obtained in example 1 (200 g) was sampled and then 20.0g of the aqueous solution containing Ti obtained in example 1 was co-sprayed in portions to sufficiently mix the coprecipitation product with the aqueous solution containing Ti. Then, 20.0g of an Fe-containing aqueous solution was co-sprayed in portions several times to sufficiently mix the coprecipitation product and the Fe-containing aqueous solution. The obtained mixture was dried at 90 ℃ for 3 hours to obtain a precursor in which Ti and Fe were doped in the coprecipitation product.
Step 2:
oxide (1) was obtained in the same manner as in step 2 of example 1, except that the precursor obtained above was used.
Analysis by ICP test gave oxide (1) having a composition of Li1.000Ni0.495Mn1.485Fe0.010Ti0.010O4. D of oxide (1) measured by a particle size tester508.45 μm, and the specific surface area of the oxide (1) measured by the BET test method was 0.88m2/g。
This oxide (1) was used as the positive electrode active material in example 5.
Example 6
Step 1:
the coprecipitation product obtained in example 1 (200 g) was sampled and then mixed with the Fe-containing aqueous solution (20.0 g) of the Fe-containing aqueous solution of example 5 in portions (several times). The obtained mixture was dried at 90 ℃ for 3 hours to obtain a precursor in which Fe was doped in the coprecipitation product.
Step 2:
oxide (1) was obtained in the same manner as in step 2 of example 1, except that the precursor obtained above was used.
By the ICP test, the composition of the oxide (1) was determined to be Li1.000Ni0.498Mn1.493Fe0.010O4. D of oxide (1) measured by a particle size tester508.48 μm, and the specific surface area of the oxide (1) measured by the BET test method was 1.14m2/g。
This oxide (1) was used as the positive electrode active material in example 6.
Example 7
Step 1:
ammonium zirconium carbonate ((NH) containing 12 wt% of Zr was prepared4)2[Zr(CO3)2(OH)2]) An aqueous solution.
200g of the coprecipitation product obtained in example 1 was taken out and 20.0g of a Zr-containing aqueous solution was co-sprayed in portions to sufficiently mix the coprecipitation product with the Zr-containing aqueous solution. The resulting mixture was dried at 90 ℃ for 3 hours to obtain a precursor in which Zr was doped in the coprecipitation product.
Step 2:
oxide (1) was obtained in the same manner as in step 2 of example 1, except that the precursor obtained above was used.
Composition of oxide (1) measured by ICP tester as Li1.000Ni0.498Mn1.493Zr0.010O4. D of oxide (1) measured by a particle size tester508.15 μm, and the specific surface area of the oxide (1) measured by the BET test method was 0.94m2/g。
This oxide (1) was used as the positive electrode active material in example 7.
Example 8
Step 1:
200g of the coprecipitation product obtained in example 1 was taken out, and 20.0g of the Al-containing aqueous solution obtained in example 2 was co-sprayed in portions so that the coprecipitation product and the Al-containing aqueous solution were sufficiently mixed. The resulting mixture was dried at 90 ℃ for 3 hours to obtain a precursor in which Al was doped in the coprecipitation product.
Step 2:
oxide (1) was obtained in the same manner as in step 2 of example 1, except that the precursor obtained above was used.
Analysis by ICP test gave oxide (1) having a composition of Li1.000Ni0.498Mn1.493Al0.010O4. D of oxide (1) measured by a particle size tester508.58 μm, and the specific surface area of the oxide (1) measured by the BET test method was 1.21m2/g。
This oxide (1) was used as the positive electrode active material in example 8.
Example 9
Step 1:
200g of the coprecipitation product obtained in example 1 was removed, and 20.0g of the aqueous solution containing Ti obtained in example 1 was co-sprayed in portions to sufficiently mix the coprecipitation product with the aqueous solution containing Ti. The obtained mixture was dried at 90 ℃ for 3 hours to obtain a precursor in which Ti was doped in the coprecipitation product.
Step 2:
oxide (1) was obtained in the same manner as in step 2 of example 1, except that the precursor obtained above was used.
