Polymer coated silicon carbon material, preparation method and application thereof, and battery

Abstract

The invention discloses a polymer coated silicon carbon material, a preparation method and application thereof and a battery. The preparation method comprises the following steps: (1) reacting a mixture of 1, 3-dioxolame, a lithium salt and a silicon source at 30-60 DEG C for 24-96 hours to obtain a polymer coated silicon material; the lithium salt comprises lithium tetrafluoroborate and lithium fluoride; the mass ratio of the 1, 3-dioxolame to the lithium salt is (2-10): 1; and (2) mixing the polymer-coated silicon material with a carbon source to obtain the polymer-coated silicon carbon material. The polymer-coated silicon carbon material prepared by the invention shows excellent rate capability and cycle performance when being applied to a lithium ion battery.

Description

Technical Field

[0001] The present invention specifically relates to a polymer-coated silicon-carbon material and a preparation method, application and battery thereof. Background Art

[0002] With the booming consumer electronics and electric vehicle industries, as well as breakthroughs in AI technology, the market demand for high-energy-density lithium-ion batteries is becoming increasingly urgent. Among the components of lithium-ion batteries, the negative electrode material is one of the key factors affecting the overall performance of the battery. Traditional graphite negative electrode materials are difficult to meet the growing demand for high-energy-density batteries due to their relatively low theoretical specific capacity (about 340-370mAh / g). Silicon materials are widely regarded as highly promising next-generation lithium-ion battery negative electrode materials because of their ultra-high theoretical specific capacity (up to 4200mAh / g). However, silicon materials face many severe challenges in practical applications, which seriously restrict their large-scale commercialization.

[0003] First, silicon undergoes a huge volume change (up to 300% or more) during the process of lithium ion insertion and extraction. This dramatic volume expansion and contraction will cause great stress inside the silicon negative electrode material, causing the material to pulverize and break. The contact between the pulverized silicon particles and the current collector and the conductive agent deteriorates, and the electron conduction path is destroyed, which leads to a significant increase in the internal resistance of the battery and a sharp drop in rate performance. For example, during high-rate charge and discharge, due to the obstruction of electron transmission, the battery cannot respond quickly to charge and discharge needs, and the capacity decays rapidly.

[0004] Secondly, the volume change of silicon will also cause the instability of the solid electrolyte interface (SEI) film. During the cycle of lithium-ion batteries, the SEI film will continuously rupture and reform. The repeated rupture of the SEI film will not only consume the limited lithium ions and electrolyte inside the battery, resulting in irreversible loss of battery capacity, but also the ruptured SEI film fragments may accumulate on the electrode surface, further hindering the diffusion of lithium ions and the transmission of electrons, resulting in poor rate performance of the battery and a significant shortening of the cycle life.

[0005] In order to solve the problems existing in the application of silicon materials, researchers have conducted a lot of exploration and attempts. In terms of material modification, the volume expansion effect of silicon is alleviated through nanostructuring and composite methods. For example, preparing silicon into nanoparticles, nanowires or nanotubes can reduce the stress caused by volume changes to a certain extent, but these methods often have problems such as complex preparation process, high cost and difficulty in large-scale production. In terms of electrolyte optimization, new electrolyte additives or solvent systems are developed in an attempt to improve the stability of the SEI film, but the results are still unsatisfactory.

[0006] Therefore, there is an urgent need to develop a new, simple and effective method to improve the performance of silicon anode materials to overcome their defects in rate performance and cycle life, so as to promote the widespread application of silicon anode materials in the field of lithium-ion batteries. Summary of the invention

[0007] The technical problem solved by the present invention is to overcome the defects of the silicon material in the prior art in that the rate performance and cycle performance are poor when used as the negative electrode material of lithium batteries, and to provide a polymer-coated silicon-carbon material and its preparation method, application and battery. The polymer-coated silicon-carbon material prepared by the present invention is applied to lithium-ion batteries and exhibits excellent rate performance and cycle performance.

