CN113328082A - Positive electrode lithium supplement material and lithium ion battery comprising same - Google Patents
Positive electrode lithium supplement material and lithium ion battery comprising same Download PDFInfo
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- 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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Abstract
The invention provides a positive electrode lithium supplement material and a lithium ion battery comprising the same2±xNiO2@TiO2The positive electrode lithium supplement material can be decomposed during formation charging, gas generated after decomposition can be removed during formation, generated lithium is transferred from the positive electrode to the negative electrode during charging and forms an SEI film on the negative electrode, and lithium required for forming the SEI film is filled, so that the consumption of positive electrode non-reversible lithium ions can be reduced, the irreversible capacity of the lithium ion battery is reduced, the first coulomb efficiency of the lithium ion battery is improved, and the lithium ion battery is improvedThe cycle performance of (c). After the lithium-supplementing material of the positive electrode is charged and decomposed for the first time, the main product remained on the positive electrode is LiNiO2@TiO2The product also has a reversible capacity similar to lithium nickelate, since it has TiO2Some characteristics after modification, namely the cycling stability of the LiNiO are purer2And higher.
Description
Technical Field
The invention aims at the technical field of lithium ion batteries, and mainly relates to a positive electrode lithium supplement material and a lithium ion battery comprising the same.
Background
In recent years, with the rise and development of electric automobiles, electric bicycles, and portable intelligent devices, there is an increasing demand for power sources having high energy density. At present, a ternary power battery system usually adopts high-nickel 811 anode matched graphite, and the mass energy density of the ternary power battery system is only close to 290 wh/kg; for the positive electrode material, the gram capacity of the positive electrode material is already exerted to 195mAh/g, the positive electrode material with higher nickel content is further selected, the gram capacity is only increased by 3-5 mAh/g, but the aspects of safety, cycle performance, cell stability and the like are greatly reduced, and even the positive electrode material is difficult to be applied to commercial use. For the artificial graphite of the negative electrode, the theoretical gram capacity is 372mAh/g, the gram capacity of the current commercial graphite reaches 355-363 mAh/g, the capacity is close to the theoretical capacity, and the lifting space is very limited. In order to improve the mass energy density of the battery to 300wh/kg or more, the pure graphite cathode material has been difficult to meet the energy density requirement, so more and more researchers are focusing on silicon cathode materials with gram capacity of more than 4000mAh/g, such as Si, SiC, SiOx materials, etc., but such cathode materials have the disadvantage of low first charge-discharge efficiency.
At present, during the first charging process of a commercial lithium ion battery system using graphite as a negative electrode, about 10% of active lithium in the positive electrode is consumed, and an irreversible stable SEI film is formed on the surface of the negative electrode, resulting in irreversible capacity loss, and further resulting in reduction of energy density of the lithium ion battery. When the negative electrode contains partial silicon-based materials or tin-based materials with high capacity such as silicon, silicon carbon, silicon oxide and the like, active lithium in the positive electrode is further consumed so as to meet the growth of an SEI (solid electrolyte interphase) film of the silicon-containing negative electrode and partial irreversible alloying reaction, and finally the loss of the active lithium in the full battery is more than 10 percent and even reaches 15 percent.
Li2NiO2Is a layered lithium-rich transition metal oxide, the theoretical capacity of which reaches 486mAh/g, is a good lithium supplement material, releases lithium ions at a voltage of more than 3.6V, and the material is formed into LiNiO through chemical change2The material is used as a positive electrode lithium supplement material matched with a ternary positive electrode material, and the material can greatly improve the energy density of the battery. But Li2NiO2The surface structure of the material has poor stability, the freezing phenomenon is easy to occur when the battery is homogenized, a large amount of gas is easy to generate in the charging and discharging process, and the structure is unstable so as to cause a series of side reactions.
Disclosure of Invention
In order to improve Li in the prior art2±xNiO2The invention provides a positive electrode lithium supplement material and a lithium ion battery comprising the same.
The purpose of the invention is realized by the following technical scheme:
a positive electrode lithium supplement material comprises a core material and a coating layer, wherein the core material comprises at least one compound shown in a formula 1,
Li2±xNiO2formula 1
In the formula 1, x is more than or equal to 0 and less than or equal to 0.5;
the coating layer coats the core material, the coating layer comprises metal oxide, and the metal oxide comprises TiO2。
According to an embodiment of the present invention, the positive electrode lithium supplement material is represented as Li2±xNiO2@TiO2Wherein x is more than or equal to 0 and less than or equal to 0.5.
