CN112645390B - Lithium cobaltate precursor with coating structure, preparation method and application thereof - Google Patents

Lithium cobaltate precursor with coating structure, preparation method and application thereof Download PDF

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CN112645390B
CN112645390B CN202011525496.6A CN202011525496A CN112645390B CN 112645390 B CN112645390 B CN 112645390B CN 202011525496 A CN202011525496 A CN 202011525496A CN 112645390 B CN112645390 B CN 112645390B
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lithium
precursor
lithium cobaltate
ion battery
coating
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CN112645390A (en
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邱传洲
洪斯凡
朱红庆
王理
祝媛
刘金成
刘建华
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Eve Energy Co Ltd
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    • 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
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    • C01P2004/82—Particles consisting of a mixture of two or more inorganic phases two phases having the same anion, e.g. both oxidic phases
    • C01P2004/84—Particles consisting of a mixture of two or more inorganic phases two phases having the same anion, e.g. both oxidic phases one phase coated with the other
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    • H01M2004/028—Positive electrodes
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Abstract

The invention provides a lithium cobaltate precursor with a coating structure, a preparation method and application thereof, wherein the preparation method comprises the following steps: mixing and stirring a cobalt source doped with metal elements and a metal salt solution, adding alkali liquor, continuing stirring to obtain a precursor mixture, and sintering the precursor mixture to obtain a lithium cobaltate precursor with a coating structure. According to the method, the surface of the lithium cobaltate precursor is coated with the metal hydroxide by adopting a liquid phase synthesis method, so that the coating is more uniform, the coating layer can exist stably, and a stable solid solution coating interface is formed in the subsequent multiple sintering process, so that the material structure is more stable, and the electrochemical performance is more excellent.

Description

Lithium cobaltate precursor with coating structure, preparation method and application thereof
Technical Field
The invention belongs to the technical field of preparation of a precursor of a positive electrode material, and relates to a lithium cobaltate precursor with a coating structure, a preparation method and application thereof.
Background
The lithium ion battery has the advantages of high working voltage, long cycle life, light weight, less self-discharge, no memory effect, high cost performance and the like, and is widely applied to the fields of consumer electronics and new energy automobiles at present. The positive electrode material is one of the core parts of the lithium ion battery, determines the performance of the lithium ion battery, and limits the energy density, the power density and the cycle life of the lithium ion battery. It can be said that the development of the positive electrode material determines the development direction of the lithium ion battery.
With the application of 5G mobile phones, the problem of low energy density of current consumer lithium ion batteries is fully exposed, and lithium ion batteries with higher energy density and longer service life need to be developed urgently to meet the cruising demand of people on 5G mobile phones and electronic products. The lithium ion battery has the characteristics of long service life, no memory effect, low self-discharge, environmental friendliness and the like. At present, most electronic products select a lithium ion battery as an energy storage device. Research and development personnel mainly improve the energy density of the lithium ion battery by using positive and negative electrode materials with higher gram capacity, the actual gram capacity of the lithium cobaltate is improved by improving the cut-off voltage of the lithium cobaltate in the positive electrode aspect, the negative electrode graphite is close to the theoretical capacity of the lithium cobaltate, the gram capacity of the negative electrode is improved by mainly doping a Si-containing material, and the expansion problem is caused. Therefore, the positive electrode material plays an important role in improving the energy density of the lithium ion battery as an important component of the lithium ion battery.
Lithium cobaltate is the earliest positive electrode material applied to commercial lithium ion batteries, and has the characteristics of wide application voltage range, high compaction density and high specific capacity. The method is widely applied to the 3C fields of mobile phones, notebook computers, robots, unmanned planes and the like. The theoretical gram capacity of lithium cobaltate was 274mAh/g, but the actual gram capacity was 171mAh/g (cut-off voltage 4.4V). The actual capacity and the theoretical capacity have a large difference, namely approximately 38% of lithium ions do not participate in the redox reaction, and increasing the cut-off voltage is an effective method for increasing the capacity of lithium cobaltate, so that more lithium ions can participate in the redox reaction. However, an excessively high cut-off voltage means that more lithium ions are extracted from the lithium cobaltate, and the lattice structure of the lithium cobaltate changes as the lithium ions are extracted. Along with the extraction of lithium ions, the crystal lattice of lithium cobaltate expands along the C-axis direction, the lithium ions continue to be extracted, the expansion of the crystal lattice is increased, and the crystal structure is gradually changed into a monoclinic system. When the cut-off voltage is increased to 4.55V, lithium cobaltate undergoes irreversible phase change, and lithium ions can not return to the laminated structure any more, so that the reversible capacity is reduced. In addition, the occurrence of side reactions is aggravated by the excessively high cut-off voltage, a thicker CEI film is generated on the surface of the positive electrode, the impedance of lithium ion transmission in the positive electrode and the electrolyte is increased, and the ionic conductivity is reduced. HF generated by decomposition of the electrolyte at high voltage reacts with lithium cobaltate to corrode the electrode material, reducing the surface activity of the lithium cobaltate. Therefore, it is necessary to improve the cut-off voltage of lithium cobaltate by modifying the lithium cobaltate.