[0008] The present invention utilizes the synergistic catalytic effect of LiF nanoparticles and lithium tetrafluoroborate to promote the in-situ catalytic polymerization of 1,3-dioxolane monomer (DOL) on the surface of a silicon source, thereby achieving uniform coating of a polymer solid electrolyte (poly 1,3-dioxolane) on the surface of a silicon source, effectively overcoming the slow charge transfer at the electrode / electrolyte interface and the uncontrollable reaction at the interface, and improving the rate performance and cycle life of silicon negative electrode materials. On the one hand, the presence of LiF can promote the further polymerization of DOL monomers and minimize the presence of unstable DOL monomers. DOL monomers will decompose into by-products such as CH3CH2OCH2Li and CH3OCH2CH2OLi, ethylene (C2H4) and its derivatives CH2(CH2)3OCH2O (C2H4-D) under high voltage. The presence of by-products produced by DOL monomers will affect the cycle stability of solid polymer electrolytes (SPE) when matched with high-voltage positive electrodes; on the other hand, well-dispersed LiF nanoparticles have high mechanical stability and can in-situ construct the positive electrode electrolyte interface (CEI) / negative electrode electrolyte interface (SEI), thereby improving the interface stability.

[0009] The present invention solves the above technical problems through the following technical solutions:

[0010] The present invention provides a method for preparing a polymer-coated silicon-carbon material, which comprises the following steps:

[0011] (1) reacting a mixture of 1,3-dioxolane, a lithium salt and a silicon source at 30-60° C. for 24-96 hours to obtain a polymer-coated silicon material; the lithium salt comprises lithium tetrafluoroborate and lithium fluoride; and the mass ratio of the 1,3-dioxolane to the lithium salt is (2-10):1;

[0012] (2) The polymer-coated silicon material and a carbon source are mixed to obtain the polymer-coated silicon-carbon material.

[0013] In step (1), the reaction mechanism generally includes the following process:

[0014]

[0015] H + (BF3OH) - Catalyzes the polymerization of 1,3-dioxolane monomers.

[0016] In step (1), the reaction is generally carried out in a glove box filled with an inert atmosphere (such as argon).

[0017] In step (1), the silicon source is preferably one or more of elemental silicon, silicon monoxide, silicon dioxide, silicon-carbon alloy, porous silicon, silicon nanowires and silicon-carbon composite materials, preferably elemental silicon. The particle size of the elemental silicon is preferably 10-800 nm, more preferably 10-400 nm, and further more preferably 80-100 nm.

[0018] In step (1), the particle size D of the lithium fluoride is 50 It may be 10-200 nm, preferably 10-100 nm, such as 20-50 nm.

[0019] In step (1), the method for preparing lithium fluoride preferably comprises the following steps: ball milling lithium fluoride powder.

[0020] The ball milling is generally carried out in a nitrogen-protected agate ball mill. The rotation speed of the ball milling can be 200-500 rpm, such as 300 rpm. During the ball milling, the ball-to-material ratio can be (10-30):1, such as 20:1. During the ball milling, the diameter of the grinding ball can be 5-15 mm, such as 10 mm.

[0021] In step (1), the mass ratio of the sum of the masses of the 1,3-dioxolane and the lithium salt to the mass ratio of the silicon source may be (1-20):100, preferably (5-15):100, for example, 8:100, 8.9:100, 10:100, 10.2:100, 10.3:100, 10.5:100, 10.6:100, 10.7:100, 10.8:100, 10.9:100, 11:100, 11.2:100 or 12:100.

[0022] In step (1), the mass ratio of the 1,3-dioxolane to the lithium salt is preferably (3-8):1, for example, 4:1, 4.1:1, 4.7:1, 5:1, 5.1:1, 5.3:1, 5.4:1, 5.6:1, 5.8:1, 6:1 or 6.9:1.

[0023] In step (1), the mass ratio of the 1,3-dioxolane to the silicon source may be (1-15):100, preferably (5-10):100, for example, 7.5:100, 7.8:100, 8:100, 8.5:100, 9:100 or 9.5:100.

