摘要：水系鈉離子電池電容器具有成本低、功率大、安全性好等優(yōu)點，是下一代大規(guī)模儲能系統(tǒng)的理想選擇之一。本文采用Na0.44MnO2正極、活性炭（AC）負極、6 mol?L?1 NaOH電解液和廉價的不銹鋼集流體構(gòu)建了可充電堿性鈉離子電池電容器。由于Na0.44MnO2正極在堿性電解液中具有較高的過充耐受性，通過首次充電時的原位過充預(yù)活化過程可以解決半鈉化Na0.44MnO2正極和AC負極初始庫倫效率低的缺點。因此，AC||Na0.44MnO2可充電堿性鈉離子電池電容器具有優(yōu)異的電化學(xué)性能，在功率密度為85 W?kg?1時，能量密度達26.6 Wh?kg?1，循環(huán)10000次后容量保持率為89%。同時，在50 °C的高溫和?20 °C的低溫也具有良好的電化學(xué)性能。這些結(jié)果表明AC||Na0.44MnO2可充電堿性鈉離子電池電容器具備應(yīng)用于大規(guī)模儲能的潛力。

關(guān)鍵詞：鈉離子電池電容；堿性電解液；過充自保護；低成本；寬工作溫程

中圖分類號：O646

Abstract： As the most advanced battery technology to date， lithiumionbattery has occupied the main battery markets for electric vehiclesand grid scale energy storage systems. However， the limited lithiumreserves as well as the high price raise concerns about the sustainabilityof lithium-ion battery. Although sodium-ion battery is proposed as a goodsupplement to lithium-ion battery， expensive and flammable electrolytecomponents， harsh assembly environments and potential safety hazardshave limited the rapid development to a certain extent. The organicelectrolyte was replaced with an aqueous solution to construct a newtype of aqueous sodium ion battery capacitor （ASIBC）. It is of greatsignificance for next-generation energy storage system owing to its low cost， high power， and inherent safety. However，applicable ASIBC system is rarely reported so far. Here， a rechargeable alkaline sodium ion battery capacitors constructedby using Na0.44MnO2 cathode， activated carbon （AC） anode， 6 mol?L?1 NaOH electrolyte， and cheap stainless-steel currentcollector. Because of high overcharge tolerance of Na0.44MnO2 cathode in alkaline electrolyte， the shortcomings of the halfsodiumNa0.44MnO2 cathode and low initial Coulombic efficiency of AC anode can be resolved by in situ overcharging preactivationprocess during first charging. The available capacity of Na0.44MnO2 in half cell largely increased from ～40 mAh?g?1（neutral electrolyte） to 77.3 mAh?g?1 （alkaline electrolyte） due to broadened Na+ intercalation potential region. Thus， theAC||Na0.44MnO2 ASIBC delivers outstanding electrochemical properties with a high energy density of 26.6 Wh?kg?1 at apower density of 85 W?kg?1 and long cycling stability with a capacity retention of 89% after 10，000 cycles. The advantagesof the alkaline electrolyte for the AC||Na0.44MnO2 ASIBC can be concluded as follows： （1） through the in situ electrochemicalpre-activation process， the overcharging oxygen evolution reaction during first charging process can balance the adverseeffects of the half-sodium Na0.44MnO2 cathode and low initial Coulombic efficiency of AC anode on the energy density offull cell; （2） the overcharging self-protection function can promote the generated oxygen to be eliminated at anode duringovercharging， which improves the system safety; （3） the low-cost materials in alkaline environment can be scaled up toconstruct AC||Na0.44MnO2 ASIBC. In addition， the AC||Na0.44MnO2 ASIBC also possesses wide operating temperaturerange， achieving satisfied electrochemical performance at a high temperature of 50 °C and a low temperature of ?20 °C.Considering the merits of low-cost， high safety， no toxicity and environment-friendly， we believe the AC||Na0.44MnO2rechargeable alkaline sodium-ion battery capacitors have the potential to be applied to large-scale energy storage.

