Lithium ion battery positive electrode material and preparation method and application thereof

Abstract

The invention relates to a lithium ion battery positive electrode material and a preparation method and application thereof, the chemical general formula of the positive electrode material is Li (NiaCobMnc) 1-xAlxO2-y (PO4) y, 0.5 < = a < = 0.8, 0.1 < = b < = 0.3, 0.1 < = c < = 0.2, 0 < x < = 0.02, and 0 < y < = 0.02. The positive electrode material can be prepared by the following method: S1, respectively preparing a metal salt solution, a precipitator solution and a complexing agent solution; the metal salt comprises a nickel salt, a cobalt salt, a manganese salt and an aluminum salt; s2, respectively and parallelly introducing the metal salt solution and the precipitant solution into a reaction container filled with a complexing agent solution for reaction to obtain precursor salt; and S3, uniformly mixing the precursor salt, a lithium salt and a phosphate ion source, and calcining to obtain the positive electrode material. According to the method, Al < 3 + > and PO4 < 3-> are doped in crystal lattices of the NCM ternary positive electrode material at the same time, the doping amount and proportion of Al < 3 + > and PO4 < 3-> are controlled, the cycling stability of the lithium battery can be effectively improved, and the discharge voltage drop in the battery cycling process is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and particularly to a cathode material for a lithium-ion battery, a preparation method thereof, and an application thereof. Background Art

[0002] As a new type of energy storage device with high efficiency, renewable, and environmental protection, lithium-ion batteries have been widely used in modern intelligent fields such as portable electronic products and electric vehicles. Among the components of lithium-ion batteries, the cathode material has always been the core component, and the choice of the cathode material directly determines the performance of the battery. Among them, nickel-rich layered oxides (such as NCM811) have the advantages of high discharge capacity, low cost, and less environmental pollution, and thus have become a common active cathode material for lithium-ion batteries in electric vehicles and airplanes.

[0003] Generally speaking, the higher the nickel content, the higher the discharge specific capacity of the NCM ternary material. However, the higher the nickel content, the worse the stability. The instability of the high-nickel cathode material is closely related to the lithium-nickel mixing. The reason for the lithium-nickel mixing is that during the charging process, Ni in the transition layer migrates to the lithium site after the lithium ions are released. 2+ The mixing of a large amount of lithium and nickel causes the cathode material to gradually transition from a layered structure to a spinel structure or even a rock salt structure, resulting in capacity decay and voltage drop during cycling, and further affecting its energy density. During the phase transition, the release of lattice oxygen not only destroys the layered structure but also causes a series of irreversible side reactions with the electrolyte, leading to a serious decline in the electrochemical performance of the battery.

[0004] Based on this, there is an urgent need for a method that can effectively improve the structural stability of nickel-rich NCM ternary materials during charge and discharge, so as to improve the cycle stability of high-energy-density lithium-ion batteries based on nickel-rich NCM ternary materials and reduce the voltage drop. Summary of the Invention

[0005] To solve the above problems, the present invention provides a cathode material for a lithium-ion battery, a preparation method thereof, and an application thereof. By simultaneously doping Al 3+ and PO4 3- into the high-nickel NCM ternary cathode material and controlling the doping amounts and ratios of the two, the cycle stability of the lithium battery can be effectively improved and the discharge voltage drop during battery cycling can be reduced.

[0006] Specifically, the following technical solutions are provided:

[0007] In a first aspect of the present invention, a cathode material for a lithium-ion battery is provided. The chemical general formula of the cathode material for a lithium-ion battery is Li(Ni a Co b Mn c ) 1-x Al x O2-y (PO4) y , wherein, 0.5 ≤ a ≤ 0.8, 0.1 ≤ b ≤ 0.3, 0.1 ≤ c ≤ 0.2, 0 < x ≤ 0.02, 0 < y ≤ 0.02.

[0008] Furthermore, x / y = 1.

[0009] Furthermore, x can be 0.002, 0.004, 0.008, 0.01, 0.012, 0.014, 0.016, 0.018, 0.02, etc., including but not limited to the values listed above; y can be 0.002, 0.004, 0.008, 0.01, 0.012, 0.014, 0.016, 0.018, 0.02, etc., including but not limited to the values listed above; preferably, 0.008 ≤ x ≤ 0.012 and x / y = 1, more preferably, x = y = 0.01.

[0010] The second aspect of the present invention provides a method for preparing the lithium ion battery cathode material described in the first aspect, comprising the following steps:

[0011] S1. Prepare a metal salt solution, a precipitating agent solution and a complexing agent solution respectively; the metal salts include nickel salts, cobalt salts, manganese salts and aluminum salts;

[0012] S2. Using the complexing agent solution as the bottom liquid of the reaction vessel, introduce the metal salt solution and the precipitating agent solution into the reaction vessel in parallel for reaction to obtain a precursor salt;

[0013] S3. Mix the precursor salt with a lithium salt and a phosphate ion source evenly, and obtain the lithium ion battery cathode material through calcination treatment.

[0014] Furthermore, in step S1, the metal salt solution is prepared by dissolving nickel salts, cobalt salts, manganese salts and aluminum salts in water; preferably, the concentration of the metal salt solution is 1 - 4M.

[0015] Furthermore, in step S1, the precipitating agent solution is prepared by dissolving a precipitating agent in water; preferably, the concentration of the precipitating agent solution is 4 - 5M.

[0016] Furthermore, in step S1, the complexing agent solution is prepared by dissolving a complexing agent in water; preferably, the concentration of the complexing agent solution is 2 - 4M.

