Preparation method of lithium battery with electrolyte directional permeation and lithium ion battery

Abstract

The present disclosure provides a lithium battery preparation method of electrolyte directional permeation and a lithium battery. The lithium battery preparation method of electrolyte directional permeation comprises the following steps: preparing a silicon-carbon electrode with a three-dimensional gradient pore structure, which is composed of surface layer through pores, middle layer tree branch pores and bottom layer liquid storage cavities that are connected and have a gradient increase in radial size; placing the silicon-carbon electrode and a shell assembled to form an electric core in a gradient magnetic field environment with a gradient distribution of strength; adding a magnetic additive to electrolyte, and then injecting the electrolyte into the electric core; performing temperature and pressure coordinated loading cycles on the electrolyte and the silicon-carbon electrode in the electric core; and obtaining the lithium battery after packaging. The electrolyte is three-dimensionally coordinated through structure guidance, magnetic force driving of the gradient magnetic field environment and temperature and pressure loading regulation, so that the electrolyte is directionally permeated in the silicon-carbon electrode, the speed of electrolyte soaking the silicon-carbon electrode is accelerated, and efficient permeation of the electrolyte to the silicon-carbon electrode is realized.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the technical field of lithium ion batteries, and particularly relates to a lithium battery preparation method with electrolyte directional penetration and a lithium ion battery. BACKGROUND

[0002] With the rapid development of electric vehicles and energy storage industries, the demand for high energy density of lithium ion batteries continues to rise. Silicon-carbon negative electrode materials, with a theoretical specific capacity far exceeding traditional graphite (about 10 times), have become a key choice to break through the 400 Wh / kg energy density bottleneck. The high specific surface area and porous structure characteristics of silicon-carbon negative electrodes pose serious challenges to the electrolyte infiltration process. Whether the electrolyte can quickly and uniformly penetrate into the deep pores of the electrode directly determines the lithium ion transmission efficiency, interface stability and battery cycle life.

[0003] The electrolyte infiltration process mostly uses vacuum soaking method, which relies on negative pressure environment to promote the slow penetration of electrolyte into electrode pores. For graphite negative electrodes, their pore structure is relatively simple and uniform, with a pore size of about 50-100 nm and an infiltration time of about 2-4 hours. However, the composite characteristics of silicon particles and carbon matrix in silicon-carbon negative electrodes make their pore structure complex and diverse, with both nanoscale micropores and sub-micron channels. This coexistence of multi-scale pores results in significant differences in electrolyte penetration rate under traditional vacuum method, with fast filling of large pores and residual air blockage of micropores, resulting in a measured pore filling rate of less than 85% (mercury intrusion method data) and a local dry area ratio of more than 15%. Silicon particles in silicon-carbon negative electrodes are prone to pre-reaction with electrolyte during the infiltration process, forming a non-uniform passivation layer, which further hinders the diffusion of electrolyte, exacerbates the uneven infiltration, and uneven distribution of electrolyte can cause local current density to be too high during charging and discharging, accelerating the growth of lithium dendrites and the rupture of SEI film.

[0004] Moreover, in industrial production, the contradiction between electrolyte infiltration efficiency and uniformity is more prominent. For mass production of silicon-carbon negative electrode batteries, the electrolyte infiltration time generally exceeds 12 hours, and repeated "infiltration-stand-by-liquid supplement" cycles are required, which seriously delays the production line rhythm.

[0005] As the comparative file CN202211270882.4 discloses a soft package lithium ion battery electrolyte infiltration method and its application, including the following steps: the dry cell is installed in the aluminum plastic film, the aluminum plastic film is heat pressed and packaged on three sides, and the air bag is left at one end. The opening at the air bag end is used as a liquid injection port; after vacuum drying the cell, electrolyte is injected; after the battery is injected, the battery injection port is vacuum operated, the vacuum degree is maintained for 0.5-10 min, and normal pressure is static for 1-10 min; the cell body is clamped, the battery injection port is vacuum operated, the vacuum degree is maintained for 0.5-10 min, and normal pressure is static for 1-10 min; the liquid injection and vacuum operation are repeated for several times, and the infiltration is completed. The electrolyte of the scheme penetrates slowly into the silicon-carbon negative electrode, and needs to be repeatedly "infiltrated-stationary-liquid supplementing" cycle, which seriously drags the production line rhythm.

[0006] As the comparative file CN202310187278.3 discloses a kind of electrolyte pre-injection process for battery processing, adopts high positive pressure, high negative pressure cycle injection mode, can increase pressure gradient, promote liquid passing rate, improve electrolyte infiltration efficiency. Although the penetration speed can be improved by pressure gradient method, the electrolyte "detour" large hole due to lack of directional control, so that the improvement of micropore filling rate is limited, although the large hole penetrates fast, but due to lack of guide path, electrolyte is easy to accumulate on the surface, it is difficult to penetrate into the electrode interior.

[0007] As the comparative file CN201710694561.X discloses a battery electrolyte ultrasonic injection device and method, including placing at least one base of the battery to be injected, the injection device corresponding to each battery to be injected and the ultrasonic wave generating device, the injection device includes a metering pump and an injection needle, and the ultrasonic wave generating device conducts ultrasonic waves to the electrolyte and electrode roll in each battery. However, when ultrasonic assisted infiltration is used to infiltrate silicon-carbon negative electrode, ultrasonic assisted infiltration accelerates electrolyte flow by high-frequency vibration, and the cavitation effect of ultrasonic waves can cause silicon particles to fall off from the current collector, thereby reducing the integrity of the electrode structure. SUMMARY

[0008] The purpose of the present disclosure is to overcome the shortcomings in the prior art, and to provide a lithium battery preparation method and lithium ion battery with electrolyte directional penetration of electrolyte into silicon-carbon electrode with fast and uniform penetration speed.

