中国物理海洋学研究70年：发展历程、学术成就概览

本文概略评述新中国成立70年来物理海洋学各分支研究领域的发展历程和若干学术成就。中国物理海洋学研究起步于海浪、潮汐、近海环流与水团,以及以风暴潮为主的海洋气象灾害的研究。随着国力的增强,研究领域不断拓展,涌现了大量具有广泛影响力的研究成果,其中包括:提出了被国际广泛采用的"普遍风浪谱"和"涌浪谱",发展了第三代海浪数值模式;提出了"准调和分析方法"和"潮汐潮流永久预报"等潮汐潮流的分析和预报方法;发现并命名了"棉兰老潜流",揭示了东海黑潮的多核结构及其多尺度变异机理等,系统描述了太平洋西边界流系;提出了印度尼西亚贯穿流的南海分支(或称南海贯穿流);不断完善了中国近海陆架环流系统,在南海环流、黑潮及其分支、台湾暖流、闽浙沿岸流、黄海冷水团环流、黄海暖流、渤海环流,以及陆架波方面均取得了深刻的认识;从大气桥和海洋桥两个方面对太平洋–印度洋–大西洋洋际相互作用进行了系统的总结;发展了浅海水团的研究方法,基本摸清了中国近海水团的分布和消长特征与机制,在大洋和极地水团分布及运动研究方面也做出了重要贡献;阐明了南海中尺度涡的宏观特征和生成机制,揭示了中尺度涡的三维结构,定量评估了其全球物质与能量输运能力;基本摸清了中国近海海洋锋的空间分布和季节变化特征,提出了地形、正压不稳定和斜压不稳定等锋面动力学机制;构建了"南海内波潜标观测网",实现了对内波生成–演变–消亡全过程机理的系统认识;发展了湍流的剪切不稳定理论,提出了海流"边缘不稳定"的概念,开发了海洋湍流模式,提出了湍流混合参数化的新方法等;在海洋内部混合机制和能量来源方面取得了新的认识,并阐述了混合对海洋深层环流、营养物质输运等过程的影响;研发了全球浪–潮–流耦合模式,推出一系列海洋与气候模式;发展了可同化主要海洋观测数据的海洋数据同化系统和用于ENSO预报的耦合同化系统;建立了达到国际水准的非地转(水槽/水池)和地转(旋转平台)物理模型实验平台;发展了ENSO预报的误差分析方法,建立了海洋和气候系统年代际变化的理论体系,揭示了中深层海洋对全球气候变化的响应;初步建成了中国近海海洋观测网;持续开展南北极调查研究;建立了台风、风暴潮、巨浪和海啸的业务化预报系统,为中国气象减灾提供保障;突破了国外的海洋技术封锁,研发了万米水深的深水水听器和海洋光学特性系列测量仪器;建立了溢油、危险化学品漂移扩散等预测模型,为伴随海洋资源开发所带来的风险事故的应急处理和预警预报提供科学支撑。文中引用的大量学术成果文献(每位第一作者优选不超过3篇)显示,经过70年的发展,中国物理海洋学研究培养了一支实力雄厚的科研队伍,这是最宝贵的成果。这支队伍必将成为中国物理海洋学研究攀登新高峰的主力军