[0017] Furthermore, in step S1, the ratio of the total molar amount of the nickel salts, cobalt salts and manganese salts to the molar amount of the aluminum salts is preferably 1:(0 - 0.02), more preferably 1:(0.008 - 0.012).

[0018] Further, in step S1, the nickel salt includes one or more of nickel sulfate, nickel carbonate, nickel nitrate, and their hydrates, and may also be other soluble nickel salts.

[0019] Further, in step S1, the cobalt salt includes one or more of cobalt sulfate, cobalt carbonate, cobalt nitrate, and their hydrates, and may also be other soluble cobalt salts.

[0020] Further, in step S1, the aluminum salt includes one or more of aluminum sulfate, aluminum carbonate, aluminum nitrate, and their hydrates, and may also be other soluble aluminum salts.

[0021] Further, in step S1, the precipitating agent is preferably sodium hydroxide, and the complexing agent is preferably ammonia water.

[0022] Further, in step S2, the feeding rate of the metal salt solution is preferably 6 - 10 mL / min.

[0023] Further, in step S2, the feeding rate of the precipitating agent solution is preferably 6 - 10 mL / min.

[0024] Further, in step S2, by controlling the feeding rate of the precipitating agent solution, the pH of the reaction is controlled to be 10.8 - 11.2.

[0025] Further, in step S2, the reaction is carried out under a protective atmosphere, and the protective atmosphere is an inert gas and / or nitrogen.

[0026] Further, in step S2, the reaction temperature is preferably 55 - 60 °C, and the reaction time is preferably 12 - 12.5 h.

[0027] Further, in step S2, the preparation method further includes an aging step after the reaction is completed, and the aging time is preferably 6 - 8 h.

[0028] Further, in step S3, the molar ratio of the precursor salt to the lithium salt and the phosphate ion source is 1:(1.05 - 1.1):(0 - 0.02), and more preferably 1:(1.05 - 1.1):(0.008 - 0.012).

[0029] Further, in step S3, the lithium salt includes but is not limited to lithium hydroxide and / or lithium carbonate.

[0030] Further, in step S3, the phosphate ion source is selected from one or more of NH4H2PO4, Na2HPO4, and NaH2PO4.

[0031] Further, in step S3, in the calcination treatment step: first pre-calcine at 480 - 500 °C for 300 - 320 min, and then calcine at 750 - 780 °C for 900 - 920 min.

[0032] The third aspect of the present invention provides a lithium-ion battery, comprising the lithium-ion battery cathode material described in the first aspect or the lithium-ion battery cathode material prepared by the preparation method described in the second aspect.

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0034] 1. The present invention provides a lithium-ion battery cathode material. By simultaneously doping an appropriate amount of Al 3+ and PO4 3- into the lattice of the high-nickel NCM ternary cathode material, not only can the structural order and stability of the high-nickel NCM ternary cathode material be effectively improved, thereby reducing the degree of nickel-lithium mixing during charging and inhibiting the occurrence of phase transformation; in addition, the doping of Al 3+ and PO4 3- can increase the lattice spacing of the high-nickel NCM ternary cathode material, thereby effectively improving the lithium-ion diffusion kinetics.

[0035] 2. The present invention also provides a preparation method for the above-mentioned lithium-ion battery cathode material. The aluminum salt and other transition metal salts are used to prepare the precursor salt by the coprecipitation method, and then mixed evenly with the lithium salt and the phosphate ion source and calcined to obtain the high-nickel NCM ternary cathode material co-doped with Al 3+ and PO4 3- . The above method is simple to operate, the process conditions are easy to control, and the repeatability is good. Compared with the preparation of NCM ternary materials, no additional processes are added, and it is suitable for industrial production. More importantly, the high-nickel NCM ternary cathode material co-doped with Al 3+ and PO4 3- prepared by the above method not only has a good layered structure, but also has better order and stability of the crystal structure, and can effectively improve the problems of serious capacity attenuation and voltage drop during the cycle charge and discharge of the high-nickel NCM ternary cathode material.

[0036] 3. The lithium-ion battery prepared from the lithium-ion battery cathode material provided by the present invention has a larger lithium-ion diffusion coefficient and lower impedance compared with the unmodified high-nickel NCM ternary cathode material, and the discharge specific capacity is improved at different currents, and shows better capacity retention rate and lower discharge voltage drop. Description of the Drawings

[0037] Figure 1 XRD patterns of the lithium-ion battery cathode materials prepared in Example 1, Comparative Example 1 and Comparative Example 2;

[0038] Figure 2 TEM images of the lithium-ion battery cathode materials prepared in Comparative Example 1 (left figure) and Example 1 (right figure);

[0039] Figure 3 AC impedance diagrams of the lithium-ion coin cells constructed with the lithium-ion battery cathode materials prepared in Example 1 and Comparative Example 1 cycled 100 times at 1C;

[0040] Figure 4 Relationship curves of Z′ and ω of the lithium-ion coin cells constructed with the lithium-ion battery cathode materials prepared in Example 1 and Comparative Example 1; -1 / 2 ;

[0041] Figure 5 Rate performance diagrams of the lithium-ion coin cells constructed with the lithium-ion battery cathode materials prepared in Example 1, Comparative Example 1, and Comparative Example 2;

[0042] Figure 6 Cyclic voltammograms of the lithium-ion coin cells constructed with the lithium-ion battery cathode material prepared in Example 1;