Key Words： Sodium-ion battery capacitor; Alkaline electrolyte; Overcharging self-protection; Low cost;Wide operating temperature range

1 Introduction

Recently， the influence of increasing consumption oftraditional fossil fuel and environmental pollution issue has ledthe worldwide researchers to develop advanced large-scaleenergy storage system. Among various types of current energystorage devices， electrochemical energy storage technology hasbecome the focus over the recent decade due to its advantages offlexibility， high energy conversion efficiency and simplemaintenance 1，2. The cathode and anode active substances of ionbatteries are compounds that can be reversiblyextraction/insertion. It has high energy density， but the powerdensity is insufficient and the cycle life is short， which restrictsthe development of the battery 3，4. Electrochemical capacitorswith high power density and long cycle life are known as animportant supplement to batteries in electrical energy storageapplications 5–7. However， the traditional electrochemicalcapacitors store charges via either ion adsorption-desorption orfast surface redox reactions， which requires a high weightpercent of electrolyte in full cells to support surface reaction oradsorption， consequently lowering the energy density 8，9. Tocombine the merits of both batteries and electrochemicalcapacitors， ion battery capacitor （IBC）， which is composed of abattery-type electrode （intercalation/deintercalation mechanism）and a capacitor-type electrode （physical adsorption/desorptionmechanism）， is thus proposed as a new type of energy storagedevice 10–12. Because the charge storage of the IBC is realizedthrough the transfer of only cations between cathode and anode，while the anions don't take part in， therefore only a small amountof electrolyte is needed in IBC just like in batteries.

Although most of the representative lithium-ion batterycapacitors （LIBCs） have demonstrated high energy density byemploying nonaqueous electrolyte， several critical issues alsoaccompanied， including high cost， environmental pollution andsafe risks relating to hazardous flammable organic electrolyte.Compared to organic electrolyte， aqueous electrolyte with highionic conductivity， low cost， non-toxic， and superior thermalstability shows a better application potential in LIBCs. However，the limited lithium resource and rising cost make LIBCs unableto meet the requirements of rapidly expanding large scale energystorage systems. In this case， aqueous sodium ion batterycapacitor （ASIBC） emerges as a promising candidate due to lowcostand abundance of sodium source and similar operatingprinciples to aqueous lithium-ion battery capacitor.

Constrained by the narrow operating voltage window andserious side reactions in aqueous battery， only a few cathodematerials are available for ASIBC. Among them， tunnel-type oxide， Na0.44MnO2 attracts the most attentions because of itshigh resource abundance， low cost， and environmentalcompatibility 13–15. Na0.44MnO2 possesses a unique 3D crystalstructure and abundant large S tunnels for sodium ions diffusion，showing exceptional cycling performance and remarkable ratecapability in both aqueous and nonaqueous electrolytes. Forexample， Whitacre et al. 16 fabricated a full cell using the activecarbon as the anode， Na0.44MnO2 as the cathode and 1 mol·L?1Na2SO4 as electrolyte， which demonstrates high-rate and longtermcycling performance. Although Na0.44MnO2 couldtheoretically insert/extract 0.44 Na+ with a capacity of 121mAh·g?1 during charge-discharge process， it can merely attain areversible capacity of 60 mAh·g?1 in full cells because only0.22Na+ could be extracted during the first charge， an even lowercapacity of ～40 mAh·g?1 is obtained in neutral solution （Na2SO4，NaNO3， NaCl） due to the limitation of the hydrogen ionsinsertion reaction 17. Therefore， much efforts have been made toimprove the utilization of Na0.44MnO2 in ASIBC 18，19.

