Graphite material, preparation method thereof and secondary battery
By subjecting graphite aggregate precursors to iron salt-assisted oxidation etching and high-temperature alkali treatment, porous secondary particulate graphite materials were prepared, solving the problems of pore formation and structural strength in graphite anode materials, and achieving expansion suppression and improved cycle stability of high-performance lithium-ion batteries.
Patent Information
- Application Number
- CN202511200493.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-26
- Publication Date
- 2025-12-12
AI Technical Summary
Existing technologies cannot simultaneously solve the problems of incomplete removal of impurity elements and insufficient strength of secondary particle structures during the pore-forming process of graphite anode materials, resulting in limited expansion suppression effects and failing to meet the development needs of high-performance lithium-ion batteries.
By using iron salt-assisted oxidation etching to create pores in graphite aggregate precursors and then functionalizing them with strong alkali at high temperature to form a porous structure, a secondary particulate graphite material with a particle size of 8-30 μm was prepared.
It significantly improves the structural strength of secondary particles, optimizes expansion performance, enhances battery cycle stability and volume expansion suppression performance, while removing impurity elements, reducing costs and facilitating industrial production.
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Figure CN121123274A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to a kind of graphite material and its preparation method and secondary battery, belong to lithium ion battery material technical field. BACKGROUND
[0002] As a lithium ion battery negative electrode material, graphite has been widely used in 3C products, power battery and energy storage field, but there is a significant intrinsic volume expansion problem in the process of embedding lithium-its expansion rate usually maintains between 10%-15%, far more than the expansion level of positive electrode material (positive electrode material is generally less than 6.5%), this characteristic not only becomes the core obstacle of the improvement of battery volume energy density, but also constitutes a serious challenge to the structural stability and safety performance of battery in the long-term cycle process (for example, continuous volume expansion and contraction can cause stress concentration in electrode interface, and then cause active material to fall off, electrolyte decomposition intensifies and other problems, which seriously affects the service life of battery). To solve this key bottleneck, two mainstream improvement ideas have been formed in the industry: one is to build pore structure inside the negative electrode material by pore-forming agent pore-forming technology, aiming to provide volume buffer space for high-expansion negative electrode (such as silicon-based negative electrode) in the process of embedding lithium, so as to relieve the overall expansion pressure; the second is to use aggregate granulation process to bond graphite single particles to form secondary particles, so as to reduce the anisotropy of graphite material and reduce the stress accumulation in a single direction during the cycle, and then improve the volume expansion characteristics. However, both of these two technical paths have defects that are difficult to overcome: the pore-forming agent pore-forming method has low reaction efficiency of pore-forming agent and graphite matrix due to the low chemical reaction activity of graphite itself, which makes it difficult to uniformly build pore structure and the expansion relief effect is not good. More importantly, the impurity elements introduced in the pore-forming process are difficult to completely remove by conventional means, and these residual impurities will significantly reduce the electrochemical performance of the electrode, so there are very few successful cases of using this method to prepare porous graphite negative electrode; the secondary particles obtained by conventional granulation process face the problem of structural stability. The interface bonding force between the aggregate and the binder is weak after high-temperature graphitization treatment, resulting in low overall strength of the secondary particles, and the secondary particle structure is easily disintegrated under the volume expansion and contraction stress of long-term cycle, and the constraint effect of the original single particle expansion is lost, so the expansion inhibition effect is difficult to continue. Overall, the existing technical solutions have not been able to solve the problems of purity control in the pore-forming process and structural strength improvement of secondary particles, so the expansion inhibition effect of graphite negative electrode is always at a limited level, which is difficult to meet the development needs of high-performance lithium ion batteries. SUMMARY
[0003] In view of the defects of the prior art, the present application provides a kind of graphite material, comprising:
[0004] The graphite material is a secondary particle formed by bonding graphite aggregates by an adhesive, and the particle size Dv50 of the graphite material is 8-30 μm; the particle size Dv50 of the graphite aggregate is 3-15 μm, and the surface has pores with a pore size of 10-1000 nm.
[0005] Preferably, the precursor of the graphite aggregate is at least one of needle coke, petroleum coke and pitch coke; the adhesive is at least one of pitch, coal tar, resin or starch, and the additive amount is 5-10 wt% of the mass of the aggregate.
