A recent news release from Washington State University (WSU) heralded(1) that “WSU and PNNL (Pacific Northwest National Laboratory) researchers have created a sodium-ion battery that holds as much energy and works as well as some commercial lithium-ion battery chemistries, making for a potentially viable battery technology out of abundant and cheap materials”. Naturally this news created a lot of excitement in the battery community and the general public to the extent that some even suggested that a new sodium (Na)-ion battery would replace the expensive lithium-ion batteries. The excitement encouraged this author to take a deep dive into the original WSU/PNNL reports in ACS Energy Letters,(2,3) examine the state of the art of Na-ion battery technology, and compare it to the mature and ubiquitous lithium (Li)-ion batteries. This Viewpoint, borne out of this enquiry, seeks to answer the question “how comparable are sodium-ion batteries to lithium-ion counterparts“. It is not a comprehensive review of Na-on batteries as several such reports have appeared elsewhere recently.(4−6) The chemistry and electrochemistry of electrode materials for Na-ion batteries are sufficiently different from that of their Li-ion counterparts that candidates suitable for practical batteries have become available only recently. Figure 1 displays the schematic of a Na-ion battery cell. It has a structure similar to that of Li-ion batteries.(7) Laboratory test cells and representative prototype cells have been built and evaluated with hard-carbon anodes and cathode materials selected from layered transition metal oxides, transition metal fluorophosphates, and Prussian blue and its analogues.(4,5,8−10) Figure 1. Schematic representation of a Na-ion battery cell. Layered transition metal dioxides, NaMO₂, where M = Fe, Ni, Mn, Co etc., exist in O3 and P2 crystallographic versions. In the O3-NaMO₂ phase, Na resides in octahedral sites, while in the P2-phase Na is in prismatic sites. The electrode reactions in a Na-ion battery utilizing hard-carbon (C₆) anode and a layered transition metal oxide, NaMO₂, cathode are depicted in eq 1. The discharged electrodes are on the right-hand side of eq 1.(1)The NaCoO₂ cathode, like LiCoO₂, is initially brought into the Na-ion cell in the discharged state, and the cell is activated by charging first to form the Na intercalated anode and Na deintercalated cathode in the fully charged cell. The charge and discharge voltage versus capacity curves of Li/Li_1–xCoO₂ and Na/Na_1–xCoO₂ half-cells compared in Figure 2(4) reveals stepwise voltage profiles for the Na cell. They reflect the multiple phase changes of the NaCoO₂ crystals as Na is deintercalated from it to form Na_1–xCoO₂ during charge, and vice versa during discharge. Both LiCoO₂ and NaCoO₂ have the same O3 crystal structure consisting of CoO₂ slabs alternately accommodating