反应-扩散对锂电池枝晶抑制作用研究

近年来，能源供给日益紧张的局势迫切要求人们研发兼具高能量密度和长使用寿命的金属二次电池（如锂、钠、锌、镁金属电池等），以满足电动汽车、便携式电子设备、航天电源等领域的能源需求。在上述二次电池中，锂金属作为负极时，因具有最低的还原电势（-3.04 V vs标准氢电极）和最高的理论容量（3860 mAh g-1），引起了科研工作者强烈的兴趣。但目前，锂金属电池因锂枝晶问题使其应用前景大打折扣。这主要是因为：（1）锂枝晶的生长与蔓延极易诱发电池内部短路导致电池安全问题；（2）锂枝晶在快速放电过程中，极易脱落于电解质液中形成&ldquo;死锂&rdquo;，降低电池容量和缩短电池的使用寿命。（3）锂枝晶刺破固体电解质保护层，与电解液发生副反应，消耗电解液，缩短电池的使用寿命。由此可见，锂枝晶的抑制是开发高功率密度和长使用寿命储能电池的首要前提。在过去几十年中，科研工作者通过对电解液改性、固体电解质界面保护、固态电解质、结构化或功能化负极、隔膜改性、充电方式等技术手段来抑制锂枝晶。上述有关材料创新的研究工作已取得重要进展，但锂枝晶难题依然悬而未决。从枝晶结构的生成机制角度抑制锂枝晶的研究工作鲜有报道，洞悉枝晶结构生长的驱动力将有助于提出新的抑制锂枝晶思路。结合本课题组已有研究工作基础：电沉积中，金属离子在传递受限的情况下，倾向于生成树枝状结构，而强化金属离子传质后，金属枝晶结构逐渐消失。因此，本研究在探讨锂枝晶生成机制的基础场，分别采用外加电场和外加磁场强化锂离子传输，削弱电沉积界面处离子浓度梯度，达到抑制锂枝晶生成的目的。首先，本研究对诱发锂枝晶生成的影响因素和锂枝晶对电池循环性能的影响进行了探讨。影响枝晶生成因素的研究主要涉及反应速率（电流密度）、反应时间、循环次数。具体地：（1）随着反应速率的提升（0.2 ~10 mA cm-2），锂枝晶结构会变得越来越纤长：棒状枝晶结构（长度低于5 &mu;m）过渡至线状锂枝晶（长度可达50 &mu;m）。这主要是因为较快反应条件下，锂离子供给（传递）速率低于消耗（反应）速率，在晶体生长前端形成稳定的浓度梯度，诱发锂枝晶结构的持续性生长。（2）当反应速率为定值时，随着反应时间的推移，锂枝晶的结构在反应前、中和后期分别呈现出线状（不具有分叉结构）、苔藓丛（扭曲线状团簇）、灌木丛状（具有分叉结构）。这主要是因为：反应前期，锂离子在电沉积界面处传递受限，倾向于在枝晶尖端富集、成核和生长，展现出一维线状枝晶结构；反应中期，沉积界面处锂离子进一步被消耗，枝晶尖端处的浓度场发生变化，导致枝晶生长方向发生变化，故生成由扭曲线状组成的团簇状形貌（苔藓状）；反应后期，伴随着锂离子极度消耗，锂离子逐渐在枝晶缺陷处成核，故演变成扭曲状分叉枝状团簇（灌木丛状）。（3）高电流密度充放电实验中，随着循环次数的增加，锂枝晶的长度逐渐延长，且锂枝晶在延伸过程中，锂枝晶的直径变得粗细不一，该形貌结构极易断落于电解液中形成&ldquo;死锂&rdquo;。另外，伴随着充放电循环的增加，循环至放电终点时，负极表面残余的惰性锂逐渐增多，这也是导致电池库伦效率降低的诱因。（4）采用COMSOL对负极枝晶形貌进行了模拟，发现：负极表面锂离子流分布极为不均匀和枝晶尖端存在尖锐的浓度梯度，从而验证了浓度梯度是锂枝晶生成驱动力的论断。其次，本研究采用了外加电场强化锂离子传质，削弱沉积界面处浓度梯度，高电流密度充放电下实现了锂枝晶的抑制：（1）在电池负极处施加外加交流电场（电场方向平行于负极表面，即与锂离子运动方向垂直），使得锂离子负极处均匀分布，发现适中的交流频率（30 Hz）在均布锂离子方面展现出优异的性能。在外加交流电场（5 V cm-1和30 Hz）和高电流密度充放电条件下（2 mA cm-2），电池使用寿命为同电流密度对照实验的3倍，且沉积锂形貌为小颗粒；（2）在电池外部施加外加直流电场以强化锂离子传递，所述的外加直流电场方向与电池内部正极指向负极的方向一致。故在外电场力（与锂离子运动方向同向）的作用下，可使得锂离子传质增强。研究结果表明：伴随着外加直流电场场强的增加，电池内部锂离子转移数和扩散系数均提高。且沉积界面处的浓度梯度得以削弱，这主要得益于外加电场促使锂离子向负极表面迁移，增加界面处锂离子浓度而导致的结果，该结论也被COMSOL模拟研究工作证实。接下来，外加直流电场（5 V cm-1）和高电流密度充放电测试表明电池使用寿命为同电流密度下无外场对照实验的2倍，电池循环后沉积锂的形貌为小颗粒（如珍珠状等），证明了强化传质削弱沉积界面处浓度梯度抑制锂枝晶生成的论断；（3）考察了同时采用外加交流电场（5 V cm-1和30 Hz）和外加直流电场（5 V cm-1）对电池多循环性能的影响及其对锂枝晶的抑制情况，研究发现：即便是高电流密度充放电条件下，电池的使用寿命分别是同电流密度下对照实验的5倍，且负极表面沉积锂的形貌为小颗粒，表明两场同用在保护负极和延长电池使用寿命方面表现出优异的性能。最后，本研究考察了采用外加磁场强化传质对电池循环性能的影响及其对锂枝晶的抑制情况。所述的外加磁场布置于电池负极，磁场方向与负极表面平行，即与锂离子运动方向垂直。在电池充电过程中，快速切割磁感线运动的顺磁性锂离子流受洛伦兹力的影响，在负极表面附近产生微流动，强化了锂离子传质的同时，也避免了锂离子在负极表面的局部富集，因而能够有效抑制锂枝晶的生成。研究中发现：（1）随着磁场强度的增加，锂离子扩散系数随之增大，而沉积界面处界面浓度梯度降低，证实了外加磁场强化传质的有效性。（2）适中的磁场强度（0.8 T）对延长电池使用寿命、负极保护和锂枝晶抑制等电池长使用寿命指标十分重要。磁场强度为0.8 T，电池使用寿命为同电流密度下对照实验的5.5倍，电池的电化学性能最为优异。另外，伴随着磁场强度的增加，沉积锂形貌依次表现为线状枝晶、针状枝晶、大颗粒和小颗粒沉积形貌，有效证明了强化锂离子传质调控沉积锂形貌的推断。（3）采用COMSOL模拟对负极处沉积锂形貌进行了追踪，并对负极表面至体相电解液方向的浓度分布进行了量化，模拟结果表明：无外场条件下，电池负极表面存在明显尖锐的、稳定的浓度梯度，导致锂枝晶结构的蔓延；而引入外加磁场后，电池中锂离子传输增强，削弱了负极界面处浓度梯度，锂枝晶生长驱动力得以削弱，故倾向于生成均匀沉积的形貌结构。;The ever-increasing needs of energy has stimulated the research on second metal batteries (i.e., Li, Na, Zn, etc.), which hold high energy density and show widespread uses in emerging applications represented by electrical vehicles, portable electronics, aerospace application, and etc. Among these potential candidates, lithium metal battery (LMB) stirs intense research because of its highest theoretical capacity (3860 mAh g-1) and lowest electrochemical potential (-3.04V versus standard hydrogen electrode). However, the uncontrolled dendrite formation during charging process leads to safety concern and shortened life for lithium battery. In detail, the formidable lithium dendrites during repeated cycling tend to connect the anode and cathode, resulting in internal short circuits and safety issues. Also, after piercing solid electrolyte interface (SEI layer) by dendrites, the undesired reaction between deposited lithium and electrolytes as well as the dead lithium during discharge process