A negative electrode active material, a method for preparing the same, and a lithium ion battery

Abstract

The application discloses a negative active material and a preparation method and a lithium ion battery, and relates to the technical field of lithium batteries. The negative active material is prepared from graphite after etching by an organic phosphonic acid, and the structural formula of the organic phosphonic acid is The negative active material etches the graphite by using the organic phosphonic acid, so that pores or cavities are generated on the surface of the graphite, the deintercalation sites of lithium ions are increased, the diffusion distance of lithium ions in the charging and discharging process is reduced, the polarization of the lithium ion battery is reduced, and therefore the charging and discharging capacity of the negative active material is improved, and the rate performance and the cycle performance of the lithium ion battery are improved. Meanwhile, the organic phosphonic acid has extremely stable C-P bonds, good oxidation performance, and the strong acidic organic phosphonic acid is not easy to volatilize under a high-temperature environment, and can be mass-produced and used on a large scale.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium battery, in particular, to a negative electrode active material, a preparation method thereof and a lithium ion battery. BACKGROUND

[0002] Lithium ion battery is an important direction of new energy technology development, with the rapid development of new energy technology, its performance requirements for lithium ion battery are higher and higher, such as high specific capacity, long cycle, high safety and so on. As the key main material in lithium ion battery, the negative electrode active material is concerned and valued. At present, the commercial negative electrode active material is mainly graphite, which has the advantages of low cost, rich source and stable electrical performance. However, the theoretical capacity of graphite cannot meet the demand of super fast charging and super high energy density required by today's consumer batteries, even if it reaches the limit. On the other hand, due to the low charge-discharge platform and low lithium intercalation voltage of graphite, lithium dendrite phenomenon is easy to form, thereby increasing the safety hazard of finished battery.

[0003] In view of these problems, relevant researches are carried out at home and abroad. The electrochemical performance of graphite is improved by surface modification and modification. Among them, liquid etching technology can be used for surface modification of graphite. The porosity of etched graphite is increased, the channel is increased for lithium ion deintercalation, and the lithium ion diffusion efficiency is improved. In the prior art, common acid etching solution includes sulfuric acid, hydrochloric acid, acetic acid and the like. Although these acid solutions are low in price, they cannot be used on a large scale due to their strong volatility, low concentration retention and environmental protection factors. SUMMARY

[0004] In view of the deficiencies of the prior art, the present application provides a negative electrode active material, a preparation method thereof and a lithium ion battery.

[0005] The negative electrode active material disclosed by the present application is prepared from graphite etched by organic phosphonic acid, wherein the structural formula of the organic phosphonic acid is

[0006] The preparation method of the negative electrode active material disclosed by the present application comprises the following steps:

[0007] The organic phosphonic acid and deionized water are uniformly mixed to obtain an organic phosphonic acid solution;

[0008] The graphite and the organic phosphonic acid solution are added into a reaction kettle, uniformly dispersed, and then the reaction kettle is heated to obtain an intermediate product;

[0009] After cooling, the intermediate product is washed with anhydrous ethanol, filtered and dried to obtain a crude product;

[0010] The crude product is subjected to heat treatment, washed with distilled water, and then vacuum filtered and dried to obtain a crude product;

[0011] The crude product is disintegrated and screened to obtain the negative active material.

[0012] According to an embodiment of the present application, the concentration of the organic phosphonic acid solution is 2-4 mol / L.

[0013] According to an embodiment of the present application, the material solution ratio of graphite to the organic phosphonic acid solution is (2-10) g:(40-100) mL.

[0014] According to an embodiment of the present application, the temperature of the heated reaction kettle is 100-200 ℃ and the time is 10-20 h.

[0015] According to an embodiment of the present application, the heat treatment of the crude product comprises the following steps:

[0016] The crude product is transferred to a tube furnace, and under the nitrogen atmosphere with a gas flow of 5-8 L / min, the temperature is first raised to 200-300 ℃ at a temperature raising rate of 5-10 ℃ / min, and then raised to 700-800 ℃ at a temperature raising rate of 2-5 ℃ / min, and after maintaining for 1-2 h, the temperature is naturally lowered.

