An experimental and numerical time-domain analysis of the early electric response of two kw-class Vanadium Redox Flow Batteries (VRFBs) under different state of charge, electrolyte flow and load is presented. The numerical analysis resorted to an equivalent circuit whose parameters were identified from electrochemical impedance spectroscopy measurements. Two discharge modes were investigated: natural discharge on resistors, to detect the spontaneous battery evolution, and discharge driven by an electronic load, forcing a galvanostatic evolution. Two different timescales were investigated in each discharge modes, namely 20 ms and 120 s. The millisecond mode revealed stack current and voltage swings in the is very short timescale (7 ms). This behavior suggests an initial turbulent electrochemical phase involving successive activations of vanadium species associated with coordination complexes at the positive electrode. In the latter mode, experimental and numerical results revealed that both stacks reached steady conditions much faster, in few hundreds of milliseconds. These results demonstrate that vanadium redox flow batteries are eligible for fast services in 50–60 Hz grids, provided the discharge current is driven in a current-source mode by proper interface power electronics. To the best of our knowledge, this is the first time that the fast time-domain response of large VRFBs is reported.

中文翻译：

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kW级全钒液流电池的快速响应


对两种千瓦级钒氧化还原液流电池 (VRFB) 在不同充电状态、电解液流量和负载下的早期电响应进行了实验和数值时域分析。数值分析采用等效电路，其参数通过电化学阻抗谱测量确定。研究了两种放电模式：电阻器上的自然放电，以检测自发电池演化；以及由电子负载驱动的放电，强制恒电流演化。在每种放电模式下研究了两种不同的时间尺度，即 20 毫秒和 120 秒。毫秒模式显示了极短时间尺度（7 毫秒）内的堆栈电流和电压波动。这种行为表明初始湍流电化学阶段涉及与正极配位络合物相关的钒物质的连续激活。在后一种模式中，实验和数值结果表明，两个堆栈在几百毫秒内更快地达到稳定状态。这些结果表明，只要放电电流由适当的接口电力电子设备以电流源模式驱动，钒氧化还原液流电池就可以在 50-60 Hz 电网中实现快速服务。据我们所知，这是第一次报道大型 VRFB 的快速时域响应。