deteriorate the lifespan of batteries. Thus, inhibiting lithium dendrites is the primary prerequisite for developing storage batteries with high power density and long lifespan.During the past decades, numerous investigations have been focused on suppressing dendritic lithium via electrolyte modification and additive, protecting SEI layer or in-situ formation robust SEI layer, all solid-state electrolyte, 3D and structure anodes, charging style, separator modification，and etc. Although significant progress has been achieved, this problem is still unsolved. However, there are few efforts to inhibit lithium dendrites based on the formation mechanism of dendritic structures. A good understanding on the growth mechanism of dendrites may lead to a breakthrough solution to mitigate or eliminate these structures in recharging batteries. In our previous studies, the dendritic structures are prone to form at diffusion limitation of chemicals. However, the dendritic structures can be inhibited by enhancing the transport of metal ions. Thus, in this dissertation, diffusion enhancements by external fields (i.e., electric fields, magnetic fields) are employed to suppress the formation of dendrites in lithium battery at a quick charging process.Firstly, the factors (i.e., reaction rate (current density), reaction time, and cycles) were examined to probe their effects on dendrite proliferation. Also, the battery is also tested to explore the lifespan of battery without external fields. The conclusions in this part are presented as follows: (1) higher reaction rate gives rise to the slender and elongated dendrites. With the increasing current density from 0.2 to 10 mA cm-2, the dendritic morphologies are evoluted from needle-like dendrites with length less than 5 &mu;m to wire-like dendritic structure with a length of approximate 50 &mu;m. When the reaction rate is faster than the diffusion rate of lithium ions, a concentration gradient is formed at the growth front of crystals. Once the gradient is stable, lithium ions tend to accumulate at the tip of dendrites to deposit, lengthening the dendrites. (2) With the repeated charging process at a high current density, three dendritic morphologies appear on the anode surface at the sequence of wire-like dendrites, moss-like dendrites, and shrub-like dendrites. At the initial stage, the transport of lithium ions near the anode surface is slower than the consumption rate, which results in the established of stable gradients at the growth front of crystals. Lithium ions tend to accumulate, nucleate, and grow at the tip of dendrites, lengthening the dendritic structures. During the middle stage, lithium ions are further consumed and the concentration gradients have changed, inducing the unstable growth direction and forming moss-like structures. At the last stage, the lithium ions are extremely consumed, which generates defects in the craystal and shapes twisted shrub-like dendrites. (3) The lithium dendrites are elongated with the repeated cycling. These structures tend to break into electrolyte, forming dead lithium and lowering battery capacity. In addition, more and more inactive dendrites still remain on the anode surface at the end of discharge in each cycle, deteriorating battery life. (4) The COMSOL simulation shows that lithium ions fluxs are uneven distribution at the anode surface. Also, there appears steep concentration gradient at the tip of dendrites, confirming the interface concentration gradient is the driving force for dendrite growth.Secondly, external electric field was employed to enhance the diffusion of lithium ions, lower the concentration gradient at