CN115663198B - Cobalt-free cathode material, preparation method thereof, cathode and lithium ion battery - Google Patents
Cobalt-free cathode material, preparation method thereof, cathode and lithium ion battery Download PDFInfo
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- CN115663198B CN115663198B CN202211701466.5A CN202211701466A CN115663198B CN 115663198 B CN115663198 B CN 115663198B CN 202211701466 A CN202211701466 A CN 202211701466A CN 115663198 B CN115663198 B CN 115663198B
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Abstract
The invention relates to the technical field of lithium battery materials, and discloses a cobalt-free positive electrode material, a preparation method of the cobalt-free positive electrode material, a positive electrode and a lithium ion battery. The preparation method comprises the following steps: first doping: coprecipitation preparation of high-valence metal doped precursor Ni x Mn y M z1 (OH) 2 (ii) a And (3) second doping: calcining after ball milling and mixing to obtain a primary cathode material LiNi x Mn y M z1+z2 O 2 (ii) a And (3) third doping: the product of the last step is evenly mixed with the doped metal oxide and then sintered to obtain LiNi x Mn y M z1+z2+z3 O 2 Wherein z1+ z2+ z3= z, x + y + z =1,0.005 ≤ z ≤ 0.015; m is a metal ion having a valence of 5 or 6; the cathode material is prepared by the method. And a positive electrode comprising the positive electrode material. The lithium ion battery comprises the positive electrode. The cathode material prepared by the method has good electrochemical performance.
Description
Technical Field
The invention relates to the technical field of lithium battery materials, in particular to a cobalt-free anode material and a preparation method thereof, an anode and a lithium ion battery.
Background
With the base of Li (Ni) x Co y Mn 1-x-y )O 2 (NCM) and Li (Ni) x Co y Al 1-x-y )O 2 The demand for high energy density anodes of (NCA) is rapidly increasing, with the cobalt price doubling three times within three years.
Research shows that Co is the cause of intergranular cracking and unstable oxygen redox of the material, but the capacity is low because the middle of the transformation from the second hexagonal phase (H2) to the third hexagonal phase (H3) is ended early when the cobalt-free material is in a charging voltage range of 3-4.3V, and in addition, the Li is reduced after the cobalt-free layered material is free of the cobalt + The mobility of (b) leads to a deterioration of rate capability and thus to a rapid deterioration of the cycle stability of the cobalt-free material.
In view of this, the invention is particularly proposed.
Disclosure of Invention
The invention aims to provide a cobalt-free cathode material, a preparation method thereof, a cathode and a lithium ion battery.
The invention is realized by the following steps:
in a first aspect, the present invention provides a method for preparing a high-valence metal-doped cobalt-free cathode material, comprising:
first doping: coprecipitating nickel ions, manganese ions and primary doped metal ions in a solution system to prepare a high-valence metal doped precursor Ni x Mn y M z1 (OH) 2 ；
And (3) second doping: mixing and ball-milling the doped metal precursor, the lithium source and the secondary doped metal oxide, and then adding oxygenCalcining for 10 to 14h at 700 to 800 ℃ in the atmosphere of gas to obtain a primary cathode material LiNi x Mn y M z1+z2 O 2 ；
And (3) doping for the third time: crushing the primary positive electrode material into fine materials, uniformly mixing the fine materials with the three-time doped metal oxide, and sintering at 580-700 ℃ for 4-8h to obtain the positive electrode material LiNi x Mn y M z1+z2+z3 O 2 Wherein z1+ z2+ z3= z, z1= (1/4 to 1/2) z, z2= (1/4 to 3/8) z, z3= (1/4 to 3/8) z, x + y + z =1,0.005 ≦ z ≦ 0.015;
the primary doping metal ions are 5-valence or 6-valence metal ions;
the secondary doped metal oxide and the tertiary doped metal oxide are each independently selected from oxides of 5-valent or 6-valent metals.
In an alternative embodiment, the primary doping metal is Nb 5+ 、Ta 5+ 、W 6+ And Mo 6+ At least one of (1);
the secondary doped metal oxide and the tertiary doped metal oxide are respectively and independently selected from at least one of niobium oxide, tantalum oxide, tungsten oxide and molybdenum oxide.
In alternative embodiments, the D50 of the fines is from 8 to 10 μm.