Li⁺ or Na⁺ ions between the slabs along the c-axis of the A_1–xCoO₂ crystal (where A = Li or Na). The crystal structure changes of NaCoO₂ in a Na cell begin with the removal of Na during the first charge. Sodium ions in the O3-type phase are originally stabilized at edge-shared octahedral sites within the MO6 octahedra. When Na⁺ ions are partly extracted from the O3-phase, those Na⁺ present at prismatic sites become energetically stable and transform the crystal to a P3-phase by the sliding of MO2 slabs without breaking M–O bonds. This conversion between the prismatic and octahedral phases by sliding the MO6 slabs occurs in just about all the layered transition metal oxides when they are used as cathodes in Na-ion batteries. The result is multiple voltage plateaus in the cell’s voltage versus capacity curves reflecting the phase changes (Figure 2). Mixed metal oxide cathodes exhibit additional voltage plateaus in Na-ion cells, reflecting the oxidation states of the different metals being reduced and oxidized during cell discharge and charge. The NaCoO₂ electrode has a rechargeable capacity of about 150 mAh/gram at an average voltage of 3 V. Layered transition metal dioxides investigated as Na-ion battery cathodes include NaFeO₂, NaNiO₂, NaCrO₂, NaVO₂, and NaTiO₂ and mixed metal dioxides derived from them such as NaFe_1/2Co_1/2O₂, NaNi_1/3Fe_1/3Co_1/3O_2, NaNi_1/3Fe_1/3Mn_1/3O₂, and NaNi_1/4Fe_1/4Co_1/4Mn_1/4O₂.(4,5,8,9) The WSU/PNNL Na-ion battery which motivated the writing of this Viewpoint utilizes a mixed metal oxide of the composition NaNi_0.68Mn_0.22Co_0.10O₂ with an O3-type layered crystal structure.(2) Figure 2. Comparison of charge–discharge curves of Li/LiCoO₂ and Na/NaCoO₂ half-cells. Schematic illustration of Li(Na)CoO₂ crystal is also shown (reprinted from ref (4), copyright 2014 American Chemical Society). A variety of metal phosphates and fluorophosphates have also been studied as Na intercalation cathodes for Na-ion batteries. Among these are NaFePO₄ (triphylite-type), Na₂Fe(P₂O₇), Na₄Fe₃(PO₄)₂(P₂O₇), Na₂FePO₄F, and Na/Na₂[Fe_1/2Mn_1/2]PO₄F.(4,5) Other metal phosphates examined include Na₃V₂(PO₄)₂F₃, Na₃V₂(PO₄)₃, and Na₄Co_2.4Mn_0.3Ni_0.3(PO₄)₂P₂O₇ (see Figure 23 in ref (5)). Among these, Na₃V₂(PO₄)₂F₃ showed reasonable performance in Na half-cells at room temperature with a reversible capacity of about 135 mAh/g at an average voltage of 3.8 V. Miscellaneous cathode materials investigated as Na-ion battery cathodes include Prussian blue and its analogues, KFe₂(CN)₆ and MnFe(CN)₆, and the iron(III) system Fe₂(CN)₆ without alkali metal ions.(4) They show reversible capacities of 80–120 mAh/g in Na half-cells at voltages of 3–3.5 V. A Prussian blue analogue material, Na_1.92Fe₂(CN)₆, described as Prussian white, has shown a discharge capacity of 160 mAh/g at low rates with good rechargeability in a Na half-cell.