According to an embodiment of the invention, x is 0, 0.1, 0.2, 0.3, 0.4 or 0.5. Exemplarily, x is 0, i.e., the positive electrode lithium-supplementing material is represented as Li2NiO2@TiO2。
According to an embodiment of the invention, the coating layer consists of a metal oxide.
According to an embodiment of the invention, the metal oxide is selected from TiO2(ii) a Further, selected from nano-sized TiO2。
According to an embodiment of the present invention, the TiO2The mass ratio of the compound to at least one of the compounds represented by the formula 1 is (0.01-1): 100, such as 0.01:100, 0.05:100, 0.1:100, 0.15:100, 0.2:100, 0.4:100, 0.5:100, 0.6:100, 0.8:100 or 1: 100.
According to an embodiment of the invention, the thickness of the coating layer is 2-50 nm, such as 2-20 nm, such as 2nm, 5nm, 8nm, 10nm or 20 nm. The coating layer is selected to have a thickness effective to inhibit attack by HF in the electrolyte to protect the core material while allowing free deintercalation of lithium ions.
According to an embodiment of the invention, the median particle diameter D of the core material502 to 8 μm, such as 4 to 6 μm. The core material is selected such that the median particle diameter D50The risk of increasing the internal resistance flatulence of the battery caused by longer lithium ion migration path can be avoided.
According to the embodiment of the invention, the median particle diameter D of the positive electrode lithium supplement material502 to 8 μm, such as 4 to 6 μm.
According to an embodiment of the present invention, the molar ratio of Li element in the lithium source and Ni element in the nickel source for preparing the compound represented by formula 1 is (2.05 + -x-2.5 + -x) 1.0, 0. ltoreq. x.ltoreq.0.5.
In the invention, the particle sizes of the nuclear material and the anode lithium supplement material can be tested by a scanning electron microscope or a laser particle sizer, and the thickness of the coating layer is tested by adopting profile EDS surface scanning and/or a high-resolution transmission electron microscope; the material composition was tested using profile EDS surface scanning. The specific test parameters of different instruments are different, and the test methods and parameters are also common knowledge in the field, and thus are not described herein again.
In the invention, the core material is coated by the coating layer, the structural stability of the core material is obviously improved, and the reason for analyzing is that: interaction exists between the core material and the coating layer in the positive electrode lithium supplement material with the core-shell structure. The coating of the metal oxide can inhibit the reaction between the electrolyte and the nuclear material, and meanwhile, the Ti-O bond in the coating layer is stronger than the Ni-O bond, so that the dissolution of Ni ions is inhibited, the surface of the nuclear material has better performance of resisting the acid environment in the electrolyte, and the surface stability of the anode lithium supplement material is improved. Meanwhile, the coating layer is relatively loose, which is beneficial to the diffusion of lithium ions. In addition, the coating layer comprises a layer structure obtained by metal oxide, the core material is tightly coated by the metal oxide, the electrochemical performance of the positive electrode lithium supplement material can be improved by tightly coating the core-shell structure, the corrosion of water in the air to the core material is isolated, the stability of the positive electrode lithium supplement material in the air is improved, a harsh operating environment is not required, and the large-scale production is facilitated.
The invention also provides a preparation method of the anode lithium supplement material, which comprises the following steps:
step S1, mixing and grinding the nuclear material and the metal source to obtain a precursor mixture; the core material includes at least one of the compounds represented by formula 1,
Li2±xNiO2formula 1
In the formula 1, x is more than or equal to 0 and less than or equal to 0.5;
the metal source is selected from metal oxides, the metal comprising Ti;
and S2, drying the precursor mixture prepared in the step S1, and sintering at high temperature to prepare the anode lithium supplement material.
According to an embodiment of the present invention, in step S1, the metal oxide is preferably a nanoscale metal oxide.
Wherein the metal oxide comprises titanium oxide (TiO)2) Preferably comprising nano-sized titanium oxide (TiO)2)。
According to an embodiment of the present invention, in step S1, the mass ratio of the metal source and the core material is (0.01 to 1):100, such as 0.01:100, 0.05:100, 0.1:100, 0.15:100, 0.2:100, 0.4:100, 0.5:100, 0.6:100, 0.8:100, or 1: 100.