The structural performance and the electrochemical performance of the particles can be optimized by forming a coating layer on the surface of the lithium cobaltate, the corrosion resistance of the material is improved, and the side reaction between the material and electrolyte is reduced. The surface of the material is coated with a thin and stable coating layer, the common coating materials comprise oxide, fluoride, a lithium ion conductor and the like, the coating layer separates the material from the electrolyte while reducing the contact resistance among particles, so that the side reaction between the material and the electrolyte is reduced, and the corrosion of HF gas decomposed by the electrolyte to the anode material is prevented. Meanwhile, the electronic conductivity and the lithium ion diffusion coefficient among particles are improved, the polarization problem caused by battery reaction is reduced, and the structural stability and the thermal stability of the anode material are improved, so that the safety performance and the service life of lithium cobaltate are optimized. However, the lithium cobaltate has a large lithium removal/insertion amount, which causes a certain volume change during the circulation process. After long-term cycling, interfacial separation occurs between some coating materials and lithium cobaltate, thereby causing the protective effect of the coating layer to lose efficacy.
The prior art mainly carries out coating after synthesizing lithium cobaltate, although the electrochemical performance of the lithium cobaltate is obviously improved by a coating material, the binding force between the coating material and the lithium cobaltate is poor, uniform coating is not easy to happen, or the coating material falls off in the stirring process of slurry of the lithium cobaltate, or a certain volume change is generated because the lithium cobaltate has large lithium removal/lithium insertion amount in the charging and discharging cycle process. After long-term cycling, interfacial separation occurs between some coating materials and lithium cobaltate, thereby causing the protective effect of the coating layer to lose efficacy. Both of these conditions severely limit the coating effect. In addition, when multiple elements are required to be coated simultaneously, selective coating occurs, that is, the coating material is not uniformly distributed on the surface of the lithium cobaltate particles.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide a lithium cobaltate precursor coated with metal hydroxide, a preparation method and application thereof.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the present invention provides a preparation method of a lithium cobaltate precursor having a coating structure, the preparation method including:
mixing and stirring a cobalt source doped with metal elements and a metal salt solution, adding alkali liquor, continuing stirring to obtain a precursor mixture, and sintering the precursor mixture to obtain a lithium cobaltate precursor with a coating structure.
According to the invention, a better coating material can be obtained by coating at the precursor stage of the lithium cobaltate positive electrode material, the metal salt solution takes the lithium cobaltate precursor as a substrate material, and metal cations can be uniformly attached to the surface of the substrate material in the stirring process, so that the coating uniformity is improved. After ammonia water is added, metal cations react with hydroxyl to generate metal hydroxide, the metal hydroxide is dehydrated to form metal oxide in the subsequent sintering process, a solid solution contact interface with good crystallinity is formed between the substrate material and the metal oxide coating layer through diffusion of metal atoms and stably coats the surface of the substrate material, the surface coating layer plays a role in stabilizing a lithium cobaltate phase structure and a surface coating layer phase structure, the activity of oxygen atoms is reduced, the purposes of inhibiting oxygen precipitation and dissolving out metal elements are achieved, and the structural stability and the thermal stability of the lithium cobaltate are improved. Meanwhile, the stable surface coating layer can reduce particle breakage of the precursor in the subsequent process of synthesizing lithium cobaltate, and on the other hand, the stable surface coating layer can isolate the lithium cobaltate from the electrolyte, so that the particle interface of the lithium cobaltate is not damaged under the working voltage, the interface reaction is reduced, a solid solution structure is formed on the surface after coating, the integral conductivity of the lithium cobaltate is improved, and the cycle performance and the safety performance of the battery are effectively improved.
It should be noted that, the pre-doping method in the present invention adopts a conventional doping method in the art, such as a co-precipitation method, a solid-phase synthesis method, a sol-gel method, and the like, which are familiar to those skilled in the art, and details are not described herein. The pre-doping refers to doping of corresponding metal ions into the crystal lattice.
In a preferred embodiment of the present invention, the metal element doped in the cobalt source includes one or a combination of at least two of Al, mg, zr, ti, ni, mn, Y, zn, mo, ru, ta, W, re, sn, ge, and Ga.
Preferably, the cobalt source comprises any one of cobaltous oxide, cobalt oxide, cobaltosic oxide, cobalt hydroxide, cobalt oxyhydroxide or cobalt carbonate or a combination of at least two thereof.
Preferably, the amount of doped metal element in the cobalt source is 0.1 to 10wt%, and may be, for example, 0.1wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, or 10wt%, but is not limited to the recited values, and other values not recited in the range of values are also applicable.
Preferably, the metal element in the metal salt solution comprises any one or a combination of at least two of Al, mg, zr, ti, ni, mn, Y, zn, mo, ru, ta, W, re, sn, ge or Ga.
Preferably, the alkali liquor is ammonia water.
In a preferred embodiment of the present invention, the cobalt source doped with the metal element and the metal salt solution are mixed and stirred for 1 to 5 hours, for example, 1 hour, 2 hours, 3 hours, 4 hours or 5 hours, but the present invention is not limited to the above-mentioned values, and other values not listed in the above-mentioned range are also applicable.
Preferably, the stirring is continued for 1 to 5 hours, for example 1 hour, 2 hours, 3 hours, 4 hours or 5 hours after the addition of the lye, but not limited to the values listed, and other values not listed within this range of values are equally suitable.
Preferably, the precursor mixture is dried after being washed, prior to sintering.
Preferably, the cleaning medium is deionized water.
Preferably, the drying temperature is 50 to 60 ℃, for example, 50 ℃, 51 ℃, 52 ℃, 53 ℃, 54 ℃, 55 ℃, 56 ℃, 57 ℃, 58 ℃, 59 ℃ or 60 ℃, but is not limited to the recited values, and other values not recited in the range of the values are also applicable.
Preferably, the sintering temperature of the precursor mixture is 400 to 600 ℃, for example 400 ℃, 420 ℃, 440 ℃, 460 ℃, 480 ℃, 500 ℃, 520 ℃, 540 ℃, 560 ℃, 580 ℃ or 600 ℃, but is not limited to the recited values, and other values not recited in this range of values are equally applicable.