[0006] The application also provides a preparation method of the above graphite material, comprising the following steps:
[0007] (1) mixing a graphite aggregate precursor with an iron salt and heating to react for 1 h to obtain a porous graphite aggregate precursor;
[0008] (2) mixing the obtained porous graphite aggregate precursor with an alkali and heating to react for 2 h to obtain a functionalized porous graphite aggregate precursor;
[0009] (3) mixing the obtained functionalized porous graphite aggregate precursor with an adhesive, granulating, and shaping to obtain a secondary particle graphite precursor;
[0010] (4) performing graphitization treatment on the obtained secondary particle graphite precursor to obtain the graphite material.
[0011] Preferably, the particle size Dv50 of the graphite aggregate precursor in step 1 is 3-15 μm.
[0012] Preferably, the iron salt in step 1 is one or more of ferric chloride, ferric sulfate, ferric nitrate, ferric oxalate, ferric citrate, ferric bromide and ferric iodide; and the mass ratio of the graphite aggregate precursor to the iron salt is 100:(1-25).
[0013] Preferably, the heating reaction 1 in step 1 is performed in an air atmosphere, the reaction temperature is 600-800 ℃, and the reaction time is 10-25 h.
[0014] Preferably, the heating reaction 1 in step 1 has a temperature rising rate of 1-10 ℃ / min.
[0015] Preferably, the alkali in step 2 comprises one or more of potassium hydroxide, lithium hydroxide, sodium hydroxide, calcium hydroxide and magnesium hydroxide.
[0016] Preferably, the mass ratio of the porous graphite aggregate precursor to the alkali in step 2 is 100:(3-25).
[0017] Preferably, the reaction 2 in step 2 is carried out in a box furnace under an inert atmosphere 1, the heating rate is 1-10℃ / min, the temperature is 700-1100℃, the holding time is 10-25h, and the natural cooling is to room temperature.
[0018] Preferably, the granulation in step 3 is carried out under an inert atmosphere 2, the heating rate is 1-10℃ / min, the temperature is 600-720℃, the binder addition amount is 5-10wt% of the functionalized porous graphite aggregate precursor; and the shaping is shaped to a particle size Dv50 of 8-30μm.
[0019] Preferably, the functionalized porous graphite aggregate precursor is mixed with the binder, and the porous graphite aggregate precursor is mixed with the alkali by batch mixing or ball milling, and the mixing time is 1-5h.
[0020] Preferably, the graphitization treatment in step 4 is carried out under an inert atmosphere 3, the heating rate is 1-10℃ / min, the temperature is 2900-3000℃, the time is 2-2.5h, and the natural cooling is to room temperature.
[0021] Preferably, the inert atmosphere 1, the inert atmosphere 2 or the inert atmosphere 3 comprises a nitrogen atmosphere or an argon atmosphere.
[0022] In addition, the application also provides a secondary battery, wherein the negative electrode sheet comprises the above-mentioned graphite material.
[0023] The beneficial effects of the application are as follows:
[0024] The graphite material and the preparation method thereof have the following advantages: the graphite material is first made porous and then graphitized, which avoids the problem that the graphite material is difficult to make porous and the impurity elements introduced by the pore-making agent in the traditional pore-making process are difficult to remove completely; meanwhile, the graphite aggregate precursor is subjected to surface functionalization treatment, so that the aggregate and the binder can form stable chemical bonding in the granulation process, thereby greatly improving the structural strength of the secondary particles and effectively improving the defect that the secondary particle structure is easy to disintegrate in the cycle process. Specifically, the graphite aggregate precursor is made porous by using an iron salt assisted oxidation etching process, which not only realizes the roughening of the surface of the carbon material, but also the roughened structure of the surface is beneficial to the full immersion of the binder, thereby improving the bonding strength of the granulation particles and laying a foundation for improving the expansion performance of the material after graphitization; in addition, the activation of the carbon material at high temperature by using a strong alkali can produce a large number of oxygen-containing functional groups on the surface of the porous graphite precursor, realize the functionalization of the surface of the graphite aggregate precursor, and promote the chemical bonding of the aggregate and the binder groups, thereby significantly improving the structural strength of the secondary particles after granulation and further optimizing the expansion performance of the material after graphitization; in the graphitization stage, the impurity elements in the porous graphite precursor are completely removed by gasification decomposition while the porous graphite precursor is graphitized, and the process fully utilizes the energy consumption of the graphitization process itself without additional cost, which has the characteristics of low cost and easy industrial production. The finally prepared graphite material not only solves the purity problem of the traditional pore-making technology, but also overcomes the defect of insufficient structural strength of the secondary particles, and performs excellently in improving the cycle stability of the battery and inhibiting the volume expansion. BRIEF DESCRIPTION OF DRAWINGS
[0025] Figure 1 SEM image of the porous graphite aggregate precursor of Example 1;
[0026] Figure 2 EDS image of the functionalized aggregate of Example 1;
[0027] Figure 3 SEM image of the graphite material of Example 1. DETAILED DESCRIPTION
[0028] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, and not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative labor fall within the scope of the present application.