[0009] The purpose of the present disclosure is achieved by the following technical solutions:

[0010] A lithium battery preparation method with electrolyte directional penetration, comprising the following steps:

[0011] A silicon-carbon electrode with three-dimensional gradient pore structure is prepared, which is composed of surface straight-through pores, middle layer tree-shaped branch pores and bottom layer liquid storage cavities connected in communication and with increasing radial size gradient;

[0012] Assemble the silicon-carbon electrode and the shell to form an electric core;

[0013] Place the electric core in a gradient magnetic field environment with a gradient distribution of 0.5T-1.2T of the magnetic field strength;

[0014] Add a magnetic additive to the electrolyte, and then inject the electrolyte with the magnetic additive into the electric core;

[0015] Perform a temperature and pressure synergistic loading cycle on the electrolyte and the electrode in the electric core in sequence, including low-temperature and low-pressure penetration, high-temperature and high-pressure filling, and low-temperature and negative pressure balance;

[0016] Obtain a lithium battery after packaging.

[0017] In one of the embodiments, the magnetic additive is Fe3O4@SiO2 nanoparticles, and the magnetic susceptibility of the Fe3O4@SiO2 nanoparticles is greater than 1.0×10 -3 .

[0018] In one of the embodiments, the Fe3O4@SiO2 nanoparticles are core-shell structures composed of Fe3O4 cores and SiO2 shells, the diameter of the Fe3O4 core is 17nm-23nm, and the thickness of the SiO2 shell is 4nm-6nm.

[0019] In one of the embodiments, the concentration of the Fe3O4@SiO2 nanoparticles in the electrolyte is 0.1wt%-0.3wt%.

[0020] In one of the embodiments, the gradient increment of the magnetic field strength of the gradient magnetic field environment is set to 0.3T / cm-0.5T / cm.

[0021] In one of the embodiments, the temperature and pressure synergistic loading cycle on the electrolyte and the electrode in the electric core in sequence includes the following steps:

[0022] Load a low pressure on the electrolyte in the electric core and perform temperature rising, the loading low pressure of the low-pressure penetration is 0.5MPa-1.5MPa, the temperature of the low-pressure penetration temperature rising is 40℃-45℃, and the silicon-carbon electrode is subjected to low-pressure penetration; then load a high pressure on the electrolyte in the electric core and perform temperature rising, the loading high pressure of the high-pressure filling is 1.5MPa-2.5MPa, the temperature of the high-pressure filling temperature rising is 50℃-60℃, and the silicon-carbon electrode is subjected to high-pressure filling; then load a negative pressure on the electrolyte in the electric core and perform temperature falling, and the silicon-carbon electrode is subjected to negative pressure balance, the loading negative pressure of the negative pressure balance is -0.2Mpa to -0.1Mpa, and the temperature of the negative pressure balance temperature falling is 30℃-40℃.

[0023] In one of the embodiments, the low-pressure infiltration pressure is P1, the low-pressure infiltration temperature is T1, the high-pressure infiltration pressure is P2, the high-pressure infiltration temperature is T2, and the ratio of the temperature and pressure synergistic loading cycle satisfies the following mathematical relationship:

[0024]

[0025] In one of the embodiments, when the electrode and the electrolyte are subjected to the temperature and pressure synergistic loading cycle, the following steps are further included:

[0026] The infiltration depth of the electrolyte is measured in real time by the dielectric sensor.

[0027] In one of the embodiments, the electrode with the three-dimensional gradient pore structure is prepared by the following steps:

[0028] The PS microspheres and CaCO3 nanoparticles are dispersed in the PVDF binder and combined with the silicon-carbon composite material to form a composite electrode;

[0029] The composite electrode is transferred into a tube furnace, N2 is introduced, the temperature is raised to 450 DEG C, and the temperature is maintained for 1 h, so that the composite electrode forms a surface layer of straight-through pores;

[0030] N2 and H2 mixed gas is introduced, the temperature is raised to 550 DEG C, and the temperature is maintained for 2 h, so that the composite electrode forms a middle layer of dendritic branch pores;

[0031] Argon is introduced, the temperature is raised to 650 DEG C, and the temperature is maintained for 1 h to shape, so that the composite electrode forms a bottom layer of liquid storage cavities, and a silicon-carbon electrode with a three-dimensional gradient pore structure is obtained. A lithium ion battery is obtained by the lithium battery preparation method of electrolyte directional infiltration according to any one of the above embodiments.

[0032] Compared with the prior art, the present disclosure has at least the following advantages:

[0033] The lithium battery preparation method of electrolyte directional infiltration described above, the surface layer of straight-through pores, the middle layer of dendritic branch pores, and the bottom layer of liquid storage cavities are connected to form a guide route, so that the electrolyte infiltrates and uniformly distributes in the interior of the silicon-carbon electrode, thereby making the electrolyte fully wet the silicon-carbon electrode; the magnetic additive is added to the electrolyte, under the action of the gradient magnetic field environment, the magnetic additive drives the electrolyte to break through the interface impedance of the electrolyte wetting, accelerates the wetting of the electrolyte in the three-dimensional gradient pore structure of the silicon-carbon electrode, and thereby significantly improves the wetting efficiency of the electrolyte; the temperature and pressure synergistic loading cycle of low-pressure infiltration, high-pressure filling, and negative pressure balance is sequentially performed on the electrolyte in the battery cell, so that the electrolyte quickly fills the wetting micropores of the silicon-carbon electrode, and the electrolyte is uniformly distributed, thereby reducing the side reactions in the wetting process of the electrolyte and the silicon-carbon electrode;

[0034] The electrolyte is guided by the three-dimensional gradient pore structure, the magnetic force driving of the gradient magnetic field environment and the magnetic additive, and the temperature and pressure synergistic loading cycle regulation and control to realize three-dimensional synergy, so that the electrolyte is directionally permeated in the three-dimensional gradient pore structure of the silicon-carbon electrode, the speed of the electrolyte infiltrating the silicon-carbon electrode is accelerated, and then the efficient permeation of the electrolyte to the silicon-carbon electrode is realized. BRIEF DESCRIPTION OF DRAWINGS

[0035] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the drawings needed to be used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present disclosure, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0036] Figure 1 The step flow chart of the lithium battery preparation method for the electrolyte directional permeation of an embodiment;

[0037] Figure 2 The curve graph of different rate charge-discharge for Comparative Example 1 and Example 1;

[0038] Figure 3 The flow chart of preparing the silicon-carbon electrode with the three-dimensional gradient pore structure of an embodiment. DETAILED DESCRIPTION

[0039] In order to facilitate the understanding of the present disclosure, the present disclosure will be described more fully below with reference to the related drawings. The preferred embodiments of the present disclosure are shown in the drawings. However, the present disclosure can be implemented in many different forms, and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present disclosure more thorough and comprehensive.