When the neutral electrolyte is replaced by alkalineelectrolyte， the reversible capacity of Na0.44MnO2 can beincreased to 80 mAh·g?1 because the potential of hydrogen ionsinsertion shifts negatively in the alkaline electrolyte. Not onlythat， the alkaline electrolyte has some other advantages. Forexample， neutral system must use expensive current collectormetals （Ti， Ag， Au， etc.） to withstand the corrosion caused bypH alteration upon hydrogen or oxygen evolution reaction 20，21.Instead， alkaline system can just use cheap current collectors（stainless steel， nickel）， thus considerably reducing the cost ofASIBC. Most importantly， alkaline electrolytes can tolerateovercharging of the cell due to intrinsic oxygen-shuttleprotection mechanism， where oxygen evolution reaction mightbe used as an approach to improve the reversible capacity （～100mAh·g?1） in full cell 18，19，22. In this regard， it is feasible toconstruct ASIBC with higher energy density， lower cost andlonger-term lifetime based on Na0.44MnO2 cathode and alkalineelectrolyte.

In this work， a novel ASIBC was constructed by usingNa0.44MnO2 as cathode， active carbon （AC） as anode， 6 mol·L?1NaOH as electrolyte， and stainless steel as current collector. Theelectrochemical performance of the ASIBC was studied，including the reversible capacity， rate capability， cycling life，energy density， and power density. Also， the reaction mechanismwas detailedly explored. Furthermore， the performance ofASIBC at ?20 and 50 °C was investigated. It is believed that thelow-cost and long-life AC||Na0.44MnO2 ASIBC is a promisingcapacitor candidate for future energy storage devices.

2 Experimental

2.1 Material preparation

Rod-like Na0.44MnO2 was synthesized through a phenolformalin-assisted sol-gel method. A typical synthesis processwas as follows： CH3COONa （AR， ≥ 99.0%， Sinopharm） andMn（CH3COO）2 （AR， ≥ 99.0%， Sinopharm） with a stoichiometric ratio of 0.462 ： 1 first dissolved in mixed solution of deionizedwater and ethyl alcohol （1 ： 1 by vol.） with vigorous stirring at70 °C. After the solution stirred for 30 min， 0.3 g of phenol （AR，≥ 98.0%， Sinopharm） and 0.4 mL of formalin （AR， 37.0%–40.0%， Sinopharm） were added into the above solution insuccession， stirred for 6 h at 80 °C until vaporize both water andethyl alcohol to obtain pale pink gel precursor. After drying at100 °C for overnight in a vacuum oven， the precursor wasground into powder and then heated in a muffle furnace at 900 °Cfor 15 h with a heating rate of 2 °C to obtain the final products.

2.2 Characterizations

The crystallographic information was characterized by X-raydiffractometer （XRD， Bruker D8 ADVANCE， Germany） with aCu Kα X-ray source over a range of 2θ angles from 10° to 70° ata scan rate of 4 （°）·min?1. The morphology analysis wasconducted on scanning electron microscopy （SEM， ZEISSMerlin Compact， Germany） and transmission electronmicroscopy （TEM， JEM-2100FEF， Japan）.

2.3 Electrochemical tests

The Na0.44MnO2 electrodes were prepared via mixing activematerial， Super P and polytetrafluoroethylene emulsion with amass ratio of 8 ： 1 ： 1. Firstly， the active material and conductivecarbon were well mixed by grounding. And then， binder andisopropanol were added and stirred to form a gum-like mixture.The mixture was pressed on stainless steel net and dried at100 °C for more than 10 h. And the average mass loading ofelectrode is about 5 mg·cm?2. The AC electrodes were fabricatedusing same method except that Ketjen Black was selected asconductive carbon and the mass ratio of active material，conductive carbon and binder is 7 ： 2 ： 1.