[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those familiar to those skilled in the art. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to this invention. The preferred embodiments and materials described herein are for illustrative purposes only and do not limit the scope of this application.
[0030] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, and the experimental materials used in the following examples are all purchased from commercial channels.
[0031] Example 1
[0032] (1) Raw material pretreatment: Grinding is carried out using a roller pressing-shaping integrated grinding mill to pulverize needle coke into powder.
[0033] Needle-shaped coke aggregate with a Dv50 of 8-9 μm;
[0034] (2) Preparation of porous graphite aggregate precursor: Take 1000 kg of needle coke aggregate obtained in step (1) and 10 kg of FeCl3 and put them into a batch mixer. Mix for 2 hours, then put them into a reaction vessel. Under air atmosphere, heat up to 700℃ at 5℃ / min, keep warm for 20 hours, and then cool down naturally to obtain porous graphite aggregate precursor.
[0035] (3) Preparation of functionalized porous graphite aggregate precursor: Take 500 kg of the porous graphite aggregate precursor obtained in step (2) and 15 kg of KOH into a ball mill jar, ball mill at 200 rpm for 3 h, then put it into a box furnace, and heat it to 800 ℃ at 5 ℃ / min under nitrogen atmosphere, keep it at 15 h, and then cool it down naturally to obtain the functionalized porous graphite aggregate precursor.
[0036] (4) Preparation of secondary particulate graphite precursor: Take 100 kg of functionalized porous graphite aggregate precursor obtained in step (3) and 7.5 kg of Dv50=3-5μm asphalt and put them into a batching machine. Mix for 2 hours, then put them into a horizontal reactor. Under nitrogen atmosphere, granulate at 720℃ at 5℃ / min for 3 hours. Then use a batching machine to deaggregate the particle size to Dv50=13-14μm to obtain secondary particulate graphite precursor.
[0037] (5) Preparation of graphite material: The secondary particulate graphite precursor obtained in step (4) is loaded into a medium frequency furnace, heated to 3000℃ at 5℃ / min under nitrogen atmosphere, held for 2h, and then cooled naturally to obtain graphite material.
[0038] This embodiment prepares a graphite material. The graphite material is prepared using a graphite aggregate precursor as raw material, first by iron salt-assisted oxidation etching to create pores (e.g., ...). Figure 1 As shown, the material has a porous structure, and then it undergoes functionalization treatment using an alkali (such as...).Figure 2 as shown, a large number of oxygen-containing functional groups exist on the surface and inside of the material), followed by granulation, shaping, and finally graphitization (as shown, the final graphite material). Figure 3
[0039] Example 2
[0040] (1) Raw material pretreatment: the needle coke was crushed to Dv50 = 10-11 pm by using a roller-shaping integrated pulverizer;
[0041] Dv50 = 10-11 pm needle coke;
[0042] (2) Preparation of porous graphite aggregate precursor: 1000 kg of the needle coke aggregate obtained in step (1) and 15 kg of FeCl3 were placed into a mixing machine, mixed for 2 h, then loaded into a reaction kettle, and heated to 750°C at a rate of 5°C / min under an air atmosphere, and held for 15 h. After natural cooling, a porous graphite aggregate precursor was obtained;
[0043] (3) Preparation of functionalized porous graphite aggregate precursor: 500 kg of the porous graphite aggregate precursor obtained in step (2) and 20 kg of KOH were placed into a ball mill tank, and ball-milled at 200 rpm for 3 h, then loaded into a box furnace, and heated to 850°C at a rate of 5°C / min under a nitrogen atmosphere, and held for 12 h. After natural cooling, a functionalized porous graphite aggregate precursor was obtained;
[0044] (4) Preparation of secondary granular graphite precursor: 100 kg of the functionalized porous graphite aggregate precursor obtained in step (3) and 8.5 kg of pitch with Dv50 = 3-5 pm were placed into a mixing machine, mixed for 2 h, then loaded into a horizontal reaction kettle, and granulated at 650°C for 5 h under a nitrogen atmosphere, and then the particle size was adjusted to Dv50 = 13-14 pm using a mixing machine to obtain a secondary granular graphite precursor;
[0045] (5) Preparation of graphite material: the secondary granular graphite precursor obtained in step (4) was loaded into a medium-frequency furnace, and heated to 3000°C at a rate of 5°C / min under a nitrogen atmosphere, and held for 2 h. After natural cooling, a graphite material was obtained.