[0017] According to an embodiment of the present application, the preparation of the organic phosphonic acid comprises the following steps:

[0018] The phosphorous acid is placed in a three-neck flask of a reflux dropping device, acetonitrile is placed in a constant pressure dropping funnel of the reflux dropping device, and then the phosphorous acid is stirred and heated;

[0019] After the phosphorous acid is completely melted, the temperature is maintained and the dropping time is controlled, acetonitrile is dropped into the phosphorous acid, and after the reaction is stopped, white precipitate is obtained;

[0020] After cooling, the white precipitate is soaked with sufficient anhydrous ethanol, and then is subjected to suction filtration and drying to obtain the organic phosphonic acid.

[0021] According to an embodiment of the present application, the mass ratio of the phosphorous acid to acetonitrile is (200-320):(30-70).

[0022] According to an embodiment of the present application, during the process of dropping acetonitrile into the phosphorous acid, the temperature is maintained at 140-160 ℃ and the dropping time is controlled at 40-60 min.

[0023] The present application discloses a lithium ion battery, which comprises a negative electrode sheet prepared from the negative active material as described above.

[0024] Compared with the prior art, the negative active material, the preparation method thereof and the lithium ion battery have the following advantages:

[0025] The negative active material of the present application etches graphite with organic phosphonic acid, so that pores or cavities are generated on the surface of the graphite, the deintercalation sites of lithium ions are increased, the diffusion distance of lithium ions in the charging and discharging process is reduced, the polarization of the lithium ion battery is reduced, and thus the charging and discharging capacity of the negative active material is improved, and the rate performance and cycle performance of the lithium ion battery are improved. Meanwhile, the organic phosphonic acid has a very stable C-P bond, good oxidation performance, and the strong acidic organic phosphonic acid is not easy to volatilize in a high temperature environment, and can be mass produced and used in large quantities. DETAILED DESCRIPTION

[0026] The embodiments of the present application will be described below. Many practical details will be described in the following description for the purpose of clear illustration. However, it should be understood that these practical details should not be used to limit the present application. That is, in some embodiments of the present application, these practical details are not necessary.

[0027] In addition, the technical solutions of each embodiment can be combined with each other, but it must be based on the fact that a person skilled in the art can realize it. When the combination of technical solutions appears contradictory or unachievable, it should be considered that the combination of technical solutions does not exist, and is not within the protection scope required by the present application.

[0028] Embodiment one

[0029] The present embodiment provides a negative active material, which is prepared from graphite etched by organic phosphonic acid, wherein the structural formula of the organic phosphonic acid is

[0030] The negative active material etches graphite with organic phosphonic acid, so that pores or cavities are generated on the surface of the graphite, the deintercalation sites of lithium ions are increased, the diffusion distance of lithium ions in the charging and discharging process is reduced, the polarization of the lithium ion battery is reduced, and thus the charging and discharging capacity of the negative active material is improved, and the rate performance and cycle performance of the battery cell are improved.

[0031] The organic phosphonic acid has a very stable C-P bond, good oxidation performance, and the strong acidic organic phosphonic acid is not easy to volatilize in a high temperature environment, and can be mass produced and used in large quantities.

[0032] Embodiment two

[0033] The present embodiment provides a preparation method of a negative active material, which is used to prepare the negative active material of embodiment one. The preparation method of the negative active material mainly includes two preparation processes, one is to prepare organic phosphonic acid, and the other is to prepare the negative active material by using the prepared organic phosphonic acid. The specific preparation method is as follows:

[0034] (1) Preparation of organic phosphonic acid, including the following steps:

[0035] Put the phosphorous acid into a three-neck flask of a reflux dropping device, put the acetonitrile into a constant pressure dropping funnel of the reflux dropping device, then stir and heat the phosphorous acid;

[0036] After the phosphorous acid is completely melted, keep the temperature and control the dropping time, drop the acetonitrile into the phosphorous acid, after the reaction is stopped, white precipitate is obtained;

[0037] After cooling, soak the white precipitate in sufficient anhydrous ethanol, then perform suction filtration and drying to obtain the organic phosphonic acid.