(10) A drawback of Prussian blue and its analogues is low density. For example, Prussian blue has a density of 1.8 g/cm³, which would provide lower volumetric energy densities for Na-ion batteries, compared to those using transition metal oxide cathodes of the same specific capacity (in mAh/g). The anode material in most studies has been hard-carbon, although other low-voltage Na intercalating materials such as Na₂Ti₃O₇, Na₃Ti₂(PO₄)₃, and Na alloys have been investigated.(4−6,11) A hard-carbon anode has a practically useful reversible capacity of about 250 mAh/g, corresponding to the formation of Na_0.67C₆ at an average voltage of 0.25 V versus Na/Na⁺.(4) Electrode materials useful for anodes in Na-ion batteries should have low Na intercalation and deintercalation voltages, preferably below 0.5 V versus the Na/Na⁺ electrode, and capacities exceeding 250 mAh/g. Note that it is the Na deintercalation voltage of the anode material that is important because Na⁺ ions are deintercalated from the anode and intercalated into the cathode during discharge of a Na-ion cell. The difference between these two electrode voltages is the cell voltage. The choice of the electrolytes is important for developing practical Na-ion batteries. Organic carbonate solvent-based electrolytes containing sodium salts such as NaPF₆, NaN(SO₂CF₃)₂, and NaClO₄ are used together with small amounts of additives to stabilize the anode and cathode during cycling.(8) The aforementioned WSU/PNNL cell used the additive bis(2,2,2-trifluoroethyl) ether (BTFE), while other studies have used fluoroethylene carbonate (FEC).(12) Typically, mixed organic carbonate solvents selected from ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethylmethyl carbonate(EMC) are used to produce electrolytes that provide optimal discharge and charge over a wide temperature range, thermal stability, high rate capability, and long cycle life and shelf life in Na-ion batteries.(8) Sodium-Ion Battery Prototypes. An 18650-size cell reported by the French research agency CNRS CEA appears to be the first Na-ion battery commercial product.(13) Note that the number 18650 comes from the dimensions of a cylindrical cell in a metal container having 18 mm diameter and 65 mm height. In the case of Li-ion batteries, an 18650 cell is the most advanced commercial cell in terms of engineering and chemistry. The CEA Na-ion cell reportedly has a specific energy of 90 Wh/kg and was cycled more than a thousand times. However, no information was provided on electrode and electrolyte materials used, cell capacity, voltage, and cycling parameters. The cell was claimed to be have high-power capability. We can estimate a few additional specifications of this cell as follows. First, assume that the cell has a weight of 46 g similar to the weight of a commercial 18650 Li-ion cell.