[0046] Example 3
[0047] (1) Raw material pretreatment: the needle coke was crushed to Dv50 = 10-11 pm by using a roller-shaping integrated pulverizer;
[0048] Dv50 = 10-11 pm needle coke;
[0049] (2) Porous graphite aggregate precursor preparation: take 1000 kg of needle coke aggregate obtained in step (1) and 25 kg of FeCl3into a mixing machine, mix for 2 h, then load into a reaction kettle, heat to 800 ℃ at a rate of 5 ℃ / min under an air atmosphere, and keep the temperature for 12 h. After natural cooling, a porous graphite aggregate precursor is obtained;
[0050] (3) Functionalized porous graphite aggregate precursor preparation: take 500 kg of the porous graphite aggregate precursor obtained in step (2) and 25 kg of KOH into a ball mill tank, mill at 200 rpm for 3 h, then load into a box furnace, heat to 900 ℃ at a rate of 5 ℃ / min under a nitrogen atmosphere, and keep the temperature for 10 h. After natural cooling, a functionalized porous graphite aggregate precursor is obtained;
[0051] (4) Secondary granular graphite precursor preparation: take 100 kg of the functionalized porous graphite aggregate precursor obtained in step (3) and 6.5 kg of pitch with Dv50 = 3-5 μm into a mixing machine, mix for 2 h, then load into a horizontal reaction kettle, granulate at 600 ℃ for 7 h under a nitrogen atmosphere, and then use a mixing machine to depolymerize the particle size to Dv50 = 13-14 μm to obtain a secondary granular graphite precursor;
[0052] (5) Graphite material preparation: load the secondary granular graphite precursor obtained in step (4) into a medium-frequency furnace, heat to 3000 ℃ at a rate of 5 ℃ / min under a nitrogen atmosphere, and keep the temperature for 2 h. After natural cooling, a graphite material is obtained.
[0053] Example 4
[0054] (1) Raw material pretreatment: use a roller-shaping integrated powder mill to crush needle coke to Dv50 = 10-11 μm;
[0055] Dv50 = 10-11 μm needle coke aggregate;
[0056] (2) Porous graphite aggregate precursor preparation: take 1000 kg of needle coke aggregate obtained in step (1) and 25 kg of FeCl3into a mixing machine, mix for 2 h, then load into a reaction kettle, heat to 800 ℃ at a rate of 5 ℃ / min under an air atmosphere, and keep the temperature for 12 h. After natural cooling, a porous graphite aggregate precursor is obtained;
[0057] (3) Functionalized porous graphite aggregate precursor preparation: take 500 kg of the porous graphite aggregate precursor obtained in step (2) and 25 kg of KOH into a ball mill tank, mill at 200 rpm for 3 h, then load into a box furnace, heat to 900 ℃ at a rate of 5 ℃ / min under a nitrogen atmosphere, and keep the temperature for 10 h. After natural cooling, a functionalized porous graphite aggregate precursor is obtained;
[0058] (4) Secondary particle graphite precursor preparation: take 100 kg of the functionalized porous graphite aggregate precursor obtained in step (3) and 5 kg of Dv50 = 3-5 pm of pitch into a mixing machine, mix for 2 h, then load into a horizontal reaction kettle, under nitrogen atmosphere, heat up to 600 °C at 5 °C / min, granulate for 7 h, then use a mixing machine to depolymerize the particle size to Dv50 = 13-14 pm, to obtain a secondary particle graphite precursor;
[0059] (5) Graphite material preparation: load the secondary particle graphite precursor obtained in step (4) into a medium frequency furnace, under nitrogen atmosphere, heat up to 2900 °C at 5 °C / min, keep for 2 h, and after natural cooling, a graphite material is obtained.