[0043] Figure 7 Cyclic voltammograms of the lithium-ion coin cells constructed with the lithium-ion battery cathode material prepared in Comparative Example 1;

[0044] Figure 8 Cycling performance diagrams of the lithium-ion coin cells constructed with the lithium-ion battery cathode materials prepared in Example 1, Comparative Example 1, and Comparative Example 2;

[0045] Figure 9 Average discharge voltage curves during cycling of the lithium-ion coin cells constructed with the lithium-ion battery cathode materials prepared in Example 1, Comparative Example 1, and Comparative Example 2. Detailed implementation manners

[0046] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which this invention belongs. The terms used in the description of this invention herein are for the purpose of describing specific embodiments only and are not intended to limit the invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items. The "including" or "comprising" described in this invention can also be replaced by the closed "consisting of" or "consisting of...".

[0047] As described in the background art, high-nickel NCM ternary cathode materials have problems such as serious lithium-nickel mixing, easy phase change, and poor structural stability during charge and discharge, which seriously affect their electrochemical properties such as cycle stability and voltage drop.

[0048] To solve the above problems, a part of the embodiments of the present invention provides a cathode material for a lithium-ion battery, and its chemical general formula is Li(Ni a Co b Mn c ) 1-x Al x O 2-y (PO4) y , where 0.5 ≤ a ≤ 0.8, 0.1 ≤ b ≤ 0.3, 0.1 ≤ c ≤ 0.2, 0 < x ≤ 0.02, 0 < y ≤ 0.02.

[0049] Based on the poor structural stability of the high-nickel NCM ternary cathode material during charge and discharge, which seriously affects the electrochemical performance such as the cycle stability and voltage drop of high-energy-density lithium-ion batteries, the present invention simultaneously dopes an appropriate amount of Al 3+ and PO4 3- into the lattice of the high-nickel NCM ternary cathode material. Among them, Al 3+ ions enter the transition metal ion layer to replace the transition metal ions, and coordinate with lattice O 2- in the high-nickel NCM ternary cathode material to form an AlO6 octahedral structure similar to TMO6, which is beneficial to stabilizing the layered structure of the high-nickel NCM ternary cathode material during cyclic charge and discharge and reducing the migration of Ni 2+ . At the same time, the introduction of an appropriate amount of PO4 3- replaces part of the oxygen in the high-nickel NCM ternary cathode material to combine with the transition metal ions or Al 3+ ions, and uses the strong metal-oxygen-phosphorus bond to further improve the stability of the layered structure, reduce the degree of nickel-lithium mixing during charging, and the strong bonding ability of PO4 3- can anchor the lattice oxygen and reduce the loss of lattice oxygen, thereby reducing the occurrence of side reactions. In addition, under the co-doping effect of an appropriate amount of Al 3+ and PO4 3- , the lattice spacing of the high-nickel NCM ternary cathode material is larger, which is beneficial to promoting the diffusion of lithium ions, and significantly reduces the diffusion resistance of lithium ions and electrons at the electrode / electrolyte interface, reduces the electrode polarization, and thus effectively improves the kinetic performance of the lithium-ion battery.

[0050] In the present invention, if the doping amount of Al 3+ in the high-nickel NCM cathode material is too much, it will block the lithium layer channel, which will not only affect the battery capacity, but also deteriorate the rate performance of the battery; while if the doping amount of PO4 3- is too much, the excessive negative charge will cause the valence state of the transition metal to increase, thereby reducing the migratable electrons or holes in the cathode material, and the excessive PO4 3- will destroy the continuity of the transition metal layer and hinder the electron transition, thereby deteriorating the conductivity of the high-nickel NCM ternary cathode material. Through Al 3+and PO4 3- Co-doping of high-nickel NCM ternary cathode materials can improve the effect of single PO4 3- doping on the conductivity of cathode materials, but the doping amounts of Al 3+ and PO4 3- need to be controlled within a suitable range, such as 0 < x ≤ 0.02, 0 < y ≤ 0.02, to obtain a lithium-ion battery cathode material with good structural stability and high electrical and ionic conductivity.

[0051] In the present invention, the doping amount x of Al 3+ can be 0.002, 0.004, 0.008, 0.01, 0.012, 0.014, 0.016, 0.018, 0.02, etc., including but not limited to the values listed above; the doping amount y of PO4 3- can be 0.002, 0.004, 0.008, 0.01, 0.012, 0.014, 0.016, 0.018, 0.02, etc., including but not limited to the values listed above.

[0052] More preferably, x / y = 1. By controlling the doping amounts of Al 3+ and PO4 3- to be consistent, the prepared lithium-ion battery cathode material will not introduce excessive negative or positive charges due to the doping of high-valent cations or anions, avoiding the influence of doping on the conductivity of the cathode material. In some preferred embodiments of the present invention, 0.008 ≤ x ≤ 0.012 and x / y = 1, for example, x = y = 0.01.

[0053] The embodiment part of the present invention also provides a preparation method of the above lithium-ion battery cathode material, including the following steps:

[0054] S1. Prepare metal salt solutions, precipitant solutions and complexing agent solutions respectively; the metal salts include nickel salts, cobalt salts, manganese salts and aluminum salts;

[0055] S2. Using the complexing agent solution as the bottom liquid of the reaction vessel, introduce the metal salt solution and the precipitant solution into the reaction vessel in parallel for reaction to obtain a precursor salt;

[0056] S3. Mix the precursor salt with a lithium salt and a phosphate ion source evenly, and obtain the lithium-ion battery cathode material through calcination treatment.

