Study on retaining good classification performance when reducing training effort is valuable for the development of brain-computer interface (BCI). In this paper, an improved self-training algorithm using only a small number of labeled samples is adapted for motor imagery EEG classification. Unlike the traditional self-training algorithm that uses only one classifier, an additional classifier is introduced in the improved version for sample selection, which helps to reduce the error reinforcement, increases the classification accuracy, and improves the convergence in the iteration process. Experiment results show that the improved self-training algorithm outperforms its prototype in the two-class classifications. Even for the subjects who have performance degradation when using the traditional self-training algorithm, the improved algorithm still increases the classification performance iteration by iteration. We also compare the improved method with a supervised method which uses all the training data, and there are no significant differences in classification accuracy. It can achieve a little higher performance comparing with an existing semi-supervised method on the same data.

Conductive polymer polypyrrole (PPy)-coated lithium-rich manganese-based Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ (LMNCO) nanotube cathode materials were synthesized by electrospinning and subsequently subjected to low-temperature vapor-phase polymerization. X-ray diffraction (XRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) results confirm that the successful coating of the PPy layer (~2 nm) on the surface of LMNCO nanotubes did not destroy their morphologies or structures. Electrochemical tests indicate that the electrochemical performance of PPy-coated LMNCO nanotubes has been significantly enhanced. At a rate of 1 C, the discharge capacity of the PPy-coated LMNCO cell is 200.1 mAh g⁻¹, and the capacity retention is 99% after 120 cycles. This excellent stability is attributed to the inhibition of side reactions and the protective function of the tubular structure due to the PPy coating layer. Additionally, the rate capability is also improved at a high current density due to the higher electronic and ionic conductivity.