[0024] In step (1), the mass ratio of the lithium tetrafluoroborate to the lithium fluoride may be (1-5):1, preferably (1.1-3):1, for example, 1.25:1, 1.5:1, 1.7:1, 1.75:1, 1.9:1, 2:1, 2.2:1 or 2.5:1.

[0025] In step (1), the lithium salt preferably includes other lithium salts besides lithium tetrafluoroborate and lithium fluoride. The other lithium salts preferably include lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and / or lithium hexafluorophosphate (LiPF6).

[0026] The mass percentage of the other lithium salts to the lithium salt may be 30%-90%, preferably 40%-80%, for example 46%, 48%, 53%, 54%, 55%, 57%, 59%, 60%, 62%, 63%, 64%, 65% or 68%.

[0027] In step (1), the method for preparing the mixture of 1,3-dioxolane, lithium salt and silicon source preferably comprises the following steps: uniformly mixing 1,3-dioxolane and a lithium salt other than lithium fluoride, and then adding lithium fluoride and silicon source.

[0028] In certain preferred embodiments, the lithium salt is lithium tetrafluoroborate, lithium fluoride and lithium bis(trifluoromethanesulfonyl)imide.

[0029] In certain more preferred embodiments, the lithium salt is lithium tetrafluoroborate, lithium fluoride and lithium bis(trifluoromethanesulfonyl imide), and the mass percentage of lithium bis(trifluoromethanesulfonyl imide) in the lithium salt is 40%-80%, for example 46%, 48%, 53%, 54%, 55%, 57%, 59%, 60%, 62%, 63%, 64%, 65% or 68%.

[0030] In certain preferred embodiments, the lithium salt is lithium tetrafluoroborate, lithium fluoride and lithium hexafluorophosphate.

[0031] In certain more preferred embodiments, the lithium salt is lithium tetrafluoroborate, lithium fluoride and lithium hexafluorophosphate, and the mass percentage of the lithium hexafluorophosphate in the lithium salt is 40%-80%, for example 46%, 48%, 53%, 54%, 55%, 57%, 59%, 60%, 62%, 63%, 64%, 65% or 68%.

[0032] In step (1), the reaction temperature is preferably 30-50° C., such as 35° C., 40° C. or 45° C. The reaction time is preferably 24-72 h, such as 48 h, 54 h or 60 h.

[0033] In step (2), the carbon source preferably includes one or more of graphite, carbon nanotubes, pyrolytic carbon, amorphous carbon, hard carbon, soft carbon and carbon black.

[0034] The method for preparing amorphous carbon preferably comprises the following steps: calcining a carbon-containing organic matter under the protection of an inert atmosphere. The carbon-containing organic matter may be conventional in the art, such as a phenolic resin. The calcination temperature is preferably 600-1000° C., such as 800° C. or 900° C. The calcination time may be 2-8 hours, such as 4 hours or 6 hours.

[0035] In step (2), the mass ratio of the polymer-coated silicon material to the carbon source may be 100:(20-200), preferably 100:(80-110), for example 100:100.

[0036] In step (2), the mixing method can be conventional in the art, such as grinding. The mixing is generally performed in a glove box. The mixing time can be 5-20 minutes, such as 5 minutes.

[0037] The present invention also provides a polymer-coated silicon-carbon material prepared by the above-mentioned preparation method.

[0038] The present invention also provides an application of the aforementioned polymer-coated silicon-carbon material in a lithium-ion battery.

[0039] The present invention also provides a lithium ion battery, which comprises the polymer-coated silicon-carbon material as described above.

[0040] On the basis of being in accordance with the common sense in the art, the above-mentioned preferred conditions can be arbitrarily combined to obtain the preferred embodiments of the present invention.

[0041] The reagents and raw materials used in the present invention are commercially available.