(7) Then, the energy of the 18650 Na-ion cell is 4.14 Wh. The volume of the 18650 cylindrical metal housing is 16.5 mL. Therefore, the volumetric energy density of this 4.4 Wh Na-ion cell is 250 Wh/l. We can now estimate from the 4.14 Wh energy and an average voltage of 3 V, as found in many Na-ion cathode materials, that the CEA 18650 Na-ion cell has a capacity of 1.38 Ah (4.14 Wh divided by 3 V). Now let us take a look at the Na-ion battery described in the Washington University/PNNL announcement.(1,2) It has a hard-carbon anode and utilizes O3-NaNi_0.68Mn_0.22Co_0.10O₂ as the cathode material. At the C/10 rate of 0.25 mA/cm², the cell delivered a capacity of 184 mAh/g based on the hard-carbon anode and 141 mAh/g based on the metal oxide cathode. A pouch cell of 60 mAh capacity exhibited a specific energy of 290 Wh/kg based on the active materials which the authors extrapolate to a practical specific energy of 156 Wh/kg. This estimated value of the WSU/PNNL Na-ion battery is much higher than what was actually found in the aforementioned CEA 18650 cell. It should be noted that the 156 Wh/kg is an extrapolated value from the specific energy of 290 Wh/kg determined for electrodes, using a conversion factor of 55%, taking into account the masses of the electrolyte, electrode current collectors, separator, metal container, and other inert materials, as found in commercial 18650 Li-ion cells. We can estimate the practical specific energy for another Na-ion cell, fabricated from the Na₃V₂(PO₄)₂F₃ cathode mentioned earlier(5) and hard-carbon anode. This cell has a voltage of 3.5 V, and its specific energy is 295 Wh/kg based on the electrode materials. At 50% laboratory cell to commercial cell conversion efficiency, a practical cell from this chemistry would exhibit about 150 Wh/kg, similar to the estimated value for the WSU/PNNL cell. It is interesting to note that Alistore-European research agency(14) built an 18650 cell using an Na₃V₂(PO₄)₂F₃ cathode and a hard-carbon anode, and it demonstrated 75 Wh/kg and 4000 cycles at the 1C rate. Clearly, the specific energy of this 18650 cell is only half of the value estimated above from electrode capacities in lab cells. Realistically, considering the reversible capacities and voltages of the numerous cathode materials examined and the specific capacity of hard-carbon anode of about 250 mAh/gram, a specific energy of 100–150 Wh/kg appears to the best that can be expected for a fully developed Na-ion battery. From the rate capability information available for the electrode materials in Na battery cells and the reported Na⁺ diffusion coefficients in cathode and anode materials,(15) Na-ion batteries can be expected to provide good rate capability comparable to that of Li-ion batteries. An important question to answer for this discussion is “how do Na-ion batteries compare to their Li-ion counterparts” in terms of energy