[0040] It should be noted that when an element is referred to as being "fixed" to another element, it can be directly on the other element or there can be an intervening element. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or there can be an intervening element. The terms "vertical", "horizontal", "left", "right", and similar expressions used herein are for illustrative purposes only and are not intended to be limiting.

[0041] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. The terminology used in the description of the disclosure herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0042] In order to better understand the technical solutions and beneficial effects of the present disclosure, the present disclosure will be further described in detail below in combination with specific embodiments:

[0043] The present application relates to a kind of electrolyte directional penetration lithium battery preparation method, comprising the following steps: preparation of three-dimensional gradient pore structure silicon-carbon electrode, the three-dimensional gradient pore structure is composed of surface layer straight-through hole, middle layer dendritic branch hole and bottom layer liquid storage cavity that are connected and the radial size gradient increases.In the embodiment, the different gradient size of the three-dimensional gradient pore structure of silicon-carbon electrode surface layer straight-through hole, middle layer dendritic branch hole and bottom layer liquid storage cavity pore structure, it is favorable for the infiltration of electrolyte.The silicon-carbon electrode is formed into battery with shell shape.The battery is placed in gradient magnetic field environment with 0.5T-1.2T gradient distribution of magnetic field intensity;Magnetic additive is added to electrolyte, and then electrolyte with magnetic additive is injected into battery;The temperature and pressure of the electrolyte in the battery and electrode are sequentially loaded in low-temperature low-pressure penetration, high-temperature high-pressure filling and low-temperature negative pressure balance cycle;Lithium battery is obtained after packaging.

[0044] Please refer to Figure 1 , which is the electrolyte directional penetration lithium battery preparation method of an embodiment of the present application, comprising the following steps:

[0045] S101 preparation of three-dimensional gradient pore structure silicon-carbon electrode, the three-dimensional gradient pore structure is composed of surface layer straight-through hole, middle layer dendritic branch hole and bottom layer liquid storage cavity that are connected and the radial size gradient increases.In the embodiment, the different gradient size of the three-dimensional gradient pore structure of silicon-carbon electrode surface layer straight-through hole, middle layer dendritic branch hole and bottom layer liquid storage cavity pore structure, it is favorable for the infiltration of electrolyte.

[0046] S103 the silicon-carbon electrode is formed into battery with shell shape.

[0047] S105 the battery is placed in gradient magnetic field environment with 0.5T-1.2T gradient distribution of magnetic field intensity;

[0048] S107 magnetic additive is added to electrolyte, and then electrolyte with magnetic additive is injected into battery;

[0049] S109 the temperature and pressure of the electrolyte in the battery and silicon-carbon electrode are sequentially loaded in low-temperature low-pressure penetration, high-temperature high-pressure filling and low-temperature negative pressure balance cycle;

[0050] S111 lithium battery is obtained after packaging.

[0051] In the embodiment, the different gradient sizes of the pore structures of the surface layer through hole, the middle layer dendritic branch hole and the bottom layer liquid storage cavity of the three-dimensional gradient pore structure of the silicon-carbon electrode, the pore network formed by the surface layer through hole accelerates the penetration speed of the electrolyte, the pore branch structure of the middle layer dendritic branch hole enhances the capillary force, improves the electrolyte infiltration, and the bottom layer liquid storage cavity with a larger pore diameter improves the absorption amount of the electrolyte, thereby facilitating the electrolyte to infiltrate the silicon-carbon electrode.

[0052] It can be understood that, after the magnetic additive is added to the electrolyte, under the regulation of the external magnetic field, the magnetic additive moves towards the direction where the magnetic field strength decreases, the magnetic additive drives the electrolyte to penetrate in the three-dimensional gradient pore structure of the silicon-carbon electrode in a directional manner, the interface impedance of the electrolyte infiltration is greatly reduced, and the electrolyte can quickly migrate and penetrate to the deep layer middle layer dendritic branch hole and the bottom layer liquid storage cavity along the through hole, thereby significantly improving the infiltration efficiency of the electrolyte.

[0053] It can be understood that, when the silicon-carbon electrode is subjected to low-pressure penetration, the temperature rise reduces the viscosity of the electrolyte, and the electrolyte quickly fills the larger pores of the silicon-carbon electrode; when the silicon-carbon electrode is subjected to high-pressure filling, the temperature rise further reduces the viscosity of the electrolyte, and the increased pressure makes the electrolyte further penetrate into the micropores to improve the absorption amount; when the silicon-carbon electrode is subjected to negative pressure balancing, the residual bubbles and excess electrolyte can be extracted, the electrolyte is uniformly distributed, the temperature drop makes the electrolyte viscosity rise, the electrolyte and the silicon-carbon electrode maintain stable infiltration, the electrolyte is uniformly distributed in the three-dimensional gradient pore structure of the silicon-carbon electrode, and the side reaction between the electrolyte and the silicon-carbon electrode is reduced.

[0054] The above-mentioned lithium battery preparation method for directional penetration of electrolyte, the surface layer through hole, the middle layer dendritic branch hole and the bottom layer liquid storage cavity are connected to form a guide route, so that the electrolyte penetrates and is uniformly distributed in the interior of the silicon-carbon electrode, thereby making the electrolyte fully infiltrate the silicon-carbon electrode; the magnetic additive is added to the electrolyte, under the action of the gradient magnetic field environment, the magnetic additive drives the electrolyte to break through the interface impedance of the electrolyte infiltration, accelerates the electrolyte to infiltrate the three-dimensional gradient pore structure of the silicon-carbon electrode, thereby significantly improving the infiltration efficiency of the electrolyte; the temperature and pressure of the electrolyte in the battery are sequentially subjected to low-pressure penetration, high-pressure filling and negative pressure balancing, and the temperature and pressure are cyclically loaded in cooperation, so that the electrolyte quickly fills the infiltration micropores of the silicon-carbon electrode, and the electrolyte is uniformly distributed, thereby reducing the side reaction between the electrolyte and the silicon-carbon electrode during the infiltration process; the electrolyte is three-dimensionally cooperated through the three-dimensional gradient pore structure guidance, the magnetic force driving of the gradient magnetic field environment and the magnetic additive, and the temperature and pressure cooperative loading cycle regulation, so that the electrolyte penetrates in the three-dimensional gradient pore structure of the silicon-carbon electrode in a directional manner, accelerates the speed of the electrolyte to infiltrate the silicon-carbon electrode, and then realizes the efficient penetration of the electrolyte to the silicon-carbon electrode.