Preferably, the sintering time of the precursor mixture is 5 to 12 hours, for example 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours or 12 hours, but is not limited to the recited values, and other values not recited within the range of values are equally applicable.
In a second aspect, the invention provides a lithium cobaltate precursor prepared by the preparation method of the first aspect, the lithium cobaltate precursor comprises a core and a coating layer coated on the outer surface of the core, and the coating layer is a metal oxide.
In a preferred embodiment of the present invention, the mass fraction of the metal oxide is 0.01 to 5wt%, for example, 0.01wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt%, or 5wt%, based on 100wt% of the total mass fraction of the lithium cobaltate precursor, but the present invention is not limited to the above-mentioned values, and other values not shown in the above-mentioned value range are also applicable.
In a third aspect, the present invention provides a preparation method of a lithium cobaltate positive electrode material with a coating structure, where the preparation method includes:
and mixing and grinding the lithium cobaltate precursor and a lithium salt, and sintering to obtain the lithium cobaltate positive electrode material.
And (2) coating the surface of the lithium cobaltate precursor by using a metal oxide or a metal salt to obtain the lithium cobaltate precursor with a surface coating structure, and synthesizing the positive electrode material lithium cobaltate material for the energy storage device by using the precursor. Because the coating layer on the surface of the precursor can exist stably, the structural stability, the electrochemical performance and the corrosion resistance of the lithium cobaltate are improved remarkably, and the capacity retention rate in the charge-discharge cycle process of the battery is improved.
In a preferred embodiment of the present invention, the molar ratio of the lithium element in the lithium salt to the cobalt element in the lithium cobaltate precursor is (1.05 to 1.1): 1, and for example, 1.05.
Preferably, the grinding mode is ball milling.
Preferably, the sintering temperature of the lithium cobaltate precursor is 600 to 800 ℃, for example 600 ℃, 620 ℃, 640 ℃, 660 ℃, 680 ℃, 700 ℃, 720 ℃, 740 ℃, 760 ℃, 780 ℃ or 800 ℃, but is not limited to the recited values, and other unrecited values within the range of values are also applicable.
Preferably, the sintering time of the lithium cobaltate precursor is 5-12 h, for example, 5h, 6h, 7h, 8h, 9h, 10h, 11h or 12h, but is not limited to the recited values, and other values not recited in the range of the values are also applicable.
In a fourth aspect, the invention provides a lithium cobaltate positive electrode material with a coating structure, and the lithium cobaltate positive electrode material is prepared by the preparation method in the third aspect.
In a fifth aspect, the present invention provides a lithium ion battery, where the lithium ion battery includes a housing and a battery cell located inside the housing, and the battery cell is obtained by sequentially stacking a positive electrode plate, a diaphragm, and a negative electrode plate and then winding or stacking the positive electrode plate, the diaphragm, and the negative electrode plate.
The positive pole piece is prepared by the following method:
and dispersing a positive active substance, a conductive agent and a positive binder in a solvent, mixing, coating the mixture on the surface of a positive current collector, and drying and cold-pressing to obtain the positive pole piece, wherein the positive active substance comprises the lithium cobaltate with the coating structure in the fourth aspect.
It is to be noted that the present invention does not specifically require and specifically limit the shape, size, material, and other parameters of the current collector, as long as the current collector has conductivity without causing adverse chemical changes in the fabricated battery. The material of the current collector includes, but is not limited to, an alloy synthesized by one or more of copper, stainless steel, aluminum, nickel and titanium. The current collector may include a fine irregular coating on the surface thereof to enhance the adhesion of the current collector to the active material. The shape of the current collector includes, but is not limited to, a film, a sheet, a foil, a mesh, a porous structure, or a foam structure.
As a preferred embodiment of the present invention, the conductive agent includes any one or a combination of at least two of acetylene black, ketjen black, natural graphite, carbon black, cellulose, metal powder, and metal fiber.
Preferably, the solvent comprises any one of or a combination of at least two of N-methyl pyrrolidone, acetone or water.
Preferably, the negative electrode binder includes any one or a combination of at least two of polyvinylidene fluoride, polyvinylidene chloride, carboxymethyl cellulose, polyvinyl acetate, polyvinyl pyrrolidone, polypropylene, or polyethylene.
Preferably, the negative electrode plate is prepared by the following method:
and dispersing the negative active material, the conductive agent, the negative binder and the sodium carboxymethylcellulose in a solvent, mixing, coating on the surface of a current collector, drying and cold-pressing to obtain the negative pole piece.
Preferably, the negative active material includes any one or a combination of at least two of lithium metal, a lithium alloy, a transition metal oxide, a non-transition metal oxide, or a carbon-based material.
Preferably, the transition metal oxide includes lithium titanium oxide and/or lithium vanadium oxide.
Preferably, the non-transition metal oxide comprises SiO 2 And/or SnO 2 。
Preferably, the carbon material comprises crystalline carbon and/or amorphous carbon.
Preferably, the crystalline carbon comprises natural graphite and/or artificial graphite.
Preferably, the amorphous carbon comprises any one of soft carbon, hard carbon, or mesophase pitch carbonization products, or a combination of at least two thereof.
Preferably, the material of the isolating membrane is polyethylene.
Preferably, the electrolyte is injected into the shell.
Preferably, the electrolyte includes a non-aqueous electrolyte and a lithium salt.
Preferably, the non-aqueous electrolyte solvent includes any one of methyl propionate, ethyl acetate, methyl formate, diethyl carbonate, dimethyl carbonate or ethylene carbonate or a combination of at least two thereof.
