Effect of new electrodes on the life of lithium ion batteries

Is there a moment in your life, do you think that technology is falling behind?

Yes, when we unpacked the iPad, one of the most expensive consumer-grade personal computers of our time, a sense of powerlessness swept the whole body, and a large piece of black in the middle occupied the vast majority of the entire machine. What is it? It is a battery!

When the vibration motor can be so precise, what restricts the development of electronic products toward safer and lighter? It is a battery!

In order to replace the traditional lithium battery, the researchers pay attention to the development of a new type of lithium ion battery with excellent cycle performance. It is found that when the particle size is reduced and the electrode is nanostructure, the electrode can work normally even in the lithiation and delithiation process even if the volume strain is large. . Some researchers have also pointed out that the coated (core-shell) morphology electrode material has a low degree of wear during the charge and discharge cycle. However, new problems have arisen in electrode nanostructure materials: low volume capacity (low tap density), high resistance characteristics, thereby increasing manufacturing costs and low coulombic efficiency due to side reactions.

In view of the above problems, the anode composite material can solve these shortcomings. The base composite anode material represented by graphene has the advantages of high electrical conductivity, high mechanical strength, strong connection with lithium active components, fast lithium ion transmission, etc., but disadvantages. There are the following aspects: 1.The total capacitance potential has limitations. 2. Synthetic technology is expensive. 3. The first cycle loss is large and the cycle efficiency is low.

Recently, the foreign Gurpreet Singh group has synthesized an ordered, cross-over, self-standing large-area anode composite material with the composition of SiOC and reduced graphene oxide (rGO). The anode material has a higher volumetric capacity than the reported Si/C nanotubes, and the redox graphene sheet serves as a base material for the SiOC particles, and the combination of the two exhibits high electron transport channels, high cycle, high current density, and structure, high stability and other advantages. In addition, it compensates for the defects of other types of lithium batteries, the first cycle charging capacity is high (702mAhg-1), the stable charging specific capacity is large (543mAhg-1), and the charging current density is high (2400mAg-1). What is more worthy of attention is that this composite anode material has excellent strain failure characteristics (more than 2%), which is greater than the failure characteristics of the simple paper-like reduced graphene oxide.

Silicon and graphene have high theoretical bearing capacity, which is a good anode material for lithium batteries, but its low energy density, low efficiency and poor stability limit its practical application. Here we report a self-standing anode material consisting of carbon silica glass particles embedded in a chemically modified graphene matrix. The simplified porous graphene oxide matrix is used as a highly efficient electron transporter and is a stable structure current collector. It can be used together with amorphous silicon oxycarbide to enable lithium batteries to have high coulombic efficiency. In 1020 cycles, the energy density of the paper electrode reached 588mAhg-1 without any signs of mechanical failure.

The article also pointed out that the reduction of some unnecessary materials, such as current collectors or polymer binders, to produce efficient lightweight batteries.

(a) Scanning electron microscopic pattern of SiC particles formed by decomposition of TTCS (1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane). It can be observed that the glassy particles are composed of submicron sized particles.

(b) Crosslinked TTCS and pyrolyzed silicon oxycarbide characterized by X-ray energy spectroscopy.

(c) It is a silicon oxynitride spectrum under high power X-ray scanning.

(f) The peak of the Raman spectrum of the silicon oxycarbide is characterized by graphite (D1-peak: 1,350 cm-1; G-peak: 1,590 cm -1)

(g) Fourier transforms infrared spectroscopy of SiC and crosslinked TTCS (γ: tensile vibration mode; σ: bending vibration mode)

(h) Atomic structure model of the carbon oxychloride particles after pyrolysis.

(i) A transmission electron micrograph of a composite material composed of silicon oxycarbide and graphene oxide. Large graphene oxide white spots cover the surface of the silicon oxycarbide.

(j) The use of amorphous silicon oxycarbide and heavily deposited graphene oxide sheet material with a weak circular pattern, due to its polymorphism, the corresponding transmission electron microscopy selected area electron diffraction pattern appears as a multi-point mode.

(k) Cross-sectional elemental view of the focused ion beam of 60SiOC, Si, C, and O are represented by blue, red, and green, respectively.

