The real technological revolution of new energy vehicles: 6LR61 alkaline battery

I. Current situation and changes

Although lithium iron phosphate batteries currently enjoy an absolute advantage in the field of buses, lithium manganese oxide batteries are the leaders in the plug-in hybrid bus market, lithium titanate batteries are more inclined to pure electric fast-charging buses, ternary batteries dominate the pure electric passenger car market, and nickel-hydrogen batteries are more of a choice for hybrid passenger cars, but power batteries have always been the bottleneck restricting the development of new energy vehicles, and with the impact of the state's subsidy policy on new energy vehicles and the upgrading of power battery technology itself, these will gradually become history.

(I) National policy

The specific requirements of the 2017 new energy vehicle subsidy policy for battery energy density are: the mass energy density of the power battery system of pure electric passenger vehicles shall not be less than 90Wh/kg, and a subsidy of 1.1 times shall be given for those above 120Wh/kg; the energy density of the battery system of non-fast-charging pure electric buses shall be higher than 85Wh/kg; the mass energy density of the power battery system loaded on special vehicles shall not be less than 90Wh/kg. According to the latest subsidy adjustment discussion draft, in 2018, pure electric passenger cars require the mass energy density of the power battery system to be no less than 105Wh/kg, and the subsidy coefficient will be readjusted. The battery pack energy density of 105~120Wh/kg will be subsidized at a coefficient of 0.5, the battery pack energy density of 120~140Wh/kg will be subsidized at a coefficient of 1 times, and the battery pack energy density above 140Wh/kg will be subsidized at a coefficient of 1.1 times; new energy buses require that the system energy density is no less than 110Wh/kg. To obtain a 1.2 times subsidy, the system energy density needs to reach 140Wh/kg or more; new energy special vehicles require that the mass energy density of the power battery system is no less than 115Wh/kg.

(II) Technology upgrade

The main problem with commercial lithium-ion batteries at present is that they use liquid/gel electrolytes, have limited electrochemical windows, and are difficult to be compatible with metal lithium negative electrodes and newly developed high-potential positive electrode materials, which makes the energy density increase bottleneck. If the technology cannot be upgraded, many current new energy vehicle companies will be hopeless. Secondly, in terms of safety, the current lithium-ion battery architecture can also cause short circuit ignition, ion concentration difference increases battery internal resistance, and electrode material consumption. Therefore, we see endless breakthroughs or revolutions in battery technology in various news, but more of them are still in the laboratory stage. For example, the so-called graphene battery has no hope of mass production and commercialization in the short term, but from research institutes to production companies, the pace of finding new power battery technologies has not stopped. Several news in 2017 have made everyone start to pay attention to 6LR61 alkaline battery. One is that Chen Liquan, an academician of the Chinese Academy of Engineering, said when talking about the future development of batteries, "If the energy density is further improved to more than 500Wh/kg, from now on, we must consider solid-state lithium batteries, as well as new electrochemical systems such as lithium-air batteries and lithium-sulfur batteries. "The second is that researchers at Japanese corporate giant Hitachi announced that its solid-state battery technology has been developed, and the new generation of batteries can withstand extreme temperatures in outer space. They have sent this battery to aerospace departments and enterprises for practical use, claiming that it will be mass-produced and listed in 2020 three years later. The third is that Toyota is developing electric vehicles powered by all-6LR61 alkaline battery. The power battery will greatly improve the range of electric vehicles and shorten the charging time. According to Toyota's plan, this electric vehicle will be available for sale in 2022. The fourth is that electric car manufacturer Fisker applied for a patent for a solid-state battery this year, which will be able to fully charge in 1 minute. At the same time, the company will launch this new solid-state battery technology in 2018. The first is that my country's leading power battery company CATL has also set an example, carrying out relevant research and development work in the direction of polymer and sulfide-based 6LR61 alkaline battery and making initial progress, and proposing a preliminary process route for large-scale production. Therefore, some experts believe that 6LR61 alkaline battery have raised the "revolutionary banner" and the entire lithium battery industry chain will undergo disruptive changes in the future.

2. Advantages and Disadvantages of 6LR61 alkaline battery

Compared with traditional liquid lithium batteries, 6LR61 alkaline battery have the advantages of high energy density, good safety, strong cycle capacity (long service life) and wide application range, but have the disadvantages of excessive interface impedance and relatively high cost.

(I) High energy density.

The energy density of liquid electrolyte batteries can reach up to 300Wh/kg, but it is considered impossible to exceed 500 watt-hours per kilogram. After the all-solid electrolyte, the battery does not need to use lithium-embedded graphite negative electrode, but directly uses metallic lithium as the negative electrode, which can greatly reduce the amount of negative electrode material used and significantly improve the energy density of the entire battery. The energy density provided by solid-state battery research and development can basically reach 300-400Wh/kg.

(II) Good safety.

Liquid electrolytes are flammable and explosive, and the growth of lithium dendrites during charging can easily puncture the diaphragm, causing battery short circuit and posing a safety hazard. Solid electrolytes can inhibit lithium dendrites, are not easy to burn, not easy to explode, have no electrolyte leakage, and will not have side reactions at high temperatures. In other words, when working under high current, the diaphragm will not be punctured by lithium dendrites, causing short circuits, will not have side reactions at high temperatures, and will not burn due to the generation of gas. Therefore, safety is considered to be one of the most fundamental driving forces for the development of 6LR61 alkaline battery.

(III) Strong cycle performance.