The three-electrode system was assembled using Na0.44MnO2or AC as working electrode， zinc foil as reference electrode andcounter electrode， 6 mol·L?1 NaOH as electrolyte at roomtemperature in air. The electrochemical properties of sodium ionbattery capacitors were evaluated in 2032-coin cells withNa0.44MnO2 as cathode， AC as anode， non-woven fabric asseparator， and 6 mol·L?1 NaOH as electrolyte at same conditionswith three-electrode system. The mass ratio of cathode andanode is about 1 ： 0.9. The galvanostatic charge/dischargemeasurements are carried out using a LANDCT2001A （LandElectronic Co.， Ltd.， Wuhan， China）. Cyclic voltammetry （CV）measurements were conducted on the AutoLab PGSTAT 128 N（Eco Chemie， Netherlands）.

3 Results and discussion

The XRD pattern of Na0.44MnO2 powders synthesized via solgelmethod showed that the sample was crystallized in theorthorhombic structure （Pbam space group， JCPDS No. 27-0750） of the tunnel-type material （Fig. S1， SupportingInformation）， in agreement with previous results 23，24. Themorphology of Na0.44MnO2 sample was characterized by SEM，TEM and High Resolution Transmission Electron Microscope（HRTEM）. As shown in Fig. 1a，b， the sample is composed ofshort rod-like particles with a length range of 4–8 μm and widthchanging from 1 to 3 μm. The smaller length/width ratio isbeneficial for fast diffusion of sodium ion in crystal structure，which have been demonstrated by our previous work 22 and otherrelated reports 17，25. The TEM image in Fig. 1c shows rod-likestructure， which is consistent with the SEM results. The latticefringe with a spacing of 0.25 nm in HRTEM images （Fig. 1d） isclearly seen， corresponding to the （360） plane in theorthorhombic structure.

The electrochemical properties of Na0.44MnO2 electrode weretested in 6 mol·L?1 NaOH solution. And CV profiles，galvanostatic charge-discharge profiles， rate capability and longtermcycling stability of Na0.44MnO2 cathode in the potentialrange of 1.1–1.95 V （vs. Zn/Zn2+） are indicated in Fig. 2. Fourpairs strong redox peaks （1.22/1.15， 1.44/1.38， 1.75/1.70 and1.95/1.92 V） and two pairs weak peaks （1.28/1.23， 1.83/1.80 V）were observed in CV curve （Fig. 2a）， representing the differentinsertion/extraction processes of sodium ions into/from tunnelstructure. Symmetrical oxidation and reduction peaks reveal thelow electrochemical polarization of Na0.44MnO2 in alkalinesolution. The shape and relative position of CV peaks are prettyconsistent with those measured in nonaqueous electrolytes，implying the similar reaction mechanism in both electrolytes. Inaddition， at the current rate of 0.5C， the Na0.44MnO2 electrodecould release a reversible discharge capacity of 78.4 mAh·g?1（Fig. 2b）， corresponding to the intercalation of 0.285 Na+ in eachNaxMnO2 molecule （0.22 lt; x lt; 0.66） 26，27. And some complexand inconspicuous voltage platforms in good agreement with theCV profiles were obtained. The initial Coulombic efficiency was86.9%， which probably attributed to some inescapable sidereaction in aqueous electrolyte at a low current density， such asoxygen evolution reaction on the surface of electrode and currentcollector. The discharge capacities of Na0.44MnO2 electrode atvarious current rates were also investigated and shown inFig. 2c. When the current density was increased to 1C， 2C， 5C，10C， 20C and 50C， the capacity of Na0.44MnO2 electrode was 74，70.8， 67.4， 62.1， 53.9， 48.4 and 43.7 mAh·g?1， respectively， andstill capable of maintaining above 40 mAh·g?1， which is higherthan that in the neutral electrolyte. The impressive rate capabilitycould be attributed to the intrinsically fast sodium ion transferkinetics in tunnel-type oxide and high ionic conductivity （～400mS·cm?1） in 6 mol·L?1 NaOH solution. In Fig. 2d， at the rate of10C， Na0.44MnO2 electrode can gain an excellent capacityretention of 95.1% with Coulombic efficiency approaching100% over 100 cycles. These favorable electrochemicalperformances make Na0.44MnO2 as a potential cathode materialfor high-performance ASIBC.