[0057] In the present invention, the aluminum salt and other transition metal salts are used to prepare a precursor salt by the co-precipitation method, and then mixed evenly with a lithium salt and a phosphate ion source and calcined to prepare Al 3+ and PO4 3-Co-doped high-nickel NCM ternary cathode material. The above preparation method is simple in operation, easy to control process conditions, and has good repeatability. Compared with the preparation of NCM ternary materials, no additional processes are added, making it suitable for industrial production. More importantly, the Al 3+ and PO4 3- co-doped high-nickel NCM ternary cathode material not only has a good layered structure, but also has better order and stability in the crystal structure, which can effectively improve the problems of severe capacity decay and voltage drop during the charge-discharge cycle of the high-nickel NCM ternary cathode material; in addition, compared with the undoped and unmodified high-nickel NCM ternary cathode material, the lithium-ion battery cathode material prepared by the above method can significantly reduce the diffusion resistance of lithium ions and electrons at the electrode / electrolyte interface, reduce electrode polarization, and is beneficial to the optimization of the rate performance of lithium-ion batteries.

[0058] In step S1 of the present invention, the metal salt solution is prepared by dissolving nickel salt, cobalt salt, manganese salt and aluminum salt in water; wherein, the concentration of the metal salt solution is preferably 1-4M, such as 1M, 2M, 3M, 4M, etc., including but not limited to the concentration values listed above.

[0059] In step S1 of the present invention, the ratio of the total molar amount of nickel salt, cobalt salt and manganese salt to the molar amount of aluminum salt in the metal salt solution is preferably 1:(0-0.02), such as 1:0.008, 1:0.01, 1:0.012, 1:0.014, 1:0.016, 1:0.018, 1:0.02, etc., including but not limited to the ratios listed above.

[0060] In some preferred embodiments of the present invention, the nickel salt includes one or more of nickel sulfate, nickel carbonate, nickel nitrate and their hydrates, and can also be other soluble nickel salts; the cobalt salt includes one or more of cobalt sulfate, cobalt carbonate, cobalt nitrate and their hydrates, and can also be other soluble cobalt salts; the aluminum salt includes one or more of aluminum sulfate, aluminum carbonate, aluminum nitrate and their hydrates, and can also be other soluble aluminum salts.

[0061] In step S1 of the present invention, the precipitant solution is prepared by dissolving a precipitant in water; wherein, the concentration of the precipitant solution is preferably 4-5M, such as 4M, 4.5M, 5M, etc., including but not limited to the concentration values listed above.

[0062] In step S1 of the present invention, the complexing agent solution is prepared by dissolving a complexing agent in water; wherein, the concentration of the complexing agent solution is 2-4M, such as 1M, 2M, 3M, 4M, etc., including but not limited to the concentration values listed above.

[0063] In some preferred embodiments of the present invention, the precipitant is sodium hydroxide and the complexing agent is ammonia water.

[0064] In step S2 of the present invention, the feeding rate of the metal salt solution is preferably 6-10 mL / min, such as 6 mL / min, 7 mL / min, 8 mL / min, 9 mL / min, 10 mL / min, etc., and the feeding rate of the precipitant solution is preferably 6-10 mL / min, such as 6 mL / min, 7 mL / min, 8 mL / min, 9 mL / min, 10 mL / min, etc.; preferably, by controlling the feeding rate of the precipitant solution, the pH of the reaction is controlled within the range of 10.8-11.2.

[0065] In step S2 of the present invention, the reaction is carried out under a protective atmosphere, and the protective atmosphere can be an inert gas and / or nitrogen.

[0066] In step S2 of the present invention, the reaction temperature is preferably 55-60 °C, and the reaction time is preferably 12-12.5 h, for example, the reaction is carried out at 55 °C for 12 h.

[0067] In step S2 of the present invention, the above preparation method further includes an aging step after the reaction is completed, and the aging time is preferably 6-8 h.

[0068] In step S3 of the present invention, the molar ratio of the precursor salt to the lithium salt and the phosphate ion source is 1:(1.05-1.1):(0-0.02), more preferably 1:(1.05-1.1):(0.008-0.012), such as 1:1.05:0.01.

[0069] In step S3 of the present invention, the lithium salt includes but is not limited to lithium hydroxide and / or lithium carbonate, and other lithium salts commonly used in the art can also be used; the phosphate ion source is preferably one or more of NH4H2PO4, Na2HPO4, and NaH2PO4. Using the above phosphate ion source can avoid introducing other impurities.

[0070] In step S3 of the present invention, in the calcination treatment step: first pre-calcine at 480-500 °C for 300-320 min, and then calcine at 750-780 °C for 900-920 min.

[0071] In addition, the embodiment part of the present invention also provides a lithium ion battery, which includes the lithium ion battery cathode material prepared by the above preparation method. This lithium ion battery not only has lower ohmic resistance and higher lithium ion diffusion coefficient, but also shows better capacity retention rate and lower discharge voltage drop during the charge and discharge cycle.

[0072] The present invention will be further described below in conjunction with specific embodiments and the accompanying drawings, so that those skilled in the art can better understand the present invention and be able to implement it, but the specific embodiments cited do not limit the present invention.

