HIGH-SAFETY TERNARY POSITIVE ELECTRODE MATERIAL AND METHOD FOR PREPARING SAME

Abstract

The present disclosure discloses a high-safety ternary positive electrode material and a method for preparing the same; wherein the ternary positive electrode material has a chemical composition of Li.sub.a(Ni.sub.xCo.sub.yMn.sub.1-x-y).sub.1-bMbO.sub.2-cA.sub.c, wherein 0.75?a?1.2, 0.75?x<1, 0<y?0.15, 1?x?y>0, 0?b?0.01, 0?c?0.2, M is one or more selected from the group consisting of Al, Zr, Ti, Y, Sr, W and Mg, and A is one or more selected from the group consisting of S, F and N; and C.sub.Mn?(1?x?y)?0.07; C.sub.Co?y?0.05; 0?[C.sub.Mn?(1?x?y)]/(C.sub.Co?y)?2.0. The ternary positive electrode material of the present disclosure is a high-nickel single crystal material with gradient concentration; it has the advantages of high capacity and high thermal stability, and the preparation method is simple, and is suitable for large-scale production.

Claims

1. A ternary positive electrode material for a lithium ion battery, wherein the ternary positive electrode material has a chemical composition of Li.sub.a(Ni.sub.xCo.sub.yMn.sub.1-x-y).sub.1-bMbO.sub.2-cA.sub.c, wherein 0.75?a?1.2, 0.75?x<1, 0<y?0.15, 1?x?y>0, 0?b?0.01, 0?c?0.2, M is one or more selected from the group consisting of Al, Zr, Ti, Y, Sr, W and Mg, and A is one or more selected from the group consisting of S, F and N; wherein the ternary positive electrode material has a single crystal morphology, and C.sub.Mn?(1?x?y)?0.07, wherein C.sub.Mn is an atomic ratio of Mn element to a sum of three elements of Ni, Co, and Mn obtained by using XPS to test a surface of the material; C.sub.Co?y?0.05, wherein C.sub.Co is an atomic ratio of Co element to the sum of three elements of Ni, Co, and Mn obtained by using XPS to test the surface of the material; 0?[C.sub.Mn?(1?x?y)]/(C.sub.Co?y)?2.0.

2. The ternary positive electrode material for a lithium ion battery according to claim 1, wherein C.sub.Mn?(1?x?y)?0.15.

3. The ternary positive electrode material for a lithium ion battery according to claim 1, wherein C.sub.Co?y?0.1.

4. The ternary positive electrode material for a lithium ion battery according to claim 1, wherein when a cumulative particle volume distribution of the ternary positive electrode material reaches 50%, the corresponding particle size D.sub.v50 satisfies 2.5 ?m?D.sub.v50?55 ?m.

5. A method for preparing the ternary positive electrode material for a lithium ion battery of claim 1, wherein the method comprises the following steps: step S1: selecting a ternary positive electrode precursor containing Ni, Co, and Mn and mixing it with lithium hydroxide to form a mixture A; step S2: heating the mixture A in an air or oxygen atmosphere, wherein the mixture A is held at 700?1,100? C. for 4?15 hours, followed by rolling and pulverization to obtain an intermediate product B; step S3: mixing the intermediate product B with a Mn-containing solid powder and a Co-containing solid powder to form a mixture C, wherein a molar ratio of Mn element in the Mn-containing solid powder to the intermediate product B is 0.5?4%, and a molar ratio of Co element in the Co-containing solid powder to the intermediate product B is 2?4%; step S4: heating the mixture C in an air or oxygen atmosphere, wherein the mixture C is held at 700?1,100? C. for 4?15 hours, followed by rolling and pulverization to obtain the ternary positive electrode material for a lithium ion battery.

6. The method for preparing the ternary positive electrode material for a lithium ion battery according to claim 5, wherein an oxide of element M is added as a dopant in step S1; and/or an oxide of element M is added as a coating agent in step S3; and/or an element A-containing compound is added as a dopant in step S1; and/or an element A-containing compound is added as a coating agent in step S3.

