Surface-modified positive electrode material and surface modification method thereof

Abstract

The application relates to the technical field of batteries, in particular to a surface-modified positive electrode material and a surface modification method thereof. The application provides a positive electrode material surface modification method, which comprises the following steps: S1, mixing a cobalt source with an organic solvent to obtain an intermediate, and adopting a chemical deposition method to deposit the intermediate on a graphite sheet to obtain a coating material; and S2, mixing the positive electrode material and the coating material obtained in the step S1, and calcining to obtain the surface-modified positive electrode material. The cobalt source is deposited on the graphite sheet through the chemical deposition method to form the graphite sheet coated with cobalt hydroxide on the surface, which can not only improve the stability of the structure of the coating material, but also further improve the electrochemical activity of the cobalt hydroxide in the coating material; the graphite sheet coated with the cobalt hydroxide on the surface is used as the coating material to be sintered with the positive electrode material to obtain the surface-modified positive electrode material, which has good structural stability and high specific capacity, and can improve the cycle retention rate of the battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery, in particular to a surface modified positive electrode material and a surface modification method thereof. BACKGROUND

[0002] Lithium nickel cobalt manganese ternary material has become a common positive electrode material for power battery due to its high energy density, low cost and reliable safety. However, due to the side reaction between the interface of the surface of high-nickel material and electrolyte, the electrochemical reaction first occurs on the surface during the charging and discharging process, and the mechanical stress during the charging and discharging process and other factors, the positive electrode material will gradually degrade. At present, the positive electrode material is usually coated and modified to form a protective barrier on the surface of the positive electrode material to improve the stability of the positive electrode material, but the specific capacity of the positive electrode material after coating and modification is low.

[0003] The prior art discloses a preparation method of graphene carbon coated modified lithium nickel cobalt manganese oxide ternary positive electrode material, and obtains a positive electrode material with a carbon coating layer, which effectively prevents the reaction between the electrode material and the electrolyte and improves the electrochemical performance of the material. However, the cycle performance of the positive electrode material after carbon coating modification is poor. SUMMARY

[0004] Therefore, the technical problem to be solved by the present application is to overcome the defect that the cycle performance of the positive electrode material after coating modification in the prior art is poor, thereby providing a surface modified positive electrode material and a surface modification method thereof.

[0005] In one aspect, the present application provides a positive electrode material coating method, comprising the following steps: S1, mixing a cobalt source with an organic solvent to obtain an intermediate, and depositing the intermediate on a graphite sheet by a chemical deposition method to obtain a coating material; S2, mixing the positive electrode material and the coating material obtained in step S1, and calcining to obtain a surface modified positive electrode material.

[0006] In some embodiments, the step of depositing the intermediate on the graphite sheet in step S1 is repeated 2-6 times, preferably 3-5 times.

[0007] In some embodiments, the organic solvent in step S1 includes at least one of an alcohol solvent and dimethyl sulfoxide.

[0008] Preferably, the alcohol solvent includes a C1-C6 alcohol solvent.

[0009] More preferably, the alcohol solvent includes at least one of ethylene glycol, ethanol and methanol.

[0010] In some embodiments, the cobalt source includes at least one of cobalt acetate, cobalt citrate and cobalt tartrate.

[0011] In some embodiments, the concentration of the cobalt source in the intermediate is 0.04-0.06 M.

[0012] In some embodiments, the cobalt source and the organic solvent are mixed under ultrasonic conditions, the power of the ultrasonic is 38-42 kHz, and the processing time is 15-60 min.

[0013] In some embodiments, the concentration of the organic solvent is 1.5-5% vol, preferably 1.5-3% vol.

[0014] In some embodiments, the chemical deposition method is a microwave method, the power of the microwave is 600-1100 W, preferably 700-1000 W, the frequency is 2000-3000 MHz, and the processing time is 30-60 s.

[0015] In some embodiments, the ratio of the graphite sheet to the mixed solution is 1:(50-100) g:mL.

[0016] In some embodiments, in step S2, the mass ratio of the positive electrode material to the coating material is 500:(0.1-3).

[0017] In some embodiments, the mixing in step S2 includes mixing the positive electrode material and the coating material at a speed of 800-1200 rpm for 2-5 min, then mixing at a speed of 1800-2500 rpm for 2-10 min, and then mixing at a speed of 3500-4500 rpm for 8-20 min.