[0055] In one embodiment, the magnetic additive is Fe3O4@SiO2 nanoparticles, and the magnetic susceptibility of the Fe3O4@SiO2 nanoparticles is greater than 1.0 x 10 -3 In this embodiment, the magnetic susceptibility of the Fe3O4@SiO2 is greater than 1.0 x 10 -3 When the magnetic susceptibility of the Fe3O4@SiO2 is greater than 1.0 x 10

[0056] In one embodiment, the concentration of the Fe3O4@SiO2 nanoparticles added to the electrolyte is in the range of 0.1wt%-0.3wt%. In this embodiment, when the amount of the Fe3O4@SiO2 nanoparticles added is less than 0.1wt%, the magnetic field gradient acts on the Fe3O4@SiO2 nanoparticles, and the efficiency of the electrolyte filling the micropores is reduced, thereby slowing down the infiltration of the electrolyte into the silicon-carbon electrode and restricting the production efficiency of the lithium battery; when the amount of the Fe3O4@SiO2 nanoparticles added is greater than 0.3wt%, the excess nanoparticles can cause the viscosity of the electrolyte to rise, and the excessive aggregation of the Fe3O4@SiO2 nanoparticles can easily block the pores with smaller pore sizes, resulting in uneven infiltration.

[0057] In one embodiment, the Fe3O4@SiO2 nanoparticles are core-shell structures composed of Fe3O4 cores and SiO2 shells, the diameter of the Fe3O4 core is 17nm-23nm, and the thickness of the SiO2 shell is 4-6nm. In this embodiment, the diameter of the Fe3O4 core is 17nm-23nm, and the thickness of the SiO2 shell is 4-6nm, which makes the radius of the Fe3O4@SiO2 nanoparticles smaller, reducing the blocking of the pores of the silicon-carbon electrode by the Fe3O4@SiO2 nanoparticles; the Fe3O4@SiO2 nanoparticles use Fe3O4 as the magnetic attraction core, and the SiO2 shell protects the Fe3O4 core from oxidation and corrosion, improving the chemical stability of the Fe3O4@SiO2 nanoparticles.

[0058] In one embodiment, the magnetic field strength gradient increment of the gradient magnetic field environment is set to 0.3T / cm-0.5T / cm. In this embodiment, the gradient magnetic field environment is a Halbach permanent magnet array, the Z-axis direction magnetic field gradient is ΔB / Δz=0.3T / cm-0.5T / cm, the Halbach permanent magnet array is superimposed by parallel magnetic field and radial magnetic field, which greatly improves the magnetic field strength on one side and reduces the magnetic field on the other side; by adjusting the magnet arrangement and size, the magnetic field strength gradient increment of 0.3T / cm-0.5T / cm in the Z-axis direction can be accurately controlled, thereby affecting the magnetic field strength layer gradient change of the magnetic additive in the electrolyte along the Z-axis direction, so that the direction of the electrolyte magnetic field strength layer gradient change penetrates on the silicon-carbon electrode.

[0059] In one embodiment, the electrolyte and electrode in the battery cell are sequentially subjected to low-temperature and low-pressure penetration, high-temperature and high-pressure filling, and low-temperature and negative pressure balance temperature and pressure synergistic loading cycle, including the following steps:

[0060] The electrolyte in the battery cell is loaded with low pressure and heated, the low pressure infiltration loading low pressure is 0.5-1.5 MPa, the low pressure infiltration heating temperature is 40-45℃, and the silicon-carbon electrode is subjected to low pressure infiltration; the electrolyte in the battery cell is loaded with high pressure and heated, the high pressure filling loading high pressure is 1.5-2.5 MPa, the high pressure filling heating temperature is 50-60℃, and the silicon-carbon electrode is subjected to high pressure filling; the electrolyte of the battery cell is loaded with negative pressure and cooled, and the silicon-carbon electrode is subjected to negative pressure balance, the negative pressure balance loading negative pressure is-0.2 to-0.1 MPa, and the negative pressure balance cooling temperature is 30-40℃. In this embodiment, heating reduces the viscosity of the electrolyte, and the electrolyte quickly fills the larger pores of the silicon-carbon electrode; when the silicon-carbon electrode is subjected to high pressure filling, heating further reduces the viscosity of the electrolyte, and the increased pressure makes the electrolyte further penetrate into the micropores, increasing the absorption capacity; when the silicon-carbon electrode is subjected to negative pressure balance, the residual bubbles and excess electrolyte can be extracted, the electrolyte is uniformly distributed, and cooling makes the electrolyte viscosity rise, keeping the electrolyte and silicon-carbon electrode wetting stable; the low pressure infiltration heating temperature range is 40-45℃, which reduces the viscosity of the electrolyte to promote electrolyte wetting, the loading low pressure is 0.5-1.5 MPa, the loading low pressure is greater than 0.5 MPa, which makes the electrolyte quickly fill the larger pores of the silicon-carbon electrode, and the low pressure is less than 1.5 MPa, which forms a gradient pressure with the loading high pressure, reduces the deep penetration effect of the loading high pressure, and improves the uniformity of wetting; the loading high pressure is 1.5-2.5 MPa, the loading high pressure is less than 2.5 MPa, which reduces the force on the battery shell, avoids deformation of the battery shell, and the loading high pressure is greater than 1.5 MPa, which makes the electrolyte have good penetration effect on the micropores of the silicon-carbon electrode; the loading negative pressure is-0.2 to-0.1 MPa, when the loading negative pressure is small, the loading negative pressure is beneficial to extract residual bubbles and excess electrolyte, and realizes uniform distribution of electrolyte, when the loading negative pressure is large, more electrolyte is extracted, leading to insufficient wetting of the motor, and when the loading negative pressure is small, the excess bubbles and electrolyte cannot be effectively extracted.