Among those anode materials matched with alkalineelectrolyte， activated carbon （AC） is considered as one of thebest choices due to its superior cycling stability and wide varietyof raw materials. The electrochemical properties of AC anode in6 mol·L?1 NaOH were also studied using three-electrodemethods with zinc plates as both reference electrode and counterelectrode. Fig. 3a shows the CV curve of the AC electrode，exhibiting typical capacitive behavior in 6 mol·L?1 NaOHelectrolyte 28. The oxidative cutoff potential is limited to 1.1 V（vs. Zn/Zn2+） in view of the reductive cutoff potential ofNa0.44MnO2 cathode. The charge-discharge curves of the ACelectrode at 1C are displayed in Fig. 3b. Within the voltagewindow of 0.3-1.1 V， the AC electrode can release specificcapacity of 71.6 mAh·g?1， corresponding to a high specificcapacitance of 322.2 F·g?1， which is largely higher than that inneural electrolyte 16. The reversible capacity of AC electrodeunder different current densities was also tested. As shown in Fig. 3c， AC electrode delivered desirable rate capability with thereversible capacity of 73.1， 66.6， 62.8， 60.1 and 56.9 mAh·g?1 at1C， 2C， 5C， 10C and 20C. Even at a very high rate of 50C， thereversible capacity of 53.3 mAh·g?1 was reserved. When the current rate goes back to 1C， the capacity of 71.6 mAh·g?1 canbe restored， showing excellent rate capability andelectrochemical reversibility. The high performance of the ACelectrode is mainly due to the high ionic conductivity provided by alkaline electrolyte and the energy storage mechanism ofelectrical double-layer capacitor for the AC electrode 29.Similarly， the long-term cycling performance at the rate of 10Cis shown in Fig. 3d. It can be manifested that the AC electrodepossessed superior cyclic stability with a capacity retention of90.7% after 2000 cycles （reversible capacities for the 1st and2000th cycle is 64.6 and 58.6 mAh·g?1， respectively）. Theexcellent electrochemical performance of the AC electrodeprovides a strong guarantee for the construction of high-energydensity，high-power and long-term-lifetime AC||Na0.44MnO2ASIBC.

Based on the above discussion， both Na0.44MnO2 cathode andAC anode exhibit preeminent electrochemical performance，which inspires us to assemble a novel sodium ion batterycapacitorwith Na0.44MnO2 and AC. The typical CV curves ofthe AC||Na0.44MnO2 ASIBC are presented in Fig. 4a， and thecharge/discharge voltage range of AC||Na0.44MnO2 ASIBC iscontrolled between 0 and 1.65 V according to the working rangof cathode and anode （1.1–1.95 and 0.3–1.65 V， respectively）. Itis well known that Na0.44MnO2 can only release 0.22Na+ duringthe first charge process， which means that a capacity of merely50 mAh·g?1 can be utilized in full cells. For example， in 6mol·L?1 NaOH， the initial charge capacity of Na0.44MnO2electrode is 44.1 mAh·g?1， but the discharge capacity reaches78.2 mAh·g?1， nearly two times of charge capacity （Fig. S2）. Inorder to improve the available reversible capacity， someadditional procedures are needful， such as pre-cycling or presodiumwhich would increase manufacturing cost of Na0.44MnO2. As for the AC anode， the irreversible absorptionoccurs on AC at the first cycle would consume extra sodium ionsfrom cathode （Fig. S3）， thus leading to an extremely low initialCoulombic efficiency （ICE）. Obviously， the low initial chargecapacity for Na0.44MnO2 cathode and low initial Coulombicefficiency for AC anode are major obstacles for theirapplications. Fortunately， these problems could be perfectlyresolved by overcharging AC||Na0.44MnO2 full cell upon initialcharge process in alkaline electrolyte. The first charge curves ofsodium ion battery capacitor are shown in Fig. 4b. The initialcharge process could be divided into two steps： open-circuitvoltage to 1.25 V， and 1.25 to 1.6 V. For the first stage， sodiumions deintercalate from tunnel structure of Na0.44MnO2 cathodeand sodium ions in the electrolyte are absorbed on the surface ofAC anode simultaneously （Fig. 4c）. Through the calculation ofcharge capacity in this stage （51.4 mAh·g?1 for Na0.44MnO2），approximately 0.19Na+ extracted from the tunnel structure. Onbasis of the mass ratio of cathode and anode （1 ： 0.9）， thesolidated anode can be written as Na0.026C. Thus， theelectrochemical reactions of this charge step can be formulatedas follows：