[0018] In some embodiments, the calcination temperature is 400-800°C, and the sintering time is 4-10 h.

[0019] In some embodiments, the chemical formula of the positive electrode material is Li x (Ni a Co b Mn 1-a-b )O2, wherein 1≤x≤1.05, 0.7≤a≤0.95, and 0.01≤b≤0.1.

[0020] In another aspect, the present application provides a surface-modified positive electrode material, which is obtained by the positive electrode material surface coating method described above.

[0021] In some embodiments, the particle size of the positive electrode material is 300-400 mesh.

[0022] The technical solution of the present application has the following advantages:

[0023] The application provides a positive electrode material surface modification method, which comprises the following steps: S1, mixing a cobalt source with an organic solvent to obtain an intermediate, and depositing the intermediate on a graphite sheet by a chemical deposition method to obtain a coating material; and S2, mixing the positive electrode material and the coating material obtained in step S1 and calcining to obtain a surface-modified positive electrode material. The cobalt source is deposited on the graphite sheet by the chemical deposition method to form the graphite sheet coated with cobalt hydroxide uniformly on the surface. The cobalt hydroxide and the graphite sheet are synergistically used, on one hand, the graphite sheet has good conductivity, which promotes charge transfer and improves the electrochemical activity of the cobalt hydroxide, on the other hand, the graphite sheet can provide mechanical support for the cobalt hydroxide, so that the cobalt hydroxide does not agglomerate or degrade during the electrochemical reaction process after the battery is formed, and thus the activity of the cobalt hydroxide is reduced. Therefore, the combination of the graphite sheet and the cobalt hydroxide can not only improve the stability of the structure of the coating material, but also further improve the electrochemical activity of the cobalt hydroxide in the coating material. The graphite sheet coated with the cobalt hydroxide on the surface is used as the coating material and sintered with the positive electrode material to obtain a surface-modified positive electrode material, which has good structural stability, high specific capacity and can improve the cycle retention rate of the battery.

[0024] 2. The application provides a positive electrode material surface coating method, and the step of depositing the intermediate on the graphite sheet in step S1 is repeated 2-6 times, preferably 3-5 times. By repeating the deposition times, the application can not only realize the uniform distribution of the cobalt hydroxide on the surface of the graphite sheet, but also improve the loading amount of the cobalt hydroxide on the graphite sheet, thereby improving the performance of the positive electrode material.

[0025] 3. The application provides a positive electrode material surface modification method, and the organic solvent in step S1 comprises at least one of an alcohol solvent and dimethyl sulfoxide. The alcohol solvent or dimethyl sulfoxide organic solvent is used to form a cobalt source-organic solvent complex when mixed with the cobalt source, which can not only improve the solubility of the cobalt source, but also avoid the agglomeration effect, improve the uniformity of the distribution of the cobalt hydroxide on the surface of the graphite sheet, and further improve the stability of the material.

[0026] 4. The application provides a positive electrode material surface modification method, and the concentration of the organic solvent is 1.5-5%vol, preferably 1.5-3%vol. By diluting the concentration of the organic solvent with water, the application can not only improve the microwave heating efficiency, but also play a promoting role in many reactions, and improve the quality and stability of the deposit.

[0027] 5.The positive electrode material surface modification method provided by the application, the chemical deposition method adopts a microwave method to realize coating of cobalt hydroxide on the surface of graphite sheets, microwave energy is used to promote the interaction between cobalt hydroxide and graphite sheets, the interface bonding between cobalt hydroxide and graphite sheets is promoted, and the stability of the structure of the coating material is improved. Compared with electrochemical deposition or physical vapor deposition, the microwave deposition method provided by the application is simple to operate and can realize the purpose of optimizing the material performance without strict control conditions.

[0028] 6.The positive electrode material surface modification method provided by the application, the power of the microwave is 600-1100W, preferably 700-1000W. By limiting the power of the microwave, on the one hand, the chemical reaction rate during the deposition process is avoided to be too fast, the reaction area is locally overheated, the temperature is too high, and the deposition effect is affected, on the other hand, the reaction rate is avoided to be too slow, and the efficiency of the deposition process is low. By selecting the power of the microwave as 600-1100W, preferably 700-1000W, the reaction rate can be improved, and the deposition effect can be ensured, and the stability of the positive electrode material is improved. BRIEF DESCRIPTION OF DRAWINGS

[0029] In order to more clearly illustrate the specific embodiments of the application or the technical solutions in the prior art, the following will briefly introduce the drawings needed to be used in the specific embodiments or the prior art description. Obviously, the drawings in the following description are some embodiments of the application, and those skilled in the art can also obtain other drawings according to these drawings without creative labor.