Preferably, the lithium salt comprises any one of lithium hexafluorophosphate, lithium perchlorate, lithium hexafluoroarsenate, lithium tetrafluoroborate or lithium chloride or a combination of at least two of the same.
Preferably, the electrolyte further comprises an additive.
Preferably, the additive comprises any one of acetonitrile, succinonitrile, adiponitrile or 1,3,6-hexanetrinitrile or a combination of at least two thereof.
Compared with the prior art, the invention has the beneficial effects that:
the invention advances the coating process to the synthesis stage of the lithium cobaltate precursor. Adding metal salt (such as nitrate, acetate, sulfate and the like) in the process of synthesizing the lithium cobaltate precursor, and sintering after liquid-phase coating to obtain the lithium cobaltate precursor with a metal oxide coating layer on the surface. And the precursor is used for synthesizing the anode material lithium cobaltate for the energy storage device. Because the coating layer on the surface of the precursor can exist stably, the stability, the electrochemical performance and the corrosion resistance of the lithium cobaltate are improved obviously, and the capacity retention rate of the battery in the charge-discharge cycle process is improved. And the preparation method is simple and is easy to realize large-scale production.
Drawings
FIG. 1 is an electron micrograph of a lithium cobaltate positive electrode material prepared in example 1 of the present invention;
FIG. 2 is a diagram showing the distribution of Co element in the lithium cobaltate precursor prepared in example 1 of the present invention;
FIG. 3 is an element distribution diagram of Mg element in a precursor of lithium cobaltate prepared in example 1 of the present invention;
FIG. 4 is an element distribution diagram of Ti element in a precursor of lithium cobaltate prepared in example 1 of the present invention;
FIG. 5 is an element distribution diagram of Zr element in a lithium cobaltate precursor prepared in example 1 of the present invention;
FIG. 6 is an element distribution diagram of Al element in a lithium cobaltate precursor prepared in example 1 of the present invention;
FIG. 7 is a graph showing the cycle test of example 1 of the present invention and comparative example 1.
Detailed Description
The technical scheme of the invention is further explained by the specific implementation mode in combination with the attached drawings.
Example 1
The embodiment provides a preparation method of a lithium cobaltate precursor with a coating structure, which specifically comprises the following steps:
(1) Pre-doping Co with Mg, ti and Al 3 O 4 Magnetic stirring with deionized water in a beaker, co 3 O 4 The content of pre-doped Mg is 0.1wt%, the content of Ti is 0.5wt%, the content of Al is 0.1wt%, stirring for 3h, and dropwise adding zirconium nitrate aqueous solution, wherein each 100g of Co 3 O 4 Adding 1.742g of zirconium nitrate, stirring for 3h, then dropwise adding an ammonia solution, and then continuously stirring for 3h to obtain a precursor mixture;
(2) Washing the precursor mixture for 3 times by deionized water, and drying at 60 ℃ to obtain a lithium cobaltate precursor with the surface coated with zirconium hydroxide;
(3) Sintering the zirconium hydroxide-coated lithium cobaltate precursor obtained in the step (2) at 500 ℃ for 10h, crushing and grinding to obtain a zirconium oxide-coated lithium cobaltate precursor, and mixing with Co 3 O 4 The mass fraction of (B) is 100wt%, and the mass fraction of zirconia is 0.5wt%.
The embodiment also provides a preparation method of the lithium cobaltate positive electrode material, which comprises the following steps:
mixing and ball-milling the prepared lithium cobaltate precursor and a lithium salt in a ball mill for 9 hours, wherein the rotating speed of the ball mill is 90r/min, the molar ratio of a lithium element in the lithium salt to a cobalt element in the lithium cobaltate precursor is 1.1, and sintering the mixed powder at 700 ℃ for 10 hours to obtain the lithium cobaltate cathode material.
And analyzing the morphology structure and element distribution of the prepared lithium cobaltate precursor by adopting a scanning electron microscope. The morphology of the lithium cobaltate precursor is shown in fig. 1, and it can be seen from fig. 1 that a uniform coating layer is formed on the surface of the lithium cobaltate precursor. The element distribution diagrams are shown in fig. 2 to 6, and it can be seen from fig. 2 to 6 that the distribution of the Co element, the Mg element, the Ti element, the Zr element, and the Al element is relatively uniform.
Example 2
The embodiment provides a preparation method of a lithium cobaltate precursor with a coating structure, which specifically comprises the following steps:
(1) Pre-doping Co (OH) with Mn and Zn 2 Magnetic stirring with deionized water in a beaker, co (OH) 2 The content of pre-doped Mn in the solution is 0.1wt%, the content of Zn in the solution is 0.1wt%, stirring the solution for 3h, and then dropwise adding magnesium nitrate aqueous solution, wherein each 100g of Co (OH) 2 Adding 0.037g of magnesium nitrate, stirring for 3 hours, then dropwise adding an ammonia solution, and then continuously stirring for 3 hours to obtain a precursor mixture;
(2) Washing the precursor mixture with deionized water for 3 times, and drying at 50 ℃ to obtain a lithium cobaltate precursor coated with magnesium hydroxide on the surface;
(3) Sintering the magnesium hydroxide-coated lithium cobaltate precursor obtained in the step (2) at 400 ℃ for 12h, crushing and grinding to obtain a magnesium oxide-coated lithium cobaltate precursor, and mixing with Co 3 O 4 The mass fraction of magnesium oxide is 0.01wt% based on 100 wt%.
The embodiment also provides a preparation method of the lithium cobaltate positive electrode material, which comprises the following steps:
and mixing the prepared lithium cobaltate precursor with a lithium salt in a ball mill for ball milling for 6 hours, wherein the rotating speed of the ball mill is 120r/min, the molar ratio of a lithium element in the lithium salt to a cobalt element in the lithium cobaltate precursor is 1:1, and sintering the mixed powder at 600 ℃ for 14 hours to obtain the lithium cobaltate cathode material.