[0073] Example 1

[0074] This embodiment relates to a cathode material for lithium-ion batteries, specifically including the following steps:

[0075] (1) Weigh NiSO4·6H2O, CoSO4·7H2O, MnSO4·H2O, and Al2(SO4)3·18H2O according to the molar ratio of Ni:Co:Mn:Al being 8:1:1:0.01 and dissolve them in water to obtain a transition metal salt solution with a concentration of 2M; dissolve the NaOH solution in water to obtain a NaOH solution with a concentration of 4M; prepare an ammonia water solution with a concentration of 4M.

[0076] (2) Add the ammonia water in step (1) to the reaction vessel as the bottom liquid; under a nitrogen atmosphere, add the transition metal salt solution and the NaOH solution in step (1) to the reaction vessel at a flow rate of 6 mL / min. By controlling the flow rate of the NaOH solution, control the reaction pH during the reaction at around 11; the reaction temperature is 55°C, react for 12 h, stop stirring after the reaction is completed, age for 6 h, and obtain the NCM811 precursor through filtration and washing, then transfer it to a vacuum drying oven and dry for 12 h.

[0077] (3) Mix the precursor prepared in step (2) with LiOH·H2O and NH4H2PO4 in a molar ratio of 1:1.05:0.01, transfer the obtained mixture to a tubular furnace for calcination, continuously introduce oxygen during the calcination process, and the calcination program is pre-calcination at 480°C for 300 min, calcination at 750°C for 900 min, and then cool to room temperature at a rate of 5°C / min to obtain the cathode material NCM-PA for lithium-ion batteries.

[0078] The XRD of the cathode material for lithium-ion batteries prepared in this embodiment is as Figure 1 shown. It can be seen from the figure that the co-doped cathode material has a good layered structure.

[0079] Example 2

[0080] This embodiment relates to a cathode material for lithium-ion batteries. The difference from Example 1 is only that in step (1), weigh NiSO4·6H2O, CoSO4·7H2O, MnSO4·H2O, and Al2(SO4)3·18H2O according to the molar ratio of Ni:Co:Mn:Al being 8:1:1:0.002 and dissolve them in water to obtain a transition metal salt solution with a concentration of 2M; the other conditions are the same, and the corresponding cathode material NCM-PA for lithium-ion batteries is prepared.

[0081] Example 3

[0082] This example relates to a cathode material for lithium-ion batteries. The difference from Example 1 is only that in step (1), NiSO4·6H2O, CoSO4·7H2O, MnSO4·H2O, and Al2(SO4)3·18H2O are weighed according to the molar ratio of Ni:Co:Mn:Al of 8:1:1:0.005 and dissolved in water to obtain a transition metal salt solution with a concentration of 2M; the remaining conditions are the same, and the corresponding lithium-ion battery cathode material NCM-PA is prepared.

[0083] Example 4

[0084] This example relates to a cathode material for lithium-ion batteries. The difference from Example 1 is only that in step (1), NiSO4·6H2O, CoSO4·7H2O, MnSO4·H2O, and Al2(SO4)3·18H2O are weighed according to the molar ratio of Ni:Co:Mn:Al of 8:1:1:0.008 and dissolved in water to obtain a transition metal salt solution with a concentration of 2M; the remaining conditions are the same, and the corresponding lithium-ion battery cathode material NCM-PA is prepared.

[0085] Example 5

[0086] This example relates to a cathode material for lithium-ion batteries. The difference from Example 1 is only that in step (1), NiSO4·6H2O, CoSO4·7H2O, MnSO4·H2O, and Al2(SO4)3·18H2O are weighed according to the molar ratio of Ni:Co:Mn:Al of 8:1:1:0.012 and dissolved in water to obtain a transition metal salt solution with a concentration of 2M; the remaining conditions are the same, and the corresponding lithium-ion battery cathode material NCM-PA is prepared.

[0087] Example 6

[0088] This example relates to a cathode material for lithium-ion batteries. The difference from Example 1 is only that in step (3), the precursor is mixed with LiOH·H2O and NH4H2PO4 in a molar ratio of 1:1.05:0.005; the remaining conditions are the same, and the corresponding lithium-ion battery cathode material NCM-PA is prepared.

[0089] Example 7

[0090] This example relates to a cathode material for lithium-ion batteries. The difference from Example 1 is only that in step (3), the precursor is mixed with LiOH·H2O and NH4H2PO4 in a molar ratio of 1:1.05:0.015; the remaining conditions are the same, and the corresponding lithium-ion battery cathode material NCM-PA is prepared.

[0091] Comparative Example 1

[0092] This comparative example relates to a cathode material for a lithium-ion battery. The difference from Example 1 is only that: Al is not doped 3+ and PO4 3- , that is, Al2(SO4)3·18H2O is not added in step (1), and NH4H2PO4 is not added in step (3); the other conditions are the same, and the corresponding cathode material NCM for a lithium-ion battery is prepared. It can be seen from Figure 1 that the cathode material NCM for a lithium-ion battery prepared in this comparative example has a layered structure.

[0093] Comparative Example 2

[0094] This comparative example relates to a cathode material for a lithium-ion battery. The difference from Example 1 is only that: Al is not doped 3+ , that is, Al2(SO4)3·18H2O is not added in step (1); the other conditions are the same, and the corresponding cathode material NCM-P for a lithium-ion battery is prepared. It can be seen from Figure 1 that the cathode material NCM-P for a lithium-ion battery prepared in this comparative example has a layered structure.

[0095] Comparative Example 3

[0096] This comparative example relates to a cathode material for a lithium-ion battery. The difference from Example 1 is only that: PO4 is not doped 3- , that is, NH4H2PO4 is not added in step (3); the other conditions are the same, and the corresponding cathode material NCM-A for a lithium-ion battery is prepared.