7. The method for preparing the ternary positive electrode material for a lithium ion battery according to claim 5, wherein the Mn-containing solid powder is one or more of MnO.sub.2, Mn.sub.2O.sub.3, MnO(OH), and MnO; and the Co-containing solid powder is one or more of Co.sub.3O.sub.4, CoO, Co(OH).sub.2, COOH, and CoCO.sub.3.

8. The method for preparing the ternary positive electrode material for a lithium ion battery according to claim 5, wherein a molar ratio of Mn element to Co element in the Mn-containing solid powder and the Co-containing solid powder is 1:4?1:1 in step S3.

9. A positive electrode sheet for a lithium ion battery comprising the ternary positive electrode material of claim 1.

10. A lithium ion battery comprising the positive electrode sheet of claim 9.

11. A positive electrode sheet for a lithium ion battery comprising the ternary positive electrode material prepared by the method of claim 5.

12. A lithium ion battery comprising the positive electrode sheet of claim 11.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Other characteristics, objects and advantages of the present disclosure will become more apparent by reading the detailed description of non-limiting embodiments made with reference to the following drawings:

[0054] FIG. 1 is an SEM image of a single crystal high-nickel positive electrode material prepared according to Example 2.

DETAILED DESCRIPTION

[0055] The present disclosure will be illustrated in detail with reference to the following Examples. The following Examples will help those skilled in the art to further understand the present disclosure, but do not limit the present disclosure in any way. It should be noted that, for those skilled in the art, adjustments and improvements can be made without departing from the concept of the present disclosure. They all fall within the protection scope of the present disclosure.

Example 1

[0056] This example relates to a ternary positive electrode material for lithium ion batteries, whose theoretical chemical composition is Li.sub.1.02Ni.sub.0.805Co.sub.0.127Mn.sub.0.068O.sub.2. The preparation steps are as follows: [0057] 1) Preparation of a ternary positive electrode precursor containing Ni, Co, and Mn: first, three metal salts of nickel sulfate, cobalt sulfate, and manganese sulfate were prepared into a 2 mol/L solution at a molar ratio of 83:11:6. A peristaltic pump was used to slowly pump a mixed solution of sodium hydroxide (4 mol/L) and ammonia water (2.4 mol/L) as precipitants into a reaction kettle containing the above metal salt solution at a volume ratio of 1:1. The reaction temperature was strictly controlled at 55? C.?1? C. The reaction pH was 11.0, and the stirring speed was 1,000 r/min. Nitrogen was used as a protective gas during the reaction. After reacting for 12 hours, the material obtained by the reaction was washed several times with deionized water, and dried in vacuum at 80? C. for 24 hours to obtain a ternary hydroxide precursor; [0058] 2) The ternary positive electrode precursor containing Ni, Co, and Mn were fully mixed with lithium hydroxide at a molar ratio of lithium hydroxide:precursor of 1.05:1 to form a mixture A; [0059] 3) The mixture A was heated in an oxygen atmosphere and held at 910? C. for 9 hours. An intermediate product B was obtained after rolling and pulverization. [0060] 4) The intermediate product B was fully mixed with MnO(OH) and Co(OH).sub.2 to form a mixture C, wherein the molar ratio of MnO(OH) to the intermediate product B was 0.7%, the molar ratio of Co(OH).sub.2 to the intermediate product B was 2.1%, and the molar ratio of the two is 1:3; [0061] 5) The mixture A was heated in an oxygen atmosphere and held at 820? C. for 5 hours. The ternary positive electrode material for lithium ion batteries was obtained after rolling and pulverization.

[0062] Subsequent Examples and Comparative Examples follow a similar process, and the difference lies in the ratio selection of precursors, the temperature/time selections in step 3) and step 5), etc., which are listed in Tables 1 and 2.

Example 2

[0063] The material preparation process was basically the same as that in Example 1, and only the ratios related to MnO(OH) and Co(OH).sub.2 in step 4) were adjusted to 1.0% and 2.0%. The theoretical chemical composition of the finally obtained material is Li.sub.1.02Ni.sub.0.806Co.sub.0.123Mn.sub.0.071O.sub.2. The SEM image of the prepared single crystal high-nickel positive electrode material is shown in FIG. 1.