In an alternative embodiment, the nickel ions, manganese ions and primary doping metal ions are co-precipitated in the solution system by:
adding a sodium hydroxide solution and ammonia water into a solution in which a nickel salt, a manganese salt and a primary metal ion-doped salt are dissolved, controlling the pH value in the reaction process to be 10.6-11.0 and the ammonia value to be 2.8-3.2g/L, and finishing the reaction when the precipitate grows until the D50 is 8-10 mu m.
In an alternative embodiment, the salt of the primary doping metal ion includes at least one of sodium tungstate, ammonium niobium sulfate, sodium tantalate, and sodium molybdate.
In an optional embodiment, after the coprecipitation reaction, the precipitate is taken out from the solution system, washed sequentially with sodium hydroxide and water, and then dried to obtain the high-valence metal doped precursor.
In alternative embodiments, x ≧ 0.8.
In a second aspect, the present invention provides a high-valence metal-doped cobalt-free cathode material prepared by the preparation method according to any one of the above embodiments.
In a third aspect, the present invention provides a positive electrode produced from the high-valence metal-doped cobalt-free positive electrode material according to the foregoing embodiment as one of the raw materials.
In a fourth aspect, the present invention provides a lithium ion battery comprising a positive electrode as in the previous embodiments.
The invention has the following beneficial effects:
1. by e.g. Nb 5+ 、Ta 5+ 、W 6+ And Mo 6+ The grain refinement realized by the doping of the high valence metal ions with 5 or 6 valences realizes the fracture toughening and the elimination of the nonuniformity of local components, thereby finally eliminating the harmful strain caused by the sudden shrinkage of crystal lattices, and the enhanced cation sequencing caused by the existence of the high valence metal ions also stabilizes the delithiation structure through the column effect;
2. the high-valence dopant (valence +5, + 6) replaces transition metal elements (+ 2, + 3), which is equivalent to a p-type semiconductor, is favorable for increasing the ionic conductivity and is favorable for the rate capability of the material;
3. the high-valence dopant is beneficial to maintaining the shape of the precursor and thin and slender crystal grains of the material, and is beneficial to the rate capability of the material;
4. the high-valence dopant inhibits the generation of cycle microcracks, and is beneficial to the stability of cycle performance;
5. because the charge balance high valence doped material surface Ni2+ is enriched, the surface performance is stable;
6. high valence state dopant (valence +5, + 6) replaces transition metal Ni 2+ 、Ni 3+ Position of (2), due to charge balance, part of Ni 3+ Will become Ni 2+ Thus making Ni in bulk by gradient doping 2+ The ions are fewer, so that the Li/Ni mutual occupation of the bulk phase is favorably reduced; and surface Ni 2+ Higher, thus being beneficial to the surface stability of the material and not easily adsorbing CO 2 And H 2 O, not easy to generate residual alkali, and is beneficial to the materialThe cycle performance of the material is improved.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and those skilled in the art can also obtain other related drawings based on the drawings without inventive efforts.
Fig. 1 is an SEM image of the cathode material of example 1;
fig. 2 is an SEM image of the positive electrode material of comparative example 7;
fig. 3 is an XRD pattern of the cathode material of example 1.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be clearly and completely described below. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are conventional products which are not indicated by manufacturers and are commercially available.
The cobalt-free cathode material provided in the embodiments of the present application, the preparation method thereof, the cathode, and the lithium ion battery are specifically described below.
The preparation method of the high-valence metal-doped cobalt-free cathode material provided by the embodiment of the application comprises the following steps:
first doping: coprecipitating nickel ions, manganese ions and primary doped metal ions in a solution system to prepare a high-valence metal doped precursor Ni x Mn y M z1 (OH) 2 ；
And (3) second doping: mixing and ball-milling a doped metal precursor, a lithium source and a secondary doped metal oxide, and calcining at 700 to 800 ℃ for 10 to 14h in an oxygen-containing atmosphere to obtain a primary cathode material LiNi x Mn y M z1+z2 O 2 ；
And (3) third doping: pulverizing the primary cathode material intoFine material, mixing the fine material and the triple doped metal oxide evenly, and sintering at 580 to 700 ℃ for 4 to 8h to obtain the cathode material LiNi x Mn y M z1+z2+z3 O 2 Wherein z1+ z2+ z3= z, z1= (1/4 to 1/2) z, z2= (1/4 to 3/8) z, z3= (1/4 to 3/8) z, x + y + z =1,0.005 ≦ z ≦ 0.015;
the primary doping metal ion is Nb 5+ 、Ta 5+ 、W 6+ And Mo 6+ At least one of (1);
the secondary doped metal oxide and the tertiary doped metal oxide are each independently selected from at least one of an oxide of niobium, an oxide of tantalum, an oxide of tungsten, and an oxide of molybdenum.