[0097] Comparative Example 4

[0098] This comparative example relates to a cathode material for a lithium-ion battery. The difference from Example 1 is only that: MgSO4·7H2O is used to replace Al2(SO4)3·18H2O in step (1), and the molar amount of Mg ions is the same as that of Al ions; the other conditions are the same, and the corresponding cathode material NCM-M for a lithium-ion battery is prepared.

[0099] Comparative Example 5

[0100] This comparative example relates to a cathode material for a lithium-ion battery. The difference from Example 1 is only that: Ti(SO4)2 is used to replace Al2(SO4)3·18H2O, and the molar amount of Ti ions is the same as that of Al ions; the other conditions are the same, and the corresponding cathode material NCM-T for a lithium-ion battery is prepared.

[0101] Comparative Example 6

[0102] This comparative example relates to a cathode material for a lithium-ion battery. The only difference from Example 1 is that Zr(SO4)2·4H2O is used to replace Al2(SO4)3·18H2O, and the molar amount of Zr ions is the same as that of Al ions; the other conditions are the same, and the corresponding cathode material NCM-Z for the lithium-ion battery is prepared.

[0103] Comparative Example 7

[0104] This comparative example relates to a cathode material for a lithium-ion battery. The only difference from Example 1 is that NH4Cl is used to replace NH4H2PO4; the other conditions are the same, and the corresponding cathode material NCM-Cl for the lithium-ion battery is prepared.

[0105] Comparative Example 8

[0106] This comparative example relates to a cathode material for a lithium-ion battery. The only difference from Example 1 is that in step (1), NiSO4·6H2O, CoSO4·7H2O, MnSO4·H2O, and Al2(SO4)3·18H2O are weighed according to the molar ratio of Ni:Co:Mn:Al of 8:1:1:0.025 and dissolved in water to obtain a transition metal salt solution with a concentration of 2M; in step (3), the precursor is mixed with LiOH·H2O and NH4H2PO4 in a molar ratio of 1:1.05:0.025; the other conditions are the same, and the corresponding cathode material NCM-PA for the lithium-ion battery is prepared.

[0107] Comparative Example 9

[0108] This comparative example relates to a cathode material for a lithium-ion battery. The only difference from Example 1 is that NH4H2PO4 in step (3) is directly added to the transition metal salt solution in step (1); the other conditions are the same, and the corresponding cathode material for the lithium-ion battery is prepared.

[0109] Application and Performance Test

[0110] (1) To study the effects of different ion doping on the structure and nickel-lithium mixing degree of the cathode material, GSAS was used to perform refined processing on the XRD spectra of the materials, and the processing results are shown in Table 1 below:

[0111] Table 1

[0112]

[0113] In the table: a and b are the edge lengths of the unit cell, v is the volume of the unit cell, I 003 / 104 is the ratio of the diffraction peak intensity of the crystal plane (003) to the diffraction peak intensity of the crystal plane (104), and R wp is the weighted profile residual variance factor (R wpThe smaller the value is, the better the fitting degree between the refinement result and the experimental data).

[0114] As can be seen from Figure 1 and Table 1 above, the lithium-ion battery cathode materials prepared in Example 1, Comparative Example 1 and Comparative Example 2 all have a layered structure. Among them, compared with the undoped and modified NCM, the degree of nickel-lithium mixing of NCM-P prepared by single doping with PO4 3- is reduced to some extent, but the improvement is not significant. While using Al 3+ and PO4 3- co-doping modification to prepare the cathode material NCM-PA, the degree of nickel-lithium mixing is significantly reduced, and the structural order and stability of the material are improved.

[0115] In addition, the present invention uses a transmission electron microscope to observe the lattice spacing of the material before and after doping. As Figure 2 shown, the left figure is the transmission electron microscope image of NCM prepared in Comparative Example 1. It can be seen from the figure that the lattice spacing of NCM is 0.473 nm, while the lattice spacing of the cathode material NCM-PA (right figure) prepared by co-doping modification with Al 3+ and PO4 3- is 0.477 nm. It can be seen from this that after co-doping modification with Al 3+ and PO4 3- the lattice spacing of the cathode material becomes larger.

[0116] (2) The lithium-ion battery cathode materials prepared in the above examples and comparative examples were respectively used to construct lithium-ion button batteries, and the specific operations are as follows:

[0117] Weigh the cathode active material, conductive agent (carbon black) and binder (PVDF) according to a mass ratio of 8:1:1 and add them to a mortar. Ethanol is used as a dispersant, and the mixture is ground until the ethanol completely evaporates. Add an appropriate amount of solvent NMP and ball mill for 1 h to obtain a slurry. The slurry is evenly coated on an aluminum foil and placed in a vacuum drying oven for 12 h. Finally, it is cut into a positive electrode sheet with a diameter of 12 mm. In a glove box filled with argon, a CR2016 button battery is assembled in the order of positive electrode shell - positive electrode sheet - separator - electrolyte - lithium sheet - nickel foam - negative electrode shell. The electrolyte is LiPF6 dissolved in EC / EMC / DMC with a volume ratio of 1:1:1.