[0038] In this example, the mass ratio of the phosphorous acid to the acetonitrile is (200-320):(30-70).

[0039] In this example, the stirring rate of the phosphorous acid is 1000-2000 r / min, and the heating temperature is 100-200℃.

[0040] In this example, the temperature is kept at 140-160℃ during the process of dropping the acetonitrile into the phosphorous acid, and the dropping time is controlled at 40-60 min.

[0041] In this example, the condition for judging that the reaction of the phosphorous acid and the acetonitrile is stopped is that the white precipitate with a vinegar smell appears in a block shape.

[0042] In this example, after the white precipitate is cooled to room temperature, it is soaked in sufficient anhydrous ethanol for 10-12 h.

[0043] (2) Preparation of the negative electrode active material, comprising the following steps:

[0044] Mix the organic phosphonic acid and deionized water uniformly to obtain an organic phosphonic acid solution;

[0045] Add the graphite and the organic phosphonic acid solution into a reaction kettle, uniformly disperse, heat the reaction kettle, and obtain an intermediate product;

[0046] After cooling, wash the intermediate product with anhydrous ethanol, filter and dry to obtain a crude product;

[0047] After heat treatment, wash the crude product with distilled water, then perform vacuum filtration and drying to obtain a crude product;

[0048] Crush and sieve the crude product to obtain the negative electrode active material.

[0049] In this example, the concentration of the organic phosphonic acid solution is 2-4 mol / L.

[0050] In this example, the solid-liquid ratio of the graphite to the organic phosphonic acid solution is (2-10) g:(40-100) mL.

[0051] In this example, graphite and organic phosphonic acid solution are added into the reactor, and stirred at a speed of 1000-2000 r / min for 4-6 h to achieve uniform dispersion.

[0052] In this example, the reactor is placed into a blast drying oven to heat the reactor, and the heating temperature is 100-200℃, and the heating time is 10-20 h.

[0053] In this example, the intermediate product is washed with anhydrous ethanol for 3-5 times after cooling to room temperature.

[0054] In this example, the heat treatment of the crude product is used to volatilize most of the organic phosphonic acid, and the heat treatment includes the following steps:

[0055] The crude product is transferred into a tube furnace, and first heated to 200-300℃ at a heating rate of 5-10℃ / min under a nitrogen atmosphere with a gas flow of 5-8 L / min, and then heated to 700-800℃ at a heating rate of 2-5℃ / min, and kept for 1-2 h, and then naturally cooled.

[0056] In this example, the crude product is washed with distilled water for 3-5 times after heat treatment, and the purpose is to remove residual organic phosphonic acid. The heat-treated crude product is dried in a vacuum oven at 70-80℃ for 2-3 h to obtain the crude product.

[0057] In this example, the crude product is crushed and sieved to 100-250 mesh.

[0058] Example Three

[0059] This example provides a lithium ion battery comprising a negative electrode sheet. The negative electrode sheet is prepared using the negative electrode active material of Example One.

[0060] In order to further illustrate the invention, eight samples of lithium ion batteries are provided, and the samples are described below.

[0061] Sample One

[0062] The lithium ion battery provided by Sample One comprises a negative electrode sheet, and the negative electrode sheet is prepared using a negative electrode active material.

[0063] The preparation method of the lithium ion battery comprises three preparation processes, namely, preparation of organic phosphonic acid, preparation of a negative electrode active material using the prepared organic phosphonic acid, and preparation of a lithium ion battery using the prepared negative electrode active material, and the specific preparation method is as follows:

[0064] (1) Preparation of organic phosphonic acid

[0065] Put 300 g of phosphorous acid into a three-necked flask of a reflux dropping device, put 60 g of acetonitrile into a constant pressure dropping funnel of the reflux dropping device, then stir and heat the phosphorous acid, the stirring rate is 2000 r / min, and the heating temperature is 150°C;

[0066] After the phosphorous acid is completely melted, acetonitrile is added dropwise into the phosphorous acid, the temperature is kept at 150°C during the dropping process, and the time is controlled within 50 min, the reaction is stopped when a blocky, acetic acid-smelling white precipitate appears, and a white precipitate is obtained;

[0067] After cooling, the white precipitate is soaked in sufficient anhydrous ethanol for 12 h, then filtered and dried to obtain an organic phosphonic acid.