densities, cost, applications, and overall consumer acceptance. How Do Sodium-Ion Batteries Compare to Their Lithium-Ion Counterparts? In order to answer this question let us first take a look at the specific energies and energy densities of commercial Li-ion batteries. The highly engineered 18650 size cells are the most appropriate for this comparison. Specific energies of 18650 size commercial Li-ion batteries with graphite anode (∼350 mAh/g capacity) and different types of cathodes are presented in Table 1.(7) The cells with the layered transition metal cathodes LiCoO₂ (LCO), LiNi_0.33Mn_0.33Co_0.33O₂ (NMC), and LiN_0.8Co_0.15Al_0.05O₂ (NCA) have capacities of 2.4, 2.4, and 3.6 Ah, respectively, which convert to specific energies of 206, 210, and 285 Wh/kg, respectively, and to volumetric energy densities between 530 and 785 Wh/l. The cells with LiFePO₄ and LiMn₂O₄ cathodes have lower specific energies of about 130 Wh/kg and volumetric energy densities of around 330 Wh/l. Considering the reversible capacities of the various Na intercalating metal oxide and metal phosphate cathode materials presented in this account, we can project that 18650 size Na-ion cells utilizing these cathodes and hard-carbon anodes will have specific energies around 150 Wh/kg at best, closer to that of Li-ion cells with LiFePO₄ cathode. What that says is that Na-ion batteries, when fully developed, would be suitable for applications similar to those where LiFePO₄ batteries are currently deployed. These include short-range electric vehicles; energy storage systems (ESS) for solar, wind and other alternative energy conversion facilities; power backup in electric utilities; and many other applications where energy density required of the battery is less demanding than that offered by their Li-ion batteries but substantially higher than the energy densities of the traditional rechargeable batteries Pb-acid, Ni/Cd, and Ni/MH.(7) The foremost advantage of Na-ion batteries comes from the natural abundance and lower cost of sodium compared with lithium. The abundance of Na to Li in the earth’s crust is 23600 ppm to 20 ppm, and the overall cost of extraction and purification of Na is less than that of Li. Moreover, Na-containing metal oxide and polyanion cathode materials can be fabricated from naturally abundant transition metals such as iron, manganese, vanadium, and titanium, without using cobalt, making Na-ion batteries sustainable and affordable in rich and poor countries alike. Sanders from Avicenne, a French battery market forecast company, has reported(16) that the worldwide Li-ion battery market will grow to more than $150 billion by 2025. The ESS market alone is expected to be >$50 billion. The higher volume of battery materials production in response to this rising market is expected to reduce the cost of Li-ion batteries at the pack level to about $100/kWh