[0042] The positive and progressive effects of the present invention are:

[0043] The polymer-coated silicon-carbon material prepared by the present invention has excellent rate performance and cycle life, and the preparation method is simple. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 This is a SEM image of the polymer-coated silicon material prepared in Example 1;

[0045] Figure 2This is the XRD pattern of the polymer-coated silicon material prepared in Example 1;

[0046] Figure 3 The infrared spectra of DOL, the solid electrolyte-coated silicon material (PDOL SE) prepared in step (2) of Example 1, and the polymer-coated silicon-carbon material (PDOL-LiF CSE) prepared in step (3) of Example 1 are shown. DETAILED DESCRIPTION

[0047] The present invention is further described below by way of examples, but the present invention is not limited to the scope of the examples. The experimental methods in the following examples without specifying specific conditions are carried out according to conventional methods and conditions, or selected according to the product specifications.

[0048] The preparation method of the amorphous carbon used in the following examples and comparative examples is as follows: under nitrogen protection, phenolic resin is calcined at 800° C. for 4 h to obtain amorphous carbon.

[0049] Example 1

[0050] Step (1): Add lithium fluoride powder to a nitrogen-protected agate ball mill with a ball-to-material ratio of 20:1, a single grinding ball with a diameter of 10 mm, and a ball mill speed of 300 rpm. Mill for 20 min to obtain lithium fluoride nanoparticles with a particle size D 50 20-50nm;

[0051] (2) At room temperature, in a glove box filled with argon, 90 parts by mass of 1,3-dioxolane (DOL), 10 parts by mass of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and 5 parts by mass of lithium tetrafluoroborate (LiBF4) were added to a beaker and stirred evenly, and then 1000 parts by mass of nano-silicon (Cruder, 80-100 nm) and 2 parts by mass of lithium fluoride nanoparticles were added to the beaker to obtain a precursor solution, and the precursor solution was reacted at 35° C. for 60 h to obtain a polymer-coated silicon material;

[0052] (3) The solid electrolyte-coated silicon material and amorphous carbon were uniformly ground in a glove box in a mortar at a mass ratio of 100:100 for 5 minutes to obtain a polymer-coated silicon-carbon material.

[0053] Example 2

[0054] Compared with Example 1, except that 1000 parts by mass of nano-silicon (Cluder 80-100 nm) in step (2) is changed to 1200 parts by mass of nano-silicon (Cluder 80-100 nm), other operations and conditions are the same as those in Example 1.

[0055] Example 3

[0056] Compared with Example 1, except that the nano silicon in step (2) of Example 1 is replaced by sand-ground silicon with a particle size of 200 nm (ie, silicon powder is obtained by sand-grinding with an ethanol medium), other operations and conditions are the same as those of Example 1.

[0057] Example 4

[0058] Compared with Example 1, except that the nano-silicon in step (2) of Example 1 is replaced by silicon monoxide (Cruder, 1400), other operations and conditions are the same as those of Example 1.

[0059] Example 5

[0060] Compared with Example 1, except that the nano-silicon in step (2) of Example 1 is replaced by porous carbon-deposited silicon (Cruder, 1800), other operations and conditions are the same as those of Example 1.

[0061] Example 6

[0062] Compared with Example 1, except that the nano-silicon in step (2) of Example 1 is replaced by silicon-carbon alloy (Cruder, 650-K), other operations and conditions are the same as those of Example 1.

[0063] Example 7

[0064] Compared with Example 1, except that the amount of DOL in step (2) was adjusted to 85 parts by mass, the other operations and conditions were the same as those in Example 1.

[0065] Example 8

[0066] Compared with Example 1, except that the amount of DOL in step (2) was adjusted to 95 parts by mass, the other operations and conditions were the same as those in Example 1.

[0067] Example 9

[0068] Compared with Example 1, except that the amount of LiBF4 in step (2) is adjusted to 4 parts by mass, the other operations and conditions are the same as those in Example 1.

[0069] Example 10

[0070] Compared with Example 1, except that the amount of LiBF4 in step (2) is adjusted to 3.5 parts by mass, the other operations and conditions are the same as those in Example 1.