Example 3
The embodiment provides a preparation method of a lithium cobaltate precursor with a coating structure, which specifically comprises the following steps:
(1) Magnetically stirring CoO pre-doped with Ni and Y and deionized water in a beaker, wherein the content of the pre-doped Ni in the CoO is 5wt%, the content of the Y is 3wt%, dropwise adding a zinc nitrate aqueous solution after stirring for 3h, adding 3.655g of zinc nitrate into every 100g of CoO, dropwise adding an ammonia aqueous solution after stirring for 3h, and then continuously stirring for 3h to obtain a precursor mixture;
(2) Washing the precursor mixture with deionized water for 3 times, and drying at 55 ℃ to obtain a lithium cobaltate precursor with the surface coated with zinc hydroxide;
(3) Sintering the lithium cobaltate precursor coated with the zinc hydroxide obtained in the step (2) at 450 ℃ for 8h, crushing and grinding to obtain the lithium cobaltate precursor coated with the zinc oxide on the surface, and mixing with Co 3 O 4 The mass fraction of (2) is 100wt%, and the mass fraction of zinc oxide is 1wt%.
The embodiment also provides a preparation method of the lithium cobaltate positive electrode material, which comprises the following steps:
mixing and ball-milling the prepared lithium cobaltate precursor and a lithium salt in a ball mill for 8 hours, wherein the rotating speed of the ball mill is 100r/min, the molar ratio of a lithium element in the lithium salt to a cobalt element in the lithium cobaltate precursor is 1.05, and sintering the mixed powder at 650 ℃ for 9 hours to obtain the lithium cobaltate cathode material.
Example 4
The embodiment provides a preparation method of a lithium cobaltate precursor with a coating structure, which specifically comprises the following steps:
(1) Magnetically stirring cobalt oxyhydroxide pre-doped with Mo, ru and Sn and deionized water in a beaker, wherein the content of the pre-doped Mo in the cobalt oxyhydroxide is 3wt%, the content of the Ru is 3wt%, and the content of the Sn is 4wt%; stirring for 3h, dropwise adding a manganese nitrate aqueous solution, adding 6.171g of manganese nitrate into every 100g of cobalt oxyhydroxide, stirring for 3h, dropwise adding an ammonia aqueous solution, and then continuously stirring for 3h to obtain a precursor mixture;
(2) Washing the precursor mixture for 3 times by deionized water, and drying at 57 ℃ to obtain a lithium cobaltate precursor coated with manganese hydroxide on the surface;
(3) Sintering the lithium cobaltate precursor coated with the manganese hydroxide obtained in the step (2) at 550 ℃ for 6 hours, crushing and grinding to obtain the lithium cobaltate precursor coated with the manganese dioxide on the surface, and mixing with Co 3 O 4 The mass fraction of manganese dioxide is 3wt% based on 100 wt%.
The embodiment also provides a preparation method of the lithium cobaltate positive electrode material, and the preparation method comprises the following steps:
and mixing and ball-milling the prepared lithium cobaltate precursor and a lithium salt in a ball mill for 10 hours, wherein the rotating speed of the ball mill is 80r/min, the molar ratio of a lithium element in the lithium salt to a cobalt element in the lithium cobaltate precursor is 1:1, and sintering the mixed powder at 750 ℃ for 8 hours to obtain the lithium cobaltate cathode material.
Example 5
The embodiment provides a preparation method of a lithium cobaltate precursor with a coating structure, which specifically comprises the following steps:
(1) Magnetically stirring cobalt carbonate pre-doped with W and Ga and deionized water in a beaker, wherein the content of the pre-doped W in the cobalt carbonate is 2wt%, and the content of Ga is 3wt%; stirring for 3h, dropwise adding yttrium nitrate aqueous solution, adding 8.482g of yttrium nitrate into every 100g of cobalt carbonate, stirring for 3h, dropwise adding ammonia water solution, and then continuously stirring for 3h to obtain a precursor mixture;
(2) Washing the precursor mixture for 3 times by deionized water, and drying at 60 ℃ to obtain a lithium cobaltate precursor with the surface coated with yttrium hydroxide;
(3) Sintering the yttrium hydroxide coated lithium cobalt oxide precursor obtained in the step (2) at 600 ℃ for 5 hours, crushing and grinding to obtain an yttrium oxide coated lithium cobalt oxide precursor, and using Co to prepare the yttrium oxide coated lithium cobalt oxide precursor 3 O 4 The mass fraction of yttrium oxide is 5wt%, calculated as 100 wt%.
The embodiment also provides a preparation method of the lithium cobaltate positive electrode material, which comprises the following steps:
mixing and ball-milling the prepared lithium cobaltate precursor and a lithium salt in a ball mill for 12 hours, wherein the rotating speed of the ball mill is 60r/min, the molar ratio of a lithium element in the lithium salt to a cobalt element in the lithium cobaltate precursor is 1.1, and sintering the mixed powder at 800 ℃ for 6 hours to obtain the lithium cobaltate cathode material.