According to an embodiment of the present invention, in step S1, the mixing and milling is performed using methods known in the art, such as using a high-speed mixer.
According to the embodiment of the invention, in step S2, the high-temperature sintering is performed in a pure oxygen atmosphere, which is selected to ensure that the synthesized positive electrode lithium supplement material has good crystallinity and purity.
According to an embodiment of the present invention, in step S2, the temperature of the high temperature sintering is 500 to 900 ℃, the time of the high temperature sintering is 4 to 40 hours, for example, the temperature of the high temperature sintering is 600 to 800 ℃, and the time of the high temperature sintering is 4 to 36 hours.
According to an embodiment of the present invention, the core material is prepared by the following method:
uniformly mixing a lithium source and a nickel source, then roasting, cooling and sieving to prepare the nuclear material, wherein the nuclear material comprises at least one of the compounds shown in the formula 1,
Li2±xNiO2formula 1
In the formula 1, x is more than or equal to 0 and less than or equal to 0.5.
Wherein the lithium source is selected from Li2O、LiOH、Li2CO3At least one of (1).
Wherein the nickel source is selected from NiO, Ni (OH)2、NiCO3At least one of (1).
Wherein the molar ratio of Li element in the lithium source to Ni element in the nickel source is (2.05 +/-x-2.5 +/-x) 1.0, and x is more than or equal to 0 and less than or equal to 0.5; such as 2.05:1.0, 2.1:1.0, 2.2:1.0, 2.3:1.0, 2.4:1.0, 2.5:1.0, 2.6:1.0, 2.7:1.0, 2.8:1.0, 2.9:1.0, or 3.0: 1.0. It was found that an excessive amount of lithium source can prevent the material from losing lithium volatilization during firing to deteriorate the crystallinity of the material.
Wherein the firing is performed in a muffle furnace.
Wherein the firing is performed in an oxygen atmosphere, and the firing in the oxygen atmosphere is effective for decomposing Li2CO3And the material takes part in oxidation reaction to synthesize the material with good crystallinity.
Wherein the roasting conditions are as follows: roasting for 4-8 h at 500-550 ℃; roasting for 4-8 h at 600-750 ℃; roasting for 8-12 h at 800-950 ℃; preferably, roasting at 500 ℃ for 5 h; roasting at 720 ℃ for 5 h; roasting at 800 deg.c for 10 hr.
According to an embodiment of the invention, the method comprises the steps of:
(1) raw material Li of lithium supplement additive2O can be selected from LiOH and Li2CO3LiOH mixed Li2CO3Or other substances decomposed or combined, NiO may be formed from Ni (OH)2、NiCO3Decomposing or combining nickel-containing substances to obtain;
(2) mixing for 1-20h in a high-speed mixer according to the molar ratio of Li element to Ni element (2.05 +/-x-2.5 +/-x) of 1.0 and x not less than 0 and not more than 0.5; the excessive lithium source is added to prevent the material from being poor in crystallinity caused by lithium volatilization loss in high-temperature sintering;
(3) sintering the mixture for 4-40 h at 500-900 ℃ in an oxygen atmosphere, cooling, crushing, and screening to obtain Li2±xNiO2Wherein x is more than or equal to 0 and less than or equal to 0.5;
(4) the obtained Li2±xNiO2Same nano-scale TiO2Mixing uniformly, wherein the TiO2With Li2±xNiO2The mass ratio of (0.01-1): 100, and the second sintering is carried out for 4-40 h at 500-900 ℃ in the oxygen atmosphere, and TiO is obtained after cooling2Coated Li2±xNiO2Are denoted by Li2±xNiO2@TiO2Wherein x is more than or equal to 0 and less than or equal to 0.5.
The invention also provides a positive electrode, wherein the positive electrode comprises a positive electrode current collector and a positive electrode active material layer coated on the positive electrode current collector, and the positive electrode active material layer comprises the positive electrode lithium supplement material and the positive electrode active material.
According to an embodiment of the present invention, the content of the positive electrode lithium supplement material is 1 to 5 wt%, for example, 1 wt%, 2 wt%, 3 wt%, 4 wt%, or 5 wt% of the total mass of the positive electrode active material layer.
According to an embodiment of the present invention, the positive electrode active material layer further includes a binder and a conductive agent.
According to an embodiment of the present invention, the content of the positive electrode active material is 85 to 97 wt% of the total mass of the positive electrode active material layer.