[0068] (2) Preparation of the negative electrode active material

[0069] The organic phosphonic acid is uniformly mixed with deionized water to obtain an organic phosphonic acid solution with a concentration of 2 mol / L;

[0070] 5 g of graphite and 80 mL of the organic phosphonic acid solution are added into a reaction kettle, stirred at a rate of 2000 r / min for 6 h, then the reaction kettle is put into a blast drying oven and heated at 100°C for 10 h to obtain an intermediate product;

[0071] After cooling, the intermediate product is washed with anhydrous ethanol for 5 times, then vacuum filtered through a polytetrafluoroethylene membrane, and dried to obtain a crude product;

[0072] The crude product is transferred into a tube furnace, first heated to 200°C at a temperature rising rate of 10°C / min under a nitrogen atmosphere with a gas flow rate of 5 L / min, then heated to 800°C at a temperature rising rate of 5°C / min, kept for 2 h, and naturally cooled down; after washing with distilled water for 5 times, vacuum filtering, and drying in a vacuum oven at 80°C for 1 h, a crude product is obtained;

[0073] The crude product is crushed and sieved through a 250-mesh sieve to obtain a negative electrode active material.

[0074] (3) Preparation of the lithium ion battery

[0075] The negative electrode active material, the conductive agent and the binder with a mass ratio of 80:10:10 are mixed and pressed into a circular negative electrode sheet with a diameter of 1 cm, a lithium sheet is used as a counter electrode, hexafluorophosphoric acid is used as an electrolyte, and a PE / PP / PE three-layer composite microporous membrane is used as a separator to prepare a lithium ion battery in a button type CR2032; wherein the conductive agent is carbon black, and the binder is polytetrafluoroethylene.

[0076] Sample two

[0077] The main difference between sample two and sample one is that the concentration of the prepared organic phosphonic acid solution is 4 mol / L.

[0078] Sample three

[0079] The main difference between sample three and sample one is that the concentration of the prepared organic phosphonic acid solution is 6 mol / L.

[0080] Sample four

[0081] The main difference between sample four and sample one is that the reaction kettle is placed in a blast drying oven and heated at 140℃ for 10h.

[0082] Sample five

[0083] The main difference between sample five and sample one is that the reaction kettle is placed in a blast drying oven and heated at 160℃ for 10h.

[0084] Sample six

[0085] The main difference between sample six and sample four is that the reaction kettle is placed in a blast drying oven and heated at 140℃ for 5h.

[0086] Sample seven

[0087] The main difference between sample seven and sample four is that the reaction kettle is placed in a blast drying oven and heated at 140℃ for 20h.

[0088] Sample eight

[0089] The negative electrode active material, the conductive agent and the binder with a mass ratio of 80:10:10 are mixed and then pressed into a circular negative electrode sheet with a diameter of 1cm. Lithium sheet is used as the counter electrode, hexafluorophosphoric acid is used as the electrolyte, and PE / PP / PE three-layer composite microporous membrane is used as the separator to prepare a lithium ion battery in a button type CR2032. The negative electrode active material is unetched graphite, the conductive agent is *** and the binder is ***.

[0090] The lithium ion batteries obtained from samples one to eight are respectively subjected to charge-discharge performance test. The charge-discharge conditions for the first charge-discharge capacity retention rate (%) are 0.5C and 0.005-2.0V, and the charge-discharge conditions for the 500cls capacity retention rate (%) are 3C and 0.005-2.0V, wherein 1C=353mA / g. The test results are as follows:

[0091] Table 1 Charge-discharge performance test of samples

[0092]

[0093] It can be known by comparison that samples one to seven use the graphite etched by the organic phosphonic acid as the negative active material, and sample eight uses the graphite without etching as the negative active material. The test results show that the first charge-discharge capacity retention rate and the 500 cls cycle capacity retention rate of samples one to seven are both high, and the first charge-discharge capacity retention rate and the 500 cls cycle capacity retention rate of sample eight are both low, which indicates that the rate performance and the cycle performance of the lithium ion battery prepared by using the graphite etched by the organic phosphonic acid as the negative active material can be improved.