from the present $150/kWh. According to Sanders, the cathode is the costliest component of a Li-ion battery at about 25% of the total cost. An examination of Li-ion and Na-ion battery components reveals that the nature of the cathode material is the main difference between the two batteries. Because the preparation cost of the cathode from raw materials is more or less the same for both Li-ion and Na-ion technologies, the main cost reduction for Na-ion batteries comes from raw materials. On the basis of the information currently available we can project the cost of Na-ion batteries to be about 10–20% less than that of their Li-ion counterparts. The major advantage of Na-ion batteries is sustainability, which is important for a world striving to be free of carbon-based energy sources. We can foresee Na-ion batteries with hard-carbon anodes and cobalt-free cathodes as sustainable lower-cost alternatives to Li-ion batteries for applications such as short-range electric vehicles and large-scale energy storage (ESS) in a world that is increasingly being transformed to wind, solar, and hydroelectric power, which depend on battery energy storage for uninterrupted, around-the-clock, performance. Future research should focus on discovering advanced anode and cathode materials for Na-ion batteries with higher specific capacities and voltages so as to produce practical Na-ion batteries with specific energies approaching 200 Wh/kg. Efforts should also be made to develop advanced electrolytes that enable Na-ion battery performance at high charge–discharge rates over a wide temperature range while exhibiting the long cycle-life and shelf life required for large-scale energy storage applications. Research also should focus on gaining a deeper understanding of the crystal structure–ion transport property relationships in Na intercalation electrodes in order to acquire the ability to systematically design and develop high-capacity, reversible electrodes for Na-ion batteries. Research and development efforts should also continue on Na-ion battery prototypes with particular emphasis on evaluating their temperature- and rate-dependent performance and safety hazards. Views expressed in this Viewpoint are those of the author and not necessarily the views of the ACS. The author declares no competing financial interest. This article references 16 other publications.

中文翻译：

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钠离子电池与锂离子对口的可比性如何？

