Investigating the efficacy of inverse-charging of lead-acid battery electrodes for cycle life and specific energy improvement

Although competitive today, traditional PbA (4000 cycles) will not be able to compete with lithium and flow batteries by 2020. To compete with novel zinc, lithium and flow batteries, the PbA chemistry needs to achieve significant performance improvements, primarily through sustainable increases to specific energy (Wh/kg), while not negatively impacting cycle life. Inverse charging has been examined for its potential in improving PbA cycle life as a battery maintenance procedure, and as a potential technique for improving electrode specific capacity (mAh/kg) during battery manufacturing and formation. A thorough levelized cost of energy (LCOE) shows that for traditional PbA batteries with cycle lives 4000 cycle life) was proven to worsen battery economics, as additional costs of capital and maintenance fail to outweigh savings achieved through reductions in replacement cost. On the other hand, inverse charging employed as a manufacturing practice to increase specific energy dramatically reduces the cost of the PbA and ALAB systems, ensuring future cost competitiveness. Inverse charging as a maintenance strategy should be restricted to devices with <2000 cycles and to projects with long project lives (20 years) that require frequent replacement. Inverse charging as a manufacturing strategy (to increase specific energy) is highly preferable in all instances. When successful, inverse charging increases the specific capacity and active material utilization of studied battery electrodes significantly. Successful inverse charging of battery electrodes and pure lead rods show improvements in discharge capacities over a range of discharge rates with negligible impact to coulombic and energy efficiency values. The extent of success, however, depends on several important variables. Thorough examination of inverse charging on Pb rods and porous battery electrodes illustrates the importance of the degree of prior electrode sulfation and obstruction of transport of H₂SO₄. Other important factors include the composition of electrode grid alloys, the peak oxidation voltage applied to the negative electrode during inverse charging, initial particle sizes, and electrolyte additives. Significant challenges to inverse charging exist. For heavily sulfated batteries and lead metals, impeded electrolyte transport results in excessive internal pore pH increases, creating semipermeable membranes through an electrode hydration mechanism, resulting in dramatic inverse charging failure. Additionally, impedance, voltage, x-ray and BET data hint that post-inverse charging, agglomeration of finely divided Pb and PbSO₄ particles occurs, coupled with negative electrode conductive pathway destruction. As such, the influence of expander materials and nucleation additives should be investigated to better prevent sulfation failure, and to better control the nucleation and growth of lead and lead sulfate structures during inverse charging. Cycle life studies on flooded lead antimony batteries subjected to periodic inverse charging illustrate that inverse charging is highly successful on all batteries independent of states-of-health. Batteries with poor states-of-health (discharge capacities <15% of initial values) experienced almost perfect discharge capacity restoration post-inverse charging. Traditional methods of extending cycle life (i.e. prolonged overcharging techniques) were demonstrated to be inadequate at appreciably regenerating battery capacities, providing only marginal increases. The benefits of inverse charging, however, are met with significant challenges to battery redesign. Temporary antimony poisoning effects lead to declines in round-trip-efficiency for batteries with antimony-based positive plates. Tin dissolution results in diminished grid to active material conductivity and reduced capacity for batteries with tin-based positives. For the negative electrode, Brunauer–Emmett–Teller (BET) surface area and x-ray measurements indicate that although large PbSO₄ crystals are oxidized during inverse charging, creating extensive micropore networks during conversion from Pb to PbO₂, surface area and capacity gains are lost during reconversion back to sponge lead due to uncontrolled nucleation and particle fusion. Additionally, active material shedding of the positive and negative electrodes is observed to spike during and after inverse charging. Negative electrode active material suffers excessive degradation and loss of cohesion, particularly for electrodes with small initial particle feature sizes, resulting in a loss of structure upon completion of the technique. Positive electrode composition changes to weakly interconnected b-PbO₂, dramatically increasing electrode capacity while simultaneously accelerating electrode failure through shedding. Loss of particle cohesion in both electrodes promotes excessive shedding and sludging, creating intra-cellular short-circuits. In addition, inverse charging aggravates grid growth, promoting inter-cellular short-circuiting by creating pathways for cell-to-cell electrolyte contact upon seal destruction in current monoblock designs