[0071] Embodiment 11

[0072] Compared with Example 1, except that the amount of lithium fluoride in step (2) is adjusted to 3 parts by mass, the other operations and conditions are the same as those in Example 1.

[0073] Example 12

[0074] Compared with Example 1, except that the amount of lithium fluoride in step (2) is adjusted to 4 parts by mass, the other operations and conditions are the same as those in Example 1.

[0075] Example 13

[0076] Compared with Example 1, except that the amount of LiTFSI in step (2) was adjusted to 6 parts by mass, the other operations and conditions were the same as those in Example 1.

[0077] Embodiment 14

[0078] Compared with Example 1, except that the amount of LiTFSI in step (2) was adjusted to 15 parts by mass, the other operations and conditions were the same as those in Example 1.

[0079] Embodiment 15

[0080] Compared with Example 1, except that LiTFSI in step (2) is replaced by LiPF6, the other operations and conditions are the same as those in Example 1.

[0081] Example 16

[0082] Compared with Example 1, except that the reaction temperature in step (3) is adjusted to 45°C, the other operations and conditions are the same as those in Example 1.

[0083] Embodiment 17

[0084] Compared with Example 1, except that the reaction time in step (3) is adjusted to 48 h, the other operations and conditions are the same as those in Example 1.

[0085] Comparative Example 1

[0086] Step (1): Grind nanosilicon (Cluder 80-100 nm) and ethanol at a mass ratio of 100:10 for 10 min, then put them into a nitrogen-protected agate ball mill, with a ball-to-material ratio of 20:1, a single grinding ball diameter of 10 mm, a ball mill speed of 300 rpm, and ball milling for 5 min;

[0087] Step (2): After uniformly grinding the product prepared in step (1) and amorphous carbon at a mass ratio of 100:100 for 5 minutes, the mixed sample is prepared into a slurry with a solid content of 35% in ethanol and pumped into a spray granulator. Spray granulation is carried out under the conditions of an air inlet temperature of 190°C and an air outlet temperature of 120°C. The mixture is then sieved through a 200-mesh sieve to obtain a silicon-carbon composite material.

[0088] Comparative Example 2

[0089] Step (1): same as in Example 1;

[0090] Step (2): except that 1,3-dioxolane (DOL) is not added, other conditions are the same as those in Example 1.

[0091] Step (3): Same as Example 1.

[0092] Comparative Example 3

[0093] Step (1): Not performed.

[0094] Step (2): except that lithium fluoride nanoparticles are not added, other conditions are the same as those in Example 1.

[0095] Step (3): Same as Example 1.

[0096] Comparative Example 4

[0097] Step (1): same as in Example 1;

[0098] Step (2): Except for not adding LiTFSI, other conditions are the same as those in Example 1.

[0099] Step (3): Same as Example 1.

[0100] Comparative Example 5

[0101] Step (1): Same as Example 1;

[0102] Step (2): Except for not adding LiBF4, other conditions are the same as those in Example 1.

[0103] Step (3): Same as Example 1.

[0104] Effect Example

[0105] (1) Morphological characterization

[0106] Figure 1 This is a SEM image of the polymer-coated silicon-carbon material prepared in Example 1; Figure 2 This is the XRD pattern of the polymer-coated silicon-carbon material prepared in Example 1; Figure 3 The infrared spectra of DOL, the solid electrolyte-coated silicon material (PDOL SE) prepared in step (2) of Example 1, and the polymer-coated silicon-carbon material (PDOL-LiF CSE) prepared in step (3) of Example 1 are shown.

