Lithium metal batteries, with their high energy density, have shown broad application prospects in consumer electronics and electric vehicles. However, traditional lithium metal batteries use lithium foil as a negative electrode, which is not only costly, but also has certain safety risks in the manufacturing process. In this context, negative-free lithium metal batteries came into being, which use only the collector fluid as the negative material, theoretically enabling higher energy density and lower cost. However, the problem of lithium deposition on the collector has been a key factor limiting the development of negative-free lithium metal batteries. Lithium is deposited inhomogeneous on the collector fluid, which is easy to produce dead lithium and lithium dendrites. These problems can shorten the battery cycle life and may cause safety hazards such as short circuit and thermal runaway. For example, in some existing technologies, lithium metal will preferentially deposit on the surface of the fluid collector, blocking the holes, and then forming lithium dendrites, affecting the battery performance. Recently, BYD’s patent for a negative-free lithium metal battery was made public, proposing an innovative fluid collector to solve this problem.
In the patent, BYD offers an innovative fluid collector containing lipophilic metal elements (such as lithium, sodium, magnesium, aluminum, etc.) and inert metal elements (such as gold, silver, platinum, titanium, etc.), with a porous cavernous structure with a thickness of 10-100 μm and a porosity of 30-80%. It is unique in that from one side of the fluid collection to the other, the lithiophile gradually increases and the pore size gradually decreases.
Structural characteristics:
The porous structure of the fluid collection is composed of interconnected ligaments (enriched by inert metal elements) and interconnected holes (formed by dissolution or precipitation of lithiophilic metal elements), forming a bicontinuous distribution structure. From one side of the fluid collection to the other, the average ligament size gradually decreases from 0.1-10 μm to 10-200 nm. This structure is conducive to the infiltration of electrolyte, improve ion/electron conductivity, and ensure the electrochemical consistency of the battery. At the same time, the curvature of ligaments and pores can increase the specific surface area and reduce the actual current density during lithium deposition, thus easing the growth of lithium dendrites. Preparation method: Corrosion solution (such as hydrochloric acid and ammonium chloride mixture, molar ratio 1:(3-6)) along the thickness direction of alloy foil (such as brass foil), corrosion mode can be selected in chemical dealloying single-side etching method, etching temperature control at 50-200 ℃ (preferably 80-120 ℃). The etching time is 8-120h (preferably 24-48h), and then after cleaning, drying and other processing steps, the final fluid collection is obtained. Battery application: The collector fluid is applied to a non-negative lithium metal battery, which also includes a lithium inset positive electrode material (such as LiNi_0.80Co_0.10Mn_0.10O_2, etc.), a positive collector fluid, a diaphragm and an electrolyte.
1. Orderly deposition: the Liphilic gradient of fluid collection encourages lithium ions to be preferentially deposited at the bottom, achieving bottom-up growth mode and effectively avoiding the generation of dendrites. The pore size gradient makes the internal small holes guide the dense deposition of lithium ions, while the large surface holes ensure the rapid ion transport and improve the charge and discharge efficiency of the battery.
Performance improvement:
Cycle life extension: Experimental data show that the cycle life of the battery using the new fluid collector is significantly improved. For example, for the battery S1 assembled in Embodiment 1, the number of cycles corresponding to 80% of the remaining capacity can reach 96; In contrast, the DS1 battery, which uses ordinary copper foil as a fluid collector in proportion 1, has only 34 cycles, and the new fluid collector improves the battery cycle life by 1.8 times.
Improved capacity retention rate: The battery in the embodiment has a higher initial discharge capacity and a slower capacity decay rate during the cycle. For example, the S2 initial discharge gram capacity of embodiment 2 is 193.9mAh/g, which can still maintain a relatively high capacity after multiple cycles, showing good capacity retention performance.
Enhanced safety performance: From the point of view of the negative electrode thickness change rate after the battery cycle, the new fluid collector significantly improves the safety performance of the battery. The DS1 negative electrode thickness change rate of ratio 1 is as high as 35.3%, which may lead to safety problems such as bulging during the use of the battery; However, the change rate of S4 negative electrode thickness in Embodiment 4 is only 9.2%, which is small, effectively reducing the risk of safety problems caused by battery negative electrode expansion.