[0060] Example 5
[0061] (1) Raw material pretreatment: use a roller-shaping integrated powder mill to grind the needle coke to
[0062] Dv50 = 8-9 pm of needle coke aggregate;
[0063] (2) Porous graphite aggregate precursor preparation: take 1000 kg of the needle coke aggregate obtained in step (1) and 25 kg of FeBr3into a mixing machine, mix for 2 h, then load into a reaction kettle, under air atmosphere, heat up to 650 °C at 5 °C / min, keep for 15 h, and after natural cooling, a porous graphite aggregate precursor is obtained;
[0064] (3) Functionalized porous graphite aggregate precursor preparation: take 500 kg of the porous graphite aggregate precursor obtained in step (2) and 15 kg of NaOH into a ball mill tank, mill at 200 rpm for 5 h, then load into a box furnace, under nitrogen atmosphere, heat up to 900 °C at 5 °C / min, keep for 20 h, and after natural cooling, a functionalized porous graphite aggregate precursor is obtained;
[0065] (4) Secondary particle graphite precursor preparation: take 100 kg of the functionalized porous graphite aggregate precursor obtained in step (3) and 7.5 kg of coal tar into a fusion machine, mix for 2 h, then load into a horizontal reaction kettle, under nitrogen atmosphere, heat up to 650 °C at 5 °C / min, granulate for 5 h, then use a mixing machine to depolymerize the particle size to
[0066] Dv50 = 13-14 pm, to obtain a secondary particle graphite precursor;
[0067] (5) Graphite material preparation: load the secondary particle graphite precursor obtained in step (4) into a medium frequency furnace, under nitrogen atmosphere, heat up to 3000 °C at 5 °C / min, keep for 2 h, and after natural cooling, a graphite material is obtained.
[0068] Example 6
[0069] (1) Raw material pretreatment: Petroleum coke is pulverized using a roller pressing-shaping integrated grinding mill to a fine powder.
[0070] Petroleum coke aggregate with a Dv50 of 8-9 μm;
[0071] (2) Preparation of porous graphite aggregate precursor: Take 1000 kg of petroleum coke aggregate obtained in step (1) and 20 kg of FeBr3 and put them into a batch mixer. Mix for 3 hours, then put them into a reaction vessel. Under air atmosphere, heat up to 600℃ at 5℃ / min, keep warm for 25 hours, and then cool down naturally to obtain porous graphite aggregate precursor.
[0072] (3) Preparation of functionalized porous graphite aggregate precursor: Take 500 kg of the porous graphite aggregate precursor obtained in step (2) and 20 kg of LiOH and put them into a ball mill jar. Ball mill at 200 rpm for 5 h. Then put them into a box furnace and heat them to 1000 ℃ at 5 ℃ / min under nitrogen atmosphere. Keep them at the temperature for 25 h. After natural cooling, functionalized porous graphite aggregate precursor is obtained.
[0073] (4) Preparation of secondary particulate graphite precursor: Take 100 kg of the functionalized porous graphite aggregate precursor obtained in step (3) and 7.5 kg of resin and put them into a blending machine. Mix for 3 hours. Then, put them into a horizontal reactor and granulate at 700℃ for 3 hours under a nitrogen atmosphere at a rate of 5℃ / min. Then, use a batch mixer to deaggregate the particles to the specified size.
[0074] Dv50 = 14-15μm, resulting in a secondary particle graphite precursor;
[0075] (5) Preparation of graphite material: The secondary particulate graphite precursor obtained in step (4) is loaded into a medium frequency furnace, heated to 3000℃ at 5℃ / min under nitrogen atmosphere, held for 2h, and then cooled naturally to obtain graphite material.
[0076] Example 7
[0077] (1) Raw material pretreatment: The asphalt coke is pulverized using a roller pressing-shaping integrated grinding mill to a fine powder.
[0078] Pitch coke aggregate with a Dv50 of 8-9 μm;
[0079] (2) Preparation of porous graphite aggregate precursor: Take 1000 kg of asphalt coke aggregate obtained in step (1) and 10 kg of Fe2(SO4)3 and put them into a batching machine. Mix for 2 hours, then put them into a reaction vessel. Under air atmosphere, heat up to 700℃ at 5℃ / min, keep warm for 20 hours, and then cool down naturally to obtain porous graphite aggregate precursor.
[0080] (3) Functionalized porous graphite aggregate precursor preparation: take 500 kg of the porous graphite aggregate precursor obtained in step (2) and 15 kg of Mg(OH)2, put them into a ball mill tank, mill at 200 rpm for 3 h, then put them into a box furnace, heat to 1100℃ at a rate of 5℃ / min under nitrogen atmosphere, keep for 10 h, and get the functionalized porous graphite aggregate precursor after natural cooling;
[0081] (4) Secondary particle graphite precursor preparation: take 100 kg of the functionalized porous graphite aggregate precursor obtained in step (3) and 10 kg of starch, put them into a batcher, batch for 2 h, then put them into a horizontal reaction kettle, granulate at 700℃ for 5 h under nitrogen atmosphere, and then use the batcher to depolymerize the particle size to
[0082] Dv50 = 15-16 μm, and get the secondary particle graphite precursor;
[0083] (5) Graphite material preparation: put the secondary particle graphite precursor obtained in step (4) into a medium frequency furnace, heat to 3000℃ at a rate of 5℃ / min under nitrogen atmosphere, keep for 2 h, and get the graphite material after natural cooling.
