Li has an atomic weight of 3, and its ultra-light weight makes it very suitable as a carrier in chemical batteries, which can greatly increase the energy density of batteries. At present, the weight energy density of lithium ion batteries has reached 250Wh/kg or more, and Going towards the goal of 300Wh/kg, many power battery manufacturers have already claimed that the specific power of their own battery has reached more than 300Wh/kg.
If we take a brief look at the periodic table of chemical elements, we can see that there is a lighter element above Li—H element. The H element is the lightest in nature, and is the most common element in the universe (not considered H isotopes). There is only one proton in the nucleus of element H. An electron outside the nucleus rotates around the nucleus. When the H atom loses electrons, it becomes a bare proton with a positive charge. Its weight is only Li+. 1/7, it can be said that it is a near-perfect carrier for chemical batteries.
However, the application of hydrogen ion batteries has an insurmountable obstacle - H element is usually in the form of H2 gas, unlike Li element in the form of solid metal, which greatly increases the difficulty of H element storage (if we can prepare Metal hydrogen, I am afraid that the entire energy storage industry will be subverted. Therefore, the current common H+ carrier for chemical batteries is mainly hydrogen fuel cells, H elements are stored in the form of H2 or hydrogen storage metal in the battery outside When used, the H2 enters the porous anode inside the fuel cell, loses electrons to H+, O2 in the air acquires electrons at the porous cathode, and then combines with H+ in the electrolyte to generate water. Recently, Shahin of Australia's Royal Melbourne Institute of Technology Heidari combines hydrogen storage materials with fuel cells to develop a 'proton' battery that can be recharged. Porous carbon electrodes made of phenolic resin and Teflon can be 1 wt% H, and reactivated during discharge Released 0.8% of H, showing a high hydrogen storage capacity and reversibility.
The proton battery is a hybrid energy storage battery that combines the advantages of fuel cells and energy storage cells. When charging, H2O will be electrolyzed into H and O. H will be combined with hydrogen storage material through the perfluorosulfonic acid membrane. In order to avoid the generation of H2. H stored in the process of discharge will lose an electron to generate H +, into the solution (as shown below). Proton battery was first proposed by Andrews and Seif Mohanmmadi, with Ni, Co Alloys of La and Bismuth are used as hydrogen storage materials and need to use flowing water to provide enough H sources, hence also called 'proton flow' batteries.
The efficiency of the early 'proton flow' cell was very low, and the hydrogen storage metal was able to store 0.6% H by weight during charging, but only 0.01% by weight could be released during the discharge. This is mainly due to the difference between H and metal elements. The strength of the chemical bond is too large, resulting in the storage of H can not be released again. In addition, due to the presence of Ni atom catalysis, resulting in the charging process, in addition to H will be stored in the alloy, a considerable part of H will The appearance of H2 causes the coulombic efficiency of the battery to be too low. In addition, the high price of the hydrogen storage alloy also limits its promotion and application. In 2002, Jurewicz et al. found that the activated carbon has an electrochemical hydrogen storage capacity (up to 1.8wt%). , To solve the 'proton flow' battery hydrogen storage problem provides a new idea (the following table for some hydrogen storage capacity of carbon materials, hydrogen storage capacity).
Following the above thinking, Shahin Heidari improved the 'proton-flow' battery design proposed by Andrews and Seif Mohanmmadi, replacing the hydrogen storage alloy with a porous carbon electrode, and added a strong acid solution as a proton to the perfluorosulfonic acid solid electrolyte. The conductor, which significantly improves the performance of the 'proton' battery, is shown in the figure below.
In the battery designed by Shahin Heidari, two types of hydrogen storage negative electrodes were used, in which the content of PTFE was 10% by weight and 30% by weight, respectively. The constant current charging curve of 80mA for both batteries is shown in the figure below. 30wt% of PTFE The initial charge voltage of the battery is 0.95V, and it reaches 1.85V after 1700 seconds. The initial voltage of the 10% PTFE battery is 1.05V, and it reaches 1.85V after 2000 seconds. Before the voltage reaches 1.85V, the negative electrode generates H2. The phenomenon is not obvious, but the speed at which the anode produces H2 after 1.85V increases greatly. At this point, we can also see many small fluctuations in the voltage curve. This is mainly because the H2 bubbles begin to form on the surface of the electrode ( When the H2 bubble covers the surface of the electrode, the voltage begins to rise. When the H2 bubble leaves, the voltage drops). The rate of H2 production finally reaches about twice that of O2, indicating that H cannot be fully stored in the porous electrode at this time. The process also ends here.
After the 'proton' battery was fully charged, the discharge test was performed after standing for 30 min. In order to fully release H present in the porous electrode, Shahin Heidari formulated two types of batteries with PTFE content of 30 wt% and 10 wt%. A step current discharge system (shown below) was used to reduce the polarization. Experiments have shown that the electrode containing 10% PTFE has the best performance, can store 1 wt% of H during charging, and can be released during discharge. 0.8wt%, showed good reversibility.
From the above introduction, we can easily see that the so-called 'proton' battery is actually a product that combines the fuel cell and the hydrogen storage material. The H generated during the charging process is stored in the hydrogen storage material. O2 enters the air, and the discharge process is completely in accordance with the mode of the fuel cell. Although this is a very good design concept, the 'proton' battery is still far from the lithium-ion battery in terms of performance under current technical conditions. Large gaps, such as the volume energy density, proton battery is only about 100Wh/L, but the current lithium-ion battery volume energy density up to 600Wh/L, in addition to the 'proton' battery charging efficiency is also very doubted Xiaobian, During the charging process, a large amount of H2 will be generated. These H2 will eventually leave the electrode and will not be stored in the electrode. This leads to a very low coulombic efficiency of the 'proton' battery. In general, the 'proton' battery The idea is very good. The H element has a wide range of sources and low prices. However, from the current state of the art, the 'proton' battery needs a long way to go. Only the above problem is truly solved. The 'proton' It is only possible for batteries to challenge the status of lithium-ion batteries.