Analysis by ICP test gave the composition of oxide (1) represented by Li1.000Ni0.498Mn1.493Ti0.010O4. D of oxide (1) measured by a particle size tester507.83 μm, and the specific surface area of the oxide (1) measured by the BET test method was 1.06m2/g。
This oxide (1) was used as the positive electrode active material in example 9.
Example 10
A coprecipitation product containing Ni, Mn, and Al was obtained in the same manner as in step 1 of example 1 except that aluminum sulfate was added to the aqueous metal salt solution in step 1 of example 1, and a precursor was obtained.
Oxide (1) was obtained in the same manner as in step 2 of example 1, except that the precursor obtained above was used.
Analysis by ICP test gave the composition of oxide (1) represented by Li1.000Ni0.488Mn1.463Al0.050O4. D of oxide (1) measured by a particle size tester505.45 μm, and the specific surface area of the oxide (1) measured by the BET test method was 1.94m2/g。
This oxide (1) was used as the positive electrode active material of example 10.
Example 11
In step 1 of example 1, a coprecipitation product containing Ni, Mn, and Fe was prepared in the same manner as in step 1 of example 1 except that iron (III) sulfate was added to the aqueous metal salt solution, and a precursor was obtained.
Oxide (1) was obtained in the same manner as in step 2 of example 1, except that the precursor obtained above was used.
Obtained by the ICP test, the composition of the oxide (1) was Li1.000Ni0.488Mn1.463Fe0.050O4. D of oxide (1) measured by a particle size tester507.27 μm, and the specific surface area of the oxide (1) measured by the BET test method was 1.86m2/g。
This oxide (1) was used as the positive electrode active material in example 11.
Example 12
Step 1:
preparing an ammonium fluoride aqueous solution with the F content of 2.1 wt% to obtain an F-containing aqueous solution;
200g of the coprecipitation product obtained in example 1 was taken out, and 20.0g of an F-containing aqueous solution was sprayed in portions to sufficiently mix the coprecipitation product with the F-containing aqueous solution. The resulting mixture was dried at 90 ℃ for 3 hours to obtain a precursor in which the coprecipitation product was doped with F.
Step 2:
oxide (1) was obtained in the same manner as in step 2 of example 1, except that the precursor obtained above was used.
Analysis by ICP test gave the composition of oxide (1) represented by Li1.000Ni0.495Mn1.485Ti0.010O3.99 5F0.01. D of oxide (1) measured by a particle size tester507.13 μm, and the specific surface area of the oxide (1) measured by the BET test method was 0.96m2/g。
This oxide (1) was used as the positive electrode active material in example 12.
Comparative example 1
The precursor obtained in example 1 and 44.730g of lithium carbonate (Li content: 26.85mol/kg) were mixed, and the resulting mixture was subjected to heat treatment at 850 ℃ for 24 hours and further subjected to secondary heat treatment at 700 ℃ for 8 hours in an oxygen-containing atmosphere to obtain an oxide.
Obtained by ICP test, the composition of the oxide being Li1.000Ni0.495Mn1.485Mg0.010Ti0.010O4. D of oxide measured by a particle size tester508.53 μm, and a specific surface area of the oxide measured by the BET test method of 0.84m2/g。
This oxide was used as the positive electrode active material of comparative example 1.
Comparative example 2
50.0g of the oxide obtained in comparative example 1 was taken, 10.0g of the aqueous Al solution of example 2 was co-sprayed in portions several times, and heat-treated at 450 ℃ for 8 hours to obtain the positive electrode active material of comparative example 2 in which an Al compound (2)) was present on the surface of the oxide.
The relative ratio of the number of moles of Al contained in the compound (2) to the number of moles of the oxide was 0.01 as obtained by the ICP test.
XRD test
XRD tests were performed on the positive electrode active materials of examples 1 to 11 and comparative examples 1 to 2, and the results are shown in FIGS. 1 to 8. FIGS. 9 and 10 are respectively a crystal structure with space group Fd-3m and a crystal structure with space group P4332 crystalBulk structured LiNi0.5Mn1.5O4XRD standard curve of (a).
In fig. 1, XRD curves of the positive electrode active materials of examples 1 to 4 and comparative examples 1 to 2 are shown as curves 1 to 6, i.e., example 1-curve 1, example 2-curve 2, example 3-curve 3, example 4-curve 4, comparative example 1-curve 5, and comparative example 2-curve 6, respectively.