[0107] (2) Lithium-ion battery electrochemical performance test

[0108] The polymer-coated silicon-carbon materials prepared in Examples 1 to 17 and the silicon-carbon composite materials prepared in Comparative Examples 1-5 were subjected to half-cell tests. The test method is: the above materials are uniformly mixed with a binder CMC (sodium carboxymethyl cellulose) and conductive carbon black in a mass ratio of 80:10:10, adjusted into a slurry, coated on a copper foil with a coating thickness of 100 microns, and dried at 80°C in vacuum for 12 hours to prepare a lithium battery negative electrode sheet. The simulated battery assembly was carried out in an argon-filled glove box, using a 1 mol / L LiPF6 electrolyte (the solvent is EC, DMC and FEC, EC:DMC=1:1 (volume ratio), and FEC accounts for 5% of the total volume of the solvent), a polypropylene microporous membrane as a diaphragm, and a metal lithium sheet as a counter electrode. The electrochemical performance test was carried out on a LandCT2001A battery tester at a temperature of 25°C and a charge and discharge voltage range of 0.01 to 1.5V (1C=1000mAh g -1 ), the test results are shown in Table 1.

[0109] Table 1

[0110]

[0111] By comparing Example 1 with Comparative Example 1, it can be found that the silicon-carbon composite material prepared in Comparative Example 1 has poor ion conductivity of the overall sample, and lithium ions are difficult to fully deintercalate, because the raw materials are not coated with in-situ polymerized solid electrolytes. Therefore, the specific capacity and cycle life at 2C / 10C are poor. By comparing Example 1 with Comparative Example 2, Comparative Example 3, and Comparative Example 5, it can be found that the silicon-carbon composite material prepared in Comparative Example 2 cannot undergo solid electrolyte polymerization reaction due to the lack of polymerization raw materials. Comparative Examples 3 and Comparative Examples 5 have poor polymerization efficiency due to the lack of catalysts, and it is difficult to achieve solid electrolyte coating, so the 10C rate capacity and cycle life are significantly reduced. By comparing Example 1 with Comparative Example 4, since the mass ratio of 1,3-dioxolane to the lithium salt in Comparative Example 4 is high, that is, the lithium salt content is low, which reduces the ion migration ability, thereby affecting the rate performance.

[0112] Although the specific embodiments of the present invention are described above, it should be understood by those skilled in the art that this is only for illustration and the protection scope of the present invention is defined by the appended claims. Those skilled in the art may make various changes or modifications to these embodiments without departing from the principles and essence of the present invention, but these changes and modifications all fall within the protection scope of the present invention.

Claims

1. A method for preparing a polymer-coated silicon-carbon material, characterized in that: It includes the following steps: (1) reacting a mixture of 1,3-dioxolane, a lithium salt and a silicon source at 30-60° C. for 24-96 hours to obtain a polymer-coated silicon material; the lithium salt comprises lithium tetrafluoroborate and lithium fluoride; and the mass ratio of the 1,3-dioxolane to the lithium salt is (2-10):1; (2) The polymer-coated silicon material and a carbon source are mixed to obtain the polymer-coated silicon-carbon material.

2. The method for preparing a polymer-coated silicon-carbon material according to claim 1, characterized in that: Step (1) satisfies one or more of the following conditions: (1) The silicon source is one or more of elemental silicon, silicon monoxide, silicon dioxide, silicon-carbon alloy, porous silicon, silicon nanowires and silicon-carbon composite materials, preferably elemental silicon; Wherein, the particle size of the elemental silicon is preferably 10-800nm, more preferably 10-400nm; (2) Particle size D of the lithium fluoride 50 10-200nm, preferably 10-100nm; (3) The preparation method of lithium fluoride comprises the following steps: ball milling lithium fluoride powder; The rotation speed of the ball mill is preferably 200-500 rpm; during the ball milling process, the ball-to-material ratio is preferably (10-30):1; during the ball milling process, the diameter of the grinding balls is 5-15 mm.