Example 3

[0064] The material preparation process was basically the same as that in Example 1, and only the ratios related to MnO(OH) and Co(OH).sub.2 in step 4) were adjusted to 3.5% and 4.0%. The theoretical chemical composition of the finally obtained material is Li.sub.1.03Ni.sub.0.764Co.sub.0.135Mn.sub.0.101O.sub.2.

Example 4

[0065] The material preparation process was basically the same as that in Example 1. The molar ratio of three metal salts of nickel sulfate, manganese sulfate and cobalt sulfate in step 1) was adjusted to 90:5:5. The heating temperature in step 3) was adjusted to 890? C. The MnO(OH) in step 4) was adjusted to MnO.sub.2. The Co(OH).sub.2 in step 4) was adjusted to COOH. The molar ratio of MnO.sub.2 to the intermediate product B was 1.5%, and the molar ratio of CoOOH to the intermediate product B was 2.5%. The heating temperature in step 5) was adjusted to 800? C. The theoretical chemical composition of the finally obtained material is Li.sub.1.03Ni.sub.0.856Co.sub.0.076Mn.sub.0.068O.sub.2.

Example 5

[0066] The material preparation process was basically the same as that in Example 4, and the molar ratios related to MnO.sub.2 and CoOOH in step 4) were adjusted to 3.0% and 3.5%. The theoretical chemical composition of the finally obtained material is Li.sub.1.02Ni.sub.0.833Co.sub.0.084Mn.sub.0.083O.sub.2.

Example 6

[0067] The material preparation process was basically the same as that in Example 5, and the step 2) was adjusted to adding ZrO.sub.2 as a dopant with a molar ratio of ZrO.sub.2 to the precursor of 0.2% during the operation. The theoretical chemical composition of the finally obtained material is Li.sub.1.02Ni.sub.0.830Co.sub.0.087Mn.sub.0.081Zr.sub.0.002O.sub.2, i.e., Li.sub.1.02(Ni.sub.0.832Co.sub.0.087Mn.sub.0.081).sub.0.998Zr.sub.0.002O.sub.2.

Comparative Example 1

[0068] The material preparation process was basically the same as that in Example 1, and MnO(OH) and Co(OH).sub.2 were not added in step 4). The theoretical chemical composition of the finally obtained material is Li.sub.1.04Ni.sub.0.830Co.sub.0.108Mn.sub.0.062O.sub.2.

Comparative Example 2

[0069] The material preparation process was basically the same as that in Example 1, and the ratios related to MnO(OH) and Co(OH).sub.2 in step 4) were adjusted to 0.4% and 2.4%. The theoretical chemical composition of the finally obtained material is Li.sub.1.02Ni.sub.0.801Co.sub.0.132Mn.sub.0.067O.sub.2.

Comparative Example 3

[0070] The material preparation process was basically the same as that in Example 1, and the ratios related to MnO(OH) and Co(OH).sub.2 in step 4) were adjusted to 1.0% and 0.7%. The theoretical chemical composition of the finally obtained material is Li.sub.1.03Ni.sub.0.813Co.sub.0.114Mn.sub.0.073O.sub.2.

Comparative Example 4

[0071] The material preparation process was basically the same as that in Example 2, and the MnO(OH) and Co(OH).sub.2 in step 4) were adjusted to MnSO.sub.4 and CoSO.sub.4 respectively. The theoretical chemical composition of the finally obtained material is Li.sub.1.02Ni.sub.0.800Co.sub.0.125Mn.sub.0.075O.sub.2.

[0072] Material Characterization

[0073] Particle size test: the sample was dispersed in water and added to a laser particle size analyzer for testing. The particle refractive index was set to 1.741, the absorbance was set to 1, and the solvent refractive index was set to 1.330. The internal ultrasound of the test instrument was turned on during the test, and the shading degree was set to 10?20%. The volume distribution differential curve was selected and D.sub.v50 was read by software.