[0084] Comparative Example 1
[0085] (1) Raw material pretreatment: use a roller-shaping integrated grinding mill to grind the needle coke to
[0086] Dv50 = 8-9 μm aggregate;
[0087] (2) Graphite material preparation: put the single particle graphite precursor obtained in step (1) into a medium frequency furnace, heat to 3000℃ at a rate of 5℃ / min under nitrogen atmosphere, keep for 2 h, and get the graphite material after natural cooling.
[0088] Comparative Example 2
[0089] (1) Raw material pretreatment: use a roller-shaping integrated grinding mill to grind the needle coke to
[0090] Dv50 = 8-9 μm aggregate;
[0091] (2) Secondary particle graphite precursor preparation: take 100 kg of the graphite aggregate precursor obtained in step (1) and 7.5 kg of Dv50 = 3-5 μm pitch, put them into a batcher, batch for 2 h, then put them into a horizontal reaction kettle, granulate at 720℃ for 3 h under nitrogen atmosphere, and then use the batcher to depolymerize the particle size to
[0092] Dv50 = 13-14 μm, and get the secondary particle graphite precursor;
[0093] (3) Graphite material preparation: the secondary particle graphite precursor obtained in step (3) was loaded into a medium frequency furnace, and was heated to 3000°C at a rate of 5°C / min under a nitrogen atmosphere, and was kept for 2h, and the graphite material was obtained after natural cooling.
[0094] Comparative Example 3
[0095] (1) Raw material pretreatment: the needle coke was ground to a size of 0.5-1mm by using a roller-shaping integrated grinding mill, and was sieved to obtain a size of 0.5-1mm;
[0096] Dv50 = 8-9pm aggregate;
[0097] (2) Functionalized graphite aggregate precursor preparation: 500kg of the graphite aggregate precursor obtained in step (1) and 15kg of KOH were put into a ball mill tank, and were ball milled at 200rpm for 3h, and then were loaded into a box furnace, and were heated to 800°C at a rate of 5°C / min under a nitrogen atmosphere, and were kept for 15h, and the functionalized graphite aggregate precursor was obtained after natural cooling;
[0098] (3) Secondary particle graphite precursor preparation: 100kg of the functionalized graphite aggregate precursor obtained in step (2) and 7.5kg of Dv50 = 3-5pm pitch were put into a mixing machine, and were mixed for 2h, and then were loaded into a horizontal reaction kettle, and were granulated at 720°C for 3h under a nitrogen atmosphere, and then the particle size was depolymerized to Dv50 = 13-14pm by using a mixing machine, and the secondary particle graphite precursor was obtained;
[0099] (4) Graphite material preparation: the secondary particle graphite precursor obtained in step (3) was loaded into a medium frequency furnace, and was heated to 3000°C at a rate of 5°C / min under a nitrogen atmosphere, and was kept for 2h, and the graphite material was obtained after natural cooling.
[0100] Comparative Example 4
[0101] (1) Raw material pretreatment: the needle coke was ground to a size of 0.5-1mm by using a roller-shaping integrated grinding mill, and was sieved to obtain a size of 0.5-1mm;
[0102] Dv50 = 8-9pm aggregate;
[0103] (2) Porous graphite aggregate precursor preparation: 1000kg of the needle coke aggregate obtained in step (1) and 10kg of FeCl3 were put into a mixing machine, and were mixed for 2h, and then were loaded into a reaction kettle, and were heated to 700°C at a rate of 5°C / min under an air atmosphere, and were kept for 20h, and the porous graphite aggregate precursor was obtained after natural cooling;
[0104] (3) Secondary particle graphite precursor preparation: take 100 kg of porous graphite aggregate precursor obtained in step (2) and 7.5 kg of Dv50 = 3-5 μm pitch into a mixing machine, mix for 2 h, then load into a horizontal reaction kettle, under nitrogen atmosphere, heat up to 720℃ at 5℃ / min, granulate for 3 h, then use the mixing machine to depolymerize the particle size to
[0105] Dv50 = 13-14 μm, to obtain a secondary particle graphite precursor;
[0106] (4) Graphite material preparation: load the secondary particle graphite precursor obtained in step (4) into a medium frequency furnace, under nitrogen atmosphere, heat up to 3000℃ at 5℃ / min, keep for 2 h, after natural cooling, obtain a graphite material.
