Can sodium ion battery replace lithium-ion battery

What is meant by sodium ion battery

Sodium ion battery is a secondary battery that mainly relies on sodium ions to move between the positive and negative electrodes. It works similarly to lithium-ion batteries, and both are called “rocking chair” batteries.

How do sodium ion battery work

The reversible deintercalation of sodium ions (Na+) between the positive and negative electrode materials is used to realize charge and discharge.

When charging, Na+ comes out of the positive electrode and is inserted into the negative electrode through the electrolyte through the battery separator, so that the positive electrode is in a high-potential sodium-poor state, and the negative electrode is in a low-potential sodium-rich state. The discharge process is the opposite. Na+ is released from the negative electrode, and re-embedded into the anode material through the electrolyte through the separator, so that the positive electrode returns to a sodium-rich state. In order to maintain charge balance, the same number of electrons are transferred through the external circuit during charging and discharging, and migrate between the positive and negative electrodes together with Na+, so that the positive and negative electrodes undergo oxidation and reduction reactions. The working principle of sodium-ion batteries is basically similar to that of lithium-ion batteries.

Composition of sodium ion battery

The main components of a sodium-ion battery are positive electrode, negative electrode, separator, electrolyte, and current collector. The structure and performance of the positive electrode and negative electrode materials determine the sodium storage performance of the entire battery. The positive and negative electrodes are separated by a diaphragm to prevent short circuit, the electrolyte infiltrates the positive and negative electrodes as a medium for ion circulation, and the current collector plays the role of collecting and transmitting electrons.

Cathode material

The positive electrode material mainly provides the ion source for the battery, which determines the energy density of the battery. At present, there are mainly three routes for positive electrode materials, namely layered transition metal oxides, Prussian compounds and polyanionic compounds. The former two are more widely used in commercial applications, and the typical representatives are Zhongke and CATL.

Negative material

The negative electrode material is the carrier of ions and electrons during the charging and discharging process of the sodium ion battery, which determines energy storage and release, and carbon-based materials are preferred.

Electrolyte

Electrolyte is a carrier for transporting ions and consists of electrolytes, solvents and additives. The electrolyte of sodium-ion batteries is very similar to that of lithium-ion batteries. Sodium salts are used instead of lithium salts, such as sodium perchlorate, and their cost is lower than that of lithium salts. Solvents are divided into aqueous and non-aqueous, and most of them continue to use ester organic solvents used in lithium batteries. In terms of additives, there is almost no difference compared with lithium-ion batteries.

Diaphragm

The diaphragm is used to separate the positive and negative electrodes, and on the other hand, it forms a charging and discharging circuit to allow ions to pass through. The technology of the diaphragm of sodium ion battery and lithium ion battery is similar. The PP/PE diaphragm widely used in lithium battery can be reused, but the sodium ion Batteries use more glass fiber separators, and the cost is lower.

Collector

The current collector of sodium electricity uses aluminum foil, and the cost is much lower than that of lithium electricity. The current collector is used to connect the powdered active material, collect and output the current generated by the active material, and input the electrode current to the active material. In graphite-based lithium batteries, because lithium reacts with aluminum to form alloys, copper foil must be used as a current collector for the negative electrode. In sodium ion batteries, sodium and aluminum do not react to form alloys, so both positive and negative current collectors can use aluminum foil, and the cost is much lower than that of lithium batteries.

What is the benefit of sodium ion battery

The technical feasibility of sodium-ion batteries can be considered from the following aspects.

Abundant sodium resources and low cost

Sodium and lithium are both alkali metal elements, and have similar physical and chemical properties. Both can be used as carriers for battery metal ions. In recent years, with the large-scale application of lithium-ion batteries, lithium resources have entered a supply-demand pattern that exceeds supply. The sodium resource has a higher element abundance in the earth’s crust and a lower cost.

Sodium ion battery has excellent performance

From the perspective of battery performance, sodium ion batteries are also excellent. The solvation energy of sodium ion is lower than that of lithium ion, that is, it has better interfacial ion diffusion ability. At the same time, the Stokes diameter of sodium ions is smaller than that of lithium ions, and the electrolyte with the same concentration has higher ionic conductivity than lithium salt electrolyte. Higher ion diffusion capacity and higher ion conductivity mean that the rate performance of the sodium ion battery is better, and the power output and acceptance capacity are stronger. The disclosed sodium-ion batteries have a charge-discharge rate of 3C and above, and the large-scale energy storage When applied when FM, it can be well applied.

High and low temperature performance is better

More than 70% of the capacity can be released at a low temperature of -40°C, and it can be recharged and discharged at a high temperature of 80°C, which will reduce the power quota of the air conditioning system at the level of the energy storage system such as Powerwall, home power storage etc. It can also reduce the online time of the temperature control system, thereby reducing the primary input cost and operating cost of the energy storage system.

Sodium ion batteries are safer than lithium batteries

The internal resistance of sodium-ion batteries is slightly higher than that of ternary lithium and lithium iron phosphate batteries. Once thermal runaway short circuit occurs, the short-circuit current of sodium ion batteries is relatively low, and the instantaneous heat generation is relatively weak. Also, sodium-ion batteries can be discharged to 0V. If the lithium battery is over-discharged, it will cause the negative electrode to absorb copper, and it is easy to pierce the diaphragm, causing internal short circuit and thermal runaway. The sodium battery will not catch fire or explode when it is acupunctured, so there is no problem at all.

Strong competitive advantage in environmental protection

Aluminum foil is used for the positive and negative electrodes in sodium batteries, the structure and components of the battery are simpler, and it is easier to recycle and reuse, making sodium batteries green and environmentally friendly. In contrast, the lead and acid components contained in lead-acid batteries will pollute the environment, so they are less environmentally friendly.

Although the core energy density and cycle life indicators of sodium batteries are weaker than those of lithium batteries, their cost advantage still makes them more economical in downstream application scenarios such as energy storage.

Taking lead-acid batteries, lithium iron phosphate batteries, ternary lithium batteries and sodium ion battery energy storage as examples, the model is used to calculate the full life-cycle cost of electricity of various batteries in peak-shaving application scenarios, taking into account power loss , the upper limit of the electricity cost of sodium batteries is 52.2%, 32.4%, and 54.3% lower than that of lead-acid batteries, lithium iron phosphate batteries, and ternary lithium batteries, respectively.

The future development of sodium ion batteries

China’s relevant policies have clearly defined the policy guidelines for vigorously developing commercial energy storage in the next few years. Compared with pumped water storage and compressed air energy storage, electrochemical energy storage does not need to consider geographical conditions at all. It can configure energy storage devices of any capacity in almost any location, and has a high charge and discharge efficiency. This is China’s next few years. One of the important reasons for vigorously developing electrochemical energy storage in recent years. At the same time, in order to achieve energy transformation and reduce or avoid curtailment of wind and light, China’s wind power photovoltaic industry must be equipped with energy storage equipment.

The market policy of electrochemical energy storage has brought development opportunities for sodium ion battery. The theoretical cost of sodium-ion batteries is lower, the operating temperature is wider, and the performance is more compatible with the energy storage environment. Its capacity retention rate at -20°C is greater than 88%, which means that compared with lithium-ion batteries, sodium ion batteries can effectively solve the problem of low efficiency of energy storage power stations in alpine regions.

Due to the huge scale of the energy storage market, even if lithium-ion batteries are currently used in various energy storage projects, their coverage is very small. That is to say, even if sodium ion batteries can be really applied in the energy storage industry after a few years, their market space will not be occupied by lithium-ion batteries too much, and they can still be loaded and applied on a large scale.