华盛顿州立大学（WSU）最近发布的新闻预告（1）：“ WSU和PNNL（太平洋西北国家实验室）的研究人员已经创造出一种钠离子电池，该钠离子电池可以容纳尽可能多的能量，并且可以像某些商用锂离子电池一样工作化学，利用丰富而廉价的材料制造出可能可行的电池技术”。当然，这一消息在电池界和公众中引起了极大的兴奋，甚至有人建议用新的钠（Na）离子电池代替昂贵的锂离子电池。激动的心情鼓励作者深入研究ACS Energy Letters中的原始WSU / PNNL报告。，（2,3）研究了钠离子电池技术的发展水平，并将其与成熟且普遍存在的锂离子电池进行了比较。从此询问得出的观点旨在回答“钠离子电池与锂离子电池的可比性如何”这一问题。这不是对钠离子电池的全面综述，因为最近在其他地方已有数篇此类报告。（4-6）钠离子电池电极材料的化学和电化学与锂离子电池的化学材料和电化学材料有足够的差异，因此可以候选仅在最近才提供适用于实际电池的电池。图1显示了Na离子电池的原理图。它的结构类似于锂离子电池。（7）已经建立了实验室测试室和代表性的原型室并使用硬碳阳极和阴极材料进行了评估，这些材料选自层状过渡金属氧化物，过渡金属氟磷酸盐和普鲁士蓝及其类似物。（4,5,8-10）图1. Na离子电池的示意图。层状过渡金属二氧化碳，NaMO₂，其中M =铁，镍，锰，钴等，存在于O3和P2结晶的版本。在O3-NaMO ₂相中，Na存在于八面体位置，而在P2相中，Na存在于棱柱形位置。在钠离子电池利用硬碳（C电极反应₆）阳极和层状过渡金属氧化物，那末₂，阴极在当量1中所描绘的放电电极上当量1的右手侧（ 1） NaCoO ₂阴极，如LiCoO ₂首先，将其以放电状态带入Na离子电池中，并通过首先充电激活电池，以在充满电的电池中形成Na嵌入阳极和Na脱嵌阴极。图2（4）中比较的Li / Li _{1– x} CoO ₂和Na / Na ₁ – _x CoO ₂半电池的充电和放电电压与容量曲线显示了Na电池的逐步电压曲线。它们反映了NaCoO ₂晶体的多相变化，这是因为在充电过程中将Na从其中脱嵌而形成Na _{1- x} CoO ₂，反之亦然。LiCoO ₂和NaCoO ₂具有相同的O3晶体结构，该结构由CoO ₂平板组成，沿着A _{1– x} CoO ₂晶体的c轴（其中A = Li或Na），在平板之间交替容纳Li ⁺或Na ⁺离子。Na电池中NaCoO ₂的晶体结构变化始于在第一次充电过程中除去Na。O3型相中的钠离子最初稳定在MO6八面体内边缘共享的八面体位置。当从O3相中部分提取Na ⁺离子时，那些Na ⁺存在于棱柱形部位的能量变得稳定，并通过MO2平板的滑动将晶体转变为P3相，而不会破坏M-O键。通过将MO6平板滑动，在棱柱相和八面体相之间的这种转换几乎在所有层状过渡金属氧化物用作钠离子电池的阴极时都发生。结果是电池电压与容量曲线中的多个电压平稳期反映了相位变化（图2）。混合的金属氧化物阴极在Na离子电池中表现出额外的电压平稳状态，反映出在电池放电和充电过程中不同金属的氧化态被还原和氧化。NaCoO ₂电极具有约150毫安时/克的在3个V.层状过渡金属二氧化物的平均电压的可再充电容量研究作为钠离子电池的阴极包括NaFeO ₂，NaNiO ₂，NaCrO ₂，NAVO ₂，和NATIO ₂和混合的金属二氧化物衍生自它们，例如NaFe _1/2 Co _1/2 O ₂，NaNi _1/3 Fe _1/3 Co _1/3 O _2， NaNi _1/3 Fe _1/3 Mn _1/3 O ₂和NaNi _{1 / 4}铁_1/4钴_1/4锰_1/4 O _2。（4,5,8,9）WSU / PNNL Na-离子电池激发了此观点的写作，它使用的成分为NaNi _0.68 Mn _0.22 Co _0.10 O ₂和O3-类型的层状晶体结构。（2）图2. Li / LiCoO ₂和Na / NaCoO ₂半电池的充放电曲线比较。还显示了Li（Na）CoO ₂晶体的示意图（转载自参考文献（4），版权所有2014 American Chemical Society）。还已经研究了多种金属磷酸盐和氟磷酸盐作为用于钠离子电池的钠嵌入阴极。其中有NaFePO ₄（三叶沸石型），Na₂ Fe（P ₂ O ₇），Na ₄ Fe ₃（PO ₄）₂（P ₂ O ₇），Na ₂ FePO ₄ F和Na / Na ₂ [F e _1/2 M n _1/2 ] PO ₄ F.（4,5）检查的其他金属磷酸盐包括Na ₃ V ₂（PO ₄）₂ F ₃，Na ₃ V ₂（PO ₄）₃和Na ₄ Co _2.4 Mn_0.3 Ni _0.3（PO ₄）₂ P ₂ O ₇（参见参考文献（5）中的图23）。其中，Na ₃ V ₂（PO ₄）₂ F ₃在Na半电池中在室温下表现出合理的性能，在3.8 V的平均电压下可逆容量约为135 mAh / g。离子电池阴极包​​括普鲁士蓝及其类似物KFe ₂（CN）₆和MnFe（CN）₆，以及铁（III）系统Fe ₂（CN）₆（4）它们在3-3.5 V的电压下，在Na半电池中的可逆容量为80-120 mAh / g。普鲁士蓝类似物Na _1.92 Fe ₂（CN）₆，被称为普鲁士人白色，在Na半电池中低速放电容量为160 mAh / g，并且具有良好的充电能力。（10）普鲁士蓝及其类似物的缺点是密度低。例如，普鲁士蓝的密度为1.8 g / cm ³，与使用相同比容量（以mAh / g为单位）的过渡金属氧化物阴极的电池相比，这将为Na离子电池提供更低的体积能量密度。大多数研究中的阳极材料都是硬碳，尽管其他低压Na嵌入材料（例如Na _2）已经研究了Ti ₃ O ₇，Na ₃ Ti ₂（PO ₄）₃和Na合金。（4-6,11）硬碳阳极实际上具有约250 mAh / g的可逆容量，相当于在相对于Na / Na ⁺的平均电压为0.25 V的情况下形成Na _0.67 C _6。（4）用于Na离子电池阳极的电极材料应具有较低的Na嵌入和脱嵌电压，相对于Na / Na最好低于0.5 V ⁺电极，容量超过250 mAh / g。注意，重要的是负极材料的Na脱嵌电压，因为Na ⁺在Na离子电池放电期间，离子从阳极脱嵌并插入阴极。这两个电极电压之间的差是电池电压。电解质的选择对于开发实用的Na离子电池很重要。包含钠盐（例如NaPF ₆，NaN（SO ₂ CF ₃）₂和NaClO ₄）的有机碳酸盐溶剂基电解质与少量添加剂一起使用以稳定循环过程中的阳极和阴极。（8）上述WSU / PNNL电池使用了添加剂双（2,2,2-三氟乙基）醚（BTFE），而其他研究则使用了氟乙烯（12）通常，使用选自碳酸亚乙酯（EC），碳酸亚丙酯（PC），碳酸二甲酯（DMC），碳酸二乙酯（DEC）和碳酸乙基甲基酯（EMC）的混合有机碳酸酯溶剂可以在宽温度范围内提供最佳放电和充电性能，高热稳定性，高倍率性能，长循环寿命和保质期的电解质。（8）钠离子电池原型。法国研究机构CNRS CEA报告的一种18650尺寸的电池似乎是第一个钠离子电池商业产品。（13）请注意，数字18650来源于直径为18 mm的金属容器中的圆柱形电池的尺寸， 65毫米高。就锂离子电池而言，就工程和化学而言，18650电池是最先进的商用电池。据报道，CEA Na离子电池的比能为90 Wh / kg，并且循环了1000多次。但是，没有提供有关所用电极和电解质材料，电池容量，电压和循环参数的信息。据称该电池具有高功率能力。我们可以如下估算此单元格的一些其他规格。第一，假设该电池的重量为46 g，类似于商用18650锂离子电池的重量。（7）然后，该18650 Na离子电池的能量为4.14 Wh。18650圆柱形金属外壳的体积为16.5 mL。因此，该4.4 Wh Na离子电池的体积能量密度为250 Wh / l。