[0107] Performance detection:
[0108] 1. Pole piece preparation:
[0109] Take the final product obtained in examples 1 to 7 and comparative examples 1 to 3 as active material, polyvinylidene fluoride as binder, carbon black Super-P as conductive agent, mix the three according to a mass ratio of 91:7:2, add an appropriate amount of N-methyl pyrrolidone solvent, form a uniform slurry, then coat on a copper foil, then put it into a 100℃ oven, bake for more than 2 h, take out, punch, and obtain a diameter of 14 mm electrode piece, finally put the pole piece in a 105℃ vacuum box and bake for 4 h, then quickly put it into a glove box to wait for assembly into a button cell.
[0110] 2. Button cell assembly and test:
[0111] Take the pole piece as working electrode, lithium sheet as counter electrode, polypropylene microporous membrane as separator, and electrolyte as 1M LiPF6+EC:DEC:DMC = 1:1:1 (volume ratio), assemble into a CR2430 type button cell in an argon atmosphere glove box. The charge and discharge test of the button cell is carried out on the battery test system of Wuhan Blue Electronic Co., Ltd., under normal temperature conditions, using 0.1C constant current charge and discharge, the charge and discharge voltage is limited to 0.005V to 2.0V, test the 0.1C initial reversible specific capacity, 100 cycle pole piece expansion rate and 100 cycle capacity retention rate; use 3C constant current charge and discharge, the charge and discharge voltage is limited to 0.005V to 2.0V, test the 3C initial reversible specific capacity, the results are shown in Table 1.
[0112] Table 1 test results
[0113]
[0114] Table 1 is the electrochemical performance test results of the samples of Examples 1-7 and Comparative Examples 1-4. As can be seen from Table 1, the graphite materials prepared in Examples 1-7 have excellent performance in terms of capacity, expansion performance, capacity retention rate and rate performance.
[0115] In terms of capacity, the 0.1C initial reversible capacity of Examples 1-7 is greater than 358 mAh / g, which is significantly higher than the 0.1C initial reversible capacity of Comparative Examples 2 and 3 (both secondary particles without porous structure) (Comparative Example 2: 354.2 mAh / g; Comparative Example 3: 354.4 mAh / g); this shows that graphite pore-making is beneficial to fully releasing the lithium storage performance of graphite, which is mainly due to the fact that pore-making brings more reaction active sites and the pseudo-capacitive lithium storage effect of the pores, and the connectivity of the pores (10-1000 nm pore size) ensures efficient transmission of lithium ions.
[0116] In terms of expansion and cycle performance, the 300-cycle electrode expansion rate and capacity retention rate of Examples 1-7 are less than 12% (the lowest is 10.2%) and greater than 99.2% (the highest is 99.8%), respectively, which are significantly better than Comparative Example 1 (32.7% and 77.6%) with single-particle structure, Comparative Example 2 (24.5% and 83.3%) with conventional secondary particle structure, Comparative Example 3 (16.9% and 95.1%) without porous structure, and Comparative Example 4 (16.2% and 96.2%) without functional group treatment, especially Comparative Example 4 has a porous structure but lacks functional group chemical bonding, and its expansion rate is still 35% higher than the average value of Examples. This shows that the secondary particle graphite prepared by pore-making and surface functionalization has great advantages in expansion and cycle performance. The porous structure provides a buffer zone for the volume change during lithium intercalation of graphite, and at the same time, the high proportion of pore volume can also disperse a large amount of stress, thereby avoiding the structural rupture, collapse and pulverization of the material due to the stress concentration in the local part of the material; and after the surface functionalization of the precursor before the granulation stage, the covalent bonding between the oxygen-containing functional groups and the functional groups in the binder strengthens the bonding strength between the aggregate and the binder, thereby laying a good foundation for subsequent creation of secondary particles with high structural strength.
