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Lithium ion energy storage power station
- Jun 08, 2018 -

Lithium ion energy storage power station

With the rapid development of electronic technology, more and more electronic devices are developing in the direction of thinness and flexibility. For example, Samsung and LG have R&D their own flexible folding screens and use them in foldable mobile phones, and other products which the current display components and circuits can be flexible and foldable. The biggest challenge currently is making the energy storage products can be folded. Traditional lithium-ion batteries, super capacitors and other products, not only bulky, but also can not fold, in when the volume changes too much, it may even cause a short circuit between the positive and negative electrodes, causing thermal runaway, leading to serious safety problems. Therefore, in order to adapt to the development of the next generation of flexible electronic devices, the development direction of lithium-ion batteries should also be flexibility and collapsibility.

For chemical power sources such as lithium-ion batteries and super capacitors, the greatest obstacle to achieving flexibility is the flexible design of current collectors, not only to ensure that the flexible electrodes have good mechanical properties, but also to have good electrochemical performance. 

In order to realize the flexible design of lithium-ion batteries, people have tried various ways, such as polymer batteries, cellulose-based batteries, and paper-based batteries. Studies have shown that the greatest impact on the folding performance of lithium-ion batteries is the electrodes and current collectors design, we will introduce the design and development status of the current flexible lithium-ion battery according to the technical direction.


Flexible paper battery


The paper has a rough surface and a high porosity, which is very suitable for the diffusion of ions. And the paper is easy to fold, so it is very suitable for the production of flexible lithium-ion batteries. In lithium-ion batteries, paper can be used either as a current collector or as a separator. However, it requires the modification of conventional paper, such as the application of a layer of multi-walled carbon nanotubes (SWCNTs) on the surface of paper to enhance paper. The conductivity of carbon nanotubes CNTs and cellulose composite made of flexible electrodes with good conductivity, of course, paper can also be used as a separator, in a recent report, multi-walled carbon nanotube film as a current collector, and The positive and negative electrode active materials were coated separately, and the paper was used as a separator and a supporting structure. The battery not only had good foldability characteristics but also had excellent electrochemical performance, especially the self-discharge performance of the battery, for example, the voltage was only decreased by 5.4 mV after storage for 350 H.


3D electrode flexible lithium ion battery


Lithium-ion battery capacity and rate performance are closely related to the active area of the electrode. Improvement of the electrode structure of the lithium-ion battery, enhance  the active area of the electrode, and improvement of Li+ diffusion kinetics conditions are important for improving the performance of the lithium-ion battery. The studies have illuminate that carbon textiles with a 3D structure have excellent electrical conductivity and excellent mechanical properties, and are therefore very suitable for replacing conventional metal current collectors. By growing a layer of ZnCo2O4 nanowire material on the surface of the carbon fiber, the specific capacity of the negative electrode can reach 1300 mAh/g. With this material as the negative electrode, the lithium ion battery made of lithium cobaltate as the positive electrode can also work normally under bending conditions. In the durability test, the battery can still work normally after bending several hundred times, but the main problem of the current carbon textile material is that the areal density is too high, which affects the energy density of the battery. If ultra-thin titanium foil is used as a current collector, coating a layer of active material with a 3D structure can significantly improve the battery's rate performance while ensuring good flexibility. Recently emerging graphene foam materials have attracted widespread attention due to their light weight, good electrical conductivity, and excellent foldability. For example, ultra-high magnification at 200C is achieved with a composite material of Li4Ti5O12 and graphene foam. Under this condition, a specific capacity of 86 mAh/g can still be obtained, and good foldability is maintained. At a bending radius of 5 mm, the capacity is only slightly reduced by 1%.

Solid state electrolyte


Traditional liquid electrolytes, due to thermal stability, poor mechanical stability and other issues, making the flexibility of flexible batteries has been greatly limited, and the plastic crystal electrolytes developed in recent years just solved the traditional poor stability of liquid electrolytes, The plastic crystal electrolyte is mainly composed of lithium salt and plastic crystals, and has good thermal stability and good ionic conductivity. However, the conventional plastic crystal electrolyte exhibits more liquid behavior at room temperature, resulting in its mechanical properties. Poor problems need to be reconstructed through corresponding transformation methods. By adding PET fibers in the plastic crystal electrolyte, the mechanical properties of the plastic crystal electrolyte can be significantly improved. LiCoO2 is the positive electrode, Li4Ti5O12 is the negative electrode, and the reinforced plastic is used. The crystal electrolyte is an electrolyte and a separator. The battery exhibits good bendability and can work normally even if it is wound several times. However, the thickness of the above-mentioned electrolyte is generally about 25 μm, and it is still unable to meet the design requirements for thinning and lithium ion batteries. Therefore, people study lithium-phosphorus-oxygen LPON materials, and the thickness of the solid electrolyte can be 2 um, and still can maintain a good electrochemical performance. performance.


Flexible Ion Battery Structure Design


For the design of flexible electronic components, the most restrictive of their design is the shape of the battery. Compared with the traditional battery, the linear lithium-ion battery has natural advantages in this regard, for example, LG Chem recently launched a Model, linear lithium-ion battery, the battery has a hollow spiral anode structure, modified non-woven membrane, and the external anode structure, the battery voltage platform 3.5V, capacity line density 1.0mAh/cm, the battery has Good bendability, and more importantly, the battery does not have to be placed inside the electronic device like a conventional lithium ion battery and can be placed anywhere, thereby greatly facilitating the use of the wearable device.

With the development of extensible electronic devices, flexible electronic devices not only have to withstand bending deformation, but also have to be capable of bending, stretching and compressing forms of force. Therefore, it is a great challenge to provide energy storage batteries for expandable electronic devices. The feasible technical solution is to carry out a unitized design, that is, to divide the traditional whole lithium-ion battery into a single small unit, usually an elastic silica film as a substrate, and different small units are connected to each other. Through testing, the battery prepared by this method can be extended to more than 300%, and still can maintain good electrochemical performance.

At present, the design of flexible lithium-ion batteries is still only the initial stage, and there are still many problems that need to be solved. For example, how to improve the specific energy and safety performance of lithium-ion batteries under the premise of guaranteeing good mechanical properties of batteries requires electrolytic design. With the electrolyte design, and battery structure design can be completed together.