Our current battery technology is just completely incapable of transitioning us to a %100 renewable grid at current costs and densities. Closing down nuclear plants and replacing them with a mix of renewables and lignite coal plants as we've seen in Germany has been both an ecological and economic disaster. Nuclear fission is a proven baseload power today, whereas getting renewables to cover baseload power globally requires technologies we haven't even invented yet, let alone mass manufactured.

"A cost-optimal wind-solar mix with storage reaches cost-competitiveness with a nuclear fission plant providing baseload electricity at a cost of $0.075/kWh27 at an energy storage capacity cost of $10-20/kWh. To reach cost-competitiveness with a peaker natural gas plant at $0.077/kWh, energy storage capacity costs must instead fall below $5/kWh."

https://www.cell.com/joule/fulltext/S2542-4351(19)30300-9

"The largest announced storage system, comprising more than 18,000 Li-ion batteries, is being built in Long Beach for Southern California Edison by AES Corp. When it’s completed, in 2021, it will be capable of running at 100 megawatts for 4 hours. But that energy total of 400 megawatt-hours is still two orders of magnitude lower than what a large Asian city would need if deprived of its intermittent supply. For example, just 2 GW for two days comes to 96 gigawatt-hours.

We have to scale up storage, but how? Sodium-sulfur batteries have higher energy density than Li-ion ones, but hot liquid metal is a most inconvenient electrolyte. Flow batteries, which store energy directly in the electrolyte, are still in an early stage of deployment. Supercapacitors can’t provide electricity over a long enough time. And compressed air and flywheels, the perennial favorites of popular journalism, have made it into only a dozen or so small and midsize installations. We could use solar electricity to electrolyze water and store the hydrogen, but still, a hydrogen-based economy is not imminent.

And so when going big we must still rely on a technology introduced in the 1890s: pumped storage. You build one reservoir high up, link it with pipes to another one lower down and use cheaper, nighttime electricity to pump water uphill so that it can turn turbines during times of peak demand. Pumped storage accounts for more than 99 percent of the world’s storage capacity, but inevitably, it entails energy loss on the order of 25 percent. Many installations have short-term capacities in excess of 1 GW—the largest one is about 3 GW—and more than one would be needed for a megacity completely dependent on solar and wind generation.

But most megacities are nowhere near the steep escarpments or deep-cut mountain valleys you’d need for pumped storage. Many, including Shanghai, Kolkata, and Karachi, are on coastal plains. They could rely on pumped storage only if it were provided through long-distance transmission. The need for more compact, more flexible, larger-scale, less costly electricity storage is self-evident. But the miracle has been slow in coming."

https://spectrum.ieee.org/energy/renewables/batteries-need-t...

"Given the magnitude of the battery material demand growth across all scenarios, global production capacity for Li, Co, and Ni (black lines in Fig. 3) will have to increase drastically (see Supplementary Tables 9 and 10). For Li and Co, demand could outgrow current production capacities even before 2025. For Ni, the situation appears to be less dramatic, although by 2040 EV batteries alone could consume as much as the global primary Ni production in 2019. Other battery materials could be supplied without exceeding existing production capacities (Supplementary Tables 9 and 10), although supplies may still have to increase to meet demands from other sectors5,9. The known reserves for Li, Ni, and Co (black lines in Fig. 4) could be depleted before 2050 in the SD scenario and for Co also in the STEP scenario. For all other materials known reserves exceed demand from EV batteries until 2050 (Supplementary Table 5). In 2019 around 64% of natural graphite and 64% of Si are produced in China32, which could create vulnerabilities to supply reliability."

https://www.nature.com/articles/s43246-020-00095-x