Rechargeable　batteries　electrodes　are　mainly　classical　oxides　with　single　structure,　but　their　performance　is　insufficient　to　meet　the　growing　energy　storage　needs　of　modern-society.　Recently,　composite-structure　materials　with　great　improvements　in　electrochemical　performance　have　been　developed.　However,　little　research　has　been　conducted　on　these　materials　with　regard　to　adjusting　their　structures　and　further　controlling　their　electrochemical　performance.　Herein,　composite-structure　Na2/3Ni1/3-xFexTi2/3O2　(0　＜=　x　＜=　1/3)　electrodes　for　sodium-ion　batteries　were　designed　on　the　basis　of　results　from　in-situ　high-temperature　X-ray　diffraction.　Triphase　compositions　of　P2-Na2/3Ni1/3Ti2/3O2,　tunnel-Na2.65Ti3.35Fe0.65O9,　and　tunnel-NaFeTiO4　were　prepared,　and　Na+　insertion/extraction　in　different　structures　was　observed　using　in-situ　electrochemical　X-ray　diffraction.　An　optimum　electrode　with　46%　P2-structure　presented　the　best　comprehensive　performance:　105　mAh　g(-1)　initial　reversible　capacity　along　with　86.5%　capacity-retention　after　1500　cycles.　This　work　opens　a　new　field　for　designing　and　adjusting　composite　electrodes　for　better　electrochemical　performance,　not　limited　for　sodium-ion　batteries　but　also　for　other　advanced　battery-systems.