As can be seen from XRD patterns 1 to 10, the positive electrode active materials obtained in examples 1 to 11 have peaks in the vicinity of 2 θ of 18.8 °, 36.4 ° and 44.3 °, and have no characteristic peak in the vicinity of 2 θ of 15.3 °, and the obtained positive electrode active material has a crystal structure of space group Fd-3m and does not contain space group P4332. In the XRD patterns of the positive electrode active materials of comparative examples 1 to 2, there were peaks in the vicinity of 2 θ of 18.8 °, 36.4 ° and 44.3 °, characteristic peaks were found in the vicinity of 2 θ of 15.3 °, and the positive electrode active materials of comparative examples 1 to 2 contained space group P4332.
Preparation of the Positive electrode
A positive electrode active material, carbon black, and a solution of polyvinylidene fluoride (12.1 wt%) dissolved in an N-methylpyrrolidone solvent were mixed using any one of examples 1 to 12 and comparative examples 1 to 2, and then an N-methylpyrrolidone solvent was further added to prepare a mixed slurry. The weight ratio of the positive electrode active material to the carbon black to the polyvinylidene fluoride was 85: 10: 5.
The slurry mixture was applied to an aluminum foil (positive electrode current collector) having a thickness of 20 μm. The coating gap was 100 μm. After drying at 120 ℃, rolling and rolling for 2 times to prepare the anode sheet.
The circular part is punched on the positive electrode sheet and used as a positive electrode.
Preparation of lithium ion secondary battery
The positive electrodes prepared by using the positive electrode active materials of examples 1 to 12 and comparative examples 1 to 2 were used as positive electrodes of lithium ion secondary batteries, and the negative electrodes were metal lithium foils having a negative electrode active material layer thickness of 500 μm, and the negative electrode current collectors were stainless steel plates having a thickness of 1 mm.
The separator is made of porous polypropylene material with thickness of 25 μm.
The non-aqueous electrolyte solution has a concentration of 1mol/dm3LiPF of6And (3) solution. The solvent of the non-aqueous electrolyte adopts a mixed solution of ethylene carbonate and ether carbonate (the weight ratio is 1: 1).
Using the above positive electrode, negative electrode, separator, and nonaqueous electrolyte solution, a lithium ion secondary battery was prepared in an argon glove box.
Examples of the experiments
Experimental example 1
The lithium ion batteries prepared using the positive electrode active materials of examples 1 to 4 and comparative examples 1 to 2 were subjected to a first (initial) discharge capacity test at 25 ℃.
The lithium ion battery is charged at 3.0-4.9V by CC-CV (ConstantCurrent-ConstantVoltage) at 25 ℃, and discharged at 4.9-3.0V by CC (ConstantCurrent). The discharge capacity of 4.9-3.0V is used as the first discharge capacity. The test results obtained are shown in FIG. 13. In fig. 13, the correspondence relationship: from example 1 to curve 1, example 2 to curve 2, example 3 to curve 3, example 4 to curve 4, comparative example 1 to curve 5, comparative example 2 to curve 6, it can be seen from fig. 13 that the lithium ion battery has a high efficiency discharge voltage plateau around a voltage of 5V, and an average discharge voltage as high as 4.70V.
Experimental example 2
The lithium ion batteries prepared from the positive electrode active materials of examples 1 to 5 and comparative examples 1 to 2 were subjected to a cycle test at 60 ℃.
And carrying out CC charging on the lithium ion battery at the temperature of 60 ℃ and the voltage of 3.0-4.9V, and carrying out CC discharging at the voltage of 4.9-3.0V. The same cycle was repeated 50 times, and the 1 st discharge capacity of the 4.9V charge-discharge cycle was used as the 4.9V primary discharge capacity. The ratio of the 50 th discharge capacity of the 4.9V charge-discharge cycle to the 4.9V first discharge capacity was referred to as the 50 th maintenance rate. The results are shown in tables 1 and 2.
Experimental example 3
The lithium ion batteries prepared from the positive electrode active materials of examples 6 to 11 were subjected to a cycle test at 25 ℃.