Example 6
The embodiment provides a preparation method of a lithium cobaltate precursor with a coating structure, which specifically comprises the following steps:
(1) Pre-doping Co with Mg, ti and Al 3 O 4 Magnetic stirring with deionized water in a beaker, co 3 O 4 3wt% of Mg, 2wt% of Ti and 2wt% of Al pre-doped in the aluminum nitrate solution, stirring for 3h, and adding dropwise aluminum nitrate solution into the mixture, wherein each 100g of Co 3 O 4 Adding 7.358g of aluminum nitrate, and stirring for 3 hours to obtain a precursor mixture;
(2) Washing the precursor mixture with deionized water for 3 times, and drying at 60 deg.C to obtain lithium cobaltate precursor coated with aluminum hydroxide on surfaceThe hydroxide ions in the aqueous solution are combined to form aluminum hydroxide, and the reaction process comprises the formation, the separation and the Co adsorption of aluminum hydroxide precipitates 3 O 4 The surface of the particles forms a uniform and continuous aluminum hydroxide coating layer);
(3) Sintering the lithium cobaltate precursor coated with the aluminum hydroxide obtained in the step (2) at 500 ℃ for 10 hours, crushing and grinding to obtain the lithium cobaltate precursor coated with the aluminum oxide on the surface, and using Co to 3 O 4 The mass fraction of alumina is 2wt% based on 100 wt%.
The embodiment also provides a preparation method of the lithium cobaltate positive electrode material, which comprises the following steps:
mixing and ball-milling the prepared lithium cobaltate precursor and a lithium salt in a ball mill for 9 hours, wherein the rotating speed of the ball mill is 90r/min, the molar ratio of a lithium element in the lithium salt to a cobalt element in the lithium cobaltate precursor is 1.1, and sintering the mixed powder at 700 ℃ for 10 hours to obtain the lithium cobaltate cathode material.
Example 7
The embodiment provides a preparation method of a lithium cobaltate precursor with a coating structure, which specifically comprises the following steps:
(1) Pre-doping Co with Mg, ti and Al 3 O 4 Magnetic stirring with deionized water in a beaker, co 3 O 4 The content of pre-doped Mg is 0.1wt%, the content of Ti is 0.5wt% and the content of Al is 0.1wt%, stirring for 3h, and dropwise adding aqueous solution of zirconium nitrate and aluminum nitrate, wherein each 100g of Co 3 O 4 Adding 3.488g of zirconium nitrate and 3.679g of aluminum nitrate, stirring for 3 hours, then dropwise adding an ammonia solution, and then continuously stirring for 3 hours to obtain a precursor mixture;
(2) Washing the precursor mixture with deionized water for 3 times, and drying at 60 ℃ to obtain a lithium cobaltate precursor coated with zirconium hydroxide and aluminum hydroxide on the surface;
(3) Sintering the lithium cobaltate precursor coated with zirconium hydroxide and aluminum hydroxide obtained in the step (2) at 500 ℃ for 10h, crushing and grinding to obtain the lithium cobaltate precursor coated with zirconium oxide and aluminum oxideLithium cobaltate precursor of aluminium, with Co 3 O 4 The mass fraction of zirconia is 1wt%, and the mass fraction of alumina is 1wt%.
The embodiment also provides a preparation method of the lithium cobaltate positive electrode material, which comprises the following steps:
mixing and ball-milling the prepared lithium cobaltate precursor and a lithium salt in a ball mill for 9 hours, wherein the rotating speed of the ball mill is 90r/min, the molar ratio of a lithium element in the lithium salt to a cobalt element in the lithium cobaltate precursor is 1.1, and sintering the mixed powder at 700 ℃ for 10 hours to obtain the lithium cobaltate cathode material.
Comparative example 1
The comparative example provides a preparation method of a lithium cobaltate precursor with a coating structure, and the preparation method specifically comprises the following steps:
(1) Pre-doping Co with Mg, ti and Al 3 O 4 Mixing with zirconia and ball milling to obtain precursor mixture with zirconia coated surface, co 3 O 4 The content of the pre-doped Al is 0.5wt%, the content of Mg is 0.1wt%, and the content of Al is 0.1wt%;
(2) Sintering the zirconia-coated lithium cobalt oxide precursor obtained in the step (1) at 500 ℃ for 10 hours, crushing and grinding to obtain the zirconia-coated lithium cobalt oxide precursor, and using Co to prepare the zirconia-coated lithium cobalt oxide precursor 3 O 4 The mass fraction of (B) is 100wt%, and the mass fraction of zirconia is 0.5wt%.
The comparative example also provides a preparation method of the lithium cobaltate positive electrode material, and the preparation method comprises the following steps:
mixing and ball-milling the prepared lithium cobaltate precursor and a lithium salt in a ball mill for 9 hours, wherein the rotating speed of the ball mill is 90r/min, the molar ratio of a lithium element in the lithium salt to a cobalt element in the lithium cobaltate precursor is 1.1, and sintering the mixed powder at 700 ℃ for 10 hours to obtain the lithium cobaltate cathode material.
Lithium ion batteries were prepared using the lithium cobaltate positive electrode materials prepared in examples 1 to 7 and comparative example 1 as follows, and the prepared lithium ion batteries were tested. The 0.1C discharge gram capacity mAh/g and the cycle capacity retention rate are tested.
The lithium ion battery is prepared by the following method:
(1) Preparing a positive pole piece: the method comprises the following steps of fully and uniformly stirring an active material lithium cobaltate positive electrode material, a conductive agent carbon nano tube and a binder polyvinylidene fluoride (PVDF) in an N-methyl pyrrolidone solvent according to a mass ratio of 96.
(2) Preparing a negative pole piece: the method comprises the following steps of fully stirring and uniformly mixing active substance artificial graphite, conductive agent acetylene black, binder Styrene Butadiene Rubber (SBR) and thickener sodium carboxymethyl cellulose (CMC) in deionized water according to a mass ratio of 96.
(3) And (3) isolation film: polyethylene (PE) porous polymeric films were used as separators.