According to an embodiment of the present invention, the content of the binder is 1 to 5 wt%, for example, 1 wt%, 2 wt%, 3 wt%, 4 wt%, or 5 wt% of the total mass of the positive electrode active material layer.
According to an embodiment of the present invention, the content of the conductive agent is 1 to 5 wt%, for example, 1 wt%, 2 wt%, 3 wt%, 4 wt%, or 5 wt% of the total mass of the positive electrode active material layer.
According to an embodiment of the present invention, the positive electrode active material is selected from lithium iron phosphate (LiFePO)4) Lithium nickel cobalt manganese oxide (Li)zNixCoyMn1-x-yO2Wherein z is more than or equal to 0.95 and less than or equal to 1.05, x>0，y>0，x+y<1) Lithium nickel cobalt aluminate (Li)zNixCoyAl1-x-yO2Wherein z is more than or equal to 0.95 and less than or equal to 1.05, x>0，y>0，0.8≤x+y<1) Lithium nickel cobalt oxide (LiNi)xCoyO2Wherein x is>0，y>0, x + y ═ 1), lithium nickel cobalt manganese aluminate (Li)zNixCoyMnwAl1-x-y-wO2Wherein z is more than or equal to 0.95 and less than or equal to 1.05, x>0，y>0，w>0，0.8≤x+y+w<1) Lithium titanate (LiTiO)2) Layered lithium manganate (LiMnO)2) Spinel lithium manganate (LiMn)2O4) Lithium-rich manganese-based solid solution cathode material xLi2MnO3·(1-x)LiMO2Wherein M is Ni/Co/Mn.
Illustratively, the positive electrode active material is selected from LiNi1/3Co1/3Mn1/3、LiNi0.5Co0.2Mn0.3、LiNi0.4Co0.2Mn0.4、LiNi0.6Co0.2Mn0.2、LiNi0.8Co0.1Mn0.1、LiNi0.7Co0.2Mn0.1、LiNi0.7Co0.15Mn0.15、LiNixCoyMn1-x-yO2(wherein z is more than or equal to 0.95 and less than or equal to 1.05, x is more than or equal to 0.8 and less than or equal to 0.95, x is more than or equal to 0.03 and less than or equal to 0.2, and x + y<1) At least one of (1).
According to an embodiment of the present invention, the binder may be a polymer material including, but not limited to, polyvinylidene fluoride and polyimide.
According to an embodiment of the present invention, the conductive agent may be at least one of conductive carbon black, acetylene black, ketjen black, carbon nanotubes, graphene oxide, and graphene.
According to the invention, the anode lithium supplement material, the anode active substance, the conductive agent and the binder are prepared into slurry, the slurry is coated on the aluminum foil to prepare the battery core, the irreversible capacity of 245-275mAh/g can be provided for supplementing the consumption of the negative electrode after 1-10 cycles of adding the anode lithium supplement material per gram, and the reversible capacity of 90-130mAh/g is remained, so that the energy density of the battery is greatly improved.
The invention also provides a lithium ion battery which comprises the anode lithium supplement material.
According to an embodiment of the present invention, the lithium ion battery includes the above-described positive electrode.
According to an embodiment of the present invention, the lithium ion battery further includes a negative electrode, a separator, and a nonaqueous electrolytic solution.
According to the present invention, the negative electrode includes a negative electrode active material selected from a graphite material and a silicon material.
Wherein, the graphite material is at least one of artificial graphite, natural graphite and the like.
Wherein the silicon material is, for example, Si, SiC and SiOx(0<x<2) One or more of (a).
Wherein the silicon material accounts for 0-50 wt% of the total mass of the graphite material and the silicon material and is not 0.
Illustratively, defining Q as the mass mixing ratio of silicon material and graphite material, Q being the mass of silicon material/(mass of graphite material + mass of silicon material), 0< Q ≦ 0.5, preferably, such as 0< Q ≦ 0.15. For example, 0.06 and 0.1.
According to an embodiment of the present invention, the nonaqueous electrolytic solution is a conventional electrolytic solution known in the art, and the solvent contains ethylene carbonate (abbreviated as EC), diethyl carbonate (abbreviated as DEC), propylene carbonate (abbreviated as PC), fluoroethylene carbonate (abbreviated as FEC), and the like.