The preparation method provided by the embodiment of the application has the following characteristics:
1. by e.g. Nb 5+ 、Ta 5+ 、W 6+ And Mo 6+ The grain refinement realized by the doping of the high valence metal ions with 5 or 6 valences realizes the fracture toughening and the elimination of the nonuniformity of local components, thereby finally eliminating the harmful strain caused by the sudden shrinkage of crystal lattices, and the enhanced cation sequencing caused by the existence of the high valence metal ions also stabilizes the delithiation structure through the column effect;
2. the high-valence dopant (valence +5, + 6) replaces transition metal elements (+ 2, + 3), which is equivalent to a p-type semiconductor, is favorable for increasing the ionic conductivity and is favorable for the rate capability of the material;
3. the high-valence dopant is beneficial to maintaining the shape of the precursor and thin and slender crystal grains of the material, and is beneficial to the multiplying power performance of the material;
4. the high-valence dopant inhibits the generation of cycle microcracks, and is beneficial to the stability of cycle performance;
5. high valence state doped material surface Ni due to charge balance 2+ Enrichment and stable surface performance;
6. high valence state dopant (valence +5, + 6) replaces transition metal Ni 2+ 、Ni 3+ Position of (2), due to charge balance, part of Ni 3+ Will become Ni 2+ Thus making Ni in bulk by gradient doping 2+ Less ions, which is advantageous for reducing the bulk phaseLi/Ni of (1); and surface Ni 2+ Higher, thus being beneficial to the surface stability of the material and not easily adsorbing CO 2 And H 2 O, residual alkali is not easy to generate, and the improvement of the cycle performance of the material is facilitated.
Therefore, the preparation method of the high-valence metal-doped cobalt-free anode material provided by the application can be used for preparing the cobalt-free anode material with high capacity, good rate capability and good cycling stability by doping high-valence metal ions in a gradient manner for multiple times.
Specifically, the preparation method comprises the following steps:
s1, first doping: coprecipitating nickel ions, manganese ions and primary doped metal ions in a solution system to prepare a high-valence metal doped precursor Ni x Mn y M z1 (OH) 2 。
Specifically, the method comprises the following steps:
nickel salt, manganese salt and salt of primary doping metal ions are injected into a continuously stirred reaction kettle, and the injection amount is added according to the molar ratio of Ni: mn: M = x: y: z 1.
After various metal salt solutions are injected, continuously injecting a sodium hydroxide solution and ammonia water, keeping the pH value of the injected sodium hydroxide and ammonia water in the reaction kettle at 10.6-11.0 and the ammonia value at 2.8-3.2 g/L, and finishing the reaction when the precipitate grows until the D50 is 8-10 mu m. The nitrogen is introduced as protective gas throughout the whole process.
And (3) taking the precipitate out of the solution system, washing the precipitate by adopting a sodium hydroxide solution and water in sequence (circularly washing for 3 times) to remove chemical substances remained on the surface of the precipitate, and drying the washed precipitate to obtain the high-valence metal doped precursor.
Preferably, the primary doping metal is Nb 5+ 、Ta 5+ 、W 6+ And Mo 6+ At least one of them.
Preferably, the salt of the primary doping metal ion includes at least one of sodium tungstate, ammonium niobium sulfate, sodium tantalate, and sodium molybdate.
Preferably, the concentration of the injected sodium hydroxide solution is 4mol/L and the concentration of the ammonia water is 10mol/L.
Preferably, the drying is carried out in an oven at a temperature of 100 to 140 ℃ (e.g., 100, 110 ℃, 120 ℃, or 140 ℃).