[0061] Further, the low pressure infiltration heating rate is 2℃ / min, the high pressure filling heating rate is 2℃ / min, and the negative pressure balance cooling rate is 2℃ / min. It can be understood that before low pressure infiltration and high pressure filling, the electrolyte needs to be heated, slow heating rate avoids sudden change of electrolyte temperature, reduces thermal stress damage to the structure of silicon-carbon electrode, and after electrolyte heating, the viscosity of electrolyte decreases and the fluidity increases; before negative pressure balance, the electrolyte needs to be cooled, slow cooling rate reduces the interfacial tension change of electrolyte, maintains good contact between silicon-carbon electrode and electrolyte, and after electrolyte cooling, the viscosity of electrolyte increases, keeping the electrolyte and silicon-carbon electrode wetting stable.

[0062] In one embodiment, the low-pressure infiltration pressure is P1, the temperature of the low-pressure infiltration is T1, the high-pressure infiltration pressure is P2, the temperature of the high-pressure infiltration is T2, and the ratio of the temperature and pressure synergistic loading cycle satisfies the following mathematical relationship:

[0063]

[0064] In this embodiment, for every 1 MPa increase in pressure, the temperature needs to be increased by 10.0°C to maintain the infiltration efficiency, with an allowable error of 9.5°C / MPa-10.5°C / MPa to adapt to different electrolytes; the increase in pressure can promote the flow of electrolyte and increase the capillary force to drive the electrolyte to infiltrate deep pores, and the increase in temperature reduces the viscosity of the electrolyte, thereby increasing the infiltration speed of the electrolyte; when the ratio of the temperature and pressure synergy is high, the infiltration time is shortened, and when the ratio of the temperature and pressure synergistic loading cycle is greater than 10.0±0.5°C / MPa, the uniformity of the electrolyte distribution is affected when the infiltration time is too short. When the ratio of the temperature and pressure synergy is less than 10.0±0.5°C / MPa, the infiltration time is longer, thereby reducing the infiltration efficiency; when the ratio of the temperature and pressure synergistic loading cycle is 10.0±0.5°C / MPa, the electrolyte has a high infiltration efficiency, good electrolyte distribution uniformity, and high pore filling rate. By quantifying the temperature and pressure synergy, the electrolyte maintains the optimal infiltration efficiency, thereby improving the infiltration effect of the electrolyte on the silicon-carbon electrode.

[0065] Further, the magnetic field increment direction of the gradient magnetic field is parallel to the direction of the electrolyte inlet of the battery cell. In this embodiment, the electrolyte inlet of the battery cell is arranged above the battery cell, and the electrolyte infiltrates the silicon-carbon electrode in the battery cell from top to bottom. The magnetic field strength increases from bottom to top to generate a magnetic field gradient, thereby driving the Fe3O4@SiO2 nanoparticles to guide the electrolyte to infiltrate deep into the pores of the silicon-carbon electrode along the direction of the decreasing magnetic field, thereby accelerating the infiltration process of the electrolyte.

[0066] In one embodiment, the method further comprises the following steps:

[0067] The dielectric sensor is used to measure the infiltration depth of the electrolyte in real time. In this embodiment, when the electrolyte infiltrates the silicon-carbon electrode, the dielectric constant of the electrolyte is greater than that of air or other non-conductive materials, so the capacitance value of the dielectric sensor changes, allowing the dielectric sensor to measure the infiltration depth of the electrolyte in real time, thereby monitoring the infiltration effect of the silicon-carbon electrode in a timely manner.

[0068] Further, in one embodiment, the dielectric sensor has a working frequency of 1 MHz-10 MHz, and the dielectric constant change rate Δε / Δt and the infiltration depth satisfy d=0.25×(Δε / Δt)0.67 d is the penetration depth. The feedback penetration depth can be implemented by the measured dielectric constant change rate Δε / Δt, the penetration depth and the soaking time are controlled by feedback, the pressure and temperature in the temperature and pressure synergistic loading cycle are optimized, and then the pressure and temperature in the temperature and pressure synergistic loading cycle are adjusted.

[0069] As shown in Figure 3 In one embodiment, the electrode for preparing the three-dimensional gradient porous structure comprises the following steps:

[0070] S1011 disperse the PS microspheres and CaCO3 nanoparticles in the PVDF binder and make a composite electrode with the silicon-carbon composite material;

[0071] S1013 transfer the composite electrode to a tube furnace, pass N2, and heat to 450 DEG C, keep the temperature for 1h, so that the composite electrode forms a surface layer straight-through hole;

[0072] S1015 pass a mixed gas of N2 and H2, heat to 550 DEG C, keep the temperature for 2h, so that the composite electrode forms a middle layer dendritic branch hole;

[0073] S1017 pass argon gas, heat to 650 DEG C, keep the temperature for 1h, and shape, so that the composite electrode forms a bottom layer liquid storage cavity, and a silicon-carbon electrode with a three-dimensional gradient porous structure is obtained. In this embodiment, the flow rate of N2 is 5L / min, and when N2 is passed at 450 DEG C, only PS in the composite electrode is decomposed to form a surface layer straight-through hole with high porosity; when N2 and H2 are passed at 550 DEG C, CaCO3 in the composite electrode is partially decomposed, CO2 gas is escaped to form a middle layer dendritic branch hole and PS residual carbon skeleton interweaving, and the capillary action is enhanced; when argon gas is passed at 650 DEG C, CaCO3 is completely decomposed, and gas diffusion gas is escaped to form a large-pore liquid storage cavity, so that the silicon-carbon electrode forms a three-dimensional gradient porous structure, the surface layer straight-through hole, the middle layer dendritic branch hole and the bottom layer liquid storage cavity are connected through the overflow channel of the gas, and the electrolyte penetrates the surface layer straight-through hole, the middle layer dendritic branch hole and the bottom layer liquid storage cavity smoothly.

[0074] Further, the temperature rising rate of the N2 is 5℃ / min, the temperature rising rate of the mixed hydrogen is 5℃ / min, and the temperature rising rate of the argon is 5℃ / min. In the embodiment, by controlling the temperature rising rate to be 5℃ / min, the PS microspheres are synchronously decomposed to form the network of the surface layer through holes, and local overheating and excessive expansion are avoided, so that the surface layer through holes are uniformly distributed; the decomposition rate of CaCO3 in the composite electrode is affected by temperature, and uneven local temperature caused by excessive temperature rising leads to the difference in the decomposition rate of different regions, and by slowly rising the temperature, the decomposition rate of CaCO3 tends to be consistent, so that the middle layer dendritic branch hole structure and the bottom layer liquid storage cavity with uniform pores are formed, and the uniformity of the electrolyte infiltration is improved.