[0118] a. AC impedance test: The ZIVE SP1 workstation was used to perform AC impedance tests on the coin cells constructed with the lithium-ion battery cathode materials prepared in Example 1 and Comparative Example 1. The specific test process was as follows: A sinusoidal AC signal of 5 - 10 Mv was applied to the battery, the test frequency was 0.01 Hz - 100 kHz, the test results were analyzed by fitting with ZVIEW software, the impedance data was analyzed through the Nyquist plot, and fitting was performed in combination with the equivalent circuit model (components such as Rs, Rct). The fitting analysis results are shown in Table 2 below:

[0119] Table 2

[0120]

[0121] In the table: R s Ohmic resistance, R ct Charge transfer resistance, σ dispersion coefficient, used to describe the capacitive behavior of the electrode surface, D Li+ Lithium-ion diffusion coefficient.

[0122] From Figure 3 , 4 and Table 2, it can be seen that compared with undoped NCM, the lithium-ion battery cathode material NCM-PA prepared by co-doping NCM with Al 3+ and PO4 3- can significantly reduce the diffusion resistance of lithium ions and electrons at the electrode / electrolyte interface and can reduce electrode polarization.

[0123] b. Rate performance test: The Neware charge-discharge test system was used to test the rate performance of the coin cells constructed with the lithium-ion battery cathode materials prepared in Example 1, Comparative Example 1, and 2. The test voltage was 2.8 - 4.3 V. Specifically, the battery was left standing at 25°C for 5 min, discharged at a constant current of 1C to 2.8 V, left standing for 30 min, then charged at a constant current and constant voltage of 1C to 4.3 V, left standing for 30 min, and then discharged at a constant current of 0.2C to 2.8 V; left standing for 30 min and then charged at a constant current and constant voltage of 1C to 4.3 V, left standing for 30 min, and then discharged at a constant current of 0.5C to 2.8 V; left standing for 30 min and then charged at a constant current and constant voltage of 1C to 4.3 V, left standing for 30 min, and then discharged at a constant current of 1C to 2.8 V; left standing for 30 min and then charged at a constant current and constant voltage of 1C to 4.3 V, left standing for 30 min, and then discharged at a constant current of 3C to 2.8 V; left standing for 30 min and then charged at a constant current and constant voltage of 1C to 4.3 V, left standing for 30 min, and then discharged at a constant current of 5C to 2.8 V. Each of the above rates was cycled 5 times, the discharge capacity was recorded, and finally left standing for 30 min, then charged at a constant current and constant voltage of 1C to 4.3 V, left standing for 30 min, and then discharged at a constant current of 1C to 2.8 V.

[0124] The rate performance test results are as Figure 5As shown, it can be seen from the figure that the discharge specific capacity of the coin cell constructed with the lithium-ion battery cathode material prepared in Example 1 is higher than that in Comparative Example 1 at different currents, and the difference in the discharge specific capacity between the coin cell constructed with the lithium-ion battery cathode material prepared in Example 1 and the coin cell constructed with the lithium-ion battery cathode material prepared in Comparative Example 2 increases with the increase of current, showing better rate performance.

[0125] c. Cyclic voltammetry test: Use a ZIVE SP1 type workstation to perform cyclic voltammetry tests on the coin cells constructed with the lithium-ion battery cathode materials prepared in Example 1 and Comparative Example 1. The test is carried out in the range of 2.8 - 4.3 V, the scanning speed is 0.1 mV / s, and the frequency of the applied voltage is 10 -1 -10 -5 Hz. The specific test method is as follows: Start from the set initial potential and scan in the positive direction at a constant slope until the termination potential is reached. Reverse the scanning direction at the termination potential and return to the initial potential at the same rate to form a complete CV cycle. Repeat the above process several times (such as 3 - 5 times) to observe the change trend and stability of the current peak.

[0126] The test results are as Figure 6 、 7 shown. It can be seen from the figure that the voltage difference of the coin cell constructed with the lithium-ion battery cathode material prepared in Example 1 is significantly smaller than that in Comparative Example 1. From this, it can be known that the co-doping of Al 3+ and PO4 3- can improve the reversibility of the electrode process and reduce the electrochemical polarization.

[0127] d. Capacity retention rate and discharge voltage drop test after 100 cycles: Use a Neware charge-discharge test system to test the cycling performance of the lithium-ion coin cells constructed with the lithium-ion battery cathode materials prepared in the above different examples and comparative examples. All test voltages are 2.8 - 4.3 V. Specifically as follows: Let the battery stand for 5 min at 25 °C, discharge at a constant current of 0.1C to 2.8 V, stand for 15 min, charge at a constant current and constant voltage of 0.1C to 4.3 V, stand for 15 min, discharge at a constant current of 0.1C to 2.8 V, and cycle 3 times at 0.1C; then stand for 15 min, charge at a constant current and constant voltage of 1C to 4.3 V, stand for 15 min, discharge at a constant current of 1C to 2.8 V, record the discharge capacity of the first cycle, repeat the above charge-discharge operation 100 times at 1C, and record the discharge capacity of the 100th cycle. The capacity retention rate of the 100th cycle = the discharge capacity of the 100th cycle / the discharge capacity of the first cycle.

[0128] The test results are shown in Table 3 below:

[0129] Table 3

[0130]

[0131]

[0132] As can be seen from Table 3, compared with the high-nickel NCM ternary cathode material prepared in Comparative Example 1, in Examples 1-7, by using an appropriate amount of Al 3+ and PO4 3- The lithium-ion battery cathode material prepared by co-doping and modifying the high-nickel NCM ternary cathode material has a significantly improved capacity retention rate after 100 cycles, and the discharge voltage drop (0.0214 V) after 100 cycles is significantly lower than that of Comparative Example 1 (0.1369 V).