Has the advantages that:
compared with the prior art, the invention provides a positive electrode lithium supplement material and a lithium ion battery comprising the same, and has the following advantages:
research shows that the Li rich in lithium has the function of supplementing lithium2±xNiO2The first charge capacity of the material is up to 486mAh/g, lithium ions are released at a voltage of more than 3.6V, the energy density of the battery can be greatly improved, and the material is used as a positive electrode lithium supplement material matched with a ternary positive electrode material, but Li2±xNiO2The surface structure of the material is poor in stability, the freezing phenomenon is easy to occur during battery homogenization, a large amount of gas is easy to generate in the charging and discharging process, the structure is unstable, and then a series of side reactions are caused, so that TiO is added in the sintering process2And coated to Li by high temperature solid phase sintering2±xNiO2While the surface is formed, a small amount of Ti element doped on the surface is formed, the purpose of stabilizing the surface structure of the material is achieved, and Li can be effectively inhibited2±xNiO2Gas generation and improvement of target product Li2±xNiO2The quality of (2). In the invention, modified Li is added into the positive electrode material of the lithium ion battery2±xNiO2@TiO2As a second cathode material, Li is used during initial charge and discharge2±xNiO2The irreversible capacity of the lithium battery achieves the purpose of pre-embedding lithium into the negative electrode. The lithium supplementing mode avoids the safety of lithium supplementing by metal lithium and high requirements on environment, is simple and convenient, can be produced in large batch, and provides a good mode for low cost of the lithium ion battery.
The invention can supplement lithium material Li through the anode2±xNiO2@TiO2The use of (2) reduces the loss of irreversible capacity, and improves the energy density and other electrical properties of the battery. The added anode lithium supplement material is Li2±xNiO2@TiO2The positive electrode lithium-supplementing material can be decomposed only when being formed and charged, the gas generated after decomposition can be removed when being formed, and the generated lithium is transferred from the positive electrode to the negative electrode when being charged, and an SEI film is formed on the negative electrode and filledLithium required for forming an SEI film is supplemented, so that the consumption of non-reversible lithium ions of the positive electrode can be reduced, the irreversible capacity of the lithium ion battery can be reduced, the first coulombic efficiency of the lithium ion battery can be improved, and the cycle performance of the lithium ion battery can be improved. After the lithium-supplementing material of the positive electrode is charged and decomposed for the first time, the main product remained on the positive electrode is LiNiO2@TiO2The product also has a reversible capacity similar to lithium nickelate, since it has TiO2Some characteristics after modification, namely the cycling stability of the LiNiO are purer2And higher.
The method for compensating lithium ions by the lithium ion battery provided by the invention is safe, practical and convenient to operate.
Drawings
Fig. 1 is a charge cycle curve of the lithium ion batteries of example 1 of the present invention and comparative example 1.
Detailed Description
The present invention will be described in further detail with reference to specific examples. It is to be understood that the following examples are only illustrative and explanatory of the present invention and should not be construed as limiting the scope of the present invention. All the technologies realized based on the above-mentioned contents of the present invention are covered in the protection scope of the present invention.
The experimental methods used in the following examples are all conventional methods unless otherwise specified; reagents, materials and the like used in the following examples are commercially available unless otherwise specified.