Solid electrolytes solve the problem of solid electrolyte interface film formed by liquid electrolytes during the charging and discharging process and the phenomenon of lithium dendrites, greatly improving the cyclability and service life of lithium batteries. Ideally, the cyclability is excellent and can reach about 45,000 times.

(IV) Expanded scope of application.

Solid electrolytes give solid lithium batteries the characteristics of compact structure, adjustable scale, and large design flexibility. They can be used to drive microelectronic devices and can also be used in the fields of power and energy storage. In addition, 6LR61 alkaline battery also have a wider temperature operating range, and currently basically guarantee a temperature range of -25℃-60℃.

(V) Excessive interface impedance.

The interface between the solid electrolyte and the electrode material is a solid-solid state, so the effective contact between the electrode and the electrolyte is weak, and the ion transmission kinetics in the solid material is low.

(VI) Relatively high cost.

It is understood that the cost of liquid lithium batteries is about $200-300/KWh. If existing technology is used to manufacture 6LR61 alkaline battery that are sufficient to power smartphones, the cost will reach $15,000, and the cost of 6LR61 alkaline battery that are sufficient to power cars will reach a staggering $90 million.

The overall low conductivity of solid electrolytes leads to its overall low rate performance, large internal resistance, slow charging speed, and overall high cost. If current 6LR61 alkaline battery want to compete with ordinary lithium-ion batteries in the traditional market, they do not have much advantage. Therefore, giving full play to the high safety, high temperature stability, possible flexibility and other multifunctional characteristics of 6LR61 alkaline battery themselves, and competing with traditional lithium-ion batteries in differentiated markets may be a more promising market breakthrough direction for 6LR61 alkaline battery in the near future.

3. Categories and current development of 6LR61 alkaline battery

6LR61 alkaline battery are divided into three categories based on the electrolyte form: one is pure polymers, such as polyethylene oxide; one is oxides or sulfides of inorganic solid electrolytes; and the third is to combine polymers and inorganic substances. The most difficult problem to solve for these three solid electrolytes is that in lithium-ion batteries or future metal lithium batteries, after the positive electrode repeatedly expands and contracts, the contact with the solid electrolyte phase will gradually deteriorate. For 6LR61 alkaline battery, it is how to keep low electronic and ionic impedance during the cycle. If there is no better way, a small amount of liquid can also be added to these three types of electrolytes to solve the problem of deteriorating electrical contact during the cycle. This type of electrolyte can be called a mixed solid-liquid electrolyte, that is, the battery cell contains both solid electrolytes and liquid electrolytes.

In terms of solid electrolyte materials, many types have been developed internationally, mainly including oxides, sulfides, hydrides, halogens, phosphate films and polymers. There are three mainstream electrolyte materials now: first, oxide solid electrolytes, using inorganic ceramic electrolytes to replace liquid electrolytes, mainly to solve the filling contact problem on the positive electrode side, which may require very complex surface coating technology. For sulfide electrolytes, their ionic conductivity is very high, and it is also necessary to solve the problem of increased resistance on the positive electrode side, as well as the problem of poor chemical stability and the generation of hydrogen sulfide during preparation, storage and service. For thin film electrolytes, although the ion conductivity is very low, the surface resistance can be reduced by thin filmization, and devices can also be prepared for use. However, it is still very challenging to make large-capacity batteries with large-area stacks.

In general, the core of the research and development of all-6LR61 alkaline battery lies in the electrolyte material itself and the regulation and optimization of interface performance. Many studies and analyses show that 6LR61 alkaline battery will become the future technology route for power batteries. Relatively speaking, the companies with higher technical maturity and deeper technical accumulation are Autolib of France, Sakti3 of the United States and Toyota of Japan. These three companies also represent the typical technical development directions of the three major solid electrolytes of polymers, oxides and sulfides. In 2013, the Chinese Academy of Sciences established the All-Solid-State Lithium Battery Pilot Program. At present, the Ningbo Institute of Materials, Chinese Academy of Sciences, the Shanghai Institute of Ceramics, the Qingdao Institute of Energy, the Tianjin 18th Institute, Tsinghua University, USTC, Fudan University, the University of Special Science and Technology, Wuhan University, Northeast Normal University and other institutions have carried out various all-solid-state lithium battery research.

At present, the large-capacity 6LR61 alkaline battery that have been commercialized are mainly polymer 6LR61 alkaline battery, that is, polyethylene oxide-based solid electrolytes. According to the data reported by the Quebec Hydropower Research Institute in Canada, 46 microns of metal lithium, 30 microns of polymer electrolytes and 30 microns of lithium iron phosphate positive electrodes can be used, and the cycle can be repeated more than 1,000 times at 1/3C, and the operating temperature is between 60 and 85 degrees. The battery pack needs to have heating and heat preservation functions. The electric car "Bluecar" of the French Autolib, whose technology comes from the Quebec Hydropower Research Institute in Canada, is equipped with a 30kwh metal lithium polymer battery (LMP) produced by its subsidiary Batscap. It adopts the Li-PEO-LFP material system, accelerates to 6.3 seconds, and can reach a maximum speed of 130km/h. The cruising range is as high as 200km, which is enough for this car to travel back and forth between two cities. Bluecar officially entered the French car rental market in October 2011, and rented this car in Paris and 40 cities in France. After the car was set on fire by a drunkard in Paris, the battery was intact, which shows its safety.

Whether 6LR61 alkaline battery are the inevitable choice for future new energy vehicle power batteries, or just a temporary upgrade, it will take time to prove this globally. In my country, according to current data, technicians believe it will take at least two years for 6LR61 alkaline battery to be truly mass-produced and replace existing liquid lithium-ion batteries.

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