[0030] Figure 1 is a schematic diagram of the cycle performance of the battery formed by the surface modified positive electrode material prepared in Examples 1-2 and Comparative Example 1 in the experimental examples of the application. DETAILED DESCRIPTION

[0031] The following examples are provided to better further understand the application and are not limited to the best mode, and do not constitute a limitation on the content and scope of protection of the application. Any person who obtains any product the same as or similar to the application under the inspiration of the application or by combining the application with other prior art features falls within the protection scope of the application.

[0032] If the specific experimental steps or conditions are not specified in the examples, the operation or conditions can be carried out according to the conventional experimental steps described in the literature in the art. If the reagents or instruments used are not specified by the manufacturer, they are all conventional reagent products that can be obtained by market purchase.

[0033] Example 1

[0034] The present embodiment provides a positive electrode material surface modification method, and the specific steps and parameters are as follows:

[0035] (1) Cleaning: 6 g of self-supporting flexible graphite sheet was cleaned with ethanol and deionized water in turn, and then dried in a vacuum drying oven at 60°C for 24 h to obtain clean graphite sheet;

[0036] Preparation of the mixed solution: the aqueous ethylene glycol solution and Co(CH3COO)2 were mixed, and the obtained solution was ultrasonically treated at 40 kHz for 30 min to obtain the mixed solution, wherein the concentration of Co(CH3COO)2 in the solution was 0.05 M, and the concentration of ethylene glycol in the aqueous ethylene glycol solution was 2%vol;

[0037] Microwave deposition: the clean graphite sheet was added into 500 mL of the mixed solution, and transferred into a Teflon container for microwave deposition reaction in a microwave oven, wherein the frequency of the microwave was 2450 MHz, the power was 800 W, and the treatment time was 30 s. The graphite sheet deposited with cobalt acetate was taken out and quickly cooled in cold water.

[0038] After repeating the step of microwave deposition four times, the graphene sheet deposited with Co(OH)2 was gently rinsed with acetone and deionized water in turn, and then dried in a vacuum drying oven at 60°C for 24 h to obtain the coating material.

[0039] (2) The lithium source and the ternary precursor were mixed, and then heated to 550°C at a heating rate of 2°C / min in an oxygen atmosphere with a flow rate of 2 L / min. After sintering at 550°C for 7 h, the temperature was increased to 800°C at a heating rate of 2°C / min. After sintering at 800°C for 10 h, the product was crushed and sieved through a 325 mesh screen to obtain a sintered product, wherein the lithium source was lithium hydroxide monohydrate, the ternary precursor was Ni 0.83 Co 0.05 Mn 0.12 (OH)2, and the molar ratio of the lithium source, the ternary precursor and the additive was 1:1.02.

[0040] (3) 500 g of the sintered product obtained in step (2) and 1.60 g of the coating material obtained in step (1) were placed in a high-speed mixer. After mixing at a speed of 1000 r / min for 2 min, mixing at a speed of 2000 r / min for 3 min, and finally mixing at a speed of 4000 r / min for 10 min, a mixture was obtained without setting a waiting time in between.

[0041] The mixture was heated to 600°C at a heating rate of 2°C / min in an oxygen atmosphere. After sintering at 600°C for 6 h, the temperature was naturally cooled to room temperature. Finally, the product was sieved through a 325 mesh screen to obtain a composite ternary lithium battery positive electrode material.

[0042] Example 2

[0043] The embodiment provides a positive electrode material surface modification method, and specific steps and parameters are the same as those of the embodiment 1, and the difference is that the coating material in the step (3) is 0.1 g.

[0044] Embodiment 3

[0045] The embodiment provides a positive electrode material surface modification method, and specific steps and parameters are the same as those of the embodiment 1, and the difference is that the coating material in the step (3) is 3 g.