[0133] As can be seen from Example 1 and Comparative Examples 4-7, compared with the lithium-ion battery cathode materials prepared by co-doping with magnesium, titanium, and zirconium metal ions replacing aluminum ions and chloride ions replacing phosphate ions, the effects are significantly inferior to the synergistic effect of co-doping with aluminum ions and phosphate ions; and as can be seen from Examples 1-7 and Comparative Example 8, too much or too little doping amount of aluminum ions and phosphate ions will affect the electrochemical performance of the prepared lithium-ion battery cathode material. When x = y = 0.01, the performance of the lithium-ion battery cathode material prepared by co-doping is the best.

[0134] In addition, as can be seen from Example 1 and Comparative Example 9, the step of adding the phosphate ion source will affect the performance of the prepared lithium-ion battery cathode material. The performance of the lithium-ion battery cathode material prepared by introducing the phosphate ion source during the preparation of the precursor salt and then mixing it with the lithium salt for calcination (Comparative Example 9) is significantly inferior to that of Example 1, because the phosphate ions introduced during the preparation of the precursor salt cannot be effectively doped into the cathode material, and the effective doping amount is too low to significantly improve the performance.

[0135] The above-described embodiments are only preferred embodiments given to fully illustrate the present invention, and the protection scope of the present invention is not limited thereto. Equivalent substitutions or transformations made by those skilled in the art on the basis of the present invention are all within the protection scope of the present invention. The protection scope of the present invention shall be subject to the claims.

Claims

1. A cathode material for a lithium-ion battery, characterized in that, The chemical general formula of the positive electrode material of the lithium ion battery is Li(Ni a Co b Mn c ) 1-x Al x O 2-y (PO4) y , where 0.5 ≤ a ≤ 0.8, 0.1 ≤ b ≤ 0.3, 0.1 ≤ c ≤ 0.2, 0 < x ≤ 0.02, 0 < y ≤ 0.

02.

2. The cathode material for lithium ion battery according to claim 1, characterized in that, 0.008 ≤ x ≤ 0.012 and x / y = 1.

3. A preparation method of a cathode material for a lithium-ion battery, characterized in that, It includes the following steps: S1. Prepare a metal salt solution, a precipitant solution and a complexing agent solution respectively; the metal salts include nickel salts, cobalt salts, manganese salts and aluminum salts; S2. Using the complexing agent solution as the bottom liquid of the reaction vessel, introduce the metal salt solution and the precipitant solution into the reaction vessel in parallel for reaction to obtain a precursor salt; S3. Mix the precursor salt with a lithium salt and a phosphate ion source evenly, and obtain the positive electrode material for the lithium ion battery through calcination treatment.

4. The preparation method according to claim 3, characterized in that, In step S1, it includes at least one of the following features: (1) The metal salt solution is prepared by dissolving nickel salts, cobalt salts, manganese salts and aluminum salts in water; the precipitant solution is prepared by dissolving a precipitant in water; the complexing agent solution is prepared by dissolving a complexing agent in water; (2) The ratio of the total molar amount of the nickel salt, cobalt salt and manganese salt to the molar amount of the aluminum salt is 1:(0 - 0.02); (3) The concentration of the metal salt solution is 1 - 4M; (4) The concentration of the precipitant solution is 4 - 5M; (5) The concentration of the complexing agent solution is 2 - 4M.

5. The preparation method according to claim 3, characterized in that, In step S1, the nickel salt includes one or more of nickel sulfate, nickel carbonate, nickel nitrate and their hydrates; The cobalt salt includes one or more of cobalt sulfate, cobalt carbonate, cobalt nitrate and their hydrates; The manganese salt includes one or more of manganese sulfate, manganese carbonate, manganese nitrate and their hydrates; The aluminum salt includes one or more of aluminum sulfate, aluminum carbonate, aluminum nitrate and their hydrates; The precipitant is sodium hydroxide; The complexing agent is ammonia water.

6. The preparation method according to claim 3, characterized in that, In step S2, it includes at least one of the following features: (1) The introduction rate of the metal salt solution is 6 - 10 mL / min; (2) The introduction rate of the precipitant solution is 6 - 10 mL / min; (3) By controlling the introduction rate of the precipitant solution, control the pH of the reaction at 10.8 - 11.2; (4) The reaction is carried out under a protective atmosphere, and the protective atmosphere is an inert gas and / or nitrogen; (5) The temperature of the reaction is 55 - 60 °C, and the reaction time is 12 - 12.5 h; (6) The preparation method further includes an aging step after the reaction is completed, and the aging time is 6 - 8 h.

7. The preparation method according to claim 3, characterized in that, In step S3, the molar ratio of the precursor salt, the lithium salt and the phosphate ion source is 1:(1.05 - 1.1):(0 - 0.02).

8. The preparation method according to claim 3, characterized in that, In step S3, the lithium salt includes lithium hydroxide and / or lithium carbonate; The phosphate ion source is selected from one or more of NH4H2PO4, Na2HPO4, and NaH2PO4.

9. The preparation method according to claim 3, wherein In the calcination treatment step of step S3: first pre-calcine at 480 - 500 °C for 300 - 320 min, and then calcine at 750 - 780 °C for 900 - 920 min.

10. A lithium-ion battery, characterized in that, It includes the positive electrode material for the lithium ion battery described in claim 1 or 2 or the positive electrode material for the lithium ion battery prepared by the preparation method described in any one of claims 3 - 9.

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