3. The method for preparing a polymer-coated silicon-carbon material according to claim 1, characterized in that: Step (1) satisfies one or more of the following conditions: (1) The mass ratio of the sum of the mass of the 1,3-dioxolane and the lithium salt to the mass of the silicon source is (1-20):100, preferably (5-15):100, for example, 8:100, 8.9:100, 10:100, 10.2:100, 10.3:100, 10.5:100, 10.6:100, 10.7:100, 10.8:100, 10.9:100, 11:100, 11.2:100 or 12:100; (2) the mass ratio of the 1,3-dioxolane to the lithium salt is (3-8):1, for example, 4:1, 4.1:1, 4.7:1, 5:1, 5.1:1, 5.3:1, 5.4:1, 5.6:1, 5.8:1, 6:1 or 6.9:1; (3) The mass ratio of the 1,3-dioxolane to the silicon source is (1-15):100, preferably (5-10):100, for example, 7.5:100, 7.8:100, 8:100, 8.5:100, 9:100 or 9.5:100; (4) The mass ratio of the lithium tetrafluoroborate to the lithium fluoride is (1-5):1, preferably (1.1-3):1, for example, 1.25:1, 1.5:1, 1.7:1, 1.75:1, 1.9:1, 2:1, 2.2:1 or 2.5:

1.

4. The method for preparing a polymer-coated silicon-carbon material according to claim 1, characterized in that: In step (1), the lithium salt further includes other lithium salts besides lithium tetrafluoroborate and lithium fluoride; Wherein, the other lithium salts preferably include lithium bis(trifluoromethanesulfonyl)imide and / or lithium hexafluorophosphate; the mass percentage of the other lithium salts to the lithium salt is preferably 30%-90%, more preferably 40%-80%.

5. The method for preparing a polymer-coated silicon-carbon material according to claim 1, characterized in that: In step (1), the reaction temperature is 30-50°C, for example, 35°C, 40°C or 45°C; And / or, the reaction time is 24-72 h, such as 48 h, 54 h or 60 h.

6. The method for preparing a polymer-coated silicon-carbon material according to claim 1, characterized in that: In step (1), the method for preparing the mixture of 1,3-dioxolane, lithium salt and silicon source comprises the following steps: uniformly mixing 1,3-dioxolane and lithium salt other than lithium fluoride, and then adding lithium fluoride and silicon source; Preferably, the lithium salt is lithium tetrafluoroborate, lithium fluoride and lithium bis(trifluoromethanesulfonyl imide); more preferably, the lithium salt is lithium tetrafluoroborate, lithium fluoride and lithium bis(trifluoromethanesulfonyl imide), and the mass percentage of lithium bis(trifluoromethanesulfonyl imide to the lithium salt is 40%-80%, for example, 46%, 48%, 53%, 54%, 55%, 57%, 59%, 60%, 62%, 63%, 64%, 65% or 68%; Preferably, the lithium salt is lithium tetrafluoroborate, lithium fluoride and lithium hexafluorophosphate; more preferably, the mass percentage of the lithium hexafluorophosphate in the lithium salt is 40%-80%, for example 46%, 48%, 53%, 54%, 55%, 57%, 59%, 60%, 62%, 63%, 64%, 65% or 68%.

7. The method for preparing a polymer-coated silicon-carbon material according to claim 1, characterized in that: In step (2), the carbon source includes one or more of graphite, carbon nanotubes, pyrolytic carbon, amorphous carbon, hard carbon, soft carbon and carbon black; The method for preparing amorphous carbon preferably comprises the following steps: calcining carbon-containing organic matter under the protection of an inert atmosphere; the carbon-containing organic matter is preferably a phenolic resin; the calcination temperature is preferably 600-1000° C.; the calcination time is preferably 2-8 hours; And / or, in step (2), the mass ratio of the polymer-coated silicon material to the carbon source is 100:(20-200), preferably 100:(80-110), for example 100:

100.

8. A polymer-coated silicon-carbon material obtained by the method for preparing a polymer-coated silicon-carbon material according to any one of claims 1 to 7.

9. Use of the polymer-coated silicon-carbon material as claimed in claim 8 in a lithium-ion battery.

10. A lithium ion battery, characterized in that: It comprises the polymer-coated silicon-carbon material as claimed in claim 8.

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