[0046] Embodiment 4

[0047] The embodiment provides a positive electrode material surface modification method, and specific steps and parameters are the same as those of the embodiment 1, and the difference is that the concentration of the ethylene glycol in the preparation of the mixed solution in the step (1) is 1.5%.

[0048] Embodiment 5

[0049] The embodiment provides a positive electrode material surface modification method, and specific steps and parameters are the same as those of the embodiment 1, and the difference is that the concentration of the ethylene glycol in the preparation of the mixed solution in the step (1) is 3%.

[0050] Embodiment 6

[0051] The embodiment provides a positive electrode material surface modification method, and specific steps and parameters are the same as those of the embodiment 1, and the difference is that the concentration of the ethylene glycol in the preparation of the mixed solution in the step (1) is 5%.

[0052] Embodiment 7

[0053] The embodiment provides a positive electrode material surface modification method, and specific steps and parameters are the same as those of the embodiment 1, and the difference is that the power of the microwave in the microwave deposition step in the step (1) is 700 W.

[0054] Embodiment 8

[0055] The embodiment provides a positive electrode material surface modification method, and specific steps and parameters are the same as those of the embodiment 1, and the difference is that the power of the microwave in the microwave deposition step in the step (1) is 1000 W.

[0056] Embodiment 9

[0057] The embodiment provides a positive electrode material surface modification method, and specific steps and parameters are the same as those of the embodiment 1, and the difference is that the power of the microwave in the microwave deposition step in the step (1) is 600 W.

[0058] Embodiment 10

[0059] The embodiment provides a positive electrode material surface modification method, and specific steps and parameters are the same as those in Embodiment 1, except that the power of the microwave in the microwave deposition step in step (1) is 1100 W.

[0060] Embodiment 11

[0061] The embodiment provides a positive electrode material surface modification method, and specific steps and parameters are the same as those in Embodiment 1, except that the number of repetitions of the microwave deposition step in step (1) is 3 times.

[0062] Embodiment 12

[0063] The embodiment provides a positive electrode material surface modification method, and specific steps and parameters are the same as those in Embodiment 1, except that the number of repetitions of the microwave deposition step in step (1) is 5 times.

[0064] Embodiment 13

[0065] The embodiment provides a positive electrode material surface modification method, and specific steps and parameters are the same as those in Embodiment 1, except that the number of repetitions of the microwave deposition step in step (1) is 2 times.

[0066] Embodiment 14

[0067] The embodiment provides a positive electrode material surface modification method, and specific steps and parameters are the same as those in Embodiment 1, except that the number of repetitions of the microwave deposition step in step (1) is 6 times.

[0068] Embodiment 15

[0069] The embodiment provides a positive electrode material surface modification method, and specific steps and parameters are as follows:

[0070] (1) cleaning: 6g of self-supporting flexible graphite sheet is sequentially cleaned with ethanol and deionized water, and then dried in a vacuum drying box at 60 DEG C for 24h to obtain clean graphite sheet;

[0071] Preparation of the mixed solution: the dimethyl sulfoxide aqueous solution and cobalt tartrate are mixed, the obtained solution is ultrasonically treated at 38 kHz for 60 minutes to obtain the mixed solution, wherein the concentration of cobalt tartrate in the solution is 0.04M, and the concentration of dimethyl sulfoxide in the dimethyl sulfoxide aqueous solution is 2%vol;

[0072] Microwave deposition: the clean graphite sheet is added into 600mL of the mixed solution and transferred into a Teflon container for microwave deposition reaction in a microwave oven, wherein the frequency of the microwave is 2000MHz, the power is 800W, and the treatment time is 60s, the graphite sheet deposited with cobalt tartrate is taken out and quickly cooled in cold water.

[0073] After repeating the step of microwave deposition four times, the graphene sheet on which Co(OH)2 was deposited was rinsed with acetone and deionized water in turn, and then vacuum dried at 60°C for 24 hours to obtain the coating material.

[0074] (2) mixing the lithium source and the ternary precursor, then heating to 550°C at a heating rate of 2°C / min under an oxygen atmosphere with a flow rate of 2 L / min, sintering at 550°C for 7 h, then heating to 800°C at a heating rate of 2°C / min, sintering at 800°C for 10 h, and finally crushing and passing through a 325 mesh sieve to obtain a sintered product, wherein the lithium source is lithium hydroxide monohydrate, the ternary precursor is Ni 0.83 Co 0.05 Mn 0.12 (OH)2, and the molar ratio of the lithium source, the ternary precursor and the additive is 1:1.02.