[0075] Further, the volume ratio of the PS microspheres to the CaCO3 nanoparticles is 3:6.8-7.2. In the embodiment, the PS microspheres form the initial micropore network after decomposition, and the CaCO3 nanoparticles form the macropore structure after decomposition, and when the volume of the CaCO3 nanoparticles is small, the absorption amount of the electrolyte by the silicon-carbon electrode is small; by adjusting the ratio of the PS microspheres to the CaCO3 nanoparticles, the silicon-carbon electrode forms the surface layer through holes, the middle layer dendritic branch holes and the bottom layer liquid storage cavity with stable structure and radially increasing size gradient, so that the electrolyte maintains the infiltration effect on the silicon-carbon electrode.

[0076] Further, in one of the embodiments, the radius of the through hole is 50nm-80nm, the radius of the dendritic branch hole is 100nm-150nm, and the radius of the bottom layer liquid storage cavity is 200nm-300nm. In the embodiment, the small-pore through hole and the size of the Fe3O4@SiO2 nanoparticles form a capillary effect gradient, which promotes the electrolyte to penetrate along the low-resistance path; the dendritic branch hole enhances the electrolyte distribution uniformity by increasing the specific surface area; the bottom layer liquid storage cavity accelerates the directional flow of the electrolyte under the driving of the magnetic field; the Fe3O4@SiO2 nanoparticles are significantly smaller than the through hole, the dendritic branch hole and the bottom layer liquid storage cavity of the silicon-carbon electrode, so that the Fe3O4@SiO2 nanoparticles effectively penetrate the interface barrier formed during the electrolyte infiltration process, and the gas-liquid interfacial tension is overcome by the magnetic force, so that the electrolyte infiltration speed is improved.

[0077] The application also provides a lithium battery prepared by the electrolyte directional infiltration lithium battery preparation method in any of the above embodiments. In the embodiment, the lithium battery prepared by the electrolyte directional infiltration lithium battery preparation method has a shorter infiltration time, improves the production efficiency of the lithium battery, has a better infiltration effect of the electrolyte on the silicon-carbon electrode with a three-dimensional gradient pore structure, has a higher electrolyte micropore filling rate of the electrode, has a uniform electrolyte distribution, reduces side reactions in the infiltration process, and further improves the lithium ion transmission efficiency, interface stability and battery cycle life in the lithium battery.

[0078] Compared with the prior art, the present disclosure has at least the following advantages:

[0079] The above-mentioned electrolyte directional infiltration lithium battery preparation method has the surface layer straight-through hole, the middle layer tree branch hole and the bottom layer liquid storage cavity connected to form a guide route, so that the electrolyte infiltrates into the interior of the silicon-carbon electrode, which is conducive to the full infiltration of the electrolyte into the silicon-carbon electrode; the magnetic additive is added to the electrolyte, and under the action of the gradient magnetic field environment, the magnetic additive drives the electrolyte to break through the interface impedance of the electrolyte infiltration, accelerates the electrolyte to infiltrate the three-dimensional gradient pore structure of the silicon-carbon electrode, and thus significantly improves the infiltration efficiency of the electrolyte; through the low-pressure infiltration, high-pressure filling and negative pressure balance of the electrolyte temperature and pressure in the battery in turn, the electrolyte quickly fills the silicon-carbon electrode infiltration micropore, and the electrolyte is uniformly distributed, thereby reducing the side reactions of the electrolyte and the silicon-carbon electrode in the infiltration process;

[0080] The electrolyte is three-dimensionally coordinated through the three-dimensional gradient pore structure guide, the magnetic force driving of the gradient magnetic field environment and the magnetic additive, and the temperature and pressure synergistic loading cycle regulation, so that the electrolyte directionally infiltrates in the three-dimensional gradient pore structure of the silicon-carbon electrode, accelerates the infiltration speed of the electrolyte into the silicon-carbon electrode, and thus realizes the efficient infiltration of the electrolyte into the silicon-carbon electrode.

[0081] Some specific embodiments are listed below. If % is mentioned, it means percentage by weight. It should be noted that the following examples do not exhaust all possible cases, and the materials used in the following examples can be obtained from commercial channels if not otherwise specified.

[0082] Comparative Example 1

[0083] The silicon / carbon with a specific capacity of 700 mAh / g is made into an electrode; the composite electrode is transferred to a tube furnace, N2 is passed at a flow rate of 5 L / min, the temperature is raised to 450℃ at a rate of 5℃ / min, and the temperature is kept for 1 h, so that the composite electrode forms a surface layer of straight-through holes; then N2 and H2 mixed gas (N2 / H2=95:5) is passed in, the temperature is raised to 550℃ at a rate of 5℃ / min, and the temperature is kept for 2 h, so that the composite electrode forms a middle layer of dendritic branch holes; finally, the temperature is raised to 650℃ and argon (Ar) is passed in, the temperature is kept for 1 h to shape, so that the composite electrode forms a bottom layer of liquid storage cavities, and a silicon / carbon electrode with a three-dimensional gradient pore structure is obtained.

[0084] The electrolyte is injected into the battery cell, vacuum soaking method is used, vacuum operation is performed on the liquid injection port of the battery, the pressure is reduced to-0.1 MPa, the vacuum degree is kept for 0.5-10 min, normal pressure is kept for 110 min, and the liquid injection and vacuum operation are repeated for several times until the soaking is completed.

[0085] Further, a custom-made autoclave is used, the battery cell is raised to 45℃ at a rate of 2℃ / min, and is pressurized to 0.5 MPa at a rate of 0.4 MPa / s and kept for 3 min, low-pressure penetration is performed on the silicon / carbon electrode; then the battery cell is raised to 60℃ at a rate of 2℃ / min, and is pressurized to 2 MPa at a rate of 0.4 MPa / s and kept for 5 min, high-pressure filling is performed on the silicon / carbon electrode; finally, the battery cell is reduced to 35℃ at a rate of 2℃ / min, and is depressurized to-0.1 MPa and kept for 2 min, negative pressure balance is performed on the silicon / carbon electrode; after packaging, a lithium battery is obtained.