S2, doping for the second time: mixing and ball-milling a doped metal precursor, a lithium source and a secondary doped metal oxide, and then calcining for 10-14h (for example, 10h, 11h, 12h, 13h or 14 h) in an atmosphere containing oxygen at 700-800 ℃ (for example, 700 ℃, 720 ℃, 750 ℃, 780 ℃ or 800 ℃) to obtain a micron-sized polycrystalline primary cathode material LiNi x Mn y M z1+z2 O 2 。
Specifically, ball milling and mixing are carried out according to the molar ratio of the precursor to lithium in the lithium source to the secondary doping metal being 1: z2, wherein m is 1.01 to 1.08.
The secondary doping metal oxide is an oxide of a metal having a valence of 5 or 6. Further, the secondary doped metal oxide is at least one of niobium oxide, tantalum oxide, tungsten oxide and molybdenum oxide.
Preferably, the lithium source may be lithium carbonate or lithium hydroxide, preferably lithium hydroxide.
S3, doping for the third time: pulverizing the primary positive electrode material into fine materials, uniformly mixing the fine materials with the doped metal oxide for three times, and sintering at 580-700 ℃ (such as 580 ℃, 600 ℃, 630 ℃, 650 ℃, 680 ℃ or 700 ℃) for 4-8h (such as 4h, 6h or 8 h) to obtain the positive electrode material LiNi x Mn y M z1+z2+z3 O 2 Wherein z1+ z2+ z3= z, z1= (1/4 to 1/2) z, z2= (1/4 to 3/8) z, z3= (1/4 to 3/8) z, x + y + z =1,0.005 is more than or equal to z and is less than or equal to 0.015.
For example, z is 0.005, 0.008, 0.01, 0.012 or 0.015. For example z1=1/4, z2=3/8, z3=3/8; or z1=3/8, z2=3/8, z3=1/4; or z1=1/2, z2=1/4, z3=1/4.
Specifically, the primary cathode material with micron-sized polycrystal is ground to D50=8 to 10 μm by a jaw crusher, a roll crusher and a machine to obtain a fine material. Mixing the fine material with the third-order doped metal oxide according to LiNi x Mn y M z1+z2 O 2 And (3) adding the metal element into the mixing equipment at a molar ratio of 1 to three times of doping metal elements, and stirring at 500 to 700rpm (such as 500rpm, 600rpm or 700 rpm) for 20 to 40min (such as 20min, 30min or 40 min)Mixing them uniformly, and sintering.
Preferably, in order to obtain the cathode material with good particle size uniformity, the cathode material product is obtained by further sieving through a 300-400-mesh sieve after the product is obtained by sintering.
Further, the third doped metal oxide is at least one of niobium oxide, tantalum oxide, tungsten oxide and molybdenum oxide.
Preferably, the preparation method provided by the present application has a good effect on both high-nickel and low-nickel cobalt-free cathode materials, and it should be noted that the method is particularly directed to high-nickel cathode materials, namely, liNi x Mn y M z1+z2+z3 O 2 The medium x is more than or equal to 0.8, so that the effect is obviously better because: on one hand, the high nickel (x is more than or equal to 0.8) structure has poor stability, and the performance of the material is obviously improved after doping; on the other hand, the unit cell of the high nickel material is slightly large in volume, and doping elements easily occupy the positions of transition metal elements.
The high-valence metal-doped cobalt-free cathode material provided by the embodiment of the invention is prepared by the preparation method provided by the embodiment of the application. The positive electrode material is prepared by the preparation method provided by the embodiment of the application, so that the capacity is high, the rate capability is good, and the cycling stability is good.
The positive electrode provided by the embodiment of the invention is prepared by taking the high-valence metal-doped cobalt-free positive electrode material provided by the embodiment of the invention as one of raw materials.
The lithium ion battery provided by the embodiment of the invention comprises the anode provided by the embodiment of the invention.
The features and properties of the present invention are described in further detail below with reference to examples.
Example 1
This example provides a high-valence metal-doped cobalt-free positive electrode material LiNi 0.88 Mn 0.11 M 0.01 O 2 The preparation method specifically comprises the following steps:
first doping:
injecting 2mol/L NiSO into a continuous stirring reaction kettle 4 ·6H 2 O、MnSO 4 ·5H 2 O and tungstic acidSodium mixed solution, molar ratio Ni: mn: M = 88.
After various metal salt solutions are injected, continuously injecting 4mol/L sodium hydroxide solution and 10mol/L ammonia water, keeping the pH value in the reaction kettle between 10.6 and 11.0 and the ammonia value between 2.8 and 3.2g/L in the processes of injecting the sodium hydroxide and the ammonia water, and ending the reaction when the D50 is about 8 mu m. The whole process is carried out by introducing nitrogen as protective gas.