Example 1
According to Li2CO3With NiCO3High speed mixing was performed at a molar ratio of 1.05:1.0, mixing standard reference: after mixing, the color of the mixture was controlled to be light green, in which nickel carbonate was invisible to the naked eye. And sintering the mixture for the first time in a muffle furnace, and introducing oxygen in the muffle furnace to serve as a sintering atmosphere. The synthesis is mainly carried out in three stages at constant temperature, the heating rate among the stages is 10 ℃/min: keeping the temperature of the low-temperature section at 500 ℃ for 5 hours; keeping the temperature of the medium temperature section at 720 ℃ for 5 h; keeping the temperature of the high-temperature section at 800 ℃ for 10 h; then naturally cooling the muffle furnace, taking out the materials, finely crushing the materials, and sieving the materials by a 300-mesh sieve to obtain Li2NiO2Powder material;
the Li obtained above2NiO2Same nano-grade TiO powder2Mixing uniformly, wherein the TiO2With Li2NiO2Designed according to the mass ratio of 1500ppm, the second sintering is carried out, the temperature is raised to 780 ℃ at the speed of 10 ℃/min under the oxygen atmosphere, the temperature is kept for 5 hours, and the target TiO is obtained after cooling2Coated Li2NiO2Is denoted by Li2NiO2@TiO2。
Sequentially adding Li2NiO2@TiO2100g of positive electrode active material NCM811, a conductive agent Super P and a binder PVDF are weighed according to the weight ratio of 3:93:2:2, mixed in 40g of NMP, and subjected to vacuum stirring to obtain uniform slurry, then the slurry is uniformly coated on an aluminum foil current collector, and subjected to rolling baking (rolling belt 2m/min) at 100 ℃ in a 10m baking oven and vacuum baking at 85 ℃ for 20 hours, cold pressing and slitting to obtain a positive electrode plate containing a positive electrode lithium supplement material;
sequentially mixing the following artificial graphite: silicon monoxide: conductive agent Super P: CMC: 100g of SBR is weighed according to the weight ratio of 85:10:2:1.5:1.5, is mixed in 40g of deionized water, is subjected to vacuum stirring to obtain uniform slurry, is uniformly coated on a copper foil current collector, is subjected to rolling baking at 100 ℃ in a 10m baking oven (rolling belt for 2m/min) and vacuum baking at 85 ℃ for 20 hours, and is subjected to cold pressing and slitting to obtain a negative plate;
laminating the positive plate, the negative plate and the diaphragm into a lithium ion battery cell; the lithium ion cell is put into a soft package battery and injected with lithium hexafluorophosphate (LiPF) containing 1mol/L6) Ethyl Carbonate (EC): methyl ethyl carbonate (EMC): diethyl carbonate (DEC) ═ 1: 1:1 (volume ratio), an electrolyte containing 2 wt% Vinylene Carbonate (VC) and 3 wt% 1, 3-Propane Sultone (PS);
in the formation stage, the material is charged to 3.8V at 0.1C, then charged to 4.2V at a constant current of 0.5C, and then charged at a constant voltage of 4.2V and a cut-off current of 0.05C, at this time, Li2NiO2@TiO2Decomposition occurs to release Li ions while partially converting into LiNiO as a positive electrode active material2@TiO2. And removing gas generated in the formation process through the step of air extraction, and shaping to obtain the lithium ion battery with the anode supplemented with lithium.
Example 2
Example 2 differs from example 1 in that: li in positive plate2NiO2@TiO2The weight ratio of the positive electrode active material NCM811, the conductive agent Super P and the binder PVDF is 5:91:2: 2.
Example 3
Example 2 differs from example 1 in that: li in positive plate2NiO2@TiO2The weight ratio of the positive electrode active material NCM811, the conductive agent Super P and the binder PVDF is 1:95:2: 2.
Comparative example 1
Comparative example 1 differs from example 1 in that: li in positive plate2NiO2(Li prepared in example 1)2NiO2Powder), a positive electrode active material NCM811, a conductive agent Super P and a binder PVDF in a weight ratio of 3:93:2: 2.
Comparative example 2
Comparative example 2 differs from example 1 in that: the weight ratio of the positive electrode active material NCM811, the conductive agent Super P and the binder PVDF in the positive electrode sheet is 96:2: 2.
Comparative example 3
Comparative example 3 differs from example 1 in that: the weight ratio of the positive electrode active material NCM811, the conductive agent Super P and the binder PVDF in the positive electrode sheet is 96:2: 2. The weight ratio of the artificial graphite, the conductive agent Super P, the CMC and the SBR in the negative plate is 95:2:1.5: 1.5.
And (3) performance testing:
(1) after the lithium ion batteries of examples 1 to 3 and comparative examples 1 to 3 were injected with the electrolyte, the batteries were left to stand for 24 hours, charged to 4.2V with a current of 0.1C at the design capacity, and left to stand for 10 minutes, and then discharged with a current of 0.1C at the design capacity until the voltage was cut off at 3.0V, the first charge capacity and discharge capacity of the lithium ion batteries were derived, and the first charge-discharge efficiency of the batteries was calculated, with the test results shown in table 1.
(2) The lithium ion batteries of examples 1 to 3 and comparative examples 1 to 3 were charged to 4.2V with a current of 1C of the designed capacity and charged at a constant voltage of 4.2V with a cutoff current of 0.05C, and then left to stand for 10min and discharged with a current of 1C of the designed capacity until the voltage was cut off at 3.0V, forming a charge and discharge, and left to stand for 10min and then subjected to the next cycle, the whole cycle was tested at a temperature of 45℃, and the test results are shown in table 1.