(4) Preparing an electrolyte: 1.2mol/L LiPF6 was added to a solvent of dimethyl carbonate, diethyl carbonate and ethylene carbonate of 1. Simultaneously adding 2.1 percent of 1,3,6-hexanetrinitrile, succinonitrile and adiponitrile in a mass ratio of 1.
And (3) stacking the positive pole piece, the isolating membrane and the negative pole piece in sequence, wherein the membrane is positioned between the positive pole and the negative pole to play an isolating role, and winding or laminating. And (4) placing the battery core in an outer package, injecting electrolyte and packaging.
The prepared lithium ion battery is subjected to the following performance tests:
(1) And (3) capacity testing: 10 lithium cobaltate positive electrode materials obtained in each of examples and comparative examples were prepared into lithium ion batteries, which were charged at a constant current of 0.1C to 4.5V at room temperature, and then charged at a constant voltage of 4.5V to a current of less than 0.02C, so that the batteries were in a fully charged state of 4.5V. Then constant current discharge is carried out to 3.0V under the multiplying power of 0.1C, the discharge capacity is obtained, and the discharge gram capacity is calculated by adopting the following formula:
gram capacity for discharge = discharge capacity/mass of lithium cobaltate positive electrode material.
(2) Cycle capacity retention rate test: 10 lithium cobaltate positive electrode materials obtained in the examples and the comparative examples are respectively prepared into a lithium ion battery, the lithium ion battery is subjected to charge-discharge circulation through the following test steps,
charging and discharging are carried out in the environment of room temperature, constant-current constant-voltage charging is carried out under the charging current of 0.5C until the upper limit voltage is 4.5V and the cut-off current is 0.02C; then standing for 10 minutes; then, constant current discharge was performed at a discharge current of 0.5C until 3.0V.
(ii) in the environment of 45 ℃, carry on charge and discharge, carry on the constant current constant voltage charging under the charging current of 1C, until the upper limit voltage is 4.5V, the cutoff current is 0.02C; then standing for 10 minutes; then, constant current discharge was performed at a discharge current of 0.5C until 3.0V.
The discharge capacity retention rate of the lithium ion battery is calculated by adopting the following formula:
cycle capacity retention rate test = (discharge capacity at nth cycle/discharge capacity at first cycle) × 100%.
The results of the 0.1C gram discharge capacity and the capacity retention after 100 cycles at room temperature are shown in table 1.
(3) And (3) charge-discharge cycle test: the lithium ion batteries made of the lithium cobaltate positive electrode materials prepared in example 1 and comparative example 1 were subjected to a charge-discharge cycle test in an environment of 45 ℃, and were subjected to constant-current constant-voltage charging at a charging current of 1C until the upper limit voltage was 4.5V and the cutoff current was 0.02C; then standing for 10 minutes; then, constant current discharge was performed at a discharge current of 0.5C until 3.0V. A cycle test pattern was obtained, as shown in fig. 7, from which it can be seen that the retention rate of example 1 was 95.6% at 200 cycles, and the cycle retention rate of comparative example 1 was 78.1% at this time, so that example 1 had better cycle stability and thermal stability.
TABLE 1
Figure BDA0002850672010000161
Figure BDA0002850672010000171
As can be seen from the data in table 1:
as can be seen from the test data of example 1 and comparative example 1, the only difference between example 1 and example 1 is that in the process of preparing a lithium cobaltate precursor, example 1 adopts liquid-phase coating, while comparative example 1 adopts solid-phase coating, and from the test data, the gram discharge capacity of the lithium cobaltate positive electrode material prepared in example 1 is better than that of comparative example 1, and the capacity retention rate is basically equal to that of comparative example 1, because example 1 forms a metal hydroxide by liquid-phase coating, and then obtains the metal oxide by sintering, while comparative example 1 directly coats the metal oxide by solid-phase coating, in example 1, with the addition of ammonia, metal cations react with added hydroxide radicals to generate the metal hydroxide, thereby obtaining a mixture of the metal hydroxide coated lithium cobaltate precursor and metal salt, in the subsequent sintering process, the metal hydroxide dehydrates to form the metal oxide, a solid solution contact interface is formed between the pre-doped cobalt source of the substrate material and the coating layer by diffusion of metal atoms, and the stable coating layer structure of the lithium cobaltate is stabilized, so as to inhibit the dissolution of the cobalt atoms and the dissolution of the metal elements, thereby improving the stability of the lithium cobaltate precursor and the structure of cobalt.
The applicant declares that the above description is only a specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and it should be understood by those skilled in the art that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are within the scope and disclosure of the present invention.

Claims (41)

1. A preparation method of a lithium cobaltate precursor with a coating structure is characterized by comprising the following steps:
mixing and stirring a cobalt source doped with metal elements and a metal salt solution, adding alkali liquor, continuing stirring to obtain a precursor mixture, and sintering the precursor mixture to obtain a lithium cobaltate precursor with a coating structure.
2. The method according to claim 1, wherein the metal element doped in the cobalt source comprises any one or a combination of at least two of Al, mg, zr, ti, ni, mn, Y, zn, mo, ru, ta, W, re, sn, ge or Ga.
3. The method of claim 1, wherein the cobalt source comprises any one of cobalt oxide, cobaltosic oxide, cobalt hydroxide, cobalt oxyhydroxide, or cobalt carbonate, or a combination of at least two thereof.
4. The method according to claim 3, wherein the content of the metal element doped in the cobalt source is 0.1 to 10wt%.
5. The method according to claim 1, wherein the metal element in the metal salt solution comprises any one or a combination of at least two of Al, mg, zr, ti, ni, mn, Y, zn, mo, ru, ta, W, re, sn, ge or Ga.