Intersphincteric Resection for Low Rectal Cancer: An Overview

The treatment of rectal cancer has evolved from being solely a surgical endeavor to a multidisciplinary practice. Despite the improvement in outcomes conferred by the addition of chemoradiation therapy to rectal cancer treatment, advances in surgical technique have significantly increased rates of sphincter preservation and the avoidance of a permanent stoma. In recent years, intersphincteric resection for low rectal cancer has been offered and performed in patients as an alternative to abdominoperineal resection. An overview of this procedure, including indications, oncological and functional results based on current literature, is presented herein

Strategic goal accomplishment in export ventures: the role of capabilities, knowledge, and environment

The management literature suggests that setting strategic goals facilitates the identification of appropriate business strategies and focuses management attention and available resources on their accomplishment, enabling subsequent goal realization. Yet the literature also indicates that firms often find it difficult to realize their strategic goals and may find it even more challenging to do so when operating in foreign markets. However, little is known empirically about the extent to which strategic goals enable desired strategic positions to be achieved and factors that may affect this relationship. We examine this important issue using primary data from a sample of exporting manufacturers. Results support the existence of previously theorized strategic goal–realized strategic position gaps and show that these negatively impact performance. Thus, simply setting strategic goals does not necessarily aid in accomplishing the desired outcomes, and any failure to do so is costly. Drawing on organization theory, we find that internal capabilities and knowledge, and external market factors play important roles in minimizing such strategic goal–realized strategic position gaps. Specifically, we show that businesses with stronger architectural capabilities, those with higher levels of internationalization, and those operating in less dynamic market environments are better able to realize their intended strategic objectives and thereby enjoy superior performance

Second asymptomatic carotid surgery trial (ACST-2) : a randomised comparison of carotid artery stenting versus carotid endarterectomy

Background: Among asymptomatic patients with severe carotid artery stenosis but no recent stroke or transient cerebral ischaemia, either carotid artery stenting (CAS) or carotid endarterectomy (CEA) can restore patency and reduce long-term stroke risks. However, from recent national registry data, each option causes about 1% procedural risk of disabling stroke or death. Comparison of their long-term protective effects requires large-scale randomised evidence. Methods: ACST-2 is an international multicentre randomised trial of CAS versus CEA among asymptomatic patients with severe stenosis thought to require intervention, interpreted with all other relevant trials. Patients were eligible if they had severe unilateral or bilateral carotid artery stenosis and both doctor and patient agreed that a carotid procedure should be undertaken, but they were substantially uncertain which one to choose. Patients were randomly allocated to CAS or CEA and followed up at 1 month and then annually, for a mean 5 years. Procedural events were those within 30 days of the intervention. Intention-to-treat analyses are provided. Analyses including procedural hazards use tabular methods. Analyses and meta-analyses of non-procedural strokes use Kaplan-Meier and log-rank methods. The trial is registered with the ISRCTN registry, ISRCTN21144362. Findings: Between Jan 15, 2008, and Dec 31, 2020, 3625 patients in 130 centres were randomly allocated, 1811 to CAS and 1814 to CEA, with good compliance, good medical therapy and a mean 5 years of follow-up. Overall, 1% had disabling stroke or death procedurally (15 allocated to CAS and 18 to CEA) and 2% had non-disabling procedural stroke (48 allocated to CAS and 29 to CEA). Kaplan-Meier estimates of 5-year non-procedural stroke were 2·5% in each group for fatal or disabling stroke, and 5·3% with CAS versus 4·5% with CEA for any stroke (rate ratio [RR] 1·16, 95% CI 0·86-1·57; p=0·33). Combining RRs for any non-procedural stroke in all CAS versus CEA trials, the RR was similar in symptomatic and asymptomatic patients (overall RR 1·11, 95% CI 0·91-1·32; p=0·21). Interpretation: Serious complications are similarly uncommon after competent CAS and CEA, and the long-term effects of these two carotid artery procedures on fatal or disabling stroke are comparable