the deposition interface, and suppress lithium dendrites even at a high charge current density: (1) An external alternating current field (ACF) is delicately built up perpendicular to the anode to perturb lithium ion distribution around the anode. The ACF with 30 Hz shows excellent performance in lengthening battery life and suppressing lithium dendrites due to its superior uniform distribution of Li+ along the anode surface. In detail, the battery life with ACF (5 V cm-1 and 30 Hz) are three times of the control case. The deposited morphologies at high current density are small particles, confirming the efficacy of dendrite inhibition. (2) An external direct current field (DCF) was applied to the battery to speed up the diffusion of Li+ in electrolytes. The DCF was parallel to the internal electric field, which was expected to accelerate the transport of lithium ions in electrolytes. The results show both the transfer number and diffusion coefficient of lithium ions increase with the intensity of DCF. Also, the concentration gradient decreases with the intensity of DCF, indicating that the DCF speeds up the lithium ions transport from cathode to anode. The COMSOL simulation shows that the deposited morphologies are uniform deposition layer after enhancing the transport of lithium ions. The life of the battery increases two times after the introduction of the DCF (5 V cm-1) even at high current density of 2 mA cm-2. There are no dendritic structures after cycling at the anode, confirming the effectiveness of DCF in suppressing lithium dendrites. (3) A simultaneous adoption of ACF (5 V cm-1 and 30 Hz) and DCF (5 V cm-1) was employed to investigate their effects on the electrochemical performance of the lithium battery. The lifespan of the lithium battery is almost five times of the control case at the high current density of 2 mA cm-2, showing excellent performance of DCF and ACF in protecting the anode surface, prolonging battery life, and suppressing lithium dendrites.Finally, the external magnetic field (EMF) was employed to examine its effect on battery electrochemical performance and dendrite inhibition. The EMF was parallel to the anode surface, namely vertical to the lithium ions movement. The magnetic field force (Lorentz force) could be exerted on the motional lithium ions, inducing micro fluids at the anode surface, which avoids the accumulation of lithium ions at the tip, resulting in uniform distribution of lithium ions and dendrite-free deposited morphology. The conclusions in this part are as follows: (1) Li+ diffusion coefficient increases with the intensity of EMF. Also, the increased intensity of EMF leads to the decrease of concentration gradients at the anode surface. This validates the effectiveness of EMF in the enhancement of mass transport. (2) A moderate EFM with 0.8T during battery tests is evaluated for well inhibiting lithium dendrites and prolonging battery life. The life of battery with EMF of 0.8 T is 5.5 times of the control case at the high current density of 2 mA cm-2. With the increased strength of magnetic field, the deposited morphologies are needle-like dendrites, wire-like dendrites, large particles, and tiny particles. This confirms that the enhancement of mass transport via EMF could effectively shape the deposited lithium morphologies. (3) The COMSOL simulations were conducted to track the morphologies evolution. It shows that the sharp concentration gradient exists on the tip of dendrites and drives the proliferation of dendrites. However, the enhancement of transport via EMF lowers the concentration gradient, forming dendrite-free deposited morphologies.</p