Positive： Na0.475MnO2 ? 0.19Na+ ? 0.19e? = Na0.285MnO2

Negative： 7.34C + 0.19Na+ + 0.19e? = 7.34Na0.026C

For the second stage， the drastic oxygen evolution reactionemerges around cathode， and AC anode continued absorbingsodium ions （Fig. 4c）. Based on the charge capacity of 63.4mAh·g?1 for Na0.44MnO2 in this region， the electrochemicalreaction in second stage may be described as follows：

Positive： 0.23OH? ? 0.23e? = 0.0575O2 + 0.115H2O

Negative： 7.34Na0.026C + 0.23Na+ + 0.23e? = 7.34Na0.057C

From the above description of the electrochemical mechanismof AC||Na0.44MnO2， it can be clearly seen that the in situelectrochemical pre-activation process can easily resolve thematching problem between Na0.44MnO2 cathode and AC anode.Interestingly， the overcharging oxygen evolution mechanism ofNa0.44MnO2 cathode can provide self-protection function in thealkaline electrolyte because the oxygen generated can beefficiently reduced at the negative side， which is similar to that demonstrated in Cd//Ni and MH/Ni batteries 30，31.

Undoubtedly， oxygen evolution reaction disappeared afterinitial cycle because the Na+ ion amount of Na0.44MnO2electrode can be supplemented in the discharging process， whichcould be confirmed by incremental CE in subsequent chargingand discharging curves （Fig. 4d and the inset picture）. Fig. 4eshows typical charge-discharge curves of AC||Na0.44MnO2ASIBC at 1C in the voltage range of 0–1.65 V. TheAC||Na0.44MnO2 ASIBC delivered a reversible capacity of 70.5mAh·g?1 （based on the mass of Na0.44MnO2）. The rateperformance of full cell was also evaluated to explore itsfeasibility for high power applications （Fig. 4f）. The reversiblecapacities can reach 71.8， 65.9， 61.3， 57.7， 53.8 and 49.4mAh·g?1 at 1C， 2C， 5C， 10C， 20C， and 50C， respectively. Mostimportantly， when the current rate went back to 1C， thereversible capacity swiftly returned to 71.6 mAh·g?1 （nearly100% capacity recovery）， showing a strong tolerance for fastsodium ion storage. Moreover， the full cell also exhibitedtremendous cycling stability with a capacity retention of 89%after 10000 cycles at the current rate of 10C （Fig. 5a）. Theaverage Coulombic efficiency maintained above 99% all along，indicative of a highly reversible Na-ion transfer between cathodeand anode. Ragone plots of AC||Na0.44MnO2 ASIBC are shownin Fig. 5b. The power density and energy density can becalculated according to Pm = Im × U-， and Wm = Cm × U- . U- isthe average discharge voltage， Im is the current density， andCm refers to the capacity calculated based on the total weight ofcathode and anode. At a power density of 85 W·kg?1， an energydensity of 26.6 Wh·kg?1 could be obtained. When the powerdensity reaches 4.2 kW·kg?1， it still remains an energy density of18.0 Wh·kg?1. Compared with other aqueous Mn-based systems，AC||Na0.44MnO2 ASIBC is fairly competitive in energy densityand cyclic stability （Table 1）.