[0074] ICP test: 0.4 g of a positive electrode material sample was weighed and put in a 250 ml beaker to which 10 ml HCl solution (1:1 by volume of HCl: H.sub.2O) was added. The sample was dissolved by heating at 180? C. The heated liquid was transferred to a volumetric flask, and pure water was added to its constant volume. The liquid was diluted to a measurable range, and tested using an ICP instrument. The x and y values were calculated by comparing the relative contents of the Ni, Co, and Mn elements determined by the ICP test, and a, b, and c were determined by ICP directly. If M and A each included more than one element, b and c each were equal to a sum of the contents of different elements.

[0075] XPS test: a positive electrode material powder sample was spread on an aluminum foil to which a double-sided adhesive tape was adhered. The sample was flattened using a tablet press, and then the material was tested using an XPS instrument. In the test process, a full-spectrum scan can be performed first to determine possible elements, and then a narrow-spectrum scan was performed for the existing elements. The relative atomic content of each element was calculated based on the area of the signal peak in view of the sensitivity factor of the element.

[0076] The above-mentioned particle size, ICP, and XPS tests were performed on the ternary positive electrode materials pulverized in step (5) of the Examples and Comparative Examples, and the results are shown in Table 2.

TABLE-US-00001 TABLE 1 Heating Mn-containing Co-containing Sulfate molar temperature and coating agent coating agent ratio Ni:Co:Mn LiOH:precursor time in step 3) and its ratio and its ratio Example 1 83:11:6 1.05:1 910? C./9 h MnO(OH)/0.7% Co(OH).sub.2/2.1% Example 2 83:11:6 1.05:1 910? C./9 h MnO(OH)/1.0% Co(OH).sub.2/2.0% Example 3 83:11:6 1.05:1 910? C./9 h MnO(OH)/3.5% Co(OH).sub.2/4.0% Example 4 90:5:5 1.05:1 890? C./9 h MnO.sub.2/1.5% CoOOH/2.5% Example 5 90:5:5 1.05:1 890? C./9 h MnO.sub.2/3.0% CoOOH/3.5% Example 6 90:5:5 1.05:1 890? C./9 h MnO.sub.2/3.0% CoOOH/3.5% Comparative 83:11:6 1.05:1 910? C./9 h Example 1 Comparative 83:11:6 1.05:1 910? C./9 h MnO(OH)/0.4% Co(OH).sub.2/2.4% Example 2 Comparative 83:11:6 1.05:1 910? C./9 h MnO(OH)/1.0% Co(OH).sub.2/0.7% Example 3 Comparative 83:11:6 1.05:1 910? C./9 h MnSO.sub.4/1.0% CoSO.sub.4/2.0% Example 4

[0077] No surface treatment was performed in Comparative Example 1, and none of C.sub.Mn?(1?x?y)?0.07, C.sub.Co?y?0.05, and 0?[C.sub.Mn?(1?x?y)]/(C.sub.Co?y)?2.0 are met. In Comparative Example 2, the amount of Mn coating reagent is too small, and the requirement of C.sub.Mn?(1?x?y)?0.07 as well as the requirement of 1:4-1:1 in the process are not met. In Comparative Example 3, the amount of Co coating reagent is too small, and the requirements of C.sub.Co?y?0.05 and [C.sub.Mn?(1?x?y)]/(C.sub.Co?y)?2.0, as well as the requirement of 1:4-1:1 in the process are not met. In Comparative Example 4, MnSO.sub.4 was used, it is difficult to form a layered structure, a large amount remains on the surface, and [C.sub.Mn?(1?x?y)]/(C.sub.Co?y)?2.0 is not met.