6. The method according to claim 1, wherein the alkali solution is ammonia.
7. The method according to claim 1 or 2, wherein the cobalt source doped with the metal element is mixed with the metal salt solution for 1 to 5 hours.
8. The process according to claim 1 or 2, wherein the stirring is continued for 1 to 5 hours after the addition of the alkali solution.
9. A method according to claim 1 or 2, characterized in that the precursor mixture is dried after being washed before sintering.
10. The method of claim 9, wherein the cleaning medium is deionized water.
11. The method according to claim 9, wherein the drying temperature is 50 to 60 ℃.
12. The method according to claim 1, wherein the sintering temperature of the precursor mixture is 400 to 600 ℃.
13. The method according to claim 1, wherein the sintering time of the precursor mixture is 5 to 12 hours.
14. A lithium cobaltate precursor prepared by the preparation method according to any one of claims 1 to 13, wherein the lithium cobaltate precursor comprises a core and a coating layer coated on the outer surface of the core, and the coating layer is a metal oxide.
15. The lithium cobaltate precursor according to claim 14, wherein the mass fraction of the metal oxide is 0.01 to 5wt%, based on 100wt% of the mass fraction of the cobalt source.
16. A preparation method of a lithium cobaltate positive electrode material with a coating structure is characterized by comprising the following steps:
mixing and grinding the lithium cobaltate precursor of claim 14 or 15 and a lithium salt, and sintering to obtain the lithium cobaltate positive electrode material.
17. The method according to claim 16, wherein a molar ratio of the lithium element in the lithium salt to the cobalt element in the lithium cobaltate precursor is (1.05-1.1): 1.
18. The method of claim 16, wherein the grinding is performed in a ball mill.
19. The method according to claim 18, wherein the rotation speed of the ball mill is 60 to 120r/min.
20. The method of claim 16, wherein the milling time is 6 to 12 hours.
21. The method according to claim 16, wherein the sintering temperature of the lithium cobaltate precursor is 600 to 800 ℃.
22. The method according to claim 16, wherein the sintering time of the lithium cobaltate precursor is 6 to 14 hours.
23. A lithium cobaltate positive electrode material with a coating structure, which is prepared by the preparation method of any one of claims 16 to 22.
24. A lithium ion battery is characterized by comprising a shell and a battery cell positioned in the shell, wherein the battery cell is obtained by sequentially laminating a positive pole piece, a diaphragm and a negative pole piece and then winding or laminating;
the positive pole piece is prepared by the following method:
dispersing a positive electrode active substance, a conductive agent and a positive electrode binder in a solvent, mixing, coating the mixture on the surface of a positive electrode current collector, and drying and cold-pressing to obtain the positive electrode piece, wherein the positive electrode active substance comprises the lithium cobaltate with the coating structure in the claim 23.
25. The lithium ion battery of claim 24, wherein the conductive agent comprises any one of acetylene black, ketjen black, natural graphite, carbon black, cellulose, metal powder or metal fiber or a combination of at least two thereof.
26. The li-ion battery of claim 24, wherein the solvent comprises any one of N-methyl pyrrolidone, acetone, or water, or a combination of at least two thereof.
27. The li-ion battery of claim 24, wherein the positive binder comprises any one or a combination of at least two of polyvinylidene fluoride, polyvinylidene chloride, carboxymethyl cellulose, polyvinyl acetate, polyvinyl pyrrolidone, polypropylene, or polyethylene.
28. The lithium ion battery of claim 24, wherein the negative electrode sheet is prepared by a method comprising:
and dispersing the negative active material, the conductive agent, the negative binder and the sodium carboxymethylcellulose in a solvent, mixing, coating on the surface of a current collector, drying and cold-pressing to obtain the negative pole piece.
29. The lithium ion battery of claim 28, wherein the negative active material comprises any one of or a combination of at least two of lithium metal, a lithium alloy, a transition metal oxide, a non-transition metal oxide, or a carbon-based material.
30. The lithium ion battery of claim 29, wherein the transition metal oxide comprises lithium titanium oxide and/or lithium vanadium oxide.
31. The lithium ion battery of claim 29, wherein the non-transition metal oxide comprises SiO 2 And/or SnO 2 。
32. The li-ion battery of claim 29, wherein the carbon-based material comprises crystalline carbon and/or amorphous carbon.
33. The lithium ion battery of claim 32, wherein the crystalline carbon comprises natural graphite and/or synthetic graphite.
34. The li-ion battery of claim 32, wherein the amorphous carbon comprises any one of soft carbon, hard carbon, or mesophase pitch carbonization products, or a combination of at least two thereof.
35. The lithium ion battery of claim 24, wherein the separator is made of polyethylene.
36. The li-ion battery of claim 24, wherein the housing is internally impregnated with an electrolyte.
37. The lithium ion battery of claim 36, wherein the electrolyte comprises a non-aqueous electrolyte and a lithium salt.
38. The lithium ion battery of claim 37, wherein the non-aqueous electrolyte solvent comprises any one of methyl propionate, ethyl acetate, methyl formate, diethyl carbonate, dimethyl carbonate, or ethylene carbonate, or a combination of at least two thereof.
39. The lithium ion battery of claim 37, wherein the lithium salt comprises any one of lithium hexafluorophosphate, lithium perchlorate, lithium hexafluoroarsenate, lithium tetrafluoroborate or lithium chloride, or a combination of at least two thereof.
40. The li-ion battery of claim 37, wherein the electrolyte further comprises an additive.
41. The lithium ion battery of claim 40, wherein the additive comprises any one of acetonitrile, succinonitrile, adiponitrile, or 1,3,6-hexanetrinitrile, or a combination of at least two thereof.
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