In order to further meet the requirement of practicalapplications， we evaluated the electrochemical performance ofthe AC||Na0.44MnO2 ASIBC at ?20 and 50 °C. The ratecapability under ?20， 25 and 50 °C is illustrated in Fig. 6a. At?20 °C， the discharge capacity of the AC||Na0.44MnO2 ASIBC reached 30.7， 27.7， 22.2， 17.8， and 14.5 mAh·g?1 at 1C， 2C， 5C，10C， and 20C， respectively. At 50 °C， the AC||Na0.44MnO2ASIBC exhibited higher rate capacities （42.7， 41.7， 38.9， 36.2and 32.2 mAh·g?1 at 1C， 2C， 5C， 10C， and 20C， respectively）due to faster sodium dynamics in electrode material， electrolyte，and electrode-electrolyte interface. When current rate returnedto 1C， the origin discharge capacities for three AC||Na0.44MnO2ASIBCs can be recovered， indicating outstandingelectrochemical reversibility. Additionally， the AC||Na0.44MnO2ASIBCs at ?20， 25 and 50 °C also showed excellent cyclingperformance with no obvious capacity fading within 150 cycles（Fig. 6b）. The wide operating temperature range may expand theapplication fields of AC||Na0.44MnO2 ASIBC.

4 Conclusions

In this work， we designed an alkaline sodium ion batterycapacitorwith Na0.44MnO2 cathode， AC anode， 6 mol·L?1 NaOHelectrolyte and investigated its electrochemical performance.The available capacity of Na0.44MnO2 in half cell largelyincreased from ～40 mAh·g?1 （neutral electrolyte） to 77.3mAh·g?1 （alkaline electrolyte） due to broadened Na+intercalation potential region. Thus， the fabricatedAC||Na0.44MnO2 ASIBC exhibited exceptional electrochemicalproperties with a high energy density of 26.6 Wh·kg?1 at a powerdensity of 85 W·kg?1， superior cycling stability of 89% capacityretention over 10，000 cycles and high-power capability， whichorigins from the use of alkaline electrolyte. Not only that， theadvantages of the alkaline electrolyte for the AC||Na0.44MnO2ASIBC are also reflected in the following aspects： （1） throughthe in situ electrochemical pre-activation process， theovercharging oxygen evolution reaction during first chargingprocess can balance the adverse effects of the half-sodiumNa0.44MnO2 cathode and low-ICE AC anode on the energydensity of full cell; （2） the overcharging self-protection functioncan promote the generated oxygen to be eliminated at anodeduring overcharging， which improves the system safety; （3） thelow-cost materials in alkaline environment can be scaled up toconstruct AC||Na0.44MnO2 ASIBC. In addition， theAC||Na0.44MnO2 ASIBC also possesses wide operatingtemperature range， achieving satisfied electrochemicalperformance at a high temperature of 50 °C and a lowtemperature of ?20 °C. Considering the merits of low-cost， highsafety， no toxicity and environment-friendly， AC||Na0.44MnO2ASIBC has good application prospects in the field of large-scaleenergy storage.

Author Contributions： Conceptualization， Z.C. and Y.C.;Methodology， Q.X.， S.L. and Y.Z.; Validation， Q.X.， P.S. andL.X.; Formal Analysis， Q.X.， Z.L.， B.Z. and H.L.; Investigation，Q.X.， B.W. and L.Y.; Resources， Z.C. and Y.C.; Data Curation，Q.X. and Y.Z.; Writing-Original Draft Preparation， Q.X.， Y.Z.and Z.C.; Writing-Review amp; Editing， Y.Z.， Z.C. and Y.C.;Supervision， Z.C. and Y.C.

Supporting Information： available free of charge via theinternet at http：//www.whxb.pku.edu.cn.

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