现在，根据许多钠离子阴极材料中发现的4.14 Wh能量和3 V的平均电压，我们可以估算出CEA 18650 Na离子电池的容量为1.38 Ah（4.14 Wh除以3 V）。现在让我们看一下华盛顿大学/ PNNL公告中描述的Na-离子电池。（1,2）它具有硬碳阳极，并使用O3-NaNi 现在，根据许多钠离子阴极材料中发现的4.14 Wh能量和3 V的平均电压，我们可以估算出CEA 18650 Na离子电池的容量为1.38 Ah（4.14 Wh除以3 V）。现在让我们看一下华盛顿大学/ PNNL公告中描述的Na-离子电池。（1,2）它具有硬碳阳极，并使用O3-NaNi 现在，根据许多钠离子阴极材料中发现的4.14 Wh能量和3 V的平均电压，我们可以估算出CEA 18650 Na离子电池的容量为1.38 Ah（4.14 Wh除以3 V）。现在让我们看一下华盛顿大学/ PNNL公告中描述的Na-离子电池。（1,2）它具有硬碳阳极，并使用O3-NaNi_0.68 Mn _0.22 Co _0.10 O ₂作为阴极材料。在0.25 mA / cm ²的C / 10速率下，该电池基于硬碳阳极的容量为184 mAh / g，基于金属氧化物阴极的容量为141 mAh / g。基于活性物质，容量为60 mAh的袋式电池表现出的比能量为290 Wh / kg，作者推断为实际的比能量为156 Wh / kg。WSU / PNNL Na离子电池的估算值比上述CEA 18650电池中的实际估算值高得多。应当指出的是，156 Wh / kg是从电极的290 Wh / kg的比能得出的外推值，使用55％的转换系数，并考虑了电解质，电极集电器，隔板的质量，金属容器和其他惰性材料，如在商用18650锂离子电池中发现的那样。我们可以估算出另一个Na离子电池的实际比能，较早（5）所述的₃ V ₂（PO ₄）₂ F ₃阴极和硬碳阳极。该电池的电压为3.5 V，基于电极材料，其比能为295 Wh / kg。以50％的实验室电池到商业电池的转换效率，这种化学方法产生的实际电池将显示约150 Wh / kg，类似于WSU / PNNL电池的估计值。有趣的是，Alistore-European研究机构（14）使用Na ₃ V ₂（PO ₄）₂ F ₃阴极和硬碳阳极构建了一个18650电池，并在75 Wh / kg和4000次循环下显示出1 C率。显然，此18650电池的比能仅是以上根据实验室电池的电极容量估算的比值的一半。实际上，考虑到所检查的众多正极材料的可逆容量和电压以及硬质碳负极的比容量约为250 mAh / g，因此100-150 Wh / kg的比能似乎是最好的。完全开发的Na离子电池。从可用于Na电池单元中的电极材料的速率能力信息以及报告的Na ⁺（15）钠离子电池在正极和负极材料中的扩散系数可望提供与锂离子电池相当的良好倍率能力。在能量密度，成本，应用和整体消费者接受度方面，对此讨论需要回答的一个重要问题是“钠离子电池与锂离子电池相比如何”。钠离子电池与锂离子电池相比如何？为了回答这个问题，让我们首先看一下商用锂离子电池的比能量和能量密度。高度工程化的18650尺寸电池最适合此比较。表1列出了18650尺寸的商用锂离子电池的比能，这些电池具有石墨阳极（容量约350 mAh / g）和不同类型的阴极。（7）具有层状过渡金属阴极LiCoO ₂（LCO），LiNi的电池_0.33 Mn _0.33 Co _0.33 O ₂（NMC）和LiN _0.8 Co _0.15 Al _0.05 O ₂（NCA）的容量分别为2.4、2.4和3.6 Ah，可分别转换为206、210和285 Wh / kg的比能，并转换为530至785 Wh / l的体积能密度。具有LiFePO ₄和LiMn ₂ O ₄阴极的电池具有约130 Wh / kg的较低比能和约330 Wh / l的体积能密度。考虑到此帐户中介绍的各种Na嵌入金属氧化物和金属磷酸盐阴极材料的可逆容量，我们可以预测，利用这些阴极和硬碳阳极的18650尺寸Na离子电池最多将具有约150 Wh / kg的比能。 ，更接近LiFePO ₄的锂离子电池阴极。这说明Na-ion电池完全开发后，将适合与LiFePO ₄相似的应用当前已部署电池。这些包括短程电动汽车；用于太阳能，风能和其他替代能源转换设施的储能系统（ESS）；电力公司的备用电源；以及其他许多对电池的能量密度要求不如其锂离子电池所要求的能量密度高得多的应用，但其能量密度却高于传统可充电电池Pb-酸，Ni / Cd和Ni / MH的能量密度。（7 ）Na离子电池的最主要优势是与锂相比，钠的自然丰度和较低的钠成本。地壳中Na对Li的丰度为23600 ppm至20 ppm，Na的提取和纯化的总成本低于Li。此外，含钠的金属氧化物和聚阴离子阴极材料可以由天然丰富的过渡金属（例如铁，锰，钒和钛）制成，而无需使用钴，这使得无论富国还是穷国，钠离子电池都是可持续的且价格可承受的。法国电池市场预测公司Avicenne的Sanders报告（16）称，到2025年，全球锂离子电池市场将增长到超过1500亿美元。仅ESS市场就有望超过500亿美元。响应于这一不断增长的市场，电池材料产量的提高有望将锂离子电池组的成本从目前的150美元/千瓦时降低到100美元/千瓦时左右。桑德斯认为，阴极是锂离子电池中最昂贵的组件，约占总成本的25％。对锂离子和钠离子电池组件的检查表明，正极材料的性质是两个电池之间的主要区别。由于锂离子和钠离子技术从原材料制备阴极的成本或多或少相同，因此钠离子电池的主要成本降低来自原材料。根据目前可获得的信息，我们可以预测钠离子电池的成本比锂离子电池便宜约10–20％。Na离子电池的主要优点是可持续性，这对于努力摆脱碳基能源的世界来说至关重要。我们可以预见，具有硬碳阳极和无钴阴极的Na-离子电池将是锂离子电池的可持续低成本替代品，在当今世界，短距离电动汽车和大规模储能（ESS）等应用中越来越多地转换为风能，太阳能和水力发电，而风力发电，太阳能和水力发电依靠电池储能来实现不间断的全天候运行。未来的研究应侧重于发现具有更高比容量和电压的Na离子电池的高级阳极和阴极材料，从而生产出比能量接近200 Wh / kg的实用Na离子电池。还应努力开发先进的电解质，以使Na-离子电池在宽温度范围内以高充放电速率运行，同时展现出大规模储能应用所需的长循环寿命和保质期。研究还应集中于对Na嵌入电极中的晶体结构与离子迁移特性之间的关系有更深入的了解，从而获得系统设计和开发用于Na离子电池的高容量可逆电极的能力。钠离子电池原型的研发工作也应继续进行，尤其要重点评估其温度和速率相关的性能和安全隐患。本观点中表达的观点是作者的观点，不一定是ACS的观点。作者声明没有竞争性的经济利益。本文引用了其他16个出版物。