[0094] In addition, the factors affecting the electrical performance of the lithium ion battery also relate to the preparation process parameters. It can be known by comparison that samples one to three are different in the concentration of the organic phosphonic acid solution, and the concentration of the organic phosphonic acid solution used by sample one is the smallest. The test results show that compared with samples two and three, the first charge-discharge capacity retention rate and the 500 cls cycle capacity retention rate of sample one are both high, which indicates that the rate performance and the cycle performance of sample one are relatively good. Samples one, four and five are different in the heating temperature of the reaction kettle, and the test results show that the first charge-discharge capacity retention rate and the 500 cls cycle capacity retention rate of sample four are both higher than those of sample one and sample five, which indicates that the rate performance and the cycle performance of the lithium ion battery will be deteriorated when the temperature is too low or too high. Samples four, six and seven are different in the heating time of the reaction kettle, and the test results show that the first charge-discharge capacity retention rate and the 500 cls cycle capacity retention rate of sample seven are both higher than those of sample four and sample six, which indicates that the longer the heating time is, the more sufficient the etching of the graphite by the organic phosphonic acid is, and the better the rate performance and the cycle performance of the lithium ion battery can be improved.

[0095] The above merely describes the embodiments of the present application and is not intended to limit the present application. The present application can have various modifications and changes for those skilled in the art. Any modification, equivalent replacement, improvement, etc. within the spirit and principle of the present application shall be included in the scope of the claims of the present application.

Claims

1. A method for producing a negative electrode active material, characterized by, The method comprises the following steps: mixing the organic phosphonic acid with deionized water to obtain an organic phosphonic acid solution; adding graphite and the organic phosphonic acid solution into a reaction kettle, uniformly dispersing, heating the reaction kettle, and obtaining an intermediate product; cooling, washing the intermediate product with anhydrous ethanol, filtering and drying to obtain a crude product; heat-treating the crude product, washing with distilled water, vacuum filtering and drying to obtain a crude product; crushing and screening the crude product to obtain a negative electrode active material; the negative electrode active material is prepared from graphite etched by an organic phosphonic acid, wherein the organic phosphonic acid has a structural formula ； the concentration of the organic phosphonic acid solution is 2-4 mol / L; the solid-liquid ratio of the graphite to the organic phosphonic acid solution is (2-10) g:(40-100) mL; the temperature for heating the reaction kettle is 100-200 ℃, and the time is 10-20 h; the heat treatment of the crude product comprises the following steps: transferring the crude product into a tube furnace, under a nitrogen atmosphere with a gas flow of 5-8 L / min, first increasing the temperature to 200-300 ℃ at a rate of 5-10 ℃ / min, then increasing the temperature to 700-800 ℃ at a rate of 2-5 ℃ / min, maintaining for 1-2 h, and naturally cooling.

2. The method for producing a negative electrode active material according to claim 1, characterized by, the preparation of the organic phosphonic acid comprises the following steps: putting phosphorous acid into a three-necked flask of a reflux dropping device, putting acetonitrile into a constant-pressure dropping funnel of the reflux dropping device, then stirring and heating the phosphorous acid; after the phosphorous acid is completely melted, maintaining the temperature and controlling the dropping time, dropping acetonitrile into the phosphorous acid, after the reaction is stopped, obtaining white precipitates; cooling, soaking the white precipitates in sufficient anhydrous ethanol, then performing suction filtration and drying to obtain the organic phosphonic acid.

3. The method for producing a negative electrode active material according to claim 2, characterized by, the mass ratio of the phosphorous acid to the acetonitrile is (200-320):(30-70).

4. The method for producing a negative electrode active material according to claim 2, characterized by, during the process of dropping the acetonitrile into the phosphorous acid, the temperature is maintained at 140-160 ℃, and the dropping time is controlled at 40-60 min.

5. A lithium-ion battery, characterized by the negative electrode sheet is prepared from the negative electrode active material prepared by the preparation method of claim 1.

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