[0086] Example 1

[0087] The PS microspheres and CaCO3 nanoparticles are dispersed in a PVDF binder at a volume ratio of 3:7, and a composite electrode is made from the silicon / carbon composite material with a specific capacity of 700 mAh / g; the composite electrode is transferred to a tube furnace, N2 is passed at a flow rate of 5 L / min, the temperature is raised to 450℃ at a rate of 5℃ / min, and the temperature is kept for 1 h, so that the composite electrode forms a surface layer of straight-through holes; then N2 and H2 mixed gas (N2 / H2=95:5) is passed in, the temperature is raised to 550℃ at a rate of 5℃ / min, and the temperature is kept for 2 h, so that the composite electrode forms a middle layer of dendritic branch holes; finally, the temperature is raised to 650℃ and argon (Ar) is passed in, the temperature is kept for 1 h to shape, so that the composite electrode forms a bottom layer of liquid storage cavities, and a silicon / carbon electrode with a three-dimensional gradient pore structure is obtained.

[0088] Further, the silicon-carbon electrode is assembled with the shell to form a battery cell; a Halbach magnetic field array with a size of 300mmx200mmx50mm (lengthxwidthxheight) is adopted, and the Z-axis gradient AB / Δz is adjusted to 0.402T / cm by using a Hall probe, so as to form a suitable gradient magnetic field environment; 0.2wt% of Fe3O4@SiO2 is added into the electrolyte, and then the electrolyte with Fe3O4@SiO2 is injected into the battery cell.

[0089] Further, the battery cell is heated to 45℃ at a heating rate of 2℃ / min, and is pressurized to 0.5MPa at a rate of 0.4MPa / s for 3min, so as to perform low-pressure infiltration on the silicon-carbon electrode; then the battery cell is heated to 60℃ at a heating rate of 2℃ / min, and is pressurized to 2MPa at a rate of 0.4MPa / s for 5min, so as to perform high-pressure filling on the silicon-carbon electrode; finally, the battery cell is cooled to 35℃ at a cooling rate of 2℃ / min, and is depressurized to -0.1MPa for 2min, so as to perform negative pressure balancing on the silicon-carbon electrode; and a lithium battery is obtained after packaging.

[0090] Example 2

[0091] The PS microspheres and CaCO3 nanoparticles are dispersed in a PVDF binder at a volume ratio of 3:7, and a composite electrode is prepared by using a silicon-carbon composite material with a specific capacity of 700mAh / g; the composite electrode is transferred to a tube furnace, N2 is introduced at a flow rate of 5L / min, and the temperature is raised to 450℃ at a heating rate of 5℃ / min, and the temperature is maintained for 1h, so as to form a surface layer of straight-through holes in the composite electrode; then a mixed gas of N2 and H2 (N2 / H2=95:5) is introduced, the temperature is raised to 550℃ at a heating rate of 5℃ / min, and the temperature is maintained for 2h, so as to form a middle layer of dendritic branch holes in the composite electrode; finally, the temperature is raised to 650℃ and argon (Ar) is introduced, the temperature is maintained for 1h to shape, so as to form a bottom layer of liquid storage cavities in the composite electrode, and a silicon-carbon electrode with a three-dimensional gradient porous structure is obtained.

[0092] Further, the silicon-carbon electrode is assembled with the shell to form a battery cell; a Halbach magnetic field array with a size of 300mmx200mmx50mm (lengthxwidthxheight) is adopted, and the Z-axis gradient AB / Δz is adjusted to 0.402T / cm by using a Hall probe, so as to form a suitable gradient magnetic field environment; 0.2wt% of Fe3O4@SiO2 is added into the electrolyte, and then the electrolyte with Fe3O4@SiO2 is injected into the battery cell.

[0093] Further, the silicon-carbon electrode is subjected to low-pressure infiltration by using a customized autoclave to raise the temperature of the cell to 40℃ at a rate of 2℃ / min and pressurize to 0.5 MPa at a rate of 0.4 MPa / s for 3 min; the silicon-carbon electrode is subjected to high-pressure filling by raising the temperature of the cell to 60℃ at a rate of 2℃ / min and pressurize to 1.5 MPa at a rate of 0.4 MPa / s for 5 min; and the silicon-carbon electrode is subjected to negative pressure balancing by lowering the temperature of the cell to 35℃ at a rate of 2℃ / min and depressurize to -0.1 MPa for 2 min; and a lithium battery is obtained after packaging.

[0094] Example 3

[0095] The PS microspheres and CaCO3 nanoparticles are dispersed in a PVDF binder at a volume ratio of 3:7 to form a composite electrode with a silicon-carbon composite material having a specific capacity of 700 mAh / g; the composite electrode is transferred to a tube furnace, N2 is introduced at a flow rate of 5 L / min, the temperature is raised to 450℃ at a rate of 5℃ / min, and the temperature is maintained for 1 h to form a surface layer of straight-through holes in the composite electrode; N2 and H2 mixed gas (N2 / H2=95:5) is introduced, the temperature is raised to 550℃ at a rate of 5℃ / min, and the temperature is maintained for 2 h to form a middle layer of dendritic branch holes in the composite electrode; finally, the temperature is raised to 650℃ and argon (Ar) is introduced, the temperature is maintained for 1 h to form a bottom layer of liquid storage cavities in the composite electrode, and a silicon-carbon electrode with a three-dimensional gradient porous structure is obtained.

[0096] Further, the silicon-carbon electrode is assembled with a shell to form a cell; a Halbach magnetic field array with a size of 300 mm x 200 mm x 50 mm (length x width x height) is used, and the Z-axis gradient ΔB / Δz is adjusted to 0.402 T / cm using a Hall probe to form a suitable gradient magnetic field environment; 0.2 wt% of Fe3O4@SiO2 is added to the electrolyte, and the electrolyte with Fe3O4@SiO2 is injected into the cell.