[0075] (3) placing 500 g of the sintered product obtained in step (2) and 1.6 g of the coating material obtained in step (1) into a high-speed mixer, mixing at a speed of 800 r / min for 5 min, then mixing at a speed of 2500 r / min for 2 min, and finally mixing at a speed of 3500 r / min for 20 min without setting a waiting time in between, to obtain a mixture;

[0076] under an oxygen atmosphere, heating the mixture to 400°C at a heating rate of 2°C / min, sintering at 400°C for 10 h, naturally cooling to room temperature, and finally passing through a 300 mesh sieve to obtain a positive electrode material for a composite type ternary lithium battery.

[0077] Example 16

[0078] This example provides a method for surface modification of a positive electrode material, and the specific steps and parameters are as follows:

[0079] (1) cleaning: cleaning 6 g of self-supporting flexible graphite sheet with ethanol and deionized water in turn, and then drying in a vacuum drying oven at 60°C for 24 h to obtain clean graphite sheet;

[0080] Preparation of the mixed solution: mixing the aqueous ethanol solution and the cobalt citrate to obtain a solution, and then ultrasonically treating the solution at 42 kHz for 15 min to obtain a mixed solution, wherein the concentration of cobalt citrate in the mixed solution is 0.06 M, and the concentration of ethanol in the aqueous ethanol solution is 2%vol;

[0081] Microwave deposition: adding the clean graphite sheet into 300 mL of the mixed solution, and then transferring into a Teflon container for microwave deposition reaction in a microwave oven, wherein the frequency of the microwave is 3000 MHz, the power is 800 W, and the treatment time is 30 s, and then taking out the graphite sheet on which cobalt citrate is deposited and rapidly cooling in cold water.

[0082] After repeating the step of microwave deposition four times, the graphene sheet on which Co(OH)2 was deposited was rinsed with acetone and deionized water in turn, and then vacuum dried at 60℃ for 24 hours to obtain a coated material.

[0083] (2) mixing the lithium source and the ternary precursor, and then heating to 550℃ at a heating rate of 2℃ / min under an oxygen atmosphere with a flow rate of 2L / min, sintering at 550℃ for 7h, then heating to 800℃ at a heating rate of 2℃ / min, sintering at 800℃ for 10h, and finally crushing and sieving through a 325 mesh screen to obtain a sintered product, wherein the lithium source is lithium hydroxide monohydrate, the ternary precursor is Ni 0.83 Co 0.05 Mn 0.12 (OH)2, and the molar ratio of the lithium source, the ternary precursor and the additive is 1:1.02.

[0084] (3) placing 500g of the sintered product obtained in step (2) and 1.6g of the coated material obtained in step (1) into a high-speed mixer, mixing at a rotation speed of 1200r / min for 2min, then mixing at a rotation speed of 1800r / min for 10min, and finally mixing at a rotation speed of 4500r / min for 8min, without setting a waiting time in between, to obtain a mixture;

[0085] heating the mixture to 800℃ at a heating rate of 2℃ / min under an oxygen atmosphere, sintering at 800℃ for 4h, naturally cooling to room temperature, and finally sieving through a 400 mesh screen to obtain a positive electrode material for a composite type ternary lithium battery.

[0086] Comparative Example

[0087] This comparative example provides a surface modification method for a positive electrode material, and the specific steps and parameters are the same as those of Example 1, except that an equal amount of clean graphite sheet in step (1) is used instead of the coated material in step (3).

[0088] Experimental Example

[0089] The positive electrode materials prepared in Examples 1-16 and the comparative example were respectively prepared into button cells according to the following method: uniformly mixing the positive electrode material, polyvinylidene fluoride and conductive carbon black according to a mass ratio of 95:3:2, then coating on an aluminum foil laid on a coating machine (areal density 13.3-13.5mg / cm 2 , compacted density 3.4-3.6mg / cm 2 ), and placing into a 80℃ air drying oven for drying for 3h; then punching, weighing, baking the electrode sheet, and making into button cells.