TABLE-US-00002 TABLE 2 Heating Particle size after Ni:Co:Mn in the Ni:Co:Mn on the temperature and pulverization in material measured surface measured time in step 5) step 5) by ICP by XPS Example 1 820? C./5 h 3.68 ?m 80.5:12.7:6.8 67.5:18.2:14.3 Example 2 820? C./5 h 3.72 ?m 80.6:12.3:7.1 63.7:18.0:18.3 Example 3 820? C./5 h 3.60 ?m 76.2:13.7:10.1 50.1:24.6:25.3 Example 4 800? C./5 h 3.55 ?m 85.6:7.6:6.8 65.7:17.2:17.1 Example 5 800? C./5 h 3.58 ?m 83.3:8.4:8.3 56.4:19.2:24.4 Example 6 800? C./5 h 3.47 ?m 83.1:8.8:8.1 55.9:19.5:24.6 Comparative 820? C./5 h 3.57 ?m 83.0:11.8:6.2 83.1:11.6:6.3 Example 1 Comparative 820? C./5 h 3.63 ?m 80.1:13.2:6.7 68.5:19.0:12.5 Example 2 Comparative 820? C./5 h 3.62 ?m 81.3:11.4:7.3 68.7:13.2:18.1 Example 3 Comparative 820? C./5 h 3.75 ?m 80.0:12.5:7.5 63.7:15.1:19.5 Example 4

[0078] By comparing Examples 1-3 and 4-5, it can be found that as the amount of the coating agent used increases, Co and Mn on the surface of the material will increase. By investigating Example 2 and Comparative Example 4, it will be found that if an appropriate coating agent is not used, the LiCoMnO layered structure coating layer cannot be formed under the same conditions, which may cause Mn element enrichment on the surface.

[0079] Performance Testing

[0080] The following method was adopted to make the ternary positive electrode material of Examples and Comparative Examples into battery and test their performance:

[0081] A positive electrode active material (prepared ternary positive electrode material) was mixed with carbon black as a conductive agent and polyvinylidene fluoride (PVDF) as a binder at a mass ratio of 97:1.7:1.3, added into N-methyl pyrrolidone (NMIP) as an organic solvent, and stirred at high speed to form a uniform dispersion. After the high-speed stirring was completed, negative pressure defoaming was carried out in the stirring tank to obtain a positive electrode slurry suitable for coating. The obtained positive electrode slurry was coated on an aluminum foil with a transfer coating machine. After drying, cold pressing, and slitting, a positive electrode sheet in a desired shape was made. During the cold pressing process, the compacted density of the coating area of the positive electrode active material was controlled at 3.4 g/cm.sup.3.

[0082] Graphite as a negative electrode active was mixed with carbon black as a conductive agent, styrene-butadiene rubber (SBR) as a binder, and carboxymethyl cellulose sodium (CMC-Na) according to a mass ratio of 96.8:1.2:1.2:0.8, added into deionized water, and stirred at a high speed to form a uniform dispersion. After high-speed stirring, negative pressure defoaming was carried out in the stirring tank to obtain a negative electrode slurry suitable for coating. The obtained negative electrode slurry was coated on a copper foil with a transfer coating machine. After drying, cold pressing, and slitting, a negative electrode sheet in a desired shape was made. During the cold pressing process, the compacted density of the coating area of the negative electrode active material was controlled at 1.65 g/cm.sup.3.

[0083] The positive and negative electrode sheets were placed on two sides of a 9 ?m thick PE separator respectively, and rolled up to form a roll core. An uncoated area was reserved and connected to a nickel tab by ultrasonic welding. The roll core was wrapped with an aluminum-plastic film and heat-sealed, and one side was reserved for liquid injection.

[0084] 13 wt % (based on the total mass of the electrolyte) of LiPF.sub.6, 1 wt % (based on the total mass of the electrolyte) of carbonic acid and 2 wt % (based on the total mass of the electrolyte) of DTD were added as a lithium salt and additives into a mixed solvent of EC: EMC: DEC at a mass ratio of 3:5:2 to make an electrolyte. The electrolyte was injected into the aluminum plastic film wrapping the roll core. Lithium ion batteries were obtained by further processes of vacuum packaging, standing and formation.

[0085] Rate test: a charging and discharging equipment was used to adjust the SOC state of the battery to 0% at a rate of 0.33 C (that is, 0.33 times the rated capacity of the battery in ampere-hours is set as the current value). The battery was charged with a constant current A of 0.5 C at 25? C. after standing for 30 minutes, and the capacity C1 was recorded during the charging process. 0.33 C discharge to 0% SOC was repeated. After standing for 30 minutes, the battery was charged with a constant current A of 2 C, and the capacity C2 was recorded during the discharge process. C2/C1 was investigated as a comparison index for rate performance.