And carrying out CC charging on the lithium ion battery at the temperature of 25 ℃ and the voltage of 3.0-4.9V, and carrying out CC discharging on the lithium ion battery at the voltage of 4.9-3.0V. The same cycle was repeated 50 times, and the 1 st discharge capacity of the 4.9V charge-discharge cycle was used as the 4.9V primary discharge capacity. The ratio of the 50 th discharge capacity of the 4.9V charge-discharge cycle to the 4.9V first discharge capacity was referred to as the 50 th maintenance rate. The results are shown in Table 2.
Experimental example 4
After the cycle test, the lithium ion batteries of the positive electrode active materials of examples 1 to 4 and comparative examples 1 to 2 were decomposed, and Ni and Mn dissolved components on the negative electrode side and the separator side were recovered and subjected to inductively coupled plasma mass spectrometry (ICP) analysis. The respective dissolution and precipitation ratios of Ni and Mn were calculated from the dissolution amounts with respect to the initial amounts of Ni and Mn in the positive electrode sheet. The results are shown in Table 1.
Figure GDA0003234200950000201
Figure GDA0003234200950000211
In examples 1 to 3 and comparative examples 1 to 2, a part of Ni and Mn in the oxide was replaced with other metals. As is clear from Table 1, the positive electrode active materials of examples 1 to 3 containing the crystal structure of space group Fd-3m and the space group P43The positive electrode active material of comparative examples 1 to 2 having the crystal structure of 32 showed good cycle characteristics and low dissolution rates of Ni and Mn. For example, the cycle retention rate of 50 cycles of the cycle is higher than 97.5%, preferably higher than 97.7%, and even reaches 97.9%, and the dissolution and precipitation ratios of Mn and Ni are respectively lower than 1.2% and 1.1%, and even respectively lower than 0.78% and 0.65%.
Both of examples 2 and 4 had a crystal structure of space group Fd-3 m. It is found that the positive electrode active material of example 2 in which Ni and Mn of the oxide were partially substituted with other metals was superior in cycle characteristics of the lithium ion secondary battery, and the dissolution ratios of Ni and Mn were low, compared to the positive electrode active material of example 4 in which Ni and Mn were not substituted with other metals, and the lithium ion secondary battery obtained from the positive electrode active material of example 2 was higher in cycle retention rate of 97.9% after 50 cycles than in example 4, and was higher in 97.3% than in example 4, and the dissolution precipitation ratios of Mn and Ni in example 2 were 0.92% and 0.81%, respectively, and were much lower in 1.82% and 1.67% than in example 4.
From these results, it was found that the cycle characteristics of the lithium ion battery were good for the positive electrode active material containing the crystal structure of the space group Fd-3m and the oxide (1) in which part of Ni and Mn in the crystal was replaced with other metals.
From the results of examples 1 to 3, it was found that the dissolution/precipitation ratio of Ni and Mn in oxide (1) decreased as the amount of Al (the amount of compound (2)) on the surface of oxide (1) having a crystal structure containing space group Fd-3m increased.
On the contrary, as a result of comparing comparative examples 1 and 2, it was found that space group P4 was contained3When the compound (2) is present on the surface of the oxide having the crystal structure of 32, the dissolution rates of Ni and Mn are reduced, and the dissolution rates of Mn and Ni are reduced from 1.79% and 1.53% to 1.55% and 1.27%, respectively, but the cycle characteristics are reduced from 96.8% to 95.7%.
From these results, it is understood that if the oxide belongs to the space group P4332, even if the compound (2) is present on the surface of the oxide, the cycle characteristics of the lithium ion battery are still poor, and further improvement is required.
In table 2, the positive electrode active materials of examples 6 to 11 have good all cycle characteristics of lithium secondary batteries, and the cycle retention rate of 50 cycles at 25 ℃ is higher than 97%, preferably higher than 97.8%, and even reaches 99.1%. It was shown that the metal doped with the oxide (1) is effective for improving cycle characteristics by doping other metals in addition to the combination of Mg and Ti shown in table 1.
< possibility of industrial utilization >
The positive electrode active material for a lithium ion battery of the present invention has high discharge voltage and good cycle characteristics, and can be used for a lithium ion battery.
