Aug 23, 2019 Pageview：48
Climate change, the limitations of fossil fuels and the exponential use of nomadic technologies are leading to a paradigm shift in the transformation and storage of energy by human civilization. Because of their longer energy density and their long life span, lithium-ion batteries play a very important role in this transformation.
The practical properties of Lithium-ion batteries, i.e. their energy density, charging time, duration and safety, depends on the mesostructure of the positive and negative electrodes (talking about their scales from 0.10 to 50 μm). The positive electrode is characterized by the spatial positioning of the active material particles (AM), aggregates of carbon additives and the binders that form the composite electrode, and is strongly determined by the parameters of the manufacturing process. A state of the art mathematical modeling plays quite an important role in understanding the functional principles of composite electrodes. Several of the previously reported LIB models have attempted to trace the influence of the electrode mesostructure on cell responses using 1D, P2D or even the 3D approaches for various chemicals from active materials such as graphite, LiNixMnyCozO2, LiFePO4, LiCoO2.
Although performance models have been successfully applied in several studies, which includes cell design, it should be noted that a lack of accurate knowledge of model parameters may result in a significant reduction in the ability to predict performance. Microscopic simulations and experimental measurements have shown that an effective diffusivity and conductivity of electrodes can differ considerably from their homogenized approximations, emphasizing the need for some higher fidelity models to be used to overcome this discrepancy. Likewise, it has been discovered that the electrochemical reaction rate at the active material-electrolyte interface varies significantly with the local mesostructure.
How does chemical performance affect the safety of lithium-ion battery?
It is first important to see the data on performance, sustainability, and aging.
Lithium-ion batteries provide particular advantages over conventional batteries, but they have some shortcomings. The power of electric vehicles requires a high energy density and a temporary power capacity. The batteries, however, must be able to be recharged quickly.
· There is a high cell voltage of about 3.0 to 4.2 V, the specific energy of about 90-240 Wh kg - 1, 200-500 Wh L-1 at the cell level, and a specific power up to 500 W kg – 1
· A high discharge speed (40C); a Fast charge speed (<3 h); and useful power; 80% DoD
· More than a thousand cycles; about 100% coulombic efficiency, Deep cycling possible;
· A low self-discharge rate of about 5-10% per month at 20°C
· A no memory effect; tolerates micro-cycles and no reconditioning required.
The use of the lithium-ion battery (LIB) has become widespread because its energy density has improved and the cost drastically decreased. In recent years, in particular, the application of LIB technology to electric vehicles and energy storage devices has been the subject of particular attention. However, LIB safety issues are considered to be one of the main obstacles to extending these application areas.
LIB's safety performance is primarily determined by the thermal stability of the lithium-ion battery materials. Safety tests, overloads, hotboxes, nails, crushes, and internal shorts are generally considered critical.
How does chemical performance affect the safety of lithium-ion batteries?
When the first lithium-ion battery was introduced by Sony in 1991, the possible safety risks were known. A reference to the previously released rechargeable lithium metal battery was a grim reminder to the discipline needed to be applied when one is using this high-energy battery system.
Due to the inherent instability of metallic lithium, research has focused on non-metallic lithium-ion batteries. Although the lithium-ion system has a slightly lower energy density, the system is safe and it is, however, prudent to take certain precautions during charge and discharge times.
Today, in the world of batteries, lithium-ion is just about the most effective and safest chemicals for batteries. There are about two billion cells produced every year.
There are two major types of chemicals used for lithium-ion cells, these are the cobalt and manganese (spinel). Cell phones, laptops, digital cameras, etc. use cobalt lithium ions for maximum battery life. But Manganese is the latest of the two chemicals and it provides superior thermal stability. It can withstand temperatures up to 250°C before it becomes unstable. Besides, manganese has a low internal resistance and can also provide high power when needed. These batteries are increasingly used to power tools as well as medical devices.
The major drawback of spinel is its lower energy density. As a general rule, a pure manganese cathode cell provides just about half of the cobalt capacity. Users of mobile phones and laptops would be disgusted that their device batteries are discharged at about half the time of their intended use. To find a viable compromise between the issue of high energy density, reliability, and good power delivery, lithium-ion battery manufacturers can get the metals mixed to get a better result. The cathode materials used are manganese, iron phosphate, cobalt, and nickel.
How to design a lithium-ion battery solution
In our world today, a world of portable electronics, there is hardly anyone who can go without the need to use a lithium-ion battery. Because these batteries power mobile phones, your smartwatches, our tablets, laptops, and even power our means of transportation like cars, bicycles, and planes, etc. the batteries become almost indispensable. Unfortunately, these batteries should be developed by professionals and in a factory, because of the hazard involved in the mixing and combining of chemicals. Making Lithium-ion cell production can be dangerous and may not be safe if there is an error in the manufacturing process, the mechanical design of the battery, as well as the electrical aspect of the product.
In conclusion, lithium is quite a volatile chemical and poses many safety concerns compared to other battery chemicals, but its high energy density, the long life, and its maintenance-free operation put it in a very attractive position to consumers and manufacturers of electronics. But then, these safety issues can be solved by selecting appropriate lithium battery cells, and an electrical and mechanical design suitable for proper cell management.
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