Filtering out the precipitate from the solution system, respectively washing with 1 mol/L70 deg.C sodium hydroxide solution and water sequentially, repeating washing for 3 times to remove residual chemical substances on the precipitate surface, and drying the washed precipitate at 120 deg.C to obtain high-valence metal-doped precursor Ni 0.88 Mn 0.11 M 0.005 (OH) 2 。
And (3) second doping:
mixing and ball-milling the doped metal precursor obtained in the last step, lithium hydroxide and sodium tungstate according to the molar ratio of tungsten in the precursor, the lithium hydroxide and the tungsten oxide of 1.05.
Calcining for 12 hours at 750 ℃ in an oxygen atmosphere to obtain micron-sized polycrystalline primary cathode material LiNi 0.88 Mn 0.11 M 0.0075 O 2 。
And (3) doping for the third time:
the micron-sized polycrystalline primary positive electrode material was mechanically ground to D50=8 μm using a jaw crusher, a roll mill, to obtain a fine material.
Mixing the fine powder with niobium oxide according to LiNi 0.88 Mn 0.11 M 0.0075 O 2 And (2) putting the raw materials into a mixing device according to the molar ratio of 1 to the tungsten element of 0.0025, stirring the raw materials at the rotating speed of 600rpm for 30min to fully and uniformly mix the raw materials and the tungsten element, and then sintering the mixture at the sintering temperature of 650 ℃.
And sieving the sintered product by a 300-mesh sieve to obtain the high-valence metal-doped cobalt-free anode material.
Example 2
This example provides a high-valence metal-doped cobalt-free positive electrode material LiNi 0.88 Mn 0.105 M 0.015 O 2 Preparation method of (1)The body is as follows:
first doping:
injecting 2mol/L NiSO into a continuous stirring reaction kettle 4 ·6H 2 O、MnSO 4 ·5H 2 And O and ammonium niobium sulfate, wherein the molar weight ratio of Ni to Mn to M =88 to 10.5 to 0.5 in the reaction kettle.
After various metal salt solutions are injected, continuously injecting 4mol/L sodium hydroxide solution and 10mol/L ammonia water, keeping the pH value in the reaction kettle between 10.6 and 11.0 and the ammonia value between 2.8 and 3.2g/L in the process of injecting the sodium hydroxide and the ammonia water, and finishing the reaction when the precipitate grows to the D50 of about 9 mu m. The nitrogen is introduced as protective gas throughout the whole process.
Filtering out the precipitate from the solution system, respectively washing with 1mol/L sodium hydroxide solution at 70 deg.C and water sequentially, repeating the washing for 3 times to remove residual chemical substances on the surface of the precipitate, and drying the washed precipitate at 100 deg.C to obtain high-valence metal-doped precursor Ni 0.88 Mn 0.105 M 0.005 (OH) 2 。
And (3) second doping:
mixing and ball-milling the doped metal precursor obtained in the last step, lithium hydroxide and niobium oxide according to the molar ratio of niobium in the precursor, the lithium hydroxide and the niobium oxide of 1.05.
Calcining for 10 hours at 700 ℃ in an oxygen atmosphere to obtain micron-sized polycrystalline primary cathode material LiNi 0.88 Mn 0.105 M 0.01 O 2 。
And (3) doping for the third time:
the primary cathode material of micron-sized polycrystal was pulverized to D50=9 μm using a jaw crusher, a roll crusher, a mechanical mill to obtain a fine material.
Mixing the fine powder with niobium oxide according to LiNi 0.88 Mn 0.105 M 0.01 O 2 And the molar ratio of the niobium element to the niobium element is 1.005, the mixture is put into a mixing device, stirred for 40min at the rotating speed of 500rpm to be fully and uniformly mixed, and then sintered, wherein the sintering temperature is 580 ℃.
And sieving the sintered product by a 400-mesh sieve to obtain the high-valence metal-doped cobalt-free anode material.
Example 3
This example provides a high-valence metal-doped cobalt-free positive electrode material LiNi 0.88 Mn 0.115 M 0.005 O 2 The preparation method specifically comprises the following steps:
2mol/L NiSO is injected into a continuous stirring reaction kettle 4 ·6H 2 O、MnSO 4 ·5H 2 And (3) mixing O and sodium tantalate, wherein the molar weight ratio of Ni to Mn to M =88 to 11.5 to 0.2 in the reaction kettle.