The invention has been described in detail with reference to the preferred embodiments and illustrative examples. It should be noted, however, that these specific embodiments are only illustrative of the present invention and do not limit the scope of the present invention in any way. Various modifications, equivalent substitutions and alterations can be made to the technical content and embodiments of the present invention without departing from the spirit and scope of the present invention, and these are within the scope of the present invention. The scope of the invention is defined by the appended claims.

Claims (1)

1. A method for preparing a positive electrode active material for a lithium ion battery is characterized in that,
the method comprises the following steps:
step 1:
1086.4g of nickel sulfate hexahydrate, 2989.6g of manganese sulfate pentahydrate and 6814.6g of distilled water are weighed, and the nickel sulfate hexahydrate, the manganese sulfate pentahydrate and the distilled water are mixed and dissolved to be used as a metal salt aqueous solution;
weighing 109.4g of ammonium sulfate and 641.6g of distilled water, mixing and dissolving the ammonium sulfate and the distilled water to be used as an ammonium sulfate aqueous solution;
weighing 158.4g of ammonium sulfate and 3841.6g of distilled water, mixing and dissolving the ammonium sulfate and the distilled water, and using the mixture as mother liquor;
weighing 800g of sodium hydroxide and 1200g of distilled water, and using the sodium hydroxide and the distilled water as a pH regulator after mixing and dissolving;
adding mother liquor into a 4L glass manufacturing reaction tank with a bubbling function, heating the solution in a heating jacket to 60 ℃, controlling the pH value to be 11.0, keeping the solution in the reaction tank stirred, adding 10.0 g/min of metal salt aqueous solution and 2.0 g/min of ammonium sulfate aqueous solution, precipitating and separating Ni and Mn to obtain a coprecipitation product, adding a pH regulator to keep the pH value of the reaction solution in the reaction tank to be 11.0 in the process of adding the metal salt aqueous solution, introducing 1.0L/min of nitrogen gas into the reaction tank for preventing the precipitated coprecipitation product from being oxidized, and continuously pumping out the reaction solution for ensuring that the liquid amount in the reaction tank does not exceed 4L;
repeatedly performing pressure filtration and dispersion washing of the obtained filter cake in distilled water to remove impurity ions from the coprecipitation product, wherein the washing process is completed when the conductivity of the filtrate reaches 25 μ S/cm or less, and drying the coprecipitation product at 120 deg.C for 12 hr;
the obtained coprecipitation product D508.2 μm, a specific surface area of 25.7m2The composition analysis result of the coprecipitation product showed that Ni: the molar ratio of Mn is 0.248:0.752, and the total content of Ni and Mn is 11.576 mol/kg;
34.356g of titanate aqueous solution containing 8.1 wt% of Ti and 0.7 pH was added to 65.644g of distilled water to prepare a Ti-containing aqueous solution having a pH of 6;
15.430g of magnesium nitrate hydrous compound is added into 84.570g of distilled water to prepare Mg-containing aqueous solution;
co-spraying 20.0g of a Ti-containing aqueous solution to 200g of the co-precipitation product in batches for multiple times to mix and contact the co-precipitation product with the Ti-containing aqueous solution, then spraying 20.0g of an Mg aqueous solution by the same method to mix and contact the co-precipitation product with the Mg-containing aqueous solution, and drying the obtained mixture at 90 ℃ for 3 hours to obtain a precursor of the co-precipitation product doped with Ti and Mg;
step 2:
mixing the precursor obtained in the step 1 with 44.727g of lithium carbonate, wherein the amount of Li element in the lithium carbonate is 26.85mol/kg, and carrying out heat treatment on the obtained mixture at 850 ℃ for 24 hours in an oxygen-containing atmosphere to obtain an oxide (1);
the oxide (1) was subjected to an ICP test to determine that the composition of the oxide (1) was Li1.000Ni0.495Mn1.485Mg0.010Ti0.010O4；
Testing the granularity of the oxide (1) by adopting a Malvern MS3000 granularity tester to obtain the D of the oxide (1)508.50 μm;
the specific surface area of the oxide (1) was 0.74m as measured by the BET test method2/g；
The oxide (1) has a crystal structure of a space group Fd-3m and does not have a space group P4332.
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