[0090] The specific test method of electrochemical performance is to put the button cell into a blue electric test system for electric performance test, the test voltage range is 2.5-4.25V, the discharge specific capacity of the button cell at different discharge rates and the capacity retention rate after 50 cycles are tested, the test results are shown in Table 1, and the capacity retention rate of the battery formed by the positive electrode material prepared in Examples 1-2 and the comparative example at each cycle number within 50 cycles is plotted, see Figure 1 .

[0091] Table 1 Performance test results of button cell

[0092]

[0093]

[0094]

[0095] According to Table 1 and Figure 1 It can be seen that, compared with the positive electrode coated with graphite sheet as the coating material in the comparative example, the positive electrode material provided in the present application can significantly improve the discharge specific capacity and the capacity retention rate, which proves that the positive electrode material provided in the present application can improve the electrochemical performance and the cycle stability of the positive electrode material.

[0096] Obviously, the above examples are only examples for clearly illustrating, but not limit the embodiments. For those skilled in the art, on the basis of the above description, other different forms of changes or variations can also be made. Here, it is not necessary and also impossible to enumerate all the embodiments. The obvious changes or variations derived therefrom are still within the protection scope of the present application.

Claims

1. A method for coating the surface of a positive electrode material, characterized in that, Includes the following steps, S1, mix the cobalt source with an organic solvent to obtain a mixture; S2, the cobalt source in the mixture is deposited on the graphite sheet by chemical deposition to form a graphite sheet with cobalt hydroxide uniformly coated on the surface; S3, mix the cathode material and the graphite sheet obtained in step S2, and calcine to obtain a surface-modified cathode material; The chemical deposition method is a microwave method; The general chemical formula of the cathode material is Li. x (Ni a Co b Mn 1-a-b O2, where 1≤x≤1.05, 0.7≤a≤0.95, 0.01≤b≤0.1; The calcination temperature is 400-800℃, and the calcination time is 4-10 hours.

2. The method for coating the surface of a positive electrode material according to claim 1, characterized in that, In step S2, the step of depositing the cobalt source in the mixture onto the graphite sheet is repeated 2-6 times; and / or, The organic solvent in step S1 includes at least one of an alcohol solvent and dimethyl sulfoxide; and / or, The cobalt source includes at least one of cobalt acetate, cobalt citrate, and cobalt tartrate; and / or, The concentration of the cobalt source in the mixture is 0.04-0.06 M.

3. The method for coating the surface of the positive electrode material according to claim 2, characterized in that, The alcohol solvent includes C1-C6 alcohol solvents; and / or, Under ultrasonic conditions, a cobalt source and an organic solvent are mixed, wherein the ultrasonic power is 38-42 kHz and the processing time is 15-60 min; and / or, The concentration of the organic solvent is 1.5-5% vol.

4. The method for coating the surface of the positive electrode material according to claim 3, characterized in that, The microwave power is 600-1100W, the frequency is 2000-3000MHz, and the processing time is 30-60s; and / or, The alcohol solvent includes at least one of ethylene glycol, ethanol, and methanol.

5. The method for coating the surface of the positive electrode material according to claim 4, characterized in that, The ratio of graphite sheets to the mixture is 1:(50-100), with units of g:mL.

6. The method for coating the surface of a positive electrode material according to claim 5, characterized in that, In step S3, the mass ratio of the positive electrode material to the graphite sheet is 500:(0.1-3); and / or, The mixing step in step S3 includes mixing the positive electrode material and graphite sheet at a speed of 800-1200 rpm for 2-5 minutes, then mixing at a speed of 1800-2500 rpm for 2-10 minutes, and finally mixing at a speed of 3500-4500 rpm for 8-20 minutes.

7. The method for coating the surface of a positive electrode material according to claim 2, characterized in that, The step of depositing the cobalt source in the mixture onto the graphite sheet is repeated 3-5 times.

8. The method for coating the surface of a positive electrode material according to claim 3, characterized in that, The concentration of the organic solvent is 1.5-3% vol.

9. The method for coating the surface of a positive electrode material according to claim 4, characterized in that, The power of the microwave is 700-1000W.

10. A surface-modified cathode material, characterized in that, The cathode material obtained by the cathode material surface coating method according to any one of claims 1-9.

11. The surface-modified cathode material according to claim 10, characterized in that, The particle size of the positive electrode material is 300-400 mesh.

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