(l) X-ray diffraction patterns of crosslinked TTCS, SiOC, GO, and composite paper materials before and after heat treatment.

(m) Thermogravimetric analysis of graphene oxide paper and unannealed paper (heated from 30 degrees Celsius to 800 in a smooth airflow at 10 degrees Celsius per minute)

Electrochemical characteristics and lithium storage mechanism

(a) A pattern of various paper electrode charge capacities and charging efficiencies in the case where the current density is increased in an asymmetrical form when the charge and discharge cycle is performed.

(b) The long-term cycling of the rGO and 60SiOC electrodes is at 1600mAh per gram. After 970 cycles, the electrode exhibited good recovery performance per gram when the current density dropped to 100mA. The inset is a scanning electron micrograph of the RGO and 60SiOC electrodes.

(c) Voltage curve of the 60SiOC electrode.

(d) Different capacity curves for the first, second, and tenth cycles.

(e) Cyclic performance of 60SiOC below zero. When cooled to minus 15 degrees Celsius, the battery shows a capacity of approximately 200mAh per gram. When the temperature rises to room temperature, about 25 degrees Celsius, the battery capacity is again changed to about 86%.

(f) Schematic diagram of lithium or non-lithium in carbon oxychloride particles. Most of the lithium is distributed in the random carbon phase, and these carbon phases are uniformly distributed in the SiOC amorphous matrix. The large RGO sheet acts as a highly efficient electronic conductor and elastic support.

Mechanical test

(a) The photograph taken when the rGO paper is broken is the schematic diagram of the tensile force test, and the scale indicates that the change in length is 0.28 mm.

(b) Strain patterns drawn from load-displacement data, and their corresponding modulus values.

(c) Coefficient values of RGO, 10SiOC, 40SiOC, and 60SiOC with errors of 26.8, 7.6, 41.5, 24.1MPa, respectively

(d) RGO paper exhibits a stretching phenomenon and a rearrangement of graphene sheets before failure.

(e) For the 60SiOC paper, some fine stretching and rearrangement occurred, and the broken line was gradually cracked as the SiOC particles were embedded in the RGO white spot.

Preparation of Preparation Method Preparation of SiOC Ceramics: SiOC was prepared by polymer pyrolysis, and liquid TTCS was cross-linked for 5 hours in an argon atmosphere at 380 ° C to finally form a white insoluble matter. The insoluble matter was then ball-milled into a powder and then pyrolyzed at 1000 ° C for 10 h in an argon atmosphere to finally become a black SiOC ceramic powder. Preparation of GO and SiOC: GO was prepared using modified Hummer's, and 20 ml of GO colloidal suspension was prepared by ultrasonication of water and isopropanol at a volume ratio of 1:1. Different weight percentages of SiOC particles were added to the solution, and the solution was ultrasonically shaken for 1 hour, stirred for 6 hours, and then the composite was vacuum filtered with a 10 micron filter membrane. The GO/SiOC was carefully scraped off from the filter paper, dried, and kept at 500 ° C for 2 h in an argon atmosphere. Also, polypropylene was used as a filter paper to prepare a 60SiOC large-area paper. The heat-treated paper was cut into small circles and used as a working electrode material for a half-cell of a lithium ion battery. Button cell assembly and electrochemical measurement: Lithium batteries are assembled in a glove box filled with argon. A 25 micron thick glass (19 mm in diameter) was immersed in the electrolyte between the working electrode and metallic lithium (diameter 14.3 mm, 75 micron thick) as the counter electrode. The gasket, the spring, the battery can, and the like are sequentially assembled and then press molded.

Outlook: Lithium batteries continue to move toward higher energy density, lighter weight and safer direction, which will lead more mobile terminals to all aspects of our lives, so that our lives will last forever!

The SiO glass-graphene composite paper electrode prepared by the research group has excellent cycle characteristics. The electrode material has low specific capacity loss after repeated cycles, the first cycle has higher specific capacity and longer durability time, and the research team has determined the non- The ingredients of the active ingredients provide the direction for the production of lightweight batteries.

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