[0117] In terms of rate performance, the 3C first reversible specific capacity of Examples 1-7 is all greater than 300 mAh / g (the highest is 322.1 mAh / g), and the 10C capacity retention rate is > 85%, all greater than Comparative Examples 1-3 (227.4 mAh / g, 255.8 mAh / g and 258.1 mAh / g) and Comparative Example 4 (298.3 mAh / g), proving that the rate performance is still severely limited without functionalization. Notably, the rate (298.3 mAh / g) of Comparative Example 4 is significantly higher than that of Comparative Examples 2-3 without pores, but lower than that of all process examples (average > 310 mAh / g), and we believe that there are two reasons: first, the good lithium ion migration channel caused by the binder graphitization in the secondary particles, the impedance is reduced, which reduces the potential barrier of lithium ion intercalation and speeds up the reaction completion; the second is that the porous structure increases the infiltration degree of the graphite surface and the electrolyte and shortens the ion intercalation path and diffusion time, and the stable interface formed by the functionalization process after granulation further reduces the interfacial impedance between the particles, thereby significantly improving the rate performance of the material.
[0118] As can be seen from the above, the synergistic effect of pore forming and functionalization makes the graphite material prepared by the method balance in porosity, functional group density and structural strength, and it is a negative electrode material with high capacity, low expansion, long cycle and high rate, especially suitable for fast charging scenarios.
[0119] Although embodiments of the present application have been shown and described, it is to be understood that for the purpose of the present application, the embodiments change, modify, replace and vary in many ways without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalents.
[0120] The above describes the present application and its embodiments, which is not restrictive, and the drawings shown are only one of the embodiments of the present application, and the actual application is not limited thereto. In summary, if a person skilled in the art is inspired by it, without departing from the purpose of the present application, without creative design, similar ways and embodiments of the technical solution should belong to the protection scope of the present application.
Claims
1. A graphite material, characterized in that: Graphite material is a secondary particle formed by bonding graphite aggregate with an adhesive, and its particle size Dv50 is 8-30μm. The graphite aggregate has a particle size Dv50 of 3-15μm and a surface distribution of pores with a diameter of 10-1000nm.
2. The graphite material according to claim 1, characterized in that: The precursor of the graphite aggregate is at least one of needle coke, petroleum coke, and pitch coke; the binder is at least one of pitch, coal tar, resin, or starch, and the amount added is 5-10 wt% of the aggregate mass.
3. A method for preparing the graphite material according to claim 1 or 2, characterized in that: Includes the following steps: (1) Take graphite aggregate precursor and mix it with iron salt, heat and react 1 to obtain porous graphite aggregate precursor; (2) The obtained porous graphite aggregate precursor is mixed with alkali and heated to react 2 to obtain functionalized porous graphite aggregate precursor. (3) The obtained functionalized porous graphite aggregate precursor is mixed with a binder, granulated, and then shaped to obtain a secondary particulate graphite precursor. (4) The obtained secondary particulate graphite precursor is graphitized to obtain graphite material.
4. The method for preparing graphite material according to claim 3, characterized in that: The graphite aggregate precursor in step 1 has a particle size Dv50 of 3-15 μm; the iron salt is one or more of ferric chloride, ferric sulfate, ferric nitrate, ferric oxalate, ferric citrate, ferric bromide, and ferric iodide; the mass ratio of the graphite aggregate precursor to the iron salt is 100:(1-25).
5. The method for preparing graphite material according to claim 3, characterized in that: The heating reaction 1 described in step 1 is carried out in an air atmosphere at a temperature of 600-800℃, with a heating rate of 1-10℃ / min and a reaction time of 10-25h.
6. The method for preparing graphite material according to claim 3, characterized in that: The alkali mentioned in step 2 includes one or more of potassium hydroxide, lithium hydroxide, sodium hydroxide, calcium hydroxide, and magnesium hydroxide; the mass ratio of the porous graphite aggregate precursor to the alkali is 100:(3-25).
7. The method for preparing graphite material according to claim 3, characterized in that: The heating reaction 2 described in step 2 is carried out in a box furnace under an inert atmosphere 1, with a heating rate of 1-10℃ / min, and held at 700-1100℃ for 10-25h, and then naturally cooled to room temperature.
8. The method for preparing graphite material according to claim 3, characterized in that: The granulation in step 3 is carried out under an inert atmosphere 2, with a heating rate of 1-10℃ / min and a temperature of 600-720℃. The amount of binder added is 5-10wt% of the functionalized porous graphite aggregate precursor. The shaping is carried out until the particle size Dv50 is 8-30μm.
9. The method for preparing graphite material according to claim 3, characterized in that: The graphitization process described in step 4 is carried out under an inert atmosphere 3, with a heating rate of 1-10℃ / min, a temperature of 2900-3000℃, and a time of 2-2.5h, followed by natural cooling to room temperature.
10. A secondary battery, characterized in that: The negative electrode sheet includes the graphite material as described in any one of claims 1 to 2 or the graphite material prepared by the preparation method described in any one of claims 3 to 9.