[0086] Thermal stability test: a charging and discharging equipment was used to adjust the SOC state of the battery to 100% at a rate of 0.33 C. The battery was disassembled in a glove box and the positive electrode sheet was taken out. A sample of about 2 mm*2 mm was taken from the coating area of the sheet, weighed in the air to obtain mi, and put into a high-pressure crucible. ? m.sub.1 of the electrolyte was measured out, dropped into the high-pressure crucible with a pipette gun, and packaged. The test was carried out on a DSC device at a heating rate of 5? C./min. The temperature corresponding to the highest peak point in the curve was taken as a comparison index for thermal stability.

[0087] High-temperature gas production test: a charging and discharging equipment was used to adjust the SOC state of the battery to 100% at a rate of 0.33 C. The battery volume V1 was measured and recorded. Then the battery was stored in an oven at a constant temperature of 70? C., and the battery volume V2 was recorded after 72 hours. The volume growth rate V2/V1?1 caused by gas production was investigated as a comparison index for high-temperature gas production.

[0088] Cycle life: a charging and discharging equipment was used to cyclically charge and discharge the battery at a rate of 1 C at 45? C. The capacity retention rate at 1,000 cycles was recorded as a comparison index for cycle life.

[0089] The performance test results are shown in Table 3.

TABLE-US-00003 TABLE 3 Rate Thermal Gas production at Cycle performance stability high temperature performance Example 1 87.6% 224.7? C. 23.6% 84.2% Example 2 86.2% 227.3? C. 20.5% 86.7% Example 3 88.4% 235.1? C. 17.8% 90.4% Example 4 87.7% 218.9? C. 24.1% 86.3% Example 5 87.2% 225.6? C. 19.3% 88.7% Example 6 87.4% 227.3? C. 18.9% 89.9% Comparative Example 1 85.2% 214.4? C. 43.7% 81.4% Comparative Example 2 86.1% 217.5? C. 37.6% 83.5% Comparative Example 3 77.4% 220.2? C. 45.1% 84.1% Comparative Example 4 75.3% 218.3? C. 41.4% 83.7%

[0090] By comparing Examples 1-3 and Comparative Example 1, it can be found that co-coating the material with Co/Mn within the preferred range of the present disclosure can effectively improve its thermal stability and cycle stability on the basis of maintaining the kinetic performances of the material, and at the same time, it reduces the gas production of materials in high-temperature storage environments. From Examples 4-5, it can be seen that this trend is also applicable to precursors with a Ni content equal to or above 90%. From Example 5 and Example 6, it can be seen that the addition of the doping element Zr in step S1 does not affect the effect of the subsequent co-coating treatment, and the effects of both can be exerted at the same time. The amount of coating agent added in the coating process of Comparative Example 2 is close to that of Example 1, but the amount of Mn-containing coating agent added in Comparative Example 2 is too small to effectively improve the surface stability of the material. In Comparative Example 3, the ratio of the Mn-containing coating agent to the Co-containing coating agent added during the coating process is not appropriate, so that the differences between the contents of Mn and Co elements on the surface of the material and the contents of Mn and Co in the whole do not meet the preferred conditions of the present disclosure, and a LiCoMnO layer structure coating layer cannot be formed on the surface of the material, making it difficult to exert the effect. The Mn-containing coating agent used in Comparative Example 4 cannot react with the Co-containing coating agent and the residual lithium salt on the surface to form a LiCoMnO layered structure. Although Mn and Co elements are also enriched on the surface of the material, they not only fail to improve the high temperature stability of the material, but lead to a decrease in the kinetic performances of the material.

[0091] Specific embodiments of the present disclosure have been described above. It should be understood that the present disclosure is not limited to the specific embodiments described above, and those skilled in the art may make various changes or modifications within the scope of the claims, which do not affect the essence of the present disclosure.