Table 1 results of performance test of lithium ion batteries of examples 1 to 3 and comparative examples 1 to 3
As can be seen from the test results of table 1: after the lithium is supplemented to the positive plate of the lithium ion battery, when the content of the lithium supplement additive is 1-5%, compared with a comparative example 2 without the lithium supplement additive, the first discharge capacity of the lithium ion battery is obviously improved, the capacity retention rate is higher than that without the lithium supplement additive after 1000 cycles of circulation, and the capacity and the service life of the lithium ion battery are effectively improved. From the test results in Table 1, the Li additives for comparative example 1, example 2 and example 3 were selected to have a content of 3%, 5% and 1%, respectively2NiO2@TiO2The energy density of the lithium ion battery and the first discharge capacity of the battery are increased along with the increase of the lithium supplement additive. This is because the lithium supplied to the positive electrode can effectively replace a part of lithium originally released from the main positive electrode active material, and becomes a component of the SEI film in the negative electrode, thereby improving the use efficiency of lithium ions in the main positive electrode active material in the positive electrode sheet. In addition, the consumption of lithium released from the NCM811 positive electrode is reduced, so that the lithium ion battery has good protection effect on the structural stability of the positive electrode, and the cycle performance of the lithium ion battery can be effectively improved. However, too much addition may have negative effects, such as lowering the cycle performance of the battery. The preparation method of the lithium ion battery is simple, easy to operate, good in repeatability, low in cost, small in environmental pollution and suitable for industrial production.
Comparative example 1 and comparative example 1, which are lithium ion batteries added with the same content of positive electrode lithium supplement, wherein example 1 is added with modified Li with 3 percent of content2NiO2@TiO2In comparative example 1, 3% was addedContent of Li2NiO2As a lithium supplement additive. After 1000 cycles, the cycle retention of example 1 is significantly higher than that of comparative example 1, because the lithium supplement additive used in example 1 has better stability and has less weakening effect on the battery system.
The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiment. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. A positive electrode lithium supplement material comprises a core material and a coating layer, wherein the core material comprises at least one compound shown in a formula 1,
Li2±xNiO2formula 1
In the formula 1, x is more than or equal to 0 and less than or equal to 0.5;
the coating layer coats the core material, the coating layer comprises metal oxide, and the metal oxide comprises TiO2。
2. The positive electrode lithium supplement material of claim 1, wherein the core material comprises Li2NiO2。
3. The positive electrode lithium supplement material according to claim 1 or 2, wherein the TiO is2The mass ratio of the compound to at least one of the compounds represented by the formula 1 is (0.01-1): 100.
4. The positive electrode lithium supplement material according to any one of claims 1 to 3, wherein the coating layer has a thickness of 2 to 50 nm.
5. The positive electrode lithium supplement material according to any one of claims 1 to 4, wherein the positive electrode lithium supplement material has a median particle diameter D502 to 8 μm.
6. The positive electrode lithium supplement material according to any one of claims 1 to 5, wherein the molar ratio of the Li element in the lithium source and the Ni element in the nickel source for producing the compound represented by formula 1 is (2.05. + -. x to 2.5. + -. x):1.0, 0. ltoreq. x.ltoreq.0.5.
7. A positive electrode comprising a positive electrode current collector and a positive electrode active material layer coated on the positive electrode current collector, wherein the positive electrode active material layer comprises the positive electrode lithium supplement material according to any one of claims 1 to 6 and a positive electrode active material.
8. The positive electrode according to claim 7, wherein the positive electrode lithium supplement material is contained in an amount of 1 to 5 wt% based on the total mass of the positive electrode active material layer; and/or the content of the positive electrode active material accounts for 85-97 wt% of the total mass of the positive electrode active material layer.
9. The positive electrode according to claim 7 or 8, wherein the positive electrode active material layer further comprises a binder and a conductive agent, wherein the binder is contained in an amount of 1 to 5 wt% based on the total mass of the positive electrode active material layer, and the conductive agent is contained in an amount of 1 to 5 wt% based on the total mass of the positive electrode active material layer.
10. A lithium ion battery comprising the positive electrode lithium supplement material of any one of claims 1 to 6, or the lithium ion battery comprising the positive electrode of any one of claims 7 to 9.
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