[0097] Further, the silicon-carbon electrode is subjected to low-pressure infiltration by using a customized autoclave to raise the temperature of the cell to 46.5℃ at a rate of 2℃ / min and pressurize to 0.5 MPa at a rate of 0.4 MPa / s for 3 min; the silicon-carbon electrode is subjected to high-pressure filling by raising the temperature of the cell to 60℃ at a rate of 2℃ / min and pressurize to 2 MPa at a rate of 0.4 MPa / s for 5 min; and the silicon-carbon electrode is subjected to negative pressure balancing by lowering the temperature of the cell to 35℃ at a rate of 2℃ / min and depressurize to -0.1 MPa for 2 min; and a lithium battery is obtained after packaging.

[0098] Table 1

[0099]

[0100] From Table 1 andFigure 2 It can be seen that, compared with Comparative Example 1, the infiltration time of Examples 1-3 is greatly shortened, the electrolyte is more uniformly distributed, the porosity filling rate is improved, and the interfacial impedance of the electrolyte is reduced during the infiltration process. The retention rate of the cycle capacity of the lithium battery prepared in Example 1 is better than that of Comparative Example 1 through different rate charge-discharge, indicating that the lithium ion transmission efficiency, interface stability and battery cycle life of the lithium battery prepared in Example 1 are better.

[0101] The temperature and pressure synergy ratio of Example 1 is 10.0±0.5℃ / MPa, the temperature and pressure synergy ratio of Example 2 is greater than 10.0±0.5℃ / MPa, and the temperature and pressure synergy ratio of Example 3 is less than 10.0±0.5℃ / MPa. The infiltration time of Examples 1 and 2 is shorter, and the electrolyte distribution uniformity of Example 1 is better than that of Example 2, indicating that a higher temperature and pressure synergy ratio is beneficial to improving the uniformity of electrolyte distribution. The porosity filling rate of Examples 1 and 3 is good, and the electrolyte infiltration time of Example 1 is better than that of Example 3, indicating that a temperature and pressure synergy ratio of 10.0±0.5℃ / MPa is beneficial to improving the infiltration efficiency of the electrolyte.

[0102] The above-described examples only express several embodiments of the present disclosure, and the description is more specific and detailed, but it should not be understood as limiting the scope of the disclosed patent. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the present disclosure, several modifications and improvements can be made, which are within the scope of the present disclosure. Therefore, the protection scope of the present disclosure patent should be subject to the appended claims.

Claims

1. A method for the preparation of a lithium battery with electrolyte directional permeation, characterized by, The method comprises the following steps: The method for preparing the silicon-carbon electrode with three-dimensional gradient porous structure comprises the following steps: The PS microspheres and CaCO3 nanoparticles are dispersed in the PVDF binder and combined with the silicon-carbon composite material to form a composite electrode; The composite electrode is transferred into a tube furnace, N2 is introduced, and the temperature is raised to 450℃ and kept for 1h, so that the composite electrode forms surface layer straight-through pores; N2 and H2 mixed gas is introduced, and the temperature is raised to 550℃ and kept for 2h, so that the composite electrode forms middle layer dendritic branch pores; Argon is introduced, the temperature is raised to 650℃ and kept for 1h for shaping, so that the composite electrode forms bottom layer liquid storage cavities, and a silicon-carbon electrode with three-dimensional gradient porous structure is obtained; The three-dimensional gradient porous structure is composed of surface layer straight-through pores, middle layer dendritic branch pores and bottom layer liquid storage cavities which are connected and have increasing radial size gradient; The silicon-carbon electrode is assembled with a shell to form a battery cell; The battery cell is placed in a gradient magnetic field environment with a gradient distribution of magnetic field strength of 0.5T-1.2T; A magnetic additive is added to the electrolyte, and the electrolyte with the magnetic additive is injected into the battery cell; The temperature and pressure synergistic loading cycle of the electrolyte and the silicon-carbon electrode in the battery cell comprises the following steps: The electrolyte in the battery cell is loaded with low pressure and heated, the low pressure of the low pressure penetration is 0.5MPa-1.5MPa, the temperature of the low pressure penetration is 40℃-45℃, and the silicon-carbon electrode is subjected to low pressure penetration; then the electrolyte in the battery cell is loaded with high pressure and heated, the high pressure of the high pressure filling is 1.5MPa-2.5MPa, the temperature of the high pressure filling is 50℃-60℃, and the silicon-carbon electrode is subjected to high pressure filling; then the electrolyte of the battery cell is loaded with negative pressure and cooled, and the silicon-carbon electrode is subjected to negative pressure balance, the negative pressure of the negative pressure balance is-0.2Mpa to-0.1Mpa, and the temperature of the negative pressure balance is 30℃-40℃; After packaging, a lithium battery is obtained.

2. The method of claim 1, wherein the electrolyte-directed permeation lithium battery is prepared by the steps of: The magnetic additive is Fe3O4@SiO2 nanoparticles, and the magnetic susceptibility of the Fe3O4@SiO2 nanoparticles is greater than 1.0 x 10 -3 .

3. The method of claim 2, wherein the electrolyte is a lithium salt in a non-aqueous solvent. The Fe3O4@SiO2 nanoparticles are core-shell structures composed of Fe3O4 core and SiO2 shell, the diameter of the Fe3O4 core is 17nm-23nm, and the thickness of the SiO2 shell is 4nm-6nm.

4. The method of claim 2, wherein the electrolyte is a lithium salt in a non-aqueous solvent. The concentration of the Fe3O4@SiO2 nanoparticles added to the electrolyte in the electrolyte is 0.1wt%-0.3wt%.

5. The method for preparing a lithium battery by electrolyte directional permeation according to claim 1, characterized in that, The magnetic field strength gradient increment of the gradient magnetic field environment is set to 0.3T / cm-0.5T / cm.

6. The method for the fabrication of electrolyte-directed permeation lithium battery of claim 1, wherein, The low pressure penetration pressure is P1, the low pressure penetration temperature is T1, the high pressure penetration pressure is P2, the high pressure penetration temperature is T2, and the ratio of the temperature and pressure synergistic loading cycle satisfies the following mathematical relationship: = 10.0 ± 0.5°C / MPa.

7. The method for preparing a lithium battery by directional electrolyte permeation according to claim 1, characterized in that, When the electrode and the electrolyte are subjected to temperature and pressure synergistic loading cycle, the following steps are further included: The penetration depth of the electrolyte is measured in real time by a dielectric sensor.

8. A lithium-ion battery, characterized by, The lithium battery is prepared by the electrolyte directional penetration method of any one of claims 1-7.

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