有机添加剂对超级电容器中水系电解液理化性能的影响

以6 mol/L KOH水溶液为电解液,高比表面积的活性炭为活性物质,研究了有机添加剂对体系润湿性、电导率、工作电压窗口及阻抗的影响,测试了超级电容器的电化学性能。结果表明,适量添加有机添加剂可明显抑制体系的极化现象,提高超级电容器的工作电压窗口。添加10vol%异丙醇时,电极材料和电解液间的润湿性大幅提高,比电容从79.3 F/g提高至113.2 F/g。添加20vol%异丙醇时,超级电容器的能量密度达19.4 Wh/kg,体系的电荷转移电阻明显降低,在10 A/g电流密度下的比电容比0.5 A/g时下降13.9%,而不加添加剂时下降30.3%。添加30vol%异丙醇时,电解液电导率迅速下降,比电容降低,电导率是影响比电容的关键因素

有机添加剂对超级电容器中水系电解液理化性能的影响

以6 mol/L KOH水溶液为电解液,高比表面积的活性炭为活性物质,研究了有机添加剂对体系润湿性、电导率、工作电压窗口及阻抗的影响,测试了超级电容器的电化学性能。结果表明,适量添加有机添加剂可明显抑制体系的极化现象,提高超级电容器的工作电压窗口。添加10vol%异丙醇时,电极材料和电解液间的润湿性大幅提高,比电容从79.3 F/g提高至113.2F/g。添加20vol%异丙醇时,超级电容器的能量密度达19.4Wh/kg,体系的电荷转移电阻明显降低,在10A/g电流密度下的比电容比0.5 A/g时下降13.9%,而不加添加剂时下降30.3%。添加30vol%异丙醇时,电解液电导率迅速下降,比电容降低,电导率是影响比电容的关键因素

有机添加剂对超级电容器中水系电解液理化性能的影响

以6 mol/L KOH水溶液为电解液,高比表面积的活性炭为活性物质,研究了有机添加剂对体系润湿性、电导率、工作电压窗口及阻抗的影响,测试了超级电容器的电化学性能。结果表明,适量添加有机添加剂可明显抑制体系的极化现象,提高超级电容器的工作电压窗口。添加10vol%异丙醇时,电极材料和电解液间的润湿性大幅提高,比电容从79.3 F/g提高至113.2 F/g。添加20vol%异丙醇时,超级电容器的能量密度达19.4 Wh/kg,体系的电荷转移电阻明显降低,在10 A/g电流密度下的比电容比0.5 A/g时下降13.9%,而不加添加剂时下降30.3%。添加30vol%异丙醇时,电解液电导率迅速下降,比电容降低,电导率是影响比电容的关键因素

Formal analysis of power separation mechanism based on Biba model

　　强制访问控制是建设高级别安全信息系统的必要条件。本文基于Biba模型，重点给出了信息系统中系统管理员、安全管理员和安全审计员三权分立的形式化分析。通过分析，给出三权分立管理机制下，保障信息系统安全管理的条件。本文的结果在某国家级信息系统的具体建设中得到了应用。Mandatory access control is a necessary condition for constructing a high level of security information system. In this paper, based on Biba model, we give formal analysis for power separation mechanism under the condition which administrators are divided into system administrators, security administrators and security auditors, through the analysis, we give the conditions of guaranteeing the security of the information system management under separation of the three powers management mechanism. The results of this paper have been applied to the construction of a national information system