After various metal salt solutions are injected, continuously injecting 4mol/L sodium hydroxide solution and 10mol/L ammonia water, keeping the pH value in the reaction kettle between 10.6 and 11.0 and the ammonia value between 2.8 and 3.2g/L in the process of injecting the sodium hydroxide and the ammonia water, and finishing the reaction when the precipitate grows to the D50 of about 10 mu m. The whole process is carried out by introducing nitrogen as protective gas.
Filtering out the precipitate from the solution system, respectively washing with 1mol/L sodium hydroxide solution at 70 deg.C and water sequentially, repeating the washing for 3 times to remove residual chemical substances on the surface of the precipitate, and drying the washed precipitate at 140 deg.C to obtain high-valence metal-doped precursor Ni 0.88 Mn 0.115 M 0.002 (OH) 2 。
And (3) second doping:
and mixing and ball-milling the doped metal precursor obtained in the last step, lithium hydroxide and tantalum oxide according to the molar ratio of the precursor to the tantalum in the lithium hydroxide to the tantalum in the tantalum oxide of 1.05.
Calcining for 14h at 800 ℃ in an oxygen atmosphere to obtain micron-sized polycrystalline primary cathode material LiNi 0.88 Mn 0.115 M 0.0035 O 2 。
And (3) doping for the third time:
the micron-sized polycrystalline primary positive electrode material was mechanically ground to D50=8 μm using a jaw crusher, a roll mill, to obtain a fine material.
Mixing the fine powder with tantalum oxide according to LiNi 0.88 Mn 0.115 M 0.0035 O 2 And (2) feeding the mixture into a mixing device at a molar ratio of 1:0.0015 to the tantalum element, and stirring at a rotating speed of 700rpmMixing the two materials for 20min, and sintering at 700 deg.C.
And sieving the sintered product by a 300-mesh sieve to obtain the high-valence metal-doped cobalt-free anode material.
Example 4
This embodiment is substantially the same as embodiment 1 except that:
the doping salt used for the first doping is sodium molybdate; the oxide used for the second doping is molybdenum oxide; the oxide used for the third doping is molybdenum oxide.
Example 5
This embodiment is substantially the same as embodiment 1 except that:
the doping salt used for the first doping is sodium molybdate; the oxide used for the second doping is niobium oxide; the oxide used for the third doping was the same as in example 1.
Example 6
This embodiment is substantially the same as embodiment 1 except that:
the doping salt used for the first doping is ammonium niobium sulfate; the oxide used for the second doping was the same as in example 1; the oxide used for the third doping is tantalum oxide.
Example 7
This embodiment is substantially the same as embodiment 1 except that:
preparation of low-nickel cathode material LiNi 0.5 Mn 0.4 M 0.1 O 2 And M is tungsten.
Comparative example 1
This comparative example is essentially the same as example 1 except that:
sodium tungstate is not added in the first doping process; in the second doping process, tungsten oxide is added in a molar ratio of 0.75% to the precursor, and the amount of tungsten oxide added in the second doping process is equivalent to the sum of the amount of tungsten oxide added in the first doping process of example 1 and the amount of tungsten oxide added in the second doping process.
Comparative example 2
This comparative example is essentially the same as example 1, except that:
tungsten oxide is not added in the second doping process; in the first doping process, the amount of sodium tungstate added was such that Ni: mn: M = 88.
Comparative example 3
This comparative example is essentially the same as example 1, except that:
the third doping step is not carried out; in the second doping process, tungsten oxide was added in a molar ratio of 0.5% to the precursor in an amount equivalent to the sum of the amounts of tungsten oxide added in the second doping process and the third doping process of example 1.
Comparative example 4
This comparative example is essentially the same as example 1 except that:
tungsten oxide is not added in the second doping process, and the third doping step is not carried out; the amount of added sodium tungstate was such that Ni: mn: M = 88.
Comparative example 5
This comparative example is substantially the same as example 1 except that sodium tungstate used in the first doping step is replaced with aluminum sulfate in an equimolar amount. The second and third doping steps are each replaced with equimolar amounts of alumina.
Comparative example 6
This comparative example is substantially the same as example 2 except that the sintering temperature for the third doping is 500 c.
Comparative example 7
Providing an undoped cobalt-free cathode material: liNi 0.88 Mn 0.12 O 2 。
Comparative example 8
Providing an undoped cobalt-free cathode material: liNi 0.5 Mn 0.5 O 2 。
Experimental example 1
When SEM images of the cathode materials obtained in example 1 and comparative example 7 were taken, as shown in fig. 1 and 2, and when fig. 1 and 2 were compared, it was seen that the primary particles of fig. 1 were thin and elongated, and the primary particles of fig. 2 were irregular in shape, mainly in the shape of rectangular parallelepiped. It can be seen that the cathode material prepared in example 1 has better electrochemical properties than those of comparative example 7.
The XRD pattern of the cathode material prepared in example 1 is shown in fig. 3, and it can be seen from fig. 3 that the ternary material with higher crystallinity can be prepared in example 1, and the peak splitting degrees of the groups (018) and (110) are all obvious, which indicates that the material maintains a better layered structure.
Experimental example 2
The positive electrode materials prepared in examples and comparative examples were assembled into a button cell. The specific method comprises the following steps:
the anode material, the conductive agent Super P and the adhesive PVDF are mixed according to the mass ratio of 90:5: 5. preparing high-price metal-doped cobalt-free anode material slurry by using a defoaming machine, adjusting the solid content of the slurry to 38% by using N-methylpyrrolidone (NMP), coating the adjusted slurry on an aluminum foil by using an automatic coating machine, drying the slurry in a vacuum drying box at 120 ℃, rolling the slurry by using a roller press, punching a sheet by using a slicing machine, assembling a button 2025 battery in a glove box, and obtaining LiPF (lithium ion power factor) with 1.2mol/L electrolyte 6 Wherein the solvent is EC: EMC =3 (volume ratio), the diaphragm is Celgard polypropylene membrane, and the metal lithium piece is adopted as the counter electrode. And (3) carrying out charge-discharge test on the button half cell in a voltage interval of 3-4.3V on a blue light tester. And testing the first charge specific capacity, the first discharge specific capacity and the coulombic efficiency of 0.1C, and testing the capacity retention rate after 1C is cycled for 50 circles at 45 ℃. The test results are recorded in the table below.
TABLE 1 electrochemical Properties of cathode materials prepared in examples and comparative examples
| Group of | Specific capacity for first charge (mAh/g) | Specific capacity of first discharge (mAh/g) | Coulombic efficiency (%) | Capacity retention ratio (%) |
| Example 1 | 234.0 | 216.7 | 92.6 | 98.0 |
| Example 2 | 234.1 | 216.1 | 92.3 | 97.8 |
| Example 3 | 233.3 | 215.6 | 92.4 | 97.6 |
| Example 4 | 233.2 | 214.4 | 92.0 | 97.6 |
| Example 5 | 235.1 | 214.4 | 91.2 | 97.4 |
| Example 6 | 235.8 | 214.0 | 90.8 | 97.0 |
| Example 7 | 191.2 | 170.2 | 89.0 | 97.0 |
| Comparative example 1 | 237.1 | 212.0 | 89.4 | 95.8 |
| Comparative example 2 | 234.8 | 212.5 | 90.5 | 95.6 |
| Comparative example 3 | 235.3 | 213.4 | 90.7 | 95.8 |
| Comparative example 4 | 234.2 | 211.6 | 90.4 | 95.2 |
| Comparative example 5 | 233.8 | 210.9 | 90.2 | 94.9 |
| Comparative example 6 | 233.4 | 213.8 | 91.6 | 95.1 |
| Comparative example 7 | 234.2 | 209.6 | 89.5 | 94.0 |
| Comparative example 8 | 190.2 | 168.1 | 88.4 | 95.9 |
As can be seen from table 1, the cathode materials prepared in the examples of the present application all have good electrochemical properties. Comparing example 1 with comparative examples 1-4, it can be seen that the electrochemical performance of the cathode material prepared in example 1 is significantly better than that of comparative examples 1-4, and thus, it can be seen that the effect of performing gradient doping 3 times is better than that of performing doping once or twice. Comparing example 1 with comparative example 5, it can be seen that the tungsten doping of example 1 is replaced by the common aluminum metal doping, and the effect is relatively poor, which indicates that the effect is better when the gradient doping of the high-valence metal is adopted than when the gradient doping of the low-valence metal is adopted. Comparing example 2 with comparative example 6, the electrochemical performance of the cathode material prepared in example 2 is obviously better, which shows that when the third sintering temperature is in the range required by the application, the cathode material with better electrochemical performance can be obtained. Comparing example 1 with comparative example 7 and comparing example 7 with comparative example 8, it can be seen that the electrochemical performance of example 1 is greatly improved compared with comparative example 7 and that example 7 is greatly improved compared with comparative example 8, which shows that the improved scheme of gradient doping with high-valence metals has a significant effect on cobalt-free cathode materials. The improvement rate of the fastening capacitance of example 1 is 3.4 percent relative to the fastening capacitance of comparative example 7, the improvement rate of the fastening capacitance of example 7 is 1.3 percent relative to the fastening capacitance of comparative example 8, and the improvement rate of the performance of example 1 is greater than that of example 7, which shows that the method provided by the application is more suitable for the high-nickel cobalt-free material.
In summary, the method for preparing the cobalt-free cathode material doped with the high-valence metal provided by the embodiment of the application can prepare the cobalt-free cathode material with high capacity, good rate capability and good cycling stability by doping the high-valence metal ions in a gradient manner for multiple times.
The above is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and various modifications and changes will occur to those skilled in the art. 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 preparation method of a high-valence metal-doped cobalt-free cathode material is characterized by comprising the following steps:
first doping: coprecipitating nickel ions, manganese ions and primary doping metal ions in a solution system to prepare a high-valence metal doping precursor Ni x Mn y M z1 (OH) 2 ；
And (3) second doping: mixing and ball-milling the doped metal precursor, the lithium source and the secondary doped metal oxide, and calcining for 10-14h at 700-800 ℃ in an atmosphere containing oxygen to obtain a primary cathode material LiNi x Mn y M z1+z2 O 2 ；
And (3) third doping: crushing the primary cathode material into fine materials, uniformly mixing the fine materials with a triple-doped metal oxide, and sintering at 580 to 700 ℃ for 4 to 8h to obtain a cathode material LiNi x Mn y M z1+z2+z3 O 2 Wherein z1+ z2+ z3= z, z1= (1/4 to 1/2) z, z2= (1/4 to 3/8) z, z3= (1/4 to 3/8) z, x + y + z =1,0.005 is more than or equal to z and is less than or equal to 0.015;
the primary doping metal ions are 5-valent or 6-valent metal ions;
the secondary doped metal oxide and the tertiary doped metal oxide are each independently selected from oxides of 5-valent or 6-valent metals.
2. The method of claim 1, wherein the primary doping metal is Nb 5+ 、Ta 5+ 、W 6+ And Mo 6+ At least one of (a) and (b);
the secondary doped metal oxide and the tertiary doped metal oxide are each independently selected from at least one of an oxide of niobium, an oxide of tantalum, an oxide of tungsten, and an oxide of molybdenum.
3. The method of claim 1, wherein the D50 of the fine material is 8 to 10 μm.
4. The method of claim 1, wherein the nickel ions, the manganese ions, and the primary dopant metal ions are co-precipitated in the solution system by:
adding a sodium hydroxide solution and ammonia water into the solution in which the nickel salt, the manganese salt and the primary metal ion-doped salt are dissolved, controlling the pH value in the reaction process to be 10.6-11.0 and the ammonia value to be 2.8-3.2 g/L, and finishing the reaction when the precipitate grows until the D50 is 8-10 mu m.
5. The method according to claim 4, wherein the salt of the primary doping metal ion comprises at least one of sodium tungstate, ammonium niobium sulfate, sodium tantalate, and sodium molybdate.
6. The preparation method according to claim 3, wherein after the coprecipitation reaction, the precipitate is taken out of the solution system, washed with sodium hydroxide and water in sequence, and then dried to obtain the high-valence metal doped precursor.
7. The process according to claim 1, wherein x is 0.8 or more.
8. A high-valence metal-doped cobalt-free cathode material is characterized by being prepared by the preparation method of any one of claims 1 to 7.
9. A positive electrode produced from the high-valence metal-doped cobalt-free positive electrode material according to claim 8 as one of the raw materials.
10